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). The interaction of NO with 1 at low temperature involves ligand addition to give the nitrito-nitrosyl complexes Fe(Por)(eta1-ONO)(NO) (3); however, these isomerize to the nitro-nitrosyl analogs Fe(Por)(eta1-NO2)(NO) (4) upon warming. Experiments with labeled nitrogen oxides argue for an intramolecular isomerization ("flipping") mechanism rather than one involving dissociation and rebinding of NO2. The Fe(III) centers in the 6-coordinate species 3 and 4 are low spin in contrast to 1, which appears to be high-spin, although DFT computations of the porphinato models Fe(P)(nitrite) suggest that the doublet nitro species and the quartet and sextet nitrito complexes are all relatively close in energy. The nitro-nitrosyl complex 4 is stable under an NO atmosphere but decomposes under intense pumping to give a mixture of the ferrous nitrosyl complex Fe(Por)(NO) and the ferric nitrito complex Fe(Por)(eta1-ONO) indicating the competitive dissociation of NO and NO2. Hence, loss of NO from 4 is accompanied with nitro --> nitrito isomerization consistent with 1 being the more stable of the 5-coordinate NO2 complexes of iron porphyrins.     

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.     

Comparative IR study of nitric oxide reactions with sublimed layers of iron(II)- and ruthenium(II)-meso-tetraphenylporphyrinates

The interactions of nitric oxide gas with thin layers of Fe(II)(TPP) and Ru(II)(TPP), obtained by sublimation onto low-temperature substrate (77 K), has been investigated by means of IR spectroscopy (TPP = meso-tetraphenylporphyrinate). Only simple addition of NO to form Fe(TPP)(NO) is observed for the iron-porphyrin Fe(II)(TPP), while, in contrast, Ru(II)(TPP) promotes NO disproportionation to form the nitrosyl-nitrito complex Ru(TPP)(NO)(ONO) and N(2)O. Thin layers of Fe(TPP)(NO) are inert to further reaction with excess NO; however, the nitrosyl-nitro complex Fe(TPP)(NO)(NO(2)) is readily formed when traces of dioxygen are added to the NO atmosphere. When the NO(2) concentrations in the NO/NO(2) mixture are relatively high, the nitrato complex Fe(TPP)(NO(3)) is also formed. Spectral data are given indicating that moderate shifts in the nitrosyl stretching frequency of Fe(TPP)(NO) are due to crystal packing effects, rather than to the H-bonding of coordinated NO with protic contaminants suggested in an earlier publication. Removal of NO by exhaustive evacuation from layers containing Fe(TPP)(NO)(NO(2)) leads to formation of Fe(TPP)(NO) and Fe(TPP)(NO(3)).     

Hexacoordinate oxy-globin models Fe(Por)(NH3)(O2) react with NO to form only the nitrato analogs Fe(Por)(NH3)(η1-ONO2), even at ~100 K

The oxy-globin models Fe(Por)(NH(3))(O(2)), prepared by sequential reactions of O(2) ((18)O(2)) and NH(3) with thin porous layers of Fe(II)(Por), react with NO ((15)NO) at 80-100 K to form only the low-spin nitrato complexes Fe(Por)(NH(3))(η(1)-ONO(2)), thus implying that peroxynitrite intermediates, if formed, must undergo very facile isomerization to the nitrato analog.     

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. Characterization of NO and NO2 dissociation from Fe(TPP)(NO2)(NO) by flash photolysis and rapid dilution techniques: Fe(TPP)(NO2) as an unstable intermediate

Described are studies directed toward elucidating the controversial chemistry relating to the solution phase reactions of nitric oxide with the iron(II) porphyrin complex Fe(TPP)(NO) (1, TPP = meso-tetraphenylporphinato2-). The only reaction observable with clean NO is the formation of the diamagnetic dinitrosyl species Fe(TPP)(NO)2 (2), and this is seen only at low temperatures (K(1) < 3 M(-1) at ambient temperature). However, 1 does readily react reversibly with N2O3 in the presence of excess NO to give the nitro nitrosyl complex Fe(TPP)(NO2)(NO) (3), suggesting that previous claims that 1 promotes NO disproportionation to give 3 may have been compromised by traces of air in the nitric oxide sources. It is also noted that 3 undergoes reversible loss of NO to give the elusive nitro species Fe(TPP)(NO2) (4), which has been implicated as a powerful oxygen atom transfer agent in reactions with various substrates. Furthermore, in the presence of excess NO2, the latter undergoes oxidation to the stable nitrato analogue Fe(TPP)(NO3) (5). Owing to such reactivity of Fe(TPP)(NO2), flash photolysis and stopped-flow kinetics rather than static techniques were necessary for the accurate measurement of dissociation equilibria characteristic of Fe(TPP)(NO2)(NO) in 298 K toluene solution. Flash photolysis of 3 resulted in competitive NO2 and NO dissociation to give Fe(TPP)(NO) and Fe(TPP)(NO2), respectively. The rate constant for the reaction of 1 with N2O3 to generate Fe(TPP)(NO2)(NO) was determined to be 1.8 x 10(6) M(-1) s(-1), and that for the NO reaction with 4 was similarly determined to be 4.2 x 10(5) M(-1) s(-1). Stopped-flow rapid dilution techniques were used to determine the rate constant for NO dissociation from 3 as 2.6 s(-1). The rapid dilution experiments also demonstrated that Fe(TPP)(NO2) readily undergoes further oxidation to give Fe(TPP)(NO3). The mechanistic implications of these observations are discussed, and it is suggested that NO2 liberated spontaneously from Fe(P)(NO2) may play a role in an important oxidative process involving this elusive species.     

A quantum chemical survey of metalloporphyrin-nitrosyl linkage isomers: insights into the observation of multiple FeNO conformations in a recent crystallographic determination of nitrophorin 4

Using density functional theory-based geometry optimizations, we have searched for eta(1)-NO, eta(1)-ON (isonitrosyl), and eta(2)-NO (side-on bound NO) linkage isomers of a number of metalloporphyrin-NO complexes, M(Por)(NO)(L), where Por = porphinato dianion, M = Mn(II), Fe(II), Fe(III), Ru(II), Ru(III), Co(II), and Rh(II), and L = no ligand, SMe, Ph, and imidazole. The eta(1)-NO isomer had the lowest energy in all cases, and the isonitrosyl isomer was also located as a higher energy potential energy minimum in a number of cases. The eta(2)-NO isomer was only located as a minimum for Mn(II) (L = no ligand), Fe(III) (L = no ligand), and Ru(III) (L = Ph, imidazole, pyrdine), suggesting that an [MNO](6) electron count is important for stabilization of the eta(2) mode of ligation. However, in the presence of axial ligands L, the side-on isomers of [FeNO](6) complexes were not stable and opened up to an unusual geometry where the FeN(O) and NO vectors were tilted in opposite directions relative to the heme normal. Exactly such a geometry, as well as a "normal" upright geometry, has been observed in a recent crystallographic determination of nitrophorin 4 (Nature Struct. Biol. 2000, 7, 551), a salivary protein from the blood-sucking insect Rhodnius prolixus. Together, the calculated and experimental result illustrate the extreme softness of the FeNO potential energy surface toward various forms of tilting and bending deformations.     

Chemistry of nitrosyliron complexes supported by a β-diketiminate ligand

Several nitrosyl complexes of Fe and Co have been prepared using the sterically hindered Ar-nacnac ligand (Ar-nacnac = anion of [(2,6-diisopropylphenyl)NC(Me)](2)CH). The dinitrosyliron complexes [Fe(NO)(2)(Ar-nacnac)] (1) and (Bu(4)N)[Fe(NO)(2)(Ar-nacnac)] (2) react with [Fe(III)(TPP)Cl] (TPP = tetraphenylporphine dianion) to generate [Fe(II)(NO)(TPP)] and the corresponding mononitrosyliron complexes. The factors governing NO transfer with dinitrosyliron complexes (DNICs) 1 and 2 are evaluated, together with the chemistry of the related mononitrosyliron complex, [Fe(NO)Br(Ar-nacnac)] (4). The synthesis and properties of the related cobalt dinitrosyl [Co(NO)(2)(Ar-nacnac)] (3) is also discussed for comparison to DNICs 1 and 2. The solid-state structures of several of these compounds as determined by X-ray crystallography are reported.     

Binding and photodissociation of CO in iron(II) complexes for application in positron emission tomography (PET) radiolabelling

(R-DAB)FeI(2) complexes containing bidentate diimide ligands (R-DAB = RN=CH-CH=NR; R = (i)Pr, c-C(6)H(11)) have been investigated for their ability to react with carbon monoxide to form iron(II) dicarbonyl complexes, (R-DAB)FeI(2)(CO)(2). Solution IR spectroscopy revealed two νCO stretches between 2000 and 2040 cm(-1) corresponding to a cis-arrangement of the carbonyl ligands around the iron. Photochemical decarbonylation was achieved by UV irradiation (365 nm), which occurred within 5 min as evidenced by solution IR spectroscopy. (c-C(6)H(11)-DAB)FeI(2) has been characterised by X-ray crystallography. Reactions using (11)C-labelled carbon monoxide were investigated and revealed that both (R-DAB)FeI(2) species were not effective as trapping complexes due to the low concentrations of [(11)C]CO used in these experiments. A Fe(TPP)(THF)(x) (TPP = tetraphenylporphyrin) complex was investigated with unlabelled CO and the monocarbonyl adduct Fe(TPP)(THF)CO was formed in situ as identified by IR spectroscopy (νCO = 1966 cm(-1)) yet was stable to CO loss upon UV irradiation. Carbonylation reactions of in situ-generated Fe(TPP)(THF)(x) using [(11)C]CO revealed that 97% of the [(11)C]CO stream could be trapped in one pass of the gas at room temperature and at atmospheric pressure.     

Nitric Oxide Dioxygenation Reaction by Oxy-Coboglobin Models: In-situ Low-Temperature FTIR Characterization of Coordinated Peroxynitrite

The oxy-cobolglobin models of the general formula (NH(3))Co(Por)(O(2)) (Por = meso-tetra-phenyl and meso-tetra-p-tolylporphyrinato dianions) were constructed by sequential low temperature interaction of NH(3) and dioxygen with microporous layers of Co-porphyrins. At cryogenic temperatures small increments of NO were introduced into the cryostat and the following reactions were monitored by the FTIR and UV-visible spectroscopy during slow warming. Upon warming the layers from 80 to 120 K a set of new IR bands grows with correlating intensities along with the consumption of the ν(O(2)) band. Isotope labeling experiments with (18)O(2), (15)NO and N(18)O along with DFT calculations provides a basis for assigning them to the six-coordinate peroxynitrite complexes (NH(3))Co(Por)(OONO). Over the course of warming the layers from 140 to 170 K these complexes decompose and there are spectral features suggesting the formation of nitrogen dioxide NO(2). Upon keeping the layers at 180-210 K the bands of NO(2) gradually decrease in intensity and the set of new bands grows in the range of 1480, 1270, and 980 cm(-1). These bands have their isotopic counterparts when (15)NO, (18)O(2) and N(18)O are used in the experiments and certainly belong to the 6-coordinate nitrato complexes (NH(3))Co(Por)(η(1)-ONO(2)) demonstrating the ability of oxy coboglobin models to promote the nitric oxide dioxygenation (NOD) reaction similar to oxy-hemes. As in the case of Hb, Mb and model iron-porphyrins, the six-coordinate nitrato complexes are not stable at room temperature and dissociate to give nitrate anion and oxidized cationic complex Co(III)(Por)(NH(3))(1,2).     

In situ FT-IR and UV-vis spectroscopy of the low-temperature NO disproportionation mediated by solid state manganese(II) porphyrinates

The heterogeneous reaction between NO gas and sublimed layers of manganese(II) porphyrinato complexes Mn(Por) (Por = TPP (tetraphenylporphyrinato dianion), TMP (tetramesitylporphyrinato dianion), or TPP(d20) (perdeuterated tetraphenylporphyrinato dianion)) has been monitored by IR and optical spectroscopy over the temperature range of 77 K to room temperature. These manganese porphyrins promote NO disproportionation to NO2 species and N2O, and the reaction proceeds via several distinct stages. At 90 K, the principal species observed spectrally are the nitric oxide dimer, cis-ONNO, two manganese nitrosyls, the simple NO adduct Mn(Por)(NO), and another intermediate (1) that is apparently critical to the disproportionation mechanism. This key intermediate is formed prior to N2O evolution, and proposals regarding its likely structure are offered. When the system is warmed to 130 K, the disproportionation products, N2O and the O-coordinated nitrito complex Mn(Por)(NO)(ONO) (2), are formed. IR spectral changes show that, upon further warming to 200 K, 2 isomerizes into the N-bonded nitro linkage isomer Mn(Por)(NO)(NO2) (3). After it is warmed to room temperature, the latter species loses NO and converts to the known 5-coordinate nitrito complex Mn(Por)(ONO) (4).     

Redox properties of ruthenium nitrosyl porphyrin complexes with different axial ligation: structural, spectroelectrochemical (IR, UV-visible, and EPR), and theoretical studies

Experimental and computational results for different ruthenium nitrosyl porphyrin complexes [(Por)Ru(NO)(X)] ( n+ ) (where Por (2-) = tetraphenylporphyrin dianion (TPP (2 (-) )) or octaethylporphyrin dianion (OEP (2-)) and X = H 2O ( n = 1, 2, 3) or pyridine, 4-cyanopyridine, or 4- N,N-dimethylaminopyridine ( n = 1, 0)) are reported with respect to their electron-transfer behavior. The structure of [(TPP)Ru(NO)(H 2O)]BF 4 is established as an {MNO} species with an almost-linear RuNO arrangement at 178.1(3) degrees . The compound [(Por)Ru(NO)(H 2O)]BF 4 undergoes two reversible one-electron oxidation processes. Spectroelectrochemical measurements (IR, UV-vis-NIR, and EPR) indicate that the first oxidation occurs on the porphyrin ring, as evident from the appearance of diagnostic porphyrin radical-anion vibrational bands (1530 cm (-1) for OEP (*-) and 1290 cm (-1) for TPP (*-)), from the small shift of approximately 20 cm (-1) for nu NO and from the EPR signal at g iso approximately 2.00. The second oxidation, which was found to be electrochemically reversible for the OEP compound, shows a 55 cm (-1) shift in nu NO, suggesting a partially metal-centered process. The compounds [(Por)Ru(NO)(X)]BF 4, where X = pyridines, undergo a reversible one-electron reduction. The site of the reduction was determined by spectroelectrochemical studies to be NO-centered with a ca. -300 cm (-1) shift in nu NO. The EPR response of the NO (*) complexes was essentially unaffected by the variation in the substituted pyridines X. DFT calculations support the interpretation of the experimental results because the HOMO of [(TPP)Ru(NO)(X)] (+), where X = H 2O or pyridines, was calculated to be centered at the porphyrin pi system, whereas the LUMO of [(TPP)Ru(NO)(X)] (+) has about 50% pi*(NO) character. This confirms that the (first) oxidation of [(Por)Ru(NO)(H 2O)] (+) occurs on the porphyrin ring wheras the reduction of [(Por)Ru(NO)(X)] (+) is largely NO-centered with the metal remaining in the low-spin ruthenium(II) state throughout. The 4% pyridine contribution to the LUMO of [(TPP)Ru(NO)(py)] (+) is correlated with the stability of the reduced form as opposed to that of the aqua complex.     

Naked five-coordinate Fe(III)(NO) porphyrin complexes: vibrational and reactivity features

Model ferric heme nitrosyl complexes, [Fe(TPP)(NO)](+) and [Fe(TPFPP)(NO)](+), where TPP is the dianion of 5,10,15,20-tetrakis-phenyl-porphyrin and TPFPP is the dianion of 5,10,15,20-tetrakis-pentafluorophenyl-porphyrin, have been obtained as isolated species by the gas phase reaction of NO with [Fe(III)(TPP)](+) and [Fe(III) (TPFPP)](+) ions delivered in the gas phase by electrospray ionization, respectively. The so-formed nitrosyl complexes have been characterized by vibrational spectroscopy also exploiting (15)N-isotope substitution in the NO ligand. The characteristic NO stretching frequency is observed at 1825 and 1859 cm(-1) for [Fe(III)(TPP)(NO)](+) and [Fe(III)(TPFPP)(NO)](+) ions, respectively, providing reference values for genuine five-coordinate Fe(III)(NO) porphyrin complexes differing only for the presence of either phenyl or pentafluorophenyl substituents on the meso positions of the porphyrin ligand. The vibrational assignment is aided by hybrid density functional theory (DFT) calculations of geometry and electronic structure and frequency analysis which clearly support a singlet spin electronic state for both [Fe(TPP)(NO)](+) and [Fe(TPFPP)(NO)](+) complexes. Both TD-DFT and CASSCF calculations suggest that the singlet ground state is best described as Fe(II)(NO(+)) and that the open-shell AFC bonding scheme contribute for a high-energy excited state. The kinetics of the NO addition reaction in the gas phase are faster for [Fe(III)(TPFPP)](+) ions by a relatively small factor, though highly reliable because of a direct comparative evaluation. The study was aimed at gaining vibrational and reactivity data on five-coordinate Fe(III)(NO) porphyrin complexes, typically transient species in solution, ultimately to provide insights into the nature of the Fe(NO) interaction in heme proteins.     

Interaction of nitrogen oxides with sublimed layers of (meso-tetraphenylporphyrinato)cobalt(II); IR evidence of oxo-transfer from (nitro)porphyrinatocobalt(III) to free nitric oxide

Interaction of a low-pressure NO2 with sublimed layers of (meso-tetraphenylporphyrinato)cobalt(II) (Co(TPP)) leads to formation of 5-coordinate nitro complex Co(III)(TPP)(NO2). Upon exposure of these layers to pyridine vapors, the fast reaction with formation of 6-coordinate nitro-pyridine porphyrins (Py)Co(III)(TPP)(NO2) occurs. By means of IR spectroscopy and use of nitrogen oxide isotopomers, it is shown that an oxo-transfer reaction occurs from 5-coordinate species to free nitric oxide (NO) while the 6-coordinate complex is rather inert. It is also demonstrated that the stepwise addition of low-pressure NO2 to nitrosyl complex Co(TPP)(NO) leads to formation of the nitro complex most likely by an exchange reaction.     

Tuning the reactivity of dioxoruthenium(VI) porphyrins toward an arylimine by altering porphyrin substituents

Reaction of dioxoruthenium(VI) porphyrins [Ru(VI)(Por)O2] with arylimine HN=CPh2 in dichloromethane afforded bis(methyleneamido)ruthenium(IV) porphyrins [Ru(IV)(Por)(N=CPh2)2] for Por = 4-Cl-TPP and TMP; (methyleneamido)hydroxoruthenium(IV) porphyrins [Ru(IV)(Por)(N=CPh2)(OH)] for Por = TPP and TTP; and bis(arylimine)ruthenium(II) porphyrins [Ru(II)(Por)(HN=CPh2)2] for Por = 3,5-Cl2TPP and 3,5-(CF3)2TPP. In dichloromethane solution exposed to air, complex [Ru(II)(3,5-Cl2TPP)(HN=CPh2)2] underwent oxidative deprotonation to form [Ru(IV)(3,5-Cl2TPP)(N=CPh2)2]. The new ruthenium porphyrins were identified by 1H NMR, UV-vis, IR, and mass spectroscopy, along with elemental analysis. X-ray crystal structure determinations of [Ru(IV)(4-Cl-TPP)(N=CPh2)2], [Ru(IV)(TPP)(N=CPh2)(OH)], and [Ru(II)(3,5-(CF3)2TPP)(HN=CPh2)2] revealed the Ru-N(methyleneamido) or Ru-N(arylimine) distances of 1.897(5) A (average), 1.808(4) A, and 2.044(2) A (average), respectively.     

Dinitrosyl iron complexes (DNICs) containing S/N/O ligation: transformation of Roussin's red ester into the neutral {Fe(NO)2}10 DNICs

Addition of the Lewis base [OPh]- to the THF solution of Roussin's red ester [Fe(mu-SC6H4-o-NHCOPh)(NO)2]2 (1) and [Fe(mu-SC6H4-o-COOH)(NO)2]2 (2), respectively, yielded the EPR-active, anionic {Fe(NO)2}9, [(SC6H4-o-NCOPh)Fe(NO)2]- (3) with the anionic [SC6H4-o-NCOPh]2- ligand bound to the {Fe(NO)2} core in a bidentate manner (S,N-bonded) and [(SC6H4-o-COO)Fe(NO)2]- (4) with the anionic [SC6H4-o-COO]2- ligand bound to the {Fe(NO)2} core in a bidentate manner (S,O-bonded), characterized by IR, UV-vis, EPR, and single-crystal X-ray diffraction. In contrast to the bridged-thiolate cleavage yielding the neutral {Fe(NO)2}9, [(SC6H4-o-NHCOPh)(Im)Fe(NO)2] (Im=imidazole), by addition of 2 equiv of imidazole to complex 1 observed in the previous study, the addition of the stronger sigma-donating and pi-accepting PPh3 ligand triggered the reductive elimination of bridged thiolates of complex 1 to yield the neutral {Fe(NO)2}10, [(PPh3)2Fe(NO)2]. These results unambiguously illustrate one aspect of how the nucleophile L (L=imidazole, PPh3, [OPh]-) functions to control the reaction pathways (bridged-thiolate cleavage, reductive elimination, and deprotonation) upon the reaction of complex 1 and the nucleophile L. The EPR-active, dimeric {Fe(NO)2}9 dinitrosyl iron complex (DNIC) [Fe(mu-SC7H4SN)(NO)2]2 (6), with S and N atoms of the anionic [-SC7H4SN-]- (2-benzothiozolyl thiolate) ligands bound to two separate {Fe(NO)2}9 cores, was also synthesized from reaction of bis(2-benzothiozolyl) disulfide and [(NO)2Fe(PPh3)2]. A straightforward reaction of complex 6 and 4 equiv of [N3]- conducted in THF led to the anionic {Fe(NO)2}9, [(N3)2Fe(NO)2]- (7). Conclusively, the EPR-active, {Fe(NO)2}9 DNICs can be classified into the anionic {Fe(NO)2}9 DNICs with S/N/O ligation, the neutral {Fe(NO)2}9 DNIC with one thiolate and one neutral imidazole ligation, and the cationic {Fe(NO)2}9 DNICs with the neutral N-/P-containing coordinated ligands.     

Geometric and electronic structure of the heme-peroxo-copper complex [(F8TPP)FeIII-(O22-)-CuII(TMPA)](ClO4)

The geometric and electronic structure of the untethered heme-peroxo-copper model complex [(F(8)TPP)Fe(III)-(O(2)(2)(-))-Cu(II)(TMPA)](ClO(4)) (1) has been investigated using Cu and Fe K-edge EXAFS spectroscopy and density functional theory calculations in order to describe its geometric and electronic structure. The Fe and Cu K-edge EXAFS data were fit with a Cu...Fe distance of approximately 3.72 A. Spin-unrestricted DFT calculations for the S(T) = 2 spin state were performed on [(P)Fe(III)-(O(2)(2)(-))-Cu(II)(TMPA)](+) as a model of 1. The peroxo unit is bound end-on to the copper, and side-on to the high-spin iron, for an overall mu-eta(1):eta(2) coordination mode. The calculated Cu...Fe distance is approximately 0.3 A longer than that observed experimentally. Reoptimization of [(P)Fe(III)-(O(2)(2)(-))-Cu(II)(TMPA)](+) with a 3.7 A Cu...Fe constrained distance results in a similar energy and structure that retains the overall mu-eta(1):eta(2)-peroxo coordination mode. The primary bonding interaction between the copper and the peroxide involves electron donation into the half-occupied Cu d(z)2 orbital from the peroxide pi(sigma) orbital. In the case of the Fe(III)-peroxide eta(2) bond, the two major components arise from the donor interactions of the peroxide pi*(sigma) and pi*(v) orbitals with the Fe d(xz) and d(xy) orbitals, which give rise to sigma and delta bonds, respectively. The pi*(sigma) interaction with both the half-occupied d(z)2 orbital on the copper (eta(1)) and the d(xz) orbital on the iron (eta(2)), provides an effective superexchange pathway for strong antiferromagnetic coupling between the metal centers.     

Ruthenium complexes with a terminal hydrazido ligand. Synthesis, spectroscopy, and X-ray crystal structure

Bis(1,1-diphenylhydrazido(1-))ruthenium(IV) porphyrins, [Ru(IV)(Por)(NHNPh2)2] (Por = TPP, TTP, 4-Cl-TPP, 4-MeO-TPP), were prepared in approximately 60% yields through the reaction of dioxoruthenium(VI) porphyrins, [Ru(VI)(Por)O2], with 1,1-diphenylhydrazine in ethanol. This new type of ruthenium complex has been characterized by 1H NMR, IR, UV-vis, and FABMS with elemental analysis. The crystal structure of [Ru(IV)(TTP)(NHNPh2)2], which reveals an eta1-coordination mode for both hydrazido axial ligands, has been determined. The average Ru-NHNPh2 distance and Ru-N-N angle were found to be 1.911(3) A and 141.1(3) degrees, respectively. The porphyrin ring exhibits a ruffling distortion that is unprecedentedly large for ruthenium complexes with simple porphyrinato ligands (such as TTP). This is probably due to the steric effect of the axial hydrazido(1-) ligands.     

Synthesis and coordination chemistry of phosphine oxide decorated dibenzofuran platforms

A four-step synthesis for 4,6-bis(diphenylphosphinoylmethyl)dibenzofuran (4) from dibenzofuran and a two-step synthesis for 4,6-bis(diphenylphosphinoyl)dibenzofuran (5) are reported along with coordination chemistry of 4 with In(III), La(III), Pr(III), Nd(III), Er(III), and Pu(IV) and of 5 with Er(III). Crystal structure determinations for the ligands, 4·CH(3)OH and 5, the 1:1 complexes [In(4)(NO(3))(3)], [Pr(4)(NO(3))(3)(CH(3)CN)]·0.5CH(3)CN, [Er(4)(NO(3))(3)(CH(3)CN)]·CH(3)CN, [Pu(4)Cl(4)]·THF and the 2:1 complex [Nd(4)(2)(NO(3))(2)](2)(NO(3))(2)·(H(2)O)·4(CH(3)OH) are described. In these complexes, ligand 4 coordinates in a bidentate POP'O' mode via the two phosphine oxide O-atoms. The dibenzofuran ring O-atom points toward the central metal cations, but in every case it is more than 4 ? from the metal. A similar bidentate POP'O' chelate structure is formed between 5 and Er(III) in the complex, {[Er(5)(2)(NO(3))(2)](NO(3))·4(CH(3)OH)}(0.5), although the nonbonded Er···O(furan) distance is reduced to ～3.6 ?. The observed bidentate chelation modes for 4 and 5 are consistent with results from molecular mechanics computations. The solvent extraction performance of 4 and 5 in 1,2-dichloroethane for Eu(III) and Am(III) in nitric acid solutions is described and compared against the extraction behavior of n-octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (OΦDiBCMPO) measured under identical conditions.     

Novel hetero-bimetallic metalla-macrocycles based on the bis-1-pyridyl ferrocene [Fe(eta 5-C5H(4)-1-C5H4N)2] ligand. Design,synthesis and structural characterization of the complexes [Fe(eta 5-C5H(4)-1-C5H4N)2](AgI)2(2+)/(CuII)2(4+)/(ZnII)2(4+)

The bidentate sandwich ligand [Fe(eta 5-C5H(4)-1-C5H4N)2] has been prepared, structurally characterized and employed in the preparation of the novel supramolecular heterobimetallic metalla-macrocycles [Fe(eta 5-C5H(4)-1-C5H4N)2]Ag2(NO3)(2).1.5H2O, [Fe(eta 5-C5H(4)-1-C5H4N)2]Cu2(CH3COO)(4).3H2O and [Fe(eta 5-C5H(4)-1-C5H4N)2]Zn2Cl4.