Interconversion and reactivity of manganese silyl, silylene, and silene complexes

摘要

Manganese disilyl hydride complexes [(dmpe) _(2) MnH(SiH _(2) R) _(2) ] ( 4 ~(Ph) : R = Ph, 4 ~(Bu) : R = ~( n ) Bu) reacted with ethylene to form silene hydride complexes [(dmpe) _(2) MnH(RHSiCHMe)] ( 6 ~(Ph,H) : R = Ph, 6 ~(Bu,H) : R = ~( n ) Bu). Compounds 6 ~(R,H) reacted with a second equivalent of ethylene to generate [(dmpe) _(2) MnH(REtSiCHMe)] ( 6 ~(Ph,Et) : R = Ph, 6 ~(Bu,Et) : R = ~( n ) Bu), resulting from apparent ethylene insertion into the silene Si–H bond. Furthermore, in the absence of ethylene, silene complex 6 ~(Bu,H) slowly isomerized to the silylene hydride complex [(dmpe) _(2) MnH(SiEt ~( n ) Bu)] ( 3 ~(Bu,Et) ). Reactions of 4 ~(R) with ethylene likely proceed via low-coordinate silyl {[(dmpe) _(2) Mn(SiH _(2) R)] ( 2 ~(Ph) : R = Ph, 2 ~(Bu) : R = ~( n ) Bu)} or silylene hydride {[(dmpe) _(2) MnH(SiHR)] ( 3 ~(Ph,H) : R = Ph, 3 ~(Bu,H) : R = ~( n ) Bu)} intermediates accessed from 4 ~(R) by H _(3) SiR elimination. DFT calculations and high temperature NMR spectra support the accessibility of these intermediates, and reactions of 4 ~(R) with isonitriles or N-heterocyclic carbenes yielded the silyl isonitrile complexes [(dmpe) _(2) Mn(SiH _(2) R)(CNR′)] ( 7a–d : R = Ph or ~( n ) Bu; R′ = o -xylyl or ~( t ) Bu), and NHC-stabilized silylene hydride complexes [(dmpe) _(2) MnH{SiHR(NHC)}] ( 8a–d : R = Ph or ~( n ) Bu; NHC = 1,3-diisopropylimidazolin-2-ylidene or 1,3,4,5-tetramethyl-4-imidazolin-2-ylidene), respectively, all of which were crystallographically characterized. Silyl, silylene and silene complexes in this work were accessed via reactions of [(dmpe) _(2) MnH(C _(2) H _(4) )] ( 1 ) with hydrosilanes, in some cases followed by ethylene. Therefore, ethylene (C _(2) H _(4) and C _(2) D _(4) ) hydrosilylation was investigated using [(dmpe) _(2) MnH(C _(2) H _(4) )] ( 1 ) as a pre-catalyst, resulting in stepwise conversion of primary to secondary to tertiary hydrosilanes. Various catalytically active manganese-containing species were observed during catalysis, including silylene and silene complexes, and a catalytic cycle is proposed.