Ionisation of the Zinc-Iodine Bond of Alkylzinc Iodides in Dimethylformamide from Theory and Experiment

A study was carried out to demonstrate the ionization of the zinc-iodine bond of alkylzinc iodides in dimethylformamide from theory and experiment. The experiments show that in the absence of any solvent, the two energetically most important local minima were identified, featuring internal coordination of zinc by the carbonyl oxygen atoms of both the ester group and the carbamate protecting group, or simply by the carbamate group alone, which was the more stable structure. It appears that hydrogen bonding in 1b between the carbamate NH rendered more acidic by coordination of the carbamate to zinc, and the ester carbonyl is preferred to coordination of the ester carbonyl to zinc. Further calculations also were conducted to understand the influence of solvent, with the addition of one, two, and three molecules of dimethylformamide, forming the adducts 2,3, and 4, respectively.