How Strong Is an Agostic Bond? Direct Assessment of Agostic Interactions Using the Generalized Compliance Matrix

The strength of an α-agostic bond in CH 2 TiHF has been evaluated using the generalized compliance matrix from HF (Hartree−Fock), MP2 (second-order Møller−Plesset perturbation), CCSD(T) (coupled cluster theory with single and double substitutions with noniterative triple excitations), and several formulations of DFT (density functional theory) in combination with large all-electron basis sets. While HF underestimates the agostic interaction, both MP2 and the local spin density approximation (LSDA) dramatically overestimate the agostic Ti···H interaction strength. Hybrid DFT (B3LYP) and pure DFT (BLYP) are in line with the CCSD(T) level of theory. The DFT compliance constants and their coupling values are further used to characterize the agostic C−H···W interaction in W(⋮CCMe 3 )( CHCMe 3 )(CH 2 CMe 3 )(dmpe) ( 1; dmpe = (dimethylphosphino)ethane). The strength of this agostic bond is analyzed as a function of the metal atom and the molecular environment.