The effect of replacing carbonyl with acetonitrile on the reactivity of the bimetallic system [Mo2Cp2(μ-SMe)3(L)2]+ (L=CO, CH3CN).: Crystal structure of [Mo2Cp2(μ-sMe)2(CH3CN)4](BF4)2

[Mo2Cp2(mu-SMe)(3)(CH3CN)(2)] (BF4) (1) reacts with H[BF4] in acetonitrile at room temperature to give the tetrakis (acetonitrile) compound [Mo2Cp2(mu-sMe)(2)(CH3CN)(4)](BF4)(2) (3) through replacement of one SMe bridge by two terminal CH3CN ligands. In sharp contrast, the carbonyl analogue [Mo2Cp2(mu-SMe)(3)(CO)(2)](+) (2) fails to undergo a similar reaction. This suggests that the electronic properties of the ancillary ligands L in the [Mo2Cp2(mu-SMe)(3)L-2](+) moiety govern the activation of a sulfur atom in protonation reactions. An X-ray diffraction study shows that 3 contains two CpMo(CH3CN)(2) units bridged by two SMe groups and linked by a long Mo-Mo bond of 3.000(1) Angstrom. (C) 1999 Elsevier Science S.A. All rights reserved.