Abstract
My research is about copper-catalyzed C-N cross coupling reaction. Initially, a mixture of diphenylamine, 4-iodotoluene, NaOtBu, CuI and 1,10-phenanthroline was allowed to stir in toluene at room temperature. A yellow precipitate was obtained and identified as complex [Na(phen)3][Cu(NPh2)2] (2). This complex was allowed to react with two equivalents of 4-iodotoluene in the absence of NaOtBu and obtained 70.3% (GC yield). These observation suggest that complex 2 is an intermediate in the CuI/phen/NaOtBu catalytic system. ESI-MS analysis of the reaction solution was undertaken and the [Cu(NPh2)2]-, [Cu(NPh2)I]- and Na[Cu(NPh)2(p-tolyl)]+ were observed, which are confirmed to their isotopic distribution. Base on these results, we proposed that the complex 2 first react with 4-iodotoluene then through an reductive elimination to produce the product. In addition, a mixed base (K2CO3/NaOtBu) copper(I)-catalyzed C-N cross coupling reaction was found to have a higher than double catalytic reactivity than that of using only NaOtBu as the base. In situ ESI-MS analysis for the catalytic system under the catalytic reaction condition reveals the presence of [Cu(NPh2)2]-, [Cu(NPh2)I]- and K[(phen)Cu(NPh2)(p-tolyl)]+ suggesting that they are intermediates in the reaction. The formation of the Cu(II) complex, K[(phen)Cu(NPh2)(p-tolyl)]+, implies that a free radical [CH3C6H4]• reacts with the [(phen)Cu(NPh2)] by a radical path. In order to confirm the existence of the free radical path, the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) was added and the yield of the reaction reduced from 93% to 64%. While the addition of TEMPO to the catalytic system with NaOtBu as the base, the yield only slightly reduced by 7% (38% to 35%). Based on these observations, a reaction mechanism composed of a free radical path and a 2e oxidative addition path is proposed. Furthermore, complexes [K3(phen)8][Cu(NPh2)2]3 (4) and 2 have been isolated from the catalytic C-N cross coupling reaction with the CuI-phen- MOtBu (for M= K, Na) respectively. The stoichiometric reaction of complex 2 with 4-iodotoluene undergoes more efficiently than that of complex 4 under the similar conditions. The yield of the stoichiometric reaction of complex 4 with 4-iodotoluene decreased dramatically from 50% to 12% by the addition of TEMPO, indicating that the reaction was major going through a radical pathway. When TEMPO was added to the stoichiometric reaction of complex 2 with 4-iodotoluene, the yield of the reaction decreased only slightly from 61% to 50% indicating that the reaction was major going through a 2e oxidative addition pathway.