Octa- and Nonamethylfluorene and an Electron-Rich Permethylfluorenyl Ruthenocene Derivative

Two highly methylated fluorene derivatives have been synthesized and used for the preparation of mixed-ligand fluorenyl ruthenocenes. Specifically, reaction of 2,2',3,3',4,4',5,5'-octamethylbiphenyl with paraformaldehyde in the presence of CF3CO2H provided 1,2,3,4,5,6,7,8-octamethylfluorene (C13Me8H2), which was subsequently methylated by reaction with n-BuLi followed by addition of MeI to yield 1,2,3,4,5,6,7,8,9-nonamethylfluorene (C13Me9H). Reaction of the lithium fluorenyl derivatives with [Cp*RuCl]4 generated the mixed-ligand ruthenocenes Cp*(C13Me8H)Ru and Cp*(C13Me9)Ru. Electrochemical measurements indicate that these ruthenocene derivatives undergo quasi-reversible oxidations at low potentials consistent with strongly donating character for the highly methylated fluorenyl ligands. X-ray diffraction studies on C13Me8H2, C13Me9H, and Cp*(C13Me9)Ru revealed a twisted fluorene core in all cases.