Hydroesterification of styrene using an in situ formed Pd(OTs)2(PPh3)2 complex catalyst |
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| Institution: | 1. Homogenous Catalysis Division, National Chemical Laboratory, Pune 411008, India;2. Departmento di Chimica, Universita di Venezia, Calle Large-S, Marta 2137-30123, Venice, Italy;1. Institute of Applied Chemistry, Shanxi University, Taiyuan 030006, People’s Republic of China;2. Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, China;3. Scientific Instrument Center, Shanxi University, Taiyuan 030006, People’s Republic of China;1. Yale Chemistry Department, 225 Prospect St., New Haven, CT 06520, USA;2. Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA;3. Instituto de Investigaciones Químicas (IIQ), Departamento de Química Inorgánica and Centro de Innovación en Química Avanzada (ORFEO-CINQA), Universidad de Sevilla and Consejo Superior de Investigaciones Científicas (CSIC), Avenida Américo Vespucio 49, 41092 Sevilla, Spain;4. Department of Chemistry, University of Oslo, Centre of Excellence for Theoretical and Computational Chemistry (CTCC), N-0315, Norway;1. Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Novosibirsk 630090, Russian Federation;2. Department of Physics, Novosibirsk State University, Novosibirsk 630090, Russian Federation;3. Department of Chemical Sciences, University of Padova, 35131 Padova, Italy;4. Institute of Biomolecular Chemistry, Padova Unit, CNR, 35131 Padova, Italy |
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| Abstract: | Hydroesterification of styrene to 3-phenyl propionate 1, and 2-phenyl propionate 2, has been studied using a Pd(OTs)2(PPh3)2 catalyst formed in situ from Pd(OAc)2, PPh3 and p-toluenesulfonic acid (p-tsa). Because of the weakly coordinating properties of the TsO? ligand, the catalyst has vacant coordination sites capable of easy activation of reactants. The presence of water is found to be necessary for the reaction and hydrogen enhances the catalytic activity under certain conditions (with Pd:p-tsa=1). The beneficial effect of hydrogen, p-tsa and water is discussed in terms of favoring the formation of a Pd–H species, which initiates the catalytic cycle through the insertion of styrene into this bond with formation of a Pd-alkyl intermediate, which inserts CO to give a Pd-acyl intermediate, which, upon nucleophilic attack of the alkanol on the carbon atom of the acyl ligand, yields the final product and the starting hydride back to the catalytic cycle. p-tsa would favor the formation of a Pd–H species by reactivating any Pd(0) species that may form during the course of catalysis. Water would favor the formation of a Pd–H species through a reaction closely related to the water–gas shift reaction. The effect of various ligands, promoters, solvents and alcohols on catalytic activity as well as selectivity pattern has been studied. Regioselectivity to the branched product, 2, increases with decrease in basicity of the phosphorous ligands as well as steric bulk around the palladium center and polarity of the medium. |
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