Hydrosulfide (HS-) Coordination in Iron Porphyrinates

Recent reports of potential physiological roles of hydrogen sulfide have prompted interest in heme-sulfide interactions. Heme-H2S and/or heme-HS- interactions could potentially occur during endogenous production, transport, signaling events, and catabolism of H2S. We have investigated the interaction of the hydrosulfide ion (HS-) with iron porphyrinates. UV-vis spectral studies show the formation of [Fe(Por)(SH)](-), [Fe(Por)(SH)(2)](2-), and the mixed-ligand species [Fe(Por)(lm)(SH)](-). UV-vis binding studies of [Fe(OEP)] and [Fe(T-p-OMePP)] (OEP = octaethylporphyrinate; T-p-OMePP = tetra-p-methoxyphenylporphyrinate) with HS- allowed for calculation of the formation constants and extinction coefficients of mono- and bis-HS- complexes. We report the synthesis of the first HS--bound iron(II) porphyrin compounds, [Na(222)][Fe(OEP)(SH)]center dot 0.5C(6)H(6) and [Na(222)][Fe(T-p-OMePP)(SH)]center dot C6H5Cl (222=Kryptofix-222). Characterization by single-crystal X-ray analysis, mass spectrometry, and Mossbauer and IR spectroscopy is all consistent with that of known sulfur-bound high-spin iron(II) compounds. The Fe-S distances of 2.3929(5) and 2.3887(13) angstrom are longer than all reported values of [Fe-II(Por)(SR)](-) species. An analysis of the porphyrin nonplanarity for these derivatives and for all five-coordinate high-spin iron(II) porphyrinate derivatives with an axial anion ligand is presented. In our hands, attempts to synthesize iron(III) HS- derivatives led to iron(I) species.