Enrique Roman

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.

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  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  Me) in the presence of t-BuOK. Whereas the known reaction of CpFe(CO)2Cl with Na+S2CNMe2− gives Ib (R  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.

Solvent-dependent dynamic stereochemistry about Fe in ferrocenylcyclohexenones and access to optically active Cp∗Fe+ arene salts

Abstract Intramolecularinversionofthechiralplaneinferrocenylcyclohexenones >Intramolecular inversion of the chiral plane in ferrocenylcyclohexenones in the presence of AlCl 3 occurs in CH 3 NO 2 but not in benzene. In this latter solvent ligand exchange occurs with retention of configuration, and gives optically active Cp ∗ Fe + C 6 H 6 salts with an optical purity close to 100%. This solvent dependence is best accounted for in terms of AlCl 3 cleavage of CpFe bonds in benzene and by AlCl 3 cleavage of acylcyclopentadieneiron bonds or rearrangement in CH 3 NO 2 . The intramolecularity of the inversion process observed in CH 3 NO 2 is confirmed by tritium labellin experiments, and can be explained by rotation of the ions CpFe + and (AlCl 3 · acylcyclopentadiene) − in a caged ion pair; an alternative mechanism involves a σ–ρ rearrangement which can proceed by η 1 ↔ η 5 interconversion of the alCl 3 · acylclopentadiene ligand or by direct insertion of Fe into a fulvene CH bond. Epimerization of substituted ferrocenylcyclohexenones also proceeds by inversion of the quarternary asymmetric carbon.

Indenyl complexes of germanium(II)

Abstract The first indenyl complexes of germanium(II), Ge(1,3-(Me 3 Si) 2 C 9 H 5 ) 2 ( 1 ) and Ge(1,3-(Me 3 Si) 2 C 9 H 5 )(Me 5 C 5 ) ( 2 ), have been prepared by treatment of Li(1,3-(Me 3 Si) 2 C 9 H 5 with GeCl 2 ·dioxane and [(η-Me 5 C 5 )Ge]BF 4 , respectively. The structure of 2 has been determined by X-ray crystallography.

Regio- and stereo-specific electroreduction of cationic acylcyclopentadienylareneiron complexes

Activation of a carbonyl group in cationic organometallic substrates such as the acylcyclopentadienylareneiron complexes(I), (V), and (VII) renders its electrochemical reduction easy and stereospecific, providing a route to the primary and secondary cationic alcohols (II) and (VI) or to the dinuclear dicationic pinacols (III).

9-9′-Bifluorenylidene (BFD) complexes of ruthenium [{(η5-C5Me5)Ru}n(BFD)]x (x = 0, n = 1' x = 1+, n = 2): EPR and spectroelectrochemical studies. X-ray structure of [{(η5-C5Me5Ru}(BFD)](OSO2CF3)

Abstract [( η 5 -C 5 Me 5 Ru] + coordinates to the six-membered aromatic rings of the bifluorenylidene (BFD) chromophore to afford mononuclear [( η 5 -C 5 Me 5 )Ru(BFD)] + and dinuclear {[( η 5 -C 5 Me 5 )Ru] 2 9BFD)} 2+ compounds which could be isolated as trifluoromethane sulfonate salts, 1 (OTf) and 2 (OTf) 2 , respectively. The X-ray structure of 1 was determined and both compounds were studied by spectroelectrochemical methods and their reduced species by EPR.

Piano-stool acylcyclopentadienyl iron complexes: photolytic syntheses and X-ray crystal structure of [Fe(η5-C5H4COMe)(dppe)(NCMe)]PF6

Photolysis of monoacyl iron(II) metallocenes, [Fe(η5-C5H4COR)(η6-arene)] PF6(R = Me or Ph), in solvents of low electron donicity, at 273 K, and in the presence of two-electron ligands L [L = P(OMe)3, NCCH3, CO, or dppe (Ph2PCH2CH2PPh2)], leads to exchange of the arene by three L ligands. Thermal ligand exchange of the derived piano-stool cations [Fe(η5-C5H4COR)L1(L2)L3]PF6, [L1= L2= P(OMe)3, or L1–L2= dppe; L3= NCMe] in the dark and at low CO pressure (5 atm) leads to the corresponding carbonyl derivatives [Fe(η5-C5H4COR) L1(L2)(CO)]PF6. In acetonitrile and under irradiation with visible light, the latter yield the corresponding acetonitrile complexes [Fe(η5-C5H4COR)L1(L2)(NCMe)]PF6. A new series of acyl substituted piano-stool cations [graphic omitted] is obtained showing chirality at the acetylcyclopentadienyl ring. Diastereotopic phenomena in the racemic series of these asymmetric compounds have been observed by 1H and 31P n.m.r. spectroscopy. The X-ray structure of the acyl derivative [Fe(η5-C5H4COMe)(dppe)(NCMe)]PF6 has been determined and compared with the unsubstituted cyclopentadienyl piano-stool acetonitrile and carbonyl cationic complexes.

Photo-activated valence isomerization of hexamethyl(Dewar benzene)(HMDB) assisted by arene–iron(II) complexes: luminescence properties of [HMDB ⋯(η5-C5R5)Fe(η6-arene)]* adducts

Hexamethyl(Dewar benzene)(HMDB) isomerizes to hexamethylbenzene (HMB) under light irradiation in the presence of stoicheiometric or catalytic amounts of the cationic complexes [(η5-C5R5)Fe(η6-arene)]+X–, (R = H, Me; X = BF4–, PF6–), (1a–e) and (2), in dichloromethane solutions at 273 K; mixtures of HMDB and (1b–e) or (2) in dichloromethane exhibit a luminescence band at 530–540 nm probably due to formation of the corresponding exciplex.