Monomeric 16-Electron π‑Diborene Complexes of Zn(II) and Cd(II)

Despite the prevalence of stable π-complexes of most d10 metals, such as Cu­(I) and Ni(0), with ethylene and other olefins, complexation of d10 Zn­(II) to simple olefins is too weak to form isolable complexes due to the metal ion’s limited capacity for π-backdonation. By employing more strongly donating π-ligands, namely neutral diborenes with a high-lying π­(BB) orbital, monomeric 16-electron M­(II)-diborene (M = Zn, Cd) π-complexes were synthesized in good yields. Metal–B2 π-interactions in both the solid and solution state were confirmed by single-crystal X-ray analyses and their solution NMR and UV–vis absorption spectroscopy, respectively. The M­(II) centers adopt a trigonal planar geometry and interact almost symmetrically with both boron atoms. The MB2 planes significantly twist out of the MX2 planes about the M-centroid­(B–B) vector, with angles ranging from 47.0° to 85.5°, depending on the steric interactions between the diborene ligand and the MX2 fragment.