Journal Publications

Simon Doherty, Colin R. Newman, Christopher Hardacre, Mark Nieuwenhuyzen, and Julian G. Knight, Organometallics, 2003, 22, 1452.

Abstract: In chloroform, [RuCl₂(nbd)(py)₂] (1) (nbd = norbornadiene; py = pyridine) reacts with 1,4-bis(diphenylphosphino)-1,2,3,4-tetramethyl-1,3-butadiene (1,2,3,4-Me₄-NUPHOS) to give the dimer [Ru₂Cl₃(h⁴-1,2,3,4-Me₄-NUPHOS)₂]Cl (2a), whereas, in THF [RuCl₂(1,2,3,4-Me₄-NUPHOS)(py)₂] (3) is isolated as the sole product of reaction. Compound 2 exists as a 4:1 mixture of two noninterconverting isomers, the major with C₁ symmetry and the minor with either C_s or C₂ symmetry. A single-crystal X-ray analysis of [Ru₂Cl₃(h⁴-1,2,3,4-Me₄-NUPHOS)₂][SbF₆] (2b), the hexafluoroantimonate salt of 2a, revealed that the diphosphine coordinates in an unusual manner, as a h⁴-six-electron donor, bonded through both P atoms and one of the double bonds of the butadiene tether. Compounds 2a and 3 react with 1,2-ethylenediamine (en) in THF to afford [RuCl₂(1,2,3,4-Me₄-NUPHOS)(en)] (4), which rapidly dissociates a chloride ligand in chloroform to give [RuCl(h⁴-1,2,3,4-Me₄-NUPHOS)(en)][Cl] (5a). Complexes 4 and 5a cleanly and quantitatively interconvert in a solvent-dependent equilibrium, and in THF 5a readily adds chloride to displace the h²-interaction and re-form 4. A single-crystal X-ray structure determination of [RuCl(h⁴-1,2,3,4-Me₄-NUPHOS)(en)][ClO₄] (5b) confirmed that the diphosphine coordinates in an h⁴-manner as a facial six-electron donor with the h²-coordinated double bond occupying the site trans to chloride. The h⁴-bonding mode can be readily identified by the unusually high-field chemical shift associated with the phosphorus atom adjacent to the h²-coordinated double bond. Complexes 2a, 2b, 4, and 5a form catalysts that are active for transfer hydrogenation of a range of ketones. In all cases, catalysts formed from precursors 2a and 2b are markedly more active than those formed from 4 and 5a.