Rhodium complexes carbon dioxide

As2CioHI6, Arsine, o-phenylenebis(dimethyl-, rhodium complex, 21 101 As4C102RhC2iH32, Rhodium(l +), (carbon dioxide)bis[o-phenylenebis(dimethylar-sine)]-, chloride, 21 101 As ClRhC20H32, Rhodium( 1 +), bis[o-phenyl-enebis(dimethylarsine)]-, chloride, 21 101 As4Cl6Nb2C20H32, Niobium(UI), hexachlo-robis[o-phenylenebis(dimethylarsine)]di-, 21 18... 

Rasmussen, S.C., Richter, M.M., Yi, E., Place, H. and Brewer, KJ. (1990) Synthesis and characterization of a series of novel rhodium and iridium complexes containing polypyridyl bridging ligands Potential uses in the development of multimetal catalysts for carbon dioxide reduction. Inorg. Chem., 29, 3926—3932. 

In the past, this field has been dominated by ruthenium, rhodium and iridium catalysts with extraordinary activities and furthermore superior enantioselectivities however, some investigations were carried out with iron catalysts. Early efforts were reported on the successful use of hydridocarbonyliron complexes HFcm(CO) as reducing reagent for a, P-unsaturated carbonyl compounds, dienes and C=N double bonds, albeit complexes were used in stoichiometric amounts [7]. The first catalytic approach was presented by Marko et al. on the reduction of acetone in the presence of Fe3(CO)12 or Fe(CO)5 [8]. In this reaction, the hydrogen is delivered by water under more drastic reaction conditions (100 bar, 100 °C). Addition of NEt3 as co-catalyst was necessary to obtain reasonable yields. The authors assumed a reaction of Fe(CO)5 with hydroxide ions to yield H Fe(CO)4 with liberation of carbon dioxide since basic conditions are present and exclude the formation of molecular hydrogen via the water gas shift reaction. H Fe(CO)4 is believed to be the active catalyst, which transfers the hydride to the acceptor. The catalyst presented displayed activity in the reduction of several ketones and aldehydes (Scheme 4.1) [9]. 

Sellin, M.F., Bach, I., Webster, J.M., Montilla, F., Rosa, V., Aviles, T., Poliakoff, M. and Cole-Hamilton, D.J. (2002) Hydroformylation of alkenes in supercritical carbon dioxide catalysed by rhodium trialkylphosphine complexes. /. Chem. Soc., Dalton Trans., 4569. 

Reactions that combine C-H activation with a C-C bond-forming event are invaluable synthetic tools, allowing concise construction of carbon frameworks. Rhodium(i) catalysts have been shown to catalyze alkane carbonylation [21]. Recently, Sakakura and co-workers succeeded in subjecting methane to a catalytic acetaldehyde synthesis [22], They found that, in dense carbon dioxide, the complex [RhCl(PMe3)3] catalyzed the carbonylation of methane with 77 turnovers. 

The procedure described here is based on the observation that amine monohydroxo complexes of cobalt(III), rhodium(IIl), and iridium(III) react directly with carbon dioxide to form the corresponding carbonato complexes,2 3 without effect on the configuration of the amine ligands.4 The amine monoaqua complex is allowed to react with lithium carbonate or carbon dioxide gas at room temperature at pH 8.0 for a few minutes, and the carbonato complex is isolated by adding alcohol. The procedure has been used to prepare salts of the following cations pentaammine(carbonato)-cobalt(III),2 ds-ammine(carbonato)bis(ethylenediamine)cobalt(III),5 trans-... 

All of the carbonato cobalt(III) complexes reported here are reddish in color and extremely soluble in water. The rhodium complex is pale-yellow, whereas the iridium salt is virtually white they are both soluble in water. Treatment with dilute acid immediately gives the corresponding aqua complex with evolution of carbon dioxide. The characterization and the mechanistic details of acid hydrolysis of these complexes have been reported.3,4,11... 

Catalytic asymmetric hydrogenations have also been performed in supercritical carbon dioxide [79-81]. For example, a-enamides were hydrogenated in high enantioselectivities comparable to those observed in conventional solvents, using a cationic rhodium complex of the EtDuPHOS ligand (Fig. 7.24) [79]. More recently, catalytic asymmetric hydrogenations have been performed in scC02 with... 

Tlte catalytic fixation of carbon dioxide to formic acid is possible, using a combination of Group Vlil transition metal complexes and bases in the presence of water. Typical catalysts are Pdfdppe) and RuH (PPh3)4, but nickel, rhodium. 

Another important example of COj-hydrogenation is the synthesis of form-amides. In 1970, Haynes c/tf/. of Shell Development Co. discovered the reaction of carbon dioxide, hydrogen and certain amines, when catalyzed under mild conditions by cobalt, rhodium, iridium and palladium complexes [ I70. ... 

Tn transition Group Villa, complexes of iron, cobalt, nickel and rhodium are active in CO3 dcoxygenation. The reactivity of a series of metal carbonyl anions with carbon dioxide has been found to parallel their relative nucleophilicities. The highly nucleophilic (CpFefCO) ] reacts to form the dimer [CpFefCO) ] 2 and carbonate, whereas (CofCO) ]" is unrcactivc [284]. 

A range of metal catalysts have also been studied in aqueous solution for the transformation of carbon dioxide, including rhodium, ruthenium and iridium bipyridine or phenanthroline complexes.One of the most effective systems is the iridium complex shown in Figure 3.14. The ligand design concept used in this study is very clever. The catalytic activity of the complex and its solubility in aqueous solution can be tuned by the pH of the solution.Under acidic... 

A side reaction related directly to the carbonylation of methyl acetate is the formation of acetone and carbon dioxide via methylation of the acetyl rhodium complex intermediate [63] through addition of a second molecule of methyl iodide (eqs. (18)-(21)) ... 

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