T. V. Gryaznova

Electrochemical properties of diphosphonate-bridged palladacycles and their reactivity in arene phosphonation

A series of diphosphonate-bridged dipalladacycles [(phpy)Pd(EtO)2P(O)]2, [(bhq)Pd(EtO)2P(O)]2, [(phpz)Pd(EtO)2P(O)]2 (phpy=2-phenylpyridine, bhq=benzo[h]quinoline, phpz=1-phenylpyrazole), which are known to be involved in catalytic C–H phosphonation reactions, was prepared and characterized by NMR spectroscopy and cyclic voltammetry in acetonitrile solutions and in carbon paste electrode. Diphosphonate dipalladacycles are oxidized irreversibly at more positive potentials as distinguished from related acetate palladacycles. Electrochemical preparative oxidations carried out under mild conditions without any specially added oxidants quantitatively afforded corresponding arylphosphonates. For complete conversion of dipalladacycles into arylphosphonates, four electrons per each palladium atom are required, that probably indicates a mechanism involving Pd(IV)/Pd(II) redox couple.

Ligand-directed electrochemical functionalization of C(sp2)—H bonds in the presence of the palladium and nickel compounds

The recent achievements of electrochemical functionalization of C—H bonds in aromatic substrates containing the pyridine moiety and acting as a ligand directing substitution to the ortho-position in the presence of the palladium and nickel compounds are analyzed and generalized in the review. Acetoxylation, perfluoroacetoxylation, perfluoroalkylation, and phosphorylation are considered for 2-phenylpyridine (PhPy) as an example. The PdII metallocycles with the Pd-bound acetate, perfluoroacetate, and perfluoroheptanoate substituents were isolated and characterized as possible intermediates: binuclear [(PhPy)Pd(µ-OAc)]2 and [(PhPy)Pd(µ-TFA)]2 and mononuclear [(PhPy)Pd(TFA)](MeCN), [(PhPy)Pd(TFA)](PhPy), [(PhPy)Pd(PFH)](PhPy), and [(PhPy)Pd(EtO)2P(O)]2. Their electrochemical properties were studied. The fluorinated derivatives are in solvent-dependent equilibrium between the mononuclear and binuclear forms. Cyclic voltammetry was used to establish the redox properties of the palladium cycles and routes of their oxidation to the final products. A new approach to CH-substitution products based on the electrochemical generation of Pd or Ni in high oxidation states in the presence of substrate-ligand was proposed.

New method of metal-induced oxidative phosphorylation of benzene

A new approach to phosphorylation of benzene with diethyl phosphite is suggested, which is based on the electrocatalytic oxidation of a mixture of benzene and diethyl phosphite (1 : 1) under mild conditions (room temperature, normal pressure) in the presence of bimetallic catalytic systems MnII/CoIIL (MnSO4/CoCl2dmphen or MnCl2/CoCl2bipy). This method gives diethyl phenylphosphonate in high yield (up to 90%) and practically 100% conversion of the phosphite.

Electrochemical C-H phosphorylation of 2-phenylpyridine in the presence of palladium salts

A new approach was developed to the introduction of the phosphonate group into arylpyridines using 2-phenylpyridine as an example. The approach is the electrochemical oxidation of a mixture of 2-phenylpyridine, diethyl phosphite, and palladium acetate at room temperature. An intermediate dipalladium cyclic complex was isolated that is formed by the ortho-palladation of 2-phenylpyridine and substitution of acetate ions by phosphonate ions. The preparative oxidation of this complex selectively results in the product of the phosphorylation of the C-H bond in 2-phenylpyridine.

One-stage synthesis of FcP(O)(OC2H5)2 from ferrocene and α-hydroxyethylphosphonate

A new approach is proposed for ferrocene phosphorylation using α-hydroxylalkylphosphonate as a “masked” phosphorylating agent, by electrochemical reduction of a ferrocene and (Me)2C(OH)P(O)(OC2H5)2 mixture at −50 °C. The method makes it possible to obtain the product of diethyl ferrocenyl phosphonate with a high yield (87–89%) and 100% conversion of the initial phosphonate in one stage. It is evidenced with experiments that ferrocene reduction is carried out with preservation of the iron charge in the ferrocene fragment and with the formation of a cyclopentadienyl ligand radical anion at −3.3 V ref. Ag/AgCl (at −50 °C).

Electrocatalytic fluoroalkylation of olefins. Perfluoroalkylation of 2-vinylpyridine

Perfluoroalkylation of 2-vinylpyridine was conducted under conditions for the formation of low-valent nickel complexes during electroreduction of NiBr2L (L is the bipy, terpy) in DMF solutions. Depending on the electrosynthesis conditions, either dimeric products of addition of perfluoroalkyl substituents at the double bond of the olefin or (in the presence of triethylamine) 1-perfluorohexyl-2-pyridinethylene were formed.

Electrochemistry of nitronyl and imino nitroxides

Redox potentials of a wide group of azolyl-substituted nitronyl and imino nitroxides were determined by classic cyclic voltammetry (CV). Conclusions have been made for this group of compounds, and their peculiarities were emphasized in comparison with methyl-, phenyl-, iodo-, and cyano-substituted nitroxides.

New Calix[4]Resorcinols with Thiophosphoryl-Containing Fragments

Abstract The condensation of thiophosphorylated aldehydes 1 and 2 with resorcinol and its derivatives leads to the formation of the new type of calix[4]resorcinols with four thiophosphoryl groups inserted to the substituents located in methylidene bridges of the molecule. The conformation of these compounds was found to be “flattened partial cone” or “chair,” which was determined by NMR methods and a single-crystal X-ray diffraction study. GRAPHICAL ABSTRACT

Electrochemical phosphorylation of coumarins catalyzed by transition metal complexes (Ni—Mn, Co—Mn)

A possibility of electrochemical phosphorylation of coumarins (coumarin, 6-methylcoumarin, 7-methylcoumarin) with diethyl phosphite was shown. The approach is based on the oxidation of a mixture of the aromatic compound and diethyl phosphite (1: 1) under mild conditions (room temperature, atmospheric pressure) in the presence of a bimetallic catalytic systems: MnIIbipy/NiIIbipy and MnIIbipy/CoIIbipy (bipy is the 2,2´-bipyridine). This method allows one to obtain diethyl arylphosphonates in high yields (up to 70%) and 100% conversion of the phosphite.

Redox trends in cyclometalated palladium( ii ) complexes

A series of diverse binuclear and mononuclear cyclometalated palladium(ii) complexes of different structure was investigated by electrochemical techniques combined with density functional theory (DFT) calculations. The studies including cyclic and differential pulse voltammetry, X-ray structure analysis and quantum chemical calculations revealed a regularity of the complexes oxidation potential on the metal-metal distance in the complexes: the larger Pd-Pd distance, the higher oxidation potentials. The reduction potentials feature unusually high negative values while no correlation depending on the structure could be observed. These results are in a good agreement with the electron density distribution in the complexes. Additionally, ESR data obtained for the complexes upon oxidation is reported.