Rh(Xantphos)L催化氢化肉桂醛和降冰片二烯间转移加氢甲酰化反应的理论研究

采用密度泛函理论方法 M11-L/6-31G(d,p)对氢化肉桂醛与降冰片二烯(nbd)在活化催化剂aRh(Xantphos)L,L=苯甲酸根,Xantphos=4,5-双二苯基膦-9,9-二甲基氧杂蒽]催化下发生转移加氢甲酰化反应生成主产物苯乙烯(3)的反应机理进行理论研究.结果表明,参与反应的醛类化合物在α碳(α-C)上应至少连接一个氢原子,这可以减少醛类反应物和抗衡离子的空间排斥作用.通过反应能垒图可见,受体nbd发生加氢甲酰化反应,促进了脱氢甲酰化反应的进行,进而促使整个转移加氢甲酰化循环不可逆进行.还研究了氢化肉桂醛发生脱羰化生成少量副产物苯乙烷(4)的机理过程.结果表明,苯甲酸根作为抗衡离子抑制了脱羰化反应的竞争,理论计算得到脱氢甲酰化反应的选择性为苯乙烯(3)∶苯乙烷(4)99∶1.简单醛(如丙醛)在活化催化剂a催化下更易于发生脱羰反应而不是脱氢甲酰化反应.

Theoretical Studies on the Mechanisms of Transfer Hydroformylation Between Hydrocinnamaldehyde and Norbornadiene Catalyzed by Rh(Xantphos) L Complexes

The mechanism of transfer hydroformylation reactions of hydrocinnamaldehyde with norbornadiene ( nbd) catalyzed by the catalyst a Rh( Xantphos) L] complex at M11?L/6?31G( d,p) was calculated( Pathway A) . The α?C in the reactive aldehyde molecules actually bonds with one hydrogen atom at least to reduce the steric interaction between the aldehyde reactant and counterion section in C—H oxidative addition step. A little of alkane products observed experimentally, the mechanism of reactive course of decarbonylation of hydrocinnamaldehyde(Pathway B) was calculated. The theoretical study indicates that decarbonylation reac?tion is suppressed and the selectivity for dehydroformylation is calculated to be( styrene∶phenylethane>99∶1) with benzoate as counterion. The calculation results show that simple aldehyde propanal would prefer dehydro?formylation reaction rather than decarbonylation reaction catalyzed by active catalyst a. Based on the reactive energy barrier profile, the hydroformylation of acceptor nbd accelerated the occurrence of dehydroformylation and made the whole transfer hydroformylation irreversible.