title: Thermodynamic studies and hydride transfer reactions from a rhodium complex to BX3 compounds.
abstract: This study examines the use of transition-metal hydride complexes that can be generated by the heterolytic cleavage of H(2) gas to form B-H bonds. Specifically, these studies are focused on providing a reliable and quantitative method for determining when hydride transfer from transition-metal hydrides to three-coordinate BX(3) (X = OR, SPh, F, H; R = Ph, p-C(6)H(4)OMe, C(6)F(5), (t)Bu, Si(Me)(3)) compounds will be favorable. This involves both experimental and theoretical determinations of hydride transfer abilities. Thermodynamic hydride donor abilities (DeltaG(o)(H(-))) were determined for HRh(dmpe)(2) and HRh(depe)(2), where dmpe = 1,2-bis(dimethylphosphinoethane) and depe = 1,2-bis(diethylphosphinoethane), on a previously established scale in acetonitrile. This hydride donor ability was used to determine the hydride donor ability of [HBEt(3)](-) on this scale. Isodesmic reactions between [HBEt(3)](-) and selected BX(3) compounds to form BEt(3) and [HBX(3)](-) were examined computationally to determine their relative hydride affinities. The use of these scales of hydride donor abilities and hydride affinities for transition-metal hydrides and BX(3) compounds is illustrated with a few selected reactions relevant to the regeneration of ammonia borane. Our findings indicate that it is possible to form B-H bonds from B-X bonds, and the extent to which BX(3) compounds are reduced by transition-metal hydride complexes forming species containing multiple B-H bonds depends on the heterolytic B-X bond energy. An example is the reduction of B(SPh)(3) using HRh(dmpe)(2) in the presence of triethylamine to form Et(3)N-BH(3) in high yields.
authors.affiliation: Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Mock
authors.forename: Robert G
authors.initials: RG
authors.lastname: Potter
authors.forename: Donald M
authors.initials: DM
authors.lastname: Camaioni
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: William G
authors.initials: WG
authors.lastname: Dougherty
authors.forename: W Scott
authors.initials: WS
authors.lastname: Kassel
authors.forename: Brendan
authors.initials: B
authors.lastname: Twamley
authors.forename: Daniel L
authors.initials: DL
authors.lastname: DuBois