Chiral [Mo3S4H3(diphosphine)3]+ Hydrido Clusters and Study of the Effect of the Metal Atom on the Kinetics of the Acid-Assisted Substitution of the Coordinated Hydride: Mo vs W

The molybdenum(IV) cluster hydrides of formula [Mo3S4H3(diphosphine)3]+ with diphosphine = 1,2-(bis)dimethylphosphinoethane (dmpe) or (+)-1,2-bis-(2R,5R)-2,5-(dimethylphospholan-1-yl)ethane ((R,R)-Me-BPE) have been isolated in moderate to high yields by reacting their halide precursors with borohydride. Complex [Mo3S4H3((R,R)-Me-BPE)3]+ as well as its tungsten analogue are obtained in optically pure forms. Reaction of the incomplete cuboidal [M3S4H3((R,R)-Me-BPE)3]+ (M = Mo, W) complex with acids in CH2Cl2 solution shows kinetic features similar to those observed for the related incomplete cuboidal [W3S4H3(dmpe)3]+ cluster. However, there is a decrease in the value of the rate constants that is explained as a result of the higher steric effect of the diphosphine. The rate constants for the reaction of both clusters [M3S4H3((R,R)-Me-BPE)3]+ (M = Mo, W) with HCl have similar values, thus indicating a negligible effect of the metal center on the kinetics of reaction of the hydrides coordinated to any of both transition metals.