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.