Intrinsic Gas-Phase Reactivity toward Methanol of Trinuclear Tungsten W3S4 Complexes Bearing W-X (X = Br, OH) Groups

Electrospray ionization (ESI) tandem mass spectrometry is used to investigate the gas-phase dissociation of trinuclear sulfide W3S4 complexes containing three diphosphane ligands and three terminal bromine atoms, namely, [W3S4(dmpe)(3)(Br)(3)](+) (1(+)) or hydroxo groups, [W3S4(dmpe)(3)(OH)(3)](+) (2(+)) (dmpe = 1,2-bis(dimethylphosphanyl)ethane). Sequential evaporation of two diphosphane ligands is the sole fragmentation channel for the 1(+) cation that yields product ions with one or two unsaturated W-Br functional groups, respectively. Conversely, evaporation of one diphosphane ligand followed by two water molecules is observed for cation 2(+). Complementary deuterium-labeling experiments in conjunction with computational studies provide deep insight into the thermodynamically favored product ion structures found along the fragmentation pathways. From these results, the formation of a series of cluster cations with W-Br, W-OH, and W=O functional groups either on saturated or unsaturated metal sites is proposed. The effect of the properties of these cluster cations, among them chemical composition and coordinative saturation, on their reactivity toward methanol is discussed.