The Synthesis, Characterization, and Reactivity of an Unusual, Amphoteric (Tetrahydroborato)ruthenium Hydride Complex of a Chelating Triphosphine, Ru(H)(η2-BH4)(ttp)

Article abstract of DOI:10.1021/ja00378a019

Treatment of x with excess sodium tetrahydroborate in refluxing tetrahydrofuran produces the yellow, microcrystalline complex RuH(η²-BH4)(ttp), 4, which shows discrete proton NMR signals for the metal hydride, each of the two bridging protons, and the two terminal B-H protons at ambient temperature.A variable-temperature 1H NMR study shows scrambling of the BH4^- protons at two different temperatures, and the exchange process can be interpreted as a two-step process.Owing to the presence of both Ru-H and doubly bridged Ru-BH4 linkages in 4, addition of acid or base in the presence of neutral ligands L produces two different series of products, i. e., ⁺, L= CO, CH3CN, and P(OMe)3, and RuH2(L)(ttp), L= CO, PPh3, and P(OMe)3.In the case of P(OMe)3, three different isomers (i. e., trans, cis0syn, and cis-anti) are obtained, depending on the sequence of addition of reagents, solvents, and reaction conditions.The cis-syn and cis-anti isomers of ⁺ are the first detected examples where the different structures are due to the fixed stereochemical orientatiin of the phenyl group on the central phosphorus atom of ttp.When P(OPh)3 is used as the ligand, the ortho-metalated product RuH(P(OPH)2OPh)(ttp) is obtained instead of the target complex RuH2(P(OPh3)(ttp, analogous to the RuH2(P(OMe)3(ttp) complex.The complexes have been characterized by elemental analyses, conductivity, infrared, proton, and phosphorus-31 NMR spectra, as well as an X-ray structure determination of complex 5d.Complex 4 in the presence of NEt3 catalytically hydrogenates 1-octene to octane at a rate comparable to that of RhCl(PPH3)3; in the presence of 1 equiv of HBF4*Et2O, 4 catalytically hydrogenates 1-octene at a rate ca. 0.75 that of RhCl(PPh3)3.