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The formation of aryl -carbon and aryl -heteroatom bonds using copper(I) catalysts
Copper(I) complexes of type [Cu(PPh3)3X] (where X: Br, Cl), [Cu(PPh3)2NO3], Cu(L)(PPh 3)2X (where X: PF6, NO3, ClO4 and L: phenanthroline, diimine, neocuproine), Cu(L)(PPh3)X (where X: Br and L: phenanthroline, di-imine, neocuproine) are synthesized and characterized to study their catalytic activities in carbon-heteroatom bond formation reactions. The geometrical parameters illustrate that there is a correlation between bite angles and copper-phosphorous bond lengths in mononuclear chelated copper(I) complexes. These complexes had wider bite angles than mononuclear non-chelated copper(I) complexes. Screening of the mononuclear copper(I) complexes in aryl-oxygen bond formation reactions show that the complexes [Cu(PPh3)3Br] and [Cu(neocup)(PPh3)Br] catalyzed the formation of a range of substituted diphenyl ethers at 20 mol% and 10 mol% catalyst loadings respectively. The polynuclear copper(I) complexes fail to catalyze the same reaction. In aryl-nitrogen bond formation reactions, the same complexes [Cu(PPh3)3Br] and [Cu(neocup)(PPh 3)Br] enable the formation of a range of diaryl and triaryl amines. The protocol with [Cu(PPh3)3Br] is used for the successful synthesis of o.o′.o ″-amino-trisbenzoic acid-trimethylester at 170°C in o-dichlorobenzene. This molecule is eluded by the Hartwig-Buchwald protocol. The well-defined complex [Cu(neocup)(PPh3)Br] is further investigated for the formation of aryl-sulfur and aryl-selenium bonds. Optimization and control experiments in this area show that using neocuproine as an additive with CuI, in the presence of NaOt-Bu, in toluene allows the development of protocols for a range of aryl-sulfides and aryl-selenides. In the second protocol, the change of base to K2CO3 allows the coupling of a range of electron-poor iodides to the respective diaryl selenides. The observed results point to the potential of copper(I) catalysts as alternatives to palladium-based protocols, for the formation of aryl-O, N, S and Se bonds under mild conditions.
Gujadhur, Rattan K, "The formation of aryl -carbon and aryl -heteroatom bonds using copper(I) catalysts" (2003). Doctoral Dissertations Available from Proquest. AAI3110494.