Rhodium complexes irradiation

Like the ammines, rhodium complexes of ligands like bipy and phen have a significant photochemistry. Therefore, on irradiation, solutions of cw-[Rh(L-L)2X(H20)]2+ (X = halogen) gradually convert to c/s-[Rh(L-L)2X(H20)]2+, though much more slowly than with the ammines [101]. 

Several approaches have been undertaken to construct redox active polymermodified electrodes containing such rhodium complexes as mediators. Beley [70] and Cosnier [71] used the electropolymerization of pyrrole-linked rhodium complexes for their fixation at the electrode surface. An effective system for the formation of 1,4-NADH from NAD+ applied a poly-Rh(terpy-py)2 + (terpy = terpyridine py = pyrrole) modified reticulated vitreous carbon electrode [70]. In the presence of liver alcohol dehydrogenase as production enzyme, cyclohexanone was transformed to cyclohexanol with a turnover number of 113 in 31 h. However, the current efficiency was rather small. The films which are obtained by electropolymerization of the pyrrole-linked rhodium complexes do not swell. Therefore, the reaction between the substrate, for example NAD+, and the reduced redox catalyst mostly takes place at the film/solution interface. To obtain a water-swellable film, which allows the easy penetration of the substrate into the film and thus renders the reaction layer larger, we used a different approach. Water-soluble copolymers of substituted vinylbipyridine rhodium complexes with N-vinylpyrrolidone, like 11 and 12, were synthesized chemically and then fixed to the surface of a graphite electrode by /-irradiation. The polymer films obtained swell very well in aqueous... 

When a Rhodium complex 740 was irradiated in 2,5-dimethylthio-phene, a complex mixture of products (741-743) was obtained. 

Using Vaska s complex, hydrogenation of methyl acrylate is accelerated by weak UV irradiation. A related rhodium complex, [RhH(CO)(PPh3)3], is also activated by UV irradiation in the hydrogenation of ethyl acrylate. ... 

In contrast, N-methylpyrrole underwent direct arylations atthe 3-position [93], and a comparable result was obtained in direct arylations of N-phenylpyrrole employing the electron-deficient rhodium complex 114, in combination with Ag2C03 under microwave irradiation [74b]. Selected examples of regioselective arylations of substituted five-membered heteroarenes are summarized in Table 9.3. 

Other methods have been used for the decomposition of carbonyl precursors. For example, an early report on nickel particles preparation through UV irradiation of Ni(CO)4 was published by Tanner et al. Triangular particles of ca. 6 nm mean size were produced in this way. Similarly, the irradiation of a solution of the carbonyl polyoxoanion rhodium complex [Rh(C0)2-P2WisNb3062] in the presence of H2 and cyclohexene involves the formation of a black precipitate containing Rh(0) nanoclusters with a size in the range l.O. Onm. ... 

The reaction of alkanes with the complex Cp+Rh(H)2PMe3 takes place analogously under irradiation at a temperature below -30 °C [14b], The selectivity (both substrate and positional selectivity) proved to be much higher for the rhodium complex than for the iridium one. 

Photolysis of solutions of C6o(OH)ig at low solute concentration leads to [C6o(OH)i8] by electron transfer from Me2C(OH) radicals or from hydrated electrons, and this has enabled the reduction potential of the C6o(OH)ig/ [C6o(OH)ig] couple to be estimated. The kinetics of the photoreduction of hexanal using RhCl(PMe3)2CO as catalyst have been measured and the feasibility of a photocatalytic synthesis of hexanol from pentane, CO, and H2 in the presence of rhodium complexes has been demonstrated. Irradiation of a chiral bimolecular crystal of acridine and R-(-)- or S-(+)-2-phenylpropionic acid induces photodecarboxylation followed by stereoselective condensation to give a mixture of three optically active products, and the 3-0-S-methyl dithiocarbo-nate derivatives of oleanolic and ursolic methyl esters have been used as models for the photodeoxygenation of alcohols. ... 

The essential question to be addressed is whether the rhodium complex re-enters the decarbonylation sequence previously discussed (Equation 7) or if a different pathway is available at elevated temperature. Loss of CO from RhCl(CO)(PPh3)2 is not observed even at high temperature (300 C) or under UV irradiation.Therefore, mechanisms that have been proposed involve either oxidative addition to this complex " or loss of CO from the alkyl-rhodium carbonyl complex. These two mechanisms... 

Rhodium-catalyzed direct arylahons of arenes can be achieved in the absence of any directing groups. Thus, a rhodium complex displaying a strong it-accepting ligand [P(OCH(CF3)2]3 led to a direct arylation of anisole (29) using electron-deficient aryl iodide 30 under microwave irradiation (Scheme 9.11) [23]. As a... 

The carbonylation of methane is catalyzed by RhCl(P(CH3)3)3 under irradiation to yield acetaldehyde (eq. (49)) (11). The utilization of dense CO2 as a stable and CH4-miscible reaction medium is the key to accomplish the reaction. The reaction presumably proceeds via the oxidative addition of the C—H bond to the rhodium center. The C—H oxidative addition product obtained from RhCl(P(CH3)3)3 and benzene was successfully isolated, and the structure was unambiguously determined by X-ray analysis (compound B, eq. (50) (76). The resulting complex is a (phenyl)(hydrido)rhodium complex, as expected and gave benzene and benzaldehyde upon treating with CO. 

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