[1,2-Bis(diiso-propyl-phosphan-yl)ethane-κ2 P,P'](2-fluoro-N-{[(2-fluoro-phen-yl)aza-nid-yl]carbon-yl}anilinido-κ2 N,N')nickel(II).

The mol-ecular structure of the title complex, [Ni(C13H8F2N2O)(C14H32P2)] or Ni(oFPU)(dippe), where oFPU is the dianion of bis-(2-fluoro-phen-yl)urea and dippe is 1,2-bis-(di-iso-propyl-phosphino)ethane, comprises an NiII atom with a distorted square-planar coordination environment (geometry index τ4 = 0.195). One of the fluoro-phenyl rings of the oFPU ligand is disordered over two sets of sites in an 0.832 (7):0.168 (7) ratio. The crystal structure displays C-H⋯O and C-H⋯F hydrogen-bonding inter-actions, leading to chains with R 2 2(12) motifs extending parallel to [100]. The title compound might be of inter-est with respect to the production of urea and carbamate derivatives of nickel(II).

Nickel-catalyzed transfer hydrogenation of ketones using ethanol as a solvent and a hydrogen donor.

We report a nickel(0)-catalyzed direct transfer hydrogenation (TH) of a variety of alkyl-aryl, diaryl, and aliphatic ketones with ethanol. This protocol implies a reaction in which a primary alcohol serves as a hydrogen atom source and solvent in a one-pot reaction without any added base. The catalytic activity of the nickel complex [(dcype)Ni(COD)] (e) (dcype: 1,2-bis(dicyclohexyl-phosphine)ethane, COD: 1,5-cyclooctadiene), towards transfer hydrogenation (TH) of carbonyl compounds using ethanol as the hydrogen donor was assessed using a broad scope of ketones, giving excellent results (up to 99% yield) compared to other homogeneous phosphine-nickel catalysts. Control experiments and a mercury poisoning experiment support a homogeneous catalytic system; the yield of the secondary alcohols formed in the TH reaction was monitored by gas chromatography (GC) and NMR spectroscopy.

Bond and small-molecule activation with low-valent nickel complexes.

The use of nickel compounds in low oxidation states allowed a variety of useful transformations of interest for academia, industry and in the solution of environmental issues.

Synthesis of tetra-substituted imidazoles and 2-imidazolines by Ni(0)-catalyzed dehydrogenation of benzylic-type imines.

Ni(0)-catalyzed dehydrogenation of benzylic-type imines was performed to yield asymmetrical tetra-substituted imidazoles and 2-imidazolines. This was achieved with a single operational step while maintaining good selectivity and atom economy. The catalytic system shows low to moderate tolerance for fluoro-, trifluoromethyl-, methyl-, and methoxy-substituted benzylic-type imines. In addition, the substitution pattern at the N-heterocyclic products was easily controlled by the appropriate selection of R-groups in the starting organic substrates. Based on experimental observations, we propose a reaction mechanism in which benzylic C(sp(3))-H bond activation and insertion steps play pivotal roles in this nickel-catalyzed organic transformation.

On the catalytic hydrodefluorination of fluoroaromatics using nickel complexes: the true role of the phosphine.

Homogeneous catalytic hydrodefluorination (HDF) of fluoroaromatics under thermal conditions was achieved using nickel(0) compounds of the type [(dippe)Ni(η(2)-C6F6-nHn)] where n = 0-2, as the catalytic precursors. These complexes were prepared in situ by reacting the compound [(dippe)Ni(µ-H)]2 with the respective fluoroaromatic substrate. HDF seems to occur homogeneously, as tested by mercury drop experiments, producing the hydrodefluorinated products. However, despite previous findings by other groups, we found that these HDF reactions were actually the result of direct reaction of the alkylphosphine with the fluoroaromatic substrate. This metal- and silane-free system is the first reported example of a phosphine being able to hydrodefluorinate on its own.

One-pot synthesis of imidazoles from aromatic nitriles with nickel catalysts.

Nickel(0) catalysts were used to produce substituted imidazoles in good to high yields using benzonitrile, p-substituted benzonitriles and 4-cyanopyridine as starting materials.

Nickel(0) complexes with fluorinated alkyne ligands and their reactivity towards semihydrogenation and hydrodefluorination with water.

The current work describes the synthesis and full characterization of zerovalent nickel complexes of the type [(dippe)Ni(η(2)-C,C-F(n)-alkyne)] (dippe = 1,2-bis(di-isopropylphosphino-ethane), F(n)-alkyne = fluorinated aromatic alkyne, n = 1, 3, 5; 3a-c) and [{(dippe)Ni}(2)(µ(2)-C,C-F(n)-alkyne)] (4). Reactions with complexes 3a-c, and water as the hydrogen source, yield selective semihydrogenation of the bound alkyne to the corresponding alkene, accompanied by partial hydrodefluorination of the aromatic ring. Different alkynes were tested; on using the alkyne with five fluorine atoms over the aromatic ring, partial defluorination was achieved under the mildest reaction conditions, followed in reactivity by the alkyne with three fluorine atoms. The alkyne with only one fluorine atom was barely defluorinated. The use of triethylsilane as a sacrificial hydride source resulted in an overall increase in reactivity towards defluorination.

Catalytic desulfurization of dibenzothiophene with palladium nanoparticles.

The thermal reduction of [(PEt3)2PdMe2] (1 mol%), which was produced in situ from [(PEt3)2PdCl2] (1) and 2 equiv of MeMgBr in toluene solvent, yielded palladium nanoparticles that in conjunction with MeMgBr effected the desulfurization of dibenzothiophene (DBT). The reaction resulted in the generation of the sulfur-free compound 2,2'-dimethylbiphenyl, in high yields (60%). The use of several stabilizing agents such as sodium 2-ethylhexanoate and hexadecylamine was also addressed herein, their use resulting in a significant improvement of the desulfurization reaction that reached up to 90% conversion of DBT into the mentioned biphenyl. The palladium nanoparticles formed during the reaction were characterized by transmission electron microscopy and exhibited a smaller size and a lesser extent of agglomeration whenever stabilizers were used.

Sigma-borane coordinated to nickel(0) and some related nickel(II) trihydride complexes.

The reactions of the complexes [(dcype)NiH]2, 1, [(dippe)NiH]2, 2, and [(dtbpe)NiH]2, 3, with a mixture of BEt3 and Super-Hydride (LiHBEt3) afforded sigma-borane nickel(0) compounds of the type [(dcype)Ni(sigma-HBEt2)], 4, [(dippe)Ni(sigma-HBEt2)], 5, [(dtbpe)Ni(sigma-HBEt2)], 6, respectively, with the concomitant formation in each case of [(dcype)2Ni2)(H)3][BEt4], 7, [(dippe)2Ni2(H)3][BEt4], 8 and [(dtbpe)2Ni2(H)3][BEt4], 9, respectively. X-ray crystal structures are reported for 4 and 8. The reaction of BEt3 and LiHBEt3 was also reviewed in detail.