Functionalized NHC-incorporated Te−Fe−Cu clusters: Facile synthesis, electrochemistry, and catalytic reaction

Abstract

Two novel TeFe3(CO)9-containing functionalized NHC dicopper complexes, [TeFe3(CO)9{Cu(Me2-bimy)}2] (1) and [TeFe3(CO)9{Cu(iPr2-bimy)}2] (2), were prepared from the reaction of the ternary Te−Fe−Cu complex [TeFe3(CO)9{Cu(MeCN)}2] with bis-N-methyl- or bis-N-isopropyl-substituted benzimidazol-2-ylidene (Me2-bimy or iPr2-bimy) under appropriate conditions, respectively. X-ray analysis showed that Me2-bimy-introduced complex 1 displayed a TeFe3(CO)9Cu(Me2-bimy) trigonal-bipyramidal core geometry having the Fe2Cu face capped by a Cu(Me2-bimy) fragment with the two bonded Cu atoms, whereas the bulkier iPr2-bimy-incorporated complex 2 exhibited a similar TeFe3(CO)9Cu(iPr2-bimy) core having the Fe3 triangle coordinated by a Cu(iPr2-bimy) fragment with the two unbonded Cu atoms. On the other hand, when [TeFe3(CO)9{Cu(MeCN)}2] reacted with the 4,5-dichloro-substituted 1,3-dimethylimidazolium salt (Me2-Cl2-imy·HI) in the presence of KOtBu, a different type of [TeFe3(CO)9{Cu(Me2-Cl2-imy)}2] (3) was produced in good yields. Cluster 3 was shown to possess a tetrahedral TeFe3 core geometry in which the two Fe−Fe edges were each bridged by a Cu(Me2-Cl2-imy) group. According to solid-state packings, complex 1 revealed a cluster-based 3D-supramolecular framework and complexes 2 and 3 each formed a 1D-supramolecular chain, which was stabilized by intermolecular C−H…O interactions between COs and CH moieties of the corresponding NHC ligands. Further, these di-Cu(I) based complexes 1−3 exhibited catalytic activities toward the homocoupling of arylboronic acid with high yields. Importantly, the catalytic efficiencies of this series of functionalized NHC-incorporated TeFe3(CO)9Cu2-based complexes perfectly paralleled the ease of their first oxidation and the greater electron density of the carbene atom in the NHC ligands, which was elucidated by electrochemistry, 13C NMR, and DFT calculations.