Trevor S. Abram

Carbon-13 NMR spectra of ferrocenes and ferrocenyl-alkylium ions

Abstract The proton-coupled and proton-decoupled pulsed Fourier-transform 13 C NMR spectra of a series of neutral ferrocene derivatives and ferrocenylalkylium ions have been recorded and analysed. The influence of a substituent group upon the 13 C shifts of the carbons of the ferrocene rings has been investigated. The spectra of the ferrocenylalkylium ions are discussed in relation to the distribution of positive charge and to the various structural models which have been proposed for such species.

Metal-assisted cycloadditions. Part 3. Reactions of dicarbonyl(η5-cyclopentadienyl)(η1-2-methoxyallyl)iron with electron-deficient olefins and acetylenes

Dicarbonyl(η5-cyclopentadienyl)(η1-2-methoxyailyl)iron (3) has been treated with a number of tetra-, tri-, and disubstituted electron-deficient olefins and acetylenes. A mixture of cyclic and linear products has been formed from reaction of complex (3) with trimethyl ethylenetricarboxylate and diethyl 1 -cyanoethylene-1,2-dicarboxylate, with exclusive formation of the cyclopentyl-Fp adduct from ethyl 3,3- and 2,3-dicyanoacrylates. Reaction of complex (3) with tetramethyl ethylenetetracarboxylate, its tetraethyl analogue, diethyl methylenemalonate, t-butylcyanoketen, and dimethyl acetylenedicarboxylate has given, on the other hand, only linear adducts arising from H-transfer. Demetallation of the (η1-3,3-dicyano-4-ethoxycarbonyl-1-methoxycyclopentyl)-Fp complex (6b) with ceric ammonium nitrate and carbon monoxide has given a mixture of the corresponding cyclopentanone dimethyl acetal and olefin derivatives.

Metal-assisted cycloadditions. Part 1. Synthesis of substituted cyclopentane-derivatives obtained from the reactions of (η1-allyl)dicarbonyl(η5-cyclopentadienyl)iron with electron-deficient olefins and acetylenes

(η1-Allyl)dicarbonyl(η5-cyclopentadienyl)iron has been treated with various electron-deficient cyano- and alkoxycarbonyl-substituted olefins and dimethyl acetylenedicarboxylate. The resulting cyclopentyl–Fp [Fp = Fe(CO)2(cyclopentadienyl)] complexes have been subjected to demetallation reactions employing various reagents. Alkoxycarbonyl esters of the substituted cyclopentanes were isolated by oxidative carboxylation with ceric ammonium nitrate, and cyclic and linear products have been obtained with hydrogen chloride by cleavage of the Fe-C bond. N-Bromopyridinium bromide has yielded a mixture of bromocyclopentane derivatives and cyclo-pentenes. β-Hydride abstraction, with trityl tetrafluoroborate, of the complex (12c) has resulted in the formation of diethyl but-3-enylmalonate.

The properties of ferrocenylvinyl cations in solution: inter- and intra-molecular trapping

Abstract Ferrocenylvinyl cations have been generated in solution from alkynylferrocene precursors and their reactions have been investigated.

The formation of ethynylferrocenes in reactions of sterically crowded acetylferrocenes with a grignard reagent

Abstract Acetylferrocenes bearing a bulky 2-alkyl substituent react with isopropylmagnesium bromide to give enolate salts which are converted into ethynylferrocenes by a thermally induced elimination reaction.

Stable carbocations. Part 12. Generation, observation, and properties of ferrocenyl-stabilised vinyl cations

A series of stable ferrocenylvinyl cations has been prepared by protonation of alkynylferrocenes in trifluoroacetic acid, and their structural and chemical properties have been investigated by spectroscopic means. Their stability towards nucleophilic addition is enhanced by alkyl substitution in the ferrocene rings and by steric shielding of the reaction centre. For cations bearing a vinyl β-substituent, torsional isomerisation by rotation around the ring–C+ bond has been studied by 1H n.m.r. spectroscopy.

Stable carbocations. Part VIII. Fragmentation reactions of ferrocenylalkylium ions

In solution in trifluoroacetic acid, ferrocenylalkylium ions of the type Fc[graphic omitted]R·CH2X undergo fragmentation to X+ together with Fc[graphic omitted]RMe when X is an electrofugal group forming a sufficiently stable cation, e.g., when X = FcCRMe or Ph3C but not when X = Me3C or p-MeO·C6H4·CH2.

Stable carbocations. Part 14. Ferrocenyl-substituted allenyl ↔ propynyl cations

Whereas 3-ferrocenylprop-2-yn-1-ol undergoes protonation of the triple bond in trifluoroacetic acid to give a ferrocenylvinyl cation, the secondary alcohol 1,3-diferrocenylprop-2-yn-1-ol and the tertiary 3-ferrocenyl-1,1-dimethyl- and -diphenylpropynols undergo dehydroxylation giving mesomeric allenyl ↔ propynyl cations which are rapidly converted into trifluoroacetoxyallylium ions by solvent addition. Under similar conditions, the secondary alcohol 1-ferrocenyl-3-phenylprop-2-yn-1-ol gives the stable 1-ferrocenyl-3-phenylprop-2-ynylium ion, which can also be generated inefficiently in dichloromethane solution by hydride abstraction from 3-ferrocenyl-1-phenylpropyne. The (ferrocenylethynyl)tropylium cation has been prepared as a stable salt. The products formed on quenching solutions of these cations have been identified.

Stable carbocations. Part 13. Intra-ionic cyclisation reactions of ferrocenyl- and phenyl-stabilised vinyl cations

Ferrocenylvinyl cations bearing triarylmethyl, ferrocenylmethyl, ferrocenylcarbonyl, or cycloheptatrienyl groups attached to the vinylic β-carbon atom, and the phenylvinyl cation formed by protonation of 3-ferrocenyl-1-phenylpropyne undergo intra-ionic cyclisation to give a variety of novel mono-, bi-, and tri-cyclic derivatives.

Stable carbocations. Part IX. Reactions involving sterically crowded ferrocenylalkylium ions

The 1-ferrocenyl-1,2,2,3,3-pentamethylbutylium ion (6) is formed when 3-ferrocenyl-2,2,4,4-tetramethylpentan-3-ol (1) is dissolved in trifluoroacetic acid. At 33°, this cation reacts both by fragmentation [to give the 1-ferrocenyl-1,2-dimethylpropylium ion (7)] and by rearrangement [to the 1,2-dimethyl-1-(2-t-butylferrocenyl)propylium ion (10)]. At 65°, the cation (10) rearranges to the 2,2-dimethyl-1-(2-t-butylferrocenyl)propylium ion (14).