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)(η2-O2NO) (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)(η1-ONO2) (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 FeIII center remaining in a high-spin electronic state. These adducts are thermally unstable; warming to room temperature restores the initial Fe(Por)(η2-O2NO) species.

Six-coordinate nitrosyl and nitro complexes of meso-tetratolylporphyrinatocobalt with trans sulfur-donor ligands.

By Fourier transform infrared and optical spectroscopy, it has been observed that interactions of dimethyl sulfide and tetrahydrothiophene with nitrosyl and nitro complexes of meso-tetra-p-tolylporphyrinatocobalt [Co(TTP)] lead to the formation of previously unknown six-coordinate species. Nitrosyl complexes of the general formula (S-donor)Co(TTP)(NO) are thermally unstable and can be seen only at low temperatures both in the solid state and in solution. The nitro complexes (S-donor)Co(TTP)(NO(2)) are fairly stable at room temperature in the solid state but partly decompose upon dissolution. The binding constants for these complexation reactions were determined. In contrast to the solid-state iron nitritoporphyrin complexes, oxo-transfer reactions from the coordinated nitro group of Co(TTP)(NO(2)) to the S donors, resulting in oxidation of these sulfides and the formation of Co(TTP)(NO), were not observed.

Six-coordinate nitrato complexes of iron(III) porphyrins.

The interaction of tetrahydrofuran (THF) with thin films of the nitrato complexes Fe(III)(Por)(eta(2)-O(2)NO) [Por = meso-tetraphenylporphyrinato (TPP) and meso-tetratolylporphyrinato (TTP) dianion] at low temperature leads to the formation of the six-coordinate nitrato complex Fe(Por)(THF)(NO(3)), which was characterized by IR and UV-visible spectroscopies. Formation of the THF adduct was accompanied by nitrate linkage isomerization from bidentate to monodentate coordination. The iron(III) center remains in a high spin state in contrast with the previously observed low-spin nitratonitrosyl complex Fe(TPP)(NO)(eta(10-ONO(2)). Upon warming, THF dissociates to restore the initial five-coordinate bidentate nitrato complex.

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. The interaction of ammonia with Fe(Por)(ONO) at 140 K initially led to the nitrito species Fe(Por)(NH3)(eta1-ONO), and this species isomerized to the nitro complexes Fe(Por)(NH3)(eta1-NO2) upon warming to 180 K. When the latter were warmed to room temperature under intense pumping, the initial nitrito complexes Fe(Por)(eta1-ONO) were restored. Assignments of vibrational frequencies for the coordinated nitro group in 6-coordinate iron-porphyrin complexes are given and confirmed using 15N-labeled nitrogen dioxide to identify characteristic infrared bands. For M(Por)(B)(NO2) complexes (M = Fe or Co), an inverse correlation between the net charge transfer from the axial ligand B to the nitro group and the value of Deltanu = nua(NO2) - nus(NO2) is proposed. These observations are discussed in the context of growing interest in potential physiological roles of nitrite ion reactions with ferro- and ferri-heme proteins.

Reactions of nitrogen oxides with heme models. Spectral and kinetic study of nitric oxide reactions with solid and solute Fe(III)(TPP)(NO3).

The reaction(s) of nitric oxide (nitrogen monoxide) gas with sublimed layers containing the nitrato iron(III) complex Fe(III)(TPP)(eta(2)-O(2)NO) (1, TPP = meso-tetraphenyl porphyrinate(2)(-)) leads to formation of several iron porphyrin species that are ligated by various nitrogen oxides. The eventual products of these low-temperature solid-state reactions are the nitrosyl complex Fe(TPP)(NO), the nitro-nitrosyl complex Fe(TPP)(NO(2))(NO), and 1 itself, and the relative final quantities of these were functions of the NO partial pressure. It is particularly notable that isotope labeling experiments show that the nitrato product is not simply unreacted 1 but is the result of a series of transformations taking place in the layered material. Thus, the nitrato complex formed from solid Fe(TPP)(eta(2)-O(2)NO) maintained under a (15)NO atmosphere was found to be the labeled analogue Fe(TPP)(eta(2)-O(2)(15)NO). The reactivities of the layered solids are compared to the behaviors of the same species in ambient temperature solutions. To interpret the reactions of the labeled nitrogen oxides, the potential exchange reactions between N(2)O(3) and (15)NO were examined, and complete isotope scrambling was observed between these species under the reaction conditions (T = 140 K). Overall it was concluded from isotope labeling experiments that the sequence of reactions is initiated by reaction of 1 with NO to give the nitrato nitrosyl complex Fe(TPP)(eta(1)-ONO(2))(NO) (2) as an intermediate. This is followed by a reaction in the presence of excess NO that is equivalent to the loss of the nitrate radical NO(3)(*)( )()to give Fe(TPP)(NO) as another transient species. A plausible pathway involving NO attack on the coordinated nitrate of 2 resulting in the release of N(2)O(4) concerted with electron transfer to the metal center is proposed.