Unprecedented Solvent-Assisted Reactivity of Hydrido W3CuS4 Cubane Clusters: The Non-Innocent Behaviour of the Cluster-Core Unit

Abstract

Opening the cluster core: Substitution of the chloride ligand in the novel cationic cluster [W3CuS4H3Cl(dmpe)3]+ (see figure; dmpe=1,2-bis(dimethylphosphino)ethane) by acetonitrile is promoted by water addition. Kinetic and density functional theory studies lead to a mechanistic proposal in which acetonitrile or water attack causes the opening of the cluster core with dissociation of one of the CuS bonds to accommodate the entering ligand.

Reaction of the incomplete cuboidal cationic cluster [W3S4H3(dmpe)3]+ (dmpe=1,2-bis(dimethylphosphino)ethane) with CuI compounds produces rare examples of cationic heterodimetallic hydrido clusters of formula [W3CuClS4H3(dmpe)3]+ ([1]+) and [W3Cu(CH3CN)S4H3(dmpe)3]2+ ([2]2+). An unexpected conversion of [1]+ into [2]2+, which involves substitution of chloride by CH3CN at the copper centre, has been observed in CH3CN/H2O mixtures. Surprisingly, formation of the acetonitrile complex does not occur in neat acetonitrile and requires the presence of water. The kinetics of this reaction has been studied and the results indicate that the process is accelerated when the water concentration increases and is retarded in the presence of added chloride. Computational studies have also been carried out and a mechanism for the substitution reaction is proposed in which attack at the copper centre by acetonitrile or water causes disruption of the cubane-type core. ESI-MS experiments support the formation of intermediates with an open-core cluster structure. This kind of process is unprecedented in the chemistry of M3M′Q4 (M=Mo, W; Q=S, Se) clusters, and allows for the transient appearance of a new coordination site at the M′ site which could explain some aspects of the reactivity and catalytic properties of this kind of clusters.