Metal-salen molecular cages as efficient and recyclable heterogeneous catalysts for cycloaddition of CO2 with epoxides under ambient conditions

A salen based molecular cage, salen@cage, was synthesized and complexed with Co and Al to yield metal-salen molecular cages, Co(II)@cage, Co(III)@cage and Al(III)@cage. These cages were demonstrated to be efficient heterogeneous catalysts for the cycloaddition of CO2 with styrene oxide, achieving full conversion at 25 degrees C and 1 atm CO2. Good to excellent yields of various cyclic carbonates were also achieved under mild conditions. Al(III)@cage can be reused up to five times without any significant loss of its high catalytic activity. The capability to access a variety of heterogeneous organometallic catalysts with salen@cage offers new prospects for practical CO2 utilization and chemical manufacturing.