Influence of Temperature and Pressure on Cyclic Carbonate Synthesis Catalyzed by Bimetallic Aluminum Complexes and Application to Overall <i>syn</i>-Bis-hydroxylation of Alkenes

The effect of moderate temperatures (22–100 °C) and pressures (1–10 bar) on the synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by a combination of bimetallic aluminum complexes and tetrabutylammonium bromide is investigated. The combined bimetallic complex and tetrabutylammonium bromide catalyst system is shown to be an order of magnitude more active than the use of tetrabutylammonium bromide alone at all temperatures and pressures studied. At the higher temperatures and pressures used, disubstituted epoxides become substrates for the reaction and it is shown that reactions proceed with retention of the epoxide stereochemistry. This allowed a route for the overall <i>syn-</i>bis-hydroxylation of alkenes to be developed without the use of hazardous metal based reagents. At higher pressures it is also possible to use compressed air as the carbon dioxide source

Bimetallic Aluminum(salen) Catalyzed Synthesis of Oxazolidinones from Epoxides and Isocyanates

The bimetallic aluminum­(salen) complex [Al­(salen)]₂O is shown to catalyze the synthesis of oxazolidinones from epoxides and isocyanates. The reaction is demonstrated to proceed with overall retention of epoxide stereochemistry, and both aromatic and aliphatic isocyanates can be used as substrates. In contrast to the corresponding reactions between epoxides and carbon dioxide or carbon disulfide which are also catalyzed by [Al­(salen)]₂O, no cocatalyst is needed in the reactions with isocyanates. A mechanism is proposed which involves breaking and reforming of the Al–O–Al unit during the catalytic cycle, and this is supported by results obtained using monometallic catalysts