Reactions of lithiated 2,5-dimethylazaferrocene with selected electrophiles

Lithiation of 2,5-dimethylazaferrocene 1 with sec-BuLi/TMEDA in THF at −78 °C proceeds (as shown by quenching with D₂O) to comparable extent on the methyl groups and the Cp ring. However, the outcome of the reaction of the lithiated 1 with an electrophile depends on the nature of this electrophile. In the reaction with 4-methoxybenzaldehyde only the product originated from the lateral lithiation is formed, whereas the reaction with 4-methoxyacetophenone and 4,4′-dimethoxybenzophenone afforded mixtures of the products resulting from lateral and ring-lithiation. Similar results were also obtained in the reaction of lithiated 1 with chlorodiphenylphosphine and diphenyl diselenide. On the other hand, the exclusive formation of the Cp-substituted product was observed in the reaction of lithiated 1 with N,N-dimethylformamide. The structures of selected products (oily compounds were transformed into the corresponding crystalline W(CO)₅-complexes) were confirmed by X-ray diffraction. The presented reactions open a novel entry to specifically substituted azaferrocenes (especially those containing heteroatom substituents) with potential applications as ligands for the homogenous catalysis.     

Fe Mössbauer spectroscopic studies on M(CO)5(azaferrocene) complexes (M = Cr, Mo, W). The crystal structures of W(CO)5(azaferrocene) and W(CO)5(2,5-dimethylazaferrocene)

⁵⁷Fe Mössbauer spectroscopic studies on M(CO)₅(azaferrocene) complexes (M = Cr, Mo, W) as well as the crystal structures of W(CO)₅(azaferrocene) and W(CO)₅(2,5-dimethylazaferrocene) are reported. The complexation of azaferrocene to the M(CO)₅ moiety brings about only a small change in the quadrupole splitting. The structures of both tungsten complexes reveal a significant shortening of the W-C bonds trans to the nitrogen. These data indicate that azaferrocene behaves as a relatively strong σ-donor and there is no evidence for any π-acceptor properties.     

Friedel-Crafts acylation of W(CO)5-complexes of azaferrocenes

Blocking of the lone pair of electrons on the nitrogen in azaferrocene by co-ordination to the W(CO)₅ moiety enables Friedel-Crafts acylation of this heteroferrocene. W(CO)₅-complexes of azaferrocene and 2,5-dimethylazaferrocene react with acetyl- and propionyl chloride or acetic anhydride in the presence of aluminium chloride in dichloromethane at r.t. to give W(CO)₅-complexes of 1′-acylazaferrocenes in 10-50% isolated yields. The low yields presumably result from instability of the products in the reaction medium. The X-ray structure of the complex of 1′-acetylazaferrocene has been determined.     

The synthesis, structures, and electrochemistry of 1′-heteroaryl-2,5-dimethylazaferrocenes

We report the synthesis of 1′-heteroaryl-2,5-dimethylazaferrocenes (heteroaryl = 2-bromothiophen-5-yl and 2-bromopyrid-6-yl) via palladium catalysed cross-coupling reactions along with their crystallographically determined structures. The newly synthesized compounds as well as the parent 2,5-dimethylazaferrocene have been investigated by cyclic voltammetry (CV) and were found to exhibit reversible first oxidations followed by an irreversible oxidation at considerably higher potential.     

Electrochemical behaviour of azaferrocenes and reactivity of azaferrocenium cations

The electrooxidation of azaferrocene (AF) and 2,5-dimethylazaferrocene (DMAF) has been investigated in several solvents and under various conditions of basicity and nucleophilicity, by cyclic voltammetry at scan rates ranging between 1 and 500 V s⁻¹. The kinetics of the AF⁺ cation decomposition have been found to be first order (vs. the substrate), and strongly dependent on both the solvent and the possible presence of a base. The results tend to demonstrate that the decomposition of AF⁺ cations is more probably associated with a deprotonation reaction than with a nucleophilic attack.     

The synthesis and electrochemical behavior of 1,4-di-(2,5-dimethylazaferrocenyl)-1,3-butadiyne

Rigid-rod ferrocene capped alkynes have attracted a lot of attention recently. In this note we report an efficient synthesis of the 1,4-di-(2,5-dimethylazaferrocenyl)-1,3-butadiyne which is the first known azaferrocene capped diacetylene derivative. The cyclic voltammetry measurements at different scan rates and temperatures indicate good electronic communication between two iron centers. Better shaped reduction peaks at higher scan rates in 22 °C and −40 °C can point to increased stability of the monocation.     

Lithiation of 2,5-dimethylazaferrocene

Reaction of 2,5-dimethylazaferrocene with sec-BuLi/TMEDA in THF at −78 °C, followed by quenching with D₂O brought about incorporation of deuterium into the Cp ring (54%), methyl groups (38%) and the pyrrolyl β-position (8%). When benzyl chloride or p-methoxybenzaldehyde was used as quenchers products originated from the lateral lithiation were only formed, accompanied by recovered starting material. For this reaction a radical pathway is suggested.