U.S. Gill

Some ring replacement and nucleophilic substitution reactions of η6-subsituted arene-η5-cylopentadienyliron hexafluorophosphates

Abstract A number of nitroarene and aminoarene complexes, including the PF 6 − salts of NO 2 C 6 H 5 FeCp p+ , 0 -, m - or p -CH 3 (NO 2 )C 6 H 4 FeCp + , NH 2 C 6 H 5 FeCp p+ and 0 -, m -, or p -CH 3 (NH 2 )C 6 H 4 FeCp p+ , when heated with an excess of P(OC 2 H 5 ) 3 all gave rise to the ring replacement product, CpFe(P(OC 2 H 5 ) 3 ) 3 + PF 6 − (I). Similarly, the thermal reaction of NO 2 C 6 H 5 Fe(CH 3 )Cp + PF 6 − or NH 2 C 6 H 5 Fe(CH 3 )Cp + PF 6 − with P(OC 2 H 5 ) 3 gave CH 3 CpFe(P(OC 2 H 5 ) 3 ) 3 + PF 6 − (VII). With m -CH 3 (Cl)C 6 H 4 -FeCp + PF 6 − (XIV), heating with P(OC 2 H 5 ) 3 also gave rise to I, while the same treatment with P(OC 2 H 5 ) 3 at room temperature in CH 2 Cl 2 showed no nucleophilic substitution of the chlorine atom of XIV by P(OC 2 H 5 ) 3 . On the other hand, the chlorine atom of a number of chloroarene complexes could be readily displaced at room temperature with various amines acting as nucleophiles. Such nucleophilic substitutions were carried out on ClC 6 H 5 FeCp + PF 6 − and 0 -, m - or p -CH 3 (CI)C 6 H 4 FeCp + PF 6 − with methylamine, ethylenediamine, cyclohexylamine, benzylamine and pyrrolidine to give rise to 20 N -substituted aminoarene complexes.

Studies on nucleophilic substitution reactions with η6-o-dichlorobenzene-η5-cyclopentadienyliron hexafluorophosphate

Abstract Reaction of η 6 - o -dichlorobenzene-η 5 -cyclopentadienyliron hexafluorophosphate (IPF 6 ) with an excess of phenol or p -thiocresol in the presence of K 2 CO 3 could give disubstitution of both chloro groups of I, while a similar reaction with one equivalent of the nucleophile, and under conditions of high dilution, monosubstitution of only one of the chloro groups of I could be obtained. Similarly, di- or monosubstitution could be brought about under appropriate conditions with benzyl or methyl alcohol as the source of the nucleophile. While no reaction could take place between IPF 6 and aniline, a reaction did occur between IPF 6 and o -anisidine ( o -methoxyaniline), but only the monosubstitution product was obtained, even in the presence of an excess of o -anisidine. Similar results of monosubstitution were observed with other nucleophiles containing the NH 2 group, including NH 3 , NH 2 NH 2 , CH 3 NH 2 and C 6 H 5 CH 2 NH 2 . These findings are consistent with the reported differences in yields when IPF 6 was treated with two nucleophilic groups (OH, SH and/or NH 2 ) located in the 1,2-positions of a benzene ring to give CpFe complexes of heterocyclic systems related to 9,10-dihydroanthracene with two hetero-atoms at the 9,10-positions [15]. Reactions were also carried out between IPF 6 and the carbanion-enolate anion derived from acetylacetone, α-benzoylacetophenone, diethyl malonate or ethyl acetoacetate. In these cases, only monosubstitution of one of the chloro groups of I was observed, leading to the formation of a CC bond. A possible explanation for the formation of only monosubstitution products in reactions with N- or C-containing nucleophiles is discussed.

Zwitterionic species from deprotonation of η6-toluidine-η5-cyclopentadienyliron cations and their reactions as nucleophiles

Abstract The three isomeric η6-toluidine-η5-cyclopentadienyliron cations have been prepared from ligand exchange reactions between ferrocene and o-, m- and p-toluidine. Treatment of these cations with t-BuOK in THF gave the neutral zwitterionic species with loss of proton from the amino group, and with no deprotonation from the methyl substituent. The use of these zwitterions in situ as nucleophiles in reactions with CH3I, CS2, CH3COCl, C2H5COCl and C6H5COCl were studied, and the products obtained were similar to those from analogous reactions with the zwitterion from deprotonation of the η6-aniline-η5-cyclopentadienyliron cation.

Ligand exchange reactions with η6-arene-η5-cyclopentadienyliron cations under thermal or photochemical conditions

Reactions of various η6-arene-η5-cyclopentadienyliron or substituted cyclopentadienyliron cations with trimethyl, triethyl or triphenyl phosphite under either thermal or photochemical conditions all resulted in the replacement of the arene ligand with three phosphite ligands to give η5-tris(trimethyl, triethyl or triphenyl phosphite)-η5-cyclopentadienyliron or substituted cyclopentadienyliron cations. The yields of the phosphite complexes were higher from photolysis than from the analogous thermolysis. Photolysis of the η6-chlorobenzene-η5-cyclopentadienyliron cation (IX) carried out in the presence of a more basic or more electron-rich aromatic ligand resulted in the exchange of the chlorobenzene of IX with the more basic arene, thus providing synthetic routes to cyclopentadienyliron complexes that may be difficult to prepare by other means. New complexes synthesized in this way are the η6-2-phenylethyl tosylate-η5-cyclopentadienyliron cation and the CpFe+ complexes of thiophene, 2-methylthiophene, 3-methylthiophene and 2,5-dimethylthiophene.

The synthesis of some η6-ketoarene-η5-cyclopentadienyliron cations and their reduction with sodium borohydride

Abstract η6-Ketoarene-η5-cyclopentadienyliron cations were prepared from KMnO4 oxidation of the aqueous solution of the tetrachloroaluminate salts of η6-arene-η5-cyclo-pentadienyliron cations derived from ligand exchange reactions without the prior isolation of the product from the ligand exchange. Methylene groups α to the complexed aromatic ring were oxidized to carbonyl functions. The ketoarene complexes obtained include those with fluorenone, benzophenone and anthraquinone as the ketoarene ligand. Reduction of these complexed ketoarenes with NaBH4 or NaBD4 gave the corresponding complexed endo-alcohols derived from stereospecific exo-addition of the hydride or deuteride ion.

Keto complexes from the oxidation of η6-xanthene or thioxanthene-η5-cyclopentadienyliron cation and some reactions of the fluorenone and xanthone complexes

Abstract Ligand exchange between xanthene and ferrocene gave the η6-xanthene-η5-cyclopentadienyliron cation which was oxidized in situ with KMnO4 to give the η6-xanthone-η5-cyclopentadienyliron cation (III). Similar oxidation of the η6-thioxanthene-η6-cyclopentadienyliron cation gave a mixture of the thioxanthone complex IV and the corresponding complexed sulfone V. III and the η6-fluorenone-η5-cyclopentadienyliron cation (VI) were utilized as reactants in the synthesis of new complexes via reactions with a number of reagents. Stereospecific exo-addition to give complexed endo-alcohols were observed in the reaction of III with NaBH4, NaBD4 or CH3Li, and in the reaction of VI with CH3Li, the anion of acetonitrile, the anion of nitromethane or the phenylacetylide anion. Ring opening reactions to give complexed o,o′-disubstituted benzophenones were observed when III was treated with the anion of acetonitrile, the anion of nitromethane, methylamine, cyclohexylamine, benzylamine or pyrrolidine.

Ring opening reactions of some η6-heterocycle-η5-cyclopentadienyliron hexafluorophosphates

Ring opening upon reaction with a nucleophile for heterocyclic ligands complexed to cyclopentadienyliron has been studied. The ligands investigated included those related to fluorene with an O, S or NH at C(9) or those related to 9,10-dihydroanthracene again with O, S or NH at the C(9) or C(9) and C(10) positions. Upon treatment with pyrrolidine as the nucleophile, it was found that ring opening occurred only at the site of an O heteroatom. For example, such a reaction with the cyclopentadienyliron complex of dibenzofuran or dibenzodioxin gave, respectively, the cyclopentadienyliron complex of o-N-pyrrolidinyl-o′-hydroxybiphenyl or o-N-pyrrolidinyl-o′-hydroxydiphenyl ether. No ring cleavage was observed at the site of a S or NH as the heteroatom; for example, no reaction took place when the cyclopentadienyliron complex of dibenzothiophene or carbazole was treated with pyrrolidine. A mechanism for the formation of the ring opening products based on the activation of the complexed ring towards nucleophilic aromatic substitution is discussed.

A Conveniet Synthesis of η5-Cyclopentadienyliron Tricarbonyl Hexafluorophosphate

Abstract A one-step and high-yielding synthesis of η5 -cyclopentadienyliron tricarbonyl hexafluorophosphate is described. The procedure involves the bromination of bis (η -cyclopentadienyldicarbonyliron) carried out in the presence of an excess of AlCl3.