Reduction of iron porphyrin nitrate to the iron nitrosyl by HS/thiol. studies in sublimed layers.

Hemes play key roles in enzymatic production of the mammalian gasotransmitter NO by nitric oxide synthase as well as in conversion from inorganic nitrite. In the present study, we report a hitherto unknown pathway of nitrosyl formation thiol reduction of a iron porphyrin nitrate complex in the solid state.

Nitric Oxide Dioxygenation by O Adducts of Manganese Porphyrins.

We describe here nitric oxide dioxygenation (NOD) by the dioxygen manganese porphyrin adducts Mn(Por)(η-O) (Por = the -tetra-phenyl or -tetra--tolylporphyrinato dianions, TPP and TTP). The Mn(Por)(η-O) was assembled by adding O to sublimed layers of Mn(Por). When NO was introduced and the temperature was slowly raised from 80 to 120 K, new IR bands with correlated intensities grew concomitant with depletion of the υ(O) band.

Six-Coordinate Nitrato Complexes of Iron Porphyrins with Trans S-Donor Ligands.

The reaction of dimethyl sulfide (DMS) and tetrahydrothiophene (THT) with thin, amorphous layers of the nitrato complexes Fe(Por)(η-ONO) (Por = meso-tetraphenylporphyrinato dianion or meso-tetra- p-tolylporphyrinato dianion) at low temperature leads to formation of the corresponding six-coordinate complexes Fe(Por)(L)(η-ONO) (L = DMS, THT) as characterized by Fourier transform infrared and optical spectroscopy measurements. Adduct formation was accompanied by bidentate-to-monodentate linkage isomerization of the nitrato ligand, with the Fe center remaining in a high-spin electronic state. These adducts are thermally unstable; warming to room temperature restores the initial Fe(Por)(η-ONO) species.

Six-Coordinate Ferrous Nitrosyl Complex Fe(TTP)(PMe)(NO) (TTP = meso-Tetra-p-tolylporphyrinato Dianion).

Low-temperature in situ Fourier transform infrared and UV-vis measurements show that trimethylphosphine (PMe) reacts with microporous layers of Fe(TTP)(NO) (TTP = meso-tetra-p-tolylporphyrinato dianion; NO = nitric oxide) to form the previously unknown six-coordinate complex Fe(TTP)(PMe)(NO). Upon warming this compound to room temperature in the presence of excess phosphine, the NO ligand is completely replaced by phosphine, resulting in formation of the bis(trimethylphosphine) complex Fe(TTP)(PMe). Simultaneously, the NO released oxidizes free PMe to the corresponding phosphine oxide (OPMe) with concomitant formation of nitrous oxide (NO).

Six-coordinate nitro complexes of iron(III) porphyrins with trans S-donor ligands. Oxo-transfer reactivity in the solid state.

Spectroscopic studies demonstrate that the 5-coordinate O-nitrito complexes Fe(Por)(eta(1)-ONO) (Por--meso-tetraphenyl- or meso-tetra-p-tolyl-porphyrinato dianions) react with the thioethers (R(2)S) dimethylsulfide and tetrahydrothiophene to give the 6-coordinate N-nitrito complexes Fe(Por)(R(2)S)(NO(2)). These reactions were conducted in low-temperature porous layered solids formed in a cryostat; however, with excess R(2)S in the atmosphere, the same species are moderately stable at room temperature. Six-coordinate O-nitrito isomers were not observed with the R(2)S proximal ligands, even though DFT calculations for the Fe(P)(DMS)(eta(1)-ONO) and Fe(P)(DMS)(NO(2)) models (P = porphinato dianion, DMS = dimethyl sulfide) show the latter to be only modestly lower energy (approximately 8 kJ/mol) than the former.

Catalytic dioxygen activation by (nitro)(meso-tetrakis(2-n-methylpyridyl)porphyrinato)cobalt(III) cation derivatives electrostatically immobilized in nafion films: an experimental and DFT investigation.

Complexes of the (nitro)( meso-tetrakis(2- N-methylpyridyl)porphyinato)cobalt(III) cation, [LCoTMpyP(2)(NO 2)] (4+), in which L = water or ethanol have been immobilized through ionic attraction within Nafion films (Naf). These immobilized six-coordinate species, [LCoTMPyP(2)(NO 2)/Naf], have been found to catalyze the oxidation of triphenylphosphine in ethanol solution by dioxygen, therefore retaining the capacity to activate dioxygen catalytically without an additional reducing agent as was previously observed in nonaqueous solution for the non-ionic (nitro)cobalt porphyrin analogs. Heating these immobilized six-coordinate species under vacuum conditions results in the formation of the five-coordinate nitro derivatives, [CoTMPyP(2)(NO 2)/Naf] at 85 degrees C and [CoTMPyP(2)/Naf] at 110 degrees C.

Interaction of nitrogen bases with iron-porphyrin nitrito complexes Fe(Por)(ONO) in sublimed solids.

The reactions of the nitrogen Lewis bases (B) 1-methylimidazole (1-MeIm), pyridine (Py), and NH3 as gases with sublimed layers containing the 5-coordinate nitrito iron(III)-porphyrinato complexes Fe(Por)(eta1-ONO) (1) are described (Por = meso-tetraphenyl-porphyrinato or meso-tetra-p-tolyl-porphyrinato dianions). In situ FTIR and optical spectra are used to characterize the formation of the 6-coordinate nitro complexes formed by the reaction of 1 with B = 1-MeIm, Py, or NH3. These represent the first examples of 6-coordinate amino-nitro complexes with sterically unprotected iron-porphyrins.

Reactions of nitrogen oxides with the five-coordinate Fe(III)(porphyrin) nitrito intermediate Fe(Por)(ONO) in sublimed solids.

Detailed experimental studies are described for reactions of several nitrogen oxides with iron porphyrin models for heme/NxOy systems. It is shown by FTIR and optical spectroscopy and by isotope labeling experiments that reaction of small increments of NO2 with sublimed thin layers of the iron(II) complex Fe(Por) (Por = meso-tetraphenylporphyrinato dianion, TPP, or meso-tetra-p-tolylporphyrinato dianion, TTP) leads to formation of the 5-coordinate nitrito complexes Fe(Por)(eta1-ONO) (1), which are fairly stable but very slowly decompose under vacuum giving mostly the corresponding nitrosyl complexes Fe(Por)(NO). Further reaction of 1 with new NO2 increments leads to formation of the nitrato complex Fe(Por)(eta2-O2NO) (2).