Dimethyl-Aluminium Complexes Bearing Naphthyl-Substituted Pyridine-Alkylamides as Pro-Initiators for the Efficient ROP of ε-Caprolactone

Catalysts

Andrew P. Armitage¹  Olivier Boyron²  Yohan D. M. Champouret¹  Mehzabin Patel¹  Kuldip Singh¹  Gregory A. Solan¹ 

[1] Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, UK; E-Mails:;Laboratoire de Chimie, Catalyse, Polymères et Procédés, Université de Lyon, CNRS-UCBL, 43 Boulevard du 11 Novembre 1918, Villeurbanne 69616, France; E-Mail:

关键词: aluminum;    naphthyl-substituted N;    N-pyridine-alkylamide;    ring opening polymerization;    ε-caprolactone;    electronic effect;   

DOI  :  10.3390/catal5031425

来源: mdpi

【 摘 要 】

Three sterically-enhanced 2-imino-6-(1-naphthyl)pyridines, 2-{CMe=N(Ar)}-6-(1-C₁₀H₇)C₅H₃N [Ar = 2,6-i-Pr₂C₆H₃ (L1_dipp), 2,4,6-i-Pr₃C₆H₂ (L1_tripp), 4-Br-2,6-i-Pr₂C₆H₂ (L1_Brdipp)], differing only in the electronic properties of the N-aryl group, have been prepared in high yield by the condensation reaction of 2-{CMe=O}-6-(1-C₁₀H₇)C₅H₃N with the corresponding aniline. Treatment of L1_dipp, L1_tripp and L1_Brdipp with two equivalents of AlMe₃ at elevated temperature affords the distorted tetrahedral 2-(amido-prop-2-yl)-6-(1-naphthyl)pyridine aluminum dimethyl complexes, [2-{CMe₂N(Ar)}-6-(1-C₁₀H₇)C₅H₃N]AlMe₂ [Ar = 2,6-i-Pr₂C₆H₃ (1a), 2,4,6-i-Pr₃C₆H₂ (1b), 4-Br-2,6-i-Pr₂C₆H₂ (1c)], in good yield. The X-ray structures of 1a–1c reveal that complexation has resulted in concomitant C–C bond formation via methyl migration from aluminum to the corresponding imino carbon in L1_aryl; in solution, the restricted rotation of the pendant naphthyl group in 1 confers inequivalent methyl ligand environments. The ring opening polymerization of ε-caprolactone employing 1, in the presence of benzyl alcohol, proceeded efficiently at 30 °C producing polymers of narrow molecular weight distribution with the catalytic activities dependent on the nature of the substituent located at the 4-position of the N-aryl group with the most electron donating i-Pr derivative exhibiting the highest activity (1b > 1a > 1c); at 50 °C 1b mediates 100% conversion of the monomer to polycaprolactone (poly(CL)) in one hour. In addition to 1a, 1b and 1c, the single crystal X-ray structures are reported for L1_dipp and L1_tripp.

【 授权许可】

CC BY   
© 2015 by the authors; licensee MDPI, Basel, Switzerland.