BULKY SUBSTITUENT EFFECTS ON THE IRON(III) COMPLEXATION OF 1,4,7-TRIAZACYCLONONANE

The synthesis of two sterically encumbered macrocycles, N,N',N''-triis opropyl-1,4,7-triazacyclononane (1) and N,N',N''-triisobutyl-1,4,7-tri azacyclononane (2), and their reactions with iron(III) have been inves tigated. In alcoholic solvents, a 1:1 mixture of either 1 or 2 and FeC l3 - 6H2O does not result in complex formation. Instead, the macrocycl es are singly protonated with the iron being incorporated into the ani on. The structure of (1-H)+(FeCl4)- was determined by single crystal X -ray methods. Crystals are orthorhombic, space group Pbca (No. 61), wi th the following unit cell parameters: a = 14.921(2), b = 17.765(2), c = 17.414(2) angstrom, V = 4616.0(10) angstrom3 and Z = 8. The structu re of (2.H)+2(Fe2OCl6)2- was also determined. Crystals are triclinic, space group P1BAR (No. 2) with the following unit cell parameters: a = 9.3543(10), b = 10.1002(11), c = 14.4167(14) angstrom, alpha = 85.185 (8), beta = 73.395(8), gamma = 73.198(8)-degrees, V = 1246.6(2) angstr om3 and Z = 2. The reactivity of 1 and 2 with iron(III) is then compar ed to that of the well-studied macrocycles, 1,4,7-triazacyclononane an d N,N',N''-trimethyl-1,4,7-triazacyclononane. The inability of 1 and 2 to serve as ligands to iron(III) in protic media is attributed to ste ric interactions involving the bulky alkyl appendages of the macrocycl es.