Nickel-Catalyzed Homologation of Vinylidene Difluoride (CH═CF): Selective β-F β-H Elimination.

Hydrofluoroolefins (HFOs) constitute the newest generation of fluorocarbon refrigerants and foam-blowing agents due to their reduced global warming potential 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.

Shedding Light on the Diverse Reactivity of NacNacAl with N-Heterocycles.

The aluminum(I) compound NacNacAl (NacNac=[ArNC(Me)CHC(Me)NAr] , Ar=2,6-iPr C H , 1) shows diverse and substrate-controlled reactivity in reactions with N-heterocycles. 4-Dimethylaminopyridine (DMAP), a basic substrate in which the 4-position is blocked, induces rearrangement of NacNacAl by shifting a hydrogen atom from the methyl group of the NacNac backbone to the aluminum center. In contrast, C-H activation of the methyl group of 4-picoline takes place to produce a species with a reactive terminal methylene.

Ge(0) Compound Stabilized by a Diimino-Carbene Ligand: Synthesis and Ambiphilic Reactivity.

The germylone dimNHCGe (, dimNHC = diimino N-heterocyclic carbene) was successfully prepared via the reduction of the germanium cation [dimNHCGeCl] with KC. The molecular structure of was unambiguously established by both NMR spectroscopy and single-crystal X-ray diffraction. The reactivity of was investigated, revealing that it undergoes oxidative addition of HCl, CHI, and PhI, accompanied by an unusual migration of the H, Me, and Ph groups from germanium to the carbene ligand.

Sequential Oxidation and C-H Bond Activation at a Gallium(I) Center.

In situ oxidation of the Ga compound NacNacGa by either N O or pyridine oxide results in the generation of a labile monomeric oxide, NacNacGa(O), which can easily cleave the C-H bonds of aliphatic and aromatic substrates featuring good donor sites. The products of this reaction are gallium organyl hydroxides. DFT calculations show that these reactions start with the formation of NacNac-Ga(O)(L) adducts, the oxo ligand of which can easily abstract protons from nearby C-H bonds, even for sp -hybridized carbon centers.

Selective Copper Complex-Catalyzed Hydrodefluorination of Fluoroalkenes and Allyl Fluorides: A Tale of Two Mechanisms.

The transition to more economically friendly small-chain fluorinated groups is leading to a resurgence in the synthesis and reactivity of fluoroalkenes. One versatile method to obtain a variety of commercially relevant hydrofluoroalkenes involves the catalytic hydrodefluorination (HDF) of fluoroalkenes using silanes. In this work it is shown that copper hydride complexes of tertiary phosphorus ligands (L) can be tuned to achieve selective multiple HDF of fluoroalkenes.

7-Metalla-1,4-diphosphanorbornadienes: cycloaddition of monovalent group 13 NacNac complexes to a stable 1,4-diphosphinine.

This work presents the first example of a dienophilic property of the monovalent group-13 NacNac complexes, which are well-known for their carbene-like reactivity, e.g., addition to multiple bonds, insertion into single bonds, and oxidative cleavage of some multiple bonds.

Nickel Fluorocarbene Metathesis with Fluoroalkenes.

Alkene metathesis with directly fluorinated alkenes is challenging, limiting its application in the burgeoning field of fluoro-organic chemistry. A new nickel tris(phosphite) fluoro(trifluoromethyl)carbene complex ([P Ni]=CFCF ) reacts with CF =CF (TFE) or CF =CH (VDF) to yield both metallacyclobutane and perfluorocarbene metathesis products, [P Ni]=CF and CR =CFCF (R=F, H). The reaction of [P Ni]=CFCF with trifluoroethylene also yields metathesis products, [P Ni]=CF and cis/trans-CFCF =CFH.

Transition-Metal-Free Formation of C-E Bonds (E = C, N, O, S) and Formation of C-M Bonds (M = Mn, Mo) from -Heterocyclic Carbene Mediated Fluoroalkene C-F Bond Activation.

Herein, a recently reported polyfluoroalkenyl imidazolium salt is shown to react with nitrogen-, oxygen- and sulfur-based nucleophiles at the C position in a stereoselective and regioselective fashion, without the use of a transition metal. In contrast, reactivity with 1-methylimidazole demonstrates net substitution at C . This product reacts quantitatively with water, affording clean transformation of a difluoromethylene group to give an ,-unsaturated trifluoromethyl ketone.

Oxidative Cleavage of the C═N Bond on Al(I).

Reaction of the cyclic guanidine TolN═SIMe with the aluminum(I) compound NacNacAl (1) results in the unprecedented cleavage of the C-N multiple bond to give, after rearrangement, the carbene-ligated Al(III) amide, NacNac'Al(NHTol)(SIMe) (6). DFT calculations revealed that these reactions proceed via a bimolecular mechanism in which either the basic Al(I) center or the transient Al═NTol species deprotonates the methyl group of the NacNac ligand.

Unusual Reactions of NacNacAl with Urea and Phosphine Oxides.

The reaction of cyclic urea 1,3-dimethyl-2-imidazolidinone with the aluminum(I) compound NacNacAl (1) gives an unexpected adduct of urea with the isomerized aluminum(III) hydride NacNac'AlH(O═SIMe) (3). A related reaction of 1 with phosphine oxides results in cleavage of the P═O bond and formation of hydroxyl derivatives NacNac'Al(OH)(O═PR) [R = Ph (5) and Et (6)]. Density functional theory calculations revealed that these reactions proceed via a bimolecular mechanism in which either the basic aluminum(I) center or the transient Al═O species deprotonate the methyl group of the NacNac ligand.

Generation of Hydrofluoronickelacycles from Trifluoroethylene and Ni(0): Ligand Effects on Regio-/Stereoselectivity and Reactivity.

Treatment of Ni(0) complexes 1a-e with sub-atmospheric pressures of trifluoroethylene (TrFE) affords hydrofluoronickelacyclopentanes LNi(CFH) 2a-e (L = PPh, P(O-o-tol), PPhMe, PPhMe, PMe). Fluorine NMR analysis of 2a-e demonstrates predominant formation of three (of the possible six) isomers upon oxidative cycloaddition of TrFE: the cis and trans head-tail isomers and the trans head-head isomer, where the CHF group is defined as the TrFE "head". The respective ratios of LNi(CFH) isomers are influenced by the nature of L, with smaller phosphines favoring the thermodynamically preferred (from DFT calculations) trans head-head isomer (cf.

Selective Activation of Fluoroalkenes with N-Heterocyclic Carbenes: Synthesis of N-Heterocyclic Fluoroalkenes and Polyfluoroalkenyl Imidazolium Salts.

Selective reactions between nucleophilic N,N'-diaryl-heterocyclic carbenes (NHCs) and electrophilic fluorinated alkenes afford NHC fluoroalkenes in high yields. These stable compounds undergo efficient and selective fluoride abstraction with Lewis acids to give polyfluoroalkenyl imidazolium salts. These salts react at Cβ with pyrrolidine to give ammonium fluoride-substituted salts, which give rise to conjugated imidazolium-enamine salts through loss of HF.