Low-spin manganese(II) and cobalt(III) complexes of N-aryl-2-pyridylazophenylamines: new tridentate N,N,N-donors derived from cobalt mediated aromatic ring amination of 2-(phenylazo)pyridine. Crystal structure of a manganese(II) complex

Two new tridentate ligands of the type NH4C5NNC6H4N(H)C6H4(R) (R = H (HL1) or CH3 (HL2)) have been synthesized by the cobalt mediated direct phenyl ring amination of co-ordinated NH4C5NNC6H5. These bind to metal ions as monoanionic N,N,N-donors (L−), affording [MnIIL2] and [CoIIIL2]ClO4 complexes in very high yields. The compounds have low-spin electronic configurations. While the manganese complexes are paramagnetic with one unpaired electron (1.65–1.70 μB) the cobalt complexes are diamagnetic. Crystal structure determination of [Mn(L1)2] has revealed the presence of a distorted octahedral MnN6 co-ordination sphere. The two aza nitrogens of the anionic tridentate ligands approach the metal centre closest with Mn–N(aza) ca. 1.89 A. The other two Mn–N distances are: Mn–N(py), 2.00; Mn–N(amido), 1.95 A. There is a significant degree of ligand backbone conjugation in the co-ordinated ligands which has resulted in shortening of the C–N bond distances and also in lengthening of the diaza (N=N) distances. In fluid solution, [MnL2] species exhibit six line EPR spectra with low hyperfine constant (A = 75 G). In frozen dichloromethane–toluene (77 K), rhombic EPR spectra are observed, consisting of an isolated signal g3 (ca. 1.91) and two relatively close signals g1 and g2 (ca. 2.06 and 2.03 respectively). Both manganese as well as cobalt complexes display multiple redox responses. The manganese complexes show MnII ⇌ MnIII oxidation at ca. 0.38 V and the cobalt analogues display reversible CoIII ⇌ CoII reduction at −0.40 V. Electrogenerated [MnIIIL2]+ shows transitions in the near IR region.