O2 activation by bis(imino)pyridine iron(II)-thiolate complexes

The new iron(II)-thiolate complexes [((iPr)BIP)Fe(II)(SPh)(Cl)] (1) and [((iPr)BIP)Fe(II)(SPh)(OTf)] (2) [BIP = bis(imino)pyridine] were prepared as models for cysteine dioxygenase (CDO), which converts Cys to Cys-SO(2)H at a (His)(3)Fe(II) center. Reaction of 1 and 2 with O(2) leads to Fe-oxygenation and S-oxygenation, respectively. For 1 + O(2), the spectroscopic and reactivity data, including (18)O isotope studies, are consistent with an assignment of an iron(IV)-oxo complex, [((iPr)BIP)Fe(IV)(O)(Cl)](+) (3), as the product of oxygenation. In contrast, 2 + O(2) results in direct S-oxygenation to give a sulfonato product, PhSO(3)(-). The positioning of the thiolate ligand in 1 versus 2 appears to play a critical role in determining the outcome of O(2) activation. The thiolate ligands in 1 and 2 are essential for O(2) reactivity and exhibit an important influence over the Fe(III)/Fe(II) redox potential.     

Direct coupling of benzene with olefin catalyzed by Pd(OAc)(2) combined with heteropolyoxometalate under dioxygen

The oxidative coupling reaction of benzenes with alkenes was successfully achieved by the Pd(OAc)(2)/molybdovanadophosphoric acid (HPMoV)/O(2) system. For example, the reaction of benzene with ethyl acrylate by the above catalytic system in acetic acid afforded ethyl cinnamate as a major product in satisfactory yield.     

Axial ligand and spin-state influence on the formation and reactivity of hydroperoxo-iron(III) porphyrin complexes

The present study focuses on the formation and reactivity of hydroperoxo-iron(III) porphyrin complexes formed in the [Fe(III)(tpfpp)X]/H(2)O(2)/HOO(-) system (TPFPP=5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin; X=Cl(-) or CF(3) SO(3)(-)) in acetonitrile under basic conditions at -15 °C. Depending on the selected reaction conditions and the active form of the catalyst, the formation of high-spin [Fe(III)(tpfpp)(OOH)] and low-spin [Fe(III)(tpfpp)(OH)(OOH)] could be observed with the application of a low-temperature rapid-scan UV/Vis spectroscopic technique. Axial ligation and the spin state of the iron(III) center control the mode of O-O bond cleavage in the corresponding hydroperoxo porphyrin species. A mechanistic changeover from homo- to heterolytic O-O bond cleavage is observed for high- [Fe(III)(tpfpp)(OOH)] and low-spin [Fe(III)(tpfpp)(OH)(OOH)] complexes, respectively. In contrast to other iron(III) hydroperoxo complexes with electron-rich porphyrin ligands, electron-deficient [Fe(III)(tpfpp)(OH)(OOH)] was stable under relatively mild conditions and could therefore be investigated directly in the oxygenation reactions of selected organic substrates. The very low reactivity of [Fe(III)(tpfpp)(OH)(OOH)] towards organic substrates implied that the ferric hydroperoxo intermediate must be a very sluggish oxidant compared with the iron(IV)-oxo porphyrin π-cation radical intermediate in the catalytic oxygenation reactions of cytochrome P450.     

Cyclic perfluorocarbon radicals and anions having high global warming potentials (GWPs): structures, electron affinities, and vibrational frequencies

Adiabatic electron affinities, optimized molecular geometries, and IR-active vibrational frequencies have been predicted for small cyclic hydrocarbon radicals C(n)H(2)(n)(-)(1) (n = 3-6) and their perfluoro counterparts C(n)F(2)(n)(-)(1) (n = 3-6). Total energies and optimized geometries of the radicals and corresponding anions have been obtained using carefully calibrated (Chem. Rev. 2002, 102, 231) density functional methods, namely, the B3LYP, BLYP, and BP86 functionals in conjunction with the DZP++ basis set. The predicted electron affinities show that only the cyclopropyl radical tends to bind electrons among the hydrocarbon radicals studied. The trend for the perfluorocarbon (PFC) radicals is quite different. The electron affinities increase with expanding ring size until n = 5 and then slightly decrease at n = 6. Predicted electron affinities of the hydrocarbon radicals using the B3LYP hybrid functional are 0.24 eV (C(3)H(5)/C(3)H(5)(-)), -0.19 eV (C(4)H(7)/C(4)H(7)(-)), -0.15 eV (C(5)H(9)/C(5)H(9)(-)), and -0.11 eV (C(6)H(11)/C(6)H(11)(-)). Analogous electron affinities of the perflurocarbon radicals are 2.81 eV (C(3)F(5)/C(3)F(5)(-)), 3.18 eV (C(4)F(7)/C(4)F(7)(-)), 3.34 eV (C(5)F(9)/C(5)F(9)(-)), and 3.21 eV (C(6)F(11)/C(6)F(11)(-)).     

Molecular paramagnetic semiconductor: crystal structures and magnetic and conducting properties of the Ni(dmit)(2) salts of 6-oxoverdazyl radical cations (dmit = 1,3-dithiol-2-thione-4,5-dithiolate)

Four kinds of 1:1 and 1:3 salts of 3-[4-(trimethylammonio)phenyl]-1,5-diphenyl-6-oxoverdazyl radical cation ([1](+)) and its mono- and dimethyl derivatives ([2](+) and [3](+)) with Ni(dmit)(2) anions (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) ([1](+)[Ni(dmit)(2)](-) (4), [2](+)[Ni(dmit)(2)](-) (5), [3](+)[Ni(dmit)(2)](-) (6), and [1](+)[Ni(dmit)(2)](3)(-) (7)) have been prepared, and the magnetic susceptibilities (chi(M)) have been measured between 1.8 and 300 K. The chi(M) values of salts 5 and 7 can be well reproduced by the sum of the contributions from (i). a Curie-Weiss system with a Curie constant of 0.376 (K emu)/mol and negative Weiss constants (THETAV;) of -0.4 and -1.7 K and (ii). a dimer system with strong negative exchange interactions of 2J/k(B) = -354 and -258 K, respectively. The dimer formations in Ni(dmit)(2) anions have been ascertained by the crystal structure analyses of salts 4-6. In salts 4 and 6, Ni(dmit)(2) dimer molecules are sandwiched between two verdazyl cations, indicating the formation of a linear tetramer in 4 and 6. The magnetic susceptibility data for salts 4 and 6 have been fitted to a linear tetramer model using an end exchange interaction of 2J(1)/k(B) = -600 K and a central interaction of 2J(2)/k(B) = -280 K for 4 and 2J(1)/k(B) = -30 K and 2J(2)/k(B) = -580 K for 6, respectively. The results of the temperature dependence of the g(T) value in salts 4-6 obtained by ESR measurement also support the above analyses. The 1:1 salts 4-6 are insulators. On the other hand, the conductivity of the 1:3 salt 7 at 20 degrees C was sigma = 0.10 S cm(-)(1) with an activation energy E(A) = 0.099 eV, showing the semiconductor property. Salt 7 is a new molecular paramagnetic semiconductor.     

Pd(OAc)2-catalyzed oxidative coupling reaction of benzenes with olefins in the presence of molybdovanadophosphoric acid under atmospheric dioxygen and air

The direct oxidative coupling reaction of benzenes with alkenes bearing an electron-withdrawing group was successfully achieved by the use of Pd(OAc)(2)/molybdovanadophosphoric acid (HPMoV) as the key catalyst under O(2) or air atmosphere. Thus, the reaction of benzene with ethyl acrylate under air (1 atm) assisted by Pd(OAc)(2)/HPMoV afforded ethyl cinnamate as a major product in satisfactory yield (74%). This catalytic system could be extended to the coupling reactions between various substituted benzenes and alkenes through the direct aromatic C-H bond activation. In the reaction of benzene with ethyl acrylate under O(2) (1 atm), the best turn-over number (TON) of Pd(OAc)(2) reached was 121. This reaction provides a green route to cinnamate derivatives, which are important precursors of a variety of pharmaceuticals.     

Rhenium oxo complexes of a chelating diyne ligand. Synthesis and study of the kinetics of protonation

A series of oxo complexes, Re(O)X(diyne) (X = I, Me, Et), have been prepared from 2,7-nonadiyne and Re(O)I(3)(PPh(3))(2). Addition of B(C(6)F(5))(3) to Re(O)I(2,7-nonadiyne) (5) results in coordination of the oxo ligand to the boron. The protonation of Re(O)(X)(2-butyne)(2) and Re(O)(X)(2,7-nonadiyne)(2) with a variety of acids has been examined. With 5 and HBF(4)/Et(2)O, the ultimate product was [Re(CH(3)CN)(3)(I)(2,7-nonadiyne)](2+) (7). The conversion of 5 to 7 changes the conformation of the diyne ligand from a "chair" to a "boat" and shifts its propargylic protons considerably downfield in the (1)H NMR. The kinetics of the protonation of Re(O)I(2,7-nonadiyne) (5) by CF(3)SO(3)H in CH(3)CN have been monitored by visible spectroscopy, in a stopped-flow apparatus, and by low temperature (1)H NMR. Two second-order rate constants, presumably successive protonations, were observed in the stopped-flow, k(1) = 11.9 M(-)(1) s(-)(1) and k(2) = 3.8 M(-)(1) s(-)(1). Low temperature (1)H NMR spectroscopy indicated that the resulting solution contained a mixture of two doubly protonated intermediates X and Y, each of which slowly formed the product 7 via an acid-independent process.     

Synthesis and characterization of carboxylate-rich complexes having the [Fe2(mu-OH)2(mu-O2CR)]3+ and [Fe2(mu-O)(mu-O2CR)]3+ cores of O2-dependent diiron enzymes

The {Fe2(mu-OH)2(mu-O2CR)}3+ and {Fe2(mu-O)(mu-O2CR)}3+ cores of the carboxylate-bridged diiron(III) centers in the enzyme active sites were reproduced by small molecule model complexes that were prepared through direct oxygenation of the mononuclear iron(II) complexes. Upon oxygenation of [Fe(O2CArTol)2(Hdmpz)2], where -O2CArTol is 2,6-di(p-tolyl)benzoate and Hdmpz is 3,5-dimethylpyrazole, [Fe2(mu-OH)2(mu-O2CArTol)(O2CArTol)3(OH2)(Hdmpz)2] was generated and characterized to share close physical properties with sMMOHox, including delta = 0.45 (2) mm/s, DeltaEQ = 1.21 (2) mm/s, and J = -7.2 (2) cm-1. The compound [Fe2(mu-O)(mu-O2CAr4-FPh)(O2CAr4-FPh)3(Hdmpz)3], where -O2CAr4-FPh is 2,6-di(4-fluorophenyl)benzoate, with delta = 0.51 (2) mm/s, DeltaEQ = 1.26 (2) mm/s, and J = -117.4 (1) cm-1, was isolated as the oxygenation product of [Fe(O2CAr4-FPh)2(Hdmpz)2].     

Speciation in the aqueous peroxovanadate-maltol and (peroxo)vanadate-uridine systems

The speciation in the aqueous H(+)/H(2)VO(4)(-)/H(2)O(2)/maltol (Ma), H(+)/H(2)VO(4)(-)/uridine (Ur) and H(+)/H(2)VO(4)(-)/H(2)O(2)/Ur systems was determined in the physiological medium of 0.150 M Na(Cl) at 25 degrees C. A combination of quantitative (51)V NMR (Bruker AMX500) and potentiometric data (glass electrode) was collected and treated simultaneously by the computer program LAKE. In the quaternary maltol system, the two species VXMa(2)(-) and VX(2)Ma(2-) (where X denotes the peroxo ligand) were found in the pH region 5-10, in addition to all binary and ternary complexes. Their formation was fast. In the ternary uridine (H(+)/H(2)VO(4)(-)/Ur) subsystem, altogether three vanadate-uridine (V-Ur) species were found in the pH region 4-10, with compositions VUr(2-), V(2)Ur(2)(2-) and V(2)Ur(2)(3-). Equilibrium was fast except in weakly acidic solutions when slowly decomposing decavanadates formed. In the quaternary H(+)/H(2)VO(4)(-)/H(2)O(2)/Ur system, five additional species were found at pH > 7. They were of VXUr and VX(2)Ur compositions. Their formation was fast. Formation constants, compositions and (51)V NMR chemical shifts are given for all the species found in the systems, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. Biological and medical relevance of the species (in the treatment of diabetes) are also discussed, with pseudo-physiological conditions modelled.     

Roles of a tetrahydroborate ligand in a facile route to ruthenium(II) ethyl hydride complexes, and a kinetic study of ethane reductive elimination

The tetrahydroborate ligand in [Ru(eta(2)-BH(4))(CO)H(PMe(2)Ph)(2)], 1, allows conversion under very mild conditions to [Ru(CO)(Et)H(PMe(2)Ph)(3)], 7, by way of [Ru(eta(2)-BH(4))(CO)Et(PMe(2)Ph)(2)], 4. Deprotection of the hydride ligand in 7(by BH(3) abstraction) occurs only in the final step, thus preventing premature ethane elimination. A deviation from the route from 4 to 7 yields [Ru(eta(2)-BH(4))(COEt)(PMe(2)Ph)(3)], 6, but does not prevent ultimate conversion to 7. Modification of the treatment of 4 yields an isomer of 7, 10. Both isomers eliminate ethane at temperatures above 250 K: the immediate product of elimination, thought to be [Ru(CO)(PMe(2)Ph)(3)], 11, can be trapped as [Ru(CO)(PMe(2)Ph)(4)], 12, [Ru(CO)H(2)(PMe(2)Ph)(3)], 3a, or [Ru(CO)(C[triple bond]CCMe(3))H(PMe(2)Ph)(3)], 13. The elimination is a simple first-order process with negative DeltaS(++) and (for 7) a normal kinetic isotope effect (k(H)/k(D)= 2.5 at 287.9 K). These results, coupled with labelling studies, rule out a rapid equilibrium with a [sigma]-ethane intermediate prior to ethane loss.     

Dioxygen activation and substrate oxygenation by a p-nitrothiophenolatonickel complex: unique effects of an acetonitrile solvent and the p-nitro group of the ligand

The nickel(II) complex [Ni(Tp(Me2)) (SC(6)H(4)NO(2))] [1a; Tp(Me2) = hydrotris(3,5-dimethylpyrazol-1-yl)borate] reacts with O(2) to form the ligand oxygenation product ArSO(2)(-) in MeCN, and also 1a catalyzes the oxygenation of external substrates such as triphenylphosphine. The reactivity may correlate to the unique quinoid-like resonance structure of the thiophenolate ligand. The structure is stabilized by a p-nitro group and induced by coordination of MeCN.     

Highly powerful and practical acylation of alcohols with acid anhydride catalyzed by Bi(OTf)(3).

Bi(OTf)(3)-catalyzed acylation of alcohols with acid anhydride was evaluated in comparison with other acylation methods. The Bi(OTf)(3)/acid anhydride protocol was so powerful that sterically demanding or tertiary alcohols could be acylated smoothly. Less reactive acylation reagents such as benzoic and pivalic anhydride are also activated by this catalysis. In these cases, a new technology was developed in order to overcome difficulty in separation of the acylated product from the remaining acylating reagent: methanolysis of the unreacted anhydride into easily separable methyl ester realized quite easy separation of the desired acylation product. The Bi(OTf)(3)/acid anhydride protocol was applicable to a wide spectrum of alcohols bearing various functionalities. Acid-labile THP- or TBS-protected alcohol, furfuryl alcohol, and geraniol could be acylated as well as base-labile alcohols. Even acylation of functionalized tertiary alcohols was effected at room temperature.     

Kinetics and mechanisms of the ozone/bromite and ozone/chlorite reactions

Ozone reactions with XO(2)(-) (X = Cl or Br) are studied by stopped-flow spectroscopy under pseudo-first-order conditions with excess XO(2)(-). The O(3)/XO(2)(-) reactions are first-order in [O(3)] and [XO(2)(-)], with rate constants k(1)(Cl) = 8.2(4) x 10(6) M(-1) s(-1) and k(1)(Br) = 8.9(3) x 10(4) M(-1) s(-1) at 25.0 degrees C and mu = 1.0 M. The proposed rate-determining step is an electron transfer from XO(2)(-) to O(3) to form XO(2) and O(3)(-). Subsequent rapid reactions of O(3)(-) with general acids produce O(2) and OH. The OH radical reacts rapidly with XO(2)(-) to form a second XO(2) and OH(-). In the O(3)/ClO(2)(-) reaction, ClO(2) and ClO(3)(-) are the final products due to competition between the OH/ClO(2)(-) reaction to form ClO(2) and the OH/ClO(2) reaction to form ClO(3)(-). Unlike ClO(2), BrO(2) is not a stable product due to its rapid disproportionation to form BrO(2)(-) and BrO(3)(-). However, kinetic spectra show that small but observable concentrations of BrO(2) form within the dead time of the stopped-flow instrument. Bromine dioxide is a transitory intermediate, and its observed rate of decay is equal to half the rate of the O(3)/BrO(2)(-) reaction. Ion chromatographic analysis shows that O(3) and BrO(2)(-) react in a 1/1 ratio to form BrO(3)(-) as the final product. Variation of k(1)(X) values with temperature gives Delta H(++)(Cl) = 29(2) kJ mol(-1), DeltaS(++)(Cl) = -14.6(7) J mol(-1) K(-1), Delta H(++)(Br) = 54.9(8) kJ mol(-1), and Delta S(++)(Br) = 34(3) J mol(-1) K(-1). The positive Delta S(++)(Br) value is attributed to the loss of coordinated H(2)O from BrO(2)(-) upon formation of an [O(3)BrO(2)(-)](++) activated complex.     

Nucleophile assistance of electron-transfer reactions between nitrogen dioxide and chlorine dioxide concurrent with the nitrogen dioxide disproportionation

The reaction of chlorine dioxide with excess NO(2)(-) to form ClO(2)(-) and NO(3)(-) in the presence of a large concentration of ClO(2)(-) is followed via stopped-flow spectroscopy. Concentrations are set to establish a preequilibrium among ClO(2), NO(2)(-), ClO(2)(-), and an intermediate, NO(2). Studies are conducted at pH 12.0 to avoid complications due to the ClO(2)(-)/NO(2)(-) reaction. These conditions enable the kinetic study of the ClO(2) reaction with nitrogen dioxide as well as the NO(2) disproportionation reaction. The rate of the NO(2)/ClO(2) electron-transfer reaction is accelerated by different nucleophiles (NO(2)(-) > Br(-) > OH(-) > CO(3)(2-) > PO(4)(3-) > ClO(2)(-) > H(2)O). The third-order rate constants for the nucleophile-assisted reactions between NO(2) and ClO(2) (k(Nu), M(-2) s(-1)) at 25.0 degrees C vary from 4.4 x 10(6) for NO(2-) to 2.0 x 10(3) when H(2)O is the nucleophile. The nucleophile is found to associate with NO(2) and not with ClO(2) in the rate-determining step to give NuNO(2)(+) + ClO(2)(-). The concurrent NO(2) disproportionation reaction exhibits no nucleophilic effect and has a rate constant of 4.8 x 10(7) M(-1) s(-1). The ClO(2)/NO(2)/nucleophile reaction is another example of a system that exhibits general nucleophilic acceleration of electron transfer. This system also represents an alternative way to study the rate of NO(2) disproportionation.     

Hydroxy-amide functionalized azolium salts for Cu-catalyzed asymmetric conjugate addition: stereocontrol based on ligand structure and copper precatalyst

A series of hydroxy-amide functionalized azolium salts have been designed and synthesized for Cu-catalyzed asymmetric conjugate addition reaction. The (CH(2))(2)-bridged hydroxy-amide functionalized azolium ligand precursors 2, in addition to the previously reported CH(2)-bridged azolium salts 1, have been prepared from readily available enantiopure β-amino alcohols. The combination of a Cu species with 1 or 2 efficiently promoted the 1,4-addition reaction of cyclic enones with dialkylzincs. For example, the reaction of 2-cyclohepten-1-one (17) with Bu(2)Zn in the presence of catalytic amounts of Cu(OTf)(2) and 1 gave (S)-3-butylcycloheptanone (20) in 99% yield and 96% ee. On the other hand, when the reaction was carried out under the influence of Cu(OTf)(2) combined with 2, (R)-20 in preference to (S)-20 was obtained in 98% yield and 80% ee. In this manner, the enantioselecvity was switched by controlling the structure of chiral ligand. Additionally, the reversal of enantioselectivity was also achieved by changing the Cu precatalyst from Cu(OTf)(2) to Cu(acac)(2) with the same ligand. The combination of Cu(acac)(2) with CH(2)-bridged azolium salt 1 in the reaction of 17 with Bu(2)Zn led to formation of (R)-20 as a major product in 55% yield and 80% ee. This result was in contrast to the Cu(OTf)(2)/1 catalytic system, where the 1,4-adduct with opposite configuration was obtained. Moreover, use of the Cu(acac)(2)/2 catalytic system produced (S)-20, while (R)-20 was formed by the Cu(OTf)(2)/2 catalytic system. Thus, it was found that either varying the linker of the chiral ligands or changing the counterion of Cu species between a OTf and acac ligand initially on the metal led to dual enantioselective control in the 1,4-addition reaction.     

模拟细胞色素P-450和仿生氧化反应研究III. 有关用TPPFe(III)Cl及TPPMn(III)Cl催化的环己烷充氧化反应机理的初步探讨

本文研究了ArIO充氧化环己烷的反应体系。在TPPFe(III)Cl及TPPMn(III)Cl催化下进行了动态UV-Vis谱和ESR分析,提出了二种催化体系可能由二种不同递氧中间体的反应机理。     

Activation of the sulfhydryl group by Mo centers: kinetics of reaction of benzyl radical with a binuclear Mo(micro-SH)Mo complex and with arene and alkane thiols

This paper provides evidence from kinetic experiments and electronic structure calculations of a significantly reduced S-H bond strength in the Mo(micro-SH)Mo function in the homogeneous catalyst model, CpMo(micro-S)(2)(micro-SH)(2)MoCp (1, Cp = eta(5)-cyclopentadienyl). The reactivity of 1 was explored by determination of a rate expression for hydrogen atom abstraction by benzyl radical from 1 (log(k(abs)/M(-)(1) s(-)(1)) = (9.07 +/- 0.38) - (3.62 +/- 0.58)/theta) for comparison with expressions for CH(3)(CH(2))(7)SH, log(k(abs)/M(-)(1) s(-)(1)) = (7.88 +/- 0.35) - (4.64 +/- 0.54)/theta, and for 2-mercaptonaphthalene, log(k(abs)/M(-)(1) s(-)(1)) = (8.21 +/- 0.17) - (4.24 +/- 0.26)/theta (theta = 2.303RT kcal/mol, 2sigma error). The rate constant for hydrogen atom abstraction at 298 K by benzyl radical from 1 is 2 orders of magnitude greater than that from 1-octanethiol, resulting from the predicted (DFT) S-H bond strength of 1 of 73 kcal/mol. The radical CpMo(micro-S)(3)(micro-SH)MoCp, 2, is revealed, from the properties of slow self-reaction, and exclusive cross-combination with reactive benzyl radical, to be a persistent free radical.     

Preparation and oxygenation of (flavonolato)copper isoindoline complexes with relevance to quercetin dioxygenase

Mesitylcopper reacts with flavonol (flaH) in the presence of 1,3-bis(2-pyridylimino)isoindoline (indH) to yield the diamagnetic complex CuI(fla)(indH), which on reaction with molecular oxygen undergoes oxidative splitting of the C2-C3 bond of the pyranone ring of the flavonolate ligand to give CuI(indH)(O-bs) (O-bs = O-benzoylsalicylate) (orthorhombic, P1, a = 8.048(7) A, b = 8.969(9) A, c = 19.240(2) A, alpha = 85.69 degrees, beta = 80.24(7) degrees, gamma = 77.87(7) degrees, V = 1337(2) A3, Z = 2) and carbon monoxide. The reaction of [CuI(CH3CN)4]ClO4, flaH, and indH with dioxygen at room temperature affords the paramagnetic complex [CuII(fla)(indH)]ClO4 (mu = 2.10 mu B), and after elimination of HClO4, CuII(fla)(ind) (orthorhombic, Pbca, a = 8.888(2) A, b = 19.169(7) A, c = 33.614(10) A, alpha = beta = gamma = 90 degrees, V = 5727(3) A3, Z = 8) with mu = 1.86 mu B is formed. The latter undergoes cleavage of the pyranone ring on oxygenation at 80 degrees C to give CuII(ind)(O-bs) (mu = 1.87 mu B, nu(CO) = 1742 cm-1, and nu(CO2) = 1581, 1387 cm-1) and carbon monoxide. CuII(fla)(ind) and [CuII(fla)(indH)]ClO4 serve as good catalysts for the oxygenation of flavonol to O-benzoylsalicyclic acid.     

Nickel-catalyzed C-H arylation of azoles with haloarenes: scope, mechanism, and applications to the synthesis of bioactive molecules

Novel nickel-based catalytic systems for the C-H arylation of azoles with haloarenes and aryl triflates have been developed. We have established that Ni(OAc)(2)/bipy/LiOtBu serves as a general catalytic system for the coupling with aryl bromides and iodides as aryl electrophiles. For couplings with more challenging electrophiles, such as aryl chlorides and triflates, the Ni(OAc)(2)/dppf (dppf = 1,1'-bis(diphenylphosphino)ferrocene) system was found to be effective. Thiazoles, benzothiazoles, oxazoles, benzoxazoles, and benzimidazoles can be used as the heteroarene coupling partner. Upon further investigation, we discovered a new protocol for the present coupling using Mg(OtBu)(2) as a milder and less expensive alternative to LiOtBu. Attempts to reveal the mechanism of this nickel-catalyzed heterobiaryl coupling are also described. This newly developed methodology has been successfully applied to the syntheses of febuxostat (a xanthine oxidase inhibitor that is effective for the treatment of gout and hyperuricemia), tafamidis (effective for the treatment of TTR amyloid polyneuropathy), and texaline (a natural product having antitubercular activity).     

Frustrated Lewis pair addition to conjugated diynes: formation of zwitterionic 1,2,3-butatriene derivatives

The frustrated Lewis pair B(C(6)F(5))(3)/P(o-tolyl)(3) (4a) reacts with 4,6-decadiyne to give the trans-1,2-addition product 5. In contrast, the B(C(6)F(5))(3)/P(t)Bu(3) FLP (4b) reacts with this substrate to give the trans-1,4-adduct trans-6. The cumulene trans-6 undergoes trans-/cis-isomerization upon photolysis to give a ca. 1:1 trans-6/cis-6 mixture. The FLP 4b reacts with 2,6-hexadiyne at r.t. to yield a ca. 4:1 mixture of their trans-1,2- and trans-1,4-addition products (7,8). DFT calculations showed that the zwitterionic 1,4-addition products are favored under thermodynamic control. Thermolysis of the kinetic trans-1,2-addition product (7) (80 °C, bromobenzene) does not lead to the thermodynamically favored 1,4-isomer (8), but instead elimination of isobutylene occurs to the formal trans-1,2-adduct (9) of the B(C(6)F(5))(3)/PH(t)Bu(2) pair. Compounds 5, 6, 7, 8, 9 were analyzed by X-ray diffraction.