Monomeric or Dimeric Aluminum Complexes as Catalysts for Cycloaddition between CO sub(2) and Epoxides

A monomeric aluminum complex containing aliphatic tetradentate ligand L1 (HOCMe sub(2)CH sub(2)NMeC H sub(2)CH sub(2)NMeCH sub(2 )CMe sub(2)OH) was synthesized and used as a catalyst for cycloaddition between CO sub(2) and epoxides in the presence of PPNCl as a cocatalyst. To check the effect of ligand L1, coordinated to the aluminum center, on the activity of cycloaddition, the new ligand HOCMe sub(2)CH sub(2)NMe sub(2), which corresponds to half of L1, was systematically designed to make monomeric or dimeric aluminum complexes. Comparison of the catalytic properties of the aluminum complex containing the tetradentate ligand with those of the two related aluminum complexes containing the bidentate ligand under the same conditions revealed that the first system showed higher activity than the other two for cycloaddition between CO sub(2) and epoxides in the presence of PPNCl, which was the best cocatalyst out of the six compounds nBu sub(4)PBr, nBu sub(4)NCl, nBu sub(4)NBr, nBu sub(4)NI, DMAP, and PPNCl. The aluminum complexes 1-3 demonstrate catalytic activity for cycloaddition between CO sub(2) and epoxides in the presence of cocatalysts.