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On the Influence of “Arm‐on, Arm‐off” Processes on Alkene Hydrogenation Catalysed by a Rhodium Triphos Complex
Author(s) -
Chaplin Adrian B.,
Dyson Paul J.
Publication year - 2007
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200700496
Subject(s) - triphos , chemistry , rhodium , 1,5 cyclooctadiene , medicinal chemistry , cyclohexene , alkene , dissociation (chemistry) , styrene , ruthenium , bimetallic strip , cyclooctadiene , hexamethylbenzene , catalysis , organic chemistry , benzene , copolymer , polymer
The influence of phosphane “arm‐on, arm‐off” association/dissociation in rhodium catalysed alkene hydrogenation using [Rh(COD)(κ 3 ‐triphos)]PF 6 { 1 , COD = cyclooctadiene, triphos = 1,1,1‐tris(diphenylphosphanylmethyl)ethane} has been investigated by comparison of the activity of 1 to mixtures of the related diphosphane complex, [Rh(COD)(κ 2 ‐dppp)]PF 6 { 2 , dppp = 1,3‐bis(diphenylphosphanyl)propane} and triphenylphosphane (THF, 50 °C, 1 bar H 2 ). These investigations are supplemented by a demonstration of the κ 2 –κ 3 fluxionally of the triphos coordination in 1 by reversible reaction with [RuCl 2 ( p ‐cymene)] 2 at room temperature in CH 2 Cl 2 . The product of this reaction, the bimetallic complex [( p ‐cymene)Cl 2 Ru{(PPh 2 CH 2 )CMe(CH 2 PPh 2 ) 2 }Rh(COD)]PF 6 , was isolated and fully characterized, including determination of the solid‐state structure by X‐ray diffraction analysis. Despite this evidence for facile arm‐off dissociation of the triphos ligand in 1 , complex 2 , with or without triphenylphosphane, was found to be more efficient for the hydrogenation of styrene and cyclohexene. Notably, use of triphenylphosphane together with 2 was found to have beneficial effects – increasing the rate of styrene hydrogenation (in some cases) and helping to stabilise the metal center during cyclohexene hydrogenation. These observations are supported by mercury poisoning experiments and reactivity experiments with 2 in medium pressure sapphire NMR tubes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)