Metal (Ti, Zr, Hf) insertion in the C–H bond of methane: Manifestation of an agostic interaction

Agostic Structure of Titanium Methylidene Hydride (CH2=TiH2): A Theoretical Investigation for the Elusive Intramolecular Interaction

“…The large delocalization energy from the C-H1 bond to the Ti-H4 anti-bond with various levels of theory (6.94-38.19 kcal/ mol) is considered as the primary origin of the agostic interaction, being consistent with the recent results of Berkaine et al 4 Table 1 also shows that the larger agostic distortion is normally accompanied with a larger occupation number of σ* (Ti-H4) and electron delocalization energy. For example, the largest MP2 σ*(Ti-H4) occupation number of 0.091 and delocalization energy of 38.19 kcal/mol lead to the largest agostic angle of 78.5°.…”

“…In comparison with the previously reported values, 1-4 the HF methods evidently underestimates the agostic interaction, whereas the MP2 method overestimates. The increases in the B3LYP and BPW91 delocalization energies to σ*(Ti-H4) with the agostic distortion from the C s structures (10.59 and 11.18 kcal/mol with the 6-311++G(3df,3pd) basis set) are comparable to the previously estimated values, 3,4 whereas the increase in the CCSD value (20.8 kcal/mol) is somewhat too high.…”

“…More recently Berkaine et al reported that in Group 4 metal methylidene systems, the occupation number of the M-H bond diagonal to the agostic C-H bond increases with the distortion while that of the C-H bond decreases. 4 However, the NBO results for CH2=ZrH2 show that the electron delocalization of the agostic C-H bond to the empty Zr d-orbital is more important than to the metal-hydrogen anti-bond (σ* (M-H)).…”

“…[6][7][8] The following theoretical studies have reproduced the distorted C 1 structure of the methylidene hydride (CH2=MH2) with two different M-H bonds. 3,4 In this study, the agostic interaction of titanium methylidene hydride (CH2=TiH2) has been examined at various levels of theory as a subsequent study of the previous report for the Zr analogue. Density functional theory (DFT) calculations were carried out using the Gaussian 03 package, 9 B3LYP density functional, and 6-311++G(3df,3pd) basis sets for C, H, and Ti (all electron basis).…”

“…While the agostic structures have been investigated by various methods, the experimental evidences are still elusive in many cases, particularly in IR region. [1][2][3][4] Moreover, the large ligands, which often contain conjugate systems for stabilization, prohibit application of high level theoretical approaches for exact reproduction of the distinct distortions.…”