镧系金属有机配合物的研究XIV:三(环戊二烯基)稀土金属配合物-氢化钠体系对烯烃的还原反应

研究了九种稀土有机配合物CP3Ln(Ln=La,Pr,Nd,Sm,Tb,Y,Er,Yb和Lu)与氢化钠组成的一种新还原体系及与烯烃还原反应的结果.CP3Ln-NaH体系在45℃,四氢呋喃溶液中能程度不同地把1-己烯还原成己烷.还原活性与稀土金属离子的离子半径密切相关.活性顺序是轻稀土>中稀土>重稀土.以CP3Sm最高,CP3Yb最低.讨论了各种因素对还原的影响及还原机理.

Studies on organolanthanide complexes XIV: Reduction of olefins with tricyclopentadienyl lanthanide-sodium hydride

Reduction of 1-hexene with Cp3Ln-NaH (Cp = cyclopentadienyl, Ln = lanthanide group metal) at 45?affords, after hydrolysis, hexane. The reductive activities of Cp3Ln strongly depend upon the ionic radius of the trivalent rare earth ion. The decrease in activity of seven Cp3Ln is in agreement with the gradually decreasing radius of Ln3+, except for variable valency elements Sm3+ and Yb3+. Therefore the general activity decreases in the order: Cp3Sm > Cp3La > Cp3Pr > Cp3Nd > Cp3Tb > Cp3Y > Cp3Er > Cp3Lu > Cp3Yb. The reaction path was strongly affected by the molar ratio of Cp3Ln to 1-hexene. If the ratio of Cp3Ln/1-hexene > 1, reduction of 1-hexene occurred predominately. When the ratio of Cp3Ln/1-hexene was 0.05, isomerization of 1-hexene took place, generating 2-hexene in excellent yield with cis- and trans-isomers in a 1:1 ratio. Moreover, Cp3Ln-NaH system is also able to reduce regioselectively dienes which contain both a terminal olefin as well as an internal double bond. By using Cp3Sm-NaH as reducing agent, the regioselective reduction of 4-vinyl-1-cyclohexene affords 4-ethyl-1-cyclohexene in high yield. A probable mechanism is proposed for reduction of 1-hexene.