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397 results on '"Couret, C."'

55. Unsaturated Germanium and Phosphorus-compounds - Reactions of Germaphosphenes With Alpha-ethylene Aldehydes and Ketones

Author

UCL, Ranaivonjatovo, H., Escudie, J., Couret, C., Declercq, Jean-Paul, Dubourg, A., Satge, J., UCL, Ranaivonjatovo, H., Escudie, J., Couret, C., Declercq, Jean-Paul, Dubourg, A., and Satge, J.

Abstract

Germaphosphenes MeS2Ge=PR (R: 2,4,6-triisopropylphenyl (Is), 1; 2,4,6-tri-tert-butylphenyl (Ar), 2) react with a-ethylene aldehydes and ketones to give [2 + 2] and [2 + 4] cycloadditions (for aldehydes) and [2 + 4] cycloadditions and 1,2-additions (for ketones). Four- and six-membered ring derivatives can be easily differentiated by P-31 NMR chemical shifts which are, respectively, +36 to +89 ppm and -33 to -77 ppm. 5a', obtained from 2 and crotonaldehyde, has been structurally characterized by X-ray diffraction: the six-membered ring (germaoxaphosphorinene) conformation is a sofa form, with large folding along the Ge-C axis. A NMR study at various temperatures for 3a, 3a', and 5a' displays dynamic phenomenon including phosphorus and ring inversion. The low DELTAG* values (respectively 18.2,13.7, and 13.2 kcal/mol) seem mainly due to substitution of phosphorus by the electropositive germanium and particularly to large steric effects; the 2,4,6-tri-tert-butylphenyl group lowers the inversion barrier by 5 kcal/mol when compared with the 2,4,6-triisopropylphenyl group.

Published
1993

56. A Compound With a Tin-carbon Double-bond, Bis(2,4,6-triisopropylphenyl)(fluorenylidene)stannane - Aspects of its Reactivity and X-ray Structure of its Dimer

Author

UCL, Anselme, G., Declercq, Jean-Paul, Dubourg, A., Ranaivonjatovo, H., Escudie, J., Couret, C., UCL, Anselme, G., Declercq, Jean-Paul, Dubourg, A., Ranaivonjatovo, H., Escudie, J., and Couret, C.

Abstract

Bis(2,4,6-triisopropylphenyl)(fluorenylidene)stannane (1) reacts nearly quantitatively with compounds having active hydrogen atoms (alcohols, amines, mineral acids, phenylacetylene) and with lithium aluminium hydride to give the corresponding stannanes. Methyl iodide also adds easily to the tin-carbon double bond. Compound 1 slowly dimerizes at room temperature in solution. The head-to-tail dimer 10 has been structurally characterized by X-ray analysis which reveals long intracyclic Sn-C bonds (2.288(4) to 2.293(5) angstrom) and a planar four-membered ring.

Published
1993

85. New stable germenes

Author

Lazraq, M., primary, Couret, C., additional, Escudie, J., additional, Satge, J., additional, and Soufiaoui, M., additional

Published
1991
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97. Reactivity of Germene Mes<INF>2</INF>Ge&dbd;CR<INF>2</INF> with Cumulative Unsaturation-Containing Compounds:  Synthesis of New Germanium Heterocycles

Author

Kettani, Ech-Cherif El, S., Lazraq, M., Ranaivonjatovo, H., Escudie, J., Couret, C., Gornitzka, H., and Atmani, A.

Abstract

Germene 1 reacts with the CO and CS double bonds respectively of phenylisocyanate and methylisothiocyanate by formal [2+2] cycloadditions, leading to four-membered ring derivatives 2 and 3. With CS2, dithiagermolane 11 and dithiadigermetane 12 are obtained; the first step of this reaction is probably a formal [2+2] cycloaddition between the Ge&dbd;C and C&dbd;S double bonds. With nitromethane, oxazadigermolidine 19 and fluorenone are obtained, the first step likely being a [2+3] cycloaddition between the Ge&dbd;C double bond and the NO2 moiety. Compounds 11 and 19 were characterized by X-ray diffraction analysis.

Published
2005

98. Varied Reactivity of the Germene Mes<INF>2</INF>Ge&dbd;CR<INF>2</INF> toward Nitriles

Author

Kettani, Ech-Cherif El, S., Lazraq, M., Ranaivonjatovo, H., Escudie, J., Couret, C., Gornitzka, H., and Merceron, N.

Abstract

The germene Mes2Ge&dbd;CR2 (1, CR2 = fluorenylidene) shows varied behavior toward nitriles. It reacts as a 1,2-dipole with t-BuCN giving a four-membered ring heterocycle, 2-aza-3-germacyclobut-1-ene, as a 1,4-dipole with PhCN, leading to a six-membered ring heterocycle, 3,4-dihydro-3-germaisoquinoline, and as a base, abstracting the α-H of R‘CH2CN to give α-cyanogermanes (R‘ = H, 2-thienyl, 2-FC6H4, 4-FC6H4).

Published
2004

100. From Chlorogermylenes to Stable Hydroxy- and Siloxy-Germylene−Tungsten Complexes

Author

Bibal, C., Mazieres, S., Gornitzka, H., and Couret, C.

Abstract

Reaction of the chlorogermylene ArGeCl [Ar = 2,6-bis((diethylamino)methyl)phenyl] with lithium amides afforded the aminogermylenes ArGeNR2 1 (1a, R = SiMe3; 1b, R = iPr); 1a was structurally analyzed by X-ray diffraction. A protic reagent such as 2,4,6-trimethylphenol (Ar‘OH) reacts with 1b, leading to the mesityloxygermylene ArGeOAr‘ 2. Subsequent hydrolysis of tungsten complexes 1·W(CO)5 gave ArGeOH·W(CO)5, 3. From 1a, ArGeOSiMe3·W(CO)5 (4) also was obtained. Compounds 3 and 4 are the first stable hydroxy- and siloxygermylene complexes. X-ray analysis of 3 shows an increased coordination of the side-chain nitrogen atoms to the germanium resulting from the complexation Ge→W. This complexation can also explain the significant acidity of the hydroxy group in 3, in the same range as triphenylgermanol Ph3GeOH.

Published
2002
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