A. Dormond

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.

Insertion of carbonyl compounds into actinide—carbon σ bonds: Reactivity of [(Me3Si)2)2N]2MCh2Si(Me)2NSiMe3

Abstract The metallacycles [(Me3Si)2N]2 MCH 2 Si(Me 2 )N SiMe3 (M = U, Th) were obtained in a quantitative one-step synthesis. Carbonyl compounds inserted into the actinide—carbon bond to give the six-membered metallacyles [(Me3Si)2N]2MOC(RR′)CH2Si(Me2)NSiMe3, which were identified by IR and NMR spectroscopy.

Metalloligands containing samarium(III). Access to binuclear f-metal (samarium)-d-metal (rhodium) complexes

The synthesis of the new dimethylphosphinotetramethylcyclopentadiene HC5Me4PMe2 and of its potassium salt KC5Me4PMe2 are reported. Reactions of this potassium salt (as well as of the known LiC5H4PPh2 and KC5Me4PPh2) with [(COT)SMCl(THF)2]2 gave a series of metalloligands (COT)Sm(C5R4PR′2(THF)n (R = H or Me; R′ = Me or Ph; n = 0 or 2; COT = η8-cyclooctatetraenyl; THF = tetrahydrofuran). The X-ray crystal structure of (COT)Sm(C5H4PPh2(THF)2 is described. These metallophosphines reacted quantitatively with (C5H5)Rh(CO)2 to give phosphido-bridged bimetallic samarium(III)-rhodium(I) complexes (COT)Sm(μ-C5R4PR′2)Rh(C5H5)(CO) (R = H or Me; R′= Me or Ph). Crystal data: C33H38O2PSm, triclinic, P1 a = 8.606(2), b = 11.458(3), c = 14.632(2) A, α = 87.09(2), β = 86.93(2), γ = 87.18(2)°, V = 1437.3 A3, Z = 2, Dx = 1.497 g cm−3, m = 21.305 cm−1, λ (Mo-Kα) = 0.71073 A, R = 0.036.

Unsolved dimeric organometallic samarium hydride versus solvated trisalkylborane supported monomeric hydride

The dimeric hydride [Cp′2SmH]2 and the monomeric trisalkylborohydride Cp′2SmHBEt3(THF)n (Cp′  C5H4tBu) are obtained from the starting dimeric chloride [Cp′2SmCl]2 by reaction with a hydridic reagent: NaHBEt3. By hydrogenolysis of Cp′2SmR (R  CH2SiMe3 or CH(SiMe3)2) in the presence of an ancillary ligand as PMe3, a monomeric hydride: Cp′2SmH(PMe3)2 is formed. The trisalkylborohydride is fairly stable in solution when other new hydrides are only moderately stable: upon standing at room temperature, an irreversible transformation into Cp′3Sm is observed. All hydrideds react with propanone to give the corresponding alkoxide: [Cp′2SmOCHMe2]2. The new alkyl complex [Cp′2SmMe]2 is isolated and characterized by NMR and elemental analysis. After hydrogenolysis of this dimer or by reaction of one equivalent of NaHBEt3 with the dimer [Cp′2SmCl]2, mixed bridged hydrides of the general formula Cp′2Sm(μ−H)(μ−X)SmCp′2 (X  Me or Cl) are formed. A mixed bridged chloroalkoxy complex Cp′2Sm(μ-OCHR2)(μ-Cl)SmCp′2 is also obtained.

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.

First NMR observation of 47Ti and 49Ti in cyclopentadienyl complexes

Abstract 47Ti and 49Ti NMR spectra of some mono and biscyclopentadienyl complexes are reported for the first time. The resonances span a relatively large range : electron donating substituents on the cyclopentadienyl ring causes an unexpected downfield shift.

Réactivité des liaisons σ uranium-carbone: réactions du méthyltris(hexaméthyldisilylamido)uranium

Abstract The uranium-carbon σ bond of the methyltris(hexamethyldisilylamido)uranium, [(SiMe 3 ) 2 N] 3 UCH 3 , was poorly reactive towards carbon monoxide insertion, but reacted readily with isocyanides, aliphatic nitriles and carbonyl compounds (aldehydes and ketones). “Acidic” hydrogens reacted under mild conditions; secondary amines gave the tetraamido compounds [(SiMe 3 ) 2 N] 3 UNR 2 and metallic hydrides gave the binuclear compounds with an isocarbonyl linkage.

Complexes biscyclopentadienyles dissymetriques et triscyclopentadienyles mixtes de l'uranium(IV). u comme centre de pseudoasymetrie

Abstract Starting from the monocyclopentadienyls U(C 5 Me 4 R)X 3 (X  Cl or NEt 2 , R  CH 3 or C 2 H 5 ), the bis-cyclopentadienyl dissymetric complexes U(C 5 Me 4 R)CpX 2 (Cp = substituted or unsubstituted cyclopentadienyl ligand) and the tris-cyclopentadienyl complexes U(C 5 Me 4 R)Cp 2 Cl are obtained. If the two Cp ligands have a chiral center, a mixture of one racemic and two meso isomers is obtained. In the meso isomers, the uranium atom is a pseudoasymmetric center.

Reactivity of the uranium-carbon σ-bond in ‘silylamido’ compounds

Abstract The uranium-methyl σ-bond of (N(SiMe3)2)3UCH3 (1)and the uranium-methylene σ-bond of the metallacycle (N(SiMe3)2)2 UCH 2 SiMe 2 N SiMe3 (2) are very reactive towards insertion reactions and nucleophilic substitution reactions. Their reactivity can be used in organic synthesis. Compounds 1 and 2 reacted readily with isocyanides, nitriles and carbonyl compounds R1R2CO. Aldehydes, ketones and esters inserted rapidly in compound 2, affording quantitatively the six-membered metallacycles: (N(SiMe3)2)2UOC(R1R2)CH2SiMe2NSiMe3. These metallacycles were hydrolyzed leading to methylketones (from esters) and to vinyl compounds (from aldehydes and ketones) in high yields. The insertion reaction was highly stereoselective. Compound 2 is a very rapid, clean and high yielding methylenation reagent. It can be used instead of ‘Tebbes reagent’ to synthesize vinyl compounds from carbonyls. 1 reacted rapidly with aldehydes, much more slowly with aliphatic, cyclic and aromatic ketones, but did not react with sterically hindered ketones or esters. Hydrolysis of the intermediate alkoxy- uranium (N(SiMe3)2)3UOCR1R2CH3 gave the corresponding secondary or tertiary alcohols. Compound 1 is a very highly chemoselective reagent of methylation of aldehydes versus ketones and a highly stereoselective reagent.