Transition-metal-substituted keggin-type germanotungstates for catalytic conversion of carbon dioxide to cyclic carbonate

The tetra-n-heptylammonium salts of transition-metal-substituted (TMS) Keggin type germanotungstates [(n-C₇H₁₅) ₄N]_nGeW₁₁MO₃₉ (M = Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn ²⁺, n = 5 or 6) were found to be efficient catalysts for cyclic carbonates synthesis from epoxides and CO₂ under solvent-free and halogen-free condition. The catalytic activities were significantly influenced by the transition metal and the countercation and a plausible mechanism was proposed. Graphical Abstract: The tetra-n-heptylammonium salts of transition-metal-substituted (TMS) Keggin type germanotungstates [(n-C ₇H₁₅)₄N]_nGeW₁₁MO ₃₉ (M = Mn²⁺, Fe³⁺, Co²⁺, Ni ²⁺, Cu²⁺ and Zn²⁺, n = 5 or 6) were found to be efficient catalysts for cyclic carbonates synthesis from epoxides and CO ₂. The catalytic activities were significantly influenced by the transition metal.[Figure not available: see fulltext.]