Aluminum Complexes with Bidentate N,N‐Dialkylaniline–arylamido Ligands: Synthesis, Structures, and Catalytic Properties for Efficient Ring‐Opening Polymerization of ϵ‐Caprolactone

Abstract

A number of Al complexes bearing bidentate N,N‐dialkylaniline–arylamido ligands, ortho‐(ArNCH2)C6H4NR2AlMe2 (R = Me, Ar = 2,6‐iPr2C6H3, 3a; 2,6‐Et2C6H3, 3b; 2,6‐Me2C6H3, 3c; 4‐MeC6H4, 3d; Ph, 3e; and R = Et, Ar = 2,6‐iPr2C6H3, 3f; 2,6‐Me2C6H3, 3g; Ph, 3h), have been synthesized from the reaction of the corresponding free ligands, ortho‐(ArNHCH2)C6H4NR2 (R = Me, Ar = 2,6‐iPr2C6H3, 2a; 2,6‐Et2C6H3, 2b; 2,6‐Me2C6H3, 2c; 4‐MeC6H4, 2d; Ph, 2e; and R = Et, Ar = 2,6‐iPr2C6H3, 2f; 2,6‐Me2C6H3, 2g; Ph, 2h), with AlMe3 (1 equiv.). All complexes were characterized by 1H and 13C NMR spectroscopy and elemental analysis. Single‐crystal X‐ray diffraction analysis of complexes 3c and 3e revealed that these Al complexes have a distorted tetrahedral geometry around the metal center. All complexes were found to be efficient catalysts for the ring‐opening polymerization of ϵ‐caprolactone (CL) in the presence of benzyl alcohol, and complexes 3a–h catalyze the polymerization of CL in a living fashion. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Synthesis and characterization of aluminum and zinc complexes supported by pyrrole-based ligands and catalysis of the aluminum complexes toward the ring-opening polymerization of ɛ-caprolactone

“…Complex 8/BnOH exhibits much higher activity than complexes 4ae4c/BnOH systems. At 60 C 8/BnOH system leads to 90% monomer conversion within 2 min, exhibiting comparable activity to that of N,N-dialkylaniline-arylamidoaluminum/BnOH [36]. The determined molecular weight by GPC closely matches the theoretical value, showing the catalytically active species to be stable at the reaction temperature.…”

“…During the polymerization an exchange takes place between the growing polymer chains and the free alcohol, which generates PCL and a new benzyloxyaluminum molecule (Scheme 3) [39]. However, it is possible that the two methyl groups in 4a were replaced by two OBn groups through reaction of 4a with two equiv of BnOH and two polymer chains grow simultaneously at the metal center [36]. A well linear relationship of the concentration change of the monomer versus time supports the polymerization to be controlled (Fig.…”

Well‐controlled ring‐opening polymerization of cyclic esters catalyzed by aluminum amido complexes: Kinetics and mechanism

“…Complex 1 crystallizes in a monoclinic space group P2(1)/c, and the aluminum center is coordinated by the two nitrogen donors of the ligand and two methyl groups in a distorted tetrahedral geometry. The N1‐Al1‐N2 bond angle of 96.62(7)°, smaller than the ideal tetrahedral bond angle of 109.5°, is close to those in related known Al complexes …”

Zinc Complexes of Piperazinyl‐Derived Aminephenolate Ligands: Synthesis, Characterization and Ring–Opening Polymerization Activity

“…The more acute bond angles around Zn, O(1)–Zn(1)–N(1) 96.82(5)°, can most probably be associated with the bite of the six‐membered C 3 NZnO chelate ring. This ring adopts a legless chair34 or slight sofa1 conformation with the C(6) atom forming the backrest and situated ca. 0.76 Å out of Zn(1)–O(1)–C(20)–C(7)–N(1) plane.…”