Kinetic Analysis of the Reaction of Isoprene with Carbon Dioxide and a Nickel(0) Complex

Abstract

The reactions of the nickel(0) complex [Ni(bipy)(COD)] (COD = cyclooctadiene, bipy = 2,2‘-bipyridine) with isoprene (ip) in the absence and presence of carbon dioxide were investigated. A detailed kinetic analysis revealed that [Ni(bipy)(COD)] reacts reversible with ip and activation parameters for the forward and back reactions were calculated from a temperature dependence study to be the following: ΔH⧧ = 35 ± 5 kJ/mol, ΔS⧧ = −79 ± 16 J/(mol K) forward reaction (ip dependence); ΔH⧧ = 58 ± 2 kJ/mol, ΔS⧧ = 58 ± 10 J/(mol K) back-reaction (COD dependence at low temperatures). It could be shown that CO2 did not react with [Ni(bipy)(COD)] directly but with the nickel ip complex to form the product complex ((3−5-η3)-3-methyl-3-pentenylato)nickel bipyridine. The reaction proceeded in an associative way, during which CO2 was inserted into a Ni−C bond in an oxidative coupling step. The activation parameters were calculated to be ΔH⧧ = 25 ± 7 kJ/mol and ΔS⧧ = − 184 ± 24 J/(mol K).