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

Abstract

For the d⁰ complex [{Zr(CpSiMe₂H)Cl₃}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_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), 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(CpSiMe₂H)Cl₃}₂]. The titanium complex [{Ti(CpSiMe₂H)Cl₃}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 d² complex [{Mo(CpSiMe₂H)Cl₃}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_dz² donation at 143.1 kcal mol⁻¹ and a 29% spatial overlap. Mo_dz² 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.