The formation and characterisation of (η2-ethene)hydrido(η5-pentamethylcyclopentadienyl)(trisubstituted-silyl)rhodium complexes; intermediates in catalytic dehydrogenative silylation reactions

Abstract

The complexes [(η⁵-C₅Me₅)Rh(H)(SiR₃)(C₂H₄)][R = Et (4a) or Me (4b)] have been detected and characterised spectroscopically [including ¹⁰³Rh n.m.r. spectra (via INEPT)] as intermediates in the thermal and photochemical reaction (i). Complex (4d)(R = OEt), which was isolated and fully [graphic omitted] characterised, and (4c)(R = Ph), were obtained from reaction of SiR₃H and [(η⁵-C₅Me₅)Rh(C₂H₄)₂]. Evidence for iridium analogues of (4) was obtained but more complex further reactions also occurred there. The complexes (4) were reasonably thermally robust; since (1) and (3) are active catalysts for the reaction, SiEt₃H + C₂H₄→ CH₂CHSiEt₃+ SiEt₄, this implies significant activation is required to reorganise the ligands in (4). The related reaction, of SiR₃H (R = Me, Et, Ph, or OEt) and [(η⁵-C₅Me₅)Rh(CO)₂], only proceeded as far as [(η⁵-C₅Me₅)Rh(H)(SiR₃)(CO)]; this was very labile and lost SiR₃H with the formation of blue [{(η⁵-C₅Me₅)Rh(CO)}₂].