Heterobimetallic complexes containing an N-heterocyclic carbene based multidentate ligand and catalyzed tandem click/Sonogashira reactions

Abstract

Mono- and polynuclear complexes containing 3-(1,10-phenanthrolin-2-yl)-1-(pyridin-2-ylmethyl)imidazolylidene (L), [NiL₂](PF₆)₂ (2), [CoL₂](PF₆)₃ (3), [PtLCl](PF₆) (4), [PdAgL₂](PF₆)₃ (5), [PdCuL₂](PF₆)₃ (6), [Pd₂L₂Cl₂](PF₆)₂ (7), and [Pd₃L₂Cl₄](PF₆)₂ (8) have been prepared and fully characterized by NMR, ESI-MS spectroscopy, and X-ray crystallography. In complexes 2–4, the ligand binds to metals in a pincer NNC fashion with the pyridine group uncoordinated. Complexes 5 and 6 are isostructural to each other in which the palladium ions are surrounded by two pyridines and two imidazolylidenes and Ag(I) or Cu(I) is coordinated by two 1,10-phenanthroline moieties. In the trinuclear palladium complex 8, one palladium ion has an identical coordination mode as in 5 and 6, and the other two palladium ions are bonded to the 1,10-phenanthroline. Complex 6 exhibits excellent catalytic activity for the tandem click/Sonogashira reaction of 1-(bromomethyl)-4-iodobenzene, NaN₃, and ethynylbenzene in which three C–N bonds and one C–C bond are formed in a single flask.