학술논문
Ruthenium Complexes of the 1,4-Bis(diphenylphosphino)-1,3-butadiene-Bridged Diphosphine 1,2,3,4-Me4 -NUPHOS: Solvent-Dependent Interconversion of Four- and Six-Electron Donor Coordination and Transfer Hydrogenation Activity
Document Type
Article
Source
Organometallics; March 2003, Vol. 22 Issue: 7 p1452-1462, 11p
Subject
Language
ISSN
02767333; 15206041
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 [Ru2 Cl3 (η4-1,2,3,4-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 Cs or C2 symmetry. A single-crystal X-ray analysis of [Ru2 Cl3 (η4-1,2,3,4-Me4 -NUPHOS)2 ][SbF6 ] (2b ), the hexafluoroantimonate salt of 2a , revealed that the diphosphine coordinates in an unusual manner, as a η4-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(η4-1,2,3,4-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 η2-interaction and re-form 4 . A single-crystal X-ray structure determination of [RuCl(η4-1,2,3,4-Me4 -NUPHOS)(en)][ClO4 ] (5b ) confirmed that the diphosphine coordinates in an η4-manner as a facial six-electron donor with the η2-coordinated double bond occupying the site trans to chloride. The η4-bonding mode can be readily identified by the unusually high-field chemical shift associated with the phosphorus atom adjacent to the η2-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 .