CO、CH_3-N≡C插入C_p~＊W(NO)(CH_2SiMe_3)(η~3-CH_2CHCHMe)中W-C键的选择性理论研究

Theoretical Study on CO and CH_3-N≡C Selective Insertion into the W-C Bond of C_p~＊ W(NO)(CH_2SiMe_3)(η~3-CH_2CHCHMe)

应用密度泛函理论计算,对CO、CH_3-N≡C插入C_p~*W(NO)(CH_2SiMe_3)(η~3-CH_2CHCHMe)中W-C键的选择性进行了理论研究.C_p~*W(NO)(CH_2SiMe_3)(η~3-CH_2CHCHMe)与CO反应时,CO选择性地插入W-CH_2SiMe_3键之间而不是W-CH_2CHCHMe键之间,研究结果表明,和与W相连的烯丙基碳原子相比,与W和Si相连的碳原子带有更多的负电荷,因而带正电的羰基碳原子更易进攻与W和Si相连的碳原子,合理的解释了实验事实.实验还证实,对于C_p~*W(NO)(CH_2SiMe_3)(η~3-CH_2CHCHMe)与CH_3-N≡C的反应,CH_3-N≡C选择性插入W-CH_2CHCHMe而不是W-CH_2SiMe_3,很显然插入的选择性与CO相比发生了逆转.研究发现导致的原因是,尽管CH_3-N≡C插入W-CH_2SiMe_3在动力学上仍然有利,但插入W-CH_2CHCHMe在热力学上有利,而且研究表明CH_3-N≡C的插入是一个热力学控制过程,正是这个热力学控制过程导致反应最终按CH_3-N≡C插入W-CH_2CHCHMe的方向进行,得到实验上得到的产物.

Selectivity of CO and CH3-N≡C insertion into the W-C bond of C＊pW（NO）（CH1SiMe3）（η3-CH2CHCHMe） has been studied by means of DFT calculations.For CO insertion, experiments demonstrate that CO selectively inserts into W-CH2SiMe3 rather than W-CH2CHCHMe. Our theoretical study gives a reasonable explanation that the C atom linking W and Si bears higher negative charge than the allylic C at- om linking W,and thus the carbonyl C atom bearing positive charge favorably attacks the C atom linking W and Si.As for CH3-N≡C insertion,experiments demonstrate that CH3-N≡C selectively inserts into W- CH2CHCHMe rather than W-CH2SiMe3. Our theoretical study gives a reasonable explanation that al- though the CH3-N≡C insertion into W-CHzSiMe3 is more favorable kinetically, the CH3-N≡C insertion into W-CH2CHCHMe is more favorable thermodynamically.And more important,we find the thermody- namic control is predominant, which is the reason leading to the product via the insertion into W- CH2CHCHMe.