Crystal copper enolates

Activation of C=N double bonds by copper Lewis acids for nucleophilic addition has also been reported (Sch. 37) [73]. The a-imino ester 157 undergoes alkylation at the imine carbon with a variety of nucleophiles when catalyzed by copper Lewis acids. The presence of the electron-withdrawing ester group increases the reactivity of the imine and also assists in the formation of a stable five-membered chelate with the Lewis acid. Evidence for Cu(I) Lewis-acid catalysis and a tetrahedral chelate was obtained by FTIR spectroscopy, from the crystal structure of the catalyst, and from several control experiments. The authors rule out the intermediacy of a copper enol-ate in these transformations. The asymmetric alkylation of A,0-acetals with enol silanes mediated by a copper Lewis acid proceeding with high selectivity has been reported [74],... 

Despite the key role that has been attributed to copper enolates as postulated intermediates in additions to enones [78], structural information is very rare for enolates of copper as well as the higher elements in group 11. A recent crystal structure of a copper(I) ester enolate 46, which functions as a relevant intermediate in catalytic enolate arylation reactions, features a cationic Cu(I) center coordinated to two phenanthroline ligands and a free unligated enolate anion (Figure 3.13) [79]. A gold(I) enolate of acetophenone is a C-bound tautomer, as expected by the low oxophilic character of the noble metal and confirmed by a crystal structure analysis [80]. 

Yield.—66% theoretical (10 gms.). Colourless crystals insoluble in water M.P. 61° gives a deep violet coloration with ferric chloride and a bluish-green crystalline precipitate of copper benzoyl acetone with alcoholic copper acetate. This shows the compound to be tautomeric, a little of the enol form being present at ordinary temperatures. The acidity of the hydroxyl group in the enol form is not so marked as it is in the case of the hydroxymethylene compounds nevertheless, the metallic salts of benzoyl acetone and such di-ketones are remarkably stable, and on account of their great crystallising power have been used for the determination of the valency and atomic weight of the rare elements. They are also of importance in the modern theory of co-ordination. (C., 1900,1., 588 B., 34, 2584.)... 

Reaction of tetrazolyl enole 45 with copper(II) acetate yields the 3D-coordination polymer [ CulL19)21 (46), the structure of which is unequivocally established by single-crystal X-ray diffraction. The formation of 46 is understandable if the enolate of 45 is considered as tridentate chelate ligand and if the intermediate formation of the coordinatively unsaturated self-complimentary copper(II) building block 47 is assumed. The monomers 47 are bidentate coordinating by the two CN donors, which leads to linking of monomers and to coordinative saturation at the copper(II) center of 47 with formation of three-dimensional 0 [Cu(L19)2] (46) (Scheme 17, Fig. 18) [163, 164],... 

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