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.