Analysis of M•••H-Si interactions in [{M(CpSiMe2H)Cl3}2], (M = Zr, Hf, Ti and Mo) complexes

For the d(0) complex [{Zr(CpSiMe2H)Cl-3}(2)] which contains a linear Si-H center dot center dot center dot Zr interaction across the dimer, DFT calculations are in good agreement with X-ray structures. The BP86 functional shows a slightly stronger interaction than B3LYP but for qualitative purposes either functional is sufficient. QTAIM analysis shows a bond critical point (bcp) for the interaction, a small negative value for the total energy density [H-(r)] and the H atomic basin decreases in energy, E(H), and atomic volume compared to the free ligand. NBO analysis showed E(2) for Si-H sigma to Zr-dz2 donation at 42.8 kcal mol (1) and a 34% spatial overlap for the interaction consistent with an inverse hydrogen bond. The Wiberg bond index for the interaction is 0.1735 (0.7205 for the Si-H bond), v((Si-H)) and (1)J((Si-H)) at 2060 cm(-1) and 145.4 Hz compared to 2183 cm(-1) and 172.1 Hz in the free ligand. Using a "synthesis by computation" approach to forming like complexes, similar features were found for [{Hf(CpSiMe2H)Cl-3}(2)]. The titanium complex [{Ti(CpSiMe2H)Cl-3}(2)] does not contain any Si-H center dot center dot center dot Ti interaction as rotation about the C-Si bond of the ligand occurs to place the Si-H bond hydrogen closer to a terminal chloro ligand across the dimer. An increase in electron density on the metal in the d(2) complex [{Mo(CpSiMe2H)Cl-3}(2)] results in a stronger interaction with a distinct QTAIM analysis bcp [rho((r)) 0.0448 a.u.], a small negative value for H-(r) and a much reduced H atomic volume. NBO analysis shows E(2) for Si-H sigma to Mo-dz2 donation at 143.1 kcal mol(-1) and a 29% spatial overlap. Mo-dz2 to Si-H sigma* donation (back donation) is minimal [E(2) 1.3 kcal mol(-1), similar to 1% spatial overlap]. The Wiberg bond index is 0.3114 (0.5667 for the Si-H bond), v((Si-H)) 2015 cm (1) and (1)J((Si-H)) 120.6 Hz.