Structural and spectroscopic features of a cis (hydroxo)-Fe^III-(carboxylato) configuration as an active site model for lipoxygenases

In our preliminary communication (Ogo, S.; Wada, S.; Watanabe, Y.; Iwase, M.; Wada, A.; Harata, M.; Jitsukawa, K.; Masuda, H.; Einaga, H. Angew. Chem., Int. Ed. 1998, 37, 2102-2104), we reported the first example of X-ray analysis of a mononuclear six-coordinate (hydroxo)iron(III) non-heme complex, [Fe^III(tnpa)(OH)(RCO₂)]-CIO₄ [tnpa = tris(6-neopentylamino-2-pyridylmethyl)amine; for 1, R = C₆H₅], which has a characteristic cis (hydroxo)-Fe^III-(carboxylato) configuration that models the cis (hydroxo)-Fe^III-(carboxylato) moiety of the proposed (hydroxo)- iron(III) species of lipoxygenases. In this full account, we report structural and spectroscopic characterization of the cis (hydroxo)-Fe^III-(carboxylato) configuration by extending the model complexes from 1 to [Fe^III(tnpa)(OH)(RCO₂)]-CIO₄ (2, R = CH₃; 3, R = H) whose cis (hydroxo)-Fe^III-(carboxylato) moieties are isotopically labeled by ¹⁸OH^-, ¹⁶OD^-, ¹⁸OD^-, ¹²CH₃¹² C¹⁸O₂^-, ¹²CH₃¹³C¹⁶ O₂^-, ¹³CH₃¹²C¹⁶ O₂^-, ¹³CH₃¹³C¹⁶ O₂^-, and H¹³C¹⁶O₂^-. Complexes 1-3 are characterized by X-ray analysis, IR, EPR, and UV-vis spectroscopy, and electrospray ionization mass spectrometry (ESI-MS).