In contrast to similar reactions reported for β‐diketiminate coordinated counterparts of 3, these C−H activations proceed with little regioselectivity, though they are considerably faster. Reaction of 3 with an excess of the pyridine, p‐NC5H4But (pytBu), gave [(Priso)Mg(pytBuH)(pytBu)2] 10, presumably via reduction of the pyridine to yield a radical intermediate, [(Priso)Mg(pytBu⋅)(pytBu)2] 11, which then abstracts a proton from the reaction solvent or a reactant. DFT calculations suggest two possible pathways to the observed arene C−H activations. One of these involves photochemical cleavage of the Mg−Mg bond of 3, generating magnesium(I) doublet radicals, (Priso)Mg⋅. These then doubly reduce the arene substrate to give “Birch‐like” products, which subsequently rearrange via C−H activation of the arene. Circumstantial evidence for the photochemical generation of transient magnesium radical species includes the fact that irradiation of a cyclohexane solution of 3 leads to an intramolecular aliphatic C−H activation process and formation of an alkyl‐bridged magnesium(II) species, [{Mg(μ‐Priso−H)}2] 12. Furthermore, irradiation of a 1 : 1 mixture of 3 and the β‐diketiminato dimagnesium(I) compound, [{(DipNacnac)Mg}2] (DipNacnac=[HC(MeCNDip)2]−), effects a “scrambling” reaction, and the near quantitative formation of an unsymmetrical dimagnesium(I) compound, [(Priso)Mg−Mg(DipNacnac)] 13. Finally, the EPR spectrum (77 K) of a glassed solution of UV irradiated 3 is dominated by a broad featureless signal, indicating the presence of a doublet radical species.UV irradiation of solutions of a guanidinate coordinated dimagnesium(I) compound, [{(Priso)Mg} A radical approach. Activations of arene C−H bonds by a photochemically excited dimagnesium(I) compound are reported . Experimental and theoretical evidence for the intermediacy of magnesium radicals in these reactions is presented. Such transition‐metal‐free C−H bond activations hold considerable potential for organic synthesis. Chemical processes involving the activation of strong, weakly polar C−H bonds in simple arenes and alkanes are integral to numerous value‐adding syntheses of larger, functionalised molecules; for example, natural products, agrochemicals and pharmaceuticals.I center.More recently, the use of reactive main group metal compounds for the C−H functionalization of organic molecules has been explored.0 catalyst.Arene C−H activation reactions are much less known for low oxidation state s‐block compounds, and well‐defined examples can be confined to those carried out by magnesium(I) compounds. Crimmin and co‐workers have shown that β‐diketiminate coordinated Mg−Mg bonded systems can functionalize a C−H bond of benzene in the presence of a PdDipNacnac)Mg}2] (DipNacnac=[HC(MeCNDip)2]−, Dip=2,6‐diisopropylphenyl), in arene solutions via blue or UV light irradiation.2 a–e and the dimeric magnesium hydride complex, [{(DipNacnac)Mg(μ‐H)}2]  compound, which appears to be more reactive than its β‐diketiminato counterparts, though less regioselective in its arene C−H activation reactivity. We also provide evidence that its irradiation does lead to cleavage of the Mg−Mg bond, and generation of transient magnesium radicals.As an extension of those studies, and as part of our systematic efforts to develop the reduction chemistry of magnesium(I) compounds,] Scheme .[14] E2] 3 (Priso=[Pri2NC(NDip)2]−) in 2007,DipNacnac)Mg}2], compound 3 is unreactive towards any of the arenes in the absence of artificial light. However, unlike [{(DipNacnac)Mg}2], it is also stable towards reaction with the arenes when irradiated with a blue light LED lamp  at room temperature for hours. This difference likely results from the fact that 3 is colorless, whereas [{(DipNacnac)Mg}2] is yellow, so the former would be expected to absorb visible light more poorly.3 in the studied arenes at 60 °C overnight, did not lead to formation of any C−H activated products.Since we reported the guanidinato‐magnesium(I) complex, [{(Priso)Mg}3 with UV light  in a 5 mm J. Young's NMR tube led to the near quantitative formation of the C−H activation product 4 after only 2 h  after work‐up. This can be compared to the irradiation of a solution of [{(DipNacnac)Mg}2] in benzene by UV light, which took 48 h to generate the doubly reduced “Birch product” .1 (n=0) at 60 °C for 12 h gave 2 a and [{(DipNacnac)Mg(μ‐H)}2]. This strongly suggests that 3 is significantly more reactive towards arene C−H activation than [{(DipNacnac)Mg}2]. Indeed, if a “Birch‐like” intermediate (cf. 1) was generated en route to 4, it is short‐lived, and was not observed when the reaction was followed by 1H NMR spectroscopy. It cannot be sure why the C−H activation of benzene by 3 gives a hydride/phenyl bridged product, while the equivalent reaction involving [{(DipNacnac)Mg}2] gave separate magnesium phenyl and magnesium hydride products. It is possible that in the latter case a hydride/phenyl bridged product is not sterically accessible, though a less hindered example, [{(MesNacnac)Mg}2(μ‐H)(μ‐Ph)] (MesNacnac=[HC(MeCNMes)2]−, Mes=mesityl), has been reported by Crimmin and co‐workers.4 is stable in benzene solutions at 60 °C for hours.In contrast to the above experiments, irradiation of a benzene solution of 3 in neat solutions of toluene, the three isomers of xylene, or mesitylene were carried out at room temperature. The reactions with toluene and xylenes were complete within 2 h and 8 h respectively, yielding the isomers of compounds 5–8 shown in Scheme DipNacnac)Mg}2], which took 24–96 h to reach completion, and were essentially regioselective. Another indication of the greater reactivity of 3, is the fact that the C−H activation of mesitylene is complete after 10 h (yielding 9), whereas [{(DipNacnac)Mg}2] is unreactive towards that arene under UV irradiation. Seemingly, the cost of the observed higher reactivity of 3 towards arene activation, is the loss of regioselectivity of the formed C−H activation isomeric product mixtures 5–7. It is of note that work‐up of all C−H activation products consistently led to partial decomposition, and formation of the guanidine PrisoH, even when moisture was rigorously excluded. Despite this, quenching of the reaction mixtures with solutions of I2 in THF allowed us to estimate the relative proportions of the generated regio‐isomers, by 1H NMR spectroscopic and GC/MS analyses of the known aryl iodide quenched products. The approximate ratios of the products are detailed in Scheme Next, UV irradiation of 3, and for sake of comparison with similar reactivity involving [{(DipNacnac)Mg}2], solutions of 3 in neat fluorobenzene, anisole or N,N‐dimethylaniline were irradiated with UV light. In all cases, the magnesium(I) compound was completely consumed within two hours, but complex mixtures of inseparable products resulted. This is similar to the irradiation of [{(DipNacnac)Mg}2] in solutions of these arenes, except for the reaction with fluorobenzene. That led, selectively, to C−F activation of the substrate, and the near quantitative formation of biphenyl and [{(DipNacnac)Mg(μ‐F)}2].In order to examine the chemo‐selectivity and functional group tolerance of arene C−H activations involving 3 with a large excess of 4‐tert‐butylpyridine in toluene was carried out. Our reasoning here was that, like [{(DipNacnac)Mg}2],3 could form a 2 : 1 adduct with the pyridine, and upon UV irradiation C−H activation of the coordinated pyridine could occur. However, in contrast to the formation of a stable pyridine adduct, the reaction between 3 and 4‐tert‐butylpyridine afforded an orange crystalline solid, which upon visual inspection appeared to contain crystals of at least two different morphologies. These could not be separated manually, or by fractional recrystallization. Only one of the crystalline materials could be characterized by X‐ray crystallography (see below), which showed it to be the magnesium(II) amide complex 10  complex of an amidinato magnesium fragment, [(Amid)Mg(CAAC⋅)] (Amid=[(DipN)2CBut]−), recently reported by Harder and co‐workers.11.Further to this work, the reaction of is bases.18, 194, 8 and 9), their NMR spectra are consistent with their proposed structures. Most notably, hydride resonances were observed in the chemical shift region of ca. δ 4.7–5.0 ppm. Although it was not possible to assign resonances to specific regio‐isomers in the NMR spectra of the inseparable isomeric mixtures of 5–7, strong evidence for the presence of all possible regio‐isomers, and their relative proportions, came from NMR spectroscopic and GC/MS analyses of the iodine quenched product mixtures, mentioned above. An analysis of the NMR spectra of the inseparable crystalline mixture that contained 10 did suggest the presence of at least two products, though the signals resulting from 10 could not be confidently assigned.Products of all the arene C−H activation reactions were characterized by NMR spectroscopy. In the case of the activated arene products where only one regio‐isomer is possible , is depicted in Figure 4 and 5 were located from difference maps, and their positional and isotropic atomic displacement parameters freely refined. Their hydride/aryl bridged structures are very similar to each other, and to Crimmin's transition metal catalyzed benzene C−H activation product, [{(MesNacnac)Mg}2(μ‐H)(μ‐Ph)].10 is monomeric, with its magnesium center exhibiting a distorted trigonal bipyramidal coordination geometry, including the protonated pyridine ligand in the equatorial plane. The Mg−N distance involving that ligand is considerably shorter than those associated with the datively bonded pyridines, as would be expected for what is now formally an amide substituent. Consistent with this is a loss of planarity for the reduced pyridine, and intra‐cyclic bond lengths which imply a more electronically localized structure than for the unreduced pyridines. The structure of 10 is comparable to those for compounds arising from the reductive de‐aromatization of pyridines, through reaction with β‐diketiminato magnesium hydride complexes, for example [(DipNacnac)Mg].X‐ray diffraction studies of the activated arene/pyridine complexes, 2 a,3 and benzene was calculated . Two possible radical pathways were identified, which are similar to those calculated for the formation of 2 a  radicals, Int2, which doubly reduce benzene to give a more stable “Birch‐like” intermediate, Int3. A competing, but lower energy  pathway to Int3 involves coordination of benzene to the photochemically activated, and elongated, Mg−Mg bond of Int1, to give the triplet species Int1a. This rearranges to give Int3. Although the overall energy barriers to Int3 are very high  for each pathway, they are both well below the energy of the incident UV light . Once formed, “Birch‐like” intermediate, Int3, undergoes an intramolecular C−H activation process (via Int4 and TS1) to give the magnesium hydride/magnesium phenyl couple Int5. Finally, this rearranges to give 4 as a thermodynamically stable species. It is of note that the overall energy barrier from Int3 to 4 is 15.5 kcal/mol, which is significantly less than the highest barrier calculated from 1 (n=0) to 2 a .1 (n=0) is an isolable species, whereas Int3 is not. Furthermore, the lower energy of 4 compared to that of a mixture of [(Priso)MgPh] and [{(Priso)Mg(μ‐H)}2], discounts the latter as the final products.So as to shed light on the mechanism of formation of the magnesium aryl complexes described above, and for sake of comparison with the reaction that gave a Figure .[22] F3 generates transient magnesium(I) radicals, which are responsible for the C−H activation of arenes described above, has been explored using synthetic and spectroscopic techniques. Firstly, cyclohexane solutions of compound 3 were irradiated with UV light over 8 h. This did not lead to C−H activation of the alkane solvent, but instead to an intramolecular C−H activation of one methyl group of the Priso ligand, and formation of an alkyl bridged dimagnesium(II) complex 12 as a colorless crystalline solid, in good isolated yield  which revealed that the most thermodynamically viable pathway involves initial generation of monomeric (Priso)Mg⋅ radicals Mg, which dimerizes to give 12 . To investigate if compound 12 is an intermediate in the formation of 4, the former was dissolved in benzene, and the solution irradiated with UV light. However, no reaction occurred, which essentially rules out that possibility.The possibility that UV irradiation of 12 suggest a much more symmetrical structure for the compound in solution than is seen in the solid state. That is, three apparent isopropyl methyl and two isopropyl methine signals were observed, with relative integrations of 1 : 1 : 1 and 2 : 1 respectively. No MgCH2 signal could be assigned in either the 1H or 13C{1H} NMR spectra of 12. This observation implies that the compound is undergoing a fluxional process in solution, which could involve the rapid and reversible transfer of a proton from one methyl group on an intact Dip substituent to the methylene fragment of the deprotonated Dip−H group on each ligand. Whatever the case, cooling d8‐toluene solutions of 12 to −60 °C led only to broadening of the resonances, implying that the fluxional process is rapid with respect to the NMR timescale, even at that temperature.The NMR spectra for compound 12 is depicted in Figure DipNacnac)Mg(μ‐Bun)2].κ3‐N,N,C‐DipNacnac−H)}2], in which both Ca centers are chelated by a deprotonated DipNacnac ligand, the methylene group of which bridges both metal atoms.The molecular structure of ac)Mgμ‐Bun2]. were carried out. The most successful experiments entailed irradiation of benzene, toluene or cyclohexane solutions of the magnesium(I) mixture with blue light. In all solvents, the scrambling reaction was very clean, and led to the near quantitative formation of the unsymmetrical dimagnesium(I) compound 13 after ca. 3 h Mg}2] were similar, a statistical equilibrium mixture of those compounds (1 : 1 : 2) would be expected to be reached under the photolysis conditions employed. However, that equilibrium clearly lies heavily to the right.If the irradiation of h Scheme . No reacDipNacnac)Mg}2] (in the absence of 3) lead to the double reduction of benzene , while 3 is unchanged after being irradiated by blue light in benzene. Therefore, it can be tentatively concluded that the dimagnesium(I) scrambling reaction is more favorable than the reduction of benzene by [{(DipNacnac)Mg}2], and that cleavage and re‐formation of the Mg−Mg bond of 3 occurs when it is irradiated by blue light in benzene (in the absence of [{(DipNacnac)Mg}2]). With that said, compound 13 could alternatively result from reaction of {(DipNacnac)Mg}⋅ radicals with intact 3, though computational studies indicate that such a pathway is not kinetically viable. Efforts to distinguish between these two possibilities by carrying out the irradiations in the presence of radical traps  were not successful, and led to intractable mixtures of products.The outcome of the irradiation experiment is surprizing for a number of reasons. Firstly, blue light irradiations of benzene solutions of [{(3 and [{(DipNacnac)Mg}2] are instead irradiated with UV light, a mixture of the scrambled product 13 and the C−H activation product 12 is formed. Moreover, UV irradiation of 13 in benzene leads to a mixture of benzene C−H activated product 4, [(DipNacnac)MgPh] 2 a and [{(DipNacnac)Mg(μ‐H)}2]. This reaction takes 5 days to reach completion, as opposed to the aforementioned faster formations of 4 from 3 (2 h), and of 2 a and [{(DipNacnac)Mg(μ‐H)}2] from [{(DipNacnac)Mg}2] (48 h),13 leads to no reaction, even after 5 days. The differences here are circumstantial evidence for the more resilient and more photo‐stable Mg−Mg bond in 13, relative to those in 3 and [{(DipNacnac)Mg}2], as proposed above.When cyclohexane solutions of a 1 : 1 mixture of 13 (and the other chemistry mentioned above) provides circumstantial evidence for the intermediacy of photochemically generated magnesium radical species in its formation, it should be emphasized that there are other possible routes to 13. Indeed, previous reports have described similar scrambling reactions that occur under heating, or even rapidly at room temperature in the absence of irradiation when smaller magnesium(I) substituents are involved..DFT calculations on ompounds,13, 163, a solution of the compound (1.0 mg) in a 3 : 1 mixture of 2,2‐dimethylbutane/tert‐butylbenzene (0.15 mL) was cooled to 77 K, and the resulting glassλmax=335 nm, 100 W Hg lamp). The X‐band EPR spectrum of the sample was then recorded at 77 K, and is depicted in Figure IBr radicals at 77 K.3 originates from traces of its known decomposition or disproportionation products, PrisoH and [Mg(Priso)2], solutions of those compounds were similarly irradiated, and their EPR spectra obtained. In neither case was any significant signal observed. The absence of a half‐field signal in the spectrum implies that the radical that gave rise to the dominant resonance in the spectrum is not a triplet species.In order to gain further evidence for the photochemical generation of radical species from 3, little success was had obtaining a suitable simulation. What is clear, is that the observed signal is a composite of a broad dominant signal, and a much less intense signal (ca. 40 : 1 ratio), the latter of which has hyperfine structure, and has been simulated. This signal potentially arises from the presence of a small amount of ligand radical, Priso⋅ (see Supporting Information for full details). With respect to the EPR spectrum, it is worth noting that DFT calculations on the monomeric (Priso)Mg⋅ radical . This might suggest that a significant hyperfine coupling of the unpaired electron to the 25Mg nucleus  would be observed in the experimental EPR spectrum of irradiated 3. However, simulations of the spectrum using a broad range of 25Mg hfc values (A(25Mg) 1–100 G) all gave broad central signals with little fine structure.IBr radical, little can be concluded about the electronic structure of the radical from the EPR spectrum. Despite this, it is worthy of mention that the EPR spectra of two related amido‐magnesium radical complexes, in which the unpaired electron is ligand based, have been recently reported, viz. Harder's [(Amid)Mg(CAAC⋅)]2(Carbazol⋅)] carbazolyl).25Mg hfc (1.6 G) was observed for the former, whereas none was recorded for the latter.Considering the broad nature of the EPR signal for irradiated 3 in various arene solvents has been explored, and compared with similar reactions reported for β‐diketiminate coordinated counterparts of 3. In no case does a reaction occur under blue light irradiation. In contrast, UV irradiation of solutions of 3 in benzene, toluene, the three isomers of xylene, and mesitylene, all lead to C−H activation of the arene and good yields of magnesium aryl products. These reactions are considerably faster than those involving β‐diketiminato dimagnesium(I) compounds, but they show little regioselectivity. DFT calculations suggest they proceed via photochemical cleavage or elongation of the Mg−Mg bond of the magnesium reactant, and reduction of the arene substrate by generated magnesium(I) radicals, prior to C−H activation processes occurring. A number of experiments have provided circumstantial evidence that the UV light irradiation of solutions of 3 leads to transient magnesium radical species. Firstly, irradiation of cyclohexane solutions of 3 results in an intramolecular aliphatic C−H activation process, and formation of a magnesium alkyl species, 12. Secondly, irradiation of a 1 : 1 mixture of 3 and a β‐diketiminato dimagnesium(I) compound leads to a “scrambling” reaction, and the near quantitative formation of an unsymmetrical dimagnesium(I) compound, 13. Finally, the EPR spectrum of a glassed solution of irradiated 3 at 77 K shows the presence of a radical species, though it cannot definitively be concluded that this arises from the magnesium(I) radical, (Priso)Mg⋅. We continue to explore the use of photochemically activated dimagnesium(I) compounds as reagents for organic transformations that normally require late transition metal complexes to proceed.In summary, the irradiation of solutions of a guanidinate coordinated dimagnesium(I) compound Experimental procedures and characterization data for all new compounds, full details of the computational studies, crystal data, and details of data collections and refinements are available in the Supporting Information.4⋅(benzene)0.5], 2182703 [for 5⋅(toluene)0.5], 2182702 [for 10⋅(benzene)0.25], 2182701 [for 12⋅(hexane)], 2182704 [for 13⋅(hexane)0.5]2182705 [for  contain(s) the supplementary crystallographic data for this paper. These data are provided free of charge by the joint Cambridge Crystallographic Data Centre and Fachinformationszentrum Karlsruhe Access Structures service.Deposition Number(s) The authors declare no conflict of interest.1As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.Supporting InformationClick here for additional data file.


In contrast, converting the native C terminal tripeptide PSI to the canonical PTS1 sequence ARL resulted in lower catalase specific activity. Localisation experiments using split superfolder green fluorescent protein revealed that catalase can be targeted to the nucleus in the absence of any pathogen effectors, and that C terminal tagging in combination with alterations of the native C terminus can interfere with nuclear localisation. These findings provide fundamental new insights into catalase targeting and pave the way for exploration of the mechanism of catalase targeting to the nucleus and its role in non‐infected plants.Catalase is a well‐known component of the cellular antioxidant network, but there have been conflicting conclusions reached regarding the nature of its peroxisome targeting signal. It has also been reported that catalase can be hijacked to the nucleus by effector proteins of plant pathogens. Using a physiologically relevant system where native untagged catalase variants are expressed in a  Arabidopsis thaliana CAT2 is targeted to the nucleus and the peroxisome. Peroxisome targeting was independent of the C terminus and required the noncanonical import pathway for optimal activity. Modification to the C terminus interfered with nuclear targeting in the absence of pathogen effectors. CAT is a target for plant pathogen‐encoded effectors, which traffic CAT to the nucleus to regulate programmed cell death  are major products of plant energy metabolism in mitochondria, chloroplasts and peroxisomes ‐(K/R/H)‐L . We identified an alternative splice variant of CAT2 gene in the TAIR database (At4g35090.2). This variant arises from non‐splicing of the last intron, which removes the last 18 amino acids of the CAT protein. Using a combination of physiological, biochemical and cell biology approches, we analysed the effects of introducing AtCAT2 variants with modified C‐termini into the cat2‐1 mutant background. The comprehensive evaluation of activity, function and targeting in a physiologically relevant context revealed that the last 18 amino acids of the CAT2 sequence are dispensable for growth, cellular redox status and targeting of the enzyme to the peroxisomes, but alteration of this region interferes with nuclear localisation.In this study, we have reinvestigated the requirements for targeting the 22.1PSI, CAT2WSQV and CAT2 ARL under the control of the CAT2 promoter, 2.4 kb genomic DNA upstream of the CAT2 gene was amplified with primers Cat2promR and Cat2prom F  and the cat2‐1 mutant . The plates were then wrapped in aluminium foil for 2 days at room temperature, the foil was removed, and plates were placed for 5 days in 16 h light. Then, seedlings were transferred into soil and grown 4 weeks in a controlled environment growth chamber . before transfer to long day conditions  for further 1 week. All samples were rapidly frozen in liquid nitrogen and stored at −80°C for subsequent analysis. All samples were taken 4–4.5 h into the photoperiod. The photorespiration‐promoting conditions were applied according to the protocol described by Waszczak et al.  and transfected according to Wu et al. (Seeds were sown on ½ MS media (with 50 µg/ml hygromycin for transgenic lines) and stratified for 2 days in the dark at 4°C followed by 6 h at 20°C in continuous white light . GSTF8, At2g47730. At3g25250, OXI 1. The expression level was calculated using the 2‐ΔΔCT method.Total RNA was extracted from leaves of 4‐week‐old plants with RNeasy plant mini kit (QIAGEN) and treated with TURBO DNA‐free kit (Invitrogen) according to the manufacturer's instructions. The first‐strand cDNA was synthesised using QuantiTect reverse transcription kit (QIAGEN). Real‐time PCR reactions were assayed using the Brilliant ®II SYBR® Green Q PCR master Mix  on a CFX connect real‐time PCR system (Bio‐Rad Laboratories). All transcripts were normalised to in Table . AGI cod2.1.34). The homogenate was centrifuged at 14 000 rpm at 4°C and the supernatant was adjusted to pH 6.0. Glutathione and ascorbate were quantified using Greiner F‐bottom 96‐well UV‐transparent plates on a FLUOstar Omega microplate reader (BMG Labtech).Glutathione and ascorbate were assayed as described , 1 mM EDTA was added to the extract. The homogenates were centrifuged for 10 min at 14 000 rpm at 4°C, and the supernatants were used for the assay. Catalase activity assay was performed according to Veljovic‐Jovanovic et al. (2PO4/K2HPO4 (pH 6.7), 2.8 mM NADH, 100 mM HPR and plant extract). Protein was assayed using BCA method . Chlorophyll quantification was determined by absorbance of the samples was measured at 646.6, 663.6 and 750 nm in a glass cuvette and calculated according to the extinction coefficients described in Porra et al.  low fat dried milk in Tris‐Buffered with Tween  1 h at room temperature (RT) with shaking. The membranes were incubated with primary antibodies  5 h (70 V) at room temperature in electrophoresis buffer . Analysis of catalase using in‐gel activity assay was carried out by using the protocol described in Weydert and Cullen . After centrifugation at 14 000 d Cullen .2.2cat2‐1, CAT2PSI, CAT2WSQV and CAT2ARL leaves were harvested and homogenised in extraction buffer  using a parsley chopper. Following cell disruption, three fractions were prepared as follows: The first fraction, the homogenate fraction (S1 supernatant), was obtained by centrifugation of the homogenate (10 min 2000 g). The second fraction, the cytosolic fraction (S2), was obtained by centrifugation of 1 ml of the S1 supernatant (20 min 12 000 g). Finally, the S2 pellet (organelle fraction) was suspended in 0.1 ml of the homogenisation buffer. For pure peroxisome isolation, 3–5 weeks‐old wild type, cat2‐1 mutant, CAT2PSI, CAT2 and CAT2ARL leaves (5–10 g) were harvested and leaf peroxisomes were isolated as described previously , a C terminal truncation arising from the retention of an intron that replaces the last 19 amino acids with a valine (terminating WSQV) and a variant in which the C terminal tripeptide was mutated to PTS1 consensus sequence (terminating ARL). Intron retention is the most common form of alternative splicing event  was dramatically increased in the s Figure , SD, LD.s Figure . The levHSP17.6, GSTF8 and OXI1) for enhanced H2O2 accumulation were also examined. Accumulation of the selected transcripts has been shown to occur under oxidative stress  a cytosol fraction (S2) and an organelle pellet (P2). Protein and catalase activity were measured in each fraction along with hydroxypyruvate reductase (HPR) as a peroxisomal marker and expressed as activity/g fresh weight  complement the various L Figure . Intereses Table cat2‐1 mutants, the peroxisomes from the CAT2PSI and CAT2WSQV lines had similar activities to the wild type. In contrast, CAT activity was lower in the CAT2ARL line peroxisomes, consistent with the data presented in Figure As the P2 fraction will contain other organelles, fractions of highly purified leaf peroxisomes were isolated using a combination of Percoll and sucrose density gradients  targeted to peroxisomes or nucleus  reconstituted sfGFP fluorescence signal in peroxisomes . A reconstituted sfGFP signal was observed in the nuclei of the protoplasts transfected with CAT2PSI‐sfGFP11 construct Figure WSQV or ARL‐sfGFP11 variants , while a much larger portion of pumpkin CAT1 comprising the C terminal 150 amino acids interacted with the N terminal part of PEX5 (Oshima et al., S. cerevisae peroxisomal catalase Cta1p is also independent of the PEX5 TPR domain for import (Rymer et al., S. cerevisae acyl CoA oxidase (Kempiński et al., cat2‐1 background as stable transformants, all folding and maturation factors and their substrates are present at natural levels and issues of overexpression, interspecies incompatibility or tag impairment of folding are therefore avoided. Thus, it can be confidently concluded that the C‐terminal 18 amino acids of CAT2 are not required for activity or peroxisome targeting.The PSI or CAT2WSQV and expressed in protoplasts derived from plants with GFP1‐10 targeted to peroxisomes, these constructs targeted to peroxisomes demonstrating that a free C terminus was not required. Conversely, CAT2ARL was not targeted to peroxisomes when GFP11 was appended to the C terminus, as might be expected if the protein now depends upon canonical PTS1‐PEX5 interaction which requires a free carboxylate on the C terminal leucine residue. However, it appears not to be able to access the pathway used by CAT2PSI and CAT2WSQV. Finally, the 3 catalase variants were co‐expressed with nuclear‐targeted GFP1‐10. CAT2PSI was efficiently targeted to the nucleus whether the sfGFP11 was at the N or C terminus but CAT2ARL and CAT2WQSV could only target to the nucleus when the sfGFP11 was at the N terminus, suggesting that alteration of the C terminus in combination with a C terminal tag interferes with the recognition by some unknown factor that promotes nuclear targeting (Figures The above discussion leads to the question of why the C‐terminal 18 amino acids of CAT2 is so highly conserved, if the sequence is apparently dispensable. Cell fractionation is not appropriate for studying dynamic changes in protein localisation so the superfolder split GFP system was employed. This system was developed to study translocation of type III secretion system substrates which are folded and whose translocation is often prevented when fused to large fluorescent proteins (Park et al.,  Figures .Phytopthora sojae to manipulate PCD (M. Zhang et al., Saccharothryx yanglingensis interacts with catalase in the nucleus and stimulates plant immunity (Y. Zhang et al., Catalases can be relocated to the nucleus through the interaction with effector proteins of The authors declare that there are no conflict of interests.Yousef Al‐Hajaya: Designed and performed experiments, analysed data, wrote the manuscript. Barbara Karpinska: Designed and performed experiments, analysed data. Christine H. Foyer: Designed and analysed experiments, wrote the manuscript. Alison Baker: Designed and analysed experiments, wrote the manuscript.Supporting information.Click here for additional data file.


Geometry optimization under symmetry constraints was performed to observe the mode of coordination that a metal-cation adopts when it resides inside the cyclophane cavity. Thermodynamic properties were investigated to note the trends of stability along a group of metals. To further investigate the bonding properties, Morokuma–Ziegler energy decomposition analysis, natural bond orbital analysis and Bader's analysis were employed. It was observed that most of the main-group metal complexes with cyclophanes prefer an η6η6η6 coordination mode where the metal-cation sits in the centre of the cyclophane cavity. There is an increased thermodynamic stability in [2.2.2]paracyclophane complexes compared to their deltaphane analogues while the reverse is true regarding the strength of coordination based on interaction energy.Density functional theory calculations using the PBE0-D3BJ hybrid functional have been employed to investigate the complexation of main-group metal-cations with [2.2.2] paracyclophane and deltaphane.Investigation of the complexation of main-group metal-cations with [2.2.2] This allows recognition of targetted guest metal-cations.7 Moreover, derivatives of metallacyclophane hosts have been reported as potential candidates for optical biomolecular recognition.8 Luminescent metal-complexes of cyclophanes have been reported to have their potential applications in thin-film nonoporous materials.9 All these applications are due to the potential of the π-rich cyclophane cavity to host electrophilic or cationic guests by making inclusion complexes, despite the fact that some smaller cyclophanes are also known to form exclusion complexes.10There is a growing interest in the donor–acceptor complexes of cyclophanes with metals due to their various applications such as the development of ion-selective electrodes,4,11,12 controlling the size of the cavity to capture guest species13 and replacing the usual phenyl ring with heterocyclic aromatic rings such as imidazolium.14 Owing to the variety of their potential applications, it is important to explore the bonding properties of different possible metallacyclophanes. In the current study, the two cyclophanes [2.2.2]paracyclophane (pCp) and deltaphane (Dp) given in The selectivity and sensitivity of cyclophanes can be improved as evident from the efforts in the past such as derivatization and functionalization using different coordination groups,pCp was first synthesized by Pierre and co-workers where they called it a π-prismand due to its π-rich prism-shaped cavity15 and demonstrated its complexation with silver triflate. Extending the concept and introducing an increased rigidity compared to that of pCp, Kang et al. reported the synthesis of Dp.16 As the systematic name of the latter i.e. cyclophane suggests, Dp has six ethano bridges compared to three in pCp. pCp and Dp consist of three phenyl rings each bridged through aliphatic chains. However, pCp is more flexible as each aromatic ring is attached to two ethyl bridges unlike its attachment to four in case of Dp.pCp is much more stable compared to other such complexes with aromatic systems.15 Similarly, the crystal structure of silver triflate complex of Dp was also reported.16 During the same period (mid to late 1980s), Schmidbaur and co-workers reported the groundbreaking complexes of pCp with some of the main-group metals.17–19 Despite these contributions in synthesis of metallacyclophanes of pCp and Dp, a lot of effort is still required to explore the bonding properties of these complexes to make use of these promising π-donating ligands on industrial scale.Due to the presence of phenyl rings, both these molecules contain π-rich cavities that can coordinate to the metal-cations to form stable complexes. It was shown earlier that the silver triflate complex of pCp and Dp.20 Earlier, the groups of Frenking and Castro carried out a computational study on the coordination mode and bonding properties of inclusion complexes of Sn2+ and Ag+ with pCp.21 They further extended the concept to computationally understand the role of formal charge of a cation in π–cation interactions by comparing the complexes of isoelectronic In+ and Cd2+ with pCp.22 In further instances, Castro et al. investigated helicenes23 and Dp24 as potential π-donors to form various π–cation interactions through relativistic DFT approach. A review of the use of relativistic computational tools to study the structural and bonding properties of these π–cation interactions has been published recently25 which shows that different avenues in this field have been opened by the groups of Castro and Frenking over the last few years. The current work is aimed at investigating the coordination and bonding properties of the complexes of group 13 , 14  and 15  with the π-rich cavity of pCp and Dp using density functional theory (DFT).In this regard, we previously reported the bonding properties of coinage metal complexes of Gaussian 09 suite of programs (Revision D.01).26 The PBE0 hybrid functional27 in conjunction with Grimme's empirical D3 correction with Becke–Johnston damping (D3BJ)28 was used in combination with the def2-TZVP basis-set29 of triple-ζ quality in all these calculations.All calculations related to geometry optimization were performed with the 30 that was carried out with the ADF2014 program.31 The TZ2P  basis set32 was employed along with the relativistic ZORA Hamiltonian.33,34 MZEDA involves the decomposition of total energy (ΔE) of a molecule as:The optimized structures were further subject to the Morokuma–Ziegler Energy Decomposition Analysis (MZEDA)Eint is the instantaneous interaction between the two molecular fragments and (ΔE1 +ΔE2) is the sum of their individual energies. The above equation implies that ΔEint is the difference between the total energy of a molecule and its fragments. ΔEint can be further subdivided as in Eelstat is the energy due to electrostatic interactions (mostly attractive in nature) between the molecular fragments. ΔEPauli is the repulsion term and it arises due to the electrons with same spin. ΔEorb indicates the interactions involving charge transfer polarization effects.In 35 given by Richard Bader was performed using Multiwfn software.36 NBO analysis was carried out with NBO 6.0 program37 as interfaced with Gaussian09.Bader's analysis based on quantum theory of atoms in molecules (QTAIM)38Molecular graphics were rendered with GaussView 5.0.9.pCp possesses a rigid geometry and has an internal cavity with diameter 2.5 Å.39 The phenyl rings are bridged at the para positions through ethyl chains. Dp is even more rigid as the phenyl rings are doubly connected to each other at the ortho and meta positions through ethano bridges. The D3 symmetric geometries were optimized at PBE0-def2TZVP level of DFT and have been characterized as minima on the potential energy surface. Additionally, the two have D3h symmetric transition structures optimized previously at the same level.20 Calculated structural data of both of these ligands is consistent with their crystal structural information16,39 except the fact that gas-phase calculated bond lengths are sometimes longer than those in a crystal structure (solid-phase) due to crystal packing forces that are absent in a gas-phase calculation.pCp, the C–C bond lengths in bridging ethyl units and that for bridgeheads are 1.54 Å and 1.51 Å compared to the experimental mean bond lengths of 1.43 Å and 1.52 Å respectively. The calculated C–C bond lengths in the phenyl rings are equivalent at 1.39 Å compared to the experimental bond lengths i.e. 1.37 Å. Dp presents a different case with a small variation of bond lengths in phenyl rings. Here, the calculated C–C bond length of the two sides of each phenyl ring attached to ethyl bridges is 1.40 Å compared to its experimental value of 1.390(2) Å while the other four bonds are calculated to be 1.39 Å compared to the experimental 1.387(3) Å bond length.In pCp (pCp–Mn+) and Dp (Dp–Mn+) with nine metal-cations of interest were optimized in their D3 and C3 symmetry and confirmed as either minima or transition structures through vibrational analysis. In the former case, the group 13 complexes and pCp–As3+ are C3 symmetric minima while group 14 and the rest of group 15 pCp–Mn+ complexes have D3 symmetry in their ground state structures. In case of group 13 pCp–M+ complexes and pCp–As3+, the D3 symmetry was possible for the transition structures only. The D3 symmetric pCp–Mn+ complexes show η6η6η6 metal–phenyl rings coordination. However, pCp–Ga+ and pCp–As3+ present a case with C3 symmetry showing η6η6η6 coordination while its counterparts i.e. pCp–In+ and pCp–Tl+ exhibit η2η2η2 coordination. As for the Dp complexes, all the nine structures were optimized as minima in C3 as well as D3 symmetry. Dp–Mn+ complexes with C3 show η1η1η1 coordination of a metal ion staying on the top of Dp cavity in each complex. D3 symmetric complexes, on the other hand, exhibit η6η6η6 coordination of the metal-cation present inside the Dp cavity. These results suggest that despite few exceptions, the pCp and Dp complexes of main-group metal-cations under discussion differ from the transition metal complexes where the metal-cation tends to come out of the cavity20,21 preferring peripheral coordination unlike current complexes where central (η6η6η6) coordination is preferred.Inclusion complexes of pCp–Mn+ and Dp–Mn+ of interest are given in pCp–Ga+, pCp–In+, pCp–Ge2+, pCp–Sn2+ and pCp–As3+ where it can be seen that computational results align well with the experimental ones. However, the distance of metal ion from the center of the pCp cavity in experimental and computational instances differs, which can be attributed to the proximity of corresponding counter anion(s) to the metal cation in experimentally reported complexes. This is in line with the computational findings reported earlier in case of pCp–Sn2+.18 The difference is highly pronounced in case of pCp–As3+ where both the calculated conformations (C3 and D3) exhibit η6η6η6 coordination mode, as mentioned earlier, with As3+ in C3 symmetry displaced by 0.266 Å from the center of the host cavity. On the other hand, the experimentally reported pCp–As3+ shows η2η2η2 coordination where AsCl3 coordinates from the top of the cavity. In addition to pCp–Sn2+, the computational findings for pCp–In+ have also been reported earlier22 which, despite small numerical differences, show a great deal of similarity with the pCp–In+ calculated in our case.Some key structural parameters of C3 and D3 symmetric conformers of pCp–Ga+ are identical except the displacement of Ga+ from the center of the cavity by 0.466 Å in C3 conformer in contrast to its exactly central location in the D3 counterpart. This is supported by identical ΔEint of both the conformers in pCp–In+ and pCp–Tl+, the metal ion is located significantly further from the center in C3 symmetry while it is exactly in the center in D3 analogue. In both of these complexes, cavity size increases upon inclusion of metal cation for η6η6η6 coordination as evident from internal radius CC–M  and pCp–Tl+  are energetically favourable by −4.73 kcal mol− and −5.2 kcal mol− than their D3  counterparts. Similarly, the D3 symmetric pCp–As3+ is less favourable by 8.47 kcal mol− than its C3 analogue as evidenced by ΔEint , the greater the thermodynamic feasibility of the corresponding complex. Ionic radii of the metal cations under discussion are given in 22 Upon moving from group 13 to 15 in a period, the formal charge in our case increases from +1 to +3 and so does the exothermic enthalpy of reaction. The trends of thermodynamic feasibility can be correlated with the results obtained from EDA and are discussed in the next section.It can be seen in The nature of bonding in the inclusion complexes under discussion was carried out using MZEDA technique, Bader's and NBO analyses. The former decomposes total interaction energy into various energy terms and hence it explains the strength of different interactions. NBO and Bader's analyses predict the type of bonding.pCp–Mn+ complexes are given in Eorb indicates the strength of covalent interaction while ΔEele shows the strength of electrostatic attraction. The ratio of ΔEorb to ΔEele explains the relative importance of covalent and ionic interactions i.e. the greater the ratio, the higher the percentage of ΔEorb will be. The total steric repulsion present in a complex is depicted as ΔEPauli. The sum of the above-mentioned three terms accounts for the instantaneous interaction energy ΔEint. However, it is advised in the literature to describe the overall interaction in terms of three separate quantities; ΔEPauli, ΔEele and ΔEorb.43The results for MZEDA of pCp–M+ complexes, interaction energy is highest on the top of group and lowest in case of pCp–Tl+. This is in line with the trends of enthalpy of reaction  than the electrostatic interaction (ΔEele). In case of pCp–In+ and pCp–Tl+, the percentage of ΔEorb is less compared to that in pCp–Ga+ and ΔEele fraction substantially increases which ultimately accounts for a decrease in strength of coordination down the group as suggested by a decreasing ΔEint. The strength of both the attraction terms may be expressed as the ratio of ΔEorb to ΔEele which is 1.2 for pCp–Ga+ while it is 1.0 for each of pCp–In+ and pCp–Tl+. The trends of EDA results for group 14 and 15 are identical to those of group 13.A deeper insight into the EDA results  shows thpCp–In+22 and pCp–Sn2+ (versus PBE0/TZ2P current) used in both studies, the trends are identical. For instance, the η2η2η2-coordinated pCp–In+ is favoured compared to its η6η6η6 analogue based on their ΔEint in both the cases. Similarly, ΔEorb is a major attractive term in η6η6η6-coordinated pCp–Sn2+ in earlier and current studies as evidenced by the percentages of their ΔEorb and ΔEele  compared to that of electrostatic interactions (ΔEele) in overall ΔEint in case of D3 complexes. On the other hand, C3 symmetric complexes are characterized by higher contribution of ΔEele than that of ΔEorb in the overall ΔEint which causes a comparatively weaker coordination in C3 complexes than their D3 analogues.The trends of EDA in the case of the Dp complexes under discussion  are simiEint increases to a great extent from one metal ion to the next  connecting a metal-cation to the host  and its various other functions.44 According to the set of these rules, a small ρ accompanied by a negative Laplacian L (or ∇2ρ > 0 since L = −∇2ρ) usually denotes a depletion of electron density along a BCP and is the characteristic of either closed-shell or donor–acceptor interactions while a small ρ along with L approaching zero indicates a shared interaction. On the other hand, a large electron density and a positive L (or ∇2ρ < 0) shows that electron density is concentrated along a BCP and the interaction will usually be classified as covalent or intermediate. To further confirm the nature of interaction, some additional parameters such as local energy density and the ratio of kinetic energy (G) to ρ are also advised by Popelier.44The results for Bader's analysis of all the complexes are given in i.e. electron sharing is enabled between the cyclophane hosts and the cationic guests. These findings are in line with the results of EDA where ΔEorb in most of the cases is a major contributor in total attraction energy compared to ΔEele. All these complexes have a small ρ and its laplacian (L), a G/ρ less than 1 and a negative value of H except pCp–Tl+ that has a positive H suggesting that it has interaction between a shared and a donor–acceptor interaction. The EDA results of pCp–Tl+ support this assumption since ΔEele has a greater percentage than ΔEorb.A careful classification based on pCp and Dp complexes under consideration was further investigated based on natural population analyses (pCp–Ga+ (C3 η6η6η6), pCp–In+ (C3 η2η2η2), pCp–Sb3+ (D3 η6η6η6) and Dp–Sn2+ (D3 η6η6η6) are given in Fig. S2 in ESI1, π2 and π3. In all the η6η6η6 complexes where the metal cation is centrally located inside the ligand cavity, π1 orbital of the cyclophane ligand coordinates with ns orbital of metal cation  giving rise to fully occupied bonding and antibonding π1ns interactions as in Fig. S2(a)n’ has the value 4, 5, 6 for 4th, 5th, and 6th-row elements respectively). However, np orbital of the metal cation can be bonded to π2 and π3 orbitals of the aromatic system such that pz interacts with π2 based on orientation while π3 has an equal chance of interaction with px and py orbitals of the metal cation. In pCp–In+ and pCp–Tl+ complexes, the bonding scheme is somewhat different as both have η2η2η2 coordination mode. We propose in these two cases that only π2 and π3 of the cyclophane cavity coordinate with ns orbital and one of the np sub-orbitals, respectively leaving behind π1 without any interaction as in Fig. S2(b).6η6η6-coordinated pCp–Ga+ where LMCT is double the amount of that in its other two counterparts.The electronic structure of the analyses . QuantitpCp–Ga+ that π1 of pCp and 4s Ga+ mix to give fully occupied bonding and antibonding MOs where bonding orbital has 15.87% contribution of Ga+ while the remaining 84.13% come from pCp. The contribution of Ga+ in antibonding MO, however, increases to 50.90%. Next, π2 and 4pz mix with a contribution of 6.86% and 83.79% from Ga+ in the resultant bonding and antibonding MOs, respectively. Moreover, π3 mixes equally with 4px and 4py (as discussed above) to give bonding (1.93% from Ga+) and antibonding (60.62% from Ga+) interactions. In contrast, we can observe an overall lesser contribution of 5p orbital of In+ in Fig. S2(b) compared to 4p of Ga+ in (a).6η6η6-coordinated pCp–Ga+ compared to that in η2η2η2-coordinated pCp–In+  pCp–In+ . A compapCp and Dp have π-rich cavities and can efficiently host the main-group metal-cations making inclusion complexes with them. However, both possess different structures that cause these π-prismands to behave somewhat differently from each other. Although pCp has a rigid geometry as stated earlier, it is still somewhat flexible due to three ethano-bridges linking the three aromatic rings compared to Dp which has six aliphatic chains bridging the three phenyl rings. It readily undergoes conformational changes and tends to adjust its geometry accordingly to accommodate the metal-cations more conveniently. Hence, the pCp complexes are thermodynamically more feasible compared to the Dp complexes.pCp complexes with their Dp analogues, there are instances where Dp complexes have an increased coordination strength. For example, group 13 pCp–M+ complexes  while the majority of the rest of Dp complexes have an increased coordination strength compared to the corresponding pCp complexes (thus opposing the trend of thermodynamic stability). This can be correlated with the fact that generally ΔEprep is lower and ΔEorb is higher for Dp–Mn+ complexes than corresponding pCp–Mn+ except group 13 complexes which result in an overall higher ΔEint for Dp–Mn+ than pCp–Mn+ of group 14 and 15. NBO analysis provided the basis for explaining in detail the electronic structure of complexes. Different parameters of Bader's analysis suggest the shared nature of M–C interactions in all these complexes except pCp–Tl+ that has a donor–acceptor type of interaction.Quantum chemical calculations were employed to investigate the pCp and Dp complexes of main-group metals. Geometry optimization under symmetry constraints shows that an ηThe authors declare that they have no conflict of interest.RA-010-D0RA05303A-s001


Hence, enabling charge compensation in sodium layered oxides is a fascinating task for extending the cycle life of sodium‐ion batteries. Herein a Ti/Mg co‐doping strategy for a model P2‐Na2/3Ni1/3Mn2/3O2 cathode material is put forward to activate charge compensation through highly hybridized O2p—TM3d covalent bonds. In this way, the interlayer O—O electrostatic repulsion is weakened upon deeply charging, which strongly affects the systematic total energy that transforms the striking P2–O2 interlayer contraction into a moderate solid‐solution‐type evolution. Accordingly, the cycling stability of the codoped cathode material is improved superiorly over the pristine sample. This study starts a perspective way of optimizing the sodium layered cathodes by rational structural design coupling electrochemical reactions, which can be extended to widespread battery researches.Layered transition‐metal (TM) oxides are ideal hosts for Li 2/3Ni1/3Mn2/3O2 (NNM) cathode material is proposed to activate oxygen charge compensation at high voltage. In this way, the interlayer O—O electrostatic repulsion is released, which modifies the P2–O2 transition into a moderate solid‐solution type evolution, and therefore remarkably enhances the cycling performance of the P2‐type NNM layered cathode.Here a Ti/Mg codoping strategy for a model P2‐Na Despite almost 30 years of commercial success, nevertheless, concerns have recently arisen about the shortage of Li resource and potentially rising costs. With this regard, searching for alternative energy storage chemistries lies at the very heart of global concerns nowadays. Contrary to the lithium raw materials, sodium resources are earth‐abundant, distributed worldwide and cost effective. In light of this, the development of sodium‐ion batteries (SIBs), using sodium instead of lithium as charge carriers, shows great promises upon overcoming the economic barriers of LIBs and therefore have attracted significant attention.With the growth of the economy, the global demands for energy have significantly increased. However, nonrenewable fossil fuels are being exhausted rapidly, and their over‐exploitation and consumption also lead to severe environmental issues. As a result, the development of energy storage techniques for sustainable energy sources  becomes necessary to a green and recycling society.1 Amon In analogy to Li‐based layered cathodes that have been widely applied in commercial LIBs, a variety of sodium layered intercalated compounds, for example, sodium layered transition‐metal (TM) oxides , have been extensively explored as cathode materials for SIBs. These materials share common advantages over lithium layered counterparts , such as high energy density, fast ionic diffusion, and good stability in air, but most of them suffer from severe capacity decay and poor structural stability of Na‐intercalated lattice. To improve the cycling stability, substantial efforts with various degree of success have been made including incorporating foreign dopants, coating protective layers, morphology control, etc. Nevertheless, more solutions with artful and in‐depth concepts for fine material design are still urgently desired.Apart from the prospect, there are still critical challenges for the widespread usage of SIBs. Especially, the exploration of suitable cathode materials has been the focus of attention, since it is the cathode materials that account for most of the overall costs of the whole cell and determine critical battery performance, such as energy density and cut‐off voltage.10 In Figure  A charge compensation mechanism between highly hybridized TM‐3d and O‐2p states has been thought to be responsible for this moderate solid solution behavior. In detail, when most of the lithium ions are extracted from the lattice at high voltage, the interlayer distance is governed heavily by the O–O electrostatic force between the layers. Meanwhile, the redox charge loss of TMs could be compensated persistently by the O2p electrons through generating electron holes . This will weaken the O–O repulsion and thereby give rise to moderate interlayer contraction for endurable cycle life. For the sodium layered oxides, the most prevailing structures applied for SIB cathodes are P2 or O3 phase, where Na+ ions are accommodated at “prismatic” or “octahedral” sites, and the stacking sequences of oxygen are “ABBA” for P2 and ABCABC for O3, respectively. For the O2 cathodes, typically, a phase transition from P2 to O2 occurs upon charging to ≈4.1–4.2 V, accompanied with a striking interlayer shrinkage in distance intercalation. Starting from a Li‐intercalated layered structure Figure 1a, the fFigure 26 A c2/3Ni1/3Mn2/3O2 (NNM), a model system of sodium layered TM oxide, for improved cycling stability. Compared with the above‐mentioned optimizing approaches, the doping strategy has been proven to be effective and fundamental, as it is capable of directly tuning the material properties at atomic and electronic levels. It has been found that the Ti/Mg codoped NNM material  shows an endurable cycling performance far superior to the pristine NNM (P‐NNM). In situ X‐ray diffraction (XRD) reveals that the D‐NNM exhibits a moderate solid‐solution‐type behavior at high voltage, instead of the P2–O2 phase transition with striking interlayer contraction observed in P‐NNM. By in situ pair distribution function (PDF) analysis, detailed local structural dynamics have been clearly encoded. Instead of the typical O2 structure, an orthorhombic phase (denoted as P2’ phase) is suggested in the high‐voltage D‐NNM, and this P2’ phase can be transformed continuously from P2 by sliding slabs along  direction. The thermodynamically preferred P2–P2’ transition is also validated with first‐principles calculations. Near‐ambient pressure X‐ray photoelectron spectroscopy (NAP‐XPS) has demonstrated that a charge compensation behavior from O to TMs occurs concomitant with the P2–P2’ transition. The present study initiates a prospective way of stabilizing the P2 structure through activating oxygen charge compensation to develop sustainable sodium layered cathode materials.Herein we put forward a synergetic Ti/Mg codoping strategy to realize this scenario, for which the oxygen charge compensation is activated in P2‐type NaTM oxide,32 for2Figure P63/mmc) without any impurity. Based on the results of Rietveld refinements  than Ni2+ (0.69 Å), as well as that of Ti4+ (0.61 Å) than Mn4+ (0.53 Å).The P2‐type P‐NNM and D‐NNM samples were prepared using a high‐temperature solid‐state reaction method (see the Methods in the Supporting Information). From the scanning electron microscopy (SEM) images  patterns were carried out with the hexagonal P63/mmc model  and extended X‐ray absorption fine‐structure (EXAFS) analysis of Ni and Mn K‐edges. From the XANES data . For the P‐NNM, a series of voltage plateaus could be observed upon charging and discharging  and Mn4+/Mn3+ (< 2.0 V) redox couples. In contrast, only Ni2+ ions are oxidized during the first charging process, accounting for a lower charge capacity of ≈170 mAh g−1. Upon further cycling, the capacity derived from the P2–O2 plateau drops severely with a remarkable increase in polarization. This capacity decay is related to the structural damage induced by repetitive strains during the P2–O2 transition.The electrochemical performance of the P‐NNM and D‐NNM electrodes was evaluated by the coin‐type half cells over the voltage range from 1.5 to 4.4 V. g Figure . Among t2 region.33 The+/vacancy ordering , an uphill plateau is observed for the D‐NNM cathode, in contract to the flat plateau of P2–O2 transition in the P‐NNM. This indicates a modified high‐voltage structural dynamical behavior in the codoped sample. In addition, the high‐voltage capacity decay and the related polarization observed in the P‐NNM are less obvious in the D‐NNM, indicating that the dopants could serve as structural stabilizers in the codoping system. Similar to the P‐NNM, the first discharge capacity delivered in the D‐NNM (≈177 mAh g−1) is higher than the first charge capacity (≈145 mAh g−1), which is derived from Mn4+/Mn3+ multiredox couples upon discharge. Nevertheless, the capacity retention of these two materials shows clear distinction  Bragg positions, accompanied with a slight weakening of the P2 intensities. This means a portion of P2 phase transforms to O2 phase, and these two phases coexists in the P‐NNM electrode. The stacking profile of the in situ XRD patterns has been also plotted to detail this behavior  peak is also observed at the initial state of discharge. Meanwhile, the (100) peak, corresponding to the a‐axis, shows a reversible feature over the entire charging–discharging process. Notably, this successively evolved peak shift also differs from the so‐called “Z‐phase” in Fe‐doped NNMs, but shares similar characteristics with the solid‐solution H2‐H3 transition in lithium layered oxides . The former Z‐phase is generally identified by a gradual fade of the (002) peak accompanied with the appearance of a new Z‐phase feature at a higher 2θ angle, which is obviously different from continuously shifted features observed in this study. Furthermore, for both the P‐ and D‐NNM cathodes, the c‐oriented reflections, such as (004), (102), and (106) reflection in Figures For the D‐NNM electrode, no newly emerged feature can be observed in the contour plot of in situ the XRD patterns Figure 5a, indicFigure 39 theP63/mmc structural model. At the initial state of charge, the D‐NNM undergoes a contraction along a‐axis and an expansion along c‐axis, which is almost consistent with the P‐NNM sample. Upon further desodiation, while the a‐axis contracts steadily, the length of c‐axis quickly decreases at the end of charge. This contraction of interlayer distance, defined as P2–P2’ transition in this work, will give rise to a contraction of 7.01% along c‐axis, which is much weaker than the P2–O2 transition in the P‐NNM. The apparent reduction of the interlayer contraction could significantly weaken the repeated lattice strains, hence reducing the electrode cracks for improved cycling stability. Upon further discharging, a slight structural break could be observed in the P2’ phase region, which accords with the splitting of the (002) peak in the XRD patterns  profiles, which matches the next nearest TM…TM atom pairs at ≈6.3 Å. For the P‐NNM, this interlayer distance continuously expands upon charging, while an additional peak could be observed in the high‐voltage profiles  fits well to the data of both uncharged P‐NNM and D‐NNM samples  larger than 0.25. Given that the P2’ structure is transformed from P2 through a successive slab sliding, a series of subgroup models are selected from the feasible sliding‐derived structures with symmetrical Na—O geometries, and an orthorhombic C2221 model gives the best description of the high‐voltage D‐NNM profile . As expected, the P2 structure model  only for the charged D‐NNM sample. This extra component, based on both theories and experiments, could arise from the lattice oxidized On− (n < 2), while the increase in BE with respect to the lattice O2− can be elucidated by the loss of negative charge on oxygen atoms. As a result, the dopants of Mg and Ti in the D‐NNM lattice could trigger a charge transfer out of oxygen upon deeply charging, so the O—O repulsion between layers is expected to be weakened for modified slab stacking behavior at high voltage.When deeply charged, most of the sodium ions are extracted out of the interlayers, so the stacking of slabs at high voltage are basically governed by O—O electrostatic interaction between layers. Thus, the anomalous P2–P2’ transition in the D‐NNM is expected to be triggered by modified O—O electrostatic force, which is closely related to the oxygen charges shared from the covalent TM—O bonds. With this regard, near‐ambient pressure X‐ray photoelectron spectroscopy (NAP‐XPS) was performed on both uncharged and charged samples to determine the redox chemistries and charge transfer behaviors. Starting from the oxygen Figure 7a, the psorbates.46 Whep spectra, the spin–orbit doublets at ≈854.7 eV (2p3/2) and ≈871.9 eV (2p1/2) correspond to the Ni2+ state, while the Ni3+ state can be distinguished by the splitting holes at ≈856.2 eV (2p3/2) and ≈873.4 eV (2p1/2), respectively. As shown in Figure 2+ with a small fraction of Ni3+. Upon charging, the Ni3+ doublets become stronger accompanied with weakening of the Ni2+ peaks. Meanwhile, additional shoulder doublets appear at ≈858.7 and ≈875.9 eV, which are assigned to the Ni4+ state. As a result, a multistep Ni2+/Ni3+/Ni4+ redox process is confirmed in both P‐NNM and D‐NNM electrodes. Remarkably, the charged D‐NNM contains less Ni4+ but more Ni3+ state in comparison with the charged P‐NNM sample. Considering the oxidized On− observed simultaneously, it is suggested that the Ni ions in the charged D‐NNM are reduced by the electrons transferred from the covalently bonded oxygen. In other word, a charge transfer from oxygen to nickel is triggered by codoping Mg and Ti into the D‐NNM lattice, where the electrons from oxygen could partly compensate the charge loss of nickel when deeply charging. On the other hand, the Mn 2p spectra shown in Figure 4+ state, and no obvious peak shift is observed upon charging for both the materials. Accordingly, the Mn ions in the NNMs are supposed not to participate in the redox reactions. The above XPS results provide key clues of oxygen charge compensation in the D‐NNM. This behavior, as mentioned above, could give rise to a decrease in the interlayer O—O repulsion and therefore play a key role in driving P2–P2’ stacking at high voltage.With the charge outflow of oxygen, there remains an open question as to whether the electrons given away from oxygen in the D‐NNM go to the external circuit for extra capacity, or to the adjacent TMs for charge compensation. To answer this question, the cationic redox behaviors in these two materials were also investigated by XPS. In the typical Ni 2ectively.53 As + removal. Structure models for the P2, P2’, and O2 phases of D‐NNM were created by expanding the primitive cells of these phases and populating the Na and metal sites with Na+/vacancy and transition metals , then all geometrically different configurations were generated and calculated with the density functional theory (DFT). Figure +/vacancy configurations on Na sites of structure models at different compositions (Na+/vacancy ratios). For the specific composition, all the Na/vacancy‐ordered configurations were relaxed, and their formation energies were computed according to the following reaction referring to the P2 phase: NaxMO2 → 3/2xNa2/3MO2 (P2) + (1‐3/2x)MO2 (P2), where M stands for the simulated transition metal composition of Ni1/4Mg1/12Mn7/12Ti1/12 . From the calculated desodiation convex hulls of Na2/3MO2‐MO2 shown in Figure x < 0.6) while the P2’ phase catches at the end of desodiation (0.6 < x < 0.67), indicating a phase transition from P2 to P2’ in the D‐NNM. A similar trend is confirmed by examining the relative energy variations of P2’ and O2 phases versus the P2 phase , accompanied by a decrease in the magnetic moment from around 1.8 μB to 1.1 μB and then to 0.4 μB. Meanwhile, magnetic moments of O and Mn barely vary, indicating the maintenance of their original oxidation states of 2− and 4+, respectively , as shown in Figure d to the valence band immediately below the Fermi level (EF) is larger than that from O 2p, so the electrons are preferentially extracted from Ni during the initial state of charge. Upon deep sodiation, surprisingly, the energy state of O 2p raises over those of all TMs 3d when x = 0.5, which confirms the preference of electron given from O instead of TM ions. This result also validates our observations in the magnetic moment examinations. On the other hand, Ti and Mn 3d orbitals always show rather low levels throughout the whole desodiation, confirming their inert natures in the redox process.In order to monitor the redox evolutions of TMs and possible participation of O, we examined the oxidation states in the desodiated compositions on the convex hull. The oxidation states can be determined by comparing the calculated magnetizations of TMs and O with the number of unpaired electrons of the corresponding ions with known oxidation states.57 As y Figure . Howeverx Figure , meanwhis Figure . This ims Figure . For fur This behavior is usually referred as H2‐H3 transition or solid‐solution transition. In the present study, we have provided solid evidence that the D‐NNM possesses similar oxygen charge compensation at high voltage. In the same voltage region, the moderate P2–P2’ transition is triggered instead of the typical P2–O2 transition. So, it is natural to suppose that the hindrance of P2–O2 is the result of the oxygen charge compensation as it enables alteration of the systematic total energy by weakening the O—O repulsion.Altogether, the above results have clarified the driving mechanism of the P2–P2’ transition in the D‐NNM instead of the P2–O2 transition in the P‐NNM. For the typical NNM materials, the P2–O2 transition at high voltage is determined by system total energy. When Na ions are depleted from the interlayers, the O—O electrostatic force becomes critical as it is the major interaction against the layers. So, any change of the O—O repulsion would affect the total energy and thereby the high‐voltage sliding behaviors. Taking the Li‐ion layered oxides as an example, the oxygen charge compensation in this counterpart could result in a decrease of O—O repulsion at high voltage, giving rise to a continuous interlayer contraction that is sustainable for long‐term cycling.27 Thi+, a crossover of formation energies between P2 and P2’ could be observed in the D‐NNM models, which recovers the P2–P2’ transition revealed in the experiments. Meanwhile, the energy of the O2 phase is higher than P2 and P2’ over the entire electrochemical process. So, the P2–O2 transition typically occurred in the P‐NNM is inhibited in the D‐NNM material. Along with the occurrence of P2–P2’ transition, it is found that the energy states of O 2p valance electrons raise over those of the TM 3d electrons. These shallow‐trapped O 2p electrons would compensate the charge loss of TMs through the TM—O covalent bonds, which explains the oxygen charge compensation behavior that triggers the P2–P2’ transition in the D‐NNM. Consequently, the roles of the Ti and Mg dopants can be summarized as the regulators of TM—O covalency and the related O—O repulsion upon charging and discharging, which are the underlying fundamentals of the anomalous P2–P2’ transition in the D‐NNM cathode.The above speculation has been further proven by the DFT calculations from combined viewpoints of energetics and electronics. With the gradual extraction of Na In the oxygen redox reaction, the electrons extracted from oxygen will flow to an external circuit and account for extra capacity. By contrast, the XPS results in this study reveal that the appearance of On− (n < 2) at high voltage is accompanied by the reduction of Ni ions, so the electrons from the oxygen transfer to Ni ions for charge compensation instead of going to the external circuit for capacity. In addition, the capacity of the D‐NNM is not higher than that of the P‐NNM, so the participation of oxygen in the redox reaction is indistinctive. Furthermore, the charge–discharge profile of D‐NNM shows no obvious high‐voltage plateau of oxygen redox. The sloping characteristic at ≈4.1 V could be related to the newly emerged P2’ phase according to our in situ XRD and in situ PDF results. As a consequence, it is the oxygen charge compensation other than the oxygen redox behavior that is triggered by the Ti and Mg dopants.Note that the oxygen charge compensation observed in the D‐NNM should be distinguished from the oxygen redox behavior in the Li‐/Na‐rich systems.58 In 32p—TM3d covalent bonds, as validated by the investigations of geometric and electronic structures as well as first‐principles calculations. In this way, the interlayer O—O electrostatic repulsion is weakened upon deeply charging, which strongly affects the systematic total energy for modulating high‐voltage slab sliding behaviors. Benefiting from the above, the D‐NNM cathode shows a dramatically improved cycling stability compared with the P‐NNM cathode. This study has realized a long‐painted scenario that the layered hosts can store Na+ in a similar way to Li+ for extended cycle life, opening a new frame‐work for developing high‐performance electrodes for SIBs.In summary, the P2‐type Ti/Mg codoped NNM layered cathode shows a moderate solid‐solution behavior at high voltage, which differs from the striking P2–O2 phase transition in P‐NNM. This abnormal behavior is driven by the activation of charge compensation through highly hybridized O4Detailed sample synthesis method for pristine and PGE‐NCM811 materials, characterizations, theoretical calculations, and electrochemical measurements are presented in the Supporting Information.The authors declare no conflict of interest.Supporting InformationClick here for additional data file.