Mild, Safe, and Versatile Reagents for (CF2)n Transfer and the Construction of Fluoroalkyl-Containing Rings

Difluoromethylene insertion into fluoroalkyl copper complexes

Herein, we report the insertion of a difluoromethylene into 1,1,2,2-tetrafluoro-2-arylethyl copper complexes to synthesize extended perfluoroalkyl-bridged compounds that have various functional groups on each edge (ArCF2CF2(CF2)nR, R = arenes, halogens, alkyl, alkenyl, and benzyloxycarbonyl). Further, the one-pot syntheses of perfluoroalkyl-bridged compounds from aryl boronic acid esters were carried out.

Synthesis, structure, and electrochemical properties of [LNi(Rf)(C4F8)]- and [LNi(Rf)3]- complexes

The new anionic nickelate complexes [(MeCN)Ni(C₄F₈)(CF₃)]^-, [(MeCN)Ni(C₄F₈)(C₂F₅)]^-, [(IMes)Ni(C₄F₈)(CF₃)]^-, [(IMes)Ni(CF₃)₃]^- (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), and [(F-NHC)Ni(R_f)₃]^- (F-NHC = 1,3-bis(2,4-F₂Ph), 2,4,6-F₃Ph- or 3,4,5-F₃Ph)imidazol-2-ylidene; (R_f = CF₃ or C₂F₅) were synthesized and structurally characterized. The electrochemical properties of all new compounds were revealed by cyclic voltammetry studies and compared to the known CF₃ analogue [(MeCN)Ni(CF₃)₃]^-. The IMes-coordinated complexes exhibited initial oxidation events that were well-separated from a second oxidation process in the cyclic voltammograms. The complexes containing F-substituted NHC ligands [(F-NHC)Ni(CF₃)₃]^- are structurally quite similar to the IMes derivative and reveal also two separated oxidation waves in their cyclic voltammograms. The absolute potentials as well as the separation between the two waves vary with the substitution pattern, suggesting that the NHC ligand environment (NHC = N-heterocyclic carbene) is an interesting platform for the development of new redox-triggered reactions that release trifluoromethyl and perfluoroalkyl radicals upon oxidation.

C,C- and C,N-Chelated Organocopper Compounds

Copper-catalyzed and organocopper-involved reactions are of great significance in organic synthesis. To have a deep understanding of the reaction mechanisms, the structural characterizations of organocopper intermediates become indispensable. Meanwhile, the structure-function relationship of organocopper compounds could advance the rational design and development of new Cu-based reactions and organocopper reagents. Compared to the mono-carbonic ligand, the C,N- and C,C-bidentate ligands better stabilize unstable organocopper compounds. Bidentate ligands can chelate to the same copper atom via η²-mode, forming a mono-cupra-cyclic compounds with at least one acute C-Cu-C angle. When the bidentate ligands bind to two copper atoms via η¹-mode at each coordinating site, the bimetallic macrocyclic compounds will form nearly linear C-Cu-C angles. The anionic coordinating sites of the bidentate ligand can also bridge two metals via μ₂-mode, forming organocopper aggregates with Cu-Cu interactions and organocuprates with contact ion pair structures. The reaction chemistry of some selected organocopper compounds is highlighted, showing their unique structure-reactivity relationships.

Solvated Nickel Complexes as Stoichiometric and Catalytic Perfluoroalkylation Agents*

The acetonitrile-solvated [(MeCN)Ni(C₂ F₅ )₃ ]^- was prepared in order to compare and contrast its reactivity with the known [(MeCN)Ni(CF₃ )₃ ]^- towards organic electrophiles. Both [(MeCN)Ni(CF₃ )₃ ]^- and [(MeCN)Ni(C₂ F₅ )₃ ]^- successfully react with aryl iodonium and diazonium salts as well as alkynyl iodonium salts to give fluoroalkylated organic products. Electrochemical analysis of [(MeCN)Ni^II (C₂ F₅ )₃ ]^- suggests that, upon electro-oxidation to [(MeCN)_n Ni^III (C₂ F₅ )₃ ], reductive homolysis of a perfluoroethyl radical occurs, with the concomitant formation of [(MeCN)₂ Ni^II (C₂ F₅ )₂ ]. Catalytic C-H trifluoromethylations of electron-rich arenes were successfully achieved using either [(MeCN)Ni(CF₃ )₃ ]^- or the related [Ni(CF₃ )₄ ]^2- . Stoichiometric reactions of the solvated nickel complexes reveal that "ligandless" nickel is exceptionally capable of serving as reservoir of CF₃ groups under catalytically relevant conditions.

Modern methods for the synthesis of perfluoroalkylated aromatics

Perfluoroalkyl-containing substances (PFAS), have become omnipresent materials in the modern world for both commercial and research applications. Compounds such as perfluoroalkylated arenes and heteroarenes have found uses in surfactants, lubricants, and flame retardants as a result of their astonishing chemical stability. Consequently, the synthesis of such compounds encompasses a large body of scientific articles and patents developed in the previous century. Most recent reviews on this subject have thus focused on summarizing this traditional literature, and have thereby spurred the development of a new wave of reaction manifolds employing modern synthesis principles. This new generation of methodologies focuses on the greener synthesis of perfluoroalkylated aromatic scaffolds, through the use of more efficient organometallic reactions, as well as by photochemical and electrochemical strategies. Herein, we will summarize this cohort of reactions while highlighting current challenges and future desirable outcomes for their environmentally friendly synthesis.

Base-promoted perfluoroalkylation of rhodium(III) porphyrin complexes

A new family of rhodium porphyrin complexes bearing a primary, secondary or benzylic perfluoroalkyl ligand RhIII(btpp)RF [btpp = 5,10,15,20-tetrakis(4-tert-butylphenyl)porphyrinato dianion] has been successfully synthesized in good yields using commercially available perfluoroalkyl iodides RFI (RF = nC3F7, iC3F7, nC4F9, nC6F13, cC6F11, nC10F21 and C6F5CF2) and the air-stable precursor RhIII(btpp)Cl under basic conditions. Mechanistic investigations suggest a halogen atom transfer pathway with a rhodium(ii) porphyrin metalloradical.

Flexible polyfluorinated bis-diazirines as molecular adhesives

Motivated by a desire to develop flexible covalent adhesives that afford some of the same malleability in the adhesive layer as traditional polymer-based adhesives, we designed and synthesized two flexible, highly fluorinated bis-diazirines. Both molecules are shown to function as effective crosslinkers for polymer materials, and to act as strong adhesives when painted between two polymer objects of low surface energy, prior to thermal activation. Data obtained from lap-shear experiments suggests that greater molecular flexibility is correlated with improved mechanical compliance in the adhesive layer.

Syntheses and crystal structures of solvate complexes of alkaline earth and lanthanoid metal iodides with N,N-dimethylformamide

The solvate complexes that can be obtained by either dissolving metal iodides in N,N-dimethylformamide (DMF) or by synthesising them in DMF have the general composition [M(DMF) x ]I y . DMF shows to behave as simple monodentate ligand with low sterical impact, so that x in the composition follows the radius of M y+. We present here the crystal structures of the alkaline earth and lanthanoid metal iodide complexes [Mg(DMF)6]I2, [Ca(DMF)6]I2, [Sr(DMF)7]I2, [Ba(DMF)8]I2, [La(DMF)9]I3, [Ln(DMF)8]I3 (isotypic series for Ln = Nd, Sm, Eu, Dy, Gd, Er, Yb and Lu) and for the tris-triiodide complex salt [Sc(DMF)6](I3)3. Their different crystal structure types can be compared on the basis of the packing topologies of the nearly spherical cationic entities which show simple sphere packing motifs.

Recent Advances of the Halogen-Zinc Exchange Reaction

For the preparation of zinc organometallics bearing highly sensitive functional groups such as ketones, aldehydes or nitro groups, especially mild halogen-zinc exchange reagents have proven to be of great potential. In this Minireview, the latest research in the area of the halogen-zinc exchange reaction is reported, with a special focus lying on novel dialkylzinc reagents complexed with lithium alkoxides. Additionally, the preparation and application of organofluorine zinc reagents and transition-metal-catalyzed halogen-zinc exchange reactions are reviewed.

Nickel-Catalyzed Reductive Coupling for Transforming Unactivated Aryl Electrophiles into β-Fluoroethylarenes

We report herein a facile synthetic method for converting unactivated (hetero)aryl electrophiles into β-fluoroethylated (hetero)arenes via nickel-catalyzed reductive cross-couplings. This coupling reaction features the involvement of FCH₂ CH₂ radical intermediate rather than β-fluoroethyl manganese species which provides effective solutions to the problematic β-fluoride side eliminations. The practical value of this protocol is further demonstrated by the late-stage modification of several complex ArCl or ArOH-derived bioactive molecules.

Electrochemically driven, cobalt–carbon bond-mediated direct intramolecular cyclic and acyclic perfluoroalkylation of (hetero)arenes using X(CF2)4X

A proof-of-concept for synthetically challenging cyclic and acyclic perfluoroalkylation of (hetero)arenes driven by the valence change of a cobalt catalyst with X(CF₂)₄X is demonstrated.

Exploiting the trifluoroethyl group as a precatalyst ligand in nickel-catalyzed Suzuki-type alkylations

We report herein the exploitment of the partially fluorinated trifluoroethyl as precatalyst ligands in nickel-catalyzed Suzuki-type alkylation and fluoroalkylation coupling reactions. Compared with the [L _n Ni^II(aryl)(X)] precatalysts, the unique characters of bis-trifluoroethyl ligands imparted precatalyst [(bipy)Ni(CH₂CF₃)₂] with bench-top stability, good solubilities in organic media and interesting catalytic activities. Preliminary mechanistic studies reveal that an eliminative extrusion of a vinylidene difluoride (VDF, CH₂[double bond, length as m-dash]CF₂) mask from [(bipy)Ni(CH₂CF₃)₂] is a critical step for the initiation of a catalytic reaction.

Copper-Catalyzed Coupling of Acyl Chlorides with gem-Difluorinated Organozinc Reagents via Acyl Dithiocarbamates

A cross-coupling of acyl chlorides with gem-difluorinated organozinc reagents affording difluorinated ketones is described. In the reaction, acyl chlorides are first treated with potassium dithiocarbamate to generate S-acyl dithiocarbamates, which couple with organozincs in the presence of a copper(I) catalyst.

Stereochemically Defined Various Multisubstituted Alkenes Bearing a Tetrafluoroethylene (-CF2CF2-) Fragment

Highly regio- and stereoselective transformation of commercially available 4-bromo-3,3,4,4-tetrafluoro-1-butene into multisubstituted alkenes having a tetrafluoroethylene fragment through Heck reactions and/or Suzuki-Miyaura cross-coupling reactions was established. Thus, the obtained alkenes underwent a smooth reductive coupling reaction with aldehydes under the influence of MeLi/LiBr-free, affording structurally unprecedented fluorinated materials.

Palladium-Catalyzed Negishi Cross-Coupling Reaction of Aryl Halides with (Difluoromethyl)zinc Reagent

The palladium-catalyzed Negishi cross-coupling reaction of aryl iodides and bromides with (difluoromethyl)zinc reagent bearing a diamine such as TMEDA is achieved to provide the difluoromethylated aromatic compounds in good to excellent yields. The advantages of (difluoromethyl)zinc reagent are that (1) the derivatives, which possess different stability and reactivity, can be readily prepared via ligand screening and (2) transmetalation of a difluoromethyl group from the zinc reagent to palladium catalyst efficiently proceeds without an activator.

Copper-Catalyzed Difluoromethylation of Aryl Iodides with (Difluoromethyl)zinc Reagent

The combination of difluoroiodomethane and zinc dust or diethylzinc can readily lead to (difluoromethyl)zinc reagents. Therefore, the first copper-catalyzed difluoromethylation of aryl iodides with the zinc reagents is accomplished to afford the difluoromethylated arenes. The reaction proceeds efficiently through the ligand/activator-free operation without addition of ligands for copper catalyst (e.g., phen and bpy) and activators for zinc reagent (e.g., KF, CsF, and NaO-t-Bu). Moreover, transmetalation of the CF2H group from zinc reagent to copper catalyst proceeds even at room temperature to form the cuprate [Cu(CF2H)2](-).

Accessing perfluoroalkyl nickel(II), (III), and (IV) complexes bearing a readily attached [C4F8] ligand

The [C4F8] ligand was shown to support well-defined terpyridyl nickel complexes in the +2 and +3 oxidation states. Notably, a cyclic voltammetry study of the nickel(iii) species indicates that an additional oxidation is accessible, providing a family of related fluoroalkyl nickel complexes spanning the +2 to +4 oxidation states.

Direct Difluoromethylation of Aryl Halides via Base Metal Catalysis at Room Temperature

A stable and isolable difluoromethyl zinc reagent has been prepared through the reaction of ICF2H with diethyl zinc and DMPU. This new zinc reagent is a free-flowing solid and can be used in combination with a nickel catalyst to difluoromethylate aryl iodides, bromides, and triflates at room temperature. Such mild conditions for the catalytic difluoromethylation of these substrates are unprecedented.