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.     

Electronic and fluorescence spectral studies of a novel porphyrin-polypyridyl ruthenium(II) hybrid linked by a butyl chain

The electronic and fluorescence spectroscopic properties of a novel porphyrin-polypyridyl ruthenium(II) hybrid, [C(4)-TPP-(ip)Ru(phen)(2)](ClO(4))(2) (TPP=5,10,15,20-tetraphenylporphyrin, ip=imidazo[4,5-f][1,10]phenanthroline and phen=1,10-Phenanthroline), in which a polypyridyl ruthenium(II) moiety is linked to a porphyrin moiety by a butyl chain have been investigated and compared to its corresponding reference compounds. The studies of electronic absorption spectra have shown that there is an electronic interaction between the porphyrin moiety and the polypyridyl ruthenium(II) moiety in the hybrid. It can be found that intramolecular photoinduced electron and energy transfer processes may occur in the hybrid from the fluorescence spectra. When exciting in Soret band and Q band of porphyrin, the fluorescence quenching of the porphyrin moiety of the hybrid takes place due to electron transfer from the lowest singlet excited state (S(1)) to the appended polypyridyl rutherium(II) moiety, while the decay of S(2) (the second-excited singlet state) of the porphyrin moiety is mainly contributed to internal conversion to S(1). When exciting in MLCT band of the polypyridyl ruthenium(II) moiety, fluorescence corresponding to the polypyridyl ruthenium(II) moiety is quenched by intramolecular energy transfer from (3)MLCT of the ruthenium moiety to the lowest-energy triplet state localized on the porphyrin moiety.     

Wavelength-dependent electron and energy transfer pathways in a side-to-face ruthenium porphyrin/perylene bisimide assembly

A new side-to-face supramolecular array of chromophores, where a pyridyl-substituted perylene bisimide dye axially binds to two ruthenium porphyrin fragments, has been prepared by self-assembly. The array is formulated as DPyPBI[Ru(TPP)(CO)](2), where DPyPBI = N,N'-di(4-pyridyl)-1,6,7,12-tetra(4-tert-butylphenoxy)perylene-3,4:9,10-tetracarboxylic acid bisimide and TPP = 5,10,15,20-tetraphenylporphyrin. The photophysical behavior of DPyPBI[Ru(TPP)(CO)](2) has been studied by fast (nanoseconds) and ultrafast (femtoseconds) time-resolved techniques. The observed behavior sharply changes with excitation wavelength, depending on whether the DPyPBI or Ru(TPP)(CO) units are excited. After DPyPBI excitation, the strong fluorescence typical of this unit is completely quenched, and time-resolved spectroscopy reveals the occurrence of photoinduced electron transfer from the ruthenium porphyrin to the perylene bisimide dye (tau = 5.6 ps) followed by charge recombination (tau = 270 ps). Upon excitation of the Ru(TPP)(CO) fragments, on the other hand, ultrafast (tau < 1 ps) intersystem crossing is followed by triplet energy transfer from the ruthenium porphyrin to the perylene bisimide dye (tau = 720 ps). The perylene-based triplet state decays to the ground state on a longer time scale (tau = 9.8 micros). The photophysics of this supramolecular array provides remarkable examples of (i) wavelength-dependent behavior (a small change in excitation wavelength causes a sharp switch from electron to energy transfer) and (ii) intramolecular sensitization (the triplet state of the perylene bisimide, inaccessible in the free dye, is efficiently populated in the array).     

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.     

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.     

Synthesis, Characterization, and Electrochemistry of Ruthenium Porphyrins Containing a Nitrosyl Axial Ligand

Two ruthenium nitrosyl porphyrins have been synthesized and characterized by spectroscopic and electrochemical methods. The investigated compounds are represented as [(TPP)Ru(NO)(H(2)O)]BF(4) and (TPP)Ru(NO)(ONO) where TPP is the dianion of 5,10,15,20-tetraphenylporphyrin. (TPP)Ru(NO)(ONO) crystallizes in the tetragonal space group I4, with a = 13.660(1) ?, c = 9.747(1) ?, V = 1818.7(3) ?(3), and Z = 2, 233 K. The most chemically interesting feature of the structure is that the nitrosyl and O-bound nitrito groups are located axial and trans to one another. Both complexes undergo an irreversible reduction at the metal center which is accompanied by dissociation of the axial ligand trans to NO. The addition of 1-10 equiv of pyridine to [(TPP)Ru(NO)(H(2)O)]BF(4) in CH(2)Cl(2) containing 0.1 M TBAP leads to the formation of [(TPP)Ru(NO)(py)](+), a species which is reversibly reduced at E(1/2) = -0.29 V. The electrochemical data indicate that (TPP)Ru(NO)(ONO) can also be converted to [(TPP)Ru(NO)(py)](+) in CH(2)Cl(2) solutions containing pyridine but only under specific experimental conditions. This reaction does not involve a simple displacement of the ONO(-) axial ligand from (TPP)Ru(NO)(ONO) but occurs after reduction of (TPP)Ru(NO)(ONO) to (TPP)Ru(NO)(py) followed by reoxidation to [(TPP)Ru(NO)(py)](+).     

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)).     

A fluorescent ammonia sensor based on a porphyrin cobalt(II)-dansyl complex

Detecting and measuring the concentration of ammonia is of interest in many scientific and technological areas. A porphyrin based cobalt(II) complex with a dansyl fluorophore has been synthesized and investigated as a ‘turn-on’ fluorescent ammonia sensor. Over sixfold increase in fluorescence emission occurs upon the treatment of NH₃ to [Co(TPP)(Ds-pip)] sensor solution, resulting from NH₃-induced displacement of the axially coordinated fluorophore.     

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.     

Reversible oxidation state change in germanium(tetraphenylporphyrin) induced by a dative ligand: aromatic GeII(TPP) and antiaromatic GeIV(TPP)(pyridine)2

Treatment of GeCl2(dioxane) with Li2(TPP)(OEt2)2 (TPP = tetraphenylporphyrin) in THF yields Ge(TPP), the first free Ge(II) porphyrin complex. In pyridine Ge(TPP) is converted to Ge(TPP)(py)2, an antiaromatic Ge(IV) complex, whereas in benzene the reaction is reversed, and pyridine dissociates from Ge(TPP)(py)2 to form Ge(TPP). That reversible reaction represents an unusual, if not unique, example of an oxidation-state change in a metal induced by coordination of a dative ligand. UV-vis and 1H NMR spectroscopy show that Ge(TPP) is an aromatic Ge(II) porphyrin complex, while the 1H NMR spectrum of Ge(TPP)(py)2 clearly indicates the presence of a strong paratropic ring current, characteristic of an antiaromatic compound. Both Ge(TPP) and Ge(TPP)(py)2 have been crystallographically characterized, and the antiaromaticity of Ge(TPP)(py)2 leads to alternating short and long C-C bonds along the 20-carbon periphery of its porphine ring system. Coordination of pyridine to Ge(TPP) greatly increases its reducing ability: the Ge(TPP)0/2+ redox potential is about +0.2 V, while the Ge(TPP)(py)2(0/+) redox potential is -1.24 V (both vs. ferrocene). The equilibrium constant of the reaction Ge(TPP) + 2 py = Ge(TPP)(py)2 in C6D6 is 22 M-2. The germanium complex of the more electron-withdrawing tetrakis[3,5-bis(trifluoromethyl)phenyl]porphyrin, Ge(TArFP), and its pyridine adduct Ge(TArFP)(py)2 were synthesized. The equilibrium constant of the reaction Ge(TArFP) + 2 py = Ge(TArFP)(py)2 in C6F6/C6D6 is 2.3 x 10(4) M-2. Density functional theory calculations are consistent with the experimental observation that M(TPP)(py)2 formation from M(TPP) and pyridine is most favorable for M=Si, borderline for Ge, and unfavorable for Sn.     

Synthesis of Vinylene-Co,N-Linked Multi(porphyrin)s by the Addition of Free-Base Porphyrins to a C(2)H(2) Complex of Cobalt(III) Porphyrin and Their Oxidative Rearrangement to Vinylene-N,N'-Linked Multi(porphyrin)s

The nucleophilic addition reaction of a pyrrole nitrogen of free-base porphyrins to a pi-complexed acetylene ligand in a cationic Co(III) porphyrin intermediate afforded good yields of vinylene-Co,N'-linked bis(porphyrin)s, (Por)Co(III)-CH=CH-(N-Por)H(2). N-substituted porphyrin free bases are N-vinylated regioselectively at the pyrrole adjacent to the original N-substituted pyrrole in this reaction. Tris- and tetrakis(porphyrin)s have been prepared by reacting a vinylene-N,N'-linked bis(meso-tetraarylporphyrin) with (OEP)Co(III)(H(2)O)(2)ClO(4) (OEP: octaethylporphyrin dianion) and acetylene. The tetrakis(porphyrin) proved to be a 1:1 mixture of C(i)()- and C(2)-symmetric regioisomers. These organometallic Co(III) complexes underwent facile oxidative migration of the Co-bound vinyl group to a porphyrin pyrrole nitrogen when treated with Fe(III) salts or HClO(4) to provide moderate to good yields of Co(II) vinylene-N,N'-linked multi(porphyrin) complexes. (Vinylene-N,N')bis(porphyrin) free bases with combinations of different porphyrins have been obtained by this procedure. The homobinuclear (2Co(II), 2Cu(II), and 2Zn(II)) and heterobinuclear (Co(II)Cu(II) and Co(II)Zn(II)) complexes have been prepared and characterized spectroscopically. The single-crystal X-ray analysis of (CH=CH-N,N')[(OEP)Co(II)Cl][(TPP)Zn(II)Cl] (TPP: meso-tetraphenylporphyrin dianion) showed a face-to-face structure with an average inter-ring separation of 4.39 ? (triclinic P&onemacr;; Z = 2; a = 14.806(4), b = 18.703(10), c = 13.796(3) ?, alpha = 97.69(3), beta = 99.57(2), gamma = 96.74(3) degrees ).     

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.     

Structural, redox, and photophysical studies of the tetra(pyridyl)porphyrin complex containing four (2,2'-bipyridine)(2,2':6',2"-terpyridine)ruthenium(II) groups

New hybrid complexes of polypyridyl ruthenium and pyridylporphyrins have been prepared by the coordination of pyridyl nitrogens to the ruthenium centers. A 1:4 hybrid complex, [{Ru(bpy)(trpy)}4(mu4-H2Py4P)]8+ ([1]8+) (bpy = 2,2'-bipyridine; trpy = 2,2':6',2"-terpyridine; H2Py4P = 5,10,15,20-tetra(4-pyridyl)porphyrin), has been characterized by the single-crystal X-ray diffraction method. A 1:1 complex, [{Ru(bpy)(trpy)}(H2PyT3P)]2+ ([2]2+) (H2PyT3P = 5-(4-pyridyl)tritolylporphyrin) has also been prepared. The Soret band of the porphyrin ring shifts to longer wavelength with some broadening, the extent of the shift being larger for [1]8+. Cyclic voltammograms of the two complexes show simple overlap of the component redox waves. The complexes are weakly emissive at room temperature, which becomes stronger at lower temperatures. While [1]8+ at >140 K and [2]2+ at 77-280 K show only porphyrin fluorescence, [1]8+ at <140 K shows ruthenium and porphyrin phosphorescence, in addition to the porphyrin fluorescence.     

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.     

Direct nitric oxide detection in aqueous solution by copper(II) fluorescein complexes

A series of FL(n) (n = 1-5) ligands, where FL(n) is a fluorescein modified with a functionalized 8-aminoquinoline group as a copper-binding moiety, were synthesized, and the chemical and photophysical properties of the free ligands and their copper complexes were investigated. UV-visible spectroscopy revealed a 1:1 binding stoichiometry for the Cu(II) complexes of FL(1), FL(3), and FL(5) in pH 7.0 buffered aqueous solutions. The reactions of FL(2) or FL(4) with CuCl(2), however, appear to produce a mixture of 1:1 and 1:2 complexes, as suggested by Job's plots. These binding modes were modeled by the synthesis and X-ray crystal structure determination of Cu(II) complexes of 2-[(quinolin-8-ylamino)methyl]phenol (modL), employed as a surrogate of the FL(n) ligand family. Two kinds of crystals, [Cu(modL)(2)](BF(4))(2) and [Cu(2)(modL')(2)(CH(3)OH)](BF(4))(2) (modL' = 2-[(quinolin-8-ylamino)methyl]phenolate), were obtained. The structures suggest that one oxygen and two nitrogen atoms of the FL(n) ligands most likely bind to Cu(II). Introduction of nitric oxide (NO) to pH 7.0 buffered aqueous solutions of Cu(FL(n)) (1 microM CuCl(2) and 1 microM FL(n)) at 37 degrees C induces an increase in fluorescence. The fluorescence response of Cu(FL(n)) to NO is direct and specific, which is a significant improvement over commercially available small molecule-based probes that are capable of detecting NO only indirectly. The NO-triggered fluorescence increase of Cu(FL(5)) occurs by reduction of Cu(II) to Cu(I) with concomitant dissociation of the N-nitrosated fluorophore ligand from copper. Spectroscopic and product analyses of the reaction of the FL(5) copper complex with NO indicated that the N-nitrosated fluorescein ligand (FL(5)-NO) is the species responsible for fluorescence turn-on. Density functional theory (DFT) calculations of FL(5) versus FL(5)-NO reveal how N-nitrosation of the fluorophore ligand brings about the fluorescence increase. The copper-based probes described in the present work form the basis for real-time detection of nitric oxide production in living cells.     

Reactivity of dioxoruthenium(VI) porphyrins toward amines. Synthesis and characterization of bis(arylamine)ruthenium(II), bis(arylamido)- and bis(diphenylamido)ruthenium(IV), and oxo(tert-butylimido)ruthenium(VI) porphyrins

Reactions of dioxoruthenium(VI) porphyrins, [Ru(VI)O2(Por)], with p-chloroaniline, trimethylamine, tert-butylamine, p-nitroaniline, and diphenylamine afforded bis(amine)ruthenium(II) porphyrins, [Ru(II)(Por)(L)2] (L-p-ClC6H4NH2, Me3N, Por=TTP, 4-Cl-TPP; L=tBuNH2, Por = TPP, 3,4,5-MeO-TPP, TTP, 4-Cl-TPP, 3,5-Cl-TPP) and bis(amido)ruthenium(IV) porphyrins, [Ru(IV)(Por)(X)2] (X=p-NO2C6H4NH, Por=TTP, 4-Cl-TPP; X = Ph2N, Por = 3,4,5-MeO-TPP, 3,5-Cl-TPP), respectively. Oxidative deprotonation of [Ru(II)(Por)(NH2-p-C6H4Cl)2] in chloroform by air generated bis(arylamido)ruthenium(IV) porphyrins, [RuIV(Por)(NH-p-C6H4Cl)2] (Por=TTP. 4-Cl-TPP). Oxidation of [RuII(Por)-(NH2tBu)2] by bromine in dichloromethane in the presence of tert-butylamine and traces of water produced oxo(imido)ruthenium(VI) porphyrins, [RuVI-O(Por)(NtBu)] (Por=TPP, 3,4,5-MeO-TPP, TTP, 4-Cl-TPP, 3,5-Cl-TPP). These new classes of ruthenium complexes were characterized by 1H NMR, IR, and UV/visible spectroscopy, mass spectrometry, and elemental analysis. The structure of [Ru(IV)(TTP)(NH-p-C6H4Cl)2 . CH2Cl2 was determined by X-ray crystallography. The Ru-N bond length and the Ru-N-C angle of the Ru-NHAr moiety are 1.956(7) A and 135.8(6) degrees, respectively.     

Anionic ligand effect on the nature of epoxidizing intermediates in iron porphyrin complex-catalyzed epoxidation reactions

We have studied an anionic ligand effect in iron porphyrin complex-catalyzed competitive epoxidations of cis- and trans-stilbenes by various terminal oxidants and found that the ratios of cis- to trans-stilbene oxide products formed in competitive epoxidations were markedly dependent on the ligating nature of the anionic ligands. The ratios of cis- to trans-stilbene oxides obtained in the reactions of Fe(TPP)X (TPP = meso-tetraphenylporphinato dianion and X(-) = anionic ligand) and iodosylbenzene (PhIO) were 14 and 0.9 when the X(-) of Fe(TPP)X was Cl(-) and CF(3)SO(3)(-), respectively. An anionic ligand effect was also observed in the reactions of an electron-deficient iron(III) porphyrin complex containing a number of different anionic ligands, Fe(TPFPP)X [TPFPP = meso-tetrakis(pentafluorophenyl)porphinato dianion and X(-) = anionic ligand], and various terminal oxidants such as PhIO, m-chloroperoxybenzoic acid (m-CPBA), tetrabutylammonium oxone (TBAO), and H(2)O(2). While high ratios of cis- to trans-stilbene oxides were obtained in the reactions of iron porphyrin catalysts containing ligating anionic ligands such as Cl(-) and OAc(-), the ratios of cis- to trans-stilbene oxide were low in the reactions of iron porphyrin complexes containing nonligating or weakly ligating anionic ligands such as SbF(6)(-), CF(3)SO(3)(-), and ClO(4)(-). When the anionic ligand was NO(3)(-), the product ratios were found to depend on terminal oxidants and olefin concentrations. We suggest that the dependence of the product ratios on the anionic ligands of iron(III) porphyrin catalysts is due to the involvement of different reactive species in olefin epoxidation reactions. That is, high-valent iron(IV) oxo porphyrin cation radicals are generated as a reactive species in the reactions of iron porphyrin catalysts containing nonligating or weakly ligating anionic ligands such as SbF(6)(-), CF(3)SO(3)(-), and ClO(4)(-), whereas oxidant-iron(III) porphyrin complexes are the reactive intermediates in the reactions of iron porphyrin catalysts containing ligating anionic ligands such as Cl(-) and OAc(-).     

Nitric oxide binding and photodelivery based on ruthenium(II) complexes of 4-arylazo-3,5-dimethylpyrazole

Two fluorescent ligands, 3,5-dimethyl-4-(6'-sulfonylammonium-1'-azonaphthyl)pyrazole (dmpzn, 1) and 3,5-dimethyl-4-(4'-N,N'-dimethylaminoazophenyl)pyrazole (dmpza, 2) were obtained by condensation of ketoenolic derivatives with hydrazine. 1 and 2 formed the novel dinuclear complexes [(H(2)O)(3)ClRu(micro-L)(2)RuCl(H(2)O)(3)] (3 or 4) and [(H(2)O)(NO)Cl(2)Ru(micro-L)(2)RuCl(2)(NO)(H(2)O)] (6 or 7) (where L 1 = 2 or , respectively) which were characterized by IR, NMR and elemental analysis. The nitrosyl complexes were prepared by bubbling purified nitric oxide through methanol solutions of the corresponding ruthenium(II) chloroderivative or by reaction of the appropriate ligands with Ru(NO)Cl(3). Complexes 3 and 4 were found to bind NO, resulting in an increase in fluorescence. Ligand 1 also formed the mononuclear nitrosyl complex [Ru(NO)(bpy)(2)(dmpzn)]Cl(2) (8) which released NO in water at physiological pH and in the solid state as revealed by fluorescence and IR measurements, respectively.     

A series of trifacial Pd6 molecular barrels with porphyrin walls

Three new nanoscopic trigonal prisms, [(tmen)(6) Pd(6) (H(2)L)(3)](NO(3))(12) (1), [(Meen)(6) Pd(6)(H(2) L)(3)](NO(3))(12) (2), and [(2,2'-bipy)(6)Pd(6) (H(2)L)(3)](NO(3))(12) (3), have been synthesized in excellent yields through single-step metal-ligand-coordination-driven self-assembly using 5,10,15,20-tetrakis(3-pyridyl)porphyrin (H(2)L) as a donor and cis-blocked Pd(II) 90° acceptors. These complexes were fully characterized by spectroscopic studies and single-crystal X-ray diffraction. All of these barrels quantitatively bind Zn(II) ions in the N(4) pockets of the porphyrin walls at room temperature. Their corresponding zinc-embedded complexes, [(tmen)(6)Pd(6)(ZnL)(3)](NO(3))(12) (1?a), [(Meen)(6) Pd(6)(ZnL)(3)](NO(3))(12) (2?a), and [(2,2'-bipy)(6)Pd(6)(ZnL)(3)](NO(3))(12) (3?a), were synthesized under ambient conditions by the post-synthetic binding of Zn(II) ions into the H(2)N(4) pockets of the porphyrin walls of these complexes. These zinc-embedded complexes were characterized by electronic absorption, fluorescence emission, (1)H?NMR spectroscopy, as well as elemental analysis. Complexes 1-3 exhibited considerable microporosity in their solid state. Complex 1 was an efficient adsorbent for nitrogen gas and EtOH, MeOH, and water vapors.     

Laser flash photolysis generation and kinetic studies of porphyrin-manganese-oxo intermediates. Rate constants for oxidations effected by porphyrin-Mn(V)-oxo species and apparent disproportionation equilibrium constants for porphyrin-Mn(IV)-oxo species

Porphyrin-manganese(V)-oxo and porphyrin-manganese(IV)-oxo species were produced in organic solvents by laser flash photolysis (LFP) of the corresponding porphyrin-manganese(III) perchlorate and chlorate complexes, respectively, permitting direct kinetic studies. The porphyrin systems studied were 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TPFPP), and 5,10,15,20-tetrakis(4-methylpyridinium)porphyrin (TMPyP). The order of reactivity for (porphyrin)Mn(V)(O) derivatives in self-decay reactions in acetonitrile and in oxidations of substrates was (TPFPP) > (TMPyP) > (TPP). Representative rate constants for reaction of (TPFPP)Mn(V)(O) in acetonitrile are k = 6.1 x 10(5) M(-1) s(-1) for cis-stilbene and k = 1.4 x 10(5) M(-1) s(-1) for diphenylmethane, and the kinetic isotope effect in oxidation of ethylbenzene and ethylbenzene-d(10) is k(H)/k(D) = 2.3. Competitive oxidation reactions conducted under catalytic conditions display approximately the same relative rate constants as were found in the LFP studies of (porphyrin)Mn(V)(O) derivatives. The apparent rate constants for reactions of (porphyrin)Mn(IV)(O) species show inverted reactivity order with (TPFPP) < (TMPyP) < (TPP) in reactions with cis-stilbene, triphenylamine, and triphenylphosphine. The inverted reactivity results because (porphyrin)Mn(IV)(O) disproportionates to (porphyrin)Mn(III)X and (porphyrin)Mn(V)(O), which is the primary oxidant, and the equilibrium constants for disproportionation of (porphyrin)Mn(IV)(O) are in the order (TPFPP) < (TMPyP) < (TPP). The fast comproportionation reaction of (TPFPP)Mn(V)(O) with (TPFPP)Mn(III)Cl to give (TPFPP)Mn(IV)(O) (k = 5 x 10(8) M(-1) s(-1)) and disproportionation reaction of (TPP)Mn(IV)(O) to give (TPP)Mn(V)(O) and (TPP)Mn(III)X (k approximately 2.5 x 10(9) M(-1) s(-1)) were observed. The relative populations of (porphyrin)Mn(V)(O) and (porphyrin)Mn(IV)(O) were determined from the ratios of observed rate constants for self-decay reactions in acetonitrile and oxidation reactions of cis-stilbene by the two oxo derivatives, and apparent disproportionation equilibrium constants for the three systems in acetonitrile were estimated. A model for oxidations under catalytic conditions is presented.