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Catalysts 2015, 5(3), 1425-1444; doi:10.3390/catal5031425

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

1
Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, UK
2
Laboratoire de Chimie, Catalyse, Polymères et Procédés, Université de Lyon, CNRS-UCBL, 43 Boulevard du 11 Novembre 1918, Villeurbanne 69616, France
*
Author to whom correspondence should be addressed.
Academic Editor: Carl Redshaw
Received: 9 July 2015 / Revised: 27 July 2015 / Accepted: 31 July 2015 / Published: 11 August 2015
(This article belongs to the Special Issue Molecular Catalysis for Precise Olefin Polymerization and ROP 2015)
View Full-Text   |   Download PDF [837 KB, uploaded 11 August 2015]   |  

Abstract

Three sterically-enhanced 2-imino-6-(1-naphthyl)pyridines, 2-{CMe=N(Ar)}-6-(1-C10H7)C5H3N [Ar = 2,6-i-Pr2C6H3 (L1dipp), 2,4,6-i-Pr3C6H2 (L1tripp), 4-Br-2,6-i-Pr2C6H2 (L1Brdipp)], 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 L1dipp, L1tripp and L1Brdipp 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 1a1c reveal that complexation has resulted in concomitant C–C bond formation via methyl migration from aluminum to the corresponding imino carbon in L1aryl; 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 L1dipp and L1tripp. View Full-Text
Keywords: aluminum; naphthyl-substituted N,N-pyridine-alkylamide; ring opening polymerization; ε-caprolactone; electronic effect aluminum; naphthyl-substituted N,N-pyridine-alkylamide; ring opening polymerization; ε-caprolactone; electronic effect
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Armitage, A.P.; Boyron, O.; Champouret, Y.D.M.; Patel, M.; Singh, K.; Solan, G.A. Dimethyl-Aluminium Complexes Bearing Naphthyl-Substituted Pyridine-Alkylamides as Pro-Initiators for the Efficient ROP of ε-Caprolactone. Catalysts 2015, 5, 1425-1444.

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