Ruthenium(II), rhodium(I) and iridium(I) complexes with [ p -(N,N-dimethylamino) phenyl]diphenylphosphine ligand: Synthesis, characterization and rhodium-catalysed carbonylation of methanol (original) (raw)
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Ligand effects in the rhodium-catalyzed carbonylation of methanol
Coordination Chemistry Reviews, 2003
The carbonylation of methanol to give acetic acid is one of the most important homogeneously catalyzed industrial processes. The original [Rh(CO)2I2]− catalyst, developed at the Monsanto laboratories and studied in detail by Forster and co-workers, is largely used for the industrial production of acetic acid and anhydride. The conditions used (30–60 bar pressure and 150–200°C) have spurred the search for
Journal of Molecular Catalysis A: Chemical, 2012
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Mechanistic Study of Rhodium/xantphos-Catalyzed Methanol Carbonylation
Organometallics, 2011
Rhodium/iodide catalysts modified with the xantphos ligand are active for the homogeneous carbonylation of methanol to acetic acid using either pure CO or CO/H 2. Residues from catalytic reactions contain a Rh(III) acetyl complex, [Rh(xantphos)(COMe)I 2 ] (1), which was isolated and crystallographically characterized. The xantphos ligand in 1 adopts a "pincer" κ 3-P,O,P coordination mode with the xanthene oxygen donor trans to the acetyl ligand. The same product was also synthesized under mild conditions from [Rh(CO) 2 I] 2. Iodide abstraction from 1 in the presence of donor ligands (L = MeCN, CO) gives the cationic acetyl species [Rh(xantphos)(COMe)I(L)] + , whereas in CH 2 Cl 2 migratory CO deinsertion gives [Rh(xantphos)(Me)I(CO)] + (4), which reacts with H 2 to liberate methane, as observed in catalytic reactions using syngas. A number of Rh(I) xantphos complexes have been synthesized and characterized. Oxidative addition of methyl iodide to the cation [Rh(xantphos)(CO)] + is very slow but can be catalyzed by addition of an iodide salt, via a mechanism involving neutral [Rh(xantphos)(CO)I] (6). IR spectroscopic data and DFT calculations for 6 suggest the existence in solution of conformers with different Rh−O distances. Kinetic data and activation parameters are reported for the reaction of 6 with MeI, which proceeds by methylation of the Rh center and subsequent migratory insertion to give 1. The enhancement of nucleophilicity arising from a Rh-O interaction is supported by DFT calculations for the S N 2 transition state. A mechanism for catalytic methanol carbonylation based on the observed stoichiometric reaction steps is proposed. A survey of ligand conformations in xantphos complexes reveals a correlation between P−M−P bite angle and M−O distance and division into two broad categories with bite angle <120°(cis) or >143°(trans).
IRC analysis of methanol carbonylation reaction catalyzed by rhodium complex
Science in China Series B, 2004
In the reaction cycle for methanol carbonylation catalyzed by Rh complex, the structure geometries of the reactant, intermediates, transition states and product of each elemental reaction have been studied by using the energy gradient method at HF/LANL2DZ level, and the changes of their potential profiles have also been calculated. Through IRC analyses of the transition states for each elemental reaction, it is confirmed that the various structure geometries obtained are stationary points on the cycle reaction pathway of methanol carbonylation catalyzed by Rh complex, and the changes are given in energies and structure geometries of the reactant molecules along the reaction pathway of lowest energy. It has been proposed that the geometrical conversions of intermediates play an important role during the cycle reaction. Through analyses of structure geometries, it has been suggested that, in addition to cis-and transstructure exchange linkage of catalysis reactive species, the two pathways, cis-and trans-catalyzed cycle reactions, can also be linked through geometrical conversion of intermediates, of which the activation energy is 49.79 kJ/mol. Moreover, the reductive elimination elemental reaction may be neither cis-cycle nor trans-one, showing that the cycle reaction can be achieved through various pathways. However different the pathway, the oxidative addition elemental reaction of CH 3 I is the rate-controlling step.
Chemistry - A European Journal, 2002
The new diphosphine ligands Ph 2 PC 6 H 4 C(O)X(CH 2 ) 2 OC(O)C 6 H 4 PPh 2 (1: X NH; 2: X NPh; 3: X O) and Ph 2 PC 6 H 4 C(O)O(CH 2 ) 2 O(CH 2 ) 2 OC(O)-C 6 H 4 PPh 2 (5) as well as the monophosphine ligand Ph 2 PC 6 H 4 C(O)X(CH 2 ) 2 OH (4) have been prepared from 2-diphenylphosphinobenzoic acid and the corresponding amino alcohols or diols. Coordination of the diphosphine ligands to rhodium, iridium, and platinum resulted in the formation of the square-planar complexes [(P À P)Rh(CO)Cl] (6: P À P 1; 7: P À P 2; 8:
Science in China Series B: Chemistry, 2001
The whole catalytic cycle of the carbonylation of methanol to acetic acid catalyzed by Rh complex is theoretically studied. All structural geometries of reactant, intermediates, transition states and product are optimized at HF/LANL2DZ level under the ECP approximation. The potential energy profiles for elementary reactions of carbonylation are calculated respectively. The transition states are further confirmed by having one and only one imaginary vibrational frequency. The results indicate that the activation energy values of CH 3 I oxidative addition, carbonyl insertion and CH 3 COI reductive elimination fundamental steps are 216.03, 128.10 and 126.55 kJ/mol, respectively; and that the CH 3 I oxidative addition step is predicted to be the rate-determining one.
Dalton Transactions, 2003
The complexes [Rh(CO)Cl(2-Ph 2 PC 6 H 4 COOMe)], 1, and trans-[Rh(CO)Cl(2-Ph 2 PC 6 H 4 COOMe) 2 ], 2, have been synthesized by the reaction of the dimer [Rh(CO) 2 Cl] 2 with 2 and 4 molar equivalents of 2-(diphenylphosphino)methyl benzoate. The complexes 1 and 2 show terminal ν(CO) bands at 1979 and 1949 cm Ϫ1 respectively indicating high electron density at the metal centre. The molecular structure of the complex 2 has been determined by single crystal X-ray diffraction. The rhodium atom is in a square planar coordination environment with the two phosphorus atoms trans to each other; the ester carbonyl oxygen atom of the two phosphine ligands points towards the rhodium centre above and below the vacant axial sites of the planar complex. The rhodium-oxygen distances (Rh ؒ ؒ ؒ O(49) 3.18 Å; Rh ؒ ؒ ؒ O(19) 3.08 Å) and the angle O(19) ؒ ؒ ؒ Rh ؒ ؒ ؒ O(49) 179Њ indicate long range intramolecular secondary Rh ؒ ؒ ؒ O interactions leading to a pseudo-hexacoordinated complex. The complexes 1 and 2 undergo oxidative addition (OA) reactions with CH 3 I to produce acyl complexes [Rh(COCH 3 )ClI(2-Ph 2 PC 6 H 4 COOMe)], 4, and trans-[Rh(COCH 3 )ClI(2-Ph 2 PC 6 H 4 COO-Me)(2-Ph 2 PC 6 H 4 COOMe)]