Nonagostic M···H–C Interactions. Synthesis, Characterization, and DFT Study of the Titanium Amide Ti2Cl6[N(t-Bu)2]2

The compound Ti2Cl6[N(t-Bu)2]2 (1) has been synthesized by treating TiCl4 with di(tert-butyl)amine, HN(t-Bu)2. Compound 1 crystallizes in two different polymorphs from pentane, both conforming to the space group P21/n. In both polymorphs, 1 exhibits a close Ti···C contact of 2.634(3) A between titanium and a γ-methyl group in one of the two tert-butyl groups of the bound amido ligand. Interestingly, the γ-methyl group adopts a rotational conformation that maximizes the Ti···H distances, the shortest of which are 2.36(2) and 2.62(2) A. Even though the former distance is within the range characteristic of agostic interactions, the rotational orientation of the methyl group suggests that the Ti···H interactions are repulsive rather than attractive. DFT and NBO analysis confirms this supposition: there is no evidence of weakening of the C–H bond closest to the titanium and no evidence of significant overlap of titanium orbitals with the C–H bonding orbitals of the γ-methyl group involved in the close contact....