5271-39-6Relevant academic research and scientific papers
[Cp2TiCH2CHMe(SiMe3)]+, an alkyl-titanium complex which (a) exists in equilibrium between a β-agostic and a lower energy γ-agostic isomer and (b) undergoes hydrogen atom
Dunlop-Briere, Alexandre F.,Baird, Michael C.,Budzelaar, Peter H. M.
, p. 17514 - 17527 (2013)
The compound [Cp2Ti(Me)(CD2Cl2)][B(C 6F5)4] reacts with trimethylvinylsilane (TMVS) to form the 1,2-insertion product [Cp2TiCH2CHMe(SiMe 3)]+ (III), which exists in solution as equilibrating β- and γ-agostic isomers. In addition, while free rotation of the β-methyl group results in a single, averaged γ-H atom resonance at higher temperatures, decoalescence occurs below ～200 K, and the resonance of the γ-agostic hydrogen atom at δ ～ -7.4 is observed. Reaction of [Cp2Ti(CD3)(CD2Cl2)]+ with TMVS results in the formation of [Cp2TiCH2CH(CD 3)(SiMe3)]+, which converts, via reversible β-elimination, to an equilibrium mixture of specifically [Cp 2TiCH2CH(CD3)(SiMe3)]+ and [Cp2TiCD2CD(CH3)(SiMe3)] +. Complementing this conventional process, exchange spectroscopy experiments show that the β-H atom of [Cp2TiCH 2CHMe(SiMe3)]+ undergoes exchange with the three hydrogen atoms of the β-methyl group (β-H/γ-H exchange) but not with the two α-H atoms. This exchange process is completely shut down when [Cp2TiCH2CH(CD3)(SiMe 3)]+ is used, suggesting an H/D kinetic isotope effect much larger (apparently >16 000) than the maximum possible for an over-the-barrier process. It is proposed that β-H/γ-H exchange is facilitated by quantum mechanical proton tunnelling in which a hydrogen atom of the 2-methyl group of the alkene-hydride deinsertion product [Cp 2TiH{CH2-CMe(SiMe3)}]+ undergoes reversible exchange with the hydride ligand via the allyl dihydrogen species [Cp2TiH2{(η3-CH2C(SiMe 3)CH2}]+. Complementing these findings, DFT calculations were carried out to obtain energies and NMR parameters for all relevant species and thence to obtain better insight into the agostic preference(s) of complex III and the observed exchange processes. In all cases where comparisons between experimental and calculated data were possible, agreement was excellent.
The Kinetic Acidity of 1,1,1-Triphenylethane
Dixon, Richard E.,Streitwieser, Andrew
, p. 6125 - 6128 (1992)
Hydrogen isotope exchange studies were carried out on the methyl group of 1,1,1-triphenylethane, 1, with cesium cyclohexylamide (CsCHA) in cyclohexylamine (CHA).Mixtures of labeled compounds were used, Ph3C-14CH3 (1-14C), Ph3CCH2T (1-t), Ph3CCH2D (1-d), a
Russian-Doll-Like Molecular Cubes
Liu, Die,Li, Kaixiu,Chen, Mingzhao,Zhang, Tingting,Li, Zhengguang,Yin, Jia-Fu,He, Lipeng,Wang, Jun,Yin, Panchao,Chan, Yi-Tsu,Wang, Pingshan
, p. 2537 - 2544 (2021)
Nanosized cage-within-cage compounds represent a synergistic molecular self-assembling form of three-dimensional architecture that has received particular research focus. Building multilayered ultralarge cages to simulate complicated virus capsids is beli
Synthesis of Trialkylamines with Extreme Steric Hindrance and Their Decay by a Hofmann-like Elimination Reaction
Banert, Klaus,Hagedorn, Manfred,Heck, Manuel,Hertel, Raphael,Ihle, Andreas,Müller, Ioana,Pester, Tom,Shoker, Tharallah,Rablen, Paul R.
, p. 13630 - 13643 (2020/11/13)
A number of amines with three bulky alkyl groups at the nitrogen, which surpass the steric crowding of triisopropylamine considerably, were prepared by using different synthetic methods. It turned out that treatment of N-chlorodialkylamines with organometallic compounds, for example, Grignard reagents, in the presence of a major excess of tetramethylenediamine offered the most effective access to the target compounds. The limits of this method were also tested. The trialkylamines underwent a dealkylation reaction, depending on the degree of steric stress, even at ambient temperature. Because olefins were formed in this transformation, it showed some similarity with the Hofmann elimination. However, the thermal decay of sterically overcrowded tertiary amines was not promoted by bases. Instead, this reaction was strongly accelerated by protic conditions and even by trace amounts of water. Reaction mechanisms, which were analyzed with the help of quantum chemical calculations, are suggested to explain the experimental results.
Rare-Earth-Metal Pentadienyl Half-Sandwich and Sandwich Tetramethylaluminates–Synthesis, Structure, Reactivity, and Performance in Isoprene Polymerization
Barisic, Damir,Buschmann, Dennis A.,Schneider, David,Maichle-M?ssmer, C?cilia,Anwander, Reiner
supporting information, p. 4821 - 4832 (2019/03/13)
Targeting the synthesis of rare-earth-metal pentadienyl half-sandwich tetramethylaluminate complexes, homoleptic [Ln(AlMe4)3] (Ln=Y, La, Ce, Pr, Nd, Lu) were treated with equimolar amounts of the potassium salts K(2,4-dmp) (2,4-dmp=2,4-dimethylpentadienyl), K(2,4-dipp) (2,4-dipp=2,4-diisopropylpentadienyl), and K(2,4-dtbp) (2,4-dtbp=2,4-di-tert-butylpentadienyl). The reactions involving the larger rare-earth-metal centers lanthanum, cerium, praseodymium, and neodymium gave selectively the desired half-sandwich complexes [(2,4-dmp)La(AlMe4)2], [(2,4-dipp)La(AlMe4)2], and [(2,4-dtbp)Ln(AlMe4)2] (Ln=La, Ce, Pr, Nd) in high crystalline yields. Smaller rare-earth-metal centers yielded preferentially the sandwich complexes [(2,4-dmp)2Ln(AlMe4)] (Ln=Y, Lu) and [(2,4-dipp)2Y(AlMe4)]. Activation with fluorinated borate/borane co-catalysts gave highly active catalyst systems for the fabrication of polyisoprene, displaying molecular weight distributions as low as Mw/Mn=1.09 and a maximum cis-1,4 selectivity of 90.4 %. The equimolar reaction of half-sandwich complex [(2,4-dtbp)La(AlMe4)2] with B(C6F5)3 led to the isolation and full characterization of the single-component catalyst {{(2,4-dtbp)La[(μ-Me)2AlMe(C6F5)]}[Me2Al(C6F5)2]}2. The reaction of the latter complex with 10 equivalents of isoprene could be monitored by 1H NMR spectroscopy. Also, a donor-induced aluminato/gallato exchange was achieved with [(2,4-dtbp)La(AlMe4)2] and GaMe3(OEt2) leading to [(2,4-dtbp)La(GaMe4)2].
3D-Printing inside the Glovebox: A Versatile Tool for Inert-Gas Chemistry Combined with Spectroscopy
Lederle, Felix,Kaldun, Christian,Namyslo, Jan C.,Hübner, Eike G.
, p. 255 - 266 (2016/05/19)
3D-Printing with the well-established 'Fused Deposition Modeling' technology was used to print totally gas-tight reaction vessels, combined with printed cuvettes, inside the inert-gas atmosphere of a glovebox. During pauses of the print, the reaction flasks out of acrylonitrile butadiene styrene were filled with various reactants. After the basic test reactions to proof the oxygen tightness and investigations of the influence of printing within an inert-gas atmosphere, scope and limitations of the method are presented by syntheses of new compounds with highly reactive reagents, such as trimethylaluminium, and reaction monitoring via UV/VIS, IR, and NMR spectroscopy. The applicable temperature range, the choice of solvents, the reaction times, and the analytical methods have been investigated in detail. A set of reaction flasks is presented, which allow routine inert-gas syntheses and combined spectroscopy without modifications of the glovebox, the 3D-printer, or the spectrometers. Overall, this demonstrates the potential of 3D-printed reaction cuvettes to become a complementary standard method in inert-gas chemistry.
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.
Early main group metal catalysis: How important is the metal?
Harder, Sjoerd,Penafiel, Johanne,Maron, Laurent
supporting information, p. 201 - 206 (2015/09/08)
Organocalcium compounds have been reported as efficient catalysts for various alkene transformations. In contrast to transition metal catalysis, the alkenes are not activated by metal-alkene orbital interactions. Instead it is proposed that alkene activation proceeds through an electrostatic interaction with a Lewis acidic Ca2+. The role of the metal was evaluated by a study using the metal-free catalysts: [Ph2N-Me4N+] and [Ph3C-][Me4N- ]. These "naked" amides and carbanions can act as catalysts in the conversion of activated double bonds (C=O and C=N) in the hydroamination of Ar-N=C=O and R-N=C=N=R (R=alkyl) by Ph2NH. For the intramolecular hydroamination of unactivated C=C bonds in H2C=CHCH2CPh2CH2NH2 the presence of a metal cation is crucial. A new type of hybrid catalyst consisting of a strong organic Schwesinger base and a simple metal salt can act as catalyst for the intramolecular alkene hydroamination. The influence of the cation in catalysis is further evaluated by a DFT study.
Comparative reactivity of Zr- and Pd-alkyl complexes with carbon dioxide
Lau, Ka-Cheong,Petro, Benjamin J.,Bontemps, Sebastien,Jordan, Richard F.
supporting information, p. 6895 - 6898 (2014/01/06)
Structure/reactivity trends and DFT studies reveal mechanistic differences and parallels for the carboxylation of Zr and Pd alkyls. CO2 reacts with Cp2ZrMe(C6D5Cl)+ >10 4 faster than with Cp2ZrMe2, yielding monoacetate products in both cases. These reactions proceed by insertion mechanisms in which Zr- - -O interactions activate the CO2. In contrast, CO2 reacts readily with [(PO-iPr)PdMe 2]- (PO-iPr- = 2-P iPr2-4-Me-C6H3SO3 -) to yield [(PO-iPr)PdMe(OAc)]- but not with (PO-iPr)PdMe(L) species. Carboxylation of [(PO-iPr) PdMe2]- occurs by direct SE2 attack of CO 2 at the Pd-Metrans-to-P group, and the nucleophilicity of the Pd-Me group controls the reactivity. However, the SE2 process is accelerated by a Li+- OCO interaction when Li+ is present.
Synthesis of β-diketiminate-ligated bimetallic and monometallic lanthanide amide complexes and their reactivity with isoprene and AlMe 3
Sun, Song,Ouyang, Hao,Luo, Yunjie,Zhang, Yong,Shen, Qi,Yao, Yingming
, p. 16355 - 16364 (2013/12/04)
The amine elimination of lanthanide tris(amide) complexes with the phenylene-bridged bis(β-diketiminate) ligands PARAMe-H 2, METAMe-H2 and PARAPr-H 2 (PARAMe-H2 = 2[2,6-Me2C 6H3NHC(Me)C(H)C(Me)N]-(para-phenylene), META Me-H2 = 2[2,6-Me2C6H 3NHC(Me)C(H)C(Me)N]-(meta-phenylene), PARAPr-H2 = 2[2,6-iPr2C6H3NHC(Me)C(H)C(Me)N]- (para-phenylene)), and the mono-β-diketiminate ligand L 2,6-iPr2Ph-H (2,6-iPr2C 6H3)NHC(Me)CHC(Me)N(C6H5)) afforded the bimetallic lanthanide amide complexes PARAMe-{Ln[N(SiMe 3)2]2}2 (Ln = Y (1), Sm (2)), METAMe-{Y[N(SiMe3)2]2}2 (3), PARAPr-{Ln[N(HSiMe2)2]2} 2 (Ln = Y (4), Sm (5)), and the monomeric complexes L 2,6-iPr2Ph-Y[N(SiMe3)2]2 (6) and L2,6-iPr2Ph-Y[N(HSiMe2) 2]2 (7). In the presence of AlR3 and on activation with 1 equiv. of [Ph3C][B(C6F5) 4], complexes 1-7 showed a high activity toward the 1,4-selective polymerization of isoprene. The heterometallic Y/Al methyl complex [L 2,6-iPr2Ph]Y[(μ-Me)2AlMe2] 2 (8) was prepared to elucidate the real active precursor in the polymerization.
