Kinetics and mechanism of the hydroformylation of styrene catalysed by the rhodium/TPP system (TPP = 1,2,5-triphenyl-1 H-phosphole)

• Published in: Journal of molecular catalysis. A, Chemical Vol. 220; no. 2; pp. 167 - 182
• Main Authors: Bergounhou, C., Neibecker, D., Mathieu, R.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 11.10.2004; Elsevier
• Subjects: 1,2,5-Triphenyl-1 H-phosphole; Catalysis; Chemistry; Exact sciences and technology; General and physical chemistry; Hydroformylation; Kinetics; Mechanism; Rhodium; Styrene; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Kinetics; Rhodium; 1,2,5-Triphenyl-1 H-phosphole; Mechanism; Hydroformylation; Styrene; Rhodium Carbonyl Complexes; Catalytic reaction; Hydrocarbon; Hydrogen; 1,2,5-Triphenyl-1H-phosphole; Organic ligand; Transition metal Complexes; Pressure effect; Rhodium Complexes; Reaction mechanism; Benzenic compound; Platinoid Complexes; Carbon monoxide
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2004.06.008

A kinetic study of the hydroformylation of styrene catalysed by the rhodium/TPP (1,3,5-triphenyl-1 H-phosphole) system is presented. The catalytic system is shown to involve an active species bearing two TPP ligands, which remain coordinated to the metal throughout the catalytic cycle. The proposed mechanistic model involves the formation of an adduct between a styrene molecule and the unsaturated species HRh(CO)(TPP) 2. An analytical equation of the reaction rate is established. The selectivity between linear and branched alkyl-rhodium derivatives appears to be under thermodynamic control. The aldehydes which are produced throughout the reaction are shown to exert an inhibiting effect reflecting their tendency to coordinate back to the metal. Subtle effects of CO and hydrogen partial pressures on the reaction rate are also emphasized. The kinetic study of the hydroformylation of styrene catalysed by the rhodium/1,3,5-triphenyl-1 H-phosphole (TPP) system has been facilitated by the fact that a catalytic system having two TPP ligands per Rh atom is maintained all along the catalytic cycle and no dissociation of a TPP ligand has to be considered during this cycle. This has allowed us to propose a model of mechanism with an association complex between the styrene and the unsaturated HRh(CO)(TPP) 2 species. An analytical equation of the reaction rate has been established which acceptably characterises the behaviour of the reaction rate according to the concentration of the various species. This study reveals that the selectivity between linear and branched alkyl-rhodium is under thermodynamic control and the reversibility of the transformation of the alkyl into acyl-rhodium isomers has not clearly been established but suggested by the observations. An inhibiting effect of the produced aldehydes, through complexation with rhodium has also been put in evidence. This study emphasizes also the complex role of the CO and H 2 partial pressures on the rate of reaction. A single catalytic cycle, only differentiated by the formation of linear or branched aldehydes, based on these observations and consistent with the kinetic equation is proposed.