A Singlet Biradicaloid Zinc Compound and Its Nonradical Counterpart

Metal
ions with radical centers in their coordination sphere are
key participants in biological and catalytic processes. In the present
study, we describe the synthesis of the cAAC:ZnCl2 adduct
(1) using a cyclic alkylaminocarbene (cAAC) as donor
ligand. Compound 1 was treated with 2 equiv of KC8 and LiB­(sec-Bu)3H to yield a
deep blue-colored dicarbene zinc compound (cAAC)2Zn (2) and the colorless hydrogenated zinc compound (cAACH)2Zn (3), respectively. Compounds 2 and 3 were well characterized by spectroscopic methods
and single-crystal X-ray structural analysis. Density functional theory
calculations were performed for 2 which indicate that
this molecule possesses a singlet biradicaloid character. Moreover,
we show the application of 2 in CO2 activation,
which yields a zwitterionic cAAC·CO2 adduct.