Nickel-Catalyzed Homologation of Vinylidene Difluoride (CH2═CF2): Selective ß-F vs ß-H Elimination.

Hydrofluoroolefins (HFOs) constitute the newest generation of fluorocarbon refrigerants and foam-blowing agents due to their reduced global warming potential vs their saturated analogues. To identify new synthetic routes to HFOs, we show that reactions of bulky Ni(0) phosphine and -NHC complexes with vinylidene difluoride (VF2) afford µ-fluoro-1,1,3-trifluorobut-3-enyl Ni complexes. Moreover, addition of triisopropylsilane allows for reductive elimination of the reduced product─2,4,4-trifluoro-1-butene─demonstrating the Ni-catalyzed hydrodefluorodimerization of VF2. Accompanying DFT calculations identify the T-shaped nickelacyclopentane intermediate that spontaneously undergoes selective intramolecular ß-F (vs ß-H) elimination.

Fluorocarbon Refrigerants and their Syntheses: Past to Present.

This Review chronicles the progress made in the field of small fluorocarbon synthesis since their invention in the early 1930s by Thomas Midgley, Jr., and his coworkers, with special focus on their application as refrigerants, foam expansion agents, aerosol propellants, and precision solvents. Divided into four generations of C1-C4 halocarbons from CFCs through HCFCs, HFCs, and HFOs, the merits and challenges of each will be discussed in the context of market demands, as well as the evolution of industrial manufacturing methods. Vital transformations, such as exchange (Swarts) fluorination, hydrodehalogenation, dehydrohalogenation, and additions (Kharasch or Prins) will feature prominently and will be discussed in detail, as well as catalysts therefor. Of the myriad of fluorocarbons described herein, the models which have reached particular commercial significance (such as chlorodifluoromethane and 1,1,1,2-tetrafluoroethane) are given special consideration as flag-bearers for the generation to which they belong. Regulatory constraints to which this industry is bound will be outlined in brief, as well as an introduction to safety designations and nomenclature put forth by the American Society for Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). This Review includes predominantly works which can only be found in the patent literature, but should be of equal interest to both academic and industrial practitioners of the art as it centers on fundamentals of organofluorine chemistry, which could equally be applied to the synthesis of larger molecules and building blocks for other applications.

A T-shaped Ni[κ2-(CF2)4-] NHC complex: unusual Csp3 -F and M-CF bond functionalization reactions.

A T-shaped octafluoronickelacyclopentane-NHC complex is prepared and characterized. While the solid-state structure includes a weak isopropyl-CH3 agostic interaction, the reactivity of this complex with Lewis- and Brønsted acids is clearly enhanced by its low coordination number. Reaction with Me3SiOTf, for example, yielded a rare metal-heptafluorocyclobutyl complex whereas carboxylic acids gave substitution at the α-carbon and/or Ni-CF bond protonolysis to afford thermally robust 4H-octafluorobutyl Ni complexes.