Dimethylaluminum complexes bearing a chiral diketiminate ligand: Synthesis, characterization and ring-opening polymerization of ε-caprolactone

Reaction of the chiral aliphatic N-substituted diketiminate ligand, N,N′-Di(R-phenylethyl)-2-amino-4-iminopent-2-ene (R,R-nacnacCH(Me)PhH), with AlMe3 affords the monomeric dimethylaluminum complex R,R-nacnacCH(Me)PhAlMe2 (R,R-1). Complex S,S-nacnacCH(i-Pr)PhAlMe2 (S,S-2) is prepared by S,S-nacnacCH(i-Pr)PhH and AlMe3. Complexes R,R-1 and S,S-2 are the first examples of chiral β-diketiminate ligands with main group metals. All these two complexes exhibit activity for the ring-opening polymerization of ε-caprolactone in the absence of alcohol, and complex R,R-1 shows a higher activity with a narrow molecular weight distribution (PDI = 1.17) in toluene.

The first example R,R-nacnacCH(Me)PhAlMe2 (R,R-1) of chiral β-diketiminate ligands with main group metals is prepared. Complex R,R-1 shows a high activity for the ring-opening polymerization of ε-caprolactone in the absence of alcohol, and has a good control over the polymerization reaction.Figure optionsDownload as PowerPoint slideHighlights
► Dimethylaluminum complexes bearing a chiral diketiminate ligand are synthesized.
► Complex R,R-1 initiates the ε-caprolactone polymerization in the absence of alcohol.
► Complex R,R-1 initiates the ε-caprolactone polymerization in a “controlled” fashion.