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

Well-controlled ring-opening polymerization of cyclic esters initiated by dialkylaluminum β-diketiminates

“…[4][5][6][7] However, in the absence of alcohol, very few aluminum alkyl complexes can act as efficient initiators for the ROP of ε-caprolactone (ε-CL), because most of the aluminum alkyls showed no or very low activity towards the polymerization and the processes were poorly controlled. [8][9][10] The catalytic performances are greatly affected by the steric and electronic properties of the ligands in metal complexes, therefore, the choice of suitable ligands is of vital importance. Although some types of ligands have already been employed in the aluminum alkyl initiators, 8,11,12 aluminum complexes bearing N,N′-substituted β-diketiminate ("nacnac") ligands and their application in ROP of cyclic esters are still scarcely investigated.…”

Ring‐Opening Polymerization of ε‐Caprolactone Initiated by Aluminium Complexes Based on Pyridine‐Substituted Asymmetric β‐Diketiminate Ligands

“…The nitrogen atom of pyridine is not involved in the coordination. The Al–C(Me) bond lengths [1.941(6) and 1.950(6) Å] are shorter than those of reported aluminium complexes with β‐diketiminate ligands, which suggests that the substituents on the amino nitrogen atom influence the Al–C bond lengths of this type of complex.…”

“…Few reports about the ROP of ε‐caprolactone initiated by aluminium alkyls in the absence of benzyl alcohol were found,, owing to the no or very low activity of the aluminium alkyl compounds. Complexes 1 and 2 are very rare examples of aluminium alkyl compounds supported by β‐diketiminate ligands, which show moderate activity towards ROP of ε‐caprolactone in the absence of benzyl alcohol …”

“…It is proposed that, in most cases, only the aluminium oxides generated in situ from the reactions between aluminium alkyls with alcohols can initiate the ROP of ε‐caprolactone . Thus, benzyl alcohol was introduced into the polymerization system.…”

“…Many different types of ligands, for example, salen, Schiff base, ketiminate, etc., have been used as ancillary ligands to initiate the ROP of ε‐caprolactone. Aluminium complexes with β‐diketiminate ligands have been reported extensively; however, their applications in the ROP of ε‐caprolactone are still less explored . β‐Diketiminate is a kind of large π‐electron‐rich ligand, which can effectively stabilize coordinatively ‐unstable or coordinatively unsaturated central metals.…”