Didier Astruc

Electrochemical reduction of η5-cyclopentadienyl Fe+ η6-arene cations in basic media: Study of the behaviour “in situ” of the corresponding radicals

Abstract The one-electron reversible electroreduction of η 5 -cyclopentadienyl iron η 6 -arene cations on mercury in basic media provides the radicals ⋆⋆ of same formula. The behaviour of these radicals [catalysis, decomposition liberating Fe(0) or Fe(II) or dimerization] depends on the nature and on the number of the substitutents on the rings and also on the medium (aqueous, alcohol aqueous, alcohol). These results are explained in terms of the stability and solubility of the intermediates.

Bis- and tris-acetonitrile complexes of iron(II)

Zusammenfassung Photolysis of [CpFe(CO) 3 ] + PF 6 − in CH 3 CN in the presence of 2-, 4- or 6-electorn ligands gives [CpFeL n (NCCH 3 ) 3− n ] + PF 6 − ( n = 1: L = CO, PPh 3 , cyclohexene, dimethylthiophene; n = 2: L 2 = dppe or n = 3: L 3 = cyclooctatetraene, or three phospholes), whereas in the absence of added ligand a thermally stable purple tris(acetonitrile) complex is isolable only using permethylated Cp. The synthetic potential of the acetonitrile complexes is illustrated by the stepwise replacement of the acetonitrile ligands.

Contribution a l'etude des metallocenes—XXIII : Reactions d'echange de ligands entre les arenes et les derives ferroceniques comportant en α un ou deux substituants complexes par le chlorure d'aluminium☆

Abstract One or two unsaturated groups complexed by AlCl 3 and conjugated with the cyclopentadienyl(s) drastically change the nature of ligand exchange reactions of ferrocenes. The reactivity of ketone, aldehyde, alcohol, acid, ester and oxime groups has been examined; simple and double ligand exchange is shown to occur together with transformations of the functionnal groups, providing a route to new polynuclear cations.

Contribution to the study of metallocenes : XXIV. on the mechanism of ligand exchange and complexation by aluminium chloride of ferrocene and its alkylated and acylated derivatives

Abstract A mechanism of ligand exchange between ferrocene and arenes catalysed by AlCl3 is presented. It is shown how the attacking sites of AlCl3 depend on the electronic effect of substituents on the ferrocene rings. In ferrocene and its alkyl derivatives, two types of complexation occur and compete with each other: complexation of a ring reversibly leads to cleavage; irreversible complexation of the metal, possible only in the absence of electron-withdrawing substituents, inhibits metal—ligand cleavage.

Reduction electrochimique regio- et stereospecifique de cetones et d'acides, activee par un greffon organo-fer cationique en α du groupement reductible☆

Abstract Ketones and acids derived from the η5-CpFe+-η6-arene series in which the function is attached to the ring are conveniently transformed into secondary alcohols or pinacols and to primary alcohols by cathodic reduction on mercury. The electroreduction is activated by the cationic organoiron group and is regiospecific on the functional group rather than on the ring, contrary to the reduction with chemical reagents. The electroreduction of α-oxotetramethylene-cyclopentadienyliron+-η6-benzene specifically occurs from the exo side, giving only the endo alcohol.

Insertion of CS2 and CSe2 into metal—amido bonds. Mono- versus bi-dentate dithiocarbamates formed by reactions of CS2 + NHR2 with {CpMo(CO)n}2 (M Fe, n 2; m Mo, n 3)

Abstract The reaction of Cp2Fe2(CO)4 with NHEt2 and CS2 gives the monodentate dithiocarbamate CpFe(CO)2-η1-SC(S)NEt2 (Ia), whereas the same reaction with CP2Mo2(CO)6 gives the chelate CPMo(CO)2-η2-S2CNEt2 (II). New complexes of amines CpFe(CO)2(NHR2)+PF6- (III, R ue5fb Me, Et, SiMe3) have been synthesized by treating CpFe(CO)2Cl with NHR2. They do not react with CS2 and give only [CpFe(CO)2]2 upon refluxing with bases such as t-BuOK or NEt(i-Pr)2, but concerted CS2 insertion in the presence of a base immediately gives I at 20°C. This clean route is used to synthesize the monodentate diselenocarbamate CpFe(CO)2-η1-SeC(Se)NMe2 (IV) by reaction of CSe2 with III (R ue5fb Me) in the presence of t-BuOK. Whereas the known reaction of CpFe(CO)2Cl with Na+S2CNMe2− gives Ib (R ue5fb Me), the analogous reaction of C5Me5Me(CO)2Br gives specifically the thermally stable chelate C5Me5Fe(CO)-η2-S2CNMe2 (Vb′).

L'electroreduction en milieu aqueux des cations η5-cyclopentadienyl-fer(II)-η6-arene: Une methode facile de synthese de dimeres organometalliques

Resume A facile and convenient route to dimerisation of paramagnetic organometallic complexes was found using aqueous electroreduction of cationic precursors on the mercury cathode at -−1.8 V/SCE. Dramatic influence of alkyl substituents on rings is shown to occur in the course of the reaction: while electroreduction of the non-alkylated cations leads to rapid decomplexation of the intermediary radical, dimerisation occurs if the ring bears at least one alkyl group but the radical, in which six methyl groups are present on a benzene ring, is sterically stabilized.

Synthesis and characterization of C5(CH3)5Fe(CO)3+ PF6− and C5(CH3)5Fe(CO)2− K+☆

Abstract C 5 (CH 3 ) 5 Fe(CO) 3 + PF 6 − is obtained in 67% yield by reaction of C 5 (CH 3 ) 5 Fe(CO) 2 Br with AlCl 3 at 60°C under a 40-atm CO pressure. {C 5 (CH 3 ) 5 Fe(CO) 2 } 2 does not react with Na/Hg, but a 2 h reduction on K mirror in THF at 20°C provides C 5 (CH 3 ) 5 Fe(CO) 2 − K + , which can be alkylated by CH 3 I to give C 5 (CH 3 ) 5 Fe(CO) 2 CH 3 in 80% overall yield.

Oxidative cleavage of the FeFe bond in [C5Me5Fe(CO)2]2 using ferrocinium ion: A facile route to the synthetically useful complexes [C5Me5Fe(CO)2(solvent)]+

Abstract Complexes of the type {Fp′(solvent)} + PF 6 − , 3a–3d , (Fp′ = (η -C 5 Me 5 )Fe(CO) 2 , solvent = THF, CH 3 COCH 3 , CH 3 CN, or pyridine) are conveniently prepared by the reaction between Fp′ 2 and Cp 2 Fe + PF 6 (Cp = η 5 -C 5 H 5 ) in the solvent under ambient conditions. The complexes {Fp′L} + PF 6 − , 3e–3g , (L = CO, PPh 3 , P(OPh) 3 ) are readily prepared from {Fp′THF} + . Fp′H is formed by treatment of 3a with NaBH 4 . Fp′SC(S)NMe 2 can be prepared from 3a or 3e and NaSC(S)NMe 2 .

Auto-condensation of aryl- and aralkylferrocenes via ligand exchange

Abstract An intermolecular exchange is described between two molecules of aryl- or aralkyl-ferrocene with AlCl3 as catalyst. The cyclopentadienyl ring of one molecule is replaced by the phenyl nucleus of another similar molecule. In the case of a 1,1′-diaralkylferrocene, this auto-condensation reaction occurs exclusively to give a single salt containing the ferrocene moiety.