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 [Ph2P(CH2)2PPh2(CH2C(O)C6H4Br)2] Br2 (S) was synthesized in the reaction of 1,2‐bis (diphenylphosphino) ethane (dppe) and related ketone. Further treatment with NEt3 gave the symmetrical α‐keto stabilized diphosphine ylide [Ph2P(CH2)2PPh2(CHC(O)C6H4Br)2] (Y1). The unsymmetrical α‐keto stabilized diphosphine ylide [Ph2P(CH2)2PPh2(CHC(O)C6H4Br)] (Y2) was synthesized in the reaction of diphosphine in 1:1 ratio with 2.3′‐dibromoacetophenone, then treatment with NEt3. The reaction of dibromo (1,5‐cyclooctadiene)palladium (II), [PdBr2(COD)] with this ligand (Y1) in equimolar ratio gave the new C,C‐chelated [PdBr2(Ph2P(CH2)2PPh2(C(H)C(O)C6H4Br)2)] (1) and with unsymmetrical phosphorus ylide [Ph2P(CH2)2PPh2C(H)C(O)C6H4Br] (Y2) gave the new P, C‐chelated palladacycle complex [PdBr2(Ph2P(CH2)2PPh2C(H)C(O)Br)] (2). These compounds were characterized successfully by FT‐IR, NMR (1H, 13C and 31P) spectroscopic methods and the crystal structure of Y1 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; K2CO3, solvent; DMF and loading of catalyst; 0.005 mmol.