Synthesis and characterization of a series of CpW(CO)2PR3H, [CpW(CO)2PR3]−, [CpW(CO)2PR3(CH3CN)]+, and [CpW(CO)2PR3]2 complexes

Abstract

A series of tungsten cyclopentadienyl carbonyl complexes were prepared and characterized to quantify their thermochemical properties and explore their reactivity. The PR3 ligand was systematically varied across a series of CpW(CO)2PR3H metal hydride complexes, where PR3 = P(OEt)3, P(Bu)3, and P(Cy)3. These complexes are known to undergo multiple proton, electron, and proton-coupled electron transfer reactions to access a variety of species including [CpW(CO)2PR3]−, [CpW(CO)2PR3(CH3CN)]+, and [CpW(CO)2PR3]2. Cyclic voltammograms of the CpW(CO)2PR3H+/0 and [CpW(CO)2PR3]0/− couples are chemically irreversible, indicating chemical reactivity upon oxidation; the anodic peak potential shifts to lower potentials as the donating ability of phosphine is increased, agreeing with previous literature on similar complexes. Additionally, voltammograms of [CpW(CO)2P(Cy)3]− become chemically reversible at scan rates above 500 mV/s, indicating that the dimerization of the [CpW(CO)2PR3] product, formed by the oxidation of [CpW(CO)2PR3]−, is slower with the sterically bulky phosphine P(Cy)3, and at high scan rates the species can be reduced before dimerization occurs. Further, as the donating ability of the phosphine increases, the pKa of the CpW(CO)2PR3H complexes increases. This work shows how ligand sterics and electronics can tune the thermochemical properties that underpin proton, electron, and proton-coupled electron transfer reactivity of these complexes.