New Chiral Pyridine Prolinol Derivatives and Preliminary Study on Asymmetric Catalytic Reaction

Two new chiral pyridine prolinol derivatives have been synthesized from N-alkylation of (S)-α,α-diphenyl-2-pyrrolidinemethanol with 2-bromomethylpyridine and 2, 6-dibromo-methyl-pyridine. The catalytic asymmetric borane reduction of prochiral ketones and the asymmetric addition ofdiethylzinc to benzaldehyde were investigated.     

Catalytic determination of cobalt at sub-nanogram levels using the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline by manual and flow-injection methods

A catalytic photometric method was developed for the determination of sub-nanogram levels of cobalt. The method is based on the catalytic effect of cobalt(II) on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (DAOS) to form a colored dye (λ_max=525 nm) in the presence of hydrogen peroxide. In this reaction system, 1,2-dihydroxybenzene-3,5-disulfonate (Tiron) acted as an effective activator for the catalysis of cobalt(II). Variation of reaction time between 5 and 10 min allows the determination range to be extended from 0.01 to 1.0 ng ml⁻¹. The reaction system can also be successfully adapted to flow-injection analysis (FIA). The dynamic range of the proposed flow-injection method was 0.01–1.0 ng ml⁻¹ and detection limit (signal/noise, S/N=3) was 5 pg ml⁻¹ at a sampling rate of 30 h⁻¹. Manual and flow-injection methods were applied to the direct determination of cobalt in pepperbush as a standard material.     

Localized molecular orbital studies on B_4C1_4,1,5-C_2B_3H_5 and B_nH_n~(2-)(n = 6-10, 12)

The wave functions, level energies and Mulliken population analysis of localized molecular orbitals (LMO's) for B4Cl4, 1,5-C2B3H5 and the closo-BnHn2- (n = 6-10, 12) are calculated by using the Edmiston-Reudenberg energy localization scheme under the CNDO/2 approximation in order to reveal the nature of quasi-aromaticity of the closo-BnHn2- (n > 5). It has been found that all the B-H or B-Cl LMO's are highly localized between the B and H (or Cl) atoms, corresponding to B-H or B-Cl o-bond, while the Bn framework bonding is formed mainly by the three-centered two-electron B-B-B bonds on the polyhedral faces. In the cases of B4Cl4 and 1,5-C2B3H5, these three-centered B-B-B bonds just fill their polyhedral faces; however, for the framework bonding of the closo-BnHn2- (n > 5), the valence electron deficiency leads to the delocalization of their three-centered B-B-B bonds, and as delocalizability of this three-centered B-B-B bond increases, some three-centered B-B-B bonds are further delocalized to become a f     

Convenient Asymmetric Borane Reduction of Ketones Catalyzed by Simple Amino Alcohols and Corresponding Amino Acids

The catalytic enantioselective borane reduction of ketones is a well-studied theme1. Since the pioneering work of Corey2, a variety of good catalysts have been synthesized through further modification on simple amino alcohols and their corresponding amino acids,3,4 . But when simple amino alcohols were directly used in the reduction their catalytic efficiency was very low. For the first time Buono5 has reported through carefully chosen reaction condition the catalytic efficiency of a simple…     

硼化学中的新共生亲核反应: 胺基二氯硼烷的三杂芳烃化

一类新反应被揭示。本文通过供试N-取代胺基二氯硼烷与一系列结构不同的杂芳基锂的反应结果, 考虑芳核软性对有关四配位三芳基硼胺络阴离子在反应中生成规律的作用。通过水解处理, 该络合物转化成相应的三杂芳基硼烷或其仲胺及外加Lewis碱分子配合物。结果表明, 胺基二氯硼烷的三杂芳烃化是以共生效应所稳定的这类络阴离子的形成为基础的新亲核反应。     

硼烷簇合物的结构规则

从超额电子数出发，提出了1种稠合型硼烷的结构规则，讨论了各种规则间的关系。     

Study of the rearrangement of cyclononatetraenyl(dipropyl)borane to 7,8-dipropyl-7-borabicyclo[4.2.2]deca-2,4,9-triene by NMR spectroscopy

Using NMR spectroscopy it was found that at ambient temperature 9-cyclononatetraenyl(dipropyl)borane (1) rapidly rearranges to give 7,8-dipropyl-7-borabicyclo[4.2.2]deca-2,4,9-triene (2),cis-endo-9-dipropylborylbicyclo[6.1.0]nona-2,4,6-triene (3a), and two isomeric boranes with dihydroindene skeletons (4a,b) (the ratio2 :3a :4a,b is 10 : 1 : 2).cis-exo-9-Dipropylborylbicyclo[6.1.01nona-2,4,6-triene (3b) is an intermediate product of the rearrangement; it is formed as a result of 8-electrocyclization inE,Z,Z,Z-cyclononatetraenyl(dipropyl)boranela. The transformation of bicycle3b to final product 2 occurs apparently via a synchronous exchange of the groups at the B atom (the transformation of the cyclopropane ring to the boracyclobutane ring accompanied by simultaneous migration of the propyl group from the B atom to thea-C atom). Borane6 formed in this rearrangement rapidly isomerizes to2 via a [1,3]-B shift.For preliminary report see Ref. 1Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. I, pp. 117–124, January, 1996.     

Time behaviour of the modifier involved in the general mechanism of Botts and Morales assuming rapid equilibrium in the modifier bindings

To date, the classification as activator or inhibitor of a modifier involved in an enzyme catalysed reaction is established according to its kinetic behaviour at the steady state. Inhibitors and activators are defined as modifiers which decrease or increase, respectively, the steady state rate of an enzyme-catalysed reaction. At this state, in some cases, a modifier always acts as an activator or as an inhibitor for all its possible concentration values. In other cases the action of a modifier as activator or inhibitor depends on its concentration. In this paper we extend the analysis of the kinetic behaviour of a modifier as inhibitor or nonessential activator to the transient phase of the reaction, i.e. to the whole course of the reaction, including both the transient phase and the steady state. Moreover, concerning to the behaviour of a modifier at the transient phase, we suggest its classification as activator or inhibitor based on the concentration and activator or inhibitor based on the rate. We have studied the behaviour of the modifier involved in the general modifier mechanisms of Botts and Morales in which the reversible bindings of the modifier to the enzyme forms are assumed in rapid equilibrium. The result is that depending on the values of the rate constants, equilibrium constants and the initial concentrations of both the involved substrate and modifier, the latter can act during the whole reaction course only as an activator, only as an inhibitor, first as an activator and then, from a determined reaction time, as inhibitor, or vice versa. Therefore, it is possible that a modifier showing an activating behaviour at the steady state behaves as an inhibitor in the transient phase, or vice versa. Novel indices pointing to the conditions under which the modifier can show any of the behaviours indicated above are suggested. The goodness of the analytical results is tested by comparison with the simulated curves obtained by numerical integration. From these results, those corresponding to several reaction mechanisms involving a modifier, and which can be regarded as particular cases of the general case analysed here, can be directly and easily obtained.     

Isolobal analogy between trivalent boron and divalent silicon

Singlet organosilylenes with a lone pair and an emptyp orbital are isolobal to trivalent borane if a B-H is equated to the lone pair on Si. Using this analogy, a particular isomer of CSi₂H₂ (24) is predicted to be a stable structure. MNDO calculations on24 and many of its possible isomers suggest that24 is at global minimum on the potential energy surface of CSi₂H₂.Ab initio calculations using a, minimal STO-3G basis set, on some selected structures also support these results.     

含金金属纳米颗粒用于液相化学氢化物催化制氢

液相化学氢化物以化学键的形式储存氢能,被认为是一类很有前景的化学储氢材料。液相化学氢化物的大规模应用很大程度上依赖于高效催化系统的开发。含金金属纳米颗粒在用于液相化学氢化物催化制氢中表现出优异的催化性能。本文综述了金纳米颗粒和含金异金属纳米颗粒用于液相氢化物催化制氢的最新研究进展。