Activation of methane by zinc: Gas-phase synthesis, structure, and bonding of HZnCH₃

The methylzinc hydride molecule, HZnCH₃, has been observed in the gas phase for the first time in the monomeric form using high-resolution spectroscopic techniques. The molecule was synthesized by two methods: the reaction of dimethylzinc with hydrogen gas and methane in an AC discharge and the reaction of zinc vapor produced in a Broida-type oven with methane in a DC discharge. HZnCH₃ was identified on the basis of its pure rotational spectrum, which was recorded using millimeter/submillimeter direct-absorption and Fourier transform microwave techniques over the frequency ranges 332-516 GHz and 18-41 GHz, respectively. Multiple rotational transitions were measured for this molecule in seven isotopic variants. K-ladder structure was clearly present in all of the spectra, indicating a molecule with C_3v symmetry and a ¹A₁ ground electronic state. Extensive quadrupole hyperfine structure arising from the ⁶⁷Zn nucleus was observed for the H⁶⁷ZnCH₃ species, suggesting covalent bonding to the zinc atom. From the multiple isotopic substitutions, a precise structure for HZnCH₃ has been determined. The influence of the axial hydrogen atom slightly distorts the methyl group but stabilizes the Zn-C bond. This study suggests that HZnCH₃ can be formed through the oxidative addition of zinc to methane in the gas phase under certain conditions. HZnCH₃ is the first metal-methane insertion complex to be structurally characterized.