Reversible CO 2 Addition to a Si=O Bond and Synthesis of a Persistent SiO 2 –CO 2 Cycloadduct Stabilized by a Lewis Donor–Acceptor Ligand

The donor‐stabilized sila‐β‐lactone 1 reacts with CO 2 via a remarkable reversible [2+2]‐cycloaddition reaction to form the spiro‐cyclic silicon carbonate derivative 2 . Furthermore, photolysis of 2 under pressure of CO 2 affords the first persistent SiO 2 –CO 2 cycloadduct 3 , presenting a Si 2 O 4 ‐like structure, which is stabilized by a Lewis donor–acceptor type ligand. As predicted by theoretical calculations, in marked contrast to the thermodynamically stable SiO 2 dimer, the SiO 2 –CO 2 mixed cycloadduct 3 is labile and readily releases CO 2 .