Reactions of methyltris(triarylphosphine)cobalt : II. Rearrangement of triarylphosphine and oxidative additions of aryl halides

Solutions of [(C₆H₅)₃P]₃CoCH₃ (I) in C₆H₅Cl yield biphenyl, triphenylphosphine, methyldiphenylphosphine and diphenylphosphine. In 4-ClC₆H₄CH₃, 4-methylbiphenyl and 4,4′-bitolyl form as well. Solutions of I in C₆H₆, C₆D₆, C₆H₅CH₃, C₆H₅Br yield only triphenylphosphine and biphenyl, while in 4-FC₆H₄I 4,4′-difluorobiphenyl is formed but no biphenyl. The cobalt compound is recovered as (Ph₃P)_nCoX or as CoX₂ (XCl, Br, I, n = 3 or 2) from reactions with arylhalides. The results are rationalized in terms of the very strong tendency for I to undergo oxidative addition reactions.     

Controlling the oxidative addition of aryl halides to Au(I)

By means of density functional theory calculations, we computationally analyze the physical factors governing the oxidative addition of aryl halides to gold(I) complexes. Using the activation strain model of chemical reactivity, it is found that the strain energy associated with the bending of the gold(I) complex plays a key role in controlling the activation barrier of the process. A systematic study on how the reaction barrier depends on the nature of the aryl halide, ligand, and counteranion allows us to identify the best combination of gold(I) complex and aryl halide to achieve a feasible (i.e., low barrier) oxidative addition to gold(I), a process considered as kinetically sluggish so far. © 2014 Wiley Periodicals, Inc.     

C-H arylation of unactivated arenes with aryl halides catalyzed by cobalt porphyrin

A general procedure for cobalt-catalyzed direct C-H arylation of unactivated arenes has been discovered. This method employs aryl halides as the direct coupling partners with arenes without using any Grignard-type reagents. This catalysis opens a new methodology for the preparation of symmetrical as well as unsymmetrical biaryls in a user-friendly approach.     

Investigation of the addition of dialkyl(aryl)phosphine oxides to alkyl(aryl)vinyldialkoxysilanes

Conclusions Alkyl(aryl){2-[dialkyl(aryl)phosphoryl]ethyl}dialkoxysilanes were obtained as a result of addition of dialkyl(aryl)phosphine oxides to alkyl(aryl)vinyldialkoxysilanes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 183–186, January, 1985.     

Radical additions of aryl iodides to arenes are facilitated by oxidative rearomatization with dioxygen

Inter- and intramolecular additions of aryl radicals derived from aryl iodides to arenes are promoted by tris(trimethylsilyl)silane and occur under exceptionally mild conditions (15-30 min at 25 degrees C) in nondegassed benzene. A chain mechanism involving reaction of the intermediate cyclohexadienyl radical with oxygen to directly generate the aromatized product and the hydroperoxy radical is proposed.     

Arylgold(I) and aryl(triphenylphosphine)gold(I)compounds

Novel monomeric benzyl- and aryl-gold(I) triphenylphosphine complexes have been prepared. Pure, uncomplexed 2-[(dimethylamino)methyl]-phenylgold(I) has been isolated from the reaction of tetranuclear bis {2-[(dimethylamino)methyl]phenyl}goldlithium (R₄ Au₂ Li₂) with trimethyltin bromide.     

Extraction and gas chromatographic determination of methyl-, ethyl-, and methoxyethylmercury(II) halides

The separation, identification, and determination of methyl-, ethyl-, and methoxyethylmercury(II) halides in biological materials were studied. The procedure developed involved a 24-h leach with 1 M sodium iodide, equilibration of the aqueous phase for 2 min with an equal volume of benzene, and then injection of an aliquot of the benzene phase onto a gas Chromatographic column consisting of 5% cyclohexanedimethanol succinate held on Anakrom ABS. Excellent baseline separation of the Chromatographic peaks was obtained. The extraction steps were monitored with RHgX compounds tagged with ²⁰³Hg. Partition coefficients are reported for methyl- and ethylmercury(II) chlorides, bromides, and iodides; several overall formation constants of the anionic complexes RHgCl_n^1-n (n=2, 3) were determined. Results are reported for the recovery of methyl- and ethylmercury(II) halides from inoculated rye seed, humic and inorganic sediment, and fish grown in an aquarium.     

Synthesis of N-heterocyclic carbene palladium(II) bis-phosphine complexes and their decomposition in the presence of aryl halides

Methylpalladium(II) carbene complexes of the type [Pd(NHC)Me(P-P)]BF(4) (NHC = N-heterocyclic carbene, P-P = chelating phosphine) have been synthesised, the complex [Pd(tmiy)Me(dcype)]BF(4) (tmiy = 1,3,4,5-tetramethylimidazol-2-ylidene, dcype = 1,2-bis(dicyclohexylphosphino)ethane) being characterised crystallographically. Complexes bearing the tmiy ligands were shown to decompose in an analogous manner to complexes bearing monodentate phosphine ligands, with the rate of decomposition being nominally linked to the size of the chelate ring. The decomposition of these complexes in the presence of aryl halides-expected to yield Pd(Ar)X(P-P)-was studied and shown instead to yield PdX(2)(P-P) and [Pd(tmiy)X(P-P)]BF(4). Additionally, Pd(Me)X(P-P) and Pd(Ar)X(P-P) were observed in some cases. Intermolecular cross-over reactions between the starting complex and Pd(Ar)X(P-P) were found to be the source of these unexpected products.     

Mechanism of the electrochemical conversion of aryl halides to arylzinc compounds by cobalt catalysis in DMF/pyridine

The study of the electrochemical behavior of cobalt bromide, CoBr2, in the presence of zinc bromide, ZnBr2, and aryl halides, ArX, in a dimethylformamide (DMF)/pyridine (9:1, v/v) mixture allowed us to complete the study of the mechanism of the electrochemical conversion of aryl halides into arylzinc compounds by using cobalt catalysis. The last step of the catalytic process has been shown to be a transmetalation reaction between the arylcobalt(II) species and zinc ions that regenerates the cobalt(II) catalyst. The effect of zinc bromide on each step of the catalytic cycle has been studied. It is especially shown that the presence of ZnBr2 stabilizes the electrogenerated Co1 but has no effect on the rate constant of the oxidative addition of aryl halides, ArX, to Co1. Rate constants for the disproportionation reaction of Co1 and the oxidative addition have been determined in the presence of ZnBr2 and compared with the values obtained in its absence.     

Thermal stability of phosphine and phosphine oxide complexes of cobalt(ii) dihalides

Thermogravimetric measurements show that complexes of cobalt(II) dihalides with aryl and alkyl substituted phosphines and triphenylphosphine oxide in an oxygen containing atmosphere decompose to yield solid phases consisting of Co₃O₄ and P₂O₅.

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Zusammenfassung Komplexe von Kobalt(II)dihalogeniden mit aryl- und alkylsubstituierten Phosphinen und Triphenylphosphinoxyd wurden einer thermogravimetrischer Prüfung unter Sauerstoff unterworfen. Die zurückbleibende feste Phase bestand aus Co₃O₄ und P₂O₅.

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Résumé On a étudié la décomposition thermique des complexes dihalogénés de cobalt(II) avec les aryl et alcoylphosphines substituées et les oxydes de triphénylphosphine. En atmosphère d'oxygène, Co₃O₄ et P₂O₅ constituent la phase solide résiduelle.

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, , , - -, , , , _{34 25}.

     

Cross-coupling reactions of (1-fluorovinyl)methydiphenylsilane(1) with aryl halides and aryl triflates

The cesium fluoride (CsF)-assisted cross-coupling reaction of (1-fluorovinyl)methyldiphenylsilane (1) with aryl halides and aryl triflates was examined. The reaction with aryl iodides smoothly proceeded to afford the corresponding (1-fluorovinyl)arenes in the presence of a catalytic amount of CuI and Pd(PPh(3))(4) in aprotic polar solvents such as DMF, DMI, DMA, and NMP in good yields. A variety of functional groups (nitro, ester, ketone, and ether) on the aromatic rings can be tolerated under these mild conditions. Aryl iodides are superior to aryl bromides as the coupling reaction partner. The cross-coupling reaction of 1 with aryl triflates instead of aryl halides was also accomplished in the presence of tetrabutylammonium iodide (n-Bu(4)NI) as the additive under similar conditions.     

Cobalt-catalyzed aminocarbonylation of (hetero)aryl halides promoted by visible light

The catalytic aminocarbonylation of (hetero)aryl halides is widely applied in the synthesis of amides but relies heavily on the use of precious metal catalysis. Herein, we report an aminocarbonylation of (hetero)aryl halides using a simple cobalt catalyst under visible light irradiation. The reaction extends to the use of (hetero)aryl chlorides and is successful with a broad range of amine nucleophiles. Mechanistic investigations are consistent with a reaction proceeding via intermolecular charge transfer involving a donor–acceptor complex of the substrate and cobaltate catalyst.

An aminocarbonylation of (hetero)aryl halides using a simple cobalt catalyst under visible light irradiation is presented.     

Reversible, electrochemically controlled binding of phosphine to iron and cobalt bis(dithiolene) complexes

The homoleptic bis(dithiolene) complexes [M(S(2)C(2)R(2))(2)](2) (M = Fe, Co; R = p-anisyl) undergo two successive reductions to form anions that display [M(S(2)C(2)R(2))(2)](2)(2-) <--> 2[M(S(2)C(2)R(2))(2)](1-) solution equilibria. The neutral dimers react with Ph3P to form square pyramidal [M(Ph(3)P)(S(2)C(2)R(2))(2)](0). Voltammetric measurements upon [M(Ph(3)P)(S(2)C(2)R(2))(2)](0) in CH(2)Cl(2) reveal only irreversible features at negative potentials, consistent with Ph(3)P dissociation upon reduction. Dissociation and reassociation of Ph(3)P from and to [Fe(Ph(3)P)(S(2)C(2)R(2))(2)](0) is demonstrated by spectroelectrochemical measurements. These collective observations form the basis for a cycle of reversible, electrochemically controlled binding of Ph(3)P to [M(S(2)C(2)R(2))(2)](2) (M = Fe, Co; R = p-anisyl). All members of the cycle ([M(S(2)C(2)R(2))(2)](2)(0), [M(S(2)C(2)R(2))(2)](2)(1-), [MM(S(2)C(2)R(2))(2)](2)(2-), [M(S(2)C(2)R(2))(2)](1-), [M(Ph(3)P)(S(2)C(2)R(2))(2)]) for M = Fe, Co have been characterized by crystallography. Square planar [Fe(S(2)C(2)R(2))(2)](1-) is the first such iron dithiolene species to be structurally identified and reveals Fe-S bond distances of 2.172(1) and 2.179(1) Angstrom, which are appreciably shorter than those in corresponding square planar dianions.     

CuI-catalyzed coupling reaction of aryl halides with terminal alkynes in the absence of palladium and phosphine

CuI/N,N-dimethylglycine-catalyzed coupling reaction of aryl halides with terminal alkynes is carried out in DMF at 100 degrees C to provide the corresponding coupling products in good to excellent yields with a great diversity.     

(Fluoroalkyl)phosphine complexes of nickel(0) and cobalt(I)

The synthesis of a series of (fluoroalkyl)phosphine complexes of nickel is reported. Treatment of (cod)₂Ni with dfepe (dfepe=(C₂F₅)₂PCH₂CH₂P(C₂F₅)₂) yields (dfepe)Ni(cod) (1), which has been structurally characterized. Treatment of 1 with CO or bipy results in the formation of (dfepe)Ni(CO)₂ (2) and (dfepe)Ni(bipy) (3), respectively. Addition of excess dfepe to 1 results in incomplete cod displacement to form (dfepe)₂Ni (4). The homoleptic complex 4 may be independently prepared in high yield by reduction of (acac)₂Ni with (ⁱBu)₃Al in the presence of butadiene and excess dfepe. Solvation of (dfepe)Ni(cod) in acetonitrile gives a new complex tentatively identified as (dfepe)Ni(MeCN)₂ (6), whereas dissolution of (dfepe)₂Ni in acetonitrile leads to a mixture of 6 and the partial displacement product (dfepe)(η¹-dfepe)Ni(MeCN) (5). In contrast to (R₃P)₄Ni(0) phosphine and phosphite complexes, which undergo protonation by strong anhydrous acids such as HCl, H₂SO₄ and CF₃CO₂H to give (R₃P)₄Ni(H)⁺ products, Treatment of (dfepe)₂Ni with neat CF₃CO₂H or excess HOTf in dichloromethane gave no spectroscopic evidence for (dfepe)₂Ni(H)⁺. Exposure for extended periods leads to dfepe loss and decomposition to Ni(II) products. The synthesis of the first cobalt complex of dfepe, (dfepe)Co(CO)₂H, is also reported.     

Electroreduction of triphenylphosphine dichloride and the efficient one-pot reductive conversion of phosphine oxide to triphenylphosphine

Electroreduction of triphenylphosphine dichloride in acetonitrile was performed successfully in an undivided cell fitted with an aluminium sacrificial anode and a platinum cathode. Further, the one-pot transformation of triphenylphosphine oxide to triphenylphosphine was achieved successfully by the treatment of triphenylphosphine oxide in acetonitrile with oxalyl chloride and subsequent electrochemical reduction.     

Thermal decomposition of Cu(I) phosphine complexes

The thermal decomposition of Cu(I) phosphine complexes of the general types (CuXPPh₃)₄, [CuX(PPh₃)₂] and [CuX(PPh₃)₃] was investigated.The thermal decomposition of (CuXPPh₃)₄, where X denotes Cl^–, Br^–, I^–, NO ₃ ^– and PPh₃=P(C₆H₅)₃, occurs with formation of a phosphine oxide intermediate. For the remaining complexes this intermediate was not proved in the thermal decomposition.

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Zusammenfassung Die thermische Zersetzung der Cu(I)-Phosphinkomplexe vom allgemeinen Typ (CuXPPh₃)₄ und [CuX(PPh₃)₂], wie auch [CuX(PPh₃)₃] wurde untersucht. Die thermische Zersetzung von (CuXPPh₃)₄, wobei X=Cl^–, Br^–, I^– und NO ₃ ^– bedeutet und PPh₃=P(C₆H₅)₃, verläuft unter Bildung eines Phosphinoxid Zwischenproduktes, bei den übrigen Komplexen konnte dieses im Laufe der thermischen Zersetzung nicht nachgewiesen werden.

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Résumé On a étudié la décomposition thermique des complexes phosphine-Cu(I) de formule générale (CuXPPh₃)₄, [CuX(PPh₃)₂], [CuX(PPh₃)₃]. La décomposition thermique de (CuXPPh₃)₄, où X désigne Cl^–, Br^–, I^– et NO ₃ ^– , et PPh₃=P(C₆H₅)₃, s'effectue avec formation d'un oxyde de phosphine intermédiaire; avec les autres complexes, cet intermédiaire n'a pas été mis en évidence au cours de la décomposition thermique.

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(CuXPPb₃)₄ [CuX(PPh₃)₂] [CuX(PPh₃)₃]. (CuXPPh₃)₄, X=Cl^–, Br^–, I^–, NO ₃ ^– , PPh₃=(₆₅)₃ . .

     

Pd(O)-catalyzed electro-reductive coupling of aryl halides

An efficient electro-reductive coupling of aryl bromides and iodides into biaryls has been performed by the electrolysis with Pd(O)-and/or Pd(II)-catalysts in a DMF-ET₄NOTs-(Pb cathode) system. 4-Bromo-and 2-bromopyridines were also converted into the corresponding bipyridyls, respectively.     

Polyethylene glycol (PEG) promoted hydrodehalogenation of aryl halides

Transition-metal-free hydrodehalogenation of aryl halides (eg. bromides) can take place efficiently in the presence of green polyethylene glycol (PEG-800) and t-BuOK without adding any extra solvents and additives. A radical mechanism is proposed for this transition-metal-free dehalogenation of aryl halides and the role of polyethylene glycol is both reaction promotor and activated alkyl CH donor.     

Microwave-assisted, Pd(0)-catalyzed cross-coupling of diazirines with aryl halides

Pd(0)-catalyzed cross-coupling reactions of diazirines with aryl halides under microwave heating conditions afford a series of substituted olefins. A reaction mechanism involving the migratory insertion of the Pd carbene intermediate is proposed.