Catalytic reduction of nitrous oxide to dinitrogen by carbon monoxide using Group 8 metal carbonyl anions

Abstract

Metal carbonyls [FeH(CO)₄]^–, [Fe₃(CO)₁₁]^2– and [Ru₃(CO)₁₂] in the presence of KO₂CMe in dimethyl sulfoxide are effective catalyst systems for the reduction of N₂O to N₂ by CO. The observed catalytic activity for [FeH(CO)₄]^– of 4.56 turnover number per h at 100 °C under a total pressure of less than 1 atm is the highest among the catalyst systems using KO₂CMe as the base. The kinetics of the reduction of N₂O by CO catalysed by the [FeH(CO)₄]^––KO₂CMe system was investigated. A first-order dependence of the rate on both P_N2O and the concentration of [FeH(CO)₄]^– was established. The activation parameters ΔH^‡ and ΔS^‡ are 56.1 kJ mol^–1 and –180 J K^–1 mol^–1, respectively. The ion [FeH(CO)₄]^– is converted into [Fe₂(CO)₈]^2– during the course of catalysis. The reaction of [Fe₂(CO)₈]^2– with N₂O yields 2.68 mol of N₂ and 1.38 mol of CO₂ per mol of the dinuclear species within 5 h at ambient temperature. This reaction is believed to be the process responsible for the catalytic reaction. A catalytic cycle including nucleophilic attack of [Fe₂(CO)₈]^2– on N₂O to give a N₂O–Fe adduct, followed by an interligand oxygen transfer from the co-ordinated N₂O to CO to give N₂ and CO₂, is proposed to account for the observed catalysis. Another possible mechanism involving an electron transfer between [Fe₂(CO)₈]^2– and N₂O as the first step is also discussed.