3234-49-9Relevant articles and documents
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Pressman,Young
, p. 705 (1944)
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Induced Fitting and Polarization of a Bromine Molecule in an Electrophilic Inorganic Molecular Cavity and Its Bromination Reactivity
Hayashi, Yoshihito,Inada, Yasuhiro,Katayama, Misaki,Kikukawa, Yuji,Kitajima, Hiromasa,Seto, Kensuke,Watanabe, Daiki,Yamashita, Shohei
supporting information, p. 14399 - 14403 (2020/07/13)
Dodecavanadate, [V12O32]4? (V12), possesses a 4.4 ? cavity entrance, and the cavity shows unique electrophilicity. Owing to the high polarizability, Br2 was inserted into V12, inducing the inversion of one of the VO5 square pyramids to form [V12O32(Br2)]4? (V12(Br2)). The inserted Br2 molecule was polarized and showed a peak at 185 cm?1 in the IR spectrum. The reaction of V12(Br2) and toluene yielded bromination of toluene at the ring, showing the electrophilicity of the inserted Br2 molecule. Compound V12(Br2) also reacted with propane, n-butane, and n-pentane to give brominated alkanes. Bromination with V12(Br2) showed high selectivity for 3-bromopentane (64 %) among the monobromopentane products and preferred threo isomer among 2-,3-dibromobutane and 2,3-dibromopenane. The unique inorganic cavity traps Br2 leading the polarization of the diatomic molecule. Owing to its new reaction field, the trapped Br2 shows selective functionalization of alkanes.
Kinetic study of the addition of trihalides to unsaturated compounds in ionic liquids. Evidence of a remarkable solvent effect in the reaction of ICl2-
Chiappe, Cinzia,Pieraccini, Daniela
, p. 6059 - 6064 (2007/10/03)
The kinetic constants and activation parameters for the reactions of Br3- and ICl2- with some alkenes and alkynes have been determined in the ionic liquids [bmim][PF6], [emim][Tf2N], [bmim][Tf2N], [hmim][TF2N], [bm2im] [Tf2N], and [bpy][TF2N] (where emim = 1-ethyl-3-methyl-imidazolium, bmim = 1-butyl-3-methylimidazolium, hmim = 1-hexyl-3-methylimidazolium, bm2im = 1-butyl-2,3-dimethylimidazolium, bpy = butylpyridinium, PF6 = hexafluorophosphate, and Tf 2N = bis(trifluoromethylsulfonyl)imide) and in 1,2-dichloroethane. The rates of both reactions increase on going from 1,2-dichloroethane to ILs. Evidence suggests that, while the hydrogen bonding ability of the imidazolium cation is probably the main factor able to increase the rate of the addition of ICl2- to double and triple bonds, this property has no effect on the electrophilic addition of Br3- to alkenes and alkynes. Furthermore, in the case of the ICl2- reaction, the hydrogen bonding ability of ILs can be exploited to suppress the unwanted nucleophilic substitution reaction on the products by the Cl - anion.
Outer-sphere and inner-sphere processes in reductive elimination. Direct and indirect electrochemical reduction of vicinal dibromoalkanes
Lexa, Doris,Savéant, Jean-Michel,Sch?fer, Hans J.,Su, Khac-Binh,Vering, Birgit,Wang, Dan Li
, p. 6162 - 6177 (2007/10/02)
The reduction of vicinal dibromoalkanes is investigated as an example of the dichotomy between outer-sphere and inner-sphere processes in reductive elimination. As a result from the analysis of the kinetic data, outer- sphere reagents such as carbon electrodes and aromatic anion radicals react with vicinal dibromoalkanes according to an "ET" mechanism in which the rate-determining step is a concerted electron- transfer bond-breaking reaction leading to the β-bromoalkyl radical. The latter is then reduced very rapidly, in a second step, most probably along another concerted electro- transfer bond-breaking pathway leading directly to the olefin in the heterogeneous case and through halogen atom expulsion in the homogeneous case. In the absence of steric constraints, the reduction goes entirely through the antiperiplanar conformer because the resulting β-bromoalkyl radical is then stabilized by delocalization of the unpaired electron over the C-C-X framework due to a favorable interaction between the pz orbital of the radical carbon and the σ* orbital of the C-Br bond. This interaction is enhanced by alkyl substitution at the reacting carbons, resulting in an approximately linear correlation between the reduction potential and the C-X bond energy of OlX2 on one hand and the vertical ionization potential of the olefin on the other. The stabilization energy is of the order of 0.2-0.3 eV for the anti conformers. It can also be taken as a measure of the rotation barrier around the C-C bond responsible for the loss of stereospecificity in the reduction. This competes with the reduction of the two stable conformers of the OlX* radicals and for the expulsion of the halogen atom. There is a remarkably good agreement between the ensuing prediction of the E:Z olefin ratio that should be found upon reduction of threo and erythro OlX2 isomers by outer-sphere reagents such as aromatic anion radicals and the experimental data. Although members of perfectly reversible redox couples, iron(I), iron("0"), and cobalt(I) porphyrins offer typical examples of inner-sphere reagents in their reaction with vicinal dibromoalkanes. They indeed react much more rapidly than outer-sphere electron donors (aromatic anion radicals) of the same standard potential. On the basis of steric hindrance experiments, it was shown that they do not react according to an SN2 rate-determining step involving the transient formation of an organometallic species. Complete stereospecificity is obtained, showing that they react along a halonium transfer E2 elimination mechanism rather than by an E1 elimination or a halogen atom transfer mechanism. As shown on a quantitative basis, this is related to the large driving force offered to halonium abstraction by the strong affinity of the iron(III) and cobalt (III) complexes toward halide ions. In regards to catalysis, the investigated systems provide typical examples showing the superiority of inner-sphere (chemical) catalysis over outer-sphere (redox) catalysis of electrochemical reactions. Not only is the catalytic efficiency much better since the rate constants of the key steps are larger, given the standard potential of the catalyst, but also selectivity is dramatically improved.
