Reversible CO2 Addition to a Si=O Bond and Synthesis of a Persistent SiO2 -CO2 Cycloadduct Stabilized by a Lewis Donor-Acceptor Ligand.

The donor-stabilized sila-ß-lactone 1 reacts with CO2 via a remarkable reversible [2+2]-cycloaddition reaction to form the spiro-cyclic silicon carbonate derivative 2. Furthermore, photolysis of 2 under pressure of CO2 affords the first persistent SiO2 -CO2 cycloadduct 3, presenting a Si2 O4 -like structure, which is stabilized by a Lewis donor-acceptor type ligand. As predicted by theoretical calculations, in marked contrast to the thermodynamically stable SiO2 dimer, the SiO2 -CO2 mixed cycloadduct 3 is labile and readily releases CO2 .

A Stable Monomeric SiO2 Complex with Donor-Acceptor Ligands.

Isolation of a monomeric SiO2 compound 3 as a stable donor-acceptor complex with two different ligands -a σ-donating ligand (pyridine, dimethylaminopyridine, N-heterocyclic carbene) and a donor-acceptor ligand (iminophosphorane)-is presented. The SiO2 complex 3 is soluble in ordinary organic solvents and is stable at room temperature in solution and in the solid state. Of particular interest, 3 remains reactive and can be used as a stable and soluble unimolecular SiO2 reagent.