Synthesis, Characterization and Reactivity of Novel Dipyridine and Pyridinyl Benzoquinoline Complexes of Zinc and Nickel

Dipyridine and pyridinyl benzoquinoline ligands and their coordination chemistry with nickel and zinc are described. The pyridinyl benzoquinoline ligand was synthesised through the photochemical Mallory reaction of the dipyridine ligand. The zinc complexes adopt distorted tetrahedral geometries, featuring one coordinated dipyridine or pyridinyl benzoquinoline ligand, with two chlorides completing the first coordination sphere. In contrast, the nickel complexes adopt octahedral geometries with two bidentate ligands and two coordinating chlorides per metal centre. Using cyclic voltammetry, catalytic reactivity of both nickel complexes with dichloromethane under reducing potentials was observed. Through kinetic analysis and investigation of the substrate scope some mechanistic details were uncovered. Surprisingly, the catalyst has a high substrate specificity, with reactivity being observed only for small, aliphatic dichlorides. Together, the paper demonstrates the potential of a new class of complexes for the electroreduction of alkyl halides.