Organo-Transition Metal Compounds Containing Perfluorinated Ligands

Abstract

This chapter discusses the effect of α-fluorine substituents on the structure and reactivity of organic ligands bound to transition-metal centers, with particular emphasis on recent chemistry of octafluorocycloocta-1,3,5,7-tetraene (OFCOT). The chemistry of transition-metal compounds containing hydrocarbon ligands continues to be intensively explored. The most common kinds of compounds are those with metal–carbon σ bonds and metal–olefin bonds. The physical properties and chemical reactivity of transition-metal compounds containing trifluoromethyl ligands are surveyed. Complexes of cyclic perfluoroolefins are also quite common. In contrast to their hydrocarbon analogues, many unsaturated fluorocarbons react with anionic transition-metal nucleophiles to yield products arising from the net displacement of fluoride ion. The fluorocarbon complexes are notably different in their chemical properties as compared to their hydrocarbon analogues. The regio- and stereochemistry of phosphine attack were unambiguously defined by a single-crystal X-ray diffraction study. The enhanced reactivity of the indenyl complexes of the transition metals toward ligand substitution, compared to their cyclopentadienyl analogues, is due to a slippage of the indenyl ligand from η 5 to an η 3 bonding mode, thus making the metal center coordinatively unsaturated. Further contrasting reactivity is observed using t-butylisocyanide (t-BuNC) as the exogenous ligand. No photochemical rearrangements or transannular ring closure chemistry were observed with the corresponding cyclopentadienyl analogues. Additional chromatography allowed for the isolation of minor amounts of a second isomeric complex that could not be totally separated from the major isomer.