97073-98-8Relevant academic research and scientific papers
Electronic and structural properties of a reactive metalloporphyrin with N-oxide axial ligands. Crystal and molecular structure of bis(2,6-lutidine N-oxide) (tetraphenylporphinato)manganese(III) perchlorate
Hill, Craig L.,Williamson, Michael M.
, p. 3024 - 3030 (2008/10/08)
Manganese and iron porphyrins are known to catalyze the transfer of oxygen from amine N-oxides to hydrocarbon substrates, yet no reactive metalloporphyrin complex containing amine N-oxide axial ligands has been structurally characterized to date. An aromatic amine N-oxide, 2,6-lutidine N-oxide, has been found that forms relatively stable, isolable, soluble, and crystalline metalloporphyrin complexes. Treatment of MnIIITPP(ClO4) with 2.5 equiv of 2,6-lutidine N-oxide in toluene solution followed by the addition of n-heptane produces two solvated crystalline modifications of the six-coordinate cationic metalloporphyrin complex bis(2,6-lutidine N-oxide)(tetraphenylporphinato)manganese(III) perchlorate (1). The magnetic moment (4.9 μB at 25°C), electronic spectrum (λ 325-700 nm), and 1H NMR spectral characteristics from -40 to +60°C of 1 clearly establish the ground electronic state of the complex to be a d4 high-spin (S = 2) MnIII system in contrast to the Mn porphyrin iodosylbenzene species characterized previously. The magnitudes, alternating signs, and temperature dependencies of the isotropic shifts of the axial N-oxide hydrogen atoms indicate clearly that these shifts are primarily contact in origin and arise through a π-delocalization mechanism. Complex 1 crystallizes in the purple-red prism habit as a heptane solvate in the monoclinic space group C2/c, with Z = 8. The unit cell has a = 36.644 (12) A?, b = 12.3158 (15) A?, c = 24.096 (6) A?, α = 89.976 (16)°, β = 95.807 (23)°, and γ = 90.073 (20)°. The Mn atom is effectively in the mean plane defined by the 24-atom porphyrin core, and the dMn-N(Por) values are typical for a S = 2 MnIII porphyrin complex. The bonds to the axial oxygen atoms are very long, dMn-O = 2.263 (4) and 2.264 (4) A?, in accord with the axial σ-antibonding character of a d4 high-spin complex, and the N-O bonds of N-oxide moieties are minimally perturbed upon complexation to manganese, dN-O = 1.331 (7) and 1.330 (6) A?. Complex 1 is six-coordinate both in the solid state and in solution from -40 to +60°C.
