Di‑, Tri‑, and Tetranuclear Copper(I) Complexes of Phenanthroline-Linked Dicarbene Ligands

A family of 2,9-di­(3-R-1H-imidazolium-1-yl)-1,10-phenanthroline iodides and hexafluorophosphates (R = allyl, benzyl, mesityl, picolyl) were synthesized from 2,9-diiodophenanthroline and imidazole or N-substituted imidazoles. Simple reactions of these diimidazolium salts with copper powder at room temperature have afforded a series of multinuclear copper­(I)–NHC complexes in good yields. The structures vary depending on the N substituents and counterions. [Cu4(L1)2(MeCN)4]­(PF6)4 (R = allyl) exhibits a zigzag Cu4 chain with two terminal [Cu­(NHC)­(MeCN)2] and two internal [Cu­(phen)­(NHC)] moieties. [Cu3(L2)2]­(PF6)3 (R = benzyl) contains a strictly linear Cu3 framework with two [Cu­(NHC)2] units and a [Cu­(phen)2] located at the center. Both complexes [Cu3(L4)2]­(PF6)3 (R = mesityl) and [Cu3(L5)2]­(PF6)3 (R = picolyl) consist of a triangular Cu3 core in which two copper­(I) ions are surrounded by a phen and a NHC group and the third copper­(I) is coordinated by two NHC groups. [Cu3(L3)2]­(PF6)3 derived from 2,9-di­(3-benzyl-1H-benzimidazolium-1-yl)-1,10-phenanthroline hexafluorophosphate can undergo transannulation of the benzimidazolylidene ring giving [Cu2(L3′)2]­(PF6)2. The decomposition process might involve solvent-induced rearrangement of the ligand and hydrolysis of carbene moieties. Treatment of 2,9-di­(3-mesityl-1H-benzimidazolium-1-yl)-1,10-phenanthroline iodide with copper powder generated dinuclear complex [Cu2(L4)2]­[Cu2(μ-I)2I2] (R = mesityl) possessing a macrocyclic cation and [Cu2(μ-I)2I2]2– anion. Tetranuclear complex [Cu4(L5)2(μ-I)2]­(CuI3) (R = picolyl) has been obtained from its diimidazolium iodide and copper powder. All Cu­(I) complexes have been characterized by X-ray single diffraction analysis, elemental analysis, and NMR spectra. Their redox behavior and fluorescent properties have also been studied.