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.