A single centre aluminium(III) catalyst and TBAB as an ionic organo-catalyst for the homogeneous catalytic synthesis of styrene carbonate

A non-symmetrical aluminium complex containing a single metal centre has been synthesised and used as a catalyst in the cycloaddition reaction of carbon dioxide to styrene oxide to yield a cyclic carbonate. The reaction proceeds to around 70% conversion using the catalyst alone; however, it can be increased to 90% conversion with the addition of tetrabutylammonium bromide (TBAB) as a co-catalyst. Interestingly, the reaction proceeds as well with the organo-catalyst TBAB alone as it does with the aluminium catalyst alone. This offers the potential for reduced cost processing and scale-up of the reaction through elimination of the aluminium catalyst due to reduced catalyst costs and ease of separation of TBAB as a salt from the reaction mixture. The rate constants for the aluminium catalysed reactions were determined as a function of process temperature in the range 80–150 °C, as well as the activation energies for the reactions determined from the Arrhenius plots. The activation energy for the aluminium catalyst alone was determined to be 34 kJ mol−1, while adding TBAB as a co-catalyst reduced the activation energy by 11 kJ mol−1.