Titanium(IV) Trifluoromethyl Complexes: New Perspectives on Bonding from Organometallic Fluorocarbon Chemistry

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

Synthesis, Characterization, and X-ray Crystallography, of the First Cyclohexadienyl Trifluoromethyl Metal Complex (η5-C6H7)Fe(CO)2CF3

Fluorochemistry is a field of tremendous developments and advances in several areas of science including materials, pharmaceuticals and agriculture. This makes the design and synthesis of fluorine-containing substances highly desirable research targets. The sub-area of synthetic perfluorinated chemistry proportionately attracts widespread interest by applying to all areas of chemistry including organic and inorganic. Particularly, the latter is much underdeveloped as metal complexes with perfluoroalkyl moieties are scarce, with the vast majority of perfluorinated analogs, of long known, halo and alkylated derivatives never having been synthesized. Focusing on the chemistry of trifluoromethyl group, which is the most important in the class of perfluoroalkyls, we set out to explore the possibility of synthesizing and completely characterizing a cyclohexadienyl metal complex. Upon utilizing a number of trifluorometylating reagents, we only arrived at an efficient preparation by the use of Morrison’s trifluormethylating reagent. As a result, the new, air- and moisture-sensitive complex (η⁵-C₆H₇)Fe(CO)₂CF₃, was prepared in 71% yield, using a nucleophilic iodo-for-trifluoromethyl substitution, and was completely characterized including by X-ray crystallography.

Synthesis and Reactivity of Mn–CF3 Complexes

The synthesis, characterization and reactivity of several bi- and tridentate, N-ligated manganese carbonyl trifluoromethyl complexes are presented. These complexes exhibit elongated Mn–CCF3 bonds (versus Mn(CF3)(CO)5), suggesting a lability that could be utilized for the transfer or insertion of the CF3 functional group into organic substrates. Unlike their Mn–X congeners (X = Cl, Br), these Mn–CF3 complexes exhibit a preference for hard donor ancillary ligands, thus enabling the synthesis of 4 N-ligated Mn–CF3 complexes including a mixed-donor tridentate complex using an NNS Schiff base ([2-(methylthio)-N-(1-(pyridin-2-yl)ethylidene)aniline]). Although we have not yet identified efficient CF3 transfer reactions, fluoride abstraction from the Mn–CF3 complexes using trimethylsilyl triflate affords the first stable Mn fluorocarbenes as evidenced by 19F NMR spectroscopy.

Fluorocarbene, fluoroolefin, and fluorocarbyne complexes of Rh

The manuscript reports the synthesis, characterization, and analysis of electronic structure in a series of complexes of small perfluorocarbon ligands with the (PNP)Rh fragment (where PNP is a diarylamido/bis(phosphine) pincer ligand). Reactions of (PNP)Rh(TBE) as the source of (PNP)Rh with CHF3 and C2HF5 produced perfluoroalkylidene complexes (PNP)Rh[double bond, length as m-dash]CF2 and (PNP)Rh[double bond, length as m-dash]C(F)(CF3). (PNP)Rh[double bond, length as m-dash]CF2 could also be obtained via the reaction of (PNP)Rh(TBE) with Me3SiCF3/CsF, with an admixture of (PNP)Rh(C2F4), where TBE = tert-butylethylene. Abstraction of fluoride from these neutral (PNP)RhC x F y complexes was successful, although only abstraction from (PNP)Rh[double bond, length as m-dash]CF2 allowed unambiguous identification of the Rh product, [(PNP)Rh[triple bond, length as m-dash]CF]+. DFT computational studies allowed comparison of relative energies of (PNP)Rh(C2F4) and [(PNP)Rh(C2F3)]+ isomers as well as comparisons between the electronic structure of the [double bond, length as m-dash]CF2, C2F4, and [triple bond, length as m-dash]CF+ complexes and their hydrocarbon analogues.

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

The reactivity of this T-shaped perfluoronickelacyclopentane–NHC complex with Lewis- and Brønsted acids is enhanced vs. 4-coordinate variants by its low coordination number.

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–C^F bond protonolysis to afford thermally robust 4H-octafluorobutyl Ni complexes.

A (pentafluoroethyl)(trifluoromethyl)carbene complex of iridium and reductive activation of its sp3 α, β, and γ carbon–fluorine bonds to give perfluoro-2-butyne, perfluoro-1,2,3-butatriene and perfluoro-1-irida-2-methyl-2-cyclobutene) complexes

Inner-sphere reduction of a (pentafluoroethyl)(trifluoromethyl)carbene ligand affords perfluorobutyne, perfluorobutatriene and perfluorometallacyclobutene ligands.

Stepwise addition of difluorocarbene to a transition metal centre

The Ruppert–Prakash reagent (Me₃SiCF₃) is used to introduce difluorocarbene (CF₂) and tetrafluoroethylene (TFE) ligands to cobalt(i) metal centres, whereby the TFE ligand is generated via [2+1] cycloaddition between [Co]CF₂ and CF₂.