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 (L-1) 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, P2(1)2(1)2(1), a = 9.4405(5) Angstrom, b = 13.3617(5) Angstrom, c = 16.710(1) Angstrom]. The complexes of L-1 with both iron(II) and manganese(II) have been characterized, including the crystal structures of [FeL1CH3CN][FeCL4] and [MnL1Cl][PF6] [monoclinic, P2(1)/n, a = 10.0460(5) Angstrom, b = 19.237(9) Angstrom, c = 15.6254(8) Angstrom, beta = 95.97(2)degrees and a = 7.745(2) Angstrom, b = 22.786(4) Angstrom, c = 14.639(4) Angstrom, beta = 105.074(10)degrees respectively]. The manganese complex is high spin with mu(eff) = 5.96 and theta = 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.