Synthesis and Properties of Iron(II) and Manganese(II) Complexes Derived from a Topologically Constrained Pentadentate Ligand

The novel bicyclic pentadentate ligand 5-methyl-1,5,9,24,25-pentaazapentacyclo[7.7.7.5.5]pentacosane-11,13,15,18(25),20,22-hexene (L1) has been synthesized. Because of its cross-bridged topology it exhibits a relatively
rigid preorganized conformation especially appropriate to complex formation, as shown by the crystal structure
of the monoprotonated ligand salt, HL1ClH2O [orthorhombic, P212121, a = 9.4405(5) Å, b = 13.3617(5) Å, c =
16.710(1) Å]. The complexes of L1 with both iron(II) and manganese(II) have been characterized, including the
crystal structures of [FeL1CH3CN][FeCL4] and [MnL1Cl][PF6] [monoclinic, P21/n, a = 10.0460(5) Å, b = 19.237(9)
Å, c = 15.6254(8) Å, β = 95.97(2)° and a = 7.745(2) Å, b = 22.786(4) Å, c = 14.639(4) Å, β = 105.074(10)°
respectively]. The manganese complex is high spin with μeff = 5.96 and θ = 2.5 ± 0.8 cm-1, indicating weak
ferromagnetic interactions. The reactions of the complexes with tert-butyl hydroperoxide and hydrogen peroxide
have been shown by ESR spectroscopy to produce the tert-butyl peroxyl and hydroperoxyl radicals, as evidenced
by their spin adducts with the spin traps N,N-dimethyl-1-pyrroline-N-oxide and N-tert-butyl−phenyl-nitrone.