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].