Sustainable and Stable Esterification Catalysts Made from Titanium–Bismuth Clusters

Titanate catalysts, such as titanium tetrabutoxide (TBT), have long been known to be effective polyesterification catalysts. However, their use on an industrial scale has been hindered by their sensitivity to moisture. Previously, this challenge has been addressed by using mixtures of titanate catalysts with tin-based catalysts, such as stannous octoate (SnOct), showing both a synergistic effect for hydrolytic stability and polyesterification activity. Unfortunately, due to toxicity concerns around tin catalysts, this efficient catalyst mixture is not a long-term viable solution. Herein we report that mixing TBT with bismuth neodecanoate (BiNeo) leads not only to greater reactivity but also improvements in hydrolytic stability of the catalyst under industrially relevant conditions while being nontoxic. We demonstrate that the 2:1 molar mixing ratio of TBT/BiNeo leads to the best hydrolytic stability. Enhanced stability of the catalyst led to increased turnovers for the catalyst vs TBT or BiNeo alone, while the inherent activity of the catalyst remained similar to monometallic systems.