Trinuclear copper(I) complex of 1,3-bis(2-pyridinylmethyl)imidazolylidene as a carbene-transfer reagent for the preparation of catalytically active nickel(II) and palladium(II) complexes

Reactions of 1,3-bis(pyridin-2-ylmethyl)-1H-imidazol-3-ium hexafluorophosphate, ([HL1](PF6), L1 = 1,3-bis(pyridin-2-ylmethyl)imidazolylidene) and 1,3-bis(pyridin-2-ylmethyl)-1H-benzimidazol-3-ium hexafluorophosphate ([HL2](PF6), L2 = 1,3-bis(pyridin-2-ylmethyl)benzoimidazolylidene) with cuprous oxide in acetonitrile readily yielded trinuclear complexes [Cu3(L1)3(PF6)3] (1) and [Cu3(L2)3(PF6)3] (2). Treatment of 1 with Ni(PPh3)2Cl2 and Pd(cod)Cl2 gave [Ni(L1)Cl](PF6) (3) and [Pd(L1)Cl](PF6) (4), respectively, due to transmetalation. [Ni(L1)2](PF6)2 (5) was obtained from the reaction of [Cu3(L1)3(PF6)3] and Raney nickel in acetonitrile. All these complexes have been fully characterized. Both 1 and 2 consist of a triangular Cu3 core with each Cu–Cu bond capped by an imidazolylidene group. Each imidazolylidene acts as a bridging ligand in a μ2 mode and is bonded equally to two Cu(I) ions. The pincer nickel and palladium complexes are square-planar and contain a tridentate NCN ligand. Complexes 3 and 4 are efficient catalyst precursors for Kumada–Corriu and Suzuki–Miyaura coupling reactions of aryl halides with organometallic reagents.

Graphical abstractTrinuclear copper(I) complexes of 1,3-bis(2-pyridinylmethyl)imidazolylidene were obtained from 1,3-bis(pyridin-2-ylmethyl)-1H-imidazol-3-ium salts and Cu2O, and the Cu–NHC complex was employed as carbene-transfer reagent for the preparation of catalytically active nickel(II), palladium(II) complexes.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Copper, nickel, palladium complexes of N-heterocyclic carbenes. ► Copper N-heterocyclic carbene complexes as carbene-transfer reagents. ► Ni–NHC complex as a catalyst for Kumada–Corriu coupling of aryl chlorides. ► Pd–NHC complex as a catalyst for Suzuki–Miyaura coupling of aryl bromides.