C-H Bond Activation by the Excited Zinc Atom: Gas-Phase Formation of Methylzinc Hydride (HZnCH) Based on Multireference Second-Order Perturbation Theory and Coupled Cluster Calculations.

The pioneering spectroscopic observations of the methylzinc hydride [HZnCH(XA)] molecule were reported previously by the Ziurys group [ , 132, 17186-17192], and the possible formation mechanisms were suggested therein, including those with the participation of excited zinc atoms in reaction with methane. Herein, the ground singlet state and the lowest excited triplet state potential energy surfaces of the Zn + CH reaction have been explored using high-level electronic structure calculations with multireference second-order perturbation theory and coupled cluster singles and doubles with perturbative triples (CCSD(T)) methods in conjunction with all-electron basis sets (up to aug-cc-pV5Z) and scalar relativistic effects incorporated via the second-order Douglas-Kroll-Hess (DK) method. Based on the ab initio results, a plausible scenario for the formation of HZnCH(XA) is proposed involving the activation of the C-H bond of methane by the lowest excited P state atomic zinc. Calculations also highlight the importance of an agostic-like Zn···H-C interactions in the pre-activation complex and good agreement between the structure of the HZnCH(XA) molecule predicted at the DK-CCSD(T)/aug-cc-pVQZ-DK level of theory and that derived from rotational spectroscopy, as well as the discrepancies between the ab initio and density functional theory predictions.