M. Rosenblum

Synthesis of ferrocenylacetylenes

Abstract The action of dimethylformamide and phosphorus oxychloride on acetylferrocene converts it, via (1-chlorovinyl)ferrocene, into (1-chloro-2-formylvinyl)ferrocene. This substance is transformed by sodium hydroxide in aqueous dioxan to ethynylferrocene. The two-step sequence constitutes a convenient synthesis of this substance. 1,1′-Diacetylferrocene is similarly converted into a bis-chloroaldehyde, but on treatment with base this gives 1-ethynyl-1′-(1-chloro-2-formylvinylferrocene as the only characterizeable product. Cuprous ferrocenylacetylide couples readily with mono- and 1,1′-diiodo-ferrocenes to give diferrocenylacetylene and 1,1′-bis(ferrocenylethynyl)ferrocene. Similar reactions may be effected with cuprous phenylacetylide. NMR spectra of all substances described are given.

The addition of heteroatomic nucleophiles to dicarbonyl-η5-cyclopentadienyl(olefin)iron cations☆

Abstract The additions of a number of heteroatomic nucleophiles, including methanol, amines, phosphines, phosphites and thiols to dicarbonyl-η 5 -cyclopentadienyl(olefin)iron cations are reported. These reactions generally occur with high regio-specificity to monosubstituted olefin complexes, affording a single adduct. The thermal stability of the adducts depends on the nature of the nucleophile and of the olefin substituent. Addition of benzylamine, dimethylamine or trimethylamine to the propene complex takes place competitive with deprotonation of the olefin ligand. Factors affecting the regiospecificity of the reactions are considered.

Thermal and photochemical interconversions of isomeric monocarbonyl η5-Cyclopentadienyl(η3-allyl)iron complexes

Abstract The photolysis of η 5 -C 5 H 5 -η 1 -C 3 H 5 Fe(CO) 2 at 10°C gives two stereoisomers of η 5 -C 5 H 5 -η 3 -C 3 H 5 Fe(CO). The less stable isomer ( endo ) thermally isomerizes to the more stable ( exo ) isomer with a moderate rate at ambient temperatures. Similarly the endo -η 3 -methallyliron complex isomerizes completely to the exo isomer with AG ≠ = 24.1 kcal/mol. Photolyses of cis - and trans -1-substituted-η 1 allyliron compounds yield the syn - and anti -η 3 -allyliron isomers stereospecifically as a mixture of endo and exo stereoisomers. In all the cases examined the exo , syn stereoisomers are the thermodynamically most stable while the endo , anti are the least stable isomers. Approximate rates for the thermal interconversion of the different stereoisomers have been determined. Anti to syn conversion occurs at a rate comparable to endo to exo isomerization and implies a similar mechanism involving a η 3 → η 1 → η 3 transformation. Theoretical arguments are presented to explain the apparent change in mechanism for endo and exo interconversion of Group VI and VIII η 3 -allyl complexes.

The preparation and properties of dicarbonyl-h5-cyclopentadienyliron h2-vinyl ether and h2-ketene acetal complexes ☆

Abstract Metallation of >-haloacetals wth sodium dicarbonyl- h 5 -cyclopentadienyl- ferrate (Fp - ) provides a convenient point of departure for the synthesis of alhyde -iron complexes (FpCHRCHO) and of h 2 -vinyl alcohol and vinyl ether cations [Fp(CH 2 =CHOR)] + . These latter complexes are shown to be best described as distorted dihapto cation. Treatment of FpCOCH 2 OMe with strong acid leads to the ketene hemiacetal cation [Fp(CH 2 =C(OH)OMe)] + rather than to the expected ketene complex. This substance, as well as the acetal cation [Fp(CH 2 =C(OMe)OEt)] + prepared by alkylation of FpCH 2 COOMe, may possess the structure of an h 1 -metal complex incorporating a carboxonium ion. A correlation is shown to exist between the chemical shift of cyclopentadienyl protons and the average infrared carbonyl stretching frequency in a variety of Fp(olefin) + FpR complexes.

Intermediates in the intramolecular ligand transfer reactions of h5-C5H5Fe(CO)2R complexes

Abstract Dissolution of h 5 -C 5 H 5 Fe(CO) 2 R (I) (R = cyclohexyl or cyclohexylmethyl) in DMSO leads to the formation of a solvent coordinated acyl complex, h 5 -C 5 H 5 Fe(CO)(COR)(DMSO) (II). Treatment of this complex with triphenylphosphine leads to its conversion to h 5 -C 5 H 5 Fe(COR)(PPh 3 ) (III). Rates for the reaction I ⇄ and II → III have been determined. A comparison of the rates of the reaction I → III in eight solvents shows no specific rate acceleration in DMSO and no correlation with solvent donicity. The results are in accord with a two step mechanism in which the first intermediate is the coordiantively-unsaturated species h 5 -C 5 H 5 Fe(COR)(CO). The small spread in rates for solvents of widely different dielectric constants suggests little charge separation in the transition state for this step.

Synthesis of [2.2]ferrocenophane-1,13-diyne☆

Abstract The synthesis of [2.2]ferrocenophane-1,13-diyne, the first member of this class of ferrocenes having bridging acetylenic elements is achieved by coupling of the cuprous salt of 1-ethynyl-1′-iodoferrocene. The physical properties of this substance are described.

The preparation and properties of cationic dicarbonylcyclopentadienyliron complexes of organic carbonyl compounds: molecular structure of dicarbonylcyclopentadienyliron(3-methylcyclohexenone) hexafluorophosphate ☆

Abstract A number of complexes CpFe(CO)2(L) (L = aldehyde, ketone, ester, amide) have been prepared either by treatment of [CpFe(CO)2]2 or CpFe(Co)2Br with AgPF6 in the presence of L or by a ligand exchange reaction employing CpFe(CO)2(isobutylene)BF4. NMR spectral data suggest that these complexes involve iron—oxygen σ-bonding rather than π-bonding to the carbonyl group. This is confirmed by an X-ray structure determination of the 3-methylcyclohexenone complex. The exchange stability of these complexes parallels their basicity.

Reaction of dicarbonyl (pentahapto-cyclopentadienyl)(olefin)iron cations with sodium azide

Abstract Reaction of the (h5-C5H5)Fe(CO)2(C2H4) cation with sodium azide yields the azido complex (h5-C5H5)Fe(CO)2N3 by ligand displacement, rather than the isocyanate complex (h5-C5H5)Fe(CO)(C2H4(NCO) as had previously been reported. The azido complex may also be obtained from other (h5-C5H5)Fe(CO)2(olefin) cations or in low yield from (h5-C5H5)Fe(CO)2Cl. The azido complex is converted to the isocyanate complex (h5-C5H5)Fe(CO)2(NCO) in low yield by photolysis, and to a triazole complex on treatment with dimethyl acetylenedicarboxylate.

Crystal and molecular structure of a segment of a stacked face-to-face ferrocene polymer

Abstract The crystal and molecular structure of a fragment of a face-to-face metallocene polymer, the [2,3]-oligomer( 2a , n = 2) of 1,8-diferrocenylnaphthalene( 1a ), has been determined in order to better define the structural features of the polymer. The molecular structure of this compound shows the same form and magnitude of molecular distortions as those found in the monomeric unit 1a . An unusual feature of the oligomer is the cis arrangement of the two naphthalene nuclei, which brings several of the carbon centers on each naphthalene ring in close proximity. These structural aspects are discussed in the context of possible structures for the related polymer.

Kinetic determination of the metalmetal bond dissociation energy in bis(dicarbonyl η5-cyclopentadienyliron)

Abstract The ironiron bond energy in [C5H5Fe(CO)2]2 (I) has been determined by measuring the rate of disproportionation of the monoacetyl complex (AcC5H4)(C5H5)Fe2(CO)4 (II) to I and [AcC5H4Fe(CO)2]2 (III). The reaction follows first order kinetics in benzene solution in the temperature range of 60–100°C with activation parameters calculated as: ΔH≠ = 26.9 ± 2.7 kcal mol−1 and ▽s≠ = 2.0 ± 3.2 cal mol−1 deg−1.