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

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 KO^tBu, 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.