peroxide to a chromium(III) superoxide upon coordination of a donor in

Subscriber access provided by Nottingham Trent University

Communication

Switching from a chromium(IV) peroxide to a chromium(III) superoxide upon coordination of a donor in the trans position Marie-Louise Wind, Santina Hoof, Beatrice Braun-Cula, Christian Herwig, and Christian Limberg J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b06826 • Publication Date (Web): 28 Aug 2019 Downloaded from pubs.acs.org on August 30, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Journal of the American Chemical Society

Switching from a chromium(IV) peroxide to a chromium(III) superoxide upon coordination of a donor in the trans position Marie-Louise Wind, Santina Hoof, Beatrice Braun-Cula, Christian Herwig, Christian Limberg* Humboldt-Universität zu Berlin, Department of Chemistry, Brook-Taylor-Straße 2, 12489 Berlin, Germany.

S ABSTRACT: O2 activation at a chromium(II) siloxide complex in EtCN leads to a chromium(III) complex with an end-on bound superoxide ligand, while the reaction in THF leads to a side-on peroxo chromium(IV) compound. The superoxide reacts faster with TEMPO-H (HAT) while the peroxide, unlike the superoxide, proved capable of deformylating aldehydes. The system was found to represent a unique case, where even a switching between the two structures can be achieved via the solvent; its ability to coordinate at the position trans to the O2 ligand is decisive, as supported by DFT studies. Altogether, the results show that subtle changes can determine for an initially formed metal-dioxygen adduct, whether it exists as a superoxide or a peroxide, which thus merits consideration in discussions on mechanisms and possible reaction routes.

The activation of O2 is a key-step in processes, by which natural or synthetic systems, convert hydrocarbons into value-added products. Hence, the profound understanding and control of O2 activation and of the initial O2 adducts formed is invaluable.1-9 Of special interest are the different binding modes of the O2 unit (end-on vs. side-on), the resulting electronic structures (peroxo vs. superoxo) as well as their further reactivity and behavior.9-12 Examples, where two different types of O2 adducts interconvert, are rare. In this context the [(TACN)Cu]2O2 systems studied by Tolman and coworkers are worth mentioning, which change between the Cu2-(µ-η2:η2-O2) and Cu2-(µ-O)2 forms dependent on the residues at the TACN ligand, solvent and counter ions.13 Conversions between peroxides and superoxides have been achieved, too, but typically these required the addition of external redox equivalents in form of a reducing metal ion or a different reductant, or via the O2 pressure (which induces redox chemistry involving the O2).14-22 Intramolecular redox conversions, leading selectively to one species or another triggered by an external stimulus (like solvent or ligand as in the abovementioned [(TACN)Cu]2O2 case) have not been reported yet. Examples, where peroxide and superoxide forms were observed for defined redox couples include spectroscopic evidence for the transformation of an initially formed heme–μ-peroxo–CuII intermediate into the heme– superoxo/CuI species in the course of the reaction between a heme-CuI precursor and O2.23 Moreover, spectroscopic evidence has been gained that reacting an iron(II) porphyrin

complex with an excess of superoxide (KO2, NaO2) 24-25 leads to FeIIO2–• and FeIIIO22– complexes co-existing in an equilibrium. Unfortunately, their independent synthesis and isolation was not possible. By contrast, using hydrogen peroxide independent synthetic routes to a NiII-superoxide and a NiIII-peroxide could be developed employing different bases for the deprotonation of the reagent. However, although the results of calculations suggested a low interconversion energy barrier, no transformation between the two complexes could be achieved.26 We herein present an unprecedented case where O2 activation in different solvents has allowed for the direct synthesis of both, an end-on CrIII superoxo complex as well as a side-on CrIV peroxo complex, which can be interconverted controlled by the solvent (without external redox equivalents) and show a different reaction behavior. We were recently able to demonstrate that the reactivity and stability of CrIII superoxo complexes of the type [PhL2Cr]M2O2 (M = Li, Na, K, L = –OPh2SiOSiPh2O–) are strongly dependent on the nature of the metal ions M+ employed, as these interact in different ways with the superoxide ligand; this leads to varying binding motifs, which were shown to be identical in solution and solid state.27,28 We also observed that the solvent has an influence on the complex properties, too, via its binding to M+: the superoxide moiety of [PhL2Cr]Li2O2 in THF (2) interacts only with one of the Li+ ions embedded into the structure, whereas in 3 ([PhL2Cr]Li2O2 in EtCN) both Li+ ions undergo electrostatic interactions (Scheme 1). This raised the question to what extent the variation of the substituents attached to the silicon atoms

Scheme 1: Solvent dependency of the structural arrangement of CrIII superoxide moieties.

ACS Paragon Plus Environment

Journal of the American Chemical Society 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

would influence the structure, reactivity, stability and type of Cr–O2 intermediates formed. Accordingly, we synthesized an analogue of [PhL2Cr]Li2(THF)4 (1) with i-propyl groups [iPrL2Cr]Li2(THF)4 (4) (L = –OiPr2SiOSiiPr2O–) as substituents. Dioxygen was then added to 4 dissolved in different solvents (THF, RCN (R = Me, Et), 0.6 mM, –80 °C) and the reaction monitored via UV/vis spectroscopy. In EtCN the positions of the bands belonging to 4+O2 are very similar to those found for [PhL2Cr]Li2O2(EtCN)4 (3) (SI Figure S5), the structure of which has been determined previously.27 Thus we conclude, that a new CrIII superoxide complex, namely [iPrL2Cr]Li2O2(EtCN)4 (5), where the THF molecules of the starting compound 4 have been replaced by EtCN and both Li+ ions are interacting with the superoxide ligand, has been formed (Scheme 2); the same observations were made with MeCN. The number of interactions (one vs. two) can be deducted from the presence or absence of an absorption band in the near infra-red region.27-28 Resonance Raman measurements on 5 dissolved in MeCN confirmed through a band at 1123 cm–1, shifting to 1063 cm–1 upon using 18O , the assignment as a superoxide.27-30 Hence, in nitriles the 2 variation of the substituents at the siloxide backbone from phenyl to i-propyl does not lead to changes with regard to the type of O2 adduct, which is formed.

in the CrII precursor complexes – is retained in THF,27-28 6 adopts a twisted structure (Figure 1) and the position trans to the O2 unit is vacant. The O–O distance is with 1.477(4) Å in good agreement with values published for peroxides (O–O = 1.4 – 1.5 Å);31 it is somewhat larger, though, compared with bond lengths found for the few examples of structurally characterized chromium(IV) peroxo compounds reported so far (e.g. 1.394 and 1.383(8) Å)32-33 perhaps due to the contact with the Li+ ions.16 Also DFT calculations strongly support the assignment of 6 as a CrIV peroxo complex (triplet ground state with two unpaired electrons at Cr, no unpaired electrons elsewhere), which is in agreement with the results obtained experimentally. In consequence, we have separately synthesized the O2 adducts [iPrL2CrIV]Li2O2(THF)4 (6) and [iPrL2CrIII]Li2O2(EtCN)4 (5), that concerning the formula only differ in the coordinated solvent molecules but feature rather different electronic structures of the CrO2Li2 cores. To compare them with regard to their potential in HAT reactions, 4 was dissolved in THF or EtCN, respectively, cooled to –80 °C, treated with an excess of O2 and TEMPO–H was added. The disappearance of the absorption bands characteristic of 6 or 5, respectively, with a pseudo-first-order decay was monitored UV/vis spectroscopically (Figure 2).

Performing the reaction in THF, however, clearly revealed a difference. When 4 was dissolved in THF and exposed to an excess of molecular dioxygen, no absorption bands characteristic of an end-on bound superoxide could be detected in the UV/vis spectra. Instead, one very strong band at 369 nm was observed, indicating the formation of a different kind of dioxygen adduct (Figure 2B, red trace). Raman measurements in THF were carried out (excitation at 355 nm or 514.5 nm) using both 16O2 and 18O2, however, no isotope sensitive bands could be observed, likely due to the temperature and light sensitivity of the compound (SI Figure S10). Fortunately, single crystals could be grown from a cooled solution of [iPrL2Cr]Li2O2(THF)4 (6) and X-ray analysis revealed the formation of an O2 adduct, in which O2 is now not bound in an end-on but in a side-on fashion and interacts with both Li+ cations (Figure 1 and Scheme 2). While in the superoxide complexes discussed so far the planar arrangement of the CrO4 framework – as found

Figure 2: UV/vis spectral changes observed for 5 dissolved in EtCN upon addition of 18 equiv. of TEMPO–H (A) and 6 dissolved in THF upon addition of 40 equiv. of TEMPO–H (B). Insets shows the time course of the absorbances at 309 nm. and 369 nm, respectively.

Figure 1. Molecular structure of 6. For clarity hydrogen atoms and THF molecules coordinated to the Li atoms are omitted.

As a product TEMPO could be detected by means of EPR spectroscopy. Through the variation of the TEMPO–H concentration second order rate constants (k2) of 8.6±0.8 M– 1s–1 and 306.6±40.2 M–1s–1 were determined for 6 and 5, respectively (SI Figure S7). Hence, at –80 °C the superoxo


Page 2 of 7

Page 3 of 7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Journal of the American Chemical Society complex 5 is approximately 35 times more reactive than the peroxo complex 6, which nicely reflects the differing electronic structures. When cyclohexanecarboxaldehyde (CCA) was used as a substrate in the reaction with 6, the disappearance of the characteristic absorption bands with a pseudo first-order decay and the formation of cyclohexene (detected by means of GC-MS) could be observed. Again, the pseudo-first-order rate constants increased proportionally with the increase of the concentration of CCA, giving a second order rate constant (k2) of 26.1±1.2 10–2 M–1s–1 at –80 °C (SI Figure S7). Consequently, 6 is capable of deformylating aldehydes via nucleophilic reaction as frequently observed for metal peroxo complexes.34-36 By contrast 5 does not exhibit any reactivity towards CCA under the same conditions, which is reasonable for a superoxide. Further investigations revealed that it is even possible to interconvert [iPrL2CrIV]Li2O2(THF)4 (6) and iPr III [ L2Cr ]Li2O2(EtCN)4 (5). Since the only difference in the synthetic procedures is the solvent, we added RCN (R = Me, Et, Ph) to a solution of 6 in THF and monitored the reaction UV/vis spectroscopically. Indeed, the transformation of [iPrL2CrIV]Li2O2(THF)4 into [iPrL2CrIII]Li2O2(RCN)4 (R = Me, Et, Ph) could be observed. The inverse transformation of [iPrL2CrIII]Li2O2(RCN)4 into [iPrL2CrIV]Li2O2(THF)4 can also be achieved, but only if a prior removal of RCN under vacuum has taken place (Scheme 2). A solution of the resulting orange powder in THF then exhibits the characteristic absorption bands for [iPrL2CrIV]Li2O2(THF)4 (6). The necessity to remove RCN beforehand can be rationalized by the hypothesis, that the axial ligand present in [iPrL2CrIII]Li2O2(RCN)4, but not in [iPrL2CrIV]Li2O2(THF)4, plays an essential role in the conversion, and its displacement can be expected to be difficult in the presence of excessive RCN.

in energy. Upon addition of an axial nitrile to the Cr center of 6 followed by re-optimization, the superoxide isomer becomes slightly favored over the peroxide (14.3 kJ/mol). Hence the presence or absence of the axial nitrile can change the energetical order of the peroxide and the superoxide isomer. The coordination of an axial ligand and concomitant conversion of the peroxide into an end-on bound superoxide ligand could be further corroborated by X-ray diffraction analysis of crystals grown from a solution of 6 in THF after addition of EtCN (1:2 ratio), which belonged to [iPrL2CrIII]Li2O2(EtCN)3(THF)2, 7. Due to disorder the solution of the structure did not reach a quality that would permit a discussion of bond lengths and angles, which, however, was also not the target here, as the structure resembles the one of 2, which has been discussed previously.28 The atom connectivity and their topological arrangement (Figure 3) is without doubt, though, and this reveals that 7 differs constitutionally from 6 only in the additional coordination of a EtCN ligand at the chromium center and a partial exchange of the THF molecules at the Li+ ions by EtCN (Figure 3). Obviously, these changes are sufficient to convert the CrIV peroxide 6 into the CrIII superoxide 7 (as further supported by DFT calculations on the electronic structure of 7, see SI). Further addition of EtCN leads to a UV/vis spectrum identical to the one of 5, that is, the remaining THF molecules in 7 are successively replaced by EtCN and in consequence the second Li+ is displaced out of the CrO4 plane forming [iPrL2CrIII]Li2O2(EtCN)4 (5) (Scheme 2).

Figure 3: Ball-and-stick diagram of the molecular structure of 7. Hydrogen atoms are omitted for clarity. From these results it is now clear that the substituents at the ligand backbone indeed severely influence the structure, reactivity, and type of Cr–O2 intermediates formed, but how? We propose that the folding of the ligand backbone in case of 6 leads to a cleft that allows access to acetonitrile but is sterically too crowded for THF to bind at the Cr center, while in case of 1 both donors can be accommodated leading to superoxide structures in both solvents. To gain further support for this hypothesis we have repeated the entire study with [MeL2Cr]Li2(THF)4 (8), that is, with methyl residues at the backbone, and found that the system behaves exactly like [PhL2Cr]Li2(THF)4 towards dioxygen (SI Figure S5 and S6) underlining that repulsion of the sixth ligand is decisive to stabilize the peroxide.

Scheme 2. Synthetic routes to 5 and 6 and their interconversion. The role of the trans ligand was addressed in DFT calculations, which, interestingly, revealed for 6 an isomer containing a superoxide moiety, which is 48.6 kJ/mol higher

In summary, we have demonstrated that O2 activation at a CrII siloxide precursor can lead to two different species - an end-on CrIII superoxo and a side-on CrIV peroxo complex – dependent on the solvent used. They exhibit different reactivities, as exemplified by studies with TEMPO-H and CCA, and variation of the solvent also allows for a switching



between the two species, which to our knowledge is unprecedented in the literature. The possibility of such a facile interconversion sheds new light on biological and artificial O2 activating systems, as more than just one intermediate species becomes conceivable.

ASSOCIATED CONTENT Supporting Information Experimental procedures; UV–vis experiments, EPR, and rR spectra; crystal data and computational results. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *Prof. C. Limberg, Humboldt-Universität zu Berlin, Department of Chemistry, Brook-Taylor-Strasse 2, 12489 Berlin, Germany, E-mail: [email protected]

Notes

The authors declare no competing financial interests.

ACKNOWLEDGMENT We are grateful to the Deutsche Forschungsgemeinschaft (LI 714/10-1 and “Unifying Systems in Catalysis”) as well as the Humboldt-Universität zu Berlin for financial support.

REFERENCES 1. Bakac, A., Reactions of Superoxo and Oxo Metal Complexes with Aldehydes. Radical-Specific Pathways for CrossDisproportionation of Superoxometal Ions and Acylperoxyl Radicals. J. Am. Chem. Soc. 2002, 124 (31), 9136-9144. 2. Bakac, A., Kinetic and mechanistic studies of the reactions of transition metal-activated oxygen with inorganic substrates. Coord. Chem. Rev. 2006, 250 (15), 2046-2058. 3. Costas, M.; Mehn, M. P.; Jensen, M. P.; Que, L., Dioxygen Activation at Mononuclear Nonheme Iron Active Sites: Enzymes, Models, and Intermediates. Chem. Rev. 2004, 104 (2), 939-986. 4. Klotz, I. M.; Kurtz, D. M., Metal-Dioxygen Complexes: A Perspective. Chem. Rev. 1994, 94 (3), 567-568. 5. Mirica, L. M.; Ottenwaelder, X.; Stack, T. D. P., Structure and Spectroscopy of Copper−Dioxygen Complexes. Chem. Rev. 2004, 104 (2), 1013-1046. 6. Solomon, E. I.; Brunold, T. C.; Davis, M. I.; Kemsley, J. N.; Lee, S.-K.; Lehnert, N.; Neese, F.; Skulan, A. J.; Yang, Y.-S.; Zhou, J., Geometric and Electronic Structure/Function Correlations in NonHeme Iron Enzymes. Chem. Rev. 2000, 100 (1), 235-350. 7. Yao, S.; Driess, M., Lessons from Isolable Nickel(I) Precursor Complexes for Small Molecule Activation. Acc. Chem. Res. 2012, 45 (2), 276-287. 8. Cramer, C. J.; Tolman, W. B., Mononuclear Cu–O2 Complexes: Geometries, Spectroscopic Properties, Electronic Structures, and Reactivity. Acc. Chem. Res. 2007, 40 (7), 601-608. 9. Cramer, C. J.; Tolman, W. B.; Theopold, K. H.; Rheingold, A. L., Variable character of O—O and M—O bonding in side-on (η2) 1:1 metal complexes of O2. Proceedings of the National Academy of Sciences 2003, 100 (7), 3635-3640. 10. Lee, J. Y.; Karlin, K. D., Elaboration of copper–oxygen mediated C–H activation chemistry in consideration of future fuel and feedstock generation. Curr. Opin. Chem. Biol. 2015, 25, 184-193.

11. Cho, J.; Sarangi, R.; Nam, W., Mononuclear Metal–O2 Complexes Bearing Macrocyclic N-Tetramethylated Cyclam Ligands. Acc. Chem. Res. 2012, 45 (8), 1321-1330. 12. Fukuzumi, S.; Lee, Y. M.; Nam, W., Structure and reactivity of the first-row d-block metal-superoxo complexes. Dalton Trans. 2019, 48 (26), 9469-9489. 13. Tolman, W. B., Making and Breaking the Dioxygen O−O Bond: New Insights from Studies of Synthetic Copper Complexes. Acc. Chem. Res. 1997, 30 (6), 227-237. 14. Huacuja, R.; Graham, D. J.; Fafard, C. M.; Chen, C.-H.; Foxman, B. M.; Herbert, D. E.; Alliger, G.; Thomas, C. M.; Ozerov, O. V., Reactivity of a Pd(I)−Pd(I) Dimer with O2: Monohapto Pd Superoxide and Dipalladium Peroxide in Equilibrium. J. Am. Chem. Soc. 2011, 133 (11), 3820-3823. 15. Rettenmeier, C. A.; Wadepohl, H.; Gade, L. H., Structural Characterization of a Hydroperoxo Nickel Complex and Its Autoxidation: Mechanism of Interconversion between Peroxo, Superoxo, and Hydroperoxo Species. Ange. Chem., Int. Ed. 2015, 54 (16), 4880-4884. 16. Duan, P.-C.; Manz, D.-H.; Dechert, S.; Demeshko, S.; Meyer, F., Reductive O2 Binding at a Dihydride Complex Leading to Redox Interconvertible μ-1,2-Peroxo and μ-1,2-Superoxo Dinickel(II) Intermediates. J. Am. Chem. Soc. 2018, 140 (14), 4929-4939. 17. Jung, B.; Karlin, K. D.; Zuberbühler, A. D., Formation and Interconversion of End-on and Side-on μ-Peroxo−Dicopper(II) Complexes. J. Am. Chem. Soc. 1996, 118 (15), 3763-3764. 18. Yao, S.; Xiong, Y.; Vogt, M.; Grützmacher, H.; Herwig, C.; Limberg, C.; Driess, M., O−O Bond Activation in Heterobimetallic Peroxides: Synthesis of the Peroxide [LNi(μ,η2:η2-O2)K] and its Conversion into a Bis(μ-Hydroxo) Nickel Zinc Complex. Angew. Chem. 2009, 121 (43), 8251-8254. 19. Cao, R.; Saracini, C.; Ginsbach, J. W.; Kieber-Emmons, M. T.; Siegler, M. A.; Solomon, E. I.; Fukuzumi, S.; Karlin, K. D., Peroxo and Superoxo Moieties Bound to Copper Ion: Electron-Transfer Equilibrium with a Small Reorganization Energy. J. Am. Chem. Soc. 2016, 138 (22), 7055-7066. 20. Kim, S.; Lee, J. Y.; Cowley, R. E.; Ginsbach, J. W.; Siegler, M. A.; Solomon, E. I.; Karlin, K. D., A N3S(thioether)-Ligated CuIISuperoxo with Enhanced Reactivity. J. Am. Chem. Soc. 2015, 137 (8), 2796-2799. 21. Liu, J.-G.; Shimizu, Y.; Ohta, T.; Naruta, Y., Formation of an End-On Ferric Peroxo Intermediate upon One-Electron Reduction of a Ferric Superoxo Heme. J. Am. Chem. Soc. 2010, 132 (11), 3672-3673. 22. Nakamoto, K.; Oshio, H.; Ōkawa, H.; Kanda, W.; Horiuchi, K.; Kida, S., Synthesis and spectroscopic properties of Co(salen) derivatives containing pendant thioether groups and their dioxygen adducts. Inorg. Chim. Acta 1985, 108 (4), 231-235. 23. Liu, J.-G.; Naruta, Y.; Tani, F., A Functional Model of the Cytochrome c Oxidase Active Site: Unique Conversion of a Heme–μperoxo–CuII Intermediate into Heme– superoxo/CuI. Angew. Chem. 2005, 117 (12), 1870-1874. 24. Dürr, K.; Jux, N.; Zahl, A.; van Eldik, R.; IvanovićBurmazović, I., Volume Profile Analysis for the Reversible Binding of Superoxide to Form Iron(II)-Superoxo/Iron(III)-Peroxo Porphyrin Complexes. Inorg. Chem. 2010, 49 (23), 11254-11260. 25. Dürr, K.; Macpherson, B. P.; Warratz, R.; Hampel, F.; Tuczek, F.; Helmreich, M.; Jux, N.; Ivanović-Burmazović, I., Iron(III) Complex of a Crown Ether−Porphyrin Conjugate and Reversible Binding of Superoxide to Its Iron(II) Form. J. Am. Chem. Soc. 2007, 129 (14), 4217-4228. 26. Cho, J.; Kang, H. Y.; Liu, L. V.; Sarangi, R.; Solomon, E. I.; Nam, W., Mononuclear nickel(II)-superoxo and nickel(iii)-peroxo complexes bearing a common macrocyclic TMC ligand. Chem. Sci. 2013, 4 (4), 1502-1508. 27. Wind, M.-L.; Hoof, S.; Herwig, C.; Braun-Cula, B.; Limberg, C., The Influence of Alkali Metal Ions on the Stability and Reactivity of Chromium(III) Superoxide Moieties Spanned by Siloxide Ligands. Chem. Eur. J. 2019, 25 (22), 5743-5750. 28. Schax, F.; Suhr, S.; Bill, E.; Braun, B.; Herwig, C.; Limberg, C., A Heterobimetallic Superoxide Complex formed through O2


Page 4 of 7

Page 5 of 7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Journal of the American Chemical Society Activation between Chromium(II) and a Lithium Cation. Ange. Chem., Int. Ed. 2015, 54 (4), 1352-1356. 29. Cho, J.; Woo, J.; Nam, W., An “End-On” Chromium(III)Superoxo Complex: Crystallographic and Spectroscopic Characterization and Reactivity in C−H Bond Activation of Hydrocarbons. J. Am. Chem. Soc. 2010, 132 (17), 5958-5959. 30. Qin, K.; Incarvito, C. D.; Rheingold, A. L.; Theopold, K. H., A Structurally Characterized Chromium(III) Superoxide Complex Features “Side-on” Bonding. Ange. Chem., Int. Ed. 2002, 41 (13), 23332335. 31. Holland, P. L., Metal–dioxygen and metal–dinitrogen complexes: where are the electrons? Dalton Trans. 2010, 39 (23), 54155425. 32. Yokoyama, A.; Han, J. E.; Cho, J.; Kubo, M.; Ogura, T.; Siegler, M. A.; Karlin, K. D.; Nam, W., Chromium(IV)–Peroxo Complex Formation and Its Nitric Oxide Dioxygenase Reactivity. J. Am. Chem. Soc. 2012, 134 (37), 15269-15272.

33. de Sousa, D. P.; Bigelow, J. O.; Sundberg, J.; Que, L.; McKenzie, C. J., Caught! Crystal trapping of a side-on peroxo bound to Cr(iv). Chem. Commun. (Cambridge, U. K.) 2015, 51 (14), 2802-2805. 34. Shook, R. L.; Gunderson, W. A.; Greaves, J.; Ziller, J. W.; Hendrich, M. P.; Borovik, A. S., A Monomeric MnIII−Peroxo Complex Derived Directly from Dioxygen. J. Am. Chem. Soc. 2008, 130 (28), 8888-8889. 35. Kim, B.; Jeong, D.; Cho, J., Nucleophilic reactivity of copper(ii)–alkylperoxo complexes. Chem. Commun. (Cambridge, U. K.) 2017, 53 (67), 9328-9331. 36. Jo, Y.; Annaraj, J.; Seo, M. S.; Lee, Y.-M.; Kim, S. Y.; Cho, J.; Nam, W., Reactivity of a cobalt(III)-peroxo complex in oxidative nucleophilic reactions. J. Inorg. Biochem. 2008, 102 (12), 2155-2159.



Page 6 of 7

SYNOPSIS TOC


6

Page 7 of 7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Journal of the American Chemical Society


peroxide to a chromium(III) superoxide upon coordination of a donor in

Recommend Documents