3524-73-0Relevant articles and documents
Controlling the Lewis Acidity and Polymerizing Effectively Prevent Frustrated Lewis Pairs from Deactivation in the Hydrogenation of Terminal Alkynes
Geng, Jiao,Hu, Xingbang,Liu, Qiang,Wu, Youting,Yang, Liu,Yao, Chenfei
, p. 3685 - 3690 (2021/05/31)
Two strategies were reported to prevent the deactivation of Frustrated Lewis pairs (FLPs) in the hydrogenation of terminal alkynes: reducing the Lewis acidity and polymerizing the Lewis acid. A polymeric Lewis acid (P-BPh3) with high stability was designed and synthesized. Excellent conversion (up to 99%) and selectivity can be achieved in the hydrogenation of terminal alkynes catalyzed by P-BPh3. This catalytic system works quite well for different substrates. In addition, the P-BPh3 can be easily recycled.
The reaction of biphenyl radical anion and dianion with alkyl fluorides. From ET to SN2 reaction pathways and synthetic applications
Pérez, Henoc,Melero, Cristóbal,Guijarro, Albert,Yus, Miguel
experimental part, p. 10769 - 10783 (2010/02/28)
The reaction of dilithium biphenyl (Li2C12H10) with alkyl fluorides has been studied from the point of view of the distribution of products. Two main reaction pathways, the nucleophilic substitution (SN2) and the electron transfer (ET), can compete to yield the same alkylation products in what is known as the SN2-ET dichotomy. SN2 seems to be the main mechanism operating with primary alkyl fluorides (n-RF). Alkylation proceeds in good yields, and the resulting alkylated dihydrobiphenyl anion (n-RC12H10Li) can be trapped with a second conventional electrophile (E+) affording synthetically interesting dearomatized biphenyl derivatives (n-RC12H10E). The reaction gives a higher amount of ET products as we move to secondary (s-RF) and to tertiary alkyl fluorides (t-RF), in which case the mechanism seems to be dominated by ET. In this case, alkylation by radical coupling is still feasible, giving access to the synthesis of t-RC12H10E, although in lower yields. A rational interpretation of this SN2-ET dichotomy is given on the basis of the full distribution of products observed when 5-hexenyl fluoride and 1,1-dimethyl-5-hexenyl fluoride were are used as radical probes in their reaction with Li2C12H10 and LiC12H10.
Competitive intramolecular Ti-C versus Al-C alkene insertions: examining the role of Lewis acid cocatalysts in Ziegler-Natta alkene insertion and chain transfer reactions
Barta, Nancy S.,Kirk, Brian A.,Stille, John R.
, p. 47 - 54 (2007/10/02)
Mechanistic aspects of Ziegler-Natta olefin insertion, which include catalyst/cocatalyst interactions, chain propagation, and chain termination, have been examined for systems which model the Cp2Ti(Cl)R/RAlCl2 and Cp2Ti(Cl)R/MgX2 catalyst complexes.The reaction of (2-butyl-6-hepten-1-yl)titanocene chloride with (2-propyl-6-hepten-1-yl)aluminum dichloride:diethyl etherate produced 78percent cyclization of the titanocene ligand, while less than 2percent of the ligand originating on aluminum cyclized.In a complementary experiment, the reaction of (2-propyl-6-hepten-1-yl)titanocene chloride and (2-butyl-6-hepten-1-yl)aluminum dichloride:diethyl etherate again produced only intramolecular insertion of the titanium ligand (58percent).Based on these results, equilibretion of ligands through transmetallation between titanium and aluminum did not occur under these reaction conditions, and selective insertion into the titanium-carbon bond was confirmed for this process.Similarly, ligand cyclization with Cp2Ti(Cl)R/MgX2 also occurred through insertion into the titanium-carbon bond.The product distribution generated by the MgX2 was highly solvent dependent.Cyclization in CH2Cl2 was very efficient, while reaction in toluene generated numerous products.Included in the toluene reaction mixture were compounds that resulted from ligand transposition/chain transfer of the titanium ligand. Keywords: Titanium; Aluminium; Magnesium; Olefin insertion; Ziegler-Natta catalysts; Chain transfer
Reactions of Methyl-Substituted Hex-5-enyl and Pent-4-enyl Radicals
Beckwith, Athelstan L. J.,Easton, Christopher J.,Lawrence, Tony,Serelis, Algirdas K.
, p. 545 - 556 (2007/10/02)
Relative and absolute kinetic data have been determined for ring closure of methyl-substituted hex-5-enyl radicals: 2-methyl-(10a), 3-methyl-(4a), 4-methyl-(5a), 2,2-dimethyl-(10c), 3,3-dimethyl-(4c) and 4,4-dimethyl-hex-5-enyl (5c) radicals, generated by interaction of tributylstannane with the corresponding bromides (1a)-(3a) and (1c)-(3c).Each radical undergoes regiospecific or highly regioselective 1,5-cyclization more rapidly than does the unsubstituted radical (4d).The rate enhancements, which arise mainly from lowering of the activation energy, can be rationalized in terms of the gem-dimethyl effect. 1,5-Ring closures of monosubstituted species are stereoselective: 2-methyl- and 4-methyl-hex-5-enyl radicals (10a) and (5a) give mainly trans products, whereas 3-methylhex-4-enyl radical gives mainly the cis.This behaviour reflects the effect of the substituent on the stabilities of cyclic transition complexes in chair-like conformations.Ring closure of 2,2-dimethylpent-4-enyl radical or of 3,3-dimethylpent-4-enyl radical (19) could not be detected.
The Kinetics and Mechanism of Ring Opening of Radicals containing the Cyclobutylcarbinyl System
Beckwith, Athelstan L. J.,Moad, Graeme
, p. 1083 - 1092 (2007/10/02)
The kinetic parameters of β-fission of radicals containing the cyclobutylcarbinyl system have been determined by analysis of the mixtures obtained when suitable chloro-compounds are treated with tributylstannane.Under these conditions ring opening is irreversible and in the rigid bicyclic system (4) is under stereoelectronic control.For ring opening of cyclobutylcarbinyl radical (8) kf = 4.3 x 103 s-1 at 60 deg C, and the best values of the activation parameters appear to be ΔH(excit.) = 12.2 kcal mol-1 and ΔS(excit.) = -7.4 cal mol-1 K-1.Monocyclic systems undergo preferential fission of the more substituted βγ-bond.Methyl substituents at the α-, β-, or δ-positions have little effect but γ-substitution strongly enhances the rate of ring opening.The transition state is reactant-like and has a similar disposition of centres to that (1) for homolytic addition.
