108-48-5Relevant articles and documents
Vapor-phase photochemistry of dimethylpyridines
Pavlik, James W.,Kebede, Naod,Thompson, Michael,Day, A. Colin,Barltrop, John A.
, p. 5666 - 5673 (1999)
Irradiation of dimethylpyridine vapors (2-5 Torr) at 254 nm results in the formation of two sets of isomerization products. One set, formed in the larger yield, is substantially quenched when the irradiations are carried out in the presence of 15-21 Torr of nitrogen and is not formed when the irradiations are carried out with light of λ > 290 nm. In addition, a second set of reactions, which involve the interconversion of 2,3- and 2,5- dimethylpyridines, is enhanced by the addition of nitrogen, and these reactions are the only photoisomerization reactions observed when the irradiations are carried out with light of λ > 290 nm. In addition to the photoisomerizations, four of the dimethylpyridines also undergo demethylation to yield monomethylpyridines, and 2,6-dimethylpyridine undergoes methylation to yield a trimethylpyridine product. A variety of crossover experiments confirmed that the photoisomerizations are intramolecular. Based on the major phototransposition products, the six dimethylpyridines can be divided into two triads. Interconversion of the three members of each triad results in the major phototransposition products. These intra-triad interconversions are suggested to occur via 2,6-bonding, originating in a vibrationally excited S2 (π,π*) state of the dimethylpyridine, followed by nitrogen migration and rearomatization. This allows nitrogen to insert within each carbon- carbon bond. Phototransposition of 2,6-dideuterio-3,5-dimethylpyridine to a mixture of 5,6-dideuterio-2,4-dimethylpyridine and 3,4-dideuterio-2,5- dimethylpyridine is consistent with this mechanism. In addition to these intra-triad reactions, 2,5-dimethylpyridine, a member of triad 1, was observed to interconvert with 2,3-dimethylpyridine, a member of triad 2. These inter-triad reactions are suggested to occur via interconverting Dewar pyridine intermediates, formed from the triplet state of the dimethylpyridines. These Dewar pyridine intermediates were also observed by 1H NMR spectroscopy after irradiation of the dimethylpyridines in CD3CN at -30 °C.
Synthesis, structural characterization, and coordination chemistry of (Trineopentylphosphine)palladium(aryl)bromide dimer complexes ([(Np3P)Pd(Ar)Br]2)
Hu, Huaiyuan,Vasiliu, Monica,Stein, Trent H.,Qu, Fengrui,Gerlach, Deidra L.,Dixon, David A.,Shaughnessy, Kevin H.
, p. 13299 - 13313 (2019)
A series of [(PNp3)Pd(Ar)Br]2 complexes (PNp3 = trineopentylphosphine, Ar = 4-tolyl, 4-tert-butylphenyl, 2-tolyl, 4-methoxy-2-methylphenyl, 2-isopropylphenyl, and 2,6-dimethylphenyl) were synthesized and structurally characterized by X-ray crystallography and density functional theory optimized structures. The trineopentylphosphine ligand is able to accommodate coordination of other sterically demanding ligands through changes in its conformation. These conformational changes can be seen in changes in percent buried volume of the PNp3 ligand. The binding equilibria of the [(PNp3)Pd(Ar)Br]2 complexes with pyridine derivatives were determined experimentally and analyzed computationally. The binding equilibria are sensitive to the steric demand of the pyridine ligand and less sensitive to the steric demand of the aryl ligand on palladium. In contrast to previous studies, the binding equilibria do not correlate with pyridine basicity. The binding equilibria results are relevant to fundamental ligand coordination steps in cross-coupling reactions, such as Buchwald-Hartwig aminations.
Allosteric Effects in Ethylene Polymerization Catalysis. Enhancement of Performance of Phosphine-Phosphinate and Phosphine-Phosphonate Palladium Alkyl Catalysts by Remote Binding of B(C6F5)3
Wilders, Alison M.,Contrella, Nathan D.,Sampson, Jessica R.,Zheng, Mingfang,Jordan, Richard F.
, p. 4990 - 5002 (2017)
Remote binding of B(C6F5)3 to (PPO)PdMeL (L = pyridine or lutidine) or {(PPO)PdMe}2 ethylene polymerization catalysts that contain phosphine-arenephosphinate or phosphine-arenephosphonate ligands (PPO- = [1-PAr2-2-PR′O2-Ph]-: Ar = R′ = Ph (1a); Ar = Ph, R′ = OEt (1b); Ar = Ph, R′ = OiPr (1c); Ar = 2-OMe-Ph, R′ = OiPr (1d)) significantly increases the catalyst activity and the molecular weight of the polyethylene (PE) product. In the most favorable case, in situ conversion of (1d)PdMe(py) to the base-free adduct {1d·B(C6F5)3}PdMe increases the ethylene polymerization activity from 9.8 to 5700 kg mol-1 h-1 and the Mn of the PE product from 9030 to 99 200 Da (80 °C, 410 psi). X-ray structural data, trends in ligand lability, and comparative studies of BF3 activation suggest that these allosteric effects are primarily electronic in origin. The B(C6F5)3 binding enhances the chain growth rate (Rgrowth) by increasing the degree of positive charge on the Pd center. This effect does not result in the large increase in the chain transfer rate (Rtransfer) and concomitant reduction in PE molecular weight seen in previous studies of analogous (PO)PdRL catalysts that contain phosphine-arenesulfonate ligands, because of the operation of a dissociative chain transfer process, which is inhibited by the increased charge at Pd.
Synthesis of 2-(lutidinyl)organoboranes and their reactivities against dihydrogen and pinacol borane
Zheng, Junhao,Lin, Yue-Jian,Wang, Huadong
, p. 6088 - 6093 (2016)
Two 2,4,6-tris(trifluoromethyl)phenyl-substituted 2-(lutidinyl)organoboranes (5a and 5b) were prepared. These complexes can function as intramolecular vicinal B/N frustrated Lewis pairs to heterolytically activate dihydrogen. When these complexes were treated with HBpin, two different reaction pathways took place. Whereas the reaction between 5a and HBpin affords a formal ligand-redistribution product, the reaction of 5b with HBpin leads to a dearomative dehydroborylation product.
Suggestion of unexpected sulfur dioxide mechanism for deoxygenations of pyridine N-oxides with alkanesulfonyl chlorides and triethylamine
Morimoto, Yoshiki,Kurihara, Hajime,Shoji, Takamasa,Kinoshita, Takamasa
, p. 1471 - 1474 (2000)
The reaction mechanism for unusual deoxygenations of pyridine N-oxides with alkanesulfonyl chlorides and triethylamine was explored. Some experimental facts suggested that sulfur dioxide generated in the reaction system might be responsible for the deoxygenations without chlorinations of the pyridine nucleus.
One-step 2,6-Lutidine Synthesis from Acetone, Ammonia and Methanol. Temperature-programmed Desorption-Reaction (TPDR)-Mass Spectrometry (MS) Study
Vatti, Francesco P.,Forni, Lucio
, p. 4381 - 4386 (1993)
The temperature-programmed desorption-reaction (TPDR)-mass spectrometry (MS) technique has been employed to study the behaviour and the reactivity of the title reactant mixture over a catalyst of amorphous silica-alumina impregnated with Sb2O3 and CuO.This catalyst exhibited acidic and redox properties, leading to oxidation, dehydration and alkylation reactions.The formation of 2,6-lutidine takes place only at high temperature, requiring a high activation energy.The reaction mechanism involves alkylation of acetone by methanol to form methyl ethyl ketone, followed by reaction of the latter with ammonia to form an imine, then reaction of the imine with a second molecule of acetone, and finally, cyclisation to 2,6-lutidine.
A MILD DEOXYGENATION OF HETEROAROMATIC N-OXIDES WITH DIPHOSPHORUS TETRAIODIDE
Suzuki, Hitomi,Sato, Naofumi,Osuka, Atsuhiro
, p. 459 - 460 (1980)
When treated with diphosphorus tetraiodide in dichloromethane under gentle reflux, the title N-oxides are easily deoxygenated to the parent bases in good yields.
NCP-Type Pincer Iridium Complexes Catalyzed Transfer-Dehydrogenation of Alkanes and Heterocycles?
Wang, Yulei,Qian, Lu,Huang, Zhidao,Liu, Guixia,Huang, Zheng
, p. 837 - 841 (2020)
A series of NCP-type pincer iridium complexes, (RNCCP)IrHCl (2a—2c) and (BQ-NCOP)IrHCl 3, have been studied for catalytic transfer alkane dehydrogenation. Complex 3 containing a rigid benzoquinoline backbone exhibits high activity and robustness in dehydrogenation of alkanes to form alkenes. Even more importantly, this catalyst system was also highly effective in the dehydrogenation of a wide range of heterocycles to furnish heteroarenes.
Mechanism of proton transfer to coordinated thiolates: Encapsulation of acid stabilizes precursor intermediate
Alwaaly, Ahmed,Clegg, William,Harrington, Ross W.,Petrou, Athinoula L.,Henderson, Richard A.
, p. 11977 - 11983 (2015)
Earlier kinetic studies on the protonation of the coordinated thiolate in the square-planar [Ni(SC6H4R′-4)(triphos)]+ (R′ = NO2, Cl, H, Me or MeO) by lutH+ (lut = 2,6-dimethylpyridine) indicate a two-step mechanism involving initial formation of a (kinetically detectable) precursor intermediate, {[Ni(SC6H4R′-4)(triphos)]...Hlut}2+ (KR1), followed by an intramolecular proton transfer step (kR2). The analogous [Ni(SR)(triphos)]BPh4 {R = Et, But or Cy; triphos = PhP(CH2CH2PPh2)2} have been prepared and characterized by spectroscopy and X-ray crystallography. Similar to the aryl thiolate complexes, [Ni(SR)(triphos)]+ are protonated by lutH+ in an equilibrium reaction but the observed rate law is simpler. Analysis of the kinetic data for both [Ni(SR)(triphos)]+ and [Ni(SC6H4R′-4)(triphos)]+ shows that both react by the same mechanism, but that KR1 is largest when the thiolate is poorly basic, or the 4-R′ substituent in the aryl thiolates is electron-withdrawing. These results indicate that it is both NH...S hydrogen bonding and encapsulation of the bound lutH+ (by the phenyl groups on triphos) which stabilize the precursor intermediate.
A Lewis Base Nucleofugality Parameter, NFB, and Its Application in an Analysis of MIDA-Boronate Hydrolysis Kinetics
García-Domínguez, Andrés,Gonzalez, Jorge A.,Leach, Andrew G.,Lloyd-Jones, Guy C.,Nichol, Gary S.,Taylor, Nicholas P.
supporting information, (2022/01/04)
The kinetics of quinuclidine displacement of BH3 from a wide range of Lewis base borane adducts have been measured. Parameterization of these rates has enabled the development of a nucleofugality scale (NFB), shown to quantify and predict the leaving group ability of a range of other Lewis bases. Additivity observed across a number of series R′3-nRnX (X = P, N; R′ = aryl, alkyl) has allowed the formulation of related substituent parameters (nfPB, nfAB), providing a means of calculating NFB values for a range of Lewis bases that extends far beyond those experimentally derived. The utility of the nucleofugality parameter is explored by the correlation of the substituent parameter nfPB with the hydrolyses rates of a series of alkyl and aryl MIDA boronates under neutral conditions. This has allowed the identification of MIDA boronates with heteroatoms proximal to the reacting center, showing unusual kinetic lability or stability to hydrolysis.
