Carbonylative ring expansion of oxetane into γ-butyrolactone using bimetallic cobaltate catalysts: Insight into the deactivation mechanism

γ-butyrolactones and their derivatives serve as the fundamental building blocks for a wide range of biologically significant and synthetically challenging natural products, which find extensive applications in various high-demand chemicals. In this study, we have successfully established a facile and atom-efficient synthesis of γ-butyrolactones through the carbonylative ring expansion of oxetanes. We employed both homogeneous and heterogenized bimetallic catalysts ([HCP-TPPM][Co(CO)₄], where HCP refers to hyper cross-linked polymer and TPP denotes tetraphenylporphyrin, with M = Cr³⁺ and Al³⁺). While the homogeneous catalysts exhibited remarkable activity, the heterogeneous catalysts offered the distinct advantages of facilitating product separation and enabling catalyst recycling. Notably, during the catalyst recycling studies, we observed a decrease in catalytic activity attributed to cobaltate leaching. The hypothesis of cobaltate leaching through β-hydrogen elimination was validated by comparative studies using substrates with and without β-hydrogen in both batch and continuous flow catalytic processes.