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)(Im)(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)]·0.5C6H6 and [Na(222)][Fe(T-p-OMePP)(SH)]·C6H5Cl (222 = Kryptofix-222). Characterization by single-crystal X-ray analysis, mass spectrometry, and Mössbauer 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) Å are longer than all reported values of [FeII(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(II) species.