Composition of catalyst resting states of hydroformylation catalysts derived from bulky mono-phosphorus ligands, rhodium dicarbonyl acetylacetonate and syngas

We thank the Eastman Chemical Company for funding of RCH, EPSRC for funding of PD (EP003868/1).The paper describes the composition of the resting states of several catalysts for alkene hydroformylation derived from bulky monophosphorus ligands. The results presented assess how bulky ligands compete with CO for the rhodium, and hence the role of ‘unmodified’ catalysts in alkene hydroformylation in the presence of these ligands. High Pressure Infra-Red (HPIR) spectroscopy was carried out at the rhodium and syngas concentrations typically used during catalysis experiments. These HPIR studies revealed that two ligands previously studied in Rh-catalysed hydroformylation react with [Rh(acac)(CO)2] and H2/CO to give the unmodified rhodium cluster, [Rh6(CO)16], as the only detectable species. Both less bulky phosphoramidites, and 1,3,5,7-Tetramethyl-6-phenyl-2,4,8-trioxa-6-phosphaadamantane, on the other hand, do not show the presence of [Rh6(CO)16], and hence catalysis proceeds by purely ligand modified species under normal conditions. In the case of the Rh/ phosphaadamantane catalysts, anecdotal evidence that this only forms a particularly useful catalyst above a certain pressure threshold can be understood in terms of how the catalyst composition varies with pressure. The ligands discussed have all been assessed in the hydroformylation of propene to separate their innate branched selectivity from their ability to isomerise higher alkenes to internal isomers.PostprintPeer reviewe

Kinetics of sulfur-transfer from titanocene (poly)sulfides to sulfenyl chlorides:rapid metal-assisted concerted substitution

The kinetics of sulfur transfer from titanocene (poly)sulfides (RCp2TiS5, Cp2TiS4CMe2, Cp2Ti(SAr)2, Cp2TiCl(SAr)) to sulfenyl chlorides (S2Cl2, RSCl) have been investigated by a combination of stopped-flow UV-Vis/NMR reaction monitoring, titration assays, numerical kinetic modelling and KS-DFT calculations. The reactions are rapid, proceeding to completion over timescales of milliseconds to minutes, via a sequence of two S-S bond-forming steps (k1, k2). The archetypical polysulfides Cp2TiS5 (1a) and Cp2TiS4C(Me2) (2a) react with disulfur dichloride (S2Cl2) through rate-limiting intermolecular S-S bond formation (k1) followed by a rapid intramolecular cyclization (k2, with k2 ≫ k1 [RSCl]). The monofunctional sulfenyl chlorides (RSCl) studied herein react in two intermolecular S-S bond forming steps proceeding at similar rates (k1 ≈ k2). Reactions of titanocene bisthiophenolates, Cp2Ti(SAr)2 (5), with both mono- and di-functional sulfenyl chlorides result in rapid accumulation of the monothiophenolate, Cp2TiCl(SAr) (6) (k1 &gt; k2). Across the range of reactants studied, the rates are relatively insensitive to changes in temperature and in the electronics of the sulfenyl chloride, moderately sensitive to the electronics of the titanocene (poly)sulfide (ρ(Ti-(SAr)) ≈ −2.0), and highly sensitive to the solvent polarity, with non-polar solvents (CS2, CCl4) leading to the slowest rates. The combined sensitivities are the result of a concerted, polarized and late transition state for the rate-limiting S-S bond forming step, accompanied by a large entropic penalty. Each substitution step {[Ti]-SR′ + Cl-SR → [Ti]-Cl + RS-SR′} proceeds via titanium-assisted Cl-S cleavage to generate a transient pentacoordinate complex, Cl-[Cp2TiX]-S(R′)-SR, which then undergoes rapid Ti-S dissociation.</p

Abstracts from the 8th International Conference on cGMP Generators, Effectors and Therapeutic Implications

This work was supported by a restricted research grant of Bayer AG

Transition-Metal-Catalyzed Regeneration of Nicotinamide Coenzymes with Hydrogen\u3csup\u3e1\u3c/sup\u3e

The nicotinamide coenzymes consumed in alcohol dehydrogenase catalyzed enantioselective reduction of ketones are expensive and thus require recycling. We have demonstrated that ruthenium(II) and rhodium(III) complexes are effective catalysts for the reduction of nicotinamide coenzymes with hydrogen, under conditions that are appropriate for in situ coupling with enzymatic reductions. The nicotinamide coenzymes consumed in alcohol dehydrogenase catalyzed enantioselective reduction of ketones are expensive and thus require recycling. We have demonstrated that ruthenium(II) and rhodium(III) complexes are effective catalysts for the reduction of nicotinamide coenzymes with hydrogen, under conditions that are appropriate for in situ coupling with enzymatic reductions

Transition-Metal-Catalyzed Regeneration of Nicotinamide Coenzymes with Hydrogen\u3csup\u3e1\u3c/sup\u3e

The nicotinamide coenzymes consumed in alcohol dehydrogenase catalyzed enantioselective reduction of ketones are expensive and thus require recycling. We have demonstrated that ruthenium(II) and rhodium(III) complexes are effective catalysts for the reduction of nicotinamide coenzymes with hydrogen, under conditions that are appropriate for in situ coupling with enzymatic reductions. The nicotinamide coenzymes consumed in alcohol dehydrogenase catalyzed enantioselective reduction of ketones are expensive and thus require recycling. We have demonstrated that ruthenium(II) and rhodium(III) complexes are effective catalysts for the reduction of nicotinamide coenzymes with hydrogen, under conditions that are appropriate for in situ coupling with enzymatic reductions

Process for Stabilizing Enzymes with Phosphine or Phosphite Compounds

The invention relates to processes for stabilizing the activity of an enzyme, comprising mixing a phosphine or phosphite with an oxidoreductase enzyme

Enzymatic Reductions with Dihydrogen via Metal Catalyzed Cofactor Regeneration

The invention provides a process for reducing an unsaturated organic compound, comprising mixing the unsaturated organic compound and H2 in the presence of a catalyst to form a reduced organic product, wherein the catalyst comprises: a) at least one metal salt or complex, b) at least one nicotinamide cofactor; and c) a nicotinamide cofactor dependent enzyme, wherein: i) when the metal salt or complex is a platinum carbonyl cluster complex, the catalyst does not comprise a redox active dye; and ii) when the metal salt or complex is a rhodium phosphine complex, the nicotinamide cofactor dependent enzyme is not a mixture of horse liver alcohol dehydrogenase and lactate dehydrogenase