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

•Synthesis and crystal structure of novel phosphine- and phosphite-substituted Fischer ethoxy-W-carbenes.•DFT understanding of oxidation and reduction centre of W-carbenes.•Relationship between redox potentials and DFT calculated energies of W-carbenes.

The electrochemical behaviour of a series of sixteen novel Fischer ethoxy- and aminocarbene complexes 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 = OEt or NHCy, (9-12) is investigated by means of cyclic voltammetry. The complexes all exhibit a two-electron oxidation process that is W-based and a one-electron reduction that is mainly localized on the carbene ligand. Complexes 1-4 and 9-12 are considerably more difficult to oxidize than 5-8 due to the better π-acceptor ability of the (CO)4(PR′3) (R′ = Ph or OPh) ligand combination than that of (CO)3(dppe). Density functional theory calculations on the neutral, reduced and oxidized complexes confirmed the role of the frontier orbitals in the oxidation and reduction processes and enabled formulation of mathematical relationships that can be used to predict experimental measured potentials. X-ray crystal structures of 2cis, 3 and 5 are discussed.

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