Highly Efficient Organocatalyzed Conversion of Oxiranes and CO2 into Organic Carbonates

A binary catalyst system based on tannic acid/NBu4X (X=Br, I) is presented as a highly efficient organocatalyst at very low catalyst loading for the coupling of carbon dioxide and functional oxiranes to afford organic carbonates in good yields. The presence of multiple polyphenol fragments within the tannic acid structure is considered to be beneficial for synergistic effects that lead to higher stabilization of the catalyst structure during catalysis. The observed turnover frequencies (TOFs) exceed 200h(-1) and are among the highest reported to date for organocatalysts in this area of CO2 conversion. This organocatalyst system presents a useful, readily available, inexpensive, and, above all, reactive alternative for most of the metal-based catalyst systems reported to date.