Palladium complexes catalyzed ethyl formate formation

Fe4S4(SR)4] , are good catalysts for reduction of CO2. Recently it was found that other compounds also facilitate such reduction. Electrolytic reduction of CO2 in acetonitrile in the presence of [Rh(dppe)2]Cl leads to the formation of The rhenium(I) compound [ReCl(CO)3 (bipy)] catalyzes electrolytic reduction of CO2 to carbon monoxide. The electrolytic reduction of CO2 in some cases probably proceeds via the radical anion C02 its formation explains various reduction products see scheme (13.241). Palladium complexes, for instance, [Pd2Cl2(dppm)2], [Pd(dppm)2], and [PdCl2(dppm)], slowly catalyze reduction of CO2 to methane, ethyl formate, and traces of ethyl oxalate. 

Copper-catalyzed C-O, C-N, and C-S Coupling. While there is an extensive variety of palladium catalysts for C(aryl)-X bond formation (X = 0, N, and S), copper corrqtlexes have recently gained renewed popularity in these coupling processes. Use of the (CuOTf)2. benzene complex allows the formation of diaryl ethers from aryl bromides or iodides and phenols in very good yields (76-93%) (eq 121). The reaction occurs in toluene in the presence of cesium carbonate as the base and a catal)4ic quantity of ethyl acetate whose role is probably to increase the solubility of the copper species. In the case of less reactive phenols, yields can be increased by the addition of a stoichiometric amount of carboxylic acid. A slight modification of these conditions has been used in the key diaryl ether formation in the synthesis of verbenachalcone. ... 

Enantioselective allylic substitutions catalyzed by transition-metal complexes are a powerful method for constructing complex organic molecules [4f,55]. Palladium-based catalysts have often given excellent results. To expand the scope of the reaction, a new enantioselective allylic alkylation catalyzed by planar-chiral ruthenium complexes was developed [56]. For example, the reaction of l,3-diphenyl-2-propenyl ethyl carbonate with sodium dimethyl malonate in the presence of 5 mol% of a planar chiral (S)-ruthenium complex (Figure 5.3) at 20 °C for 6 h in THE resulted in the formation of the corresponding chiral allylic alkylated product of dimethyl 2-((2 )(lS)-l,3-diphenylprop-2-enyl)propane-l,3-dioate in 99% yield vsdth 96% e.e. (Eq. 5.33). 

Doyle has put forward arguments against the intermediacy of such complexes in catalytic cyclopropanation . Firstly, metal coordination activates the alkene to nucleophilic attack. Hence, an electrophilic metal carbene would add only reluctantly or not at all. Secondly, the stable PdCl2 complexes of dienes 8 and 428 do not react with ethyl diazoacetate, even if Rh fOAc) or PdCljfPhCbOj is added. The diazoester is decomposed only when it is added to a mixture of the Pd complex and excess diene. These results exclude the metal-carbene-olefin intermediate, but they leave open the possibility of metal carbene interaction with an uncomplexed olefin molecule. The preferred formation of exo-cyclopropanes in the PdCyPhCN) -catalyzed reactions between 8 and N2CHCOOEt or N2CPh2, with exo. endo ratios virtually identical to those observed upon cyclopropanation of monoolefin 429, also rule out coordination of a palladium carbene to the exocyclic double bond of 8 prior to cyclopropanation of the endocyclic double bond. 

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