Crystal Structures and Solution Behavior of Paramagnetic Divalent Transition Metal Complexes (Fe, Co) of the Sterically Encumbered Tridentate Macrocycles 1,4,7-R₃-1,4,7-Triazacyclononane: Coordination Numbers 5 (R = <i>i</i>-Pr) and 6 (R = <i>i</i>-Bu)

The coordination chemistry of the sterically hindered macrocyclic triamines, 1,4,7-R3-1,4,7-triazacyclononane (R = i-Pr, i-Pr3tacn, and R = i-Bu, i-Bu3tacn) with divalent transition metals has been investigated. These ligands form a series of stable novel complexes with the triflate salts MII(CF3SO3)2 (M = Fe, Co, or Zn) under anaerobic conditions. The complexes Fe(i-Pr3tacn)(CF3SO3)2 (2), [Co(i-Pr3tacn)(SO3CF3)(H2O)](CF3SO3) (3), [Co(i-Pr3tacn)(CH3CN)2](BPh4)2 (4), Zn(i-Pr3tacn)(CF3SO3)2 (5), [Fe(i-Bu3tacn)(CH3CN)2(CF3SO3)](CF3SO3) (6), Fe(i-Bu3tacn)-(H2O)(CF3SO3)2 (7), and Co(i-Bu3tacn)(CF3SO3)2 (8) have been isolated. The behavior of these paramagnetic complexes in solution is explored by their 1H NMR spectra. The solid-state structures of four complexes have been determined by X-ray single-crystal crystallography. Crystallographic parameters are as follows. 2: C17H33F6FeN3O6S2, monoclinic, P21/n, a = 10.895(1) Å, b = 14.669(1) Å, c = 16.617(1) Å, β = 101.37(1)°, Z = 4. 3: C17H35CoF6N3O7S2, monoclinic, P21/c, a = 8.669(2) Å, b = 25.538(3) Å, c = 12.4349(12) Å, β = 103.132(13)°, Z = 4. 6: C24H45F6FeN5O6S2, monoclinic, P21/c, a = 12.953(6) Å, b = 16.780(6) Å, c = 15.790(5) Å, β = 96.32(2)°, Z = 4. 7: C20H41F6FeN3O7S2, monoclinic, C2/c, a = 22.990(2) Å, b = 15.768(2) Å, c = 17.564(2) Å, β = 107.65(1)°, Z = 8. The ligand i-Pr3tacn leads to complexes in which the metal ions are five-coordinate, while it's isobutyl homologue affords six-coordinate complexes. This difference in the stereochemistries around the metal center is attributed to steric interactions involving the bulky alkyl appendages of the macrocycles.