Synthesis and characterisation of hydrido molybdenum and tungsten complexes having a hemilabile tridentate Si,Si,O-ligand: observation of stepwise hydrosilylation of a nitrile to form an N-silylimine on the metal centre

Abstract

Photoinduced decarbonylation of Cp*M(CO)(3)Me (M = Mo and W, Cp* = η(5)-C(5)Me(5)) in the presence of xantsilH(2) [xantsil = (9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl)] in pentane gave bis(silyl)hydrido complexes Cp*M(κ(2)Si,Si-xantsil)(CO)(2)(H) (1a: M = Mo and 1b: M = W) through two-fold Si-H oxidative addition and methane elimination. Further irradiation of 1a,b in toluene afforded tridentate xantsil complexes Cp*M(κ(3)Si,Si,O-xantsil)(CO)(H) (2a: M = Mo and 2b: M = W) via CO dissociation. Reactions of complexes 2a,b with nitriles led to stoichiometric hydrosilylation at the C[triple bond, length as m-dash]N triple bond. Thus, reaction of 2a,b with t-BuCN at room temperature afforded N-silyliminoacyl complexes 3a,b, through insertion of a nitrile into the M-Si bond, and the products slowly isomerised to the corresponding N-silylimine complexes 4a,bvia intramolecular hydrogen migration. On the other hand, reaction of 2a,b with PhCN afforded N-silylimine complexes 5a,b directly. The molecular structures of 1a, 3a and 5b were determined by X-ray crystallography, revealing that complex 3a has a 3-centre-2-electron (3c-2e) Mo-Si-H bond.

Reactions of Hydrosilanes with Transition Metal Complexes

“…Certain silane systems have been used in the same sense as a chelate, that is, to tie together adjacent sites at the metal center. Examples include 1,2-(HMe 2 Si) 2 C 6 H 4 , and xantsilH 2 [xantsil = (9,9-dimethyl­xanthene-4,5-diyl)­bis­(dimethylsilyl)] (Figure ). Representative reactions are shown in eqs –.…”

Unusual Structure, Fluxionality, and Reaction Mechanism of Carbonyl Hydrosilylation by Silyl Hydride Complex [(ArN)Mo(H)(SiH2Ph)(PMe3)3]

“…Such a significant upfield shift of the signals that are due to the methylenamide proton and the carbon atoms of complex 35 suggests a k 3 -coordination mode of the N=C(Ph)ÀN= CHPh ligand, for example, through the presence of additional p coordination of the N= CHPh moiety. [55] Scheme 11. DFT-calculated mechanism for the hydrosilylation of acetone catalyzed by complex 13.…”

Silane(silyl) and Bis(silyl)hydrido Manganese Complexes with Different Mn···H···Si Interaction: Observation of Gradual Si–H Bond Activation on the Metal Center

“…4 Crystal structure analysis revealed that complexes 13 have substantially different Mn£H£Si(xantsil) interaction in the coordination sphere. By decreasing the number of CO ligands on Mn, the Mn£Si interaction is strengthened while the Si£H interaction is weakened.…”

“…8 The negligible interaction between Mn and Si(2) in 1 is attributable to both electronic and steric effects. The electronic effect is based on the relatively electron-deficient Mn(I) center of the [Mn(CO) 4 ] fragment that causes the weak ³-back donation to the silane ligand. 9 On the other hand, the steric factor is based on the steric repulsion between the xantsil(H) ligand and the [Mn(CO) 4 ] fragment.…”

“…The electronic effect is based on the relatively electron-deficient Mn(I) center of the [Mn(CO) 4 ] fragment that causes the weak ³-back donation to the silane ligand. 9 On the other hand, the steric factor is based on the steric repulsion between the xantsil(H) ligand and the [Mn(CO) 4 ] fragment. This is reflected on some interatomic distances between carbon atoms in SiMe groups and a CO ligand, i.e., C(2)£C (22) 1 in 1 to η 2 in 2 is attributable in part to the increase of electron richness of the Mn center by substitution of one CO ligand with xantheneoxygen, which leads to a stronger ³-back donation from manganese to the SiH bond.…”