C. Moise

Electrochemical studies of organometallic compounds : I. On the reversibility of the first reduction stage of titanocene dichloride

The 1e reduction of titanocene dichloride (η5-Cp2TiCl2) in various solvents has been examined in detail by polarography, voltammetry on a disk electrode, and linear potential sweep voltammetry. In all cases, the electron uptake is followed by a fast loss of Cl−, which is replaced by a neutral ligand (which can be a solvent molecule). In tetrahydrofuran, whose binding ability is weak, a pseudo reversible behaviour is observed due to a return of Cl− to the molecule. In dimethylformamide, which is strongly bonded, the reaction is irreversible. In pyridine, it can be reversible or irreversible according to the conditions.

Tandem carbonyl coupling-rearrangements promoted by the niobium(III) reagent. Dual reductive and Lewis acid properties of NbCl3(DME)

Abstract Benzaldehyde (1a) and acetophenone (6) are shown to undergo highly stereoselective reductive couplings by NbCl3(DME). When the reaction is performed at −10°C, the threo diols can be isolated. The intermediate niobiopinacols reveal the ability of subsequent transformations, due to the Lewis acid properties of the reagent used. Starting from 1a stereospecific acetalization leads to threo-2,4,5-triphenyl-1,3-dioxolane (3a), whereas 3,3-diphenyl-2-butanone (7) is obtained from 6 in a pinacol-pinacolone type rearrangement. Alkenes may also be formed in the competing, temperature controlled deoxygenation The stereoselectivity and the easy control of NbCl3 (DME) mediated reactions make it a promising reagent for further synthetic applications.

Pinacol coupling of aliphatic aldehydes promoted by niobium (III) reagent

Abstract NbCl3 (DME) was found to be a useful reagent for the intermolecular pinacol coupling of aliphatic aldehydes. The high anti diastereoselectivity of this reaction (dl / meso ≥ 9 / 1) did not depend on the variation in the aldehyde alkyl chain. With respect to intramolecular pinacolization, the loss of the stereoselectivity observed is consistent with the mechanism involving an insertion of the oxo-group into the metal-carbon bond of the intermediate niobiooxirane.

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.

Electrochemical studies on organometallic compounds

Abstract The electrochemical oxidation of titanocene monochloride, Cp 2 TiClL (L=tetrahydrofuran or dimethylphenylphosphine), has been studied by voltammetry on disc electrode, by linear potential sweep voltammetry and by controlled potential electrolysis. A first one electron step yields Cp 2 TiClL + , which then reacts with Cp 2 TiClL to give Cp 2 TiCl 2 and Cp 2 TiL 2 + . The latter is oxidized to Cp 2 TiL 2 2+ .

Synthesis of bent titanocene metalloligands with the (diphenylphosphino)tetramethylcyclopentadienyl moiety. X-ray structure of [(η5-C5Me4PPh2)2TiCl2]Mo(CO)4

The reactions of lithium(diphenylphosphino)tetramethylcyclopentadienide with CpTiCl 3 and secondly with TiCl 3 followed by CCl 4 oxidation lead to the formation of two titanocene phosphines: (η 5 -C 5 H 5 )[η 5 -C 5 Me 4 P(C 6 H 5 ) 2 ]TiCl 2 ( 2 ) and [η 5 -C 5 Me 4 P(C 6 H 5 ) 2 ] 2 TiCl 2 ( 3 ), respectively. The metalloligand 3 reacts readily with Mo(CO) 4 cod, Mo(CO) 5 THF and Mo(CO) 6 to give in each case [(η 5 -C 5 Me 4 o(CO) 4 ( 6 ) as a sole product. The structure of 6 has been determined by X-ray diffraction. Crystal data: P , a = 11.716(1), b = 11.753(2), c = 16.110(2) A, α = 99.06(1), β = 92.61(1), γ = 104.20(1)°, Z = 2. The molybdenum-titanium distance of 5.194(1) A rules out any metal-metal interaction. The chlorine substitution reactions by CO in 2 and 3 and by thiolate group (pH 3 C-C 6 H 4 -S) in 16 are reported.

Insertion of activated acetylenes into the metal-hydride bond of [(η5-C5H5)2M(CO)H] (M = Nb, Ta)

Abstract Reactions of [Cp 2 M(CO)H] (M = Nb, Ta; Cp = η 5 -C 5 H 5 ) with various acetylenes RCCR having electron-withdrawing groups were investigated. They give the σ-al- kenyl complexes [Cp 2 M(CO)(CRCHR)] via insertion of the alkyne into the MH bond. On the basis of 1 H and 19 F NMR data the reactions were shown to be: (i) regioselective, monosubstituted alkynes giving only the α-R metallated complex; (ii) stereoselective, exclusive formation of the Z -isomer being observed with hexafluorobut-2-yne. The Z isomer has been shown to exist as two conformers, the steric requirements of the ligands creating a barrier to rotation of the alkenyl group around the MC σ bond.

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.