d¹⁰ Nickel Difluorocarbenes and Their Cycloaddition Reactions with Tetrafluoroethylene

We report the first isolable nickel difluorocarbene complexes (NiP₂[P­(OMe)₃]­(CF₂); P₂ = Ph₂P­(CH₂)₂PPh₂, 2 P­(OMe)₃), which are also the only examples of formally d¹⁰ metal fluorocarbenes. These [Ni⁰]CF₂ complexes react with tetrafluoroethylene (TFE) to yield the rare perfluorometallacyclobutanes [NiP₂(κ²-CF₂CF₂CF₂−)], with potential relevance to fluoroalkene metathesis and polymerization. Preliminary kinetic experiments establish that the reactions of the new [Ni]CF₂ compounds with TFE are considerably faster than the analogous reactions of their previously reported [Co]CF₂ counterparts. Further, we show that TFE addition to <b>2</b> is a dissociative process, in contrast to [Co]CF₂, which reacts with TFE in an associative fashion. Finally, the preliminary reactivity of NiP₂(κ²-CF₂CF₂CF₂−) (P₂ = Ph₂P­(CH₂)₂PPh₂) is described