Phosphane effects on formation and reactivity of [Ru(L)(PR3)(`N2Me2S2ʹ)] complexes with L=N2, N2H4, NH3, and CO

Metal-sulfur complex fragments, to which small molecules like N2, N2H2, N2H4, NH3, or CO can bind, are desirable model compounds concerning enzymatic N2 fixation. This paper reports on the effects of the phosphane co-ligand on formation and reactivity of [Ru(L)(PR3)(`N2Me2S2ʹ)] [`N2Me2S2ʹ2−=1,2-ethanediamine-N,N′-dimethyl-N,N′-bis(2-benzenethiolate)(2−)] complexes with nitrogenase relevant ligands, especially N2, N2H4, NH3, and CO. Treatment of [Ru(NCCH3)4Cl2] with Li2`N2Me2S2ʹ, excessive LiOMe, bulky PPh3 or PCy3, respectively, led to the formation of two series of [Ru(L)(PR3)(`N2Me2S2ʹ)] complexes [for R=Ph: 1b, 1c (L=NCCH3), 6b (L=N2H4), 7b (L=N2), 8b1–3 (L=CO), 9b (L=NH3); for R=Cy: 1a (L=NCCH3), 6a (L=N2H4), 7a (L=N2), 8a (L=CO), 9a (L=NH3)]. While the use of PPh3 (θ=145°) yielded cis,trans and cis,cis isomers of [Ru(NCCH3)(PPh3)(`N2Me2S2ʹ)] (1b, 1c), no isomer formation was observed with the bulkier phosphane PCy3 (θ=170°). Sterically less demanding phosphanes (θ=118–132°) afforded bisphosphane complexes [Ru(PR3)2(`N2Me2S2ʹ)] [2d (R=Me), 2e (R=Et), 2f (R=nPr), and 2g (R=nBu)], which were practically inert and could only be converted in two cases and under drastic reaction conditions into the CO complexes [Ru(CO)(PR3)(`N2Me2S2ʹ)] [4e (R=Et), 4f (R=nPr)]. The chelating bidentate phosphane dppe (bisdiphenylphosphanoethane) yielded exclusively the mononuclear complex [Ru(dppe)(`N2Me2S2ʹ)] (3).