New mechanistic insights into the gas-phase formation of methylzinc iodide via methyl iodide C-I activation with atomic zinc in excited triplet state as offered by the CCSD(T) study

Activation of C-X bonds (X = halogen) by transition metal species is pivotal in many catalytic processes of industrial significance such as cross-coupling reactions. The relatively simple gas-phase system for studying the activation of the C-I bond (X = iodine), which was examined experimentally (J Phys Chem A 118:11204–11210) and is amenable to a high-level ab initio theoretical study, involves the reaction of methyl iodide (CH ₃ I) with atomic zinc to form the methylzinc iodide monomer [IZnCH ₃ (X ¹ A ₁ )]. Although a qualitative explanation of the underlying formation mechanism was given by the original authors, the pathways that play a role in generating the product molecule have not been well investigated in previous research. An important task here was to determine the ways by which the C-I bond of methyl iodide is activated by atomic zinc, and to suggest a plausible mechanism of formation of IZnCH ₃ (X ¹ A ₁ ). This task was performed using the CCSD(T) method (the coupled cluster singles and doubles with perturbative triples procedure) along with the correlation-consistent basis sets (through aug-cc-pV-5Z) and relativistic pseudopotentials on the I and Zn atoms.