Pallada- and platinacycle complexes of phosphorus ylides; synthesis, X-ray characterization, theoretical and electrochemical studies and application of Pd(II) complexes as catalyst in Suzuki-Miyaura coupling reaction

Abstract

The new unsymmetrical phosphonium salts [Ph2PCH2PPh2CH2C(O)C6H4R]Br (R= m-Br (S1) and p-CN (S2)) were synthesized in the reaction of 1,1-bis(diphenylphosphino)methane (dppm) and BrCH2C(O)C6H4R (R= m-Br and p-CN) ketones, respectively. Further treatment with NEt3 gave the α-keto stabilized phosphorus ylides Ph2PCH2PPh2C(H)C(O)C6H4R (R= m-Br (Y1) and p-CN (Y2)). These ligands were reacted with [MCl2(cod)] (M= Pd and Pt; cod= 1,5-cyclooctadiene) to give the pallada- and platinacycle complexes [MCl2(Ph2PCH2PPh2C(H)C(O)C6H4R)] (M= Pd, R= m-Br (3); R= p-CN (4) and M= Pt, R= m-Br (5); R= p-CN (6)). Cyclic voltammetry, elemental analysis, IR and NMR (1H, 13C and 31P) spectroscopic methods were used for characterization of the obtained compounds. Further, the structure of complexes 3 and 4 were characterized crystallographically. Palladacycles 3 and 4 were proved to be excellent catalysts for the Suzuki-Miyaura coupling reactions of various aryl chlorides and arylboronic acids in mixed DMF/H2O media. Also, the bonding situations between two interacted fragments [PtCl2] and Y1 and Y2 ligands in platinacycles 5 and 6 were investigated based on DFT method by using NBO, EDA and ETS-NOCV analysis.