Metathesis and Metallacycle Reactivity of d10 Ni Perfluorocarbenes with Alkenes

We showed previously that the d¹⁰ nickel perfluorocarbene complex, P₃Ni═CF(CF₃) [P = P(OⁱPr)₃], 1, reacts with fluoroalkenes to produce both 4-membered nickelacycles and metathesis products via separate reaction pathways. Herein, we compare the reactivity of 1 with a variety of alkenes. The reaction of 1 with hexafluoropropene [CF₂═CF(CF₃), HFP] affords a single metallacycle, taking advantage of the diradical mechanism in which the carbene carbon adds to the CF₂ end of HFP. In contrast, 1 and perfluoro(methyl vinyl ether), CF₂═CF(OCF₃), yield both metallacycle and metathesis products, with preferential formation of the more stabilized difluorocarbene [P₃Ni═CF₂ vs P₃Ni═CF(OCF₃)] and a higher ratio of metathesis to metallacycle products than using tetrafluoroethylene or vinylidene difluoride. Attempts to form fluoropolymers via ring-opening metathesis polymerization of perfluorocyclobutene and hexafluorocyclopentene briefly gave new nickel carbenes but then yielded Ni fluoroalkene complexes with the loss of the CF(CF₃) unit. Surprisingly, both ethylene and styrene derivatives gave only metallacycles, although evidence was obtained for alkene coordination to nickel; computational studies are presented to identify the origin of these observations. Finally, insertion of ethylene into the ethylene-derived nickelacyclobutane afforded a new fluorinated alkene, CH₂═CHCH₂CH₂CHFCF₃, formed presumably via nickelacyclohexane through selective β-H and reductive eliminations.