Triple ring contraction of a [2+2] macrocyclic ligand

Abstract

Schiff base condensation of 2,6-diformylpyridine and 1,3-diaminopropan-2-ol in the presence of a BaIItemplate ion yields a complex containing a [2+2] macrocycle, [Ba2(μ1,2-ClO4)2(H2L1)2], where H2L1 is 3,7,15,19,25,26-hexaazatricyclo[19.3.1.19,13]hexacosa-1(25),2,7,9(26),10,12,14,19,21,23-decaene-5,17-diol. On transmetallation with CuIIcations, the macrocycle undergoes three successive ring contractions, yielding crystals of (acetato-κO)[26,28-dioxa-3,7,15,19,25,27-hexaazahexacyclo[19.3.1.12,5.19,13.117,10.03,8]octacosa-1(25),9(27),10,12,14,21,23-heptaene-κ5N]copper(II) perchlorate, [Cu(CH3COO)(C20H22N6O2)]ClO4or [Cu(CH3COO)(L2)]ClO4, in which the macrocycle ring size has been reduced from 20 members in H2L1 to 16 inL2.