Efficient Homogeneous Catalyst Research Articles

Electrochemical reduction of carbon dioxide in the presence of RhCl(CO)(PPh3)2 and IrCl(CO)(PPh3)2

The electrochemical behaviour of MCl(CO)(PPh3)2 complexes (M = Rh and Ir) in dimethylformamide has been studied. The irreversible reduction of these complexes proceeds by a two-electron step. IrCl(CO)(PPh3)2 is an efficient homogeneous catalyst for the electrochemical reduction of CO2 to CO and formic acid.

ChemInform Abstract: Photochemical and Electrochemical Reduction of Carbon Dioxide to Carbon Monoxide Mediated by (2,2′‐Bipyridine)tricarbonylchlororhenium(I) and Related Complexes as Homogeneous Catalysts.

AbstractThe investigation of the complexes (I) shows that especially (Ia) is an efficient homogeneous catalyst for the selective photochemical or electrochemical reduction of CO2 to CO.

Photochemical and Electrochemical Reduction of Carbon Dioxide to Carbon Monoxide Mediated by (2,2′‐Bipyridine)tricarbonylchlororhenium(I) and Related Complexes as Homogeneous Catalysts

Abstract[fac‐Re(bpy) (CO)3Cl] (bpy = 2,2′‐bipyridine) is an efficient homogeneous catalyst for the selective and sustained photochemical or electrochemical reduction of CO2 to CO. A quantum yield of 14% and a faradic efficiency of 98% were measured in the presence of excess Cl− ions. The photochemical process took place under visible‐light irradiation and consumed a tertiary amine as electron donor. A formato‐rhenium complex was isolated in the absence of excess Cl− ions. Substitution by Cl− ion generated free formate, but no CO was detected. Luminescence measurements showed that the tertiary amine quenches the metal‐to‐ligand charge‐transfer excited state of the rhenium complex via a reductive mechanism, with a rate constant of 3.4 × 107M−1S−1. The 19e‐complex [Re(bpy) (CO)3X]− produced either photochemically or electrochemically appears to be the active precursor in the CO‐generation process. Detailed spectroscopic studies on 13C‐enriched carbonyl‐rhenium and formato‐rhenium complexes derived from 13C‐enriched CO2 were performed in order to confirm the origin of the products and to study the exchange of the ligands. A mechanism for the present CO2 photoreduction process is presented; it involves separate pathways for CO and formate generation, in which the [Re(bpy) (CO)3X] complex plays the role of both the photoactive and the catalytic center.

Polyoxadiphosphines-1,2 chirales: synthèses et applications en hydrogénation asymétrique

Asymmetric polyoxa-l,2-diphosphines have been prepared from 1,2- O-isopropylidene-D-glycerol. The rhodium(I) cationic complexes of these ligands are efficient asymmetric homogeneous hydrogenation catalysts for dehydroaminoacids. High optical yields are obtained, but they are dependent on the chain length. The effects of pressure and temperature on the enantioselectivity have also been studied.

Catalytic oxidation of alcohols to esters with Ru 3(CO) 12

Ru 3(CO) 12 is an efficient homogeneous catalyst precursor for the conversion 2RCH 2OH → RCO 2CH 2R. With aliphatic primary alcohols and benzylic alcohols yields and selectivities of ca. 90% are obtained. The reaction requires a hydrogen acceptor molecule; triple bonds and activated double bonds, as well as ketones and aldehydes, function as H-acceptors. The reaction proceeds in two steps, with an aldehyde intermediate which subsequently oxidatively couples with an alcohol to generate an ester. In most cases the aldehyde is present in a steady state concentration implying the presence of an equilibrium system. A disproportionation alcohol aldehyde is a component of the above system. A catalytically active intermediate complex, Ru 2(CO) 6(Ph 2C 2), was isolated when Ph 2C 2 was used as an acceptor.

Asymmetric hydrogenation using chiral phosphinite rhodium complexes

The Cu(I) complex of (1R,3R)-bis(diphenylphosphinoxy)-1,3-diphenylpropane (BDPODP) has been prepared and used for the transfer of the ligand to Rh(I). The Rh(I) complexes of this new phosphinite obtained by this method act as efficient asymmetric homogeneous hydrogenation catalysts for (Z)-α-(acylamino)-cinnamic acids.

Regioselectivity in the intramolecular carbon–hydrogen insertion in metal-catalysed decomposition of some cis-1-methyl-3-arylcyclohexyl diazomethyl ketones. A highly efficient homogeneous nickel catalyst for carbenoid insertion

The comparative effectiveness of a variety of copper catalysts and a few transition-metal chelates [Ni(acac)2, Pd(acac)2, and Co(acac)3] have been examined in the carbenoid decomposition of cis,cis-1,5-dimethyl-3-phenylcyclohexyl diazomethyl ketone (11), and cis-1 -methyl-3-phenyl- and p-methoxyphenyl-cyclohexyl diazomethyl ketones (9) and (10) with reference to the formation of the respective regioisomeric bicyclo-octanones through intramolecular carbon-hydrogen bond insertion at C-3 and C-5. The most thoroughly studied case was that of (11), which clearly revealed that intramolecular competition in this case with most of the metal-catalysts only marginally favours insertion.into Me–C–H bond leading to the bridged bicyclo[3.2.1]octanone (17) in comparison to that of Ph–C–H bond, resulting in the regioisomeric ketone (16). In the catalytic decomposition of (9) and (10) the intramolecular competition in each case strongly favours insertion into the tertiary benzylic bond leading mostly to (12) and (14) rather than the secondary ones, leading to the respective regioisomers (13) and (15). The homogeneous catalyst, Ni(acac)2 has been found to be the most effective for these insertion reactions as well as the transformations of the octahydrophenanthrene diazo ketones (1a) and (1b) to the respective tetracyclic bridged-ketones (2a) and (2b). The key cyclohexanecarboxylic acids (3), (5), and (7)[for the diazo ketones (9), (10), and (11)], and the corresponding diastereoisomeric acids (4), (6), and (8) have been synthesised through a stereocontrolled route by lithium-ammonia and catalytic reduction of the corresponding benzylic γ-lactones (18), (19), and (20) respectively, and the conformational properties of their methyl esters (26)–(31) have been studied. A mechanism for the lithium–ammonia cleavage of the lactones with retention of configuration at the benzylic asymmetric centre has been advanced. Unambiguous synthesis of the bridged-ketones (12), (14), and (17) and the transformations of (12) and (14) to the respective cis-dicarboxylic acids (51) and (52) are reported.

Electrocatalytic reduction of carbon dioxide mediated by Re(bipy)(CO)3Cl (bipy = 2,2′-bipyridine)

Re(bipy)(CO)3Cl (bipy = 2,2′-bipyridine) is an efficient homogeneous catalyst for the selective and sustained electrochemical reduction of CO2 to CO at low potential.

Asymmetric hydrogenation catalyzed by aminophosphine-phosphiniterhodium complexes derived from natural aminoalcohols and x-ray crystal structure of (1,5-cyclooctadiene)-( S)- N-(diphenylphosphino)-2-diphenylphosphinoxymethylpyrrolidinerhodium(I) perchlorate

From the cheap and readily available amino alcohols ( S)-pyrrolidinemethanol (( S)-prolinol), and ( S)-α- N-ethyl-aminobutanol, we have obtained two new aminophosphine-phosphinite ligands: ( S)- N-(diphenylphospino)-2-diphenylphos- phinooxymethylpyrrolidine (( S)-Prolophos) and ( S)-1-diphenylphosphinoxy-2- N-ethyl- N-diphenylphosphinoaminobutane (( S)-Butaphos). The rhodium(I) complexes of these phosphines act as efficient homogeneous hydrogenation catalysts at ambient temperature and pressures for dehydro N-acetyl amino acids, dehydro N-benzoyl amino acids and itaconic acid. An X-ray diffraction study of the complex [Rh(COD)(( S)-Prolophos)][ClO 4]· THF has been shown that the crystals belong to the monoclinic space group P2 1 with a 10.680(2), b 10.448(2), c 18.207(3) Å and β 104.97(1)ldg. Refinements based on 2105 significant counter reflections led to a final R value of 0.060. The cation is in a distorted square planar geometry, the rhodium atom being bound to the two phosphorus atoms and to the two double bonds of the diene molecule.

Catalyse d'hydrogenation en phase homogene des aldehydes α-β insatures. Application a la synthese asymetrique du citronellal

Complexes generated in situ from RhHCO(Pø 3) 3 + diphosphine or from Rh 6(CO) 16 or Rh 4(CO) 12 + diphosphine are found to be very efficient homogeneous catalysts for the hydrogenation of α-β ethylenic aldehydes into the corresponding saturated aldehydes. In the presence of the chiral diphosphine (+)- trans-1,2-bis(methylenephosphino)cyclobutane 4, neral is hydrogenated into (+)-citronellal (optical yield: 70 – 79%) and geranial into (—)citronellal (optical yield: 56 – 60%). Other chiral phosphines were also tested.

Platinum Metal Complexes of Substituted Aryl Phosphines

Highlights of the co-ordination chemistry of platinum metal complexes of phosphorus-oxygen chelating agents are described. The ligands of interest all contain the oxygen bearing substituent (methoxy, hydroxy, formyl, carboxy-) ortho to a phosphine on a benzene ring; complexes of these ligands are efficient homogeneous catalysts for hydrogenation, isomerisation and polymerisation reactions. Furthermore, these studies have revealed structural and reactivity patterns which are suggestive of new and improved strategies towards useful catalytic systems.

Homogeneous catalysis of the water gas shift reaction using a platinum chloride-tin chloride system

An efficient homogeneous catalyst consisting of K/sub 2/PtCl/sub 4/, SnCl/sub 4/, H/sub 2/O, and HCl dissolved in glacial acetic acid was developed for the water gas shift reaction, H/sub 2/O + CO reversible H/sub 2/ + CO/sub 2/. Requirements and features of the catalyst are: (1) no reaction takes place in the absence of the platinum chloride salt; (2) the omission of tin chlorides greatly diminishes catalytic activity, leading to decomposition and formation of a brown precipitate; (3) large excesses of the tin chlorides inhibit catalysis- e.g., at a tin/ platinum ratio of 300/1, no reaction occurs; (4) if acetic acid is replaced by water, only a trace of carbon dioxide is produced and a dark brown precipitate is obtained; (5) no catalysis occurs in the absence of either a strong protic acid or a chloride source. A mechanism involving the tin(II)/tin(IV) couple and a platinum species is proposed.

Catalytic dehydrogenation of primary and secondary alcohols by Ru(OCOCF 3) 2(CO)(PPh 3) 2

The complex Ru(OCOCF 3) 2(CO)PPh 3) 2 is an efficient homogeneous catalyst for the dehydrogenation of primary and secondary alcohols to aldehydes and ketones respectively; a mechanism involving a “β-elimination” step is proposed.

Catalytic oxidation of triphenylphosphine using a ruthenium–oxygen complex

Ru(O2)(NCS)(NO)(PPh3)2 is an efficient homogeneous catalyst for the oxidation, by molecular oxygen, of triphenylphosphine to triphenylphosphine oxide; the mechanism of this process has been studied.