New aspects on the reactivity of MoO2(S2CNEt2)2 with Me3SiX. A peculiar trans effect control

The reaction of MoO2(S2CNEt2)2 with Me3SiI and Me3SiNCS yielded MoOI2(S2CNEt2)2 and MoO(NCS)2(S2CNEt2)2, respectively, similar to results reported for Me3SiCl and Me3SiBr. On the contrary, MoO(OSiMe3)CN(S2CNEt2)2 was the only compound isolated from the reaction of MoO2(S2CNEt2)2 with Me3SiCN. To study the effects of ligands on the reactivity of siloxy compounds, ab initio calculations were undertaken for Mo(OSiH3)L(S2CNH2)2 molecules, for L = Cl, Br, I, NCS, and CN. The electronic density, ρ(r), was analysed by means of the topological theory of Atoms in Molecules (AIM). The analysis of -del2ρ(r) critical points (CPs) at the molybdenum valence shell showed, only in the case of L = CN, a local charge concentration region (N-type CPs) susceptible to electrophilic attacks. However, for L = Cl, Br, I, and NCS, local charge depletion sites (E-type CPs) were found in a bond-free region. The absence of any accessible E-type CPs and the presence of an N-type CP in the same region, opposite to the Mo=O group, justified the stability of Mo(OSiMe3)L(S2CNEt2)2 for L = CN, and the formation of MoOL2(S2CNEt2)2 for L = Cl, Br, I, and NCS by further reaction with the corresponding Me3SiL.Key words: ab initio calculation, electronic density, Mo-siloxy compound, reactivity, theoretical.