The reaction of the stable ferrocene‐based N‐heterocyclic carbene (NHC) fcN(CH 2 Mes) 2 C ( A ; fc = 1,1 ′ ‐ferrocenylene, Mes = mesityl) with CuX (1 equivalent; X = Cl, Br, I, Mes) afforded CuX( A ). AgCl( A ) is synthesized analogously. Cu( A ) 2 BF 4 is obtained by reaction of CuCl( A ) with AgBF 4 and A in a 1:1:1 stoichiometric ratio. trans ‐NiCl 2 ( A ) 2 and trans ‐PdCl 2 ( A ) 2 are obtained from NiCl 2 (DME) (DME = dimethoxyethane) and PdCl 2 (COD) (COD = 1,5‐cyclooctadiene), respectively, by reaction with A (2 equivalents). All new compounds are structurally characterized by X‐ray diffraction. Cu( A ) 2 BF 4 exhibits four methylene CH···Cu contacts ≤ 2.50 Å in the solid state, whereas the other complexes show two methylene CH···metal contacts. Nuclear magnetic resonance spectroscopic data indicate the presence of substantial anagostic methylene CH···metal interactions in solution only in the case of trans ‐NiCl 2 ( A ) 2 . According to cyclic voltammetry, Cu( A ) 2 BF 4 undergoes two quasireversible oxidations in dichloromethane solution, viz., a two‐electron process at E ½ = 0.69 V versus the saturated calomel electrode (SCE) involving the two equivalent, and essentially noninteracting, ferrocene‐based moieties (Fe II /Fe III ), which is followed by a copper‐based one‐electron process (Cu I /Cu II ) at E ½ = 0.90 V versus SCE. The previously reported gold complex AuCl( A ) is biologically active, showing strong activity against the proliferation of several cancer cell lines as well as antibacterial effects against the Gram‐positive strain Bacillus subtilis .
Mellin et al. (Sun,) studied this question.