| Abstract
| - The synthesis of the topologically constrained pentadentate amine ligand L1 and its iron(II) and manganese(II) complexes is reported. Structures show that low spin iron(II) (in [FeL1CH3CN][FeCL4]) fits the constrained ligand better than the larger high spin manganese(II) (in [MnL1Cl][PF6]). The complexes show impressive kinetic stability in aqueous solution with respect to ligand dissociation. Only peroxyl radicals are detected as intermediates in the reaction with tert-butyl hydroperoxide or hydrogen peroxide.
- 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 relativelyrigid preorganized conformation especially appropriate to complex formation, as shown by the crystal structureof 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 thecrystal 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 weakferromagnetic interactions. The reactions of the complexes with tert-butyl hydroperoxide and hydrogen peroxidehave been shown by ESR spectroscopy to produce the tert-butyl peroxyl and hydroperoxyl radicals, as evidencedby their spin adducts with the spin traps N,N-dimethyl-1-pyrroline-N-oxide and N-tert-butyl−phenyl-nitrone.
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