Reaction of hydroxyflavones with secondary phosphine chalcogenides in the CCl4/Et3N system: synthesis of a new family of phosphorylated flavonoids

Flavonoids (3-hydroxy-, 3-hydroxy-4′-methoxy-, 3-hydroxy-7-methoxy-, and 5,7-dihydroxyflavones) react with secondary phosphine chalcogenides in the CCl₄/Et₃N redox system (50–52 °C, 3–5 h) to afford chemoselectively the corresponding chalcogenophosphinates of the hydroxyflavones in 65–82% yield.     

Light‐Mediated Total Synthesis of 17‐Deoxyprovidencin

An asymmetric synthesis of the diterpenoid 17‐deoxyprovidencin is described. Key steps include an aldol addition, a base‐catalyzed Wipf‐type furan formation, a Z‐selective ring‐closing metathesis for macrocyclization, a photochemical E/Z isomerization to a highly strained and conformationally restricted ring system, and the stereoselective formation of two epoxides on the ring.     

Synthesis and Structural Characterization of the First Europium(III) Pyridylphosphine Complex, [Eu(N,N’,N”-2-Py3P)(NO3)3]

The first europium(iii) pyridylphosphine complex, [Eu(N,N’,N”-2-Py₃P)(NO₃)₃] was prepared by the reaction between Eu(NO₃)₃.6H₂O and tris(2-pyridyl)phosphine; its structure was characterized by single-crystal X-ray diffraction.     

Spectrophotometric and potentiometric study of the cobalt(II)-thiocyanate system in aqueous medium

The cobalt(II)—thiocyanate system was spectrophotometrically studied at 2.0 M ionic strength (NaClO₄) and 25°C. The following formation constants were obtained: β₁ = 6.9 M^?, β₂ = 28.9 M^?2, β₃ = 12.1 M^?3 and β₄ = 1.30 M^?4. Three wavelengths were considered, 515, 590 and 615 nm, and the molar absorptivities of each species were calculated. Linear relationships were obtained for $\text{ε}$ vs $\text{n}$ and α_i. There is strong evidence that the tetrahedral [Co(SCN)₄]^2? is virtually the only species absorbing at 590 and 615 nm. An indirect potentiometric method led to comparable equilibrium constants. The cadmium(II)—thiocyanate formation constants used in the indirect method, under the same conditions, were found to be β₁ = 21.51 ± 0.09 M^?1, β₂ = 123 ± 1 M^?2, β₃ = 130 ± 3 M^?3 and β₄ = 173 ± 1.2 M^?4, in good agreement with earlier literature data.     

KINETICS AND MECHANISM OF CATALYSIS BY FERRIHAEMS IN THE CHEMILUMINOGENIC OXIDATION OF LUMINOL BY HYDROGEN PEROXIDE

The kinetics of catalysis by deuteroferrihaem (deuterohaemin) were studied in the chemiluminogenic oxidation of luminol by hydrogen peroxide. The results imply that two distinct catalytic mechanisms operate to yield chemiluminescence from excited aminophthalate emitter in this system. The first mechanism involves initial one-electron oxidation of luminol by an oxidised derivative of deuteroferrihaem with well-established peroxidatic oxidant properties. The second mechanism involves a concerted pathway very similar to that which has been proposed [Olsson, T., L. Ewetz and A. Thore (1983), Photochem. Photobiol. 38 , 223–229] to explain protoferrihaem (haemin) catalysis in luminol oxidation. Deuteroferrihaem is a much more effective catalyst than protoferrihaem on a mole-for-mole basis and could be used with advantage in chemiluminescence analyses.     

A nitroxide diradical containing a ferrocen-1,1′-diyl-substituted 1,3-diazetidine-2,4-diimine coupler

An Aza-Wittig reaction of 1,1′-bis(triphenylphosphoranylidenamino)-ferrocene with 3-isocyanato-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-1-oxyl and subsequent intramolecular [2+2]-cycloaddition of the bis(carbodiimide) intermediate was used for the synthesis of a 1,3-diazetidine-2,4-diimine moiety bearing two radical groups and bridging the cyclopentadienyl (Cp) rings. According to single-crystal X-ray data, the planar 2,4-diimino-1,3-diazetidine moiety adopts a perpendicular orientation with respect to the eclipsed Cp rings. One of the radical groups lies almost within the plane of the four-membered 1,3-diazetidine ring, while the other has a conformationally preferred orientation with dihedral angles ±62.3°. The two Cp rings are constricted by the 1,3-diazetidine-2,4-diimine moiety so that the angle between their planes is 11.0°. The synthesized diradical contains ferrocene and nitroxide redox signaling units that can be oxidized step-by-step at E_1/2 = 0.26 and 0.48 V (vs Fc/Fc⁺), respectively. Electron spin resonance spectroscopy revealed a moderate exchange interaction (|J| ～ a_N) between the two nitroxide radical moieties and the following values of zero-field splitting parameters: ∣D∣ = 3.5 mT and E/D = 0 were obtained. These data were in agreement with density functional theory calculations. The newly developed approach to multispin systems may be interesting for the construction of weakly coupled rigid polyradicals for quantum technologies, the molecular design of magnets, and the creation of ferrocene-based electron-paramagnetic-resonance–active chemical sensors.     

Reactivity of C(sp)-Pd and C(sp)-Pd bonded palladacycles with diphosphines. Crystal and molecular structure of the novel A-frame complex [{Pd[2,5-Me2C6H2C(H)N(2,4,6-Me3C6H2)-C6]}2(μ-Ph2PCH2PPh2)2(μ-Cl)][PF6]

Treatment of the halogen-bridged complexes [Pd{2,5-Me₂C₆H₂C(H)N(2,4,6-Me₃C₆H₂)-C6,N}(μ-X)]₂ (1a, X = Cl; 2a, X = Br) with the tertiary diphosphine Ph₂PCH₂PPh₂ (dppm), regardless of the molar ratio used, gave a mixture of two complexes: [Pd{2,5-Me₂C₆H₂C(H)N(2,4,6-Me₃C₆H₂)-C6}(μ-Ph₂PCH₂PPh₂)₂(μ-X)]₂[PF₆] (5a, X = Cl; 6a, X = Br), which presents an A-frame structure, and [Pd{2,5-Me₂C₆H₂C(H)N(2,4,6-Me₃C₆H₂)-C6,N}(Ph₂PCH₂PPh₂-P,P)][PF₆], 3a, with the diphosphine as chelating. The mixture could be separated and the corresponding complexes isolated. However, reaction of 1a and 2a with the diphosphine Ph₂PC(CH₂)PPh₂ (vdpp) exclusively gave the mononuclear complex [Pd{2,5-Me₂C₆H₂C(H)N(2,4,6-Me₃C₆H₂)-C6,N}{Ph₂PC(CH₂)PPh₂-P,P}][PF₆], 4a, analogous to 3a. Treatment of the halogen-bridged complexes [Pd{1-CH₂-2-[HCN(2,4,6-Me₃C₆H₂)]-4-MeC₆H₃-C,N}(μ-X)]₂ (1a′, X = Cl; 2a′, X = Br) with dppm or vdpp in a cyclometallated complex/diphosphine 1:2 M ratio, gave mononuclear complexes with the chelating diphospines [Pd{1-CH₂-2-[HCN(2,4,6-Me₃C₆H₂)]-4-MeC₆H₃-C,N}(Ph₂PCH₂PPh₂-P,P)][PF₆], 3a′, and [Pd{1-CH₂-2-[HCN(2,4,6-Me₃C₆H₂)]-4-MeC₆H₃-C,N}{Ph₂PC(CH₂)PPh₂-P,P}][PF₆], 4a′. When the reaction was carried out using a cyclometallated complex/diphosphine 1:1 M ratio the dinuclear complexes [{Pd[1-CH₂-2-{HCN(2,4,6-Me₃C₆H₂)}-4-MeC₆H₃-C,N]}₂(μ-X)(μ-Ph₂PCH₂PPh₂)][Cl], (5a′, X = Cl; 7a′, X = Br) and [{Pd[1-CH₂-2-{HCN(2,4,6-Me₃C₆H₂)}-4-MeC₆H₃-C,N]}₂(μ-Cl){μ-Ph₂PC(CH₂)PPh₂}][Cl], 6a′, were obtained. The molecular structures of complexes 3a, 4a, 5a and 6a′ were determined by X-ray single crystal diffraction.     

Polyoxomolybdodiphosphonates: examples incorporating ethylidenepyridines

We have synthesized and structurally characterized three pyridylethylidene-functionalized diphosphonate-containing polyoxomolybdates, [{Mo(VI)O(3)}(2){Mo(V)(2)O(4)}{HO(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)](6-) (1), [{Mo(VI)(2)O(6)}(2){Mo(V)(2)O(4)}{O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)](8-) (2), and [{Mo(V)(2)O(4)(H(2)O)}(4){O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(4)](12-) (3). Polyanions 1-3 were prepared in a one-pot reaction of the dinuclear, dicationic {Mo(V)(2)O(4)(H(2)O)(6)}(2+) with 1-hydroxo-2-(3-pyridyl)ethylidenediphosphonate (Risedronic acid) in aqueous solution. Polyanions 1 and 2 are mixed-valent Mo(VI/V) species with open tetranuclear and hexanuclear structures, respectively, containing two diphosphonate groups. Polyanion 3 is a cyclic octanuclear structure based on four {Mo(V)(2)O(4)(H(2)O)} units and four diphosphonates. Polyanions 1 and 2 crystallized as guanidinium salts [C(NH(2))(3)](5)H[{Mo(VI)O(3)}(2){Mo(V)(2)O(4)}{HO(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)]·13H(2)O (1a) and [C(NH(2))(3)](6)H(2)[{Mo(VI)(2)O(6)}(2){Mo(V)(2)O(4)}{O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)]·10H(2)O (2a), whereas polyanion 3 crystallized as a mixed sodium-guanidinium salt, Na(8)[C(NH(2))(3)](4)[{Mo(V)(2)O(4)(H(2)O)}(4){O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(4)]·8H(2)O (3a). The compounds were characterized in the solid state by single-crystal X-ray diffraction, IR spectroscopy, and thermogravimetric and elemental analyses. The formation of polyanions 1 and 3 is very sensitive to the pH value of the reaction solution, with exclusive formation of 1 above pH 7.4 and 3 below pH 6.6. Detailed solution studies by multinuclear NMR spectrometry were performed to study the equilibrium between these two compounds. Polyanion 2 was insoluble in all common solvents. Detailed computational studies on the solution phases of 1 and 3 indicated the stability of these polyanions in solution, in complete agreement with the experimental findings.