Photoreduction of Diaryl Disulfides by Quadruply Bonded Dimolybdenum and Ditungsten Complexes

Hsu, Tsui Ling C; Helvoigt, Sara A.; Partigianoni, Colleen M.; Turró, Claudia; Nocera, Daniel G.

doi:10.1021/ic00128a033

Cited by 14 publications

(11 citation statements)

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“…Intermolecular or intramolecular perturbations are needed to remove the center of inversion and consequently engender an electronic asymmetry. Transient spectroscopy of M− 4 −M complexes reveal that the two-electron mixed-valence character of the zwitterionic excited state is trapped by an intramolecular ligand rearrangement to yield an edge-sharing bioctahedral (ESBO) intermediate with two electrons localized on one metal center of the bimetallic core, 42 The resultant M + − 3 −M: − zwitterion reacts in discrete two-electron steps: M 2 X 4 (PP) 2 (M = Mo(II), W(II); X = halide; PP = bridging phosphine) complexes undergo one-photon two-electron addition of YZ substrates such as alkyl iodides 43,44 and aryl disulfides 42 to yield M 2 (III,III) ESBO complexes. The same zwitterionic intermediate supports two-electron elimination reactions of isovalent ESBO complexes (the photodriven reverse of eq (4)).…”

Section: A Chemist’s Toolbox For Catalysis Of Consequence To Renewmentioning

confidence: 99%

Chemistry of Personalized Solar Energy

2009

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Personalized energy (PE) is a transformative idea that provides a new modality for the planet’s energy future. By providing solar energy to the individual, an energy supply becomes secure and available to people of both legacy and non-legacy worlds, and minimally contributes to increasing the anthropogenic level of carbon dioxide. Because PE will be possible only if solar energy is available 24 hours a day, 7 day a week, the key enabler for solar PE is an inexpensive storage mechanism. HX (X = halide or OH−) splitting is a fuel-forming reaction of sufficient energy density for large scale solar storage but the reaction relies on chemical transformations that are not understood at the most basic science level. Critical among these are multielectron transfers that are proton-coupled and involve the activation of bonds in energy poor substrates. The chemistry of these three italicized areas is developed, and from this platform, discovery paths leading to new HX and H2O splitting catalysts are delineated. For the case of the water splitting catalyst, it captures many of the functional elements of photosynthesis. In doing so, a highly manufacturable and inexpensive method has been discovered for solar PE storage.

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Section: A Chemist’s Toolbox For Catalysis Of Consequence To Renewmentioning

confidence: 99%

Chemistry of Personalized Solar Energy

2009

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“…[22][23][24][25] As anticipated for the reactivity of two-electron mixed-valence cores, this MMCT excited state promotes two-electron photoredox transformations involving quadruply bonded metal-metal complexes. [26][27][28][29][30][31] When a photon cannot be used to drive the formation of a two-electron mixedvalence intermediate, a ground-state M n+2 ‚‚‚M n species must be stabilized relative to its symmetric M n+1 ‚‚‚M n+1 congener. Yet the paucity of molecular compounds displaying two-electron mixed-valence cores highlights the inability of common ligand systems to preferentially promote this internal disproportionation.…”

Section: Introductionmentioning

confidence: 99%

“…Such is the case for quadruply bonded metal−metal dimers. A lowest-energy electronic excited-state structure of zwitterionic parentage ( + MM: - ) results from the promotion of an electron in the d xy orbital localized on one center of the bimetallic core to the neighboring d xy orbital, localized on the other metal center. − As anticipated for the reactivity of two-electron mixed-valence cores, this MMCT excited state promotes two-electron photoredox transformations involving quadruply bonded metal−metal complexes. − When a photon cannot be used to drive the formation of a two-electron mixed-valence intermediate, a ground-state M n +2 ···M n species must be stabilized relative to its symmetric M n +1 ···M n +1 congener. Yet the paucity of molecular compounds displaying two-electron mixed-valence cores highlights the inability of common ligand systems to preferentially promote this internal disproportionation.…”

Section: Introductionmentioning

confidence: 99%

Hydrido, Halo, and Hydrido-Halo Complexes of Two-Electron Mixed-Valence Diiridium Cores

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Nocera

2000

J. Am. Chem. Soc.

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Two-electron mixed-valence bimetallic cores of iridium are stabilized in a diphosphazane, MeN[P(OCH2CF3)2]2 (bis(bis(trifluoroethoxy)phosphino)methylamine, tfepma) coordination sphere. Treatment of [Ir(cod)Cl]2 with tfepma affords the Ir2 0,II complex, Ir2(tfepma)3Cl2 (1), in which the Ir0 and IrII centers assume trigonal bipyramidal and square pyramidal coordination geometries, respectively. The coordinatively unsaturated two-electron mixed-valence core of 1 supports an extensive acid−base and oxidation−reduction chemistry. As established by single crystal X-ray analysis, two-electron donor ligands are readily received at the IrII center of 1 to complete the octahedral coordination environment that is preferred by a d7 metal−metal bonded center. Alternatively, redox-active substrates rapidly add across the single metal−metal bond of 1 to form Ir2 I,III mixed-valence complexes; the chlorine and hydrochloric acid adducts, Ir2(tfepma)3Cl4 (5) and Ir2(tfepma)3HCl3 (7b), respectively, have been characterized by NMR spectroscopy and X-ray crystallography. Likewise, H2 reacts with 1 to afford an Ir2 I,III dihydride complex, Ir2(tfepma)3H2Cl2 (8). Single-crystal X-ray and NMR analyses of 8 reveal that a single hydride ligand is coordinated at each iridium center of the bimetallic core. Hydrogen is readily removed from the complex in solution and the solid state, providing the first example of the reversible addition of dihydrogen across a single metal−metal bond.

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“…2 The resultant + M-M: 2 zwitterion (formally, a M III M I intermediate for M = Mo and W) exhibits reactivity that establishes it as an excited state analog of Vaska's complex; 3 M 2 X 4 (PP) 2 (M = Mo, W; X = halide; PP = bridging phosphine) complexes undergo two-electron photoadditions of substrates to yield M III 2 complexes with edgesharing bioctahedral (ESBO) geometries. 4,5 An extensive reaction chemistry of the past decade shows these ESBO photoproducts to be inert, especially when metal-halide bonds compose the core. 6 This stability has hampered the construction of cyclic reaction schemes based on M II M II Ô M III M III photoreactivity.…”

mentioning

confidence: 99%

“…Recent work in our group shows that metal-halide bonds are susceptible to photochemical activation along reaction pathways featuring two-electron mixed-valence species. 1b Is the same M + -M: 2 two-electron mixed valence zwitterion, responsible for promoting M-4 M photoaddition reactions, [3][4][5] facilitating ESBO photoelimination chemistry? Alternatively, disproportionation of a photogenerated Mo II Mo III complex could also lead to the observed photochemistry.…”

mentioning

confidence: 99%