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.