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.