Operationally unsaturated ruthenium complex stabilized by a phosphine 1-azaallyl ligand

Abstract

Coordinatively unsaturated transition-metal compounds stabilized by supplemental electron donation from π-basic ligands are described as "operationally unsaturated". Such complexes are useful analogues of active catalyst structures that readily react with substrate molecules. We report that [Ph₂P(C₆H₄)NCHC(CH₃)₂]^- (L1) effectively stabilizes Ru(II) in an operationally unsaturated form. In the absence of Lewis bases, the 1-azaallyl group of L1 dominantly coordinates through a κ¹-N mode, but can readily and reversibly isomerize to an η³-NCC coordination mode to stabilize the metal. As an operationally unsaturated complex, Ru(Cp*)(L1) dimerizes at low temperature. At ambient temperature it rapidly reacts with pyridine or PPh₃ to form an adduct. These findings with L1 demonstrate that changes in the hapticity of a 1-azaallyl fragment offer an alternative means to stabilize low-coordinate metals.