Further studies on hydridocarbonyltris(triphenylphosphine)rhodium(I); intermediate species in hydroformylation; rhodium and iridium analogues

Abstract

An attempt has been made either to isolate and/or to characterise by i.r. and n.m.r. spectroscopy the intermediate species in the catalytic hydroformylation of alk-1-enes by use of hydridocarbonyltris(triphenylphosphine)rhodium, or, where this is not possible, to prepare analogues of similar rhodium or iridium species with less reactive metal–carbon bonds. Species of the following types have been characterised : Square alkyls and acyls : MR(CO)(PPh₃)₂(M = Rh, R = C₂F₄H; M =Ir, R = EtCO, or Ph); pentaco-ordinate alkyls and acyls : MR(CO)₂(PPh₃)₂(M = Rh, R = C₂F₄H, EtCO, or PhCO; M = Ir, R = Et, Ph, EtCO, or PhCO); MR(CO)₃(PPh₃)(M = Rh, R = C₂F₄H, EtCO, or PhCO; M = Ir, R = EtCO or PhCO); Rh(C₂F₄H)(SO₂)(CO)(PPh₃)₂; and octahedral alkyls and acyls: Rh(C₂F₄H)HCl(CO)(PPh₃)₂, lr(EtCO)HCl(CO)(PPh₃)₂. The species are shown to undergo reversible carbonylation, decarbonylation, and oxidative addition reactions and the relevance to the hydroformylation mechanism is discussed.