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

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 (C-1), Br (C-2), NO2 (C-3), OCH3(C-4)), were synthesized by the reaction of [Pd(bzq)(mu-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 [(IL)-I-1 pi ->pi*] and absorptions at lower energy, which are attributed to MLCT transition [(Pd,4d) pi ->pi* (bzq)]. The influence of the R substituent and different solvents on the UV-visible absorption of all complexes was also investigated. Furthermore, palladacycle C-3 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. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

A series of heteroleptic mononuclear cyclopalladated benzo[h]quinolinate complexes were synthesized and characterized. These complexes showed unique UV-visible absorption properties, with palladacycle C-3 exhibiting excellent catalytic activity. This study is of significance for further understanding these complex compounds.