Laser photolysis studies of the reaction of chromium(III) octaethylporphyrin complex with triphenylphosphine and triphenylphosphine oxide

The photoreaction of the chromium(III) octaethylpoprhyrin complex, [Cr(OEP)(Cl)(L)] (L = H2O, Py, OPPh3), in dichloromethane was studied using laser flash photolysis technique. Laser irradiation causes the generation of a coordinately unsaturated intermediate [Cr(OEP)(Cl)], which reacts with ligands in solution to give the parent complex, [Cr(OEP)(Cl)(L)], or a transient species, [Cr(OEP)(Cl)(H2O)], when L = Py or OPPh3. Once produced [Cr(OEP)(Cl)(H2O)] eventually exchanges the axial H2O ligand with L to regenerate [Cr(OEP)(Cl)(L)]. The kinetics of the axial ligand substitution reaction was followed spectrophotometrically, and the ligand-concentration dependence of the ligand exchange rate revealed that the reaction occurs via a limited dissociative mechanism. The photoreaction of [Cr(OEP)(Cl)(OPPh3)] containing excess PPh3 in the bulk solution leads to the unfavorable coordination of the PPh3 molecule to the chromium ion to give a transient complex, [Cr(OEP)(Cl)(PPh3)]. The dynamic and thermodynamic properties of [Cr(OEP)(Cl)(PPh3)] in solution are discussed on the basis of the kinetic parameters of the dissociation and association reactions of the PPh3 ligand together with the steric aspect of the molecular structure of the related complexes.     

Enantioselective glyoxylate-ene reactions catalysed by (salen)chromium(III) complexes

An enantioselective carbonyl-ene reaction of alkyl glyoxylates with various 1,1-disubstituted olefins, catalysed by chiral (salen)Cr(III)BF₄ complexes, has been studied. We found that a chromium complex bearing adamantyl substituents at the 3,3′-positions of the salicylidene moiety catalysed the reaction with much greater selectively than the classic Jacobsen-type catalyst. The reaction proceeded effectively under undemanding conditions in the presence of 2 mol % of the catalyst in an acceptable yield and with 59-92% ee.     

Equilibrium studies on chromium(III) complexes of salicylic acid and salicylic acid derivatives in aqueous solution

The complexes of chromium(III) ion formed by salicylic acid, SA(H(2)L), and its derivatives (H(2)L): 5-nitrosalicylic acid (5-NSA), 5-sulphosalicylic acid (5-SSA) were investigated by means of potentiometry and spectroscopy, at 25 degrees C and in ionic strength of 0.1 M KNO(3) and 0.1 M KCl, respectively. Over the acidic pH range, the coordination of Cr(III) ion to SA and its derivatives in 1 : 1 mole ratio occurs, CrL(+) type complex is formed. In the excess of ligand, the coordination of the second ligand molecule is somewhat hindered; as a result CrL(HL) type complex occurs. Their existences were verified and their formation constants were determined. At near neutral pH, CrL(OH) and CrL(HL)(OH)(-) type hydroxo complexes formed by hydrolytic equilibria and their formation constants were also defined. The stabilities of Cr(III) complexes of SA and its derivatives decrease in the following order: SA>5-SSA>5-NSA. The formation constants of Cr(III) complexes of SA and its derivatives are in comparable ranges with the corresponding complexes of the 2,x-dihydroxybenzoic acid (2,x-DHBA) of Cr(III) ion. The stabilities of SA complexes for V(IV), Cr(III) and Fe(III) ions that have similar ionic radii, increase in the order VOL相似文献   

Triamidoamine complexes of chromium(III) and chromium(IV)

Treatment of [CrCl3(THF)3] with slightly more than 1 equiv of Li3(N3N) [(N3N)(3-) = ((Me3SiNCH2CH2)3N)(3-)] affords the triamidoamine complex [Cr(N3N)] (1) in 75% yield. 1 is oxidized by PhICl2, CuCl2, or AgCl to give the chromium(IV) complex [Cr(N3N)Cl] (2) in moderate yields. Alternatively, complex 2 is obtained directly from [CrCl3(THF)3] in 50% yield after treatment with 0.5 equiv of Li3(N3N). Both compounds are high-spin complexes bearing three and two unpaired electrons, respectively. Their molecular structures are described revealing a trigonal monopyramidal and trigonal bipyramidal coordination geometry of the chromium center, respectively.     

Solid-phase ligand substitution reactions by borohydride anions in chromium(III) and cobalt(III) amine complexes

The kinetic and thermodynamic characteristics of solid-phase ligand substitution reactions were determined for chromium(III) and cobalt(III) amine complexes with B₁₀H ₁₀ ^2– and C₂B₉H ₁₂ ^– in the outer sphere. The kinetic equation of the topochemical process was found to be of the formf()=(1–)^2/3, corresponding to a reaction proceeeding on the interface between the phases (shrinking sphere). Two types of solid-phase ligand substitution reactions were found: endothermic and exothermic reactions taking place either through thermal activation of the metal-ligand bond (in substitution reactions by the anion B₁₀H ₁₀ ^2– ), or through the acid-base proton-exchange reaction between the anion C₂B₉H ₁₂ ^– entering the coordination sphere and the amine leaving it; in this case the process proceeds without mass loss. It could be demonstrated that the reactions occurring in crystalline complex salts cannot proceed by purely dissociative or associative mechanisms; depending on the structure of the crystal lattice, mutually adapted dissociative or associative mechanisms are feasible. Reactions proceeding by the first mechanism haveE _a=300–500 kJ/mol and logA=30–50; the values for reactions proceeding by the second mechanism areE _a= =180–250 kJ/mol and logA=15–25.

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Zusammenfassung Die kinetischen und thermodynamischen Kennwerte der Ligandensubstitutionsreaktionen in fester Phase bei Chrom(III)- und Kobalt(III)-Aminkomplexen mit B₁₀H ₁₀ ^2– und C₂B₉H_12/– als Anionen in der externen Sphäre wurden untersucht. Die kinetische Gleichung des topochemischen Prozesses hat die Formf()=(1–)^2/3, was einer an der Grenzfläche zwischen zwei Phasen verlaufenden Reaktion entspricht. Zwei Typen von Ligandsubstitutionsreaktionen in fester Phase wurden gefunden: endotherme und exotherme Reaktionen verlaufen entweder infolge thermischer Aktivierung der Metall-Ligand-Bindung (in Substitutionsreaktionen des Anions B₁₀H ₁₀ ^2– ) oder durch Protonenaustausch zwischen dem in die Koordinationssphäre eintretende Anion C₂B₉H ₁₂ ^– und dem daraus austretenden Amin; in diesem Falle verläuft der Prozeß ohne Massenverlust. Es konnte gezeigt werden, daß die in kristallinen Komplexsalzen vor sich gehenden Reaktionen nicht nach einem rein dissoziativen oder assoziativen Mechanismus verlaufen können; abhängig von der Struktur des Kristallgitters ist ein wechselseitig angepasster dissoziativer oder assoziativer Mechanismus wahrscheinlich. Die nach dem ersten Mechanismus verlaufenden Reaktionen weisen fürE _a Werte von 300 500 kJ/mol und für logA von 30–50 auf, während bei nach dem zweiten Mechanismus verlaufenden Reaktionen die entsprechenden Werte zwischen 180 und 250 kJ/mol bzw. 15 und 25 liegen.

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() () B₁₀H ₁₀ ^2- C₂B₉ H _12/- . , f()=(1-)^2/3, ( ). : - , - ( B₁₀H ₁₀ ^2- ), - _{29 12} ^- ; ., . . , , _a =300–500 / logA=30–50, –ina=180–250 / log=15–25.

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The authors are grateful to F. G. Szabó (ETALON Factory, Baku) for help in the application of the derivatograph for quantitative measurements and for development of a method to record thermoanalytical curves for measuring enthalpies of reactions.     

Cyclopentadienyl mesityl complexes of chromium(II) and chromium(III)

Chromium(III) mesityl complexes were synthesized by protonolysis of chromocene with 1,3-diisopropylimidazolium chloride or DBU hydrochloride, salt metathesis with MesMgBr, and single electron oxidation with iodine.     

Laser photolysis studies of spiropyran-merocyanine aggregate formation in solution

The photoinduced processes leading to formation of J-aggregate stacks of 1-(β-methacryloxyethyl)-3,3-dimethyl-6′- nitrospiro-(indoline-2,2′-[2H-[2H-1] benzopyran) d its associated ring opened merocyanine form B have been determined by N₂-laser transient spectroscopy. Detailed mechanisms for formation of complexes AB, A₂B, and J-aggregate stacks (A₂B) _n in aliphatic and aromatic solvents are presented.     

Flash photolysis studies of charge-transfer photochemistry of nickel(II) and cobalt(III) complexes

The photochemical behavior of cobalt(III) and nickel(II) complexes on excitation in the charge-transfer bands is reviewed in this article with particular reference to the study of intermediates. Investigations on the photoredox reactions of cobalt(III) and nickel(II) complexes using flash kinetic spectroscopic methods reveal details on the characteristics of the intermediates produced from the charge-transfer excited states of these metal complexes. The reactive species produced on photolysis of cobalt(III)-amine complexes activate molecular oxygen, producing mononuclear and dinuclear dioxygen species coordinated as superoxo and peroxo forms. Cobalt(III)-amino-acid complexes on photolysis lead to the formation of cobalt(III)-alkyl complexes which are identified as transients. The spectra and the decay kinetics are described with the view to elucidate mechanistic details. Nickel(II) macrocyclic complexes on excitation in the charge-transfer bands lead to oxidation of the metal centre. Scavenging experiments using dioxygen, alcohols and acids were carried out to understand the mechanistic details.     

2,5-Diphenyloxazole chromium(III) complexes

Summary Complexes of chromium(III) with 2,5-diphenyloxazole (PPO) of general formula Cr(PPO)_nX₃·m H₂O, where X=Cl^–, Br^–, I^– or NO ₃ ^su– ; n=1–3 and m=0–6, have been prepared and studied by spectroscopic and magnetic methods and by molar conductivity measurements. All the complexes seem to be hexacoordinated, generally with monodentate N-bonded ligand.     

Semicarbazone and thiosemicarbazone chromium(III) complexes

Summary Chromium(III) complexes, [Cr(ligand)₂]Cl, containing the semicarbazones and thiosemicarbazones of 2-hydroxyacetophenone and 2-hydroxynaphthaldehyde, and [Cr(ligand)₂Cl₂]Cl, formed from 4-hydroxyacetophenone semicarbazone and thiosemicarbazone, have been synthesized. The complexes were characterized by elemental analysis, conductance, magnetic moment, i.r., electronic and e.s.r. spectral studies. On the basis of physicochemical investigations tetragonal geometries are assigned to the complexes.     

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).     

Thermal studies on oxalate complexes. II. Complexes of iron (III) and chromium (III)

The decomposition of solid K₃[Fe(C₂O₄)₃] · 2 H₂O and K₃[Cr(C₂O₄)₃] · 3 H₂O has been studied using TGA and DSC. After dehydration, the chromium compound was found to decompose by the loss of CO in two steps, the loss of CO₂ and additional CO, and finally the loss of CO₂. The final product appears to be either K₃CrO₃ or the mixed oxides of chromium and potassium. Kinetic parameters and enthalpy data are presented for these reactions. In the case of K₃[Fe(C₂O₄)₃] · 2 H₂O, dehydration is followed by the loss of CO₂ and CO, CO₂ alone, and finally CO. The final product appears to be a basic carbonate of the type K₃[FE(O)₂(CO₃)]. Kinetic and thermal data are presented for most of these decomposition reactions.     

Synthesis and structural studies of novel aminopolychloroethylated chelate acetylacetonate complexes of aluminum (III) and chromium (III)

Structural Chemistry - Novel bio-medicinally promising complexes of amidotrichloroethylated acetylacetonate with Cr(III) and Al(III), which combine synthetically and pharmacologically attractive...     

Asymmetric catalysis of hetero-ene reactions with tridentate Schiff base chromium(III) complexes

Tridentate Schiff base chromium(III) complex 1 catalyzes the asymmetric hetero-ene reaction between aryl aldehydes and either 2-methoxypropene or 2-trimethylsilyloxypropene to provide a series of beta-hydroxyenol ether products in high yields and enantioselectivities. X-ray crystallographic analysis of a closely related chromium complex reveals a bridged, dimeric structure bearing aquo-bound six-coordinate Cr(III) centers. A mechanism is proposed wherein water dissociation is effected by means of a chemical desiccant (BaO or silyl enol ether), thereby revealing the site for aldehyde complexation.     

Alcoholate complexes of chromium(III) chloride

Summary A number of alcoholate complexes of chromium chloride with the general formula, CrCl₃ · xROII (R = Me, Et, i-Pr, n-Bu and n-Ilexyl; x = 3 and 4) have been synthesized by the reactions of CrCl₃ · 3 TIIF with an excess of the appropriate alcohols under reflux. Physicochemical studies such as i.r., visible reflectance, electron spin resonance spectra and thermogravimetric measurements, in addition to elemental analyses, throw light on the structure of these complexes.     

Mixed fluoroamine complexes of chromium(III)

Summary Mixed difluoro(diamine)(diamme)chromium(III) complexes have been synthesized with ethylenediamine (en), 1,3 propanediamine(tn) and 1,2-cyclohexanediamine(chxn):trans-[CrF₂(aa)(bb)]Br (aa=en, bb=tn; aa=tn, bb= chxn) andcis-[CrF₂(aa)(bb)]Br (aa=en, bb=chxn). The corresponding fluoroaqua(diamine) (diamine)chromium(III) complexes have been prepared by acid hydrolysis as perchlorate or iodide salts. All have been characterized by chemical analysis, electronic and i.r. spectra and conductivity measurements.