756480-26-9Relevant academic research and scientific papers
Oxidative addition of methyl iodide to [Rh(CO)2I]2: Synthesis, structure and reactivity of neutral rhodium acetyl complexes, [Rh(CO)(NCR)(COMe)I2]2
Haynes, Anthony,Maitlis, Peter M.,Stanbridge, Ian A.,Haak, Susanne,Pearson, Jean M.,Adams, Harry,Bailey, Neil A.
, p. 3027 - 3037 (2004)
Reaction of [Rh(CO)2I]2 (1) with MeI in nitrile solvents gives the neutral acetyl complexes, [Rh(CO)(NCR)(COMe)I 2]2 (R=Me, 3a; tBu, 3b; vinyl, 3c; allyl, 3d). Dimeric, iodide-bridged structures have been confirmed by X-ray crystallography for 3a and 3b. The complexes are centrosymmetric with approximate octahedral geometry about each Rh centre. The iodide bridges are asymmetric, with Rh-(μ-I) trans to acetyl longer than Rh-(μ-I) trans to terminal iodide. In coordinating solvents, 3a forms mononuclear complexes, [Rh(CO)(sol) 2(COMe)I2] (sol=MeCN, MeOH). Complex 3a reacts with pyridine to give [Rh(CO)(py)(COMe)I2]2 and [Rh(CO)(py)2(COMe)I2] and with chelating diphosphines to give [Rh(Ph2P(CH2)nPPh2)(COMe)I 2] (n=2, 3, 4). Addition of MeI to [Ir(CO)2(NCMe)I] is two orders of magnitude slower than to [Ir(CO)2I2] -. A mechanism for the reaction of 1 with MeI in MeCN is proposed, involving initial bridge cleavage by solvent to give [Rh(CO)2(NCMe)I] and participation of the anion [Rh(CO)2I2]- as a reactive intermediate. The possible role of neutral Rh(III) species in the mechanism of Rh-catalysed methanol carbonylation is discussed.
Evaluation of C4 diphosphine ligands in rhodium catalysed methanol carbonylation under a syngas atmosphere: Synthesis, structure, stability and reactivity of rhodium(i) carbonyl and rhodium(iii) acetyl intermediates
Lamb, Gareth,Clarke, Matthew,Slawin, Alexandra M. Z.,Williams, Bruce,Key, Lesley
, p. 5582 - 5589 (2008/09/17)
The carbonylation of methanol to acetic acid is a hugely important catalytic process, and there are considerable cost and environmental advantages if a process could be designed that was tolerant of hydrogen impurities in the CO feed gas, while eliminating by-products such as propionic acid and acetaldehyde altogether. This paper reports on an investigation into the application of rhodium complexes of several C4 bridged diphosphines, namely BINAP, 1,4-bis(diphenylphosphino)butane (dppb), bis(diphenylphosphino) xylene (dppx) and 1,4-bis(dicyclohexylphosphino)butane (dcpb) as catalysts for hydrogen tolerant methanol carbonylation. An investigation into the structure, reactivity and stability of pre-catalysts and catalyst resting states of these complexes has also been carried out in order to understand the observations in catalysis. Rh(i) carbonyl halide complexes of each of the ligands have been prepared from both [Rh2(CO)4Cl2] and dimeric μ-Cl-[Rh(L)Cl]2 complexes. These Rh(i) carbonyl complexes are either dimeric with bridging phosphine ligands (dppb, dcpb, dppx) or monomeric chelate complexes. The reaction of the complexes with methyl iodide at 140 °C has been studied, which has revealed clear differences in the stability of the corresponding Rh(iii) complexes. Surprisingly, the dimeric Rh(i) carbonyls react cleanly with MeI with rearrangement of the diphosphine to a chelate co-ordination mode to give stable Rh(iii) acetyl complexes. The Rh acetyls for L = dppb and dppx have been fully characterised by X-ray crystallography. During the catalytic studies, the more rigid dppx and BINAP ligands were found to be nearly 5 times more hydrogen tolerant than [Rh(CO) 2I2]-, as revealed by by-product analysis. The origin of this hydrogen tolerance is explained based on the differing reactivities of the Rh acetyls with hydrogen gas, and by considering the structure of the complexes. The Royal Society of Chemistry.
