In the presence of Dawson-type polyoxotungstate, α 2-[(n-C 4H 9) 4] (11-n)P 2W 17O 61(M n+·Br)[abbreviated as P 2W 17M·Br, M=Co(Ⅱ), Mn(Ⅲ), Cu(Ⅱ)] and saturated [(n-C 4H 9) 4N] 6P 2W 18O 62(abbreviated as P 2W 18), cycloaddition reaction of carbon dioxide to propylene oxide were studied under moderate reaction conditions without any additional organic solvents. The experimental results indicated that the synthesis of propylene carbonate was completed in 98% yield and 100% selectivity by using {P 2W 17Co·Br} as the catalyst, while the P 2W 18 complex showed the lowest catalytic activity with less than 1% yield of propylene carbonate. The dependency of the catalytic activity on transition metal of mono-substituted polyoxometalate, P 2W 17M·Br, as well as the nucleophilicity of the bromide ion was concluded from the process analysis.
