Synthetic Routes to Crystalline Complex Metal Alkyl Carbonates and Hydroxycarbonates via Sol-Gel Chemistry-Perspectives for Advanced Materials in Catalysis

Metal alkoxides are easily available and versatile precursors for functional materials, such as solid catalysts. However, the poor solubility of metal alkoxides in organic solvents usually hinders their facile application in sol-gel processes and complicates access to complex carbonate or oxidic compounds after hydrolysis of the precursors. In our contribution we have therefore shown three different solubilization strategies for metal alkoxides, namely the derivatization, the hetero-metallization and CO2 insertion. The latter strategy leads to a stoichiometric insertion of CO2 into the metal-oxygen bond of the alkoxide and the subsequent formation of metal alkyl carbonates. These precursors can then be employed advantageously in sol-gel chemistry and, after controlled hydrolysis, result in chemically defined crystalline carbonates and hydroxycarbonates. Cu- and Zn-containing carbonates and hydroxycarbonates were used in an exemplary study for the synthesis of Cu/Zn-based bulk catalysts for methanol synthesis with a final comparable catalytic activity to commercial standard reference catalysts.

Automated summary

Metal alkoxides are important precursors for functional materials, but their poor solubility in organic solvents limits their application in sol-gel processes. In this study, we propose three different solubilization strategies for metal alkoxides, including derivatization, hetero-metallization, and CO2 insertion. The CO2 insertion strategy allows for the formation of metal alkyl carbonates, which can be effectively used in sol-gel chemistry to synthesize crystalline carbonates and hydroxycarbonates with controlled hydrolysis. The synthesized Cu/Zn-based catalysts showed comparable catalytic activity to commercial standard reference catalysts for methanol synthesis.