2294-94-2Relevant articles and documents
Doped Complex Bases, a New Consequence of Aggregative Activation
Jamart-Gregoire, Brigitte,Fort, Yves,Quirin, Marie-Jeanne,Caubere, Paul
, p. 1459 - 1460 (1992)
According to the basic principles of aggregative activation, it has been shown that the efficiency of the complex base NaNH2-ButONa can be improved by simple addition of a potassium salt.
Multifaceted chelating μ-(η3:η3-antifacial)-(cis-C4R2H2) coordination motif in binuclear complexes
Liu, Cham-Chuen,Chan, Michael C. W.,Lo, Po-Kam,Lau, Kai-Chung,Yiu, Shek-Man
supporting information, p. 11056 - 11059 (2016/09/19)
A novel μ-C4R2H2 core structure (formed by an unprecedented regioselective, redox-neutral C(sp2)-C(sp2) coupling process) in binuclear group 4 complexes displays adaptable coordination and accommodates different metal sizes, and is sufficiently robust to promote interesting catalytic reactivity at the bimetallic centers.
Activation of heteroallenes by coordinatively unsaturated nickel(II) alkyl complexes supported by the hydrotris(3-phenyl-5-methyl)pyrazolyl borate (TpPh,Me) ligand
Abubekerov, Mark,Eymann, Léonard Y. M.,Gianetti, Thomas L.,Arnold, John
, p. 14581 - 14590 (2016/10/03)
Activation of sulfur containing heteroallenes by nickel(ii) alkyl complexes supported by the bulky hydrotris(3-phenyl-5-methylpyrazolyl)borate (TpPh,Me) ligand is described. Exposure of TpPh,MeNiCH2Ph (1a) and TpPh,MeNiCH2Si(CH3)3 (1b) to CS2 resulted in formation of the insertion products TpPh,MeNi(η2-CS2)CH2Ph (2a) and TpPh,MeNi(η2-CS2)CH2Si(CH3)3 (2b) in moderate yields. Reaction of 1a and MeNCS produced two species in a 1:1 ratio, identified as TpPh,MeNi(η2-MeNC)CH2Ph (3) and TpPh,MeNi(η2-MeNCS)SCH2Ph (4). Isolation of the unexpected insertion product (3) prompted an investigation into the activity of 1a-b in the presence of isocyanides (i.e.tBuNC), which resulted in isolation of TpPh,MeNi(η2-tBuNC)CH2Ph (5a) and TpPh,MeNi(η2-tBuNC)CH2Si(CH3)3 (5b). Similarly, reaction of 1a with OCS led to the isolation of a rare example of a Ni(i) carbonyl species TpPh,MeNiCO (6). Alternatively, complex 6 was also formed by exposure of 1a-b to an atmosphere of CO. Isolation of the intermediate species (TpPh,MeNi(η2-CO)CH2TMS (7b) and TpPh,MeNi(CO)(C(O)R, (8a-b) with R = Ph, TMS)) shed light on the formation of such species.
Nucleophilicity of Alkyl Zirconocene and Titanocene Precatalysts, and Kinetics of Activation by Carbenium Ions and by B(C6F5)3
Berionni, Guillaume,Kurouchi, Hiroaki,Eisenburger, Lucien,Mayr, Herbert
supporting information, p. 11196 - 11200 (2016/08/03)
Kinetics of activation of methyl and benzyl metallocene precatalysts by benzhydrylium ions, tritylium ions, and triarylborane B(C6F5)3were measured spectrophotometrically. The rate constants correlate linearly with the electrophilicity parameter E of the benzhydrylium and tritylium ions employed, allowing us to determine the σ-nucleophilicities of the metal–carbon bond of several zirconocenes and titanocenes. Bridging, substitution, metal, and ligand effects on the rates of metal–alkyl bond cleavage (M=Zr, Ti) were studied and structure–reactivity correlations were used to predict the kinetics of generation of metallocenium ions pairs, which are active catalysts in polymerization reactions and are highly electrophilic Lewis acids in frustrated Lewis pair catalysis.
On the structural diversity of [K(18-crown-6)EPh3] complexes (E = C, Si, Ge, Sn, Pb): Synthesis, crystal structures and NOESY NMR study
Kleeberg, Christian
, p. 8276 - 8287 (2013/07/28)
A series of homologous potassium triphenylelement complexes [K(18-crown-6)EPh3] 6a-e of group 14 elements (E = C, Si, Ge, Sn, Pb) was synthesised by alkoxide induced heterolytic cleavage of boron-element compounds. The complexes 6a-e are isolated as storable solids possibly useful as sources of nucleophilic [EPh3]- moieties. The solid state structures of 6a-e were established by X-ray crystal structure determination. Whilst all structures can be described as polymeric chains consisting of alternating [K(18-crown-6)]+ and [EPh3]- units, the interaction within each chain varies systematically with the coordination properties of E. For Si and Ge, classical E-K coordination along with secondary phenyl-K interactions are characteristic, whilst for Sn and Pb, potassium coordination via the phenyl π-system is observed due to inefficient coordination by the free electron pair localised in an 'inert' s-orbital. The carbon derivative is exceptional as the central sp2-hybridised carbon atom gives rise to extensive charge delocalisation and coordination via these partially charged π-systems. A 1H-1H NOESY NMR spectroscopic study in THF-d8 suggests appreciable anion/cation interactions for Si to Pb and hence the presence of contact ion pairs.
Reduction of carbonyl to methylene: Organosilane-Ga(OTf)3 as an efficient reductant system
Surya Prakash,Do, Clement,Mathew, Thomas,Olah, George A.
experimental part, p. 507 - 511 (2012/01/04)
Direct carbonyl reduction to methylene has been achieved by mild reductant system obtained from the combination of organosilane and gallium (III) trifluoromethanesulfonate {Ga(OTf)3}, a water tolerant, recyclable, catalyst. Among a series of organosilanes studied, dimethylchlorosilane (Me 2SiHCl, DMCS) showed the highest efficiency. Both aromatic and aliphatic ketones were effectively reduced to the corresponding methylene products with high functional groups tolerance, under very mild conditions in a relatively short period of time with good to excellent yields. Graphical Abstract: [Figure not available: see fulltext.]
Thermolysis of N-tetramethylpiperidinyl triphenylacetate: Homolytic fragmentation of a TEMPO ester
Henry-Riyad, Huda,Tidwell, Thomas T.
, p. 559 - 563 (2007/10/03)
Thermolysis of N-tetramethylpiperidinyl triphenylacetate (7, Ph 3CCO2T, T = 2,2,6,6-tetramethylpiperidinyl) in benzene at 146 °C leads to the formation of triphenylmethane (Ph3CH, 80%), tetramethylpiperidine (TH, 91%), and tetraphenylmethane (Ph4C, 9%). First-order rate constants for the decomposition at 132.8 and 150.0 °C were 2.20 × 10-6 and 2.88 × 10-5 s-1, respectively. In benzene-d6 solvent the triphenylmethane was formed as Ph3CD to the extent of 20%, as determined by 1H NMR and mass spectrometry. The results are interpreted as showing that Ph 3CCC2T undergoes thermolysis by concerted two-bond scission with formation of Ph3C., tetramethylpiperidinyl radicals and CO2. The formation of Ph4C occurs by addition of Ph3C. to benzene, followed by hydrogen atom abstraction from the resulting adduct. Calculations using DFT methods at the B3LYP/6-311++G** level were used to elucidate the bond fission of HCO2T (2), and indicate that cleavage to HCO2. and T. is favored by 7.8 kcal mol-1 relative to cleavage to HC(·)=O and TO., in agreement with the experimental results. Copyright
Zinc-Promoted Reactions. 1. Mechanism of the Clemmensen Reaction. Reduction of Benzophenone in Glacial Acetic Acid
Vona, Maria Luisa Di,Rosnati, Vittorio
, p. 4269 - 4273 (2007/10/02)
The mechanism of the Clemmensen reduction of diaryl ketones was investigated by reducing benzophenone, benzhydryl chloride, and dichlorodiphenylmethane in AcOH under a variety of conditions.Besides diphenylmethane, dimeric products were isolated that were indicative of the formation of radical species.Different product distributions were obtained from reactions run under different conditions.The reduction of deuteriated benzhydryl chloride was also performed.A quite complicated mechanistic pattern, involving ionic and nonionic reactions, emerged from the experimental p icture.Two pathways, connected through the protonated substrate, were recognized.According to the first pathway the reduction is promoted by a SET from Zn to the substrate, leading to the formation of a carbon radical having one zinc atom bound to the oxygen of the carbonyl group.Benzhydryl chloride, benzhydryl acetate, and dichlorodiphenylmethane are involved in the process.The product distributions suggest the occurrence of several SETs, which involve the formation of different radical species.Ionic reactions are responsible for the second route to the reduced products.Nucleophilic displacements also participate to the complex mechanism.
Photolysis of 1,1,1,2-Tetraarylalkanes in the Presence of 1,4-Dicyanobenzene. A Photochemical C-C Bond Cleavage Reaction of Radical Cations in Solution
Shi, Min,Okamoto, Yoshiki,Takamuku, Setsuo
, p. 1831 - 1840 (2007/10/02)
Irradiation of acetonitrile-methanol (1:1) solutions of 1,1,1,2-tetraarylalkanes or 1,1,1-triphenyl-2-methoxyethane containing 1,4-dicyanobenzene led to the formation of triarylmethane and triarylmethyl methyl ethers in good yields.This C-C bond cleavage reaction is thought to proceed via a radical cation intermediate.
