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 μ 4 -bridged copper(I) cluster ( 4b ) is formed when CuBr·SMe 2 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(CH 3 CN) 4 ]PF 6 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-BMe 2 ( 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-t Bu-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 .