Synthesis, Structure, and Gas-Phase Fragmentation of Trinuclear Mo3S4 Clusters Bearing Aminophosphine Ligands: A Combined Experimental and Theoretical Study

Abstract

Aminophosphine [Mo3S4X3(edpp)3]+ cluster complexes, 1+ (X = Cl) and 2+ (X = Br) {edpp = (2-aminoethyl)diphenylphosphine} have been quantitatively prepared by treating the [Mo3S7X6]2– anion with the edpp ligand in a one-pot synthetic procedure. Alternatively, complexes 1+ and 2+ can be synthesized using polymeric {Mo3S7X4}n phases as metal precursors. Their crystal structures show the incomplete cubane-type Mo3S4 cluster core as well as the formation of a unique isomer in which the nitrogen atoms of the amino group and the halide atoms are located above the trimetallic plane. Gas-phase reactivity studies on complexes 1+ and 2+ show the subsequent elimination of neutral HX (X = Cl, Br) molecules under collision induced dissociation (CID) conditions. The fragmentation pattern of 1+ and 2+ in combination with gas-phase DFT calculations are contrary to the general ideas involving the hemilabile character of the aminophosphine ligands and give support to the formation of unsaturated molybdenum/imine Mo=NH species. On the basis of DFT calculations, two competitive mechanisms involving a proton transfer from the amino group to a halide ligand attached to the geminal or to the vicinal molybdenum center are proposed. The first mechanism, which is a proton transfer within the nitrogen and halogen atoms bound to the same metal atom, is energetically favored from a theoretical point of view.