Structure of the model grignard-type reagent ClZnCH₃ (X̃¹A₁) by millimeter-wave spectroscopy

Pure rotational spectra of the ³⁷ClZnCH_3, ClZnCD₃, and ClZn¹³CH₃ isotopologues of monomeric ClZnCH₃ (X̃¹A₁) have been recorded using millimeter-wave direct absorption techniques in the frequency range 263–303 GHz. These species were synthesized in the gas phase in a DC discharge by the reaction of zinc vapor, produced in a Broida-type oven, with ³⁷ClCH₃ (in natural chlorine abundance), ClCD₃, or Cl¹³CH₃. Five to eight rotational transitions J + 1 ← J consisting of K ladder structure were measured for each isotopologue, identifying all three species as prolate symmetric tops. The data for each isotopologue were analyzed with a symmetric top Hamiltonian and rotational and centrifugal constants determined. In combination with previous measurements of Cl⁶⁴ZnCH₃, Cl⁶⁶ZnCH₃, and Cl⁶⁸ZnCH₃, an r_m ⁽²⁾ structure was determined for this organozinc compound. The bond lengths in ClZnCH₃ were calculated to be r_Cl-Zn = 2.0831(1) Å, r_Zn-C = 1.9085(1) Å, and r_C-H = 1.1806(5) Å, considerably different from those established from crystal structures of related species ClZnCH₂CH₃ and ClZnEtTMEDA. The H[sbnd]C[sbnd]H bond angle was found to be 110.5° – slightly larger than that in methane. These data serve to benchmark future structure calculations of organozinc compounds, which are widely used in organic synthesis.