Analysis of M?H-Si interactions in [{M(CpSiMe_2H)Cl _3}_2], (M = Zr, Hf, Ti and Mo) complexes

摘要

For the d~0 complex [{Zr(CpSiMe_2H)Cl_3} _2] which contains a linear Si-H?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 σ to Zr dz~2 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), ν_(Si-H)) and ~1J_(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(CpSiMe_2H)Cl_3} _2]. The titanium complex [{Ti(CpSiMe_2H)Cl _3}_2] does not contain any Si-H?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(CpSiMe _2H)Cl_3}_2] results in a stronger interaction with a distinct QTAIM analysis bcp [ρ_(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 σ to Mo dz~2 donation at 143.1 kcal mol~(-1) and a 29% spatial overlap. Mo dz~2 to Si-H σ* donation (back donation) is minimal [E(2) 1.3 kcal mol ~(-1), ～1% spatial overlap]. The Wiberg bond index is 0.3114 (0.5667 for the Si-H bond), ν_(Si-H) 2015 cm~(-1) and ~1J_(Si-H) 120.6 Hz.