Theoretical study on the mechanism for NH3BH3 reduction of ketones and imines

In spite of a potential hydrogen storage material, ammonia borane (AB) was recently found to be a good hydrogenation reagent. It can reduce certain ketones to alcohols or borate esters, and imines to amines. The mechanisms of these reactions are not fully understood yet, and have been systematically studied using high-level CCSD(T) calculations in this work. We have validated theoretically that the forming of alcohols and amines undergoes concerted double-hydrogen transfer (DHT) mechanism. Furthermore, we predicted that the DHT process is facile for more general ketones and imines. For the borate ester formation, we found a pretty high barrier for the experimentally derived stepwise mechanism. Alternatively, we propose that the reaction starts with the DHT process to form alcohol and NH₂BH₂, followed by alcoholysis of NH₂BH₂ to form the first B–O bond. This mechanism is in good agreement with the current experimental facts, and also explains why ketone reduction affords different products at different conditions. For these reaction systems, the performances of M06-2x and MP2 (underestimate the barrier by 5–7 kcal/mol, but with right trends) are better than B3LYP and BLYP methods (underestimate the barrier by 0–5 kcal/mol).     

Synthesis of Ammonia Borane Nanoparticles and the Diammoniate of Diborane by Direct Combination of Diborane and Ammonia

Pure nanoparticle ammonia borane (NH₃BH₃, AB) was first prepared through a solvent‐free, ambient‐temperature gas‐phase combination of B₂H₆ with NH₃. The prepared AB nanoparticle exhibits improved dehydrogenation behavior giving 13.6 wt. % H₂ at the temperature range of 80–175 °C without severe foaming. Ammonia diborane (NH₃BH₂(μ‐H)BH₃, AaDB) is proposed as the intermediate in the reaction of B₂H₆ with NH₃ based on theoretical studies. This method can also be used to prepare pure diammoniate of diborane ([H₂B(NH₃)₂][BH₄], DADB) by adjusting the ratio and concentration of B₂H₆ to NH₃.     

镧、铈对低分子量单链尿激酶基因在酵母中表达的影响

LaCl3能提高rscu-PA-32k在酵母中的表达效率，2和5mmol.L^-1LaCl3可以使表达产物活力提高13％和20％，从14．6U／ml分别增加到16．5和17．5U/ml，而CeCl3则使表达产物的活力降低，2和5mmol.L^-1 CeCl3分别使产物活力下降了21％和33％，从14＝6U／ml分别下降到11．5和9．8U/ml。     

Beiträge zur Chemie des Phosphors. 240 [1]. Zum reaktiven Verhalten von Diphosphan-boran,P2H4 · BH3

Contributions to the Chemistry of Phosphorus. 240. On the Reactive Behaviour of Diphosphane-borane, P₂H₄ · BH₃ Under mild temperature conditions, the thermal decomposition of diphosphane-borane ( 1 ) gives rise to the formation of phosphane-borane, PH₃ · BH₃, and triphosphane-2-borane, PH₂? PH(BH₃)? PH₂ ( 2 ). In the presence of diphosphane-1,2-bis(borane), triphosphane-1,3-bis(borane), BH₃? PH₂? PH? PH₂? BH₃ ( 3 ), is formed additionally. The thermolysis product at room temperature is a polymeric solid of varying composition which contains phosphorus, boron, and hydrogen. Compound 1 reacts with metalating agents such as n-BuLi, LiBH₄, and NaBH₄ to furnish the borane-trihydrogendiphosphide ion, [PH₂? PH? BH₃]^?, which immediately disproportionates to give the corresponding mono-and triphosphane derivatives. In the presence of an excess of THF-borane and in the case of a 1 : 1 molar ratio of 1 : NaBH₄, the disproportionation does not occur and the new diphosphide derivative sodium-1,1,2-tris(borane)-1,2,2-trihydrogendiphosphide, Na[(BH₃)₂PH? PH₂BH₃] ( 4 ) can be obtained. The action of additional NaBH₄ yields the diphosphide dianion with four coordinated BH₃ groups.     

A novel reduction of polycarboxylic acids into their corresponding alkanes using n-butylsilane or diethylsilane as the reducing agent

A convenient one-pot reaction has been developed for the reduction of polycarboxylic acids on aliphatic and aromatic systems to their corresponding alkanes. The reduction utilises either diethylsilane or n-butylsilane as the reducing agent in the presence of the Lewis acid catalyst tris(pentafluorophenyl)borane.     

9-BBN还原1,7-辛二烯-3-醇的研究

本文报道了用9-BBN与1,7-辛二烯-3-醇进行硼氢化反应的结果。这个反应的区域选择性极低,除生成1-辛烯-3-醇(47％)外,同时还生成了7-辛烯-3-醇(41％)和辛醇-3(12％)。     

Stability of polyhedral borane anions and carboranes

Polyhedral borane anions and carboranes that can be constructed formally from the interaction of rings and caps will be stable with six interstitial electrons. Interstitial electron count is obtained by summing the number of π electrons of the ring and the electrons of the caps involved in ring cap binding. Thus B₇H₇ ⁻² (D_5h) has 6 interstitial electrons (none from the B₅H₅ ring, two each from the twobh caps and two negative charge),mndo calculations on isoelectronic pyramidal molecules B₆H₆ ⁻⁴ (C_5v), B₅H₅CH⁻³ (C_5v), B₅H₅ ⁻⁴ (C_4v), B₄H₄CH⁻³ (C_4v), B₄H₄ ⁻⁴ (T _d) and B₃H₃CH⁻³ (C_3v) suggests a criterion based on the out-of-plane bendings of the ring B-H bonds to select the best combination of borocycles and BH or CH caps. Three-membered borocycle prefers CH cap, five-membered borocycle prefers BH cap. The preference of four-membered ring for BH or CH cap is not as pronounced. The extra stability of B₁₂H₁₂ ⁻² arises from the geometry of the icosahedron. The relative stabilities ofnido andcloso carboranes follow from these rules.     

Synthesis of novel oxazaborolidines B-C6F5 and their effectiveness as asymmetric catalysts

Novel oxazaborolidines B-C₆F₅ were synthesized by modified protocol from C₆F₅B(OMe)₂ (in place of usual C₆F₅B(OH)₂) and the corresponding amino alcohols, aiming to know the π-π stacking and electron-withdrawing effects of C₆F₅ group in asymmetric reduction of ketones. Although the results were not simply explained by the expected effects, significant difference was observed in the enantioselectivity between the catalysts with B-C₆H₅ and B-C₆F₅.     

Generation of bis(pentafluorophenyl)borane-dimethyl sulfide complex as a solution of hexane and its application to hydroboration of alk-1-yne with pinacolborane

A solution of bis(pentafluorophenyl)borane-dimethyl sulfide complex in hexane was generated by redistribution between tris(pentafluorophenyl)borane and borane-dimethyl sulfide complex. In the resulting solution a stoichiometric hydroboration of alk-1-yne with pinacolborane proceeded well at room temperature to afford (E)-alk-1-enylboronic acid pinacol ester in high yield. Bis(pentafluorophenyl)borane-dimethyl sulfide complex served as a mediator for the hydroboration.