Dmitry G. Yakhvarov

Highly reactive σ-organonickel complexes in electrocatalytic processes

Abstract The electrochemical reduction of nickel complexes with 2,2′-bipyridine in the presence of ortho -substituted organic halides or white phosphorus yields the highly reactive σ-organonickel complexes. These complexes selectively react with organic halides forming cross-coupling products. The mechanism of these processes was investigated using the method of cyclic voltammetry and preparative electrolysis. The key intermediates of electrochemical functioning of white phosphorus in conditions of metallocomplex catalysis were detected.

Experimental Evidence of Phosphine Oxide Generation in Solution and Trapping by Ruthenium Complexes

Phosphorus oxides, oxyacids, and their esters are important chemicals for industry. Apart from playing a role in most organisms in ruling their energy transformations, they find wide and diverse applications, such as fertilizers, pesticides, herbicides, lubricants, flame retardants, additives for special plastics and materials, and drugs for different diseases. Little attention has however been paid to lower-oxidation-state species, such as PO, HPO, and P2O, for which synthetic isolation procedures and even direct evidence of their existence are scarce. One of the most elusive species in this regard is phosphine oxide, H3PO (I ; Scheme 1). This molecule was first observed by reacting atomic oxygen with PH3 using a discharge–flow system equipped with molecularbeam sampling mass spectrometry. Alternatively, red-light photolysis of co-deposited PH3/O3 onto an argon matrix at 12–18 K was used to generate and trap I in a very diluted concentration together with its tautomer phosphinous acid H2P(OH) (II), which was identified by FTIR. [4] Finally, Ault and Kayser observed the formation of H3PO in argon matrices after photochemical irradiation of a mixture of VOCl3, CrO2Cl2, and PH3. [5] Both molecules have been studied by theoretical methods. Application of an adequate phosphorus basis set has recently shown that, in contrast with previous ab initio studies, I is more stable than II by only about 1 kcalmol 1 in the gas phase. In contrast, computational analysis in aqueous solution showed that upon solvation I is largely preferred by about 10 kcal mol 1 owing to stronger hydrogen bonding with the highly polar P!O bond. The possible involvement of H3PO in the oxidative polymerization of phosphine to give polyhydride phosphorus PxHy polymers has been also proposed. Herein we show that the previously unknown P I species H3PO (I) can be easily generated in solution by electrochemical methods, and we provide evidence of its solution stability, its characterization by conventional NMR spectroscopy, and its trapping as a ligand in the coordination sphere of hydrosoluble ruthenium complexes after tautomerization to II. The electrochemical generation of H3PO was performed in a single electrochemical cell with a lead cathode and a sacrificial zinc anode using P4 melted in a slightly acidic water/ ethanol solution (2:1 volume ratio, water acidified with HCl, 2m) at 60 8C (Supporting Information, Figures S1, S2). The overall electrochemical process may be divided in two parts. In the first step, the electrochemical generation of PH3 on the lead cathode takes place as previously described, 11] while in the second step, mild oxidation of PH3 to H3PO occurs at the anodic surface of the zinc electrode. In agreement with cyclic voltammetry experiments showing an irreversible oxidation wave, PH3 is electrochemically active in the anodic potential range + 0.80–1.25 V (vs. Ag/AgNO3, 0.01m in CHCN3) and can be therefore oxidized in acidic water/ethanol 2:1 solution to H3PO (Supporting Information, Figure S3). Scheme 2 shows the overall electrochemical process resulting in the cathodic reduction of P4 to PH3 and anodic oxidation of PH3 to H3PO (E = + 1.24 V vs. Ag/AgNO3, 0.01m in CHCN3). Different working conditions were investigated to optimize the production of H3PO. The best performance was Scheme 1. Phosphine oxide (I) and its tautomer, phosphinous acid (II).

Deoxygenation of Some α-Dicarbonyl Compounds by Tris(diethylamino)phosphine in the Presence of Fullerene C60

The reactions of such cyclic α-diketones as acenaphthenequinone, aceanthrenequinone, and N-alkylisatins, with hexaethyltriaminophosphine in the presence of the fullerene C(60), lead to the formation of methanofullerene derivatives under mild conditions. This process proceeds via deoxygenation of the dicarbonyl compound by the P(III) derivative and is likely to involve the intermediate formation of α-ketocarbenes. The structure of some methanofullerenes has been confirmed by NMR and XRD. The electrochemical behavior of the methanofullerenes was also investigated.

Electrochemical synthesis and catalytic activity of organonickel sigma-complexes

A new industrially applicable method of organonickel sigma-complexes production is developed. The technique is based on the reaction of the oxidative addition of ortho-substituted aromatic bromides to electrochemically generated nickel(0)-2,2′-bipyridyl complexes. Electrolysis is performed in undivided electrolyser supplied with sacrificial nickel anode with a periodic or continuous electrolyte loading. The electrochemically obtained organonickel sigma-complexes of type [NiBr(Ar)(bpy)], where Ar is 2,4,6-trimethylphenyl, 2,4,6-triisopropylphenyl, 2,6-dimethylphenyl, are highly effective precatalysts for ethylene oligomerization process, leading to the formation of linear alpha-olefines of C4–C12 fractions

Electrochemical reactions of white phosphorus

The main electrochemical transformations of elemental (white) phosphorus were considered. Special attention was given to the recently developed processes of preparation of organophosphorus compounds (OPCs) with phosphorus-carbon bonds. The electrochemical approaches to the synthesis of OPCs from white phosphorus using organonickel and organozinc reagents are described. The importance of using the electrochemical methods for the generation of highly reactive phosphorus intermediates was shown for phosphine oxide H3PO obtained for the first time. This provides significant prospects for the electrochemical approaches that could be applied for the development of technologies of the chlorine-free synthesis of OPCs from white phosphorus.

Modification of fullerene C60 by phosphorylated diazo compounds

New representatives of phosphorylated methanofullerenes were prepared by the reactions of [60]fullerene with O,O-diethyl α-diazoethyl- and O,O-diethyl α-diazobenzylphosphonates. Electrochemical reduction of the above-mentioned products proceeded stepwise and reversibly.

Kinetic features of oxidative addition of organic halides to the organonickel σ-complex

Electrochemically generated organonickel σ-complexes were used as model compounds to study the kinetics of oxidative addition of ArNiIbpy to RX, the key stage of cross-coupling of organic halides (RX). The reaction rate constants were calculated, and the sequence of relative reactivity of RX toward the electrochemically generated MesNiIbpy complex was obtained.

Novel indolin-2-one-substituted methanofullerenes bearing long n-alkyl chains: synthesis and application in bulk-heterojunction solar cells

Summary An easy, high-yield and atom-economic procedure of a C60 fullerene modification using a reaction of fullerene C60 with N-alkylisatins in the presence of tris(diethylamino)phosphine to form novel long-chain alkylindolinone-substituted methanofullerenes (AIMs) is described. Optical absorption, electrochemical properties and solubility of AIMs were studied. Poly(3-hexylthiophene-2,5-diyl) (P3HT)/AIMs solar cells were fabricated and the effect of the AIM alkyl chain length and the P3HT:AIM ratio on the solar cell performance was studied. The power conversion efficiencies of about 2% were measured in the P3HT/AIM devices with 1:0.4 P3HT:AIM weight ratio for the AIMs with hexadecyl and dodecyl substituents. From the optical and AFM data, we suggested that the AIMs, in contrast to [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), do not disturb the P3HT crystalline domains. Moreover, the more soluble AIMs do not show a better miscibility with the P3HT crystalline phase.

Reactions of activated organonickel σ-complexes with elemental (white) phosphorus

The reactivity of organonickel σ-complexes of the type [NiBr(Ar)(bpy)] (Ar is 2,4,6-tri-methylphenyl (Mes) or 2,4,6-triisopropylphenyl (Tipp); bpy is 2,2′-bipyridine) toward elemental (white) phosphorus was studied. For the reaction to occur, the complexes must be activated by removal of the bromide anion from the coordination sphere of nickel. This can be achieved either in the presence of halogen scavengers or by electrochemical reduction. The arylphosphinic acids ArP(O)(OH)H formed by hydrolysis of organic nickel phosphides are the major reaction products of the overall process.

Nickel and palladium N -heterocyclic carbene complexes. Synthesis and application in cross-coupling reactions

N-Heterocyclic carbenes (NHCs) are widely used as ligands in catalysis by transition metal complexes. The catalytic activity of transition metal NHC complexes is much higher than that of the transition metal complexes bearing the phosphine and nitrogen-containing ligands. They show excellent catalytic performance in different transformations of the organic compounds, especially in the carbon—carbon and carbon—element bond forming reactions. Palladium NHC complexes are very efficient catalysts for the cross-coupling reactions. On the other hand, nickel is less expensive and regarded as a promising alternative to palladium and, therefore, it attracts increasing attention from the researches. The present review is focused on the recent advances in the synthesis of N-heterocyclic carbene complexes of nickel and palladium and their application in catalysis of cross-coupling reactions of organic, organoelement and organometallic compounds with organic halides.