Equilibrium thermodynamic studies in water: reactions of dihydrogen with rhodium(III) porphyrins relevant to Rh-Rh, Rh-H, and Rh-OH bond energetics

Aqueous solutions of rhodium(III) tetra p-sulfonatophenyl porphyrin ((TSPP)Rh(III)) complexes react with dihydrogen to produce equilibrium distributions between six rhodium species including rhodium hydride, rhodium(I), and rhodium(II) dimer complexes. Equilibrium thermodynamic studies (298 K) for this system establish the quantitative relationships that define the distribution of species in aqueous solution as a function of the dihydrogen and hydrogen ion concentrations through direct measurement of five equilibrium constants along with dissociation energies of D(2)O and dihydrogen in water. The hydride complex ([(TSPP)Rh-D(D(2)O)](-4)) is a weak acid (K(a)(298 K) = (8.0 +/- 0.5) x 10(-8)). Equilibrium constants and free energy changes for a series of reactions that could not be directly determined including homolysis reactions of the Rh(II)-Rh(II) dimer with water (D(2)O) and dihydrogen (D(2)) are derived from the directly measured equilibria. The rhodium hydride (Rh-D)(aq) and rhodium hydroxide (Rh-OD)(aq) bond dissociation free energies for [(TSPP)Rh-D(D(2)O)](-4) and [(TSPP)Rh-OD(D(2)O)](-4) in water are nearly equal (Rh-D = 60 +/- 3 kcal mol(-1), Rh-OD = 62 +/- 3 kcal mol(-1)). Free energy changes in aqueous media are reported for reactions that substitute hydroxide (OD(-)) (-11.9 +/- 0.1 kcal mol(-1)), hydride (D(-)) (-54.9 kcal mol(-1)), and (TSPP)Rh(I): (-7.3 +/- 0.1 kcal mol(-1)) for a water in [(TSPP)Rh(III)(D(2)O)(2)](-3) and for the rhodium hydride [(TSPP)Rh-D(D(2)O)](-4) to dissociate to produce a proton (9.7 +/- 0.1 kcal mol(-1)), a hydrogen atom (approximately 60 +/- 3 kcal mol(-1)), and a hydride (D(-)) (54.9 kcal mol(-1)) in water.     

High-spin iron(III) complexes: structural,spectroscopic, and photochemical studies

Reaction of FeCl₃ with one equivalent of acac (acac = pentane-2,4-dionate) and KTp^Me2 (Tp^Me2 = hydrotris(3,5-dimethyl-pyrazol-1-yl)borate) yielded Tp^Me2Fe(acac)Cl (3), which upon reaction with methanolic solution of sodium azide resulted in the formation of a six coordinate compound Tp^Me2Fe(acac)N₃ (4) with a single azide. When the reaction of FeCl₃ and KTp^Me2 was performed with two equivalents of sodium azide and one equivalent of 3,5-dimethylpyrazole (Pz^Me2H), a six coordinate cis azide compound [Tp^Me2Fe(Pz^Me2H)(N₃)₂] (5) was obtained. These compounds were characterized by spectroscopic methods and single crystal X-ray crystallography. Electrochemical studies of 5 show that it can be irreversibly reduced at relatively lower potential than 4. The photolysis of 5 was performed at 77 K at different wavelengths (480, 419, and 330 nm) showing that 5 was photoreduced to a high-spin Fe(II) species instead of photooxidized to Fe(V).     

Complexation of nitrogen and sulphur donor Schiff's base ligand to Cr(III) and Ni(II) metal ions: synthesis, spectroscopic and antipathogenic studies

2,6-diacetyl pyridine based ligand was synthesized by the reaction of 2,6-diacetyl pyridine with thiocarbohydrazide in presence of acetic acid. The coordination compounds with Cr(III) and Ni(II) metal ions having [Cr(L)X]X2 and [Ni(L)X]X compositions (where L=ligand and X=NO3-, Cl- and CH3COO-) were synthesized and characterized by physicochemical and spectral studies. The studies like elemental analyses, molar conductance measurements, magnetic susceptibility measurements, IR, UV-Vis, NMR, mass and EPR reveal that the complexes are octahedral. The compounds were examined against the pathogenic fungal and bacterial strains like Alternaria brassicae, Aspergillus niger, Fusarium oxysporum, Xanthomonas compestris and Pseudomonas aeruginosa. A. niger causes the diseases Apergillosis and Otomycosis in humans.     

Selective reduction of allenyl(diphenyl)phosphine oxides to allyl(diphenyl)phosphine oxides

The reduction of allenyl(diphenyl)phosphine oxides with HSiCl₃ or LiAlH₄ selectively afforded the corresponding allyl(diphenyl)phosphine oxides. 3-Methylbut-2-en-1-yl(diphenyl)phosphine oxide reacted with AlCl₃ to give a mixture of 4,4-dimethyl-1-phenyl-1,2,3,4-tetrahydro-λ⁵-phosphinoline 1-oxide and 4,4-dimethyl-1-phenyl-1,4-dihydro-λ⁵-phosphinoline 1-oxide.     

Coordinating ability of rhodium(III) porphyrins toward organic bases

Reactions of hydroxo(2,3,7,8,12,13,17,18-octaethylporphyrinato)rhodium(III) and acetylacetato-(5,10,15,20-tetraphenylporphyrinato)rhodium(III) with nitrogen-containing substrates were studied by spectrophotometry. The stability constants and compositions of the resulting molecular complexes were determined, and the effects of the macrocycle nature and substrate basicity on the stability constants were estimated. The structures of the isolated rhodium porphyrin molecules and their complexes with organic bases were optimized by the PM3 quantum chemical method. The degree of macrocycle deformation was found to change in the course of metal–substrate coordination. A correlation between the metal–substrate bond energy and equilibrium constant was revealed.

     

Complexation,solubilities and thermodynamic functions for cerium(III) fluoride-water system

The solubility, solubility product and the thermodynamic functions for the CeF₃–H₂O system have been measured using the radiometric, conductometric and potentiometric techniques. The radiometric values for the solubility and solubility product, the lowest and more acceptable for reasons cited in previous papers, are 3.14·10^–5 M and 2.17·10^–17 respectively. The enthalpy change measured by the conductometric method is almost twice as that obtained by potentiometric method due to abnormal conductances registered at higher temperatures. The average values for H^o and G^o and S^o at 298 K are 53.0±17.4, 91.7±4.0 and –129.7±58.2 KJ·mol^–1 respectively. The positive values for H^o and G^o and the negative value for S^o are indicative of the low solubility of this salt in water. The stability constants for the mono- and difluoride complexes of Ce(III) have been determined potentiometrically using unsaturated solution mixtures of Ce(III) and F^–. These values for CeF⁺ and CeF ₂ ⁺ are 997±98 and (1.03±0.44)·10⁵, respectively. Studies on pH dependence of the solubility shows that the solubility reaches a minimum value at a pH of about 3.2.     

A vibrational spectroscopic study of tris triphenyl phosphine rhodium (I) chloride

In this work we report the first Raman spectrum of tris triphenyl phosphine rhodium (I) chloride. The vibrational spectrum of triphenyl phosphine has also been recorded under similar conditions to facilitate comparisons. FT-Raman spectra and diffuse reflectance mid-IR and far-IR spectra are presented and a full skeletal vibrational assignment is made.     

Synthetic,spectroscopic, thermal,and structural studies of antimony(III) bis(pyrrolidinedithiocarbamato)alkyldithiocarbonates

An account of the synthesis, spectroscopic, thermal and structural behavior of antimony(III) bis(pyrrolidinedithiocarbamato)alkyldithiocarbonates is presented. The reaction of antimony(III) bis(pyrrolidinedithiocarbamate) chloride with potassium organodithiocarbonate in equimolar ratio yielded the corresponding mixed derivatives of the type [(CH₂)₄NCS₂]₂SbS₂COR [where R = Me, Et, Pr ⁿ , Pr ⁱ , Bu ⁿ , and Bu ⁱ ]. These newly synthesized complexes have been characterized by physicochemical [molecular weight determination, melting points, and elemental analysis], spectral [UV, IR, far-IR, NMR (¹H and ¹³C)], thermal [TG, DTA, and FAB⁺ mass], and structural [powder XRD and SEM] studies. Analytical studies leads to purity and structural properties of the synthesized complexes on the other hand powder X-ray diffraction and SEM studies show that multiphase, polycrystalline, and rod-shaped complexes have been formed having nanorange crystallite size and monoclinic crystal system.     

Luminescence and triplet—triplet absorption spectra of rhodium (III) porphyrins

Photophysical studies of four rhodium(III) porphyrins [RhTPPS (H₂O)₃^3?, RhTPP (Cl) (L), RhOEP (Cl) (L) and RhMesoPMEI(CI) (L)] show that these porphyrins are characterised by a moderate phosphorescence (φ ? 10^?2) and a very weak fluorescence (φ ? 5 × 10^?4) in solution at room temperature. TPP derivatives also have moderately intense triplet—triplet absorption extending to 900 nm.     

Homodinuclear glycolate derivatives of bismuth(V) and arsenic(III): synthesis and spectroscopic studies

Ligand bridged homodinuclear derivatives of bismuth(V) of the type, (1a–1d) [where R =–C(CH₃)₂CH₂CH(CH₃)–(1a),–CH(CH₂CH₃)CH₂–(1b),–CH(CH₃)CH(CH₃)–(1c),–CH(CH₃)CH₂–(1d)] have been synthesized by reactions of equimolar oxobis(triphenylbismuth)dichloride, {[Ph₃Bi]₂O}Cl₂ with glycols, HOROH in the presence of NaOMe. Reactions of sodiumtetraisopropoxoarsonate, NaAs(OPrⁱ)₄ with in 1 : 1 molar ratio yielded homodinuclear alkoxo derivatives of arsenic(III) containing glycols, (2a–2d). All compounds were characterized by elemental analysis, molecular weight determinations, IR and NMR (¹H and ¹³C) spectral studies.     

Facile synthesis,X-ray analysis,and spectroscopic studies of di-iron propanedithiolate complexes with tris(aromatic)phosphine ligands

Three new propanedithiolate-type iron–sulfur complexes containing tris(aromatic)phosphine ligands, [{(μ-SCH₂)₂CH₂}Fe₂(CO)₅L] (L?=?P(PhOMe-p)₃, 1; P(PhMe-p)₃, 2; P(PhF-p)₃, 3), have been prepared through carbonyl substitution in the presence of Me₃NO. The new complexes 1–3 were characterized by elemental analysis, IR, ¹H, ¹³C{¹H}, and ³¹P{H} NMR spectra. The molecular structures of 1–3 were unequivocally determined by single crystal X-ray diffraction, in which the tris(aromatic)phosphine coordinated to Fe resides in an apical position of the pseudo-square-pyramidal geometry. IR spectroscopy and X-ray crystallographic analysis for 1–3 have indicated that the highly electron rich tris(aromatic)phosphine ligands (where the corresponding electron-donating abilities display the following order of P(PhOMe-p)₃?>?P(PhMe-p)₃?>?P(PhF-p)₃) result in a considerable red shift of the CO-stretching frequencies and a clear change of the Fe–Fe bond distances in 1–3.     

Pentamethylcyclopentadienyl rhodium(III) trifluorovinyl phosphine complexes and attempted intramolecular dehydrofluorinative coupling of pentamethylcyclopentadienyl and trifluorovinyl phosphine ligands

The trifluorovinyl phosphine complexes [Cp*RhCl₂{PR_3−x(CFCF₂)_x}] (1x = 1, a R = Ph, b Prⁱ, c Et; 2x = 2, R = Ph) have been prepared by treatment of [Cp*RhCl(μ-Cl)]₂ with the relevant phosphine. The salt [Cp*RhCl(CNBu^t){PPh₂(CFCF₂)}]BF₄, 3, was prepared by addition of Bu^tNC to 1a in the presence of NaBF₄. The salt [Cp*RhCl{κP,κS-(CF₂CF)PPh(C₆H₄SMe-2)}]BF₄ was prepared as a mixture of cis (5a) and trans (5b) isomers by treatment of [Cp*RhCl(μ-Cl)]₂ with the phosphine-thioether (CF₂CF)PPh(C₆H₄SMe-2), 4, in the presence of NaBF₄. The structures of 1a-c and 5a have been determined by single-crystal X-ray diffraction. Intramolecular dehydrofluorinative carbon-carbon coupling between pentamethylcyclopentadienyl and trifluorovinylphosphine ligands of 1a, 3 and 5 has been attempted. No reaction was observed on treatment of the neutral complex [Cp*RhCl₂{PPh₂(CFCF₂)}], 1a, with proton sponge, however, 5a underwent dehydrofluorinative coupling to yield [{η⁵,κP,κS-(C₅Me₄CH₂CFCF)PPh(C₆H₄SMe-2)}RhCl]BF₄, 6. Other reactions, in particular addition of HF across the vinyl bonds of 5, occurred leading to a mixture of products. The cation of 3 underwent similar reactions.     

Chromium(III) stars and butterflies: synthesis, structural and magnetic studies of tetrametallic clusters

We report the synthesis, structures and magnetic properties of a series of chromium(III) metal-centered triangle (or "star") clusters, [Cr(4){RC(CH(2)O)(3)}(2)(4,4'-R'(2)-bipy)(3)Cl(6)] [R = Et, R' = H (2); R = HOCH(2), R' = H (3); R = Et, R' = (t)Bu (4)], prepared by two-step solvothermal reactions starting from [CrCl(3)(thf)(3)]. The product of the first stage of this reaction is the salt [Cr(bipy)(2)Cl(2)](2)[Cr(2)Cl(8)(MeCN)(2)] (1). In the absence of the diimine, a different family of tetrametallics is isolated: the butterfly complexes [Cr(4){EtC(CH(2)O)(3)}(2){NH(C(R)NH)(2)}(2)Cl(6)] (R = Me (5), Et (6), Ph (7)] where the chelating N-acetimidoylacetamidine NH(C(R)=NH)(2) ligands are formed in situ via condensation of the nitrile solvents (RCN) under solvothermal conditions. Magnetic measurements show the chromium stars to have an isolated S = 3 ground state, arising from antiferromagnetic coupling between the central and peripheral metal ions, analogous to the well-known Fe(III) stars. Bulk antiferromagnetic ordering is observed at 0.6 K. The butterfly complexes have a singlet ground state, with a low-lying S = 1 first excited state, due to dominant wing-body antiferromagnetic coupling.     

pH-specific synthesis and spectroscopic, structural, and magnetic studies of a chromium(III)-citrate species. Aqueous solution speciation of the binary chromium(III)-citrate system

In an attempt to understand the aqueous interactions of Cr(III) with the low-molecular-mass physiological ligand citric acid, the pH-specific synthesis in the binary Cr(III)-citrate system was explored, leading to the complex (NH4)4[Cr(C6H4O7)(C6H5O7)].3H2O (1). 1 crystallizes in the monoclinic space group I2/a, with a = 19.260(10) A, b = 10.006(6) A, c = 23.400(10) A, beta = 100.73(2) degrees , V = 4431(4) A3, and Z = 8. 1 was characterized by elemental analysis and spectroscopic, structural, thermal, and magnetic susceptibility studies. Detailed aqueous speciation studies in the Cr(III)-citrate system suggest the presence of a number of species, among which is the mononuclear [Cr(C6H4O7)(C6H5O7)]4- complex, optimally present around pH approximately 5.5. The structure of 1 reveals a mononuclear octahedral complex of Cr(III) with two citrate ligands bound to it. The two citrate ligands have different deprotonation states, thus signifying the importance of the mixed deprotonation state in the coordination sphere of the Cr(III) species in aqueous speciation. The latter reveals the distribution of numerous species, including 1, for which the collective structural, spectroscopic, and magnetic data point out its physicochemical profile in the solid state and in solution. The importance of the synthetic efforts linked to 1 and the potential ramifications of Cr(III) reactivity toward both low- and high-molecular-mass biotargets are discussed in light of (a) the quest for well-characterized soluble Cr(III) species that could be detected and identified in biologically relevant fluids, (b) ongoing efforts to delineate the aqueous speciation of the Cr(III)-citrate system and its link to biotoxic Cr(III) manifestations, and (c) the synthetic utility of convenient Cr(III) precursors in the synthesis of advanced materials.     

Cationic methyl complexes of rhodium(III): synthesis, structure, and some reactions

Cationic methyl complex of rhodium(III), trans-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] (1) is prepared by interaction of trans-[Rh(Acac)(PPh₃)₂(CH₃)I] with AgBPh₄ in acetonitrile. Cationic methyl complexes of rhodium(III), cis-[Rh(Acac)(PPh₃)₂ (CH₃)(CH₃CN)][BPh₄] (2) and cis-[Rh(BA)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] (3) (Acac, BA are acetylacetonate and benzoylacetonate, respectively), are obtained by CH₃I oxidative addition to rhodium(I) complexes [Rh(Acac)(PPh₃)₂] and [Rh(BA)(PPh₃)₂] in acetonitrile in the presence of NaBPh₄. Complexes 2 and 3 react readily with NH₃ at room temperature to form cis-[Rh(Acac)(PPh₃)₂(CH₃)(NH₃)][BPh₄] (4) and cis-[Rh(BA)(PPh₃)₂(CH₃)(NH₃)][BPh₄] (5), respectively. Complexes 1-5 were characterized by elemental analysis, ¹H and ³¹P{¹H} NMR spectra. Complexes 1, 2, 3 and 4 were characterized by X-ray diffraction analysis. Complexes 2 and 3 in solutions (CH₂Cl₂, CHCl₃) are presented as mixtures of cis-(PPh₃)₂ isomers involved into a fluxional process. Complex 2 on heating in acetonitrile is converted into trans-isomer 1. In parallel with that isomerization, reductive elimination of methyl group with formation of [CH₃PPh₃][BPh₄] takes place. Replacement of CH₃CN in complexes 1 and 2 by anion I⁻ yields in both cases the neutral complex trans-[Rh(Acac)(PPh₃)₂(CH₃)I]. Strong trans influence of CH₃ ligand manifests itself in the elongation (in solid) and labilization (in solution) of rhodium-acetonitrile nitrogen bond.     

Synthesis,spectroscopic and thermal studies on ruthenium(III), rhodium(III) and iridium(III) complexes with hydrazones derived from 2,6-diacetylpyridine and different aromatic hydrazides

Summary The reactions of MCl₃·3H₂O (M=Ru, Rh or Ir) with hydrazones have been studied by three different methods and complexes of the types [M(LH₂)(H₂O)₂]Cl₃, [M(L)Cl(H₂O)] and [M(LH₂)Cl₂]Cl·H₂O have been isolated. Tentative structural conclusions are drawn for these products based upon elemental analysis, electrical conductance, magnetic moment, and i.r. and¹H n.m.r. data. The thermal stability and mode of decomposition for the complexes have been studied by t.g.a., d.t.g. and d.s.c. techniques.     

Tropiporphyrins, cycloheptatrienyl analogues of the porphyrins: synthesis, spectroscopy, chemistry, and structural characterization of a silver(III) derivative

Tripyrranes were condensed with 1,3,5-cycloheptriene-1,6-dicarbaldehyde in TFA-CH(2)Cl(2) to give, following oxidation with 0.1% aqueous ferric chloride solutions, a series of tropiporphyrins 9. These cycloheptatrienyl analogues of the porphyrins show strong diatropic ring currents by proton NMR spectroscopy where the internal CH gives a resonance at -7.3 ppm, although the meso-protons are not shifted as far downfield as most aromatic porphyrinoid systems. These data indicate that the seven-membered ring distorts the porphyrinoid macrocycle and decreases the overall diatropicity in tropiporphyrins. Addition of trace amounts of TFA to solutions of 9 affords the corresponding aromatic monocations, and at higher acid concentrations a nonaromatic dication is generated. The dication has undergone C-protonation at one of the meso-bridges and has lost the plane of symmetry present in the parent system. This species shows significant downfield shifts to the cycloheptatrienyl protons, indicating that this unit has taken on tropylium character. Tropiporphyrin 9a underwent a Diels-Alder cycloaddition with dimethyl acetylenedicarboxylate in refluxing xylenes to give modest yields of the related adduct. The Diels-Alder adduct 17 showed an increased diatropic ring current where the internal proton shifted beyond -9 ppm, and this indicates that the [18]annulene substructure has flattened out compared to 9a. Diimide reduction of 9a afforded a dihydrotropiporphyrin that also showed a stronger ring current. Tropiporphyrins 9 were also shown to react with silver(I) acetate in the presence of DBU in refluxing pyridine to give the corresponding silver(III) organometallic derivatives. The meso-protons for these metal complexes give proton NMR chemical shift values similar to those for the parent tropiporphyrins, indicating that the macrocycle is still distorted, but the external olefinic protons are shifted downfield compared to 9. A diphenyl-substituted silver(III) derivative 18b was further characterized by X-ray crystallography. This shows that the cycloheptatriene unit takes on a highly twisted geometry that distorts the overall conformation of the porphyrinoid macrocycle.     

Dipyrrinphenol-Mn(III) complex: synthesis, electrochemistry, spectroscopic characterisation and reactivity

Herein, we report the manganese complex with a novel trianionic ligand, the pentafluorophenyldipyrrinphenol ligand DPPH(3). The X-ray crystal structure reveals that the Mn(III) complex exists in a dimeric form in the solid state. Electrochemical studies indicate two quasi-reversible one electron oxidation processes. EPR data on the one electron oxidised species in solution support the formation of a monuclear Mn complex with an S = 3/2 spin system. Preliminary studies towards epoxidation reactions were tested in the presence of iodosylbenzene (PhIO) and are in favour of an oxygen-atom-transfer (OAT) reaction catalyzed by the Mn(III) complex.     

Sterically crowded cyclopropanation catalysts. Syn-selectivity using rhodium(III)porphyrins

Rhodium(III)porphyrins catalyze the decomposition of ethyl diazoacetate and the transfer of ethoxy-carbonylcarbene to alkenes to form cyclopropanes in moderate to high yields. When compared with other catalysts a large syn-selectivity was observed on reaction with cis-alkenes. This selectivity increased with the size of the substituents, and suggested a preferential direction of approach of the alkene towards a rhodium—carbene complex.