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.