Kinetic studies on the reactions of tricarbonyl(η-cyclo-octa-1,3-diene)-, tricarbonyl(η-cyclohexa-1,3-diene)-, and tricarbonyl(η-cyclohepta-1,3,5-triene)-iron complexes with triphenylphosphine

Abstract

Tricarbonyl(η-cycle-octa-1,3-diene) iron reacts smoothly with excess of triphenylphosphine via a second-order process to form trans-[Fe(CO)₃(PPh₃)₂]. At 60 °C in n-heptane: k₂=(3·15 ± 0·08)× 10^–3 l mol^–1 s^–1, ΔH^‡= 20·76 ± 0·22 kcal mol^–1, and ΔS^‡=–8·0 ± 0·6 cal K^–1 mol^–1. In contrast, tricarbonyl (η-cyclohepta-1,3-diene)iron and tricarbonyl(η-cyclohexa-1,3-diene)iron do not react with triphenylphosphine under these conditions. The last complex undergoes a CO-dissociative reaction at high temperatures (ΔH^‡= 42·1 ± 0·8 kcal mol^–1 and ΔS^‡= 16·5 ± 1·8 cal K^–1 mol^–1) with retention of the olefin. Tricarbonyl(η-cyclohepta-1,3,5-triene)iron is similarly unreactive, but its reaction with triphenylphosphine at 154 °C involves both first- and second-order processes.