Solution-and Solid-State Structural Studies of (Halomethyl)zinc Reagents

(Halomethyl)zinc cyclopropanation reagents have been investigated by solution NMR and X-ray crystallographic methods. Treatment of glycol-ether complexes of diethylzinc with chloroiodomethane or diiodomethane quantitatively produced glycol-ether complexes of bis(chloromethyl)zinc and bis(iodomethyl)zinc, respectively. Similarly, treatment of acetone solutions of diethylzinc with either dihalomethane produced the corresponding bis(halomethyl)zinc species. The bis(chloromethyl)zinc complexes displayed characteristic NMR resonances at 2.4-2.7 ppm (¹H) and 29.5-29.8 ppm (¹³C) for the methylene unit, while the bis(iodomethyl)zinc complexes displayed characteristic resonances at 1.35-1.40 ppm (¹H) and -16.4 to -19.6 ppm (¹³C). The first X-ray crystallographic analysis of an (iodomethyl)zinc compound, bis(iodomethyl)zinc complex 9, is also reported. Some key features of the structure include Zn-C bond lengths of 1.92-2.02 Å, C-I bond lengths of 2.13-2.21 Å, and Zn-C-I bond angles of 106.9-116.4°. In addition, bis(iodomethyl)zinc complexes were demonstrated to lose one methylene upon concentrating in vacuo, and the iodomethylzinc iodide complexes were established to exist predominantly as the bis-(iodomethyl)zinc/zinc iodide pair in acetone solution.