Reaction of oxide radical ion (O.–) with substituted pyrimidines

Pulse radiolysis technique has been used to investigate the reaction of oxide radical ion (O^.–) with 4,6-dihydroxy-2-methyl pyrimidine (DHMP), 2,4-dimethyl-6-hydroxy pyrimidine (DMHP), 5,6-dimethyl uracil (DMU) and 6-methyl uracil (MU) in strongly alkaline medium. The second-order rate constants for the reaction of O^.– with these compounds are in the range 2-5 × 10⁸ dm³ mol^–1 s^–1. The transient absorption spectra obtained with DHMP have two maxima at 290 and 370 nm and with DMHP have maxima at 310 and 470 nm. The transient spectrum from DMU is characterized by its absorption maxima at 310 and 520 nm and that of MU by its single maximum at 425 nm. The intermediate species were found to react with N,N,N,N-tetramethyl-p-phenylenediamine (TMPD) with high G(TMPD^.+) values ranged between 3.9 × 10^–7 molJ^–1 and 4.8 × 10^–7 molJ^–1. These radicals undergo decay by second-order kinetics (2k/ = 1.0-1.7 × 10⁶ s^–1). The reaction of O^.– with the selected pyrimidines is proposed to proceed through a hydrogen abstraction from the methyl group forming allyl type radicals. These are mainly oxidizing radicals and hence readily undergo electron transfer reactions with TMPD.     

A di-μ-oxomolybdenum(V) complex of 6-acetonylisoxanthopterin,undergoing oxygen atom transfer with dimethyl sulphoxide

The new compound, Na[(Mo₂ ^VO₄)(pte)(OMe)(MeOH)₂] (pte = anion of 6-acetonylisoxanthopterin), has been prepared using the redox non-innocent title ligand in MeOH–H₂O, and characterized by elemental analysis and physico-chemical methods including e.s.m.s., i.r., u.v.–vis. and ¹H-n.m.r. spectra. Rate constants data (1.4 × 10^–3 s^–1 at 300 K) for its oxygen atom transfer with dimethyl sulphoxide tally with those of synthetic analogue systems reported earlier by different authors. The negative activation entropy (–206.3 J mol^–1 deg^–1) is consistent with an associative mechanism for this reaction.     

Reaction of Substituted Group 14 Element Potassium Salts with 1-(Chloromethyl)silatrane: Substitution or Rearrangement?

Russian Journal of General Chemistry - Reactions of 1-(chloromethyl)silatrane with organic group 14 element anions [(Me3Si)3E]? (E = Si, Ge) generated in situ afforded the corresponding...     

Redox potentials of oxoiron(IV) porphyrin π-cation radical complexes: participation of electron transfer process in oxygenation reactions

The oxoiron(IV) porphyrin π-cation radical complex (compound I) has been identified as the key reactive intermediate of several heme enzymes and synthetic heme complexes. The redox properties of this reactive species are not yet well understood. Here, we report the results of a systematic study of the electrochemistry of oxoiron(IV) porphyrin π-cation radical complexes with various porphyrin structures and axial ligands in organic solvents at low temperatures. The cyclic voltammogram of (TMP)Fe(IV)O, (TMP = 5,10,15,20-tetramesitylporphyrinate), exhibits two quasi-reversible redox waves at E(1/2) = 0.88 and 1.18 V vs SCE in dichloromethane at -60 °C. Absorption spectral measurements for electrochemical oxidation at controlled potential clearly indicated that the first redox wave results from the (TMP)Fe(IV)O/[(TMP(+?))Fe(IV)O](+) couple. The redox potential for the (TMP)Fe(IV)O/[(TMP(+?))Fe(IV)O](+) couple undergoes a positive shift upon coordination of an anionic axial ligand but a negative shift upon coordination of a neutral axial ligand (imidazole). The negative shifts of the redox potential for the imidazole complexes are contrary to their high oxygenation activity. On the other hand, the electron-withdrawing effect of the meso-substituent shifts the redox potential in a positive direction. Comparison of the measured redox potentials and reaction rate constants for epoxidation of cyclooctene and demethylation of N,N-dimethylanilines enable us to discuss the details of the electron transfer process from substrates to the oxoiron(IV) porphyrin π-cation radical complex in the oxygenation mechanisms.     

Structure and properties of the ion pair charge-transfer complex of octacyanotungstate(IV) with the 2,2′-bipyridinium dication

The X-ray crystal structure of (bpyH2)2[W(CN)8]·4H2 O (bpyH2=2,2-bipyridinium) is described. The [W(CN)8]4– anion has an approximately square antiprismatic (D4d) conformation, seemingly imposed by strong anion–water–cation hydrogen-bonding interactions. Bond distances in the anion are: WC 2.150(5), 2.163(5); CN 1.128(6), 1.145(6)Å and the angles WCN are 177.6(5), 178.3(5)°. The dihydrate and the anhydrous salt are both intensely black solids, exhibiting ion-pair charge-transfer interaction between cation and anion. E.s.r. spectra indicate that 30% of the tungsten is present as WV in the solid state, but that in solution only the WIV complex is present. The electron withdrawing effect of the cation is discussed and compared with that in a series of salts with different bipyridinium cations.     

Reaction of 1-(het)aryl-3-bromoprop-2-ynones with furans in solid metal oxides or salts: cross-coupling or cycloaddition?

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A theoretical study of an unusual Y-shaped three-coordinate Pt complex: Pt(0) σ-disilane complex or Pt(II) disilyl complex?

The unusual Y-shaped structure of the recently reported three-coordinate Pt complex Pt[NHC(Dip)(2)](SiMe(2)Ph)(2) (NHC = N-heterocyclic carbene; Dip = 2,6-diisopropylphenyl) was considered a snapshot of the reductive elimination of disilane. A density functional theory study indicates that this structure arises from the strong trans influence of the extremely σ-donating carbene and silyl ligands. Though this complex can be understood to be a Pt(II) disilyl complex bearing a distorted geometry due to the Jahn-Teller effect, its (195)Pt NMR chemical shift is considerably different from those of Pt(II) complexes but close to those of typical Pt(0) complexes. Its Si···Si bonding interaction is ~50% of the usual energy of a Si-Si single bond. The interaction between the Pt center and the (SiMe(2)Ph)(2) moiety can be understood in terms of donation and back-donation interactions of the Si-Si σ-bonding and σ*-antibonding molecular orbitals with the Pt center. Thus, we conclude that this is likely a Pt(0) σ-disilane complex and thus a snapshot after a considerable amount of the charge transfer from disilane to the Pt center has occurred. Phenyl anion (Ph(-)) and [R-Ar](-) [R-Ar = 2,6-(2,6-iPr(2)C(6)H(3))(2)C(6)H(3)] as well as the divalent carbon(0) ligand C(NHC)(2) also provide similar unusual Y-shaped structures. Three-coordinate digermyl, diboryl, and silyl-boryl complexes of Pt and a disilyl complex of Pd are theoretically predicted to have similar unusual Y-shaped structures when a strongly donating ligand coordinates to the metal center. In a trigonal-bipyramidal Ir disilyl complex [Ir{NHC(Dip)(2)}(PH(3))(2)(SiMe(3))(2)](+), the equatorial plane has a similar unusual Y-shaped structure. These results suggest that various snapshots can be shown for the reductive eliminations of the Ge-Ge, B-B, and B-Si σ-bonds.     

Synthetic studies and structural aspects of novel metallacyclic compoundsof titanium(IV) incorporating nitrogen,oxygen and sulphur: 1. Reactions of cis-dialkoxy-bis(acetylacetonato)titanium(IV) with alkoxyalkanols and the crystal structure of a new modification: di-μ-oxo-bis[diacetylacetonatotitanium(IV)]

Reactions of cis-dialkoxy-bis(acetylacetonato)titanium(IV), [(acac)₂Ti(OR)₂] (R = Et, Pr ⁱ ) with alkoxyalkanols (ROCH₂CH₂OH) (R = Me, Et, n-Bu) in 1:1 and 1:2 molar ratios in refluxing benzene under anhydrous conditions yield [(acac)₂Ti(OR)_2–n (OCH₂CH₂OR) _n ] (n = 1 or 2) complexes, which were purified by distillation under reduced pressure. On the basis of i.r. and n.m.r. (¹H- and ¹³C-) spectral studies, a cis-octahedral environment around Ti^IV is proposed. On keeping the distilled dark brown-red viscous liquid [(acac)₂Ti(OEt)(OCH₂CH₂OBu)] for 2 weeks, orange yellow crystals of [(acac)₂TiO]₂ were obtained. A single crystal X-ray diffraction study suggests the product is a new modification of [(acac)₂TiO]₂.     

Interaction of thorium(IV) with nitrate in aqueous solution: medium effect or weak complexation?

Microcalorimetric titrations were performed to study the Th(IV)/nitrate interaction in aqueous solution. The results show the formation of a weak mononuclear complex of Th(IV) with nitrate and allow the determination of the complexation thermodynamic parameters at 298 K and ionic strength 1.0 mol dm(-3). The reaction is endothermic and entropy driven. Data and comparison with similar actinide(IV) complexes allow to confirm the inner-sphere nature of the Th(NO(3))(3+) complex.     

Reaction of Substituted Cyclopentadienyl-magnesium-Chloride with Carbonyl Compound ( Ⅰ )——Reaction of (1, 1-Dialkyl-3-Butenyl) Cyclopentadienyl-magnesium-chloride with Ketones

The substituted cyclopentadienyl-magnesium-chloride, obtained by exocyclic addition of 6,6-dialkylfulvene and allyl-magnesium-chloride, reacted with the ketone 3, the product was hydrolyzed and dehydrated to give the 2-(1 ,1-dialkyl-3-butenyl)-6,6-dialkyl-fulvene 5. The structure of 5 was determined by using the 1H NMR spectra of 5 and the adducts of 5 with tetracyanoethylene.     

Extended metal atom chains (EMACs) of five chromium or cobalt atoms: symmetrical or unsymmetrical?

Structural studies of pentachromium and pentacobalt extended metal atom chain (EMAC) systems are presented in which the metal chains are helically wrapped by either the pentadentate dianion tripyridyldiamide (tpda) or its diethyl-substituted analogue bis(4-ethyl-2-pyridylamido)pyridine (etpda). The compound Cr(5)(tpda)(4)(NCS)(2), has alternating long and short Cr-Cr distances, contrary to recent reports that describe it as symmetrical with essentially equally spaced chromium atoms. The linear Cr(5)(10+) chain is composed of two Cr(2)(4+) quadruply bonded units and an isolated high spin Cr(II) unit. The new compounds Cr(5)(etpda)(4)Cl(2), [Cr(5)(etpda)(4)FCl]PF(6), and Co(5)(etpda)(4)(NCS)(2)() employ the etpda ligand as "insulation" around a central pentametal-atom "wire." Compound, like all other oxidized pentachromium compounds, has very disparate alternating short-long-short-long Cr-Cr distances, 2.032(3) A, 2.560(6) A, 1.873(5) A, and 2.509(4) A. Compound shows a nearly uniform spacing of the Co atoms, although the outer Co-Co distances (2.279[4] A) are slightly longer than the inner ones (2.239[4] A).     

Reaction of α-(trialkylstannyl) acetylenes with metallic sodium

-Trialkylstannylacetylenes react under mild conditions with metallic sodium at the Sn-C(sp) bond to give hexaalkyldistannanes and sodium acetylalkynides inca. 65–85 % yields.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1109–1110, June, 1994.     

A three-component protocol for the enantiodifferentiation of amines using triphenyl borate and BINOL: is it an ion pair or an amine-coordinated complex?

The structure of the borate complex responsible for the enantiodifferentiation of amines using a previously reported three-component protocol has been established. The choice between an ion pair and an amine-coordinated complex with the N atom of the amine coordinated to the B atom is favored for the former structure based on the DFT-calculated ¹¹B NMR chemical shifts. In contrast to expectations, the anisotropies of the quadrupolar ¹¹B nucleus for the two structures were calculated to be indistinguishable with regard to their effect on the linewidth of the NMR signal.     

Reaction of 1-(R-Sulfonyl)indoles with N,N-Dibenzyl-β-amino Alcohols

The reaction of 1-(methylsulfonyl)- and 1-(phenylsulfonyl)indoles with N,N-dibenzylamino alcohols leads to the formation of a mixture of isomeric 1-(-aminoethyl)indoles.     

Reactivity of Cr(III) μ-oxo compounds: catalyst regeneration and atom transfer processes

Oxidation of CpCr[(XylNCMe)(2)CH] (Xyl = 2,6-Me(2)C(6)H(3)) with pyridine N-oxide or air generated the μ-oxo dimer, {CpCr[(XylNCMe)(2)CH]}(2)(μ-O). The μ-oxo dimer was converted to paramagnetic Cr(III) CpCr[(XylNCMe)(2)CH](X) complexes (X = OH, O(2)CPh, Cl, OTs) via protonolysis reactions. The related Cr(III) alkoxide complexes (X = OCMe(3), OCMe(2)Ph) were prepared by salt metathesis and characterized by single crystal X-ray diffraction. The interconversion of the Cr(III) complexes and their reduction back to Cr(II) with Mn powder were monitored using UV-vis spectroscopy. The related CpCr[(DepNCMe)(2)CH] (Dep = 2,6-Et(2)C(6)H(3)) Cr(II) complex was studied for catalytic oxygen atom transfer reactions with PPh(3) using O(2) or air. Both Cr(II) complexes reacted with pyridine N-oxide and γ-terpinene to give the corresponding Cr(III) hydroxide complexes. When CpCr[(DepNCMe)(2)CH] was treated with pyridine N-oxide in benzene in the absence of hydrogen atom donors, a dimeric Cr(III) hydroxide product was isolated and structurally characterized, apparently resulting from intramolecular hydrogen atom abstraction of a secondary benzylic ligand C-H bond followed by intermolecular C-C bond formation. The use of very bulky hexaisopropylterphenyl ligand substituents did not preclude the formation of the analogous μ-oxo dimer, which was characterized by X-ray diffraction. Attempts to develop a chromium-catalyzed intermolecular hydrogen atom transfer process based on these reactions were unsuccessful. The protonolysis and reduction reactions of the μ-oxo dimer were used to improve the previously reported Cr-catalyzed radical cyclization of a bromoacetal.     

Reaction of 1-hydrohexafluoroisobutenyloxytrimethylsilane with fluoride ion sources. 2,2,2’,2’-Tetrakis(trifluoromethyl)divinyl ether

The reaction of 1-hydrohexafluoroisobutenyloxytrimethylsilane (2a) with cesium fluoride in diglyme leads to elimination of trimethylfluorosilane to form the 1-hydrohexafluoroisobutenolate anion (3), which is silylated with trialkylchlorosilanes at the oxygen atom. In the presence of bis(trifluoromethyl)ketene N,N,O-trimethylaminoacetal or N-(α,α-difluoroalkyl)-dialkylamines, silane 2a is transformed into 2,2,2’,2’-tetrakis(trifluoromethyl)divinyl ether. The reaction of trifluoroacetic anhydride with N-(1,1,2,2-tetrafluoroethyl)diethylamine affords trifluoroacetyl fluoride in quantitative yield.     

Significant modification of the I(-)3 Lewis base character in the β-cyclodextrin polyiodide inclusion complex with Co2+ ion: an FT-Raman investigation

The β-cyclodextrin (β-CD) polyiodide inclusion complex (β-CD)(2)·Co(0.5)·I(7)·21H(2)O has been synthesized, characterized and further investigated via FT-Raman spectroscopy in the temperature range of 30-120°C. The experimental results point to the coexistence of I(-)(7) units (I(2)·I(-)(3)·I(2)) that seem not to interact with the Co(2+) ions and I(-)(7) units that display such interactions. The former units exhibit a disorder-order transition of both their I(2) molecules above 60°C due to a symmetric charge-transfer interaction with the central I(-)(3) [I(2)←I(-)(3)→I(2)], whereas in the latter units only one of the two I(2) molecules becomes well-ordered above 30°C. The other I(2) molecule remains disordered presenting no charge-transfer phenomena. The Co(2+) ion induces a considerable asymmetry on the geometry of the I(-)(3) anion and a significant modification of its Lewis base character. Complementary dielectric measurements suggest no important involvement of H···I contacts in the observed modification of the I(-)(3) electron-transfer properties.     

Synthesis of 1-(4-Antipyrinyl)-3-(3-Chlorophenyl)-Triazene and Its Colour Reaction with Mercury

TheantiPyrinldiazoaminoreagentsweresensitivefOrCd(II)andHg(II)11-3l-Receatly,anewreagrntlK4-antiPyrinl)-3<3-Chlorophenylytrime(APPT)wasSynthsized.ThecolourreahonofAnCPTwithmerCurywasstUdied-ThemethodfordeterminingmicroaznountofmempwithAPCPTwasmoresensitiveandhighlyselective.AnditwasusedtodeterIninemercmpcoboinnatUralwaterwithsatisfactryresults.ExperimeutalAPP~:Model75lspectrophotOmeter,ModelpH-2meter(madeinShanghai).Sbodard~solution:DissolveHgCl2(A.R.)inWate.AddseveraldroPso…     

Why intermolecular nitric oxide (NO) transfer? Exploring the factors and mechanistic aspects of NO transfer reaction

Small molecule activation and their transfer reactions in biological or catalytic reactions are greatly influenced by the metal-centers and the ligand frameworks. Here, we report the metal-directed nitric oxide (NO) transfer chemistry in low-spin mononuclear {Co(NO)}⁸, [(12-TMC)Co^III(NO⁻)]²⁺ (1-CoNO, S = 0), and {Cr(NO)}⁵, ([(BPMEN)Cr(NO)(Cl)]⁺) (4-CrNO, S = 1/2) complexes. 1-CoNO transfers its bound NO moiety to a high-spin [(BPMEN)Cr^II(Cl₂)] (2-Cr, S = 2) and generates 4-CrNOvia an associative pathway; however, we did not observe the reverse reaction, i.e., NO transfer from 4-CrNO to low-spin [(12-TMC)Co^II]²⁺ (3-Co, S = 1/2). Spectral titration for NO transfer reaction between 1-CoNO and 2-Cr confirmed 1 : 1 reaction stoichiometry. The NO transfer rate was found to be independent of 2-Cr, suggesting the presence of an intermediate species, which was further supported experimentally and theoretically. The experimental and theoretical observations support the formation of μ-NO bridged intermediate species ({Cr–NO–Co}⁴⁺). Mechanistic investigations using ¹⁵N-labeled-¹⁵NO and tracking the ¹⁵N-atom established that the NO moiety in 4-CrNO is derived from 1-CoNO. Further, to investigate the factors deciding the NO transfer reactivity, we explored the NO transfer reaction between another high-spin Cr^II-complex, [(12-TMC)Cr^II(Cl)]⁺ (5-Cr, S = 2), and 1-CoNO, showing the generation of the low-spin [(12-TMC)Cr(NO)(Cl)]⁺ (6-CrNO, S = 1/2); however, again there was no opposite reaction, i.e., from Cr-center to Co-center. The above results advocate clearly that the NO transfer from Co-center generates thermally stable and low-spin and inert {Cr(NO)}⁵ complexes (4-CrNO & 6-CrNO) from high-spin and labile Cr-complexes (2-Cr & 5-Cr), suggesting a metal-directed NO transfer (cobalt to chromium, not chromium to cobalt). These results explicitly highlight that the NO transfer is strongly influenced by the labile/inert behavior of the metal-centers and/or thermal stability rather than the ligand architecture.

Nitric oxide activation and parameters influencing intermolecular transfer of nitric oxide.     

Fluoro complexes of hexavalent uranium—VI adducts of dioxodifluorouranium (VI) with nitrogen and oxygen donor ligands

Adducts of uranyl fluoride of the types UO₂F₂·L·H₂O and UO₂F₂·L′ (where L = 2,2′-dipyridyl, 1, 10-phenathroline and 8-hydroxyquinoline; L′ = dimethyl sulphoxide, dimethyl formamide, pyridine, α-picoline and γ-picoline) have been prepared by mixing uranyl fluoride and the corresponding ligand in 1:1 mole ratio in 50% aqueous ethanolic medium. Two adducts with urea, viz. [UO₂F₂(urea)] and [UO₂F₂(urea)₂] have been obtained by reacting uranyl fluoride with urea in different mole ratios in dry methanolic medium. The molecular conductances of the complexes in methanol indicate their nonelectrolytic nature. IR spectral studies show that urea, dimethyl formamide and dimethyl sulphoxide complexes are oxygen bonded ones. Thermogravimetric analysis suggests that the dipyridyl, phenanthroline and oxine complexes contain coordinated water.