Three sterically-enhanced 2-imino-6-(1-naphthyl)pyridines, 2-{CMe=N(Ar)}-6-(1-C
10H
7)C
5H
3N [Ar = 2,6-
i-Pr
2C
6H
3 (
L1dipp), 2,4,6-
i-Pr
3C
6H
2 (
L1tripp), 4-Br-2,6-
i-Pr
2C
6H
2 (
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-C
10H
7)C
5H
3N with the corresponding aniline. Treatment of
L1dipp,
L1tripp and
L1Brdipp with two equivalents of AlMe
3 at elevated temperature affords the distorted tetrahedral 2-(amido-prop-2-yl)-6-(1-naphthyl)pyridine aluminum dimethyl complexes, [2-{CMe
2N(Ar)}-6-(1-C
10H
7)C
5H
3N]AlMe
2 [Ar = 2,6-
i-Pr
2C
6H
3 (
1a), 2,4,6-
i-Pr
3C
6H
2 (
1b), 4-Br-2,6-
i-Pr
2C
6H
2 (
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 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.
Full article
