Liquid-liquid two-phase cyclodimerization of 1,3-dienes by iron-nitrosyl dissolved in ionic liquids

The 1,3-butadiene cyclodimerization reaction by iron complexes, prepared in situ by reduction of [Fe(NO)(2)Cl](2) with metallic zinc, diethylaluminum choride or n-butyllithium, dissolved in 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF4, 1) or hexafluorophosphate (BMI.PF6, 2) ionic liquids is a typical two-phase catalytic reaction. The reaction performed in BMI.PF6, at 50 degreesC, furnished 4-vinyl-1-cyclohexene with 100% selectivity and TOF up to 1404 per hour. The 1,3-butadiene conversion is dependent on the nature of ionic liquid, reaction temperature and added phosphine. The products are removed from the reaction mixture by simple decanting. The recovered ionic catalyst solution can be reused several times without any significant changes in catalytic performance. Under similar reaction conditions, isoprene leads quantitatively to the mixture of cyclic dimers: 2-methyl-4-(1-methylethenyl)cyclohexene (3a), 1-methyl-4-(1-methylethenyl)cyclohexene (3b), 2,4-dimethyl-4-vinylcyclohexene (4a) and 1,4-dimethyl-4-vinylcyclohexene (4b). (C) 2001 Elsevier Science B.V. All rights reserved.