J. Tirouflet

Structure cristalline et configuration relative d'un complexe du titanocene presentant une chiralite plane et une chiralite centree sur l'atome de titane

Abstract The crystalline structure of the racemic form m.p. 164° C of the compound ( h 5 -3-MeC 5 H 3 C(Me 2 )C 6 H 5 )( h 5 -C 5 H 5 )Ti (2,6-Me 2 C 6 H 3 O)Cl has been determined by X-ray diffraction to establish the relative configuration of the two chiral moieties. This compound may be used further as a reference for studies on dynamic stereochemistry around the titanium atom. A systematic absolute nomenclature is proposed for this type of structure.

Recherches dans la série des métallocènes : XXVIII. Action des réctifs de grignard sur les cétones benchrotréniques chirales

Abstract Benchrotrenyl chiral ketones beating an inductive group (CH 3 or OCH 3 ) were treated with Grignard reagents. The percentage of the diastereoisomeric tertiary alcohols obtained in each case depends on the natures of the inductive group and the benchrotrenyl ketone. In some cases the yield consists mainly or solely of the two secondary alcohols, obtained via reduction process. The structure of the alcohols is established by either spectroscopic or crystallographic means. Models complying with the observed stereoselectivity are proposed in each case.

Pseudoasymetrie dans la serie du benchrotrene I. Synthese des trois glycols ortho-substitues (OC)3CrC6H4(CHOHCH3)2

Abstract The three stereoisomeric glycols (CHOHCH 3 ) 2 C 6 H 4 Cr(CO) 3 have been prepared via 1,2-diformyl- and 1,2-diacetyl-benchrotrenes. The racemic (pseudosymmetric) form and the two meso (pseudoasymmetric) forms of the glycols have been identified by chemical derivatization and analysis of the spectroscopic data. The photochemical decomplexation of these glycols is a specific route for the preparation of the two corresponding benzenic glycols. The stereoselectivity which has been observed in some reactions is discussed.

Complexes cyclopentadienyles de l'uranium(IV) : II. Complexes tricyclopentadienyles d'uranium(IV) a chiralite centro-metallee. Diastereotopie et diastereoisomerie☆

Abstract The synthesis of η 5 -Cp′ 3 UCl,η 5 -Cp-η 5 -Cp′ 2 UCl, η 5 -Cp 2 -η 5 -Cp′UCl (Cp = C 5 H 5 ; Cp′ = substituted cyclopentadienyl) complexes and of similar complexes bridged between the two cyclopentadienyl ligands is described. Several complexes of this type have a prochiral uranium atom. The bridged complexes obtained from the bidentate dianion [C 5 H 4 CHMeCH 2 CH 2 C 5 H 4 ] 2− bear a chiral carbon and a chiral uranium atom in the same structure. The two diastereoisomeric forms have not been separated but are easily identified by NMR analysis.

Complexes pseudo-tetraedriques du titane a chiralite centro-metallee

Abstract Several chiral pseudo-tetrahedric complexes of titanium are described. The chiral characteristics have been detected either by NMR owing to diastereotopic groups or by the isolation of diastereoisomeric pairs of different kinds. By asymmetric destruction of some of these complexes, optically active species have been isolated for the first time in the series of organometallic compounds of titanium. For some of this species the only chiral element is an asymmetric titanium atom.

Electron transfer processes involving [M(η5-C5H5)2X2], M = Ti or Zr, X = Cl or Br. Electrogeneration of unusual anionic species

M(η5-C5H5)2X2(M = Ti, X = Cl or Br; M = Zr, X = Cl) is reduced electrochemically in tetrahydrofuran to give, in successive electrochemical steps, [M(η5-C5H5)2X2]–, [M(η5-C5H5)2X2]2–, and [Ti(η5-C5H5)2X2]3–; [Ti(η5-C5H5)2X2]– is stable in solution and reacts with PPhMe2, while [Ti(η5-C5H5)2X2]2– dissociates into X– and [Ti(C5H5)2X]– which also reacts with PPhMe2.

Reduction electrochimique du ferrocene

Abstract A well characterized 1 e − reversible polarographic wave is observed at low temperature (⋍ −30°C) for ferrocene and methylferrocene in dimethylformamide. At higher temperatures, a 2 e reductive cleavage of the molecule occurs.

Electrochemical characterization of (η5-C5H5)2VCO)− anion and electrochemical behaviour of (η5-C5H5)2 VCO and η5-C5H5V (CO)4

Abstract With the purpose of synthesizing chiral vanodium- (111) complexes of general formula η 5 -Cpη 5 -Cp′V(CO)R an electrochemical approach has been made to obtain the ((η 5 -C 5 H 5 ) 2 VCO) − anion. This arion can be generated from the corresponding neutral complex in a one electron reversible process, but it is unstable. A study of electrochemical behaviour of (η 5 -C 5 H 5 ) 2 VCO under CO atmosphere and of η 5 -C 5 − Hs V(CO) 4 is presented to determine a possible path- way during the ECE decomposition process of the neutral carbonyl dicyclopentadienyl vanadium complex.

Complexes chiraux derives du monocyclopentadienyltitane(IV). Diastereotopie et diastereoisomerie des complexes Cp′TiA(ZZ′) presentant un ligand bidente σ

Abstract The reaction 1 has been used to obtain monocyclopentadienyltitanium(IV) (HZZ′H = disymmetric diphenol or dithiol; R• = Cl• or SR• from CCl4 or RSSR) chiral complexes with three σ bonds. The chirality at the titanium atom is detected either by NMR analysis (diastereotopy of methyl groups when Cp′ = η5-C5H4CHMe2) and by characterization of diastereoisomer pairs (Cp′ = η5-C5H4 C * CHMeC6H5).

Etude de divers types de diastereotopie par RMN de 1H et de 13C dans les series du ferrocene et du titanocene

Abstract The influence of a chiral group on the 1 H and 13 C NMR parameters of ferrocenes and titanocenes is studied. The difference of screening due to the diastereotopy of the cyclopentadienyl carbon nuclei is usually larger than the non-equivalence of corresponding proton chemical shifts. If the chiral group is the titanium atom itself a diastereotopy is also introduced into the cyclopentadienyl ring. Proton spectra obtained at 250 MHz, INDOR and off-resonance experiments, using chemical shift reagents permit a complete analysis of the proton and carbon spectra of some derivatives, especially ferrocene with a CH(CH 3 )(CH 2 CO bridge and titanocene with a CH(CH 3 )CH 2 CH 2 bridge. The result give information on the stereochemistry, and preferred conformations are identified.