Synthesis and Structures of Copper(I) Complexes with Phosphino-Functionalized N‑Heterocyclic Carbenes (NHCP) and Bis-N-Heterocyclic Carbenes (Bis-NHC)

New copper(I) complexes bearing N-phosphino- and N-phosphinomethyl-functionalized NHC ligands (NHCP systems) were synthesized and fully characterized. Using halide-containing copper(I) precursors, strikingly different structural motifs were found, dependent on the substitution pattern of the NHCP moiety. An interesting tetranuclear μ4-bridged copper(I) cluster (4b) is formed when CuBr·SMe2 is reacted with the N-phosphino-substituted ligand 1a, whereas the dinuclear complex 4a is formed in an analogous reaction with 1b. Dinuclear metallacycles (2a,b) were isolated and characterized by X-ray diffraction when the halide-free copper(I) precursor [Cu(CH3CN)4]PF6 was reacted with NHCP ligands 1a,b using the N-phosphinomethyl-substituted NHCP ligands 5a,b, as well as employing the bis-NHC ligands BIM and BIM-BMe2 (10a,b), respectively. The observed copper(I)–copper(I) distances are directly correlated with the size of the metallacycle formed. An unexpected strong influence upon the metal–metal separation was found for the charged complexes in 10a,b. Using directly N-tBu-substituted NHCP ligands led to formation of an electronically less favorable trans-C,C coordination at the copper(I) centers (3 and 6a), which inhibited the formation of a dimeric species in the case of 3.