Electronic Properties and Solid-State Packing of Isocyanofulvenes and Their Gold(I) Chloride Complexes

Two methods for the synthesis of isocyanofulvenes are reported, and a series of ligands of the type R2CHNC (4a–g, R2 = a, 9-fluorenylidene; b, 9-(2,7-dioctyloxylfluorenylidene); c, 9-(3,6-dimethoxyfluorenylidene); d, 9-(3,6-dioctylfluorenylidene); e, 5-dibenzo­[a,d]­cycloheptenylidene; f, 9-thioxanthenylidene; and g, 2,5-dimethyl-3,4-diphenylcyclopentadienylidene) were prepared along with their gold­(I) chloride complexes (R2CHNCAuCl, 5a–f). A comprehensive study of the properties of the precursors, free ligands, and gold­(I) complexes is reported and complemented by DFT calculations. Solid-state structure of two complexes (5a and 5c) show extensive aurophilic interactions and π–π stacking of the ligands. The metal centers are not involved in optical transitions. However, metal coordination leads to a consistent bathochromic shift in the absorption spectra, which signifies the effective conjugation between the isocyano group and the π-systems of the ligands. Furthermore, an additional DFT study of carbonyl complexes of the type R2CH–NC–M­(CO)5 (M = Cr, Mo, and W; R2CHNC = 4a) indicates very effective metal-to-ligand charge transfer when isocyanopentafulvenes are used as ligands.