Unusual Electronic Effects of Ancillary Ligands on the Perfluoroalkylation of Aryl Iodides and Bromides Mediated by Copper(I) Pentafluoroethyl Complexes of Substituted Bipyridines

Synthesis and application of well-defined [Ph4P]+[Cu(CF2CF3)2]- complex as a versatile pentafluoroethylating reagent

We herein describe the preparation and application of a new bispentafluoroethylated organocuprate [Ph4P]+[Cu(CF2CF3)2]-. This complex has demonstrated a remarkable range of reactivities towards carboxylic acids, diazonium salts, organic halides, boronic esters, terminal alkynes and (hetero)arenes as a versatile pentafluoroethylating reagent. The construction of C(sp3)-/C(sp2)-/C(sp)-CF2CF3 bonds can therefore be achieved using a single reagent.

Effect of Ligand Substituents on Spectroscopic and Catalytic Properties of Water-Compatible Cp*Ir-(pyridinylmethyl)sulfonamide-Based Transfer Hydrogenation Catalysts

Transition-metal-based hydrogenation catalysts have applications ranging from high-value chemical synthesis to medicinal chemistry. A series of (pyridinylmethyl)sulfonamide ligands substituted with electron-withdrawing and -donating groups were synthesized to study the influence of the electronic contribution of the bidentate ligand in Cp*Ir piano-stool complexes. A variable-temperature NMR investigation revealed a strong correlation between the electron-donating ability of the substituent and the rate of stereoinversion of the complexes. This correlation was partially reflected in the catalytic activity of the corresponding catalysts. Complexes with electron-withdrawing substituents followed the trend observed in the variable-temperature NMR study, thereby confirming the rate-determining step to be donation of the hydride ligand. Strongly electron-donating groups, on the other hand, caused a change in the rate-determining step in the formation of the iridium-hydride species. These results demonstrate that the activity of these catalysts can be tuned systematically via changes in the electronic contribution of the bidentate (pyridinylmethyl)sulfonamide ligands.

Visible-light-induced dehydrogenative amidation of aldehydes enabled by iron salts

A direct dehydrogenative amidation reaction of aldehydes and amines under a visible light mediated ligand-to-metal charge transfer (LMCT) process was described. In this protocol, aldehyde substrates were activated by photoinduced hydrogen atom abstraction (HAA), generating acyl chloride intermediates followed by nucleophilic addition of amines. The synthetic method furnishes good functional group tolerance and broad substrate scope toward both aliphatic and aromatic components.

Three-Component Perfluoroalkylvinylation of Alkenes Enabled by Dual DBU/Fe Catalysis

Herein, a simple and efficient strategy that involves dual 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)/iron-catalyzed alkene perfluoroalkylvinylation by using perfluoroalkyl iodides and 2-aminonaphthalene-1,4-diones as coupling partners is demonstrated. In terms of the developed catalytic system, various styrenes and aliphatic alkenes are well-tolerated, leading to the accurate preparation of perfluoroalkyl-containing 2-aminonaphthalene-1,4-diones in excellent regioselectivity. Moreover, the protocol can be readily applied in late-stage modifications of natural products and pharmaceuticals. The title reactions are featured by easily accessible and inexpensive catalysts and substrates, broad substrate applicability, and mild reaction conditions. Mechanistic investigations reveal a tandem C-I cleavable alkylation and C-C vinylation enabled by cooperative DBU/iron catalysis.

Room-Temperature-Stable Magnesium Electride via Ni(II) Reduction

Herein, we report the synthesis of highly reduced bipyridyl magnesium complexes and the first example of a stable organic magnesium electride supported by quantum mechanical computations and X-ray diffraction. These complexes serve as unconventional homogeneous reductants due to their high solubility, modular redox potentials, and formation of insoluble, non-coordinating byproducts. The applicability of these reductants is showcased by accessing low-valent (bipy)2Ni(0) species that are challenging to access otherwise.

Fe-Catalyzed Radical Trifluoromethyl-Alkenylation of Alkenes or Alkynes with 2-Amino-1,4-naphthoquinones

The first Fe-catalyzed three-component radical trifluoromethyl-alkenylation of alkenes with 2-amino-1,4-naphthoquinones and CF₃SO₂Na is reported. The developed reaction enables the highly regioselective preparation of a variety of valuable CF₃-substituted 1,4-naphthoquinones in acceptable yields. In the light of the catalytic system, alkynes smoothly afford the corresponding three- or four-component trifluoromethyl-alkenylation products. This protocol features use of easily available and inexpensive reagents, broad substrate scope, and simple reaction conditions.

Copper(I) activation of C-X bonds: bimolecular vs. unimolecular reaction mechanism

Experimental kinetic studies and DFT calculations show that the oxidative addition of aryl halides (Ar-X) to complexes [Cu(NHC)R] follow different paths depending on the nature of X. For X = Br a concerted addition leads to cis-[Cu(NHC)XRAr] from which the usual C-C coupled product Ar-R eliminates. However, for X = I trans-[Cu(NHC)IRAr] is formed instead, leading to the elimination of R-I in a metathesis reaction. This behaviour is accounted for by a change in the reaction mechanism for Ar-I, which involves two molecules of copper(I) complex, the second one stabilising the incipient iodide formed in the C-I breaking (oxidative addition) and C-I forming (reductive elimination) processes.

A Systematic Study of the Effects of Complex Structure on Aryl Iodide Oxidative Addition at Bipyridyl-Ligated Gold(I) Centers

A combined theoretical and experimental approach has been used to study the unusual mechanism of oxidative addition of aryl iodides to [bipyAu(C2 H4 )]+ complexes. The modular nature of this system allowed a systematic assessment of the effects of complex structure. Computational comparisons between cationic gold and the isolobal (neutral) Pd0 and Pt0 complexes revealed similar mechanistic features, but with oxidative addition being significantly favored for the group 10 metals. Further differences between Au and Pd were seen in experimental studies: studying reaction rates as a function of electronic and steric properties showed that ligands bearing more electron-poor functionality increase the rate of oxidative addition; in a complementary way, electron-rich aryl iodides give faster rates. This divergence in mechanism compared to Pd suggests that Ar-X oxidative addition with Au can underpin a broad range of new or complementary transformations.

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.

Transmetalation Reactions Triggered by Electron Transfer between Organocopper Complexes

[Cu(bipy)(C₆F₅)] reacts with most aryl iodides to form heterobiphenyls by cross-coupling, but when Rf–I is used (Rf = 3,5-dicholoro-2,4,6-trifluorophenyl), homocoupling products are also formed. Kinetic studies suggest that, for the homocoupling reaction, a mechanism based on transmetalation from [Cu(bipy)(C₆F₅)] to Cu(III) intermediates formed in the oxidative addition step is at work. Density functional theory calculations show that the interaction between these Cu(III) species and the starting Cu(I) complex involves a Cu(I)–Cu(III) electron transfer concerted with the formation of an iodine bridge between the metals and that a fast transmetalation takes place in a dimer in a triplet state between two Cu(II) units.

In copper-catalyzed cross-coupling reactions, electron-transfer processes between Cu(I) and Cu(III) species are overlooked behind RDS (C−X activation). Density functional theory studies considering two molecules of the catalyst and two spin states throughout the course of the reaction have revealed the feasibility of such a process and the transmetalation between Cu(II) species, justifying in this way the formation of homocoupling products.

Synthesis of Fluoroalkyl Sulfides via Additive-Free Hydrothiolation and Sequential Functionalization Reactions

A modular synthetic method, involving a hydrothiolation, silylation, and fluoroalkylation, for the construction of highly functionalized fluoroalkyl sulfides has been developed. The use of aprotic polar solvents enables the additive-free chemoselective hydrothiolation of tetrafluoroethylene, trifluorochloroethylene, and hexafluoropropene with various thiols. The stepwise functionalization reactions convert the hydrothiolated intermediates into the tetrafluoroethyl sulfides in high efficiency. The method avoids the use of the environmental pollutant Halon-2402, which was employed as a building block in a reported synthetic route.

Copper-based fluorinated reagents for the synthesis of CF2R-containing molecules (R ≠ F)

Over the years, the development of new methodologies for the introduction of various fluorinated motifs has gained a significant interest due to the importance of fluorine-containing molecules in the pharmaceutical and agrochemical industries. In a world eager to eco-friendlier tools, the need for innovative methods has been growing. To address these two challenges, copper-based reagents were developed to introduce CF2H, CF2RF, CF2CH3, CF2PO(OEt)2 and CF2SO2Ph motifs on a broad range of substrates. Copper-based fluorinated reagents have the advantage of being inexpensive and generally in situ generated or prepared in a few steps, which make them convenient to use. In this review, an overview of the recent advances made for the synthesis of fluorinated molecules using copper-based fluorinated reagents will be given.