Electrochemical reduction of substituted cobalticinium cations in aqueous media

Summary In aqueous base, polarography, coulometry and cyclic voltammetry show that the cobalticinium skeleton is reduced in two monoelectronic and reversible steps, leading successively to cobaltocenes and cobaltocene anions. In acid solutions, the second reduction step is only observed for derivatives having electron withdrawing substituents. The height of the second reduction wave is pH dependent. Two different schemes are discussed for the reduction in acid solution.     

Sels de cobalticinium: I. Synthese des derives homo- et hetero-disubstitues

Unlike ferrocene, cobalticinium cation is chemically inactive towards electrophilic substitutions and for this reason the number of derivatives in this series is limited. Substituted cobalticinium salts are usually prepared indirectly from substituted cyclopentadienyl derivatives. These intermediates can be obtained by treating substituted cyclopentadienes with strong bases or by reducing fulvenes. Various homo- and hereto-substituted cobalticinium salts have been prepared using this type of reaction. Due to the remarkable stability of the metallocenic skeleton of cobalticinium ion, we have succeeded in obtaining new derivatives transforming ring-substituted cobalticinium salts by known reactions.     

Synthese de nouveaux derives silicies cycliques fonctionnels

Methyl or trimethylsilyl ether derivatives of mono- or di-phenols easily undergo disilylation to give disilylated enol ethers or bis(enoxysilanes) with a 1,4-cyclohexadienic ring which are new classes of intermediates in synthesis. In the case of monophenol derivatives hydrolysis affords stable δ-silyl-β,γ-unsaturated ketones, which are converted to the corresponding conjugated cyclohexenones by desilylation (e.g. 4-allyl-2-cyclohexenone which was previously difficult to prepare). In the case of diphenol derivatives cyclohexanediones are obtained upon hydrolysis. Polysilylation occurs with methyl phenyl thio ether, pyrocatechol and even with o-cresol derivatives, to give new products.     

Lactones phenoliques halomethylees,inhibiteurs bifonctionnels de proteases—II : Preparation de derives halomethyles de la dihydro-3,4 coumarine et de la benzofuranone-2

o-Hydroxy phenyl propionic and o-hydroxy phenyl acetic acids give mixtures of ortho- and para-hydroxymethylated phenolic acid sodium salts which with thionyl chloride undergo benzylic chlorination and lactonisation; para- and ortho-chloromethylated derivatives of 3,4-dihydrocoumarin and of benzofuran-2-one are thus obtained in two steps. The bromomethylation of (nitro-3 hydroxy-2 phenyl) and (nitro-5 hydroxy-2 phenyl) propionic acids yields 3,4-dihydro-8-nitro-6-bromomethyl- and 3,4-dihydro-6-nitro-8-bromomethyl-coumarins. Some radioactive derivatives have also been synthesised.     

Cobaltocene as a spin filter

In the context of investigating organic molecules for molecular electronics, doping molecular wires with transition metal atoms provides additional means of controlling their transport behavior. The incorporation of transition metal atoms may generate spin dependence because the conduction channels of only one spin component align with the chemical potential of the leads, resulting in a spin polarized electric current. The possibility to create such a spin polarized current is investigated here with the organometallic moiety cobaltocene. According to our calculations, cobaltocene contacted with gold electrodes acts as a robust spin filter: Applying a voltage less than 0.2 V causes the current of one spin component crossing the molecular bridge to be two orders of magnitude larger than the other. We address the key issue of sensitivity to molecule-lead geometry by showing that a weak barrier generated by CH(2) groups between the cobaltocene and the leads is crucial in reducing the sensitivity to the contact geometry while only reducing the current modestly. These results suggest cobaltocene as a robust basic building block for molecular spintronics.     

Photochemical properties of ferrocene,cobaltocene and nickelocene and their complexes with 2,2,2-trichloroethanol in liquid phase

Summary Photochemical changes in the solutions of ferrocene, cobaltocene, nickelocene and their complexes with 2,2,2-trichloroethanol exposed to near u.v. and argon laser (=514.5 nm) radiation were investigated. The solutions of cobaltocene, nickelocene and their complexes were found to undergo photolysis, whereas ferrocene solutions are not sensitive to this kind of irradiation and the ferrocene bound in a complex undergoes photooxidation to give the ferricenium cation. The activating effect of laser irradiation of ferrocene was revealed as a tendency to complex formation. The quantum yield of the investigated photoreactions, equilibrium constant of complex formation,K, and their molar extinction coefficients, _c, were determined.     

Dérivés de la dihydro-2,4 triazole-1,2,4 thione-3 et de l'amino-2 thiadiazole-1,3,4 à partir de nouvelles thiosemicarbazones d'esters

A new general synthesis of 4,5-disubstituted 2,4-dihydro-1,2,4-triazole-3-thiones is proposed. These heterocycles are obtained by the action of primary amines, arylhydrazines or aroylhydrazines on the thiosemicarbazones of eaters. These last compounds are prepared by action of chlorhydrates of iminoethers on thiosemicarbazide in dimethylformamide. These thiosemicarbazones react also with strong acids, acid anhydrides and chlorides; by thermolysis and they give 2-amino-1,3,4-thiadiazole derivatives. Also, two derivatives of 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole have been prepared.     

Étude des modes normaux de vibration du furanne et de dérivés substitués

A Urey-Bradley force field, determined from vibrational frequencies of furan and six of its deuterated derivatives, has been used to compute the normal vibrations of α substituted compounds which possess a furan ring. Theoretical results give good interpretations of the vibrational spectra.     

Action d'organolithiens sur la méthyl-2 quinoxaline. Etude de la réactivité des adduits

The action of organolithium reagents such as phenyllithium or n-bulyllithium on 2-methylquinoxaline gave lithiation of the methyl group which upon reaction with electtropholesphiles produce side chain alkenyl derivatives. On the other hand organolithium reagents react with the quinoxaline azomethine bond to give I-lithio-2-alkyl)or ary-1)-3 methylquinoxalines which can be further loithiated on the methyl group to give 2-alkyl(or aryl)-3-alkenylquinoxaline derivatives. The adducts can be condensed with clectrophiles such as benzonitrile or methlyl benzoate but only methyl benzoate leads to N condensed derivatives. Furthermore substituted 1,2,3,4-terahydroqinoxalines are available via the above lithio intermediates.     

Réductions chimique et électrochimique de benzopyranno-1 as-triazines

Electrochemical reduction of [1]benzopyranno[4,3-e]-as-triazinones gives 1,4-dihydro derivatives which can either rearrange into 4,4a-dihydro compounds or be reduced with ring contraction into benzopyranno-imidazolones. The reaction of Grignard reagents on benzopyrannotriazines leads to a reduction in –α position of the benzene ring (4,4a-dihydro). Electrochemical reduction gives the 1,4-dihydro derivative which rearrange into the 1,10a-dihydro compound. The 1,4-dihydro derivatives are reduced with triazine ring contraction to give benzopyrannoimidazoles. Dihydro-1,10a compounds can be reduced into imidazoles or into tetrahydro derivatives.     

Metal-Containing Initiator Systems. XXIX. Selective Initiation of Vinyl Polymerizations with Cobaltocene

The polymerizations of acrylonitrile (AN), acrolein (AL), butadiene (BD), and isobutyl vinyl ether (EBVE) with cobaltocene were investigated. It was found that both AN and AL could polymerize in dimethyl sulfoxide through a coordination mechanism, but AN and BD polymerized by a radical mechanism in the presence of some organic halides, such as carbon tetrachloride, benzyl bromide, and allyl bromide. The initiator system of cobaltocene and organic halide also induced cationic polymerization of IBVE. On the basis of the results obtained, a mechanism for the selective initiation of polymerization is proposed and discussed.     

The magnetic susceptibilities of cobaltocene and chromocene

The magnetic susceptibilities of cobaltocene and chromocene have been measured between 83 and 293 K; for cobaltocene the results suggest an appreciable orthorhombic splitting of the ²∏(σ²πδ⁴ ground state, whilst for chromocene the data provide further support for the ³Δ(σδ³) ground state previously deduced.     

Dissymetrisation de la molecule de glyoxal: II. Action des organometalliques sur l'acetoxy-1 triethoxy-1,2,2 ethane

Various organometallic compounds are treated with 1-acetoxy-1,2,2-triethoxyethane (1) an asymmetric derivative of glyoxal. Two kinds of reactions are observed depending on the nature of the organometallic reagents. Organolithium compounds give exclusively addition to the ester carbonyl group, while organocuprate derivatives lead to substitution of the acetoxy group. With Grignard reagents both reactions occur, the proportion of addition and substitution products depending on the solvent and alkyl group. The role of Lewis acids is discussed.     

Reactivite multiple des amines stannique: cas de certains derives carbonyles conjugues

en]Organotin amines react with α-enones to give various products depending on the nature of the initial carbonyl derivatives. 1,2 or 1,4-addition or, abstraction of an hydrogen from the α position were observed; each kinetic product being able to form a more stable species.     

Etude de l'obtention d'enoxysilanes par action du triethylsilane sur des cetones enolisables,aliphatiques ou cyclaniques,en presence de catalyseurs au nickel

The preparion of alkoxysilanes and alkenoxysilanes has been achieved by the reaction of enolizable aliphatic or cyclic ketones with triethylsilane in the presence of nickel catalysts. For some catalysts, the reaction can be directed to give exclusively one or the other of these derivatives. The use of certain nickel catalysts gives very high yields of alkenoxysilanes, and this has been closely investigated.     

C-Silylation de composes a fonction nitrile. Synthese de nitriles α-silicies

The direct silylation by Me₃SiCl/Li/THF of saturated nitriles having a hydrogen atom in the α position with respect to the function leads, according to a simple and rapid process, to the corresponding α-silylated nitriles in yields that are moderate but much higher than those given by the comparable previously known routes. α, β-Unsaturated nitriles give the derivatives resulting from the disilylation of the double bond. Allyl or benzyl cyanide and diphenyl acetonitrile first undergo the elimination of the nitrile group (which behaves as a halogen atom) whereas cyanamid affords bis(trimethylsilyl)carbodiimide giving after further silylation the unexpected tris(trimethylsilyl)amine.     

Synthèses d'indoles par cyclisation réductrice. II Nouvelle mélhode de synthèse des indole carboxamides-3, donnant accés aux dérivés de la gramine

A new synthetic method for 3-indolecarboxamides, in two steps from 2-halogenonitrobenzenes, is reported. These benzene derivatives, reacting with sodium salts of cyanoacetamides in N,N-dimethylformamide, give 2-(2-nitrophenyl)cyanoacetamides. Catalytic hydrogenation of the nitro derivatives, at 80°, leads directly to 3-indolecarboxamides. Reduction of the amides by lithium aluminium hydride gives finally 3-aminomethylindoles (gramine and its derivatives), so obtained by a new synthetic route.     

Cyclisations par l'intermédiaire de fonctions phénylthioet phénoxy-carbamyle. I. Diphényl-1,2-alcoyl-5-dioxo-3,6-hexahydro-triazines-1,2,4

The N-(p-nitrophenoxy-carbonyl) and N-(phenylthio-carbonyl) derivatives of α-amino-acyl-hydrazides cyclize in presence of diazomethane, yielding hexahydro-1, 2, 4-triazines with simultaneous formation of p-nitro-anisole or thio-anisole respectively. The molecules with a phenoxycarbonyl function such as N-(phenoxycarbonyl)-glycyl-(N, N′-diphenylhydrazide) give the corresponding ring products and anisole only in solvents with high dielectric constant (e.g. nitromethane). The phenylthio-carbonyl derivatives give the same ring products in presence of lead acetate by the intervention of HO^?. The p-nitrophenoxycarbonyl derivatives give rise to the same cyclisations in the presence of pyridine by the intermediate of carbamyle-pyridinium ion acting as electrophile. These different types of intramolecular reactions are illustrated by the formation of 1, 2-diphenyl-5-alcoyl-3, 6-dioxo-1, 2, 4-hexahydro-triazines.     

Tetracyanide-bridged divanadium complexes: redox switching between strong antiferromagnetic and strong ferromagnetic coupling

Reaction of [(Me3tacn)V(CF3SO3)3] (Me3tacn = N,N',N'-trimethyl-1,4,7-triazacyclononane) with LiCN in DMF results in oligomerization of cyanide to form [(Me3tacn)2V2(CN)4(mu-C4N4)]. The structure of this binuclear complex features a planar tetracyanide unit bridging two VIV centers via imido type linkages. The conjugated pathway provided by the bridging ligand leads to strong antiferromagnetic coupling (J = -112 cm-1) and an S = 0 ground state. Reduction of the complex with cobaltocene generates the Class III mixed-valence anion [(Me3tacn)2V2(CN)4(mu-C4N4)]1-, wherein resonance exchange induces strong ferromagnetic coupling to give a well-isolated S = 3/2 ground state.     

Regioselective synthesis of substituted naphthalenes: a novel de novo approach based on a metal-free protocol for stepwise cycloaddition of o-alkynylbenzaldehyde derivatives with either alkynes or alkenes

[reaction: see text]. Iodonium ions, o-alkynyl-substituted carbonyl compounds, and alkynes react to give 1-iodonaphthalene derivatives featuring interesting substitution patterns. The reaction with alkenes instead of acetylenes affords related naphthyl ketone derivatives. These two metal-free processes are conducted at room temperature and furnish products in a regioselective manner.