Ab Initio Study on the Mechanism of Cycloaddition Reaction between Silylene Carbene (H_2Si=C:) and Acetone

The mechanism of cycloaddition reaction between singlet silylene carbene and acetone has been investigated with CCSD（T）//MP2/6-31G method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. One consists of two steps： （1） the two reactants （R1, R2） firstly form a four-membered ring intermediate （INT4） through a barrier-free exothermic reaction of 585.9 kJ/mol; （2） Then intermediate （INT4） isomerizes to CH3-transfer product （P4.1） via a transition state （TS4.1） with energy barrier of 5.3 kJ/mol. The other is as follows： on the basis of intermediate （INT4） created between R1 and R2, intermediate （INT4） further reacts with acetone （R2） to form the intermediate （INT5） through a barrier-free exothermic reaction of 166.3 kJ/mol; Then, intermediate （INT5） isomerizes to a silicic bis-heterocyclic product （P5） via a transition state （TS5）, for which the barrier is 54.9 kJ/mol. The presented rule of this reaction： the [2＋2] cycloaddition effect between the π orbital of silylene carbene and the π orbital of π-bonded compounds leads to the formation of a four-membered ring intermediate （INT4）; The unsaturated property of C atom from carbene in the four-membered ring intermediate （INT4） results in the generation of CH3-transfer product （P4.1） and silicic bis-heterocyclic compound （P5）.

Carbores P加入量对镁碳砖性能的影响

为了进一步提高镁碳砖的使用性能,在镁碳砖配料中添加质量分数分别为0、0. 5%、1%、1. 5%、2%和2. 5%的Carbores P,经配料、混练、困料后,用630 t电动螺旋压力机压制成200 mm×150 mm×100 mm的样块,于220℃保温16 h固化后,切割成40 mm×40 mm×160 mm和50 mm×50 mm×50 mm试样,分别在1 000和1 500℃埋焦炭热处理3 h,然后检测固化及埋炭热处理后试样的显气孔率和常温耐压强度,以及固化后试样的高温抗折强度和抗氧化性,并由此优选出最佳Carbores P添加量的镁碳砖在某钢厂100 t钢包渣线部位进行了现场使用试验。结果表明:Carbores P加入量对固化试样的显气孔率和常温耐压强度影响不大,高温抗折强度随Carbores P加入量的增加而增大;对埋炭处理试样,添加0. 5%(w) Carbores P的试样显气孔率最低,常温耐压强度最大,抗氧化性最好。添加0. 5%(w) Carbores P的镁碳砖应用在某钢厂100 t钢包渣线部位,侵蚀速率为每炉2. 11 mm,与未添加Carbores P的镁碳砖相比,抗侵蚀性提高了10%。

Synthesis, Structure and Property of One Bis (benzimidazolin-2-ylidene) Arene-mercury(Ⅱ) Complex

Reaction of a N-heterocycliccarbene（NHC） containing an anthracene unit and two N-picolyl moieties with Hg（OAc）2 yielded a novel mercury（Ⅱ） complex（1）. X-ray studies, UV-vis and fluorescence spectroscopy confirmed that a strong interaction exists between the mercury atom and anthracene unit.

Synthesis of N-Heterocyclic Carbine Silver(Ⅰ)and Palladium(Ⅱ)Complexes with Acylated Piperazine Linker and Catalytic Activity in Three Types of C-C Coupling Reactions

Main observation and conclusion Two bis-imidazolium salts LH_(2)·Cl_(2) and LH_(2)·(PF_(6))_(2) with acylated piperazine linker and two N-heterocyclic carbene(NHC)silver(Ⅰ)and palladium(Ⅱ)complexes[L_(2)Ag_(2)](PF_(6))_(2)(1)and[L_(2)Pd_(2)Cl_(4)](2)were prepared.The crystal structures of LH_(2)·Cl_(2) and 1 were confirmed by X-ray analysis.In 1,one 26-membered macrometallocycle was generated through two silver(Ⅰ)ions and two bidentate ligands L.The catalytic activity of 2 was investigated in Sonogashira,Heck-Mizoroki and Suzuki-Miyaura reactions.The results displayed that these C-C coupling reactions can be smoothly carried out under the catalysis of 2.

Mechanism and origin of diastereoselectivity of N-heterocyclic carbene-catalyzed cross-benzoin reaction:A DFT study

Herein,the origin of the diastereoselectivity of N-heterocyclic carbene(NHC)-catalyzed cross-benzoin reactions between an a-amino aldehyde and furfural was studied by density functional theory.The computational results showed that the reaction proceeded through four steps:nucleophilic addition of NHC onto furfural,formation of a Breslow intermediate,cross-coupling reaction between Breslow intermediate and a-amino alde hyde,and dissociation of the catalyst.The cross-coupling was identified as the diaste reoselectivity-determining step,with the R-configured product generated preferentially.Noncovalent inte raction(NCI)analysis showed that the C-H…O and C-H…F inte ractions were responsible for determining the diastereoselectivity.