Quantum Crystallography and Complementary Bonding Analysis of Agostic Interactions in Titanium Amides

Abstract

Agostic interactions involving titanium are textbook examples for C−H bond activation. Therefore, it is surprising that there is no study in the literature in which the hydrogen atom in the C−H⋅⋅⋅Ti interaction has been determined reliably, although nearly all the criteria for assessing the strength and character of the agostic interaction depend on the hydrogen atom and its position. Here, we demonstrate with quantum crystallographic techniques how hydrogen atoms in a series of three titanium amides can indeed be localized accurately and precisely based on routine single‐crystal X‐ray diffraction data. Once the hydrogen positions have been established, theoretical and experimentally fitted bonding analyses reveal that the C−H⋅⋅⋅Ti interaction becomes stronger with increasing inter‐ligand London dispersion stabilization of bulky alkyl groups.

Theoretical Studies on Relative Stability of Cationic 1,10-Phenanthroline Palladium Complexes Bearing Alkyl Groups by Using Designed Alkane Templates

“…In order to gain further understanding of the agostic interaction, second-order perturbation theory analyses were conducted for these complexes 1 – 5 and 6 – 11 based on the NBO analysis. − All of the complexes were suggested to involve interactions between a donor σ­(C β –H β ) bond and an acceptor σ*­(Pd–C α ) bond. The donor–acceptor stabilization energies E (2) (kcal/mol) associated with the donor/acceptor NBOs were summarized in Figure and showed a clear trend that the higher the number of branches on the agostic β-carbon becomes, the more complexes are stabilized from this interaction.…”