Tetrachloromethane addition to norbornene catalyzed by lanthanide(III) compounds

Abstract

Tetrachloromethane addition to olefi ns, a particular case of telomerization, is one among the methods of carbon-carbon bonds formation. Effi cient catalysts for CCl4 addition to olefi ns are complexes of transition metals of VI–VIII groups [1]. Examples of lanthanide compounds application as telomerization catalysts are rare. The addition of fluoroalkyl iodides and polyhalomethanes to olefi ns catalyzed by samarium(II) iodide was described in [2, 3]. Aiming at extension of the range of catalysts promoting the telomerization reaction we report here on the study of catalytic activity in telomerization of lanthanide complexes (complexes of praseodymium, neodymium, samarium, europium, gadolinium, terbium, and dysprosium) by an example of CCl4 addition to norbornene. In the presence of Pr(acac)3(H2O) 2 [Pr(acac)3(H2O) 2– (I)–CCl4, 0.03 : 1 : 1] at 140°С within 6 h CCl4 stereoselectively added to norbornene (I) leading to the formation of exo-2-(trichloromethyl)-endo-3chloro-bicyclo[2.2.1]heptane (II) in 26% yield. The addition of methanol [Pr(acac)3(H2O) 2–(I)–CCl4– CH3OH, 0.03 : 1 : 1 : 1] results in higher norbornene (I) conversion (up to 60%), but the presence of methanol has a negative consequence: a mixture of two isomers, exo-2-(trichloromethyl)-endo-3-chlorobicyclo[2.2.1]heptane (II) and exo-2-(trichloromethyl)exo-3-chlorobicyclo[2.2.1]heptane (III) forms in a ratio 6 : 1. Further research made it possible to optimize the ratios of reagents and the catalyst and also the reaction conditions. The increase in CCl4 concentration to 4 mmol [Pr(acac)3(H2O)2–(I)–CCl4, 0.03 : 1 : 4] favors the increase in the norbornene (I) conversion to 45%, at adding methanol [Pr(acac)3(H2O)2–(I)–CCl4–MeOH, 0.03 : 1 : 4 : 3, 140°С, 5 h] the yield of the adducts II, III mixture, 6 : 1, grows up to 90%. Yields of compounds II, III depend on temperature and are maximum (90%) at 140°С, at 130°С the yield is 60%, and at 100°С and below the reaction does not proceed. In the preceding study [4] we established that the reason of the activating effect of alcohol on the reaction between CCl4 and olefi ns was the formation of alkyl hypochlorites by reaction of alcohol with tetrachloromethane under the action of the catalyst. CH3OCl also formed in the presence of lanthanide complexes. In the reaction