Structural studies of Schiff-base [2 + 2] macrocycles derived from 2,2′-oxydianiline and the ROP capability of their organoaluminium complexes

Abstract

The molecular structures of a number of solvates of the [2 + 2] Schiff-base macrocycles {[2-(OH)-5-(R)-C₆H₂-1,3-(CH)₂][O(2-C₆H₄N)₂]}₂ (R = Me L¹H₂, tBu L²H₂, Cl L³H₂), formed by reacting 2,6-dicarboxy-4-R-phenol with 2,2′-oxydianiline (2-aminophenylether), (2-NH₂C₆H₄)₂O, have been determined. Reaction of LⁿH₂ with two equivalents of AlR′₃ (R′ = Me, Et) afforded dinuclear alkylaluminium complexes [(AlR′₂)₂L^1–3] (R = R′ = Me (1), R = tBu, R′ = Me (2), R = Cl, R′ = Me (3), R = Me, R′ = Et (4), R = tBu, R′ = Et (5), R = Cl, R′ = Et (6)). For comparative studies, reactions of two equivalents of AlR′₃ (R′ = Me, Et) with the macrocycle derived from 2,2′-ethylenedianiline and 2,6-dicarboxy-R-phenols (R = Me L⁴H₂, tBu L⁵H₂) were conducted; the complexes [(AlMe)(AlMe₂)L⁵]·2¼MeCN (7·2¼MeCN) and [(AlEt₂)₂L⁴] (8) were isolated. Use of limited AlEt₃ with L³H₂ or L⁵H₂ afforded mononuclear bis(macrocyclic) complexes [Al(L³)(L³H)]·4toluene (9·4toluene) and [Al(L⁵)(L⁵H)]·5MeCN (10·5MeCN), respectively. Use of four equivalents of AlR′₃ led to transfer of alkyl groups and isolation of the complexes [(AlR′₂)₄L^1′–3′] (R = L^2′, R′ = Me (11); L^3′, R′ = Me (12); L^1′, R′ = Et (13); L^2′, R′ = Et (14); L^3′, R′ = Et (15)), where L^1′–3′ is the macrocycle resulting from double alkyl transfer to imine, namely {[2-(O)-5-(R)C₆H₂-1-(CH)-3-C(R′)H][(O)(2-(N)-2′-C₆H₄N)₂]}₂. Molecular structures of complexes 7·2¼MeCN, 8, 9·4toluene, 10·5MeCN and 11·1¾toluene·1¼hexane are reported. These complexes act as catalysts for the ring opening polymerisation (ROP) of ε-caprolactone and rac-lactide; high conversions were achieved over 30 min at 80 °C for ε-caprolactone, and 110 °C over 12 h for rac-lactide.