Interconversion and Reactivity of Manganese Silyl, Silylene, and Silene Complexes

Manganese disilyl hydride complexes [(dmpe)MnH(SiHR)] ( : R = Ph, : R = Bu) reacted with ethylene to form silene hydride complexes [(dmpe)MnH(RHSi[double bond, length as m-dash]CHMe)] ( : R = Ph, : R = Bu). Compounds reacted with a second equivalent of ethylene to generate [(dmpe)MnH(REtSi[double bond, length as m-dash]CHMe)] ( : R = Ph, : R = Bu), resulting from apparent ethylene insertion into the silene Si-H bond. Furthermore, in the absence of ethylene, silene complex slowly isomerized to the silylene hydride complex [(dmpe)MnH([double bond, length as m-dash]SiEt Bu)] ( ). Reactions of with ethylene likely proceed low-coordinate silyl {[(dmpe)Mn(SiHR)] ( : R = Ph, : R = Bu)} or silylene hydride {[(dmpe)MnH([double bond, length as m-dash]SiHR)] ( : R = Ph, : R = Bu)} intermediates accessed from by HSiR elimination. DFT calculations and high temperature NMR spectra support the accessibility of these intermediates, and reactions of with isonitriles or N-heterocyclic carbenes yielded the silyl isonitrile complexes [(dmpe)Mn(SiHR)(CNR')] (: R = Ph or Bu; R' = -xylyl or Bu), and NHC-stabilized silylene hydride complexes [(dmpe)MnH{[double bond, length as m-dash]SiHR(NHC)}] (: R = Ph or 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 reactions of [(dmpe)MnH(CH)] () with hydrosilanes, in some cases followed by ethylene. Therefore, ethylene (CH and CD) hydrosilylation was investigated using [(dmpe)MnH(CH)] () 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.