Coordination of CO, NO, N2H2, and Other Nitrogenase Relevant Small Molecules to Sulfur-Rich Ruthenium Complexes with the New Ligand ‘tpS4’2– = 1,2-Bis(2-mercaptophenylthio)phenylene(2–)

Abstract

In the search for ruthenium complexes with sulfur-dominated coordination spheres that bind, activate, or stabilize nitrogenase relevant molecules, complexes containing the new and robust tetradentate ligand ‘tpS4’–H2 were synthesized. Treatment of [RuCl2(PPh3)3] with ‘tpS4’2– gives [Ru(PPh3)2(‘tpS4’)] (1), which contains two labile PPh3 ligands. The reaction of 1 with PEt3 or DMSO led to substitution of both PPh3 ligands, yielding [Ru(PEt3)2(‘tpS4’)] (2) and [Ru(DMSO)2(‘tpS4’)] (3), respectively. When treated with nitrogenous ligands, complex 1 lost only one PPh3 ligand to yield [Ru(L)(PPh3)(‘tpS4’)] complexes where L = py (7), NH3 (8), N2H4 (9), NH2NHMe (10), and CH3CN (12), all of which are labile. The labile acetonitrile complex [Ru(CH3CN)(PPh3)(‘tpS4’)] (12) proved to be particularly suited as a precursor for the syntheses of other [Ru(L)(PPh3)(‘tpS4’)] complexes. The 18 and 19 valence electron NO complexes [Ru(NO)(PPh3)(‘tpS4’)]BF4 (13) and [Ru(NO)(PPh3)(‘tpS4’)] (14), (NEt4)[Ru(N3)(PPh3)(‘tpS4’)] (15), [Ru(I)(PPh3)(‘tpS4’)] (16), and [Ru(N3)(PPh3)(‘tpS4’)] (17) were obtained starting from complex 12. The labile mononuclear hydrazine complex [Ru(N2H4)(PPh3)(‘tpS4’)] (9) gave the dinuclear complex [μ-N2H4{Ru(PPh3)(‘tpS4’)}2] (18) by dissociation of hydrazine. The dinuclear diazene complex [μ-N2H2{Ru(PPh3)(‘tpS4’)}2] (19) was obtained by oxidation of 9 and more readily from [Ru(CH3CN)(PPh3)(‘tpS4’)] (12) and N2H2, which was generated in situ from K2N2(CO2)2 and acetic acid. The molecular structures of 7, 13, 16, 18, and 19 were determined by X-ray structure analyses. The complexes 18 and 19 represent the first complexes containing the hydrazine/diazene couple, which enables us to compare both the bonding features and the formation of N–H···S bridges when hydrazine and diazene bind to transition metal sulfur sites.