Synthesis of Pentafluorophenyl-Substituted Cyclopentadienes and Their Use as Transition-Metal Ligands

Abstract

The reaction of NaC 5 H 5 (NaCp) and hexafluorobenzene (1:1 ratio) in THF at 25 °C for 15 h afforded, after hydrolysis, a mixture of regioisomeric (pentafluorophenyl)cyclopentadienes. This mixture was isolated as a monoisomeric dimer of 1-(pentafluorophenyl)cyclopentadiene. The structure of the dimer was determined crystallographically. Flash vacuum thermolytic cracking of the dimer at 200 °C regenerated (pentafluorophenyl)cyclopentadiene as a mixture of regioisomers. In contrast, the reaction of NaCp, NaH, and C 6 F 6 (1:2:5 ratio) in THF at reflux for 3 d affords, after hydrolysis, 1,4-bis(pentafluorophenyl)cyclopentadiene, which does not dimerize. Either the mono- or the disubsubstituted diene reacts with NaH in THF to afford the corresponding stable substituted sodium cyclopentadienides in high yields. Sodium (pentafluorophenyl)cyclopentadienide, (C 6 F 5 )C 5 H 4 Na, reacted with FeBr 2, Re(CO) 5 Br, and ZrCl 4 (THF) 2, to afford the transition metal complexes (η 5 -C 5 H 4 C 6 F 5 ) 2 Fe, (η 5 -C 5 H 4 C 6 F 5 )Re(CO) 3, and (η 5 -C 5 H 4 C 6 F 5 ) 2 ZrCl 2 . Sodium 1,3-bis(pentafluorophenyl)cyclopentadienide reacted with FeBr 2 and Re(CO) 5 Br to give the corresponding complexes [η 5 -1,3-C 5 H 3 (C 6 F 5 ) 2 ] 2 Fe and [η 5 -1,3-C 5 H 3 (C 6 F 5 ) 2 ]Re(CO) 3 . Infrared spectroscopic analysis of the tricarbonylrhenium(I) complexes and cyclic voltammetric analysis of the substituted ferrocenes quantified the strong electron-withdrawing effects of the pentafluorophenyl substituents.