Kinetic and mechanistic studies of sulfur transfer from imidomethylrhenium sulfides

The bis(2,6-diisopropylphenylimido)methylrhenium(VII) sulfide dimer, [CH(3)Re(NAr)(2)](2)(mu-S)(2) (1), reacts with a 1:1 amount of a phosphine or an alkyl isocyanide to yield a dimeric rhenium(VI) species, [CH(3)Re(NAr)(2)](2)(mu-S) (2), which has been structurally characterized. The two rhenium atoms in 2 are within bonding distance, 280 pm, more than 90 pm shorter than in 1. With excess L, 1 reacts to give a monomeric rhenium(V) complex, CH(3)Re(NAr)(2)L(2) (3A, L = PZ(3), Z = alkyl, aryl; 3B, L = isocyanide). The rate of formation of 3A is first-order with respect to [1] and second-order with respect to monodentate phosphine concentrations. With bidentate phosphines, however, the order with respect to the phosphine drops to unity. The addition of another (nonoxidizable) coordinating ligand, such as pyridine or one of its derivatives, accelerates the formation of 3A. In the presence of a pyridine ligand the reaction is first-order with respect to phosphine concentration, both monodentate and bidentate. The reactions between phosphines and 2 are slower than those with 1, which excludes [CH(3)Re(NAr)(2)](2)(mu-S) from being the intermediate in the reactions of 1. To account for that, we have proposed an intervening species that partitions between transformation to 3 with excess L and to 2 otherwise.