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

Abstract

The reaction of NaC5H5 (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 C6F6 (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, (C6F5)C5H4Na, reacted with FeBr2, Re(CO)5Br, and ZrCl4(THF)2, to afford the transition metal complexes (η5-C5H4C6F5)2Fe, (η5-C5H4C6F5)Re(CO)3, and (η5-C5H4C6F5)2ZrCl2. Sodium 1,3-bis(pentafluorophenyl)cyclopentadienide reacted with FeBr2 and Re(CO)5Br to give the corresponding complexes [η5-1,3-C5H3(C6F5)2]2Fe and [η5-1,3-C5H3(C6F5)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.

Transition metal cyclopentadienyl complexes bearing perfluoro-4-tolyl substituents

“…The waxy bulk solid was found by 1 H NMR spectroscopic analysis to contain a mixture of diarylated cyclopentadiene isomers 2a (24%), 2b (4%), 2c (63%), and 2d (9%). 1 …”

“…Systematic analyses of electron-withdrawing substituents on metal-centered reactivity are still relatively sparse, however, mainly because ''standard'' electron-withdrawing groups such as acetyl, nitro, or trifluoromethyl can engage in undesirable reactions of their own. We showed previously that up to four pentafluorophenyl (C 6 F 5 ) groups are readily attached to cyclopentadiene in one-pot procedures involving nucleophilic aromatic substitution of hexafluorobenzene [1][2][3][4][5]. C 6 F 5 -substituted Cp anions are stable as sodium salts and can be used in standard synthetic procedures to prepare complexes of both early and late transition metals.…”

Preparation of ferrocenes with high fluorous-phase affinities

“…The starting diarylferrocene complexes were prepared as described elsewhere [26,28]. Toluene and perfluoro(methylcyclohexane) were used as received from commercial sources.…”

“…Isolated product yields and NMR data are provided in Table 1. Analysis was obtained for 1a: Calcd (found) for C 26 …”

“…The method is illustrated using 1,1 0 -bis(pentafluorophenyl)-ferrocene [26], which has two aromatic fluorides that are readily displaced by alkoxides [27], and 1,1 0 -bis(4-tetrafluoropyridyl)-ferrocene [28], which has four labile fluorides. The synthesis and characterization of the resulting ponytail-substituted diarylferrocenes are reported, along with fluorocarbon/hydrocarbon partition constants determined by UV-vis spectrophotometry.…”