title: Solvent-stabilized alkylrhodium(III) hydride complexes: a special mode of reversible C-H bond elimination involving an agostic intermediate
abstract: Reaction of the complex [Rh(coe)2(solv)n]BF4 (coe=cyclooctene) with the phosphane 1-di-tert-butylphosphinomethyl-2,4,6-trimethylbenzene (1) results in selective C-H bond activation, yielding the spectroscopically characterized solvento complexes [(solv)nRhH(CH2C6H2(CH3)2[CH2P(tBu)2]]]BF4 (solv = acetone, 2a; THF, 2b; methanol, 2c). The stability of these complexes is solvent dependent, alcohols providing significant stabilization. Although cis-alkylrhodium hydride complexes containing labile ligands are generally unstable, 2a-c are stable at room temperature. Complex [ (acetone)(ketol)RhH[CH2C6H2(CH3)2[CH2P(t-Bu)2]]]BF4 (2d, ketol 4-hydroxy-4-methyl-2-pentanone, the product of acetone aldol condensation), crystallized from a solution of 2a in acetone and was structurally characterized. Unusual solvent- and temperature-dependent selectivity in reversible C-H bond elimination of these complexes, most probably controlled by a special mode of strong agostic interactions, is observed by spin saturation transfer experiments.
authors.affiliation: Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot, Israel.
authors.initials: B
authors.lastname: Rybtchinski
authors.initials: L
authors.lastname: Konstantinovsky
authors.initials: LJ
authors.lastname: Shimon
authors.initials: A
authors.lastname: Vigalok
authors.initials: D
authors.lastname: Milstein