'Ossification'- a novel approach for immobilisation of platinum group metal complex catalysts

The technique known as 'ossification' has emerged as one of the most promising approaches for immobilisation of metal complexes, generating highly selective, stable and recyclable heterogeneous counterparts of homogeneous catalysts. 'Ossification' involves modifying the ligand(s) in a metal complex catalyst to achieve inherently insoluble forms of the metal complexes, without destroying the configuration responsible for their catalytic properties. The ossified catalysts have been demonstrated to show high catalytic activity and selectivity for a number of industrially important reaction classes such as palladium-catalysed carbonylation and Suzuki coupling and rhodium-catalysed hydroformylation. The characterisation of these catalysts has also shown that the key features of their homogeneous metal complex analogues are retained on immobilisation. The approach is very useful for the design and development of immobilised catalysts with specific features and functionality for various applications. It is also advantageous for catalyst-product separation. This article reviews the recent work on ossification involving platinum group metal complex catalysts in our research group

Rh-Catalyzed Hydroformylation of 1,3-Butadiene and Pent-4-enal to Adipaldehyde in CO2-Expanded Media

The homogeneous hydroformylation of pent-4-enal, the preferred aldehyde intermediate from 1,3-butadiene hydroformylation, was systematically investigated with Rh catalyst complexes in neat and CO2-expanded toluene media at 40–80 °C, syngas partial pressures ranging from 5–50 bar, and different ligand/Rh ratios. At similar operating conditions, the TOFs are generally greater with Rh/DIOP relative to a Rh/TPP catalyst. On both catalyst complexes, the chemoselectivity toward the dialdehydes ranges from 75%–100%, with the maximum adipaldehyde selectivity reaching approximately 75% (n/i ∼ 3) at 60 °C, 10 bar syngas, and molar DIOP/Rh ratio of 2.5. By using CO2-expanded toluene, the regioselectivity toward the adipaldehyde (desired product), and therefore its yield, is significantly enhanced. Interestingly, even with the simple Rh/TPP catalyst complex, adipaldehyde selectivity of up to 85% (n/i ∼ 5.6) is achieved at 60 °C, 10 bar syngas, and 50 bar CO2. The beneficial effects of CO2-expanded media are attributed to the facile tunability of the H2/CO ratio in such a phase with a fixed syngas feed composition. This approach to accelerate pent-4-enal hydroformylation to form adipaldehyde could also help in overcoming equilibrium limitations typically associated with the catalytic isomerization of pent-3-enal (the dominant product from 1,3-butadiene hydroformylation) to pent-4-enal (the preferred isomer)

Liquid-Phase Oxidation of Ethylene Glycol on Pt and Pt–Fe Catalysts for the Production of Glycolic Acid: Remarkable Bimetallic Effect and Reaction Mechanism

A highly active and selective Pt–Fe alloy catalyst on CeO2 support is reported in this work for aqueous phase oxidation of ethylene glycol (EG) to glycolic acid. The Pt–Fe nanoparticles are highly alloyed with a face-centered cubic (fcc) type of crystal structure and a chemical state of Pt0/Fe0, as confirmed from X-ray diffraction and extended X-ray absorption fine structure characterizations, respectively. Compared to the monometallic Pt catalyst, the Pt–Fe catalyst shows more than a 17-fold higher initial TOF, while achieving complete EG conversion in 4 h at 70 °C and ambient O2 pressure under alkaline conditions. The synergistic bimetallic effect occurs due to significantly changing the O2 adsorption-dissociation characteristics on the catalyst surface. The addition of a base shows a promotional effect on both Pt and Pt–Fe catalysts at low NaOH concentrations but an inhibition effect is observed for both catalysts at sufficiently high NaOH concentrations. Furthermore, the base enhances the synergistic effect observed with Pt–Fe catalyst

A new method for the synthesis of hydrophobized, catalytically active Pt nanoparticles

A single step method for the synthesis of catalytically active, hydrophobic Pt nanoparticles by the spontaneous reduction of aqueous PtCl62− ions by hexadecylaniline molecules at a liquid-liquid interface is described

Highly efficient sulfimidation of 1,3-dithianes by Cu(I) complexes

A series of four Cu(I) complexes were tested for sulfimidation of 1,3-dithianes in the presence of [N-(p-tolysulfonyl)imino]phenyliodinane (PhI=NTs) as the nitrene-transfer agent. Cu(TMPhen)(PPh3)Br is an efficient catalyst with more than 90% yield of the corresponding product with less reaction time as compared to the literature copper(I) complexes

Absorption of carbon monoxide with reversible reaction in CuAlCl<SUB>4</SUB>-toluene-complex solutions

The absorption of CO in CuAlCl<SUB>4</SUB>-toluene-complex solutions was studied in a stirred reactor. The reaction was found to occur in a fast reaction regime. The effect of CO partial pressure, CuAlCl<SUB>4</SUB>-toluene-complex concentration and temperature on the rate of absorption was studied. The results have been interpreted using a theoretical model for mass transfer with reversible chemical reaction and the rate parameters were determined. The equilibrium constants were also determined experimentally. An interesting observation showing a decrease in the rate with an increase in temperature was made for this system. This is explained on the basis of a higher activation energy for the reverse reaction. The activation energies evaluated for the forward and reverse reactions are 32.93 and 97.42 kJ/mol, respectively

Kinetic modeling of hydroxycarbonylation of styrene using a homogeneous palladium complex catalyst

Kinetics of hydroxycarbonylation of styrene using Pd(pyca)(PPh)(OTs)/PPh/TsOH/LiCl catalyst was investigated in a stirred batch reactor. The effects of catalyst, styrene, and water concentrations and the partial pressure of CO on the rate of hydroxycarbonylation as well as the concentration-time profiles have been investigated over a temperature range of 368-388 K. A unique observation was the induction period which was CO pressure dependent leading to lower rates of carbonylation at the start of the reaction. A molecular level description of the reaction mechanism (catalytic cycle) has been proposed to explain the observed trends. The results were found to be consistent with a mechanism based on a Pd-hydride complex as an active intermediate species. The proposed mechanism also captured the experimentally observed trends of induction period. The approach of microkinetic modeling used here does not require the assumption of a rate determining step and provides a good description of the complex trends observed with respect to reaction parameters over a wide range of conditions

An analysis of mass-transfer effects in hydroformylation reactions

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