Chemical and electrochemical oxidation of group 6 cyclopentadienylmetal hydrides. First estimates of 17-electron metal-hydride cation-radical thermodynamic acidities and their decomposition of 17-electron neutral radicals

Ryan, Olav B.; Tilset, Mats; Parker, Vernon D.

doi:10.1021/ja00163a023

Cited by 133 publications

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“…[9] The molybdenum hydride [Mo(Cp)(CO) 3 H] is less acidic, with a pK a of 13.9. [9] Tilset and co-workers found [10] that one-electron oxidation of metal hydrides can produce super-acids, with a pK a of À6.0 estimated in CH 3 CN for the radicalcation complex [Mo(Cp)(CO) 3 H] + ¥ . For our purposes, we need a dihydride or dihydrogen complex as the proton donor rather than a monohydride, and it is abundantly clear that such complexes can have ample acidity.…”

Section: Introductionmentioning

confidence: 99%

Catalytic Ionic Hydrogenations

Bullock

2004

Chemistry A European J

290

206

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Catalytic ionic hydrogenation of ketones occurs by proton transfer to a ketone from a cationic metal dihydride, followed by hydride transfer from a neutral metal hydride. This contrasts with traditional catalysts for ketone hydrogenation that require binding of the ketone to the metal and subsequent insertion of the ketone into a M-H bond. Ionic hydrogenation catalysts based on the inexpensive metals molybdenum and tungsten have been developed based on mechanistic understanding of the individual steps required in the catalytic reaction.

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Section: Introductionmentioning

confidence: 99%

Catalytic Ionic Hydrogenations

Bullock

2004

Chemistry A European J

290

206

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“…These complexes have generally been accessed by one-electron oxidation of stable diamagnetic precursors. In most cases, they decompose by deprotonation, [7] disproportionation, [8] dihydrogen reductive elimination (for complexes containing at least two hydride ligands), [9] atom transfer, [10] and other pathways. [11] This multitude of available reaction pathways complicates their poten- …”

Section: Introductionmentioning

confidence: 99%

Synthesis, Structure, and Electrochemical Properties of Sterically Protected Molybdenum Trihydride Redox Pairs: A Paramagnetic “Stretched” Dihydrogen Complex?

Baya

Houghton

Daran

et al. 2007

Chemistry A European J

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Complexes [MoCp(#)(PMe(3))(2)H(3)] (Cp(#)=1,2,4-C(5)H(2)tBu(3), 2 a; C(5)HiPr(4), 2 b) have been synthesized from the corresponding compounds [MoCp(#)Cl(4)] (1 a, 1 b) and fully characterized, including by X-ray crystallography and by a neutron diffraction study for 2 a. Protonation of 2 a led to complex [Mo(1,2,4-C(5)H(2)tBu(3))(PMe(3))(2)H(4)](+) (3 a) in THF and to [Mo(1,2,4-C(5)H(2)tBu(3))(PMe(3))(2)(MeCN)H(2)](+) (4 a) in MeCN. Complex 4 b analogously derives from protonation of 2 b in MeCN, whereas the tetrahydride complex 3 b is unstable. One-electron oxidation of 2 a and 2 b by [FeCp(2)]PF(6) produces the EPR-active 17-electron complexes 2 a(+) and 2 b(+). The former is thermally more stable than the latter and could be crystallographically characterized as the PF(6) (-) salt by X-ray diffraction, providing evidence for the presence of a stretched dihydrogen ligand (H...H=1.36(6) angstroms). Controlled thermal decomposition of 2 a(+) yielded the product of H(2) elimination, the 15-electron monohydride complex [Mo(1,2,4-C(5)H(2)tBu(3))(PMe(3))(2)H]PF(6) (5 a), which was characterized by X-ray crystallography and by EPR spectroscopy at liquid He temperature. The compound establishes an equilibrium with the solvent adduct in THF. An electrochemical study by cyclic voltammetry provides further evidence for a rapid H(2) elimination process from the 17-electron complexes. In contrast to the previously investigated [MoCp*(dppe)H(3)](+) system (dppe=1,2-bis(diphenylphosphino)ethane; Cp*=pentamethylcyclopentadienyl), the decomposition of 2 a(+) by H(2) substitution with a solvent molecule appears to follow a dissociative pathway in MeCN.

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“…In contrast to the formation of the trans -isomer under catalytic conditions, hydride transfer from Cp(CO) 2 (PPh 3 )WH to Ph 3 C + , followed by addition of Et 2 CHOH, led to the isolation of cis -[CpW(CO) 2 Conversion of the kinetically favored trans -isomer to the thermodynamically favored cis -isomer has been observed in several cases of Mo and W complexes with similar structures [23,48] .…”

Section: Catalytic Ionic Hydrogenations With Mo and W Catalystsmentioning

confidence: 99%

Molybdenum and Tungsten Catalysts for Hydrogenation, Hydrosilylation and Hydrolysis

Bullock

2010

Catalysis Without Precious Metals

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Chemical and electrochemical oxidation of group 6 cyclopentadienylmetal hydrides. First estimates of 17-electron metal-hydride cation-radical thermodynamic acidities and their decomposition of 17-electron neutral radicals

Cited by 133 publications

References 0 publications

Catalytic Ionic Hydrogenations

Catalytic Ionic Hydrogenations

Synthesis, Structure, and Electrochemical Properties of Sterically Protected Molybdenum Trihydride Redox Pairs: A Paramagnetic “Stretched” Dihydrogen Complex?

Molybdenum and Tungsten Catalysts for Hydrogenation, Hydrosilylation and Hydrolysis

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