William E. Watts

Tricarbonyl(phenylacetylene)chromium and tricarbonyl(styrene)chromium

Abstract The preparation and several reactions of tricarbonyl(phenylacetylene)chromium and tricarbonyl(styrene)chromium are described.

Organocobalt complexes. Part II. Reaction of acetylenehexacarbonyldicobalt complexes, (R1C2R2)Co2(CO)6, with norbornene and its derivatives

Tetra- and hexa-hydro-4,7-methanoinden-1-ones and the analogous indacenediones (VIII)–(X) are formed stoicheiometrically by the title reaction or catalytically from acetylenes, norbornene derivatives, and carbon monoxide in the presence of octacarbonyldicobalt. The process leads stereoselectively to ketones of theexo-series and methyl or phenyl groups derived from the appropriate monosubstituted acetylenes are always found adjacent to the carbonyl group. The 1H n.m.r. spectra of the products are discussed and the use of an europium shift reagent together with spin decoupling is shown to allow clear distinction of the isomeric methanoindacenediones (VIII) and (IX).

Organocobalt complexes : VII. The role of butenolide complexes in the cobalt-catalysed synthesis of bifurandiones from acetylenes and carbon monoxide☆

Abstract The butenolide cobalt complexes derived from monosubstituted acetylenes are shown to be substituted in the α-position of the lactone ring. Their intermediacy in the catalytic formation of 2,6-disubstituted bifurandiones is demonstrated, and shown to require addition of both free acetylene and carbon monoxide.

Organocobalt complexes. Part I. Arene complexes derived from dodecacarbonyltetracobalt

A series of tetranuclear arenecobalt carbonyls, ArHCo4(CO)9, are formed by treating hexacarbonylacetylenedicobalt complexes, (R1C2R2)Co2(CO)6, with arenes in the presence of norbornene derivatives, or from the cobalt carbonyls Co4(CO)12 and Co2(CO)8 by direct reaction with arenes. Stable complexes are obtained from alkyl- and alkoxy-benzenes, but not from halogeno- or acyl derivatives. The spectroscopic properties of the new complexes are reported.

Organocobalt complexes IX. The insertion of acetylenes into butenolide complexes; crystal structure of a dicobalt complex with a novel five-carbon bridge

Abstract Preparative thin layer chromatography has yielded the first-pure insertion products from acetylenes and butenolide dicobalt hexacarbonyls; the structure of one such product has been determined by X-ray crystallography and a related formulation is suggested for the other isomer formed in comparable amounts.

Stable carbonium ions. Part V. Distribution of positive charge in ferrocenylalkylium ions and factors influencing their relative thermodynamic stabilities

From pKR+ measurements, evidence relating to the distribution of positive charge in ferrocenylalkylium ions has been obtained. The 1-ferrocenyl-1-methylethylium cation is more stabilised by methyl substitution at the β- than at the 1′-position while substitution at the α-position exerts a destabilising effect. Cation stability is also sensitive to structural deformation of the system caused by interannular bridging. The mixtures of products formed in the reactions of a series of 1-(acetylferrocenyl)-3-phenylallylium cations with sodium methoxide have been analysed. An acetyl substituent reduces the capacity of the ferrocenyl group to delocalise positive charge. A ruthenocenyl group is more effective than a ferrocenyl group in stabilising a carbonium ion.

Stable carbonium ions. Part III. Reactions involving 1,3-diarylallyl and 1-ferrocenyl-3-arylallyl cations

Equilibrium constants have been measured for the acid-catalysed equilibration of a series of 1,3-diarylpropenols (chalcols) and 1(3)-ferrocenyl-3(1)-arylallyl ethers. The thermodynamic stability of the styryl system is increased by substitution in the aromatic ring of groups exerting either a positive or a negative resonance effect (e.g., p-OMe, p-NO2) or a positive inductive effect (e.g., p-Me). The styryl system is destabilised by the introduction of groups exerting a negative inductive effect (e.g., p-Cl, m-NO2). Conjugation of a carbon–carbon double bond with a ferrocenyl group confers greater thermodynamic stability than that provided by conjugation with an aryl group. In all of these cases, the effects are small. The rate of acid-catalysed chalcol equilibration is accelerated by electrondonating substituents and retarded by electron-withdrawing substituents in the aromatic rings. Analysis of the isomeric chalcol mixtures formed under kinetic control in the solvolysis (80% aqueous acetone) of a series of 1,3-diarylallyl p-nitrobenzoates has shown that positive charge distribution in the intermediate 1,3-diarylallyl cations is moderately sensitive to the nature of the substituents present in the aromatic rings.

Stable carbonium ions. Part VII. Cycloaddition reactions of ferrocenylalkylium ions with cyclopentadiene

The reaction of ferrocenylalkylium ions with cyclopentadiene proceeds stereoselectively to give 1 : 1 cycloaddition products which incorporate a bicyclo[3.2.1]oct-6-ene skeleton fused to a cyclopentadienyl ring (giving a methanoazulenyl structure). Both stereoisomeric forms of (π-cyclopentadienyl)[η- 1–3a(8a)-4,7-methano-7,8-dihydro-4H-azulenyl]iron(II) have been synthesised from cis-3-ferrocenylcyclopentanecarboxylic acid. The stereochemical features of the cycloaddition reactions have been established from the 1H n.m.r. spectral properties of the products and their derivatives.

Stable carbonium ions. Part VI. Inter-cation exchange rearrangements of ferrocenylalkylium ions

In CF3CO2H solution, α-substituted 1-ferrocenylethylium and 1-ferrocenyl-1-methylethylium cations rearrange to a mixture of the isomeric β- and 1′-substituted cations in the presence of ferrocene or an alkylferrocene, by means of an equilibrium controlled transfer of the (MeCH) or (Me2C+) group between cations, ferrocene, or an alkyl derivative functioning as transport agent. Ruthenocenylalkylium ions, and thermodynamically more stable ferrocenylalkylium ions (e.g. FcCHPh, Fc2CH) do not undergo similar rearrangements.

Cycloheptatriene and tropylium metal complexes. Part IX. [1,5] Hydrogen migrations in cycloheptatrienes complexed to chromium

Specific migration of the ϕ-equatorial 7-endo-hydrogen atom in tricarbonylchromium complexed cycloheptatrienes has been confirmed using the 7-exo- and -endo-phenyl derivatives and the approximate rates of migration have been determined for the 7-exo-methyl and -p-tolyl complexes. In all cases sequential [1,5] migration is shown to occur giving first the 3-, then 1-, and finally 2-substituted products. In the 7-methyl case the energy of activation for rearrangement is considerably lower in the complex than in the free ligand, but the difference is much smaller in the case of aryl substituents. These findings are discussed in relation to a possible mechanism for the rearrangement reaction of the complexes.