A T-shaped Ni[k 2 -(CF 2 ) 4 –] NHC complex: unusual C sp 3–F and M–C F bond functionalization reactions† Nicholas O. Andrella, Alexandre J. Sicard, Serge I. Gorelsky, Ilia Korobkov and R. Tom Baker * A T-shaped octafluoronickelacyclopentane–NHC complex is prepared and characterized. While the solid- state structure includes a weak isopropyl-CH 3 agostic interaction, the reactivity of this complex with Lewis- and Brønsted acids is clearly enhanced by its low coordination number. Reaction with Me 3 SiOTf, for example, yielded a rare metal–heptafluorocyclobutyl complex whereas carboxylic acids gave substitution at the a-carbon and/or Ni–C F bond protonolysis to afford thermally robust 4H-octafluorobutyl Ni complexes. Introduction Fluorocarbons and their derivatives are valuable as refrigerants, agrochemicals, unique solvents/surfactants and uo- ropharmaceuticals, with annual sales of the latter alone in the billions of dollars. 1 As the demand for uorinated chemicals has increased, so too have synthetic methods for introducing uorine and uorocarbon groups. 2–4 Despite recent advances, transition metal-mediated/-catalyzed routes are rare in comparison to the well-developed organometallic chemistry of hydrocarbons. 5 The challenge rests in the stability of metal– peruoroalkyl (M–R F ) bonds, relative to metal–alkyl bonds. 6 M– C F bonds are typically inert to processes such as insertion/alkyl migration reactions, vital to metal-mediated catalytic cycles. 7 Moreover, C–F bonds are stronger than C–H bonds, 1a,b posing another obstacle to metal-based approaches. We are investigating peruoronickelacyclopentane complexes (PNCPs) as platforms for functionalized uorocar- bons with an initial focus on fundamental stoichiometric reactions. PNCPs have been synthesized previously by reaction of tetrauoroethylene (TFE, CF 2 ]CF 2 ) with Ni 0 complexes. The displacement of P ligands by bidentate ligands has also been reported (Scheme 1). 8 To date, reports concerning the reactivity of PNCPs are sparse: Burch and co-workers found that Lewis acidic BF 3 effects uoride abstraction from Ca and phosphine migration to the activated carbon (Scheme 2a). 9 Extending this reaction to the unsymmetrical P^S chelate, we showed that treatment with excess isonitrile effected cleavage of the Ni–C F bond (Scheme 2b). 10 With phosphite co-ligands, a remarkable hydrogenolysis reaction enables the selective catalytic hydrodimerization of TFE (Scheme 2c). 11 As far as we know, this reaction is the only example of a peruoro-metallacyclopentane participating in a catalytic cycle. 12 Our approach to metallacycle functionalization hinges on the reactivity of metal-activated Ca–F bonds 13 wherein we replace a C–F bond by C–Nu vs. the current paradigm C–L (Nu ¼ nucleophile, L ¼ ligand). Using N-heterocyclic carbenes (NHCs), 14 we aimed to access low-coordinate PNCPs wherein the strong M–C NHC bond may also prevent ligand migration to Ca. There is considerable precedent for such an approach to low- coordinate metal complexes. 15 Hillhouse and coworkers prepared a two-coordinate nickel–imido complex bearing the exceptionally bulky IPr* ligand (analog of IPr with 2,6-bis(di- phenyl-methyl)phenyl groups instead of 2,6-diisopropyl- phenyl). 16 Similarly, Miyazaki and coworkers synthesized a T- shaped three-coordinate nickel(I) chloride species [Ni(IPr) 2 Cl] by treatment of two-coordinate [Ni(IPr) 2 ] with aryl chlorides. 17 Also, Hartwig et al. synthesized a low-valent, three-coordinate palladium(II) norbornyl species [Pd(SIPr)(NHAr)(Nor)], which underwent facile C–N bond reductive elimination when heated. 18 In this report we show that low-coordinate NHC Ni per- uorometallacycles undergo facile C sp 3–F and M–C F bond cleavage as well as Ca-functionalization. 9 We also demonstrate Scheme 1 Synthesis of perfluoronickelacyclopentanes. Department of Chemistry and Centre for Catalysis Research and Innovation(CCRI), University of Ottawa, 30 Marie Curie, Ottawa, ON K1N 6N5 Canada † Electronic supplementary information (ESI) available: Experimental details, NMR spectra and X-ray crystallographic information. CCDC les 968465 (2), 968466 (3), 968467 (4a), 1028645 (5c) and 1412522 (3$H 2 O); For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5sc01886b Cite this: Chem. Sci., 2015, 6, 6392 Received 25th May 2015 Accepted 27th July 2015 DOI: 10.1039/c5sc01886b www.rsc.org/chemicalscience 6392 | Chem. Sci., 2015, 6, 6392–6397 This journal is © The Royal Society of Chemistry 2015 Chemical Science EDGE ARTICLE Open Access Article. Published on 06 August 2015. Downloaded on 8/13/2022 12:37:16 PM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. View Article Online View Journal | View Issue