Chiral [Mo_3S_4H_3(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

摘要

The molybdenum(IV) cluster hydrides of formula [Mo_3S _4H_3(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 [Mo_3S_4H_3((R,R)-Me-BPE)_3] ~+ as well as its tungsten analogue are obtained in optically pure forms. Reaction of the incomplete cuboidal [M_3S_4H _3((R,R)-Me-BPE)_3]~+ (M = Mo, W) complex with acids in CH_2Cl_2 solution shows kinetic features similar to those observed for the related incomplete cuboidal [W_3S _4H_3(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 [M_3S_4H_3((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.