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The reaction of both the novel mixed trinuclear organo-organic copper(I) species [Cu3(C6H2Me3-2,4,6)(μ-O2CC6H5)2] (1) and [Cu(μ-O2CC6H5)]4 (2a) with quinoline in toluene or diethyl ether yields the dimeric 1:2 copper/quinoline complex [Cu(μ-O2CC6H5)(NC9H7)2]2 (3a). The reactions of methyl-substituted copper(I) benzoates, [Cu(μ-O2CC6H4Me-x)]4 (x = 2, 2b; x = 3, 2c; x = 4, 2d), with quinoline in toluene or diethyl ether, however, afford the 1:1 copper/quinoline complexes [Cu(μ-O2CC6H4Me-x)(NC9H7)]2 (x = 2, 4b; x = 3, 4c; x = 4, 4d). The structure of complex 4b, determined by a single-crystal X-ray diffraction study, shows a dicopper(I) unit doubly bridged by two benzoato units [Cul…Cul* = 2.667(1) A]. At each copper site, the CuO bonds to the bridging benzoato groups differ considerably [Cul-Ol = 1.923(5) A; Cul-O2* = 2.134(5) A]. Coordination of a quinoline at each copper site [Cul-Nl = 1.952(5) R] produces a distorted trigonal arrangement. Crystallization of the 1:2 copper-quinoline complex 3a led to formation of crystals of the dimeric 1:1 copper/quinoline complex [Cu(μ-O2CC6H5)(NC9H7)]2, 4a. The structure of 4a is similar to that of 4b [Cul…Cul* = 2.638(2) A Cul-Ol = 1.945(6) A Cul-O2* = 2.107(6) A Cul-Nl = 1.939(7) A]. Since complexes 3 and 4 can be expected to be similar to the intermediates formed in the copper-quinoline decarboxylation reaction, the reactivity of 3 and 4 at elevated temperatures in non-coordinating solvents has been studied. It was found that the decarboxylation reaction requires more than one equivalent of quinoline per copper atom. An improved mechanism is presented for the copper-quinoline decarboxylation reaction involving dinuclear copper(I) complexes as intermediates. |
