A nickel-containing model system of acireductone dioxygenases that utilizes a C(1)-H acireductone substrate

A mononuclear Ni^II complex bearing the monoanion of 1-acetoxy-3-phenylpropane-2,3-dione (4) as a ligand has been prepared {[(6-Ph<inf>2</inf>TPA)Ni{PhC(O)C(O)CHOC(O)CH<inf>3</inf>)]ClO<inf>4</inf>, 5; 6-Ph<inf>2</inf>TPA = N,N-bis[(6-phenyl-2-pyridyl)methyl]-N-(2-pyridylmethyl)amine}. This complex was characterized by ¹H NMR, UV/Vis and IR spectroscopy, mass spectrometry, and elemental analysis. Exposure of solutions of 5 to O<inf>2</inf> did not result in any reaction over the course of hours. Deprotection of 5 by the addition of NaOCH<inf>3</inf> in methanol generated a Ni^II species (6) that contains a coordinated dianionic C(1)-H acireductone. Exposure of 6 to O<inf>2</inf> led to regioselective oxidative cleavage reactivity akin to that found for the Ni^II-containing acireductone dioxygenase enzyme. The strategy outlined herein is the first synthetic approach that enables examination of the oxidative reactivity of a synthetic Ni^II species containing a dianionic C(1)-H acireductone ligand.