Reduction of Ketones and Coupling of Ketyls by a Zn-Zn-Bonded Compound

The α-diimine-ligated Zn-Zn-bonded compound [K(THF)₂]₂[LZn-ZnL] (1, L = [(2,6-iPr₂C₆H₃)NC(Me)]₂^2-) displays diverse reactivities toward a variety of ketones. In the reaction of 1 with benzophenone or 4,4′-di-tert-butylbenzophenone, a multielectron transfer process was observed to give bimetallic (Zn/K) complexes with both ketyl radical fragments and C-C coupled pinacolate moieties (products 2 and 3). In contrast, treating 1 with 9-fluorenone only afforded pinacolate complex 5. Moreover, the reactions of 1 with N- or O-heterocycle-functionalized ketones, i.e., di(2-pyridyl)ketone, 2,2-pyrrolidinone, 9-xanthenone, or 10-methyl-9(10H)-acridone, were also carried out. Besides different transformations of the ketone moiety, the heteroatoms (nitrogen or oxygen) are also involved in coordination with zinc or potassium ions, yielding discrete aggregates or polymeric structures of products 6-9.