New dimeric phosphine ylide copper (I) complexes: Synthesis, coordination behavior, and application in Suzuki cross-coupling reactions

Abstract

The reaction of the non-symmetric phosphorus ylides, Ph 2 P(CH 2 ) n PPh 2 C(H)C(O)PhR with CuCl in equimolar ratios using dry methanol as solvent give binuclear complexes of the type [Cu(μ-Cl){Ph 2 P(CH 2 ) n PPh 2 C(H)C(O)PhR}] 2 ( n = 1: R = Br ( 1 ), OCH 3 ( 2 ); n = 2: R = Br ( 3 ), OCH 3 ( 4 )). X-ray analyses of 1 demonstrate the Cl bridged dimeric structures with P,C-chelated ligands. Characterizations of these compounds were carried out by FT-IR and multinuclear NMR technique. Elemental analysis indicate a 1:1 stoichiometry between the ylides and the Cu(I) chloride in the four complexes. The precursor complexes 1 and 3 are found to exhibit high catalytic activity in the Cu-catalyzed Suzuki cross-coupling reactions in an air atmosphere at medium catalyst loading in DMF as a solvent. The use of 5 mol% catalyst in the presence of Cs 2 CO 3 allows the coupling reaction to proceed with moderate to excellent yields. The reactions of CuCl with bidentate α-keto stabilized phosphorus ylides give binuclear complexes of the type [Cu(μ-Cl){ Ph 2 P(CH 2 ) n PPh 2 C(H)C(O)PhR}] 2 ( n = 1: R = Br ( 1 ), OCH 3 ( 2 ), n = 2: R = Br ( 3 ), and OCH 3 ( 4 )). X-ray analysis of 1 demonstrates a Cl bridged dimeric structure with P,C-chelated ligands. Highly efficient Suzuki cross-coupling reaction between various aryl halides and phenylboronic acid using 1 and 3 as catalyst precursors under aerobic conditions has been developed. • Synthesis and characterization of Cu(I) phosphine-ylide complexes are presented. • X-ray analyses demonstrate the structures (L-Cu(μ-Cl )2 Cu-L) with P, C-chelated ligands. • Elemental analysis indicate a 1:1 stoichiometry between ylides and Cu(I). • These Cu(I) complexes were used for the first time in Suzuki cross-coupling reactions. • High yields were obtained in the reaction of phenylboranic acid with various aryl halides.