405072-86-8Relevant academic research and scientific papers
On the influence of arm-on, arm-off processes on alkene hydrogenation catalysed by a rhodium triphos complex
Chaplin, Adrian B.,Dyson, Paul J.
, p. 4973 - 4979 (2008/09/17)
The influence of phosphane arm-on, arm-off association/ dissociation in rhodium catalysed alkene hydrogenation using [Rh(COD)(κ3-triphos)]PF6 {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)(κ2-dppp)]PF6 {2, dppp = 1,3-bis(diphenylphosphanyl)propane} and triphenylphosphane (THF, 50°C, 1 bar H2). These investigations are supplemented by a demonstration of the κ2-κ3 fluxionally of the triphos coordination in 1 by reversible reaction with [RuCl2(p-cymene)]2 at room temperature in CH2Cl2. The product of this reaction, the bimetallic complex [(p-cymene)Cl2Ru{(PPh2CH 2)CMe(CH2PPh2)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, 2007.
