Carbon-fluorine bond activation in fluoroolefins: clear documentation of cooperative C-F bond activation by adjacent metal centers

Nickel-Catalyzed Selective C(sp2 )-F Bond Alkylation of Industrially Relevant Hydrofluoroolefin HFO-1234yf

The selective transition-metal catalyzed C-F bond functionalization of inexpensive industrial fluorochemicals represents one of the most attractive approaches to valuable fluorinated compounds. However, the selective C(sp2 )-F bond carbofunctionalization of refrigerant hydrofluoroolefins (HFOs) remains challenging. Here, we report a nickel-catalyzed selective C(sp2 )-F bond alkylation of HFO-1234yf with alkylzinc reagents. The resulting 2-trifluoromethylalkenes can serve as a versatile synthon for diversified transformations, including the anti-Markovnikov type hydroalkylation and the synthesis of bioactive molecule analogues. Mechanistic studies reveal that lithium salt is essential to promote the oxidative addition of Ni0 (Ln ) to the C-F bond; the less electron-rich N-based ligands, such as bipyridine and pyridine-oxazoline, feature comparable or even higher oxidative addition rates than the electron-rich phosphine ligands; the strong σ-donating phosphine ligands, such as PMe3 , are detrimental to transmetallation, but the less electron-rich and bulky N-based ligands, such as pyridine-oxazoline, facilitate transmetallation and reductive elimination to form the final product.

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.

Strong Electronic Communication in Linearly Elongated Rylenes Featuring Tunable Bridges

A modified synthetic pathway towards perylene-perylene dimers and a facile purification method to obtain the regioisomerically pure syn- and anti-isomers are reported. In addition, a novel perylene-naphthalene heterodimer with 30 conjugated π-electron pairs was designed and synthesized on the basis of a previously described precursor and the resulting regioisomers were separated from each other. Thereby, the opto-electronic properties of the linearly elongated chromophores could be investigated regarding the differences in length of their aromatic system and the configuration of the isomers. Further tuning of their energy gaps was realized via protonation and methylation of the dibenzimidazole-bridging unit. Extraordinary red-shifts of the absorption maxima of 62 nm for the methylated and 92 nm for the protonated perylene-perylene anti-isomer could be achieved. Moreover, the maxima for the syn-isomer could be shifted bathochromically by 87 and 113 nm, respectively.

"Lignophines": lignin-based tertiary phosphines with metal-scavenging ability

Methacrylated lignin was reacted with PH₃(g) to prepare a phosphorus rich bio-based polymer containing PH/PH₂ functional groups, which were converted to tertiary phosphine units via the phosphane-ene reaction. This represents a straightforward method for the upconversion of low-value biomass waste to useful inorganic polymer with potential utility in metal scavenging applications.

Oxidative addition of an aromatic ortho C-H bond of tetraphosphine to asymmetric diiridium(i) centres

Reactions of a tetraphosphine, meso-bis{[(diphenylphosphinomethyl)phenyl]phosphino}propane (dpmppp), with [IrCl(cod)]2 and CO (1 atm) or isocyanide (RNC) in the presence of NH4PF6 at 80-100 °C in dichloromethane/acetonitrile/acetone and/or methanol mixed solvents afforded asymmetric diiridium(ii) complexes, [Ir2(H)(Cl)(μ-(dpmppp-H)-κP(4)C)(CO)3]PF6 (1) and [Ir2(H)(μ-(dpmppp-H)-κP(4)C)(RNC)4)]-(PF6)2 (R = 2,6-xylyl (2), 2,4,6-mesityl (3); dpmppp-H = {PPh(o-C6H4)CH2P(Ph)(CH2)3P(Ph)CH2PPh2}(-)). A similar reaction with (t)BuNC resulted in the formation of a mononuclear Ir(III) complex of [Ir(H)(dpmppp-κP(3))((t)BuNC)2](PF6)2 (4). Complexes 1-3 were characterized by ESI mass spectrometry, (1)H and (31)P NMR spectroscopy and X-ray diffraction analyses. They were found to consist of cis/trans-P,P asymmetric Ir(II)-Ir(II) bonded dinuclear structures derived from oxidative addition of an ortho C-H bond of dpmppp (Ir-Ir = 2.8044(2) Å (1), 2.8569(2) Å (2), and 2.8524(5) Å (3)), resulting in a [IrPCCIr] intermetallic cyclometal-bridge and a terminal hydride. DFT calculations indicated the presence of Ir-Ir, Ir-H, and Ir-Cortho covalent bonds. Initial stages of the reactions with CO and XylNC at room temperature were investigated by (31)P{(1)H} NMR spectroscopy and found to contain a symmetrical Ir(I) dinuclear unit with dpmppp that was readily transformed into 1 and 2 upon heating. The Ir intermediate with XylNC, [Ir2(XylNC)4(μ-dpmppp)](PF6)2 (6), was isolated and characterized by X-ray crystallography and DFT calculations as an electron-deficient 32e(-) Ir species involving a Ir(I)→Ir(I) dative bond (2.7989(5) Å). The reaction pathways from 6 to 2 were investigated by DFT calculations. The present study suggested that a novel oxidative addition of an ortho C-H bond proceeded on the cis/trans-P,P asymmetric diiridium(i) scaffold supported by the tetraphosphine, dpmppp, which was assumed to be facilitated by dimetal cooperation with switching Ir→Ir dative interactions.

Access to novel fluorovinylidene ligands via exploitation of outer-sphere electrophilic fluorination: new insights into C–F bond formation and activation

Metal fluorovinylidene complexes have been synthesised for the first time by direct electrophilic fluorination of metal alkynyls.

Competing reaction pathways of 3,3,3-trifluoropropene at rhodium hydrido, silyl and germyl complexes: C–F bond activation versus hydrogermylation

The reactivity of the Rh complexes [Rh(L)(PEt₃)₃] (L = H, Si(OEt)₃, GePh₃) towards CH₂CHCF₃ was investigated which involve C–F bond activation and germylation reactions.

Palladium-catalyzed amination of 2,3,3-trifluoroallyl esters: synthesis of trifluoromethylenamines via an intramolecular fluorine shift and CF3 group construction

The palladium-catalyzed reaction of 2,3,3-trifluoroallyl esters with amines afforded trifluoromethylenamines, which were formed by the addition of a nitrogen nucleophile at the C-2 position and the fluorine atom shift from the C-2 to C-3 position.

C-F activation at rhodium boryl complexes: formation of 2-fluoroalkyl-1,3,2-dioxaborolanes by catalytic functionalization of hexafluoropropene

Fluorinated building blocks by C-F bond cleavage: Catalytic C-F activation reactions that give novel dioxaborolanes have been developed (see scheme). The reactions proceed at room temperature, and catalytic intermediates are presumably rhodium hydride and boryl species.