Homogeneous Nickel Catalysts for the Selective Transfer of a Single Arylthio Group in the Catalytic Hydrothiolation of Alkynes

Nickel and palladium complexes of enolatefunctionalised N-heterocyclic carbenes

The reaction of chloroethyltrimethylsilylether with 1-methylimidazole furnishes an ionic liquid that undergoes methanolysis to crystalline 2-hydroxyethylimidazolium chloride (crystal structure presented). Conversion to defined hydroxyethylimidazol-2-ylidene nickel complexes failed, but was accomplished with 1-methyl-3-acetophenyl-imidazolium bromide. The bis(NHC⋂O−) nickel(II) chelate is formed, rather than a methallylnickel monochelate, but with nickelocene a monochelate NiCp complex was detected. The bulky 1-(2,6-diisopropylphenyl)-3-(2’-phenyl-enolato)-imidazol-2-ylidene allylpalladium chloride was obtained in pure form. Attempts to generate catalysts for ethylene oligomerization by in situ techniques have failed so far whereas P⋂O− ligands, comparable by the P-C diagonal relationship, provide active catalysts.

Half-sandwich NHC-nickel(II) complexes as pre-catalysts for the fast Suzuki coupling of aryl halides: a comparative study

Cationic half-sandwich nickel complexes of general formula [Ni(NHC)(NCMe)(eta(5)-C5R5)](PF6) [NHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) a, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) b; R = H, Me] were prepared from the reaction of their neutral homologues [Ni(NHC)Cl(eta(5)-C5R5)] with 1 equiv. of KPF6 in acetonitrile at room temperature. The new cationic complexes [Ni(IPr)(NCMe)(eta(5)-C5Me5)](PF6) 3a, [Ni(IMes)(NCMe)(eta(5)-C5Me5)](PF6) 3b and [Ni(IMes)(NCMe)(eta(5)-C5H5)](PF6) 4b were obtained in high yield and were fully characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, elemental analyses, and in the case of 3a by a single-crystal X-ray diffraction study. The neutral analogue of 3a, [Ni(IPr)Cl(eta(5)-C5Me5)] 1a was also structurally characterized. Their geometries were compared and no significant structural differences were observed. Nevertheless solution NMR spectroscopy established that the acetonitrile ligand of the cationic species is labile in solution. This results in the absence of any rotational significant barrier about the nickel-carbene carbon bond at ambient temperature in solution in the sterically congested cationic complexes 3a and 3b, in contrast to their neutral analogues 1a and [Ni(IMes)Cl(eta(5)-C5Me5)] 1b. The neutral and the cationic complexes catalyzed the cross-coupling of phenylboronic acid with aryl halides in the absence of co-catalysts or reductants. Surprisingly, the neutral or cationic nature of the complexes proved to have almost no influence on the reaction yields and rates. However, complexes bearing the bulky electron-rich pentamethylcyclopentadienyl ligand were much more active than those bearing the cyclopentadienyl ligand, and TOF of up to 190 h(-1), a high rate for nickel(II) complexes under similar conditions, were observed with these species.

Recyclable nanostructured catalytic systems in modern environmentally friendly organic synthesis

Modern chemical synthesis makes heavy use of different types of catalytic systems: homogeneous, heterogeneous and nano-sized. The latter--nano-sized catalysts--have given rise in the 21st century to a rapidly developing area of research encompassing several prospects and opportunities for new technologies. Catalytic reactions ensure high regio- and stereoselectivity of chemical transformations, as well as better yields and milder reaction conditions. In recent years several novel catalytic systems were developed for selective formation of carbon-heteroatom and carbon-carbon bonds. This review presents the achievements of our team in our studies on various types of catalysts containing metal nanoparticles: palladium-containing diblock copolymer micelles; soluble palladium-containing polymers; metallides on a support; polymeric metal salts and oxides; and, in addition, metal-free organic catalysts based on soluble polymers acting as nanoreactors. Representative examples are given and discussed in light of possible applications to solve important problems in modern organic synthesis.

Organoactinide-mediated hydrothiolation of terminal alkynes with aliphatic, aromatic, and benzylic thiols

Atom-efficient organoactinide-catalyzed intermolecular hydrothiolation of terminal alkynes is achieved by Th(IV) and U(IV) complexes to yield vinyl sulfides. The conversion is highly Markovnikov selective and is capable of utilizing aromatic, benzylic, and aliphatic thiols. Kinetic measurements of the transformation mediated by Me(2)SiCp(2)''Th[CH(2)(TMS)](2) (1a; Cp'' = eta(5)-Me(4)C(5)) shows the reaction is zero-order in [thiol], first-order in [1a], first-order in [alkyne] at lower alkyne concentrations, and zero-order at higher [alkyne]. The proposed catalytic cycle invokes turnover-limiting insertion of the alkyne into the Th-S bond followed by a rapid Th-C bond protonolysis. All reactions except entries 7 and 8 are quantitative by (1)H NMR.

The first N-heterocyclic carbene-based nickel catalyst for C-S coupling

We have developed the first N-heterocyclic carbene (NHC)-based transition metal catalysts for C-S coupling reactions. Ni-NHC catalysts showed good to excellent activities toward various aryl halides in C-S coupling reactions. The catalytic activities were greatly affected by the electronic and steric properties of the NHC ligands. The new catalysts were inexpensive, easy to synthesize, and environmentally friendly. They could be excellent candidates to replace Pd-organophosphanes for C-S coupling catalysis.

Addition reactions of E-E and E-H bonds to triple bond of alkynes catalyzed by Pd, Pt, and Ni complexes (E=S, Se)

The synthetic application and mechanistic aspects of transition-metal (Ni, Pd, Pt) catalyzed addition of E-E and E-H (E=S, Se) bonds to alkynes were investigated in detail. This study revealed major factors controlling the selectivity of such addition reactions. A new Ni-based catalytic system with a self-organized nanostructured catalyst has been designed to perform chemical transformation in high yield, under mild conditions.