William P. Hart

The formation and reactions of (η5-carboxycyclopentadienyl)dicarbonylcobalt

Abstract A reaction between sodium cyclopentadienide and dimethyl carbonate in THF solution produces sodium carbomethoxycyclopentadienide in high yield. The analogous carbethoxy derivative can also be readily prepared starting with diethyl carbonate. Carbomethoxycyclopentadienylthallium has been prepared by cracking carbomethoxycyclopentadiene dimer and passing the unstable monomer into an aqueous mixture of thallium(I) chloride and potassium hydroxide. Reactions of these reagents with mixtures of dicobalt octacarbonyl and iodine in THF solution afford moderate yields of the respective products (η5-carbomethoxycyclopentadienyl)dicarbonylcobalt and (η5-carbethoxycyclopentadienyl)dicarbonylcobalt. (η5-Carboxycyclopentadienyl)dicarbonylcobalt is obtained in 67–74% yield by treatment of either ester with potassium hydroxide in aqueous ethanol followed by acidification. A reaction between this acid and oxalyl chloride in benzene solution produces (η5-chloroformylcyclopentadienyl)dicarbonylcobalt in 67% yield, and the latter reacts readily with ammonia and with aniline to form the respective amide and anilide derivatives. The acid chloride also reacts with ferrocene and aluminum chloride under Friedel-Crafts conditions to afford the bimetallic product (η5-ferrocenoylcyclopentadienyl)dicarbonylcobalt. The IR and 1H NMR spectra of these new functionally-substituted derivatives of (η5-cyclopentadienyl)dicarbonylcobalt are discussed.

Functionally Substituted Cyclopentadienyl Metal Compounds

Publisher Summary The birth of cyclopentadienyl transition-metal chemistry occurred in 1951 when Pauson and Kealy discovered bis(η5–cyclopentadienyl)iron (ferrocene). Sodium cyclopentadienides containing aldehyde, ketone, or ester substituents can be synthesized easily following a method developed originally by Thiele in 1900. Peters has shown that a reaction between equimolar amounts of methyl chloroformate and sodium cyclopentadienide gave two main products. Cyclopentadienide anions possessing electron-withdrawing groups generally have greater air stability than do the corresponding unsubstituted cyclopentadienide anions. Excluding ferrocene and cymantrene, which can be halogenated indirectly via electrophilic substitution, there are two methods available for the synthesis of halocyclopentadienylmetal compounds. Wulfsberg and West have synthesized thallium pentachlorocyclopentadienide as well as other M+C5Cl5– salts and have studied their properties. In 1900, Thiele obtained the first cyclopentadienylmetal compound––sodium nitrocyclopentadienide––from a reaction between cyclopentadiene and ethyl nitrate in the presence of sodium ethoxide.Various nucleophiles reacted with 6-diene to give, after hydrolysis, substituted cyclopentadienes. Schlenk and Bergmann first observed sodium isopropenylcyclopentadienide as the product of a reaction between 6,6-dimethylfulvene and triphenylmethylsodium. Polymer-supported cyclopentadienyl compounds have been synthesized mainly for possible catalytic applications. In general, polystyrene–divinylbenzene copolymers have been used as the polymer supports.

The formation and molecular structure of acetylcyclopentadienylsodium-tetrahydrofuranate

Abstract Acetylcyclopentadienylsodium has been isolated in crystalline form as a THF adduct from a reaction between cyclopentadienylsodium and methyl acetate in THF solution. The product has been characterized by means of a single-crystal X-ray diffraction study. {[C5H4CMeO]Na·THF}n crystallizes in the monoclinic space group P21/c with unit cell parameters a 6.698(3), b 16.095(4), c 10.661(3) A, β 92.93(3)° and Dc 1.17 g cm−3 for Z = 4. Least-squares refinement led to a final R value of 0.080 based on 661 independent observed reflections. The coordination sphere around each sodium atom consists of the oxygen atoms from two C5H4CMeO ligands, the oxygen atom of the THF molecule, and an ion contact pair between the sodium and the five ring carbon atoms of the C5H4CMeO ligand.

The formation of ring-substituted titanocene derivatives containing chloro and carbomethoxy substituents

Abstract (Carbomethoxycyclopentadienyl)thallium has been prepared in high yield via a new and convenient procedure starting with sodium carbomethoxycyclopentadienide. Reactions of (carbomethoxycyclopentadienyl)thallium with either (η 5 -cyclopentadienyl)titanium trichloride or titanium tetrachloride produce carbomethoxytitanocene dichloride or 1,1′-dicarbomethoxytitanocene dichloride, respectively, in good yield. Reductions of these dichlorides in the presece of carbon monoxide have afforded carbomethoxy- and 1,1′-dicarcomethoxytitanocene dicarbonyl. Chloro- and 1,1′-dichloro-titanocene dicarbonyl can likewise be prepared via reductive carbonylation of the respective chloro-substituted titanocene dichlorides.

The formation and molecular structure of (η5-nitrocyclopentadienyl)dicarbonylrhodium

A reaction between sodium or lithium nitrocyclopentadienide and dichlorotetracarbonyldirhodium produces (η 5 -nitrocyclopendtadienyl)dicarbonylrhodium in 22–30% yield, the first η-nitrocyclopentadienyl-transition metal compound to be synthesized directly from nitrocyclopentadienide anion. The product has been characterized by spectroscopic and by X-ray diffraction techniques, the latter representing the first such structural determination for a nitrocyclopentadienylmetal compound. Red crystals of the title compound are triclinic, P ?, with a  6.247(4), b  6.484(4), c  11.311(6) A, α  76.79(5), β  79.40(5), γ  72.95(5)°, and D c  2.12 g cm -3 for Z  2. Least-squares refinement gave a final conventional R value of 0.056 for 1438 independent observed reflections. The nitrocyclopentadienyl ligand is significantly nonplanar.

The formation and reactions of (η5-formylcyclopentadienyl)dicarbonylcobalt and (η5-acetylcyclopentadienyl)dicarbonylcobalt

Abstract (η5-Formylcyclopentadienyl)dicarbonylcobalt and (η5-acetylcyclopentadienyl)dicarbonylcobalt have been prepared and the reactivity of the organic functional groups studied. These transformations include the Wittig reaction, sodium borohydride reduction, and Grignard reactions. In addition, alcohol derivatives were converted into their acrylates. Reaction pathways indicating the formation of cobalt-stabilized carbonium ions as intermediates have been implicated.

The Friedel-Crafts reactivity of (η5-cyclopentadienyl) dicarbonylcobalt

Abstract (η5-Cyclopentadienyl)dicarbonylcobalt undergoes Friedel-Crafts acylation with both organic and organometallic acid chlorides, including acetyl, benzoyl, p-toluoyl, p-anisoyl and 2-naphtthoyl chlorides, and chloroformylferrocene as well as 1,1′-di(chloroformyl)ferrocene. The resulting ketones react with triphenylphosphine to afford the corresponding carbonyl-phosphine analogs. IR and NMR spectral features of the new compounds are discussed.

The Formation and Chemistry of New Functionally Substituted η5-Cyclopentadienyl-Metal Compounds: Routes to New Vinyl Monomers

Abstract Reactions of cyclopentadienylsodium with ethyl formate, methyl or ethyl acetate, or dimethyl carbonate in THF solution have produced high yields of the functionally substituted organosodium compounds [C5H4, C(O)R]− Na+, Where R = H, CH3, or OCH3. These organosodium reagents have proved to be valuable intermediates in the formation of functionally substituted cobaltocene, nickelocene, etc., sandwich complexes as Well as for other η5-cyclopenta-dienyl-metal systems such as (η5-C5H4CHO)M(CO)2 (M = Co, Rh) and (n 5-C5H4, CHO)W(CO)3, CH3, The latter aldehydes can be readily converted into corresponding acrylate and vinyl derivatives. The polymerization chemistry of these neu organometallic monomers has been initiated.