Redox regulation in ruthenium complexes containing β-diketonate ligands and 2,6-bis(N-pyrazolyl)pyridine and its methyl-substituted derivatives

A new family of complexes of the general formula [Ru(Me(n)bpp)(R(2)mal)L] has been prepared, where Me(n)bpp is 2,6-bis(N-pyrazolyl)pyridine or a methyl-substituted derivative (n = 0, 2, or 4), R(2)mal is a 1,3-substituted beta-diketonate, and L is chloride or an N-heterocycle ligand. The bidentate beta-diketonate ligand substantially lowers the Ru(m/n) potentials relative to analogous polypyridyl complexes. The synthetic scheme presented here can be used to prepare a wide variety of complexes for which the Ru(III/II) couple can be systematically and rationally tuned over a range of 600 mV by varying the number of methyl groups on the 2,6-bis(N-pyrazolyl)pyridine ligand, and/or the substituents on the beta-diketonate ligands. Substitution at the sixth coordination site allows for further synthetic versatility of these complexes, including bridging ligands, such that these complexes may serve as precursors to bimetallic complexes.