Spectral and crystallography studies of new palladacycle complexes with P,C- and C,C-donor ligands; Application of (OAL16) to optimizing the yield of Mizoroki-Heck reaction

Abstract

The new symmetrical diphosphonium salt [Ph 2 P(CH 2 ) 2 PPh 2 (CH 2 C(O)C 6 H 4 Br) 2 ] Br 2 (S) was synthesized in the reaction of 1,2-bis (diphenylphosphino) ethane (dppe) and related ketone. Further treatment with NEt 3 gave the symmetrical α-keto stabilized diphosphine ylide [Ph 2 P(CH 2 ) 2 PPh 2 (CHC(O)C 6 H 4 Br) 2 ] (Y 1 ). The unsymmetrical α-keto stabilized diphosphine ylide [Ph 2 P(CH 2 ) 2 PPh 2 (CHC(O)C 6 H 4 Br)] (Y 2 ) was synthesized in the reaction of diphosphine in 1:1 ratio with 2.3′-dibromoacetophenone, then treatment with NEt 3. The reaction of dibromo (1,5-cyclooctadiene)palladium (II), [PdBr 2 (COD)] with this ligand (Y 1 ) in equimolar ratio gave the new C,C-chelated [PdBr 2 (Ph 2 P(CH 2 ) 2 PPh 2 (C(H)C(O)C 6 H 4 Br) 2 )] (1) and with unsymmetrical phosphorus ylide [Ph 2 P(CH 2 ) 2 PPh 2 C(H)C(O)C 6 H 4 Br] (Y 2 ) gave the new P, C-chelated palladacycle complex [PdBr 2 (Ph 2 P(CH 2 ) 2 PPh 2 C(H)C(O)Br)] (2). These compounds were characterized successfully by FT-IR, NMR ( 1 H, 13 C and 31 P) spectroscopic methods and the crystal structure of Y 1 and 2 were elucidated by single crystal X-ray diffraction. The results indicated that the complex 1 was C, C-chelated whereas complex 2 was P, C-chelated. These air/moisture stable complexes were employed as efficient catalysts for the Mizoroki-Heck cross-coupling reaction of several aryl chlorides, and the Taguchi method was used to optimize the yield of Mizoroki-Heck coupling. The optimum condition was found to be as followed: base; K 2 CO 3 , solvent; DMF and loading of catalyst; 0.005 mmol.