Cyclopalladated benzo[h]quinolinate complexes based on stabilized phosphonium-phosphine ylides: Synthesis, characterization, and application as catalyst in aqueous-phase Suzuki-Miyaura reaction

Abstract

A series of heteroleptic mononuclear cyclopalladated benzo[h]quinolinate complexes of general formula [Pd(bzq)(Ph2PCH2PPh2C(H)C(O)C6H4-p-R)]ClO4 (bzq = 7,8-benzoquinoline; R = Cl (C1), Br (C2), NO2 (C3), OCH3(C4)), were synthesized by the reaction of [Pd(bzq)(μ-Cl)]2 with 0.5 equiv of phosphorus ylides [Ph2PCH2PPh2C(H)C(O)C6H4-p-R] in CH2Cl2 solvent at room temperature. Bridge splitting with stabilized phosphorus ylides afforded new mononuclear palladacycle derivatives with two five-membered rings. The formation of the complexes was ascertained by elemental analysis, IR, UV–visible and NMR spectroscopic methods. All of the complexes exhibited absorption bands at high energy due to the intraligand transitions [1IL π → π*] and absorptions at lower energy, which are attributed to MLCT transition [(Pd,4d) π → π* (bzq)]. The influence of the R substituent and different solvents on the UV–visible absorption of all complexes was also investigated. Furthermore, palladacycle C3 was employed as an efficient catalyst in the Suzuki‐Miyaura coupling reactions of various aryl halides and phenylboronic acids in the mixed EtOH/H2O media.