Organocopper complexes reduction

Addition of a toluene solution of the cuprate, Cu2Li2(p-tolyl)4-2Et20 (1), to a solution of palladium(II) acetate in toluene leads to the in situ formation of a thermally unstable organocopper complex in which the lithium atom of 1 has been replaced by the more electronegative precious metal. Subsequent reductive elimination of the organic tolyl group from the unstable bimetallic complex in the presence of silica affords supported bimetallic particles, which without further treatment are an active catalytic system. (Equation 3)... 

The mechanism of conjugate addition reactions probably involves an initial complex between the cuprate and enone.51 The key intermediate for formation of the new carbon-carbon bond is an adduct formed between the enone and the organocopper reagent. The adduct is formulated as a Cu(III) species, which then undergoes reductive elimination. The lithium ion also plays a key role, presumably by Lewis acid coordination at the carbonyl oxygen.52 Solvent molecules also affect the reactivity of the complex.53 The mechanism can be outlined as occurring in three steps. 

Oppolzer reports that similar additions of the ether soluble organocopper-boron trifluoride-tri-n-bu-tylphosphine complexes (87c) to chiral ot,3-unsaturated esters (Scheme 20) proceed with high dia-stereoselectivity. Subsequent hydrolysis or reduction of the chiral adducts, e.g. (115) and (116), affords... 

Copper(I) catalysis is very well established to promote intramolecular [2+2] photocycloaddition reactions of l,n-dienes (review [351]). The methodology recently enjoyed a number of applications [352-354], It is assumed that CuOTf, which is commonly applied as the catalyst, coordinates the diene and in this way mediates a preorganization. The Ghosh group recently reported a number of CuOTf-catalyzed photochemical [2+2] cycloaddition reactions, in which an organocopper radical complex was proposed as a cyclization intermediate (which should, however, have a formal Cu(II) oxidation state) (selected references [355-357]). A radical complex must, however, not be invoked, since the process may either proceed by a [2+2] photocycloaddition in the coordination sphere of copper without changing the oxidation state or according to a cycloisomerization/reductive elimination process. 

These disproportionations could proceed directly or by a 2-step mechanism involving prior transfer of a g-hydrogen to iron followed by reductive elimination. Similar disproportionation processes have been described with organocopper(l), organoman-ganese(II), and organoplatinum(II) complexes.(38)... 

MacMillan has reported examples of synergistic catalysis in which copper salts are used. Although these results were driven by ad hoc hypotheses, most of these transformations are related to a Cu(i)/Cu(m) catalytic cycle. In any case, the superior performances offered by copper(i) salts, compared to strong Lewis acids tested in the processes, is an indication that the Lewis acidity of the metal salt is not playing a decisive role in these transformations. The complexation of the enamine 7i-system with Cu(iii)-R is expected to lead to rjl-iminium organocopper species that, upon reductive elimination, will form a carbon-carbon bond and liberate the active Cu(i) catalyst. Hydrolysis of the resulting iminium will also release the imidazolidinone catalyst to complete the organocatalytic cycle as shown in Scheme 18.7. 

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