Synthesis and molecular structure of biologically significant bis(1,3‐dimesityl‐4,5‐naphthoquinoimidazol‐2‐ylidene)gold(I) complexes with chloride and dichloridoaurate counter‐ions

Diffraction‐quality single crystals of two gold(I) complexes, namely bis(1,3‐dimesityl‐4,5‐naphthoquinoimidazol‐2‐ylidene)gold(I) chloride benzene monosolvate, [Au(C29H26N2O2)2]Cl·C6H6 or [(NQMes)2Au]Cl·C6H6, 2, and bis(1,3‐dimesityl‐4,5‐naphthoquinoimidazol‐2‐ylidene)gold(I) dichloridoaurate(I) dichloromethane disolvate, [Au(C29H26N2O2)2][AuCl2]·2CH2Cl2 or [(NQMes)2Au][AuCl2]·2CH2Cl2, 4, were isolated and studied with the aid of single‐crystal X‐ray diffraction analysis. Compound 2 crystallizes in a monoclinic space group C2/c with eight molecules in the unit cell, while compound 4 crystallizes in the triclinic space group P with two molecules in the unit cell. The crystal lattice of compound 2 reveals C—H…Cl− interactions that are present throughout the entire structure representing head‐to‐tail contacts between the aromatic (C—H) hydrogens of naphthoquinone and Cl− counter‐ions. Compound 4 stacks with the aid of short interactions between a naphthoquinone O atom of one molecule and the mesityl methyl group of another molecule along the a axis, leading to a one‐dimensional strand that is held together by strong π–η2 interactions between the imidazolium backbone and the [AuCl2]− counter‐ion. The bond angles defined by the AuI atom and two carbene C atoms [C(carbene)—Au—C(carbene)] in compounds 2 and 4 are nearly rectilinear, with an average value of ∼174.1 [2]°. Though 2 and 4 share the same cation, they differ in their counter‐anion, which alters the crystal lattice of the two compounds. The knowledge gleaned from these studies is expected to be useful in understanding the molecular interactions of 2 and 4 under physiological conditions. The crystal and molecular structures of two redox‐active bis(NHC)gold(I) (NHC is an N‐heterocyclic carbene) complexes have been probed in detail. The knowledge gleaned from these structural studies will be useful for simulating the interactions of these types of molecules under physiological conditions.