Rhodium complexes cyano

There has been a DFT study of the decarboxylative coupling of cyanoacetate salts with aryl halides. Decarboxylation is likely to be rate determining in the palladium-catalysed formation of a-arylnitriles. The ortho-cyanatioa of arenes carrying a DG by A -cyano-iV-phenyl-p-toluenesulfonamide is catalysed by rhodium. As shown in Scheme 21, the mechanism is likely to involve rate-determining formation of a five-membered rhoda-cycle intermediate, (160), followed by insertion of the cyanide and elimination of a tosylaniline coordinated rhodium complex. ... 

Enynes (77) can react with arylboronic acids in the presence of a catalytic amount of a rhodium(I) complex under mild conditions to give (Z)-l-(l-arylethyl- (g) idene)-2-vinylcyclopentanes (78).100 In analogy, the rhodium-catalysed cyclization of the cyano-substituted alkynes (79) with arylboronic acids has been reported to produce the cyclic ketone (80) as the first example of a nucleophilic addition of an Rh(I) species to a cyano group.101... 

There are some reports on the asymmetric catalytic hydrogenation of C=N double bonds. Rhodium phosphine complexes do not have high activity, and the stereoselectivity is low. - Homogeneous hydrogenation of oximes, Schiff s bases and cyclic imines " have been reported. A cyano cobalt complex has been used for the homogeneous catalytic hydrogenation of oximes and Schiff s bases but the degree of asymmetric induction is unknown. 

Other Nitrile Complexes. While similar additions of iron (i) and rhodium (11) hydrides to acrylonitrile to form 1-cyanoethylmetal complexes have been reported, 2-cyanoethylmetal complexes also form in certain cases (43, 51). Organotin hydrides may add to acrylonitrile in either direction, depending on the conditions of the reaction (25). Formation of the 2-cyanoalkyltin adduct apparently involves a radical mechanism, whereas a polar mechanism is operative in forming the 1-cyano-alkyl adduct. A four-center transition state was not considered probable in the latter case. 

The ability of chiral bis(camphorquinone-a-dioximato)cobalt(Il) complexes (Section 1.2.1.2.4.2.6.3.1.) to catalyze carbene transfer from diazocarbonyl compounds (diazoacetic esters, 2-diazo-l-phenylethan-l-one) to terminal alkenes conjugated with vinyl, aryl, carbonyl, and cyano groups, has already been mentioned. The ee-values are 75-88 /o at best, often lower. The highest values are again obtained with bulky diazoacetic esters. The significance of these catalysts, however, is their ability to promote cyclopropanation of electron-deficient alkenes, such as acrylates and acrylonitriles, in contrast to the rhodium and copper catalysts discussed above. 

Ito and Sawamura showed that the use of rhodium and palladium in the presence of the TRAP-type ligand generates an effective catalyst combination for the reaction of an allyl carbonate with a cyanopropionamide [128]. The palladium-TRAP complex is proposed to generate a cationic Jt-allyl species. In addition, a rhodium-TRAP species complexes the cyano group of the nucleophile and induces formation of the enolate. Reaction of the enolate with the Tt-complex in assembly I generates the observed product. Scheme 45. The notion that enoliza-tion is caused by complexation to the cyano group is based on previous results in the enantioselective rhodium-catalyzed Michael addition. 

Intramolecular rearrangement in five-co-ordinate cobalt(i) and rhodium(i) complexes of the type [ML4((CN)2C—C(CN)2 ]+, where L represents various cyano-substituted organic ligands, are shown to be due to Berry pseudorotation, to rotation around the tetracyanoethylene double bond, and to catalysis by anions due to formation of ion pairs. 

Rhodium(III) systems are formally analogous to cobalt(III) in that both are d systems. The larger Dq values for second-row transition metals makes all the Rh(III) complexes more analogous to the cyano complexes of Co(III). Studies with Rh(III) have the advantage that the rate of decay of the photoexcited states can be measured. The area was reviewed by Mpnsted and Mdnsted and by Skibsted. The photoactive state appears to be the ( E for Rh(L)5X symmetry), and the rate constants, for phosphorescent decay from this state in the solids at 77 K are given in Table 7.3. A more recent and extensive compilation has been given in a review by Forster. Some values of ik in representative solvents are given in Table 7.4. 

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