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 L(1)H2, tBu L(2)H2, Cl L(3)H2), formed by reacting 2,6-dicarboxy-4-R-phenol with 2,2'-oxydianiline (2-aminophenylether), (2-NH2C6H4)2O, have been determined. Reaction of L(n)H2 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 L(4)H2, tBu L(5)H2) were conducted; the complexes [(AlMe)(AlMe2)L(5)]·2¼MeCN (7·2¼MeCN) and [(AlEt2)2L(4)] (8) were isolated. Use of limited AlEt3 with L(3)H2 or L(5)H2 afforded mononuclear bis(macrocyclic) complexes [Al(L(3))(L(3)H)]·4toluene (9·4toluene) and [Al(L(5))(L(5)H)]·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.