MTO/H 2 O 2 /Pyrazole-Mediated N-Oxidation of meso-Tetraarylporphyrins and -chlorins, and S-Oxidation of a meso-Tetraaryldithiaporphyrin and -chlorin Subhadeep Banerjee, † Matthias Zeller, ‡ and Christian Bru ¨ckner* ,† Department of Chemistry, UniVersity of Connecticut, Unit 3060, Storrs, Connecticut 06269-3060, and Department of Chemistry, Youngstown State UniVersity, One UniVersity Plaza, Youngstown, Ohio 44555-3663 c.bruckner@uconn.edu ReceiVed March 11, 2009 The methyltrioxorhenium (MTO)/pyrazole-mediated H 2 O 2 oxidation of octaethylporphyrin and a number of meso-tetraarylporphyrins offers simple and good yielding access to the corresponding N-oxides, only few of which were prepared before. The crystal structure of a free base tetraarylporphyrin N-oxide demonstrates the degree to which the oxygenated pyrrole moiety is slanted with respect to the rest of the otherwise nearly planar macrocycle. The method is also suitable to the preparation of hitherto unknown chlorin N-oxides. Oxidation of meso-tetraphenyldithiaporphyrin and meso-tetraphenyldithiachlorin furnishes the corresponding novel S-oxides. The optical properties of the novel chromophores are described and rationalized. Introduction Porphyrin N-oxides, such as octaethylporphyrin (OEP) N- oxide 1, were first described in 1978 by Bonnett and Ridge. 1 Subsequently, it was shown that they could form metal complexes with Ni(II), Cu(II), Zn(II), Fe(III), and Tl(III) in which the oxygen bridges one N-M bond. 2-6 OEP N-oxide, in its free base or Ni(II) complex form, can be rearranged into a -oxochlorin or its metal complex, respectively. 2,7 A tet- raarylporphyrin N-oxide Fe(III) complex has been the source of an unusual ring-oxidized Fe(III) porphyrin complex. 8 The significance of the porphyrin N-oxide Fe(III) complexes with respect to possible heme degradation products or P-450 suicide reactions was also discussed. 1,3,9-12 N-Oxide 1, or its meso-tetraarylporphyrin analogues, 9,13 can be synthesized from their corresponding porphyrins by oxidation using either hypofluorous acid or organic acid peroxides, such as peracetic, permaleic acid, or m-CPBA. 2,3,14 Hypofluorous acid needs to be prepared fresh from gaseous fluorine and is po- * To whom correspondence should be addressed: Fax: (+1) 860 486-2981. Phone: (+1) 860 486-2743. † University of Connecticut. ‡ Youngstown State University. (1) Bonnett, R.; Ridge, R. J.; Appleton, E. H. J. Chem. Soc., Chem. Commun. 1978, 310–311. (2) Andrews, L. E.; Bonnett, R.; Ridge, R. J.; Appelman, E. H. J. Chem. Soc., Perkin Trans. 1 1983, 103–107. (3) Balch, A. L.; Chan, Y. W.; Olmstead, M.; Renner, M. W. J. Am. Chem. Soc. 1985, 107, 2393–2398. (4) Balch, A. L.; Chan, Y.-W.; Olmstead, M. M. J. Am. Chem. Soc. 1985, 107, 6510–6514. (5) Yang, F.-A.; Cho, K.-Y.; Chen, J.-H.; Wang, S.-S.; Tung, J.-Y.; Hsieh, H.-Y.; Liao, F.-L.; Lee, G.-H.; Hwang, L.-P.; Elango, S. Polyhedron 2004, 25, 2207–2214. (6) Yang, F.-A.; Guo, C.-W.; Chen, Y.-J.; Chen, J.-H.; Wang, S.-S.; Tung, J.-Y.; Hwang, L.-P.; Elango, S. Inorg. Chem. 2007, 46, 578–585. (7) Balch, A. L.; Chan, Y. W. Inorg. Chim. Acta 1986, 115, L45–L46. (8) Tsurumaki, H.; Watanabe, Y.; Morishima, I. J. Am. Chem. Soc. 1993, 115, 11784–11788. (9) Groves, J. T.; Watanabe, Y. J. Am. Chem. Soc. 1986, 108, 7836–7837. (10) Groves, J. T.; Watanabe, Y. J. Am. Chem. Soc. 1988, 110, 8443–8452. (11) Mizutani, Y.; Watanabe, Y.; Kitagawa, T. J. Am. Chem. Soc. 1994, 116, 3439–3441. (12) Rachlewicz, K.; Latos-Grazynski, L. Inorg. Chem. 1996, 35, 1136–1147. (13) Arasasingham, R. D.; Balch, A. L.; Olmstead, M. M.; Renner, M. W. Inorg. Chem. 1987, 26, 3562–3568. (14) For an alterative, nongeneral photochemical pathway toward the TidO complex of a porphyrin N-oxide, see: (a) Hoshino, M.; Yamamoto, K.; Lillis, J. P.; Chijimatsu, T.; Uzawa, J. Inorg. Chem. 1993, 32, 5002–5003. 10.1021/jo9005443 CCC: $40.75  2009 American Chemical Society J. Org. Chem. 2009, 74, 4283–4288 4283 Published on Web 05/07/2009