Unusual structure, fluxionality, and reaction mechanism of carbonyl hydrosilylation by silyl hydride complex [(ArN=)Mo(H)(SiH2Ph) (PMe3)3]

Andrey Y. Khalimon, Stanislav K. Ignatov, Andrey I. Okhapkin, Razvan Simionescu, Lyudmila G. Kuzmina, Judith A K Howard, Georgii I. Nikonov

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The reactions of bis(borohydride) complexes [(RN=)Mo(BH4) 2(PMe3)2] (4: R=2,6-Me2C 6H3; 5: R=2,6-iPr2C6H3) with hydrosilanes afford new silyl hydride derivatives [(RN=)Mo(H) (SiR′3)(PMe3)3] (3: R=Ar, R′3=H2Ph; 8: R=Ar′, R′3= H2Ph; 9: R=Ar, R′3=(OEt)3; 10: R=Ar, R′3=HMePh). These compounds can also be conveniently prepared by reacting [(RN=)Mo(H)(Cl)(PMe3)3] with one equivalent of LiBH4 in the presence of a silane. Complex 3 undergoes intramolecular and intermolecular phosphine exchange, as well as exchange between the silyl ligand and the free silane. Kinetic and DFT studies show that the intermolecular phosphine exchange occurs through the predissociation of a PMe3 group, which, surprisingly, is facilitated by the silane. The intramolecular exchange proceeds through a new non-Bailar-twist pathway. The silyl/silane exchange proceeds through an unusual MoVI intermediate, [(ArN=)Mo(H)2(SiH2Ph)2(PMe3) 2] (19). Complex 3 was found to be the catalyst of a variety of hydrosilylation reactions of carbonyl compounds (aldehydes and ketones) and nitriles, as well as of silane alcoholysis. Stoichiometric mechanistic studies of the hydrosilylation of acetone, supported by DFT calculations, suggest the operation of an unexpected mechanism, in that the silyl ligand of compound 3 plays an unusual role as a spectator ligand. The addition of acetone to compound 3 leads to the formation of [trans-(ArN)Mo(OiPr)(SiH2Ph)(PMe 3)2] (18). This latter species does not undergo the elimination of a Si-O group (which corresponds to the conventional Ojima′s mechanism of hydrosilylation). Rather, complex 18 undergoes unusual reversible β-CH activation of the isopropoxy ligand. In the hydrosilylation of benzaldehyde, the reaction proceeds through the formation of a new intermediate bis(benzaldehyde) adduct, [(ArN=)Mo(η2-PhC(O)H) 2(PMe3)], which reacts further with hydrosilane through a η1-silane complex, as studied by DFT calculations. Rule breakers: Silyl hydride complex [(ArN)Mo(H)(SiH2Ph)(PMe3) 3] undergoes a silane-assisted exchange of coordinated and free phosphines and catalyzes the hydrosilylation of carbonyl groups through an unexpected mechanism (see scheme), as studied by using DFT.

Original languageEnglish
Pages (from-to)8573-8590
Number of pages18
JournalChemistry - A European Journal
Volume19
Issue number26
DOIs
Publication statusPublished - Jun 24 2013
Externally publishedYes

Fingerprint

Hydrosilylation
Silanes
Hydrides
phosphine
Hydrogen
Discrete Fourier transforms
Ligands
Acetone
Phosphines
Borohydrides
Carbonyl compounds
Nitriles
Ketones
Aldehydes
Chemical activation
Derivatives
Catalysts
Kinetics

Keywords

  • fluxionality
  • hydrides
  • hydrosilylation
  • molybdenum
  • silicon

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Unusual structure, fluxionality, and reaction mechanism of carbonyl hydrosilylation by silyl hydride complex [(ArN=)Mo(H)(SiH2Ph) (PMe3)3]. / Khalimon, Andrey Y.; Ignatov, Stanislav K.; Okhapkin, Andrey I.; Simionescu, Razvan; Kuzmina, Lyudmila G.; Howard, Judith A K; Nikonov, Georgii I.

In: Chemistry - A European Journal, Vol. 19, No. 26, 24.06.2013, p. 8573-8590.

Research output: Contribution to journalArticle

Khalimon, Andrey Y. ; Ignatov, Stanislav K. ; Okhapkin, Andrey I. ; Simionescu, Razvan ; Kuzmina, Lyudmila G. ; Howard, Judith A K ; Nikonov, Georgii I. / Unusual structure, fluxionality, and reaction mechanism of carbonyl hydrosilylation by silyl hydride complex [(ArN=)Mo(H)(SiH2Ph) (PMe3)3]. In: Chemistry - A European Journal. 2013 ; Vol. 19, No. 26. pp. 8573-8590.
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abstract = "The reactions of bis(borohydride) complexes [(RN=)Mo(BH4) 2(PMe3)2] (4: R=2,6-Me2C 6H3; 5: R=2,6-iPr2C6H3) with hydrosilanes afford new silyl hydride derivatives [(RN=)Mo(H) (SiR′3)(PMe3)3] (3: R=Ar, R′3=H2Ph; 8: R=Ar′, R′3= H2Ph; 9: R=Ar, R′3=(OEt)3; 10: R=Ar, R′3=HMePh). These compounds can also be conveniently prepared by reacting [(RN=)Mo(H)(Cl)(PMe3)3] with one equivalent of LiBH4 in the presence of a silane. Complex 3 undergoes intramolecular and intermolecular phosphine exchange, as well as exchange between the silyl ligand and the free silane. Kinetic and DFT studies show that the intermolecular phosphine exchange occurs through the predissociation of a PMe3 group, which, surprisingly, is facilitated by the silane. The intramolecular exchange proceeds through a new non-Bailar-twist pathway. The silyl/silane exchange proceeds through an unusual MoVI intermediate, [(ArN=)Mo(H)2(SiH2Ph)2(PMe3) 2] (19). Complex 3 was found to be the catalyst of a variety of hydrosilylation reactions of carbonyl compounds (aldehydes and ketones) and nitriles, as well as of silane alcoholysis. Stoichiometric mechanistic studies of the hydrosilylation of acetone, supported by DFT calculations, suggest the operation of an unexpected mechanism, in that the silyl ligand of compound 3 plays an unusual role as a spectator ligand. The addition of acetone to compound 3 leads to the formation of [trans-(ArN)Mo(OiPr)(SiH2Ph)(PMe 3)2] (18). This latter species does not undergo the elimination of a Si-O group (which corresponds to the conventional Ojima′s mechanism of hydrosilylation). Rather, complex 18 undergoes unusual reversible β-CH activation of the isopropoxy ligand. In the hydrosilylation of benzaldehyde, the reaction proceeds through the formation of a new intermediate bis(benzaldehyde) adduct, [(ArN=)Mo(η2-PhC(O)H) 2(PMe3)], which reacts further with hydrosilane through a η1-silane complex, as studied by DFT calculations. Rule breakers: Silyl hydride complex [(ArN)Mo(H)(SiH2Ph)(PMe3) 3] undergoes a silane-assisted exchange of coordinated and free phosphines and catalyzes the hydrosilylation of carbonyl groups through an unexpected mechanism (see scheme), as studied by using DFT.",
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T1 - Unusual structure, fluxionality, and reaction mechanism of carbonyl hydrosilylation by silyl hydride complex [(ArN=)Mo(H)(SiH2Ph) (PMe3)3]

AU - Khalimon, Andrey Y.

AU - Ignatov, Stanislav K.

AU - Okhapkin, Andrey I.

AU - Simionescu, Razvan

AU - Kuzmina, Lyudmila G.

AU - Howard, Judith A K

AU - Nikonov, Georgii I.

PY - 2013/6/24

Y1 - 2013/6/24

N2 - The reactions of bis(borohydride) complexes [(RN=)Mo(BH4) 2(PMe3)2] (4: R=2,6-Me2C 6H3; 5: R=2,6-iPr2C6H3) with hydrosilanes afford new silyl hydride derivatives [(RN=)Mo(H) (SiR′3)(PMe3)3] (3: R=Ar, R′3=H2Ph; 8: R=Ar′, R′3= H2Ph; 9: R=Ar, R′3=(OEt)3; 10: R=Ar, R′3=HMePh). These compounds can also be conveniently prepared by reacting [(RN=)Mo(H)(Cl)(PMe3)3] with one equivalent of LiBH4 in the presence of a silane. Complex 3 undergoes intramolecular and intermolecular phosphine exchange, as well as exchange between the silyl ligand and the free silane. Kinetic and DFT studies show that the intermolecular phosphine exchange occurs through the predissociation of a PMe3 group, which, surprisingly, is facilitated by the silane. The intramolecular exchange proceeds through a new non-Bailar-twist pathway. The silyl/silane exchange proceeds through an unusual MoVI intermediate, [(ArN=)Mo(H)2(SiH2Ph)2(PMe3) 2] (19). Complex 3 was found to be the catalyst of a variety of hydrosilylation reactions of carbonyl compounds (aldehydes and ketones) and nitriles, as well as of silane alcoholysis. Stoichiometric mechanistic studies of the hydrosilylation of acetone, supported by DFT calculations, suggest the operation of an unexpected mechanism, in that the silyl ligand of compound 3 plays an unusual role as a spectator ligand. The addition of acetone to compound 3 leads to the formation of [trans-(ArN)Mo(OiPr)(SiH2Ph)(PMe 3)2] (18). This latter species does not undergo the elimination of a Si-O group (which corresponds to the conventional Ojima′s mechanism of hydrosilylation). Rather, complex 18 undergoes unusual reversible β-CH activation of the isopropoxy ligand. In the hydrosilylation of benzaldehyde, the reaction proceeds through the formation of a new intermediate bis(benzaldehyde) adduct, [(ArN=)Mo(η2-PhC(O)H) 2(PMe3)], which reacts further with hydrosilane through a η1-silane complex, as studied by DFT calculations. Rule breakers: Silyl hydride complex [(ArN)Mo(H)(SiH2Ph)(PMe3) 3] undergoes a silane-assisted exchange of coordinated and free phosphines and catalyzes the hydrosilylation of carbonyl groups through an unexpected mechanism (see scheme), as studied by using DFT.

AB - The reactions of bis(borohydride) complexes [(RN=)Mo(BH4) 2(PMe3)2] (4: R=2,6-Me2C 6H3; 5: R=2,6-iPr2C6H3) with hydrosilanes afford new silyl hydride derivatives [(RN=)Mo(H) (SiR′3)(PMe3)3] (3: R=Ar, R′3=H2Ph; 8: R=Ar′, R′3= H2Ph; 9: R=Ar, R′3=(OEt)3; 10: R=Ar, R′3=HMePh). These compounds can also be conveniently prepared by reacting [(RN=)Mo(H)(Cl)(PMe3)3] with one equivalent of LiBH4 in the presence of a silane. Complex 3 undergoes intramolecular and intermolecular phosphine exchange, as well as exchange between the silyl ligand and the free silane. Kinetic and DFT studies show that the intermolecular phosphine exchange occurs through the predissociation of a PMe3 group, which, surprisingly, is facilitated by the silane. The intramolecular exchange proceeds through a new non-Bailar-twist pathway. The silyl/silane exchange proceeds through an unusual MoVI intermediate, [(ArN=)Mo(H)2(SiH2Ph)2(PMe3) 2] (19). Complex 3 was found to be the catalyst of a variety of hydrosilylation reactions of carbonyl compounds (aldehydes and ketones) and nitriles, as well as of silane alcoholysis. Stoichiometric mechanistic studies of the hydrosilylation of acetone, supported by DFT calculations, suggest the operation of an unexpected mechanism, in that the silyl ligand of compound 3 plays an unusual role as a spectator ligand. The addition of acetone to compound 3 leads to the formation of [trans-(ArN)Mo(OiPr)(SiH2Ph)(PMe 3)2] (18). This latter species does not undergo the elimination of a Si-O group (which corresponds to the conventional Ojima′s mechanism of hydrosilylation). Rather, complex 18 undergoes unusual reversible β-CH activation of the isopropoxy ligand. In the hydrosilylation of benzaldehyde, the reaction proceeds through the formation of a new intermediate bis(benzaldehyde) adduct, [(ArN=)Mo(η2-PhC(O)H) 2(PMe3)], which reacts further with hydrosilane through a η1-silane complex, as studied by DFT calculations. Rule breakers: Silyl hydride complex [(ArN)Mo(H)(SiH2Ph)(PMe3) 3] undergoes a silane-assisted exchange of coordinated and free phosphines and catalyzes the hydrosilylation of carbonyl groups through an unexpected mechanism (see scheme), as studied by using DFT.

KW - fluxionality

KW - hydrides

KW - hydrosilylation

KW - molybdenum

KW - silicon

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