钐(II)类卡宾CH3SmCH2I与乙烯环丙烷化反应及溶剂化效应的理论研究

用密度泛函B3LYP方法研究了过渡金属钐类卡宾与乙烯的环丙烷化反应的机理. 对钐类卡宾试剂CH₃SmCH₂I和CH₂CH₂反应的反应物、中间体、过渡态和产物构型的全部结构几何参数进行了优化, 并计算了THF溶液的溶剂化效应, 用内禀反应坐标(IRC)计算和频率分析方法, 对过渡态进行了验证. 结果表明: CH₃SmCH₂I与CH₂CH₂环丙烷化反应按亚甲基转移机理(通道A)和卡宾金属化机理(通道B)都可以进行, 与锂类卡宾的反应机理相同, 通道A比通道B反应的势垒降低了14.65 kJ/mol. 溶剂化效应使通道B比通道A的反应势垒大幅度提高, 更有利于反应沿通道A进行, 而不利于通道B.     

钐(II)类卡宾CH3SmCH2I与乙烯环丙烷化反应及溶剂化效应的理论研究

用密度泛函B3LYP方法研究了过渡金属钐类卡宾与乙烯的环丙烷化反应的机理. 对钐类卡宾试剂CH₃SmCH₂I和CH₂CH₂反应的反应物、中间体、过渡态和产物构型的全部结构几何参数进行了优化, 并计算了THF溶液的溶剂化效应, 用内禀反应坐标(IRC)计算和频率分析方法, 对过渡态进行了验证. 结果表明: CH₃SmCH₂I与CH₂CH₂环丙烷化反应按亚甲基转移机理(通道A)和卡宾金属化机理(通道B)都可以进行, 与锂类卡宾的反应机理相同, 通道A比通道B反应的势垒降低了14.65 kJ/mol. 溶剂化效应使通道B比通道A的反应势垒大幅度提高, 更有利于反应沿通道A进行, 而不利于通道B.     

亚甲基环丙烷卡宾的开环与1,2-氢迁移的从头算研究

用从头计算-解析梯度法研究了亚甲基环丙烷卡宾的重排反应。开环重排经Hückel型过渡态,在过渡态前后分别属2电子和4电子反应,取对旋和顺旋方式,遵从4n+2和4n规则。1,2氢重排经迁移氢进攻卡宾碳的空p轨道发生。用RHF/6-31-G^**∥STO-3G方法算得开环势垒为24kJ/mol。1,2氢重排不是开环的竞争反应,其势垒为118kJ/mol。与环丙烷卡宾比较,亚甲基取代未改变其开环反应的类型与机理,但增大开环反应活性。     

DMP与DEP在凝聚相中裂解反应理论研究∶隧道效应与溶剂效应(英文)

采用密度泛函理论(DFT)B3LYP方法,以极化连续模型(PCM)和导体反应场模型(COSMORS)的溶剂模型为基础,结合反应动力学研究了2,2-二甲氧基丙烷(DMP)与2,2-二乙氧基丙烷(DEP)在凝聚相(溶液相)中的裂解反应.结果表明,四元环过渡态裂解反应机理是DMP与DEP裂解反应的主反应通道,溶剂效应和隧道效应对液相中的裂解反应速率有较大的影响,而且溶剂效应的影响更显著.在凝聚相反应理论研究中,溶剂效应和量子隧道效应都是不能忽略的因素.     

烯烃环丙烷化反应催化研究

本文研究了用Cu(CH3CCHCCH3)2, Ph3PCuX, Cu(O2CCF3)2等催化剂催化四甲基乙烯和重氮乙酸乙酯的环丙烷化反应。结果表明配体吸电子能力越强, 立体位阻越小, 其催化活性也越强。考察了反应物与Cu(O2CCF3)2的配比, 反应温度对Cu(O2CCF3)2催化反应活性的影响。通过对Cu(O2CCF3)2催化活性中心的研究表明,催化活性中心是一价铜配合物, 并推断四甲基乙烯环丙烷化机理是经由金属卡宾机理。     

烯烃环丙烷化反应催化研究

本文研究了用Cu(CH3CCHCCH3)2, Ph3PCuX, Cu(O2CCF3)2等催化剂催化四甲基乙烯和重氮乙酸乙酯的环丙烷化反应。结果表明配体吸电子能力越强, 立体位阻越小, 其催化活性也越强。考察了反应物与Cu(O2CCF3)2的配比, 反应温度对Cu(O2CCF3)2催化反应活性的影响。通过对Cu(O2CCF3)2催化活性中心的研究表明,催化活性中心是一价铜配合物, 并推断四甲基乙烯环丙烷化机理是经由金属卡宾机理。     

铜化合物催化重氮乙酸乙酯环丙烷化反应

研究了以铜化合物催化重氮乙酸乙酯与烯烃的环丙烷化反应,首次计算了反应关键中间体铜-卡宾的环丙烷化选择性P及该中间体的解离常数K,结果表明:1.反应体系中可能存在着铜-卡宾与游离卡宾的平衡;2.P、K与所用的催化剂有关。使用不同的催化剂,温度对反应选择性的影响也不同,对以上结果进行了理论探讨。     

反式共轭类碳烯CH2=CH-CH=C:LiF氢迁移反应的DFT研究

应用密度泛函理论DFT方法,在B3LYP/6-31G*水平上研究了反式共轭类碳烯CH2=CH-CH=C∶LiF的氢迁移反应.计算优化了反应过程中的所有反应物、中间体、过渡态和产物的几何构型,通过频率振动分析确定中间体和过渡态.结果表明,在β位上的H原子迁移过程中,经历一个带有三元环结构的中间体和两个带有三元环结构的过渡态.第一步反应势垒较大.     

反式共轭类碳烯CH_2CH—CHC∶LiF氢迁移反应的DFT研究

应用密度泛函理论DFT方法,在B3LYP/6-31G*水平上研究了反式共轭类碳烯CH2CH—CHC∶LiF的氢迁移反应.计算优化了反应过程中的所有反应物、中间体、过渡态和产物的几何构型,通过频率振动分析确定中间体和过渡态.结果表明,在β位上的H原子迁移过程中,经历一个带有三元环结构的中间体和两个带有三元环结构的过渡态.第一步反应势垒较大.     

DMP与DEP在凝聚相中裂解反应理论研究: 隧道效应与溶剂效应

采用密度泛函理论(DFT)B3LYP方法, 以极化连续模型(PCM)和导体反应场模型(COSMORS)的溶剂模型为基础, 结合反应动力学研究了2,2-二甲氧基丙烷(DMP)与2,2-二乙氧基丙烷(DEP)在凝聚相(溶液相)中的裂解反应. 结果表明, 四元环过渡态裂解反应机理是DMP与DEP裂解反应的主反应通道, 溶剂效应和隧道效应对液相中的裂解反应速率有较大的影响, 而且溶剂效应的影响更显著. 在凝聚相反应理论研究中, 溶剂效应和量子隧道效应都是不能忽略的因素.     

Samarium(III) carbenoid as a competing reactive species in samarium-promoted cyclopropanation reactions

The trivalent samarium carbenoid I2SmCH2I-promoted cyclopropanation reactions with ethylene have been investigated and are predicted to be highly reactive, similarly to the divalent samarium carbenoid ISmCH2I. The methylene transfer and carbometalation pathways were explored and compared with and without coordination of THF solvent molecules to the carbenoid. The methylene transfer was found to be favored, with the barrier to reaction going from 12.9 to 9.2 kcal/mol compared to barriers of 15.4-17.5 kcal/mol for the carbometalation pathway upon the addition of one THF molecule.     

Theoretical study of samarium (II) carbenoid (ISmCH2I) promoted cyclopropanation reactions with ethylene and the effect of THF solvent on the reaction pathways

A computational study of the cyclopropanation reactions of divalent samarium carbenoid ISmCH(2)I with ethylene is presented. The reaction proceeds through two competing pathways: methylene transfer and carbometalation. The ISmCH(2)I species was found to have a "samarium carbene complex" character with properties similar to previously investigated lithium carbenoids (LiCH(2)X where X = Cl, Br, I). The ISmCH(2)I carbenoid was found to be noticeably different in structure with more electrophilic character and higher chemical reactivity than the closely related classical Simmons-Smith (IZnCH(2)I) carbenoid. The effect of THF solvent was investigated by explicit coordination of the solvent THF molecules to the Sm (II) center in the carbenoid. The ISmCH(2)I/(THF)(n)() (where n = 0, 1, 2) carbenoid methylene transfer pathway barriers to reaction become systematically lower as more THF solvent is added (from 12.9 to 14.5 kcal/mol for no THF molecules to 8.8 to 10.7 kcal/mol for two THF molecules). In contrast, the reaction barriers for cyclopropanation via the carbometalation pathway remain high (>15 kcal/mol). The computational results are briefly compared to other carbenoid reactions and related species.     

Density functional theory study of the platinum-catalyzed cyclopropanation reaction with olefin

A computational study of the platinum-catalyzed cyclopropanation reaction with olefin is presented. The model system is formed by an ethylene molecule and the active catalytic species, which forms from a CH2 fragment and the Cl2Pt(PH3)2 complex. The results show that the active catalytic species is not a metal-carbene of the type (PH3)2Cl2Pt=CH2 but two carbenoid complexes which can exist in almost two degenerate forms, namely (PH3)2Pt(CH2Cl)Cl (carbenoid A) and (PH3)Pt(CH2PH3)Cl2 (carbenoid B). The reaction proceeds through three pathways: methylene transfer, carbometalation for carbenoid A, and the reaction of a monophosphinic species for carbenoids (A and B). The most favored reaction channel is methylene transfer pathway for (PH3)Pt(CH2PH3)Cl2 (carbenoid B) species with a barrier of 31.32 kcal/mol in gas phase. The effects of dichloromethane, THF, and benzene solvent are investigated with PCM method. For carbenoid A, both methylene transfer and carbometalation pathway barriers to reaction become remarkably lower with the increasing polarity of solvent (from 43.25 and 52.50 kcal/mol for no solvent to 25.36 and 38.53 kcal/mol in the presence of the dichloromethane). In contrast, the reaction barriers for carbenoid B via the methylene transfer path hoist 6.30 kcal/mol, whereas the barriers do not change significantly for the reaction path of a monophosphinic species for carbenoids (A and B).     

钐(Ⅱ)类卡宾CH3SmCH2X(X=Cl、Br和I)促进乙烯环丙烷化反应途径的理论研究

In order to have efficient and highly stereoselective cyclopropanating reagents, the cyclopropanation reaction of ethylene promoted with Samarium(Ⅱ) carbenoid Simmons-Smith(SS)reagent were studied by means of B3LYP hybrid density functional method. The geometries for reactants, transition states and products are completely optimized. All transition states were verified by the vibrational analysis and the intrinsic reaction coordinate (IRC) calculations. The results showed that, identical with the lithium carbenoid,CH3SmCH2X(X=Cl, Br and I) can fairly react with ethylene via both methylene transfer pathway (pathway A) and carbometalation pathway (pathway B). And the cyclopropanation reaction via methylene transfer pathway proceeds with a lower barrier and at lower temperatures.     

Reaction pathways of the Simmons-Smith reaction

The cyclopropanation reaction of an alkene with a metal carbenoid has been studied by means of the B3LYP hybrid density functional method. The cyclopropanation of ethylene with a lithium carbenoid or a zinc carbenoid [Simmons-Smith (SS) reagent] goes through two competing pathways, methylene transfer and carbometalation. Both processes are fast for the lithium carbenoid, while, for the zinc carbenoid, only the former is fast enough to be experimentally feasible. The reaction of an SS reagent (ClZnCH(2)Cl) with ethylene and an allyl alcohol in the presence of ZnCl(2) was also studied. The allyl alcohol reaction was modeled with an SS reagent/alkoxide complex (ClCH(2)ZnOCH(2)CH=CH(2)) formed from the SS reagent and allyl alcohol. Two modes of acceleration were found. The first involves the well-accepted mechanism of 1,2-chlorine migration, and the second involves a five-centered bond alternation. The latter was found to be more facile than the former and to operate equally well both with ethylene and with aggregates of SS reagent/alkoxide complexes. Calculations on the SS reaction with 2-cyclohexen-1-ol offer a reasonable model for the hydroxy-directed diastereoselective SS reaction, which has been used for a long time in organic synthesis.     

Theoretical studies of samarium carbenoid promoted cyclopropanation reaction with allylic alcohol on the reaction pathways

The density functional theory was employed to investigate the mechanism for the cyclopropanation reactions of samarium carbenoid with an allylic alcohol. Seven competitive reaction pathways were investigated. Analysis of the calculated results shows that the models 4 and 6 have relatively low reaction barriers which suggested that the deprotonation of allylic alcohol promoted by CH₃SmCH₂I plays a significant important role in the cyclopropanation reaction via a samarium carbenoid. The methylene transfer and carbometalation pathways are involved in both intermolecular and intramolecular reaction pathways. On the basis of the energetics of the reaction pathways, the methylene transfer pathway is favored over the carbometalation pathway in the whole reactions. Our computational results are in good agreement with the experimental results performed by G.A. Molander and L.S. Harring.     

On the mechanism and stereochemistry of chiral lithium-carbenoid-promoted cyclopropanation reactions

An investigation into the mechanism and stereochemistry of chiral lithium-carbenoid-promoted cyclopropanation reactions by using density functional theory (DFT) methods is reported. Previous work suggested that this type of cyclopropanation reaction may proceed by competition between a methylene-transfer mechanism and a carbometalation mechanism. In this paper, it is demonstrated that the intramolecular cyclopropanation reactions promoted by chiral carbenoids 1 and 2 proceed by the methylene-transfer mechanism. The carbometalation mechanism was found to have a much higher reaction barrier and does not appear to compete with the methylene-transfer mechanism. The Lewis base group does not enhance the carbometalation pathway enough to compete with the methylene-transfer pathway. The present computational results are consistent with experimental observations for these cyclopropanation reactions. The factors governing the stereochemistry of the intramolecular cyclopropanation reaction by the methylene-transfer mechanism were examined to help elucidate the origin of the stereoselectivity observed in experiments. Both the directing group and the configuration at the C(1) centre were found to play a key role in the stereochemistry. Carbenoid 1 has a chiral C(1) centre of R configuration. The Lewis base group directs the cyclization of carbenoid 1 to form a single product. In contrast, the Lewis base group cannot direct the cyclization of carbenoid 2 to furnish a stereoselective product due to the S configuration of the chiral C(1) centre in carbenoid 2. This relationship of the stereochemistry to the chiral character of the carbenoid has implications for the design of new efficient carbenoid reagents for stereoselective cyclopropanation.     

Theoretical study of the reactivity of (CH3)2AlCH2I promoted cyclopropanation reactions

Density functional theory calculations are reported for the cyclopropanation reactions of (CH₃)₂AlCH₂I with ethylene for two reaction channels: methylene transfer and carbometalation. These computational results suggest that the methylene transfer process is favored and the competition from the carbometalation pathway is negligible.     

Isodiiodomethane is the methylene transfer agent in cyclopropanation reactions with olefins using ultraviolet photolysis of diiodomethane in solutions: a density functional theory investigation of the reactions of isodiiodomethane, iodomethyl radical, and iodomethyl cation with ethylene.

We examine the chemical reactions of the isodiiodomethane (CH2I-I), .CH2I and CH2I(+) species with ethylene using density functional theory computations. The CH2I-I species readily reacts with ethylene to give the cyclopropane product and an I2 product via a one-step reaction with a barrier height of approximately 2.9 kcal/mol. However, the.CH2I and CH2I(+) species have much more difficult pathways (with larger potential barriers) to react with ethylene via a two-step reaction mechanism. Comparison of experimental results to our present calculation results indicates that the CH2I-I photoproduct species is most likely the methylene transfer agent for the cyclopropanation reaction of olefins via ultraviolet photoexcitation of diiodomethane.