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

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 1a-1c 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 > 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.

Use of Metal Catalysts Bearing Schiff Base Macrocycles for the Ring Opening Polymerization (ROP) of Cyclic Esters

“…Treatment with either two or four equivalents of R 3 Al afforded the complexes 13-18 and 19-22, respectively (see Scheme 4) [13]. The structure of the compound 19 is shown in Figure 1, and reveals that, as for 5, intramolecular regioselective methyl transfer to two imine moieties (originating from the same dianiline) of the macrocycle has occurred; such methyl transfers are well established in imine chemistry [26][27][28][29][30]. The bonding in 19 is asymmetrical in that one of the aluminium centres is five-coordinate, whilst the other three are distorted tetrahedral.…”

“…Furthermore, the systems 27 and 29 exhibit an induction period that, following a 15%-20% Scheme 7. Zinc complexes (27)(28)(29)(30)(31)(32).…”

Crystal structure of (acetonitrile-κN)iodido(2-(naphthalen-1-yl)-6-{1-[(2,4,6-trimethylphenyl)imino]ethyl}pyridine-κ2N,N′)copper(I)

“…Elsewhere, these compounds have been reported to be luminescent (Aslanidis et al, 2010;Gallego et al, 2012) and exhibit corrosion inhibiting properties (Tian et al, 2004). The structures of metal complexes bearing naphthyl-substituted N,N-pyridine-alkylamides were reported by Armitage et al (2015) and related structures were presented by Wattanakanjana et al (2014). Cotton et al (1999) highlighted details of the affinity of nitrile ligands for Cu I ions.…”

Molecular Catalysis for Precise Olefin Polymerization and ROP 2015

“…In this Special Issue, manuscripts focusing on aspects of new catalyst systems for the homo-or co-polymerization of α-olefins, on the ring opening polymerization (ROP) of ε-caprolactone, and on co-polymerizations involving CO 2 /cyclohexene oxide are presented [3][4][5][6][7][8]. This work will be of immense interest to those involved in catalyst design, organometallic chemistry and polymer synthesis.…”

“…In the first contribution, Solan and coworkers have employed bulky 2-imino-6-(1-napthyl)pyridine ligation at aluminium, and have studied the impact of employing N bound aryl groups bearing para substituents with differing electronic properties on the ROP ofε-caprolactone. Upon activation with benzyl alcohol, the system employing the electron donating iPr group at the para position proved to be the most active, for example at 100% conversion was achieved at 50˝C over 1 h. However, given the bromide derivative was move active that that containing a para-hydrogen, the rate of polymerization is thought to be determined by a number of factors including alkoxide nucleophilicity and the Lewis acidity at the metal [3]. The related 2-(Phenyl-2-olate)-6-(1-amidoalkyl)pyridine dimethylaluminium complexes have also shown promise in the ROP of ε-caprolactone [9].…”