Electrochemical behaviour and structure of novel phosphine- and phosphite-substituted tungsten(0) Fischer carbene complexes

Abstract

tThe electrochemical behaviour of a series of sixteen novel Fischer ethoxy- and aminocarbenecomplexes of the type [(CO)4(PPh3)W = C(X)R] with R = 2-thienyl or 2-furyl and X = OEt or NHCy,(1-4), [(CO)3(dppe)W = C(X)R] with R = 2-thienyl or 2-furyl and X = OEt or NHCy, (5-8) (dppe = 1,2-bis(diphenylphosphino)ethane) and [(CO)4P(OPh)3W = C(X)R] with R = 2-thienyl or 2-furyl and X = OEtor NHCy, (9-12) is investigated by means of cyclic voltammetry. The complexes all exhibit a two-electronoxidation process that is W-based and a one-electron reduction that is mainly localized on the carbeneligand. Complexes 1-4 and 9-12 are considerably more difficult to oxidize than 5-8 due to the better -acceptor ability of the (CO)4(PR 3) (R = Ph or OPh) ligand combination than that of (CO)3(dppe). Den-sity functional theory calculations on the neutral, reduced and oxidized complexes confirmed the role ofthe frontier orbitals in the oxidation and reduction processes and enabled formulation of mathematicalrelationships that can be used to predict experimental measured potentials. X-ray crystal structures of2cis, 3 and 5 are discussed.