Metal thiolate complexes binding molecular nitrogen under mild conditions: [μ-N2{Ru(PiPr3)(N2Me2S2)}2], the first dinuclear example

Binding N2 to the metal sulfur cofactors of nitrogenase is considered the first step of biological N2 fixation. In quest of low-molecular weight complexes modeling this step [μ-N2{Ru(PiPr3)(N2Me2S2)}2] (3) was synthesized and completely characterized. Complex 3 was obtained from [Ru(N2)(PiPr3)(N2Me2S2)] (1) that dissociates N2 under reduced partial pressure of N2. Complex 1, in turn, forms from [Ru(CH3CN)(PiPr3)(N2Me2S2)] (2) and N2 at standard conditions (20 °C, 1 bar) such that the formation of 3 corresponds with a binding of molecular nitrogen to metal thiolate complex fragments under mild conditions, not requiring abiologically strong reductants. Complex 3 forms as racemate of (R,R)-3 and (S,S)-3 enantiomers which spontaneously separate upon crystallization and could both be characterized by X-ray crystallography. Complex 3 exhibits short bonds trans to the N2 ligand, a ν(N2) frequency (2042 cm−1) low in comparison with that of 1 (2113 cm−1) and a non-linear [RuNNRu] entity. The thiolate donors of 3 represent Broensted-basic sites for reversible protonations so that 3 becomes a complex suited for investigations aiming at the reduction of N2 by nitrogenase-like coupled [2H+/2e−] transfer steps.