Pd complexes with trans-chelating ligands composed of two pyridyl groups and rigid π-conjugated backbone

1,2-Bis(2-pyridylethynyl)benzene derivatives, having two pyridyl groups and π-conjugated backbone, were prepared from the 1:2 Sonogashira reaction of 1,2-diiodobenzene with 2-alkynyl pyridines. The obtained ligands react with the palladium(II) complexes such as [PdCl2(cod)] and [PdCl2(MeCN)2] to form the complexes with the ligands coordinated in a trans-chelating bidentate mode. The ligand obtained from 1,3-diiodobenzene and 2-alkynyl pyridine bridges two Pd(II) centers, yielding a dipalladium complex. A dichloropalladium complex with the trans-chelating ligand, containing two methoxy groups in the central arylene group, promotes coupling of phenyl lithium and of phenyl acetylene to yield the respective homo-coupling products. The ligand displacement reactions of {bis(2-pyridylethynyl)benzene}palladium(II) complex with phosphine and dinitrogen ligands, such as PPh3, dppe, dppb, en, tmeda, bpy and phen, takes place smoothly to release the trans-chelating ligand.

Graphical abstract1,2-Bis(2-pyridylethynyl)benzene forms trans-chelate complex with palladium(II). The palladium(II) complexes undergo ligand displacement reactions with phosphine and dinitrogen ligands, such as PPh3, dppe, dppb, en, tmeda, bpy and phen.Figure optionsDownload full-size imageDownload as PowerPoint slide