Iron complex compounds, cations

Hydride abstraction from dienyl tricarbonyl iron complexes furnishes cationic dienyl tricarbonyl iron complexes. For example, reaction of the diene-iron tricarbonyl complex (115) with triphenyhnethyl hexafluorophosphate followed by trimethylsilyl cyanide furnished with excellent regio- and stereoselectivity a new diene iron tricarbonyl complex (116) (Scheme 170). Excellent regio- and stereoselectivity is seen upon reaction of the cationic complex (116) with trimethylsilyl cyanide (TMS-CN) (Scheme 170). Reduction of the nitrile affords a spirocyclic lactam complex. Intramolecular cyclization of in situ formed enols furnishes spirocyclic compounds again with excellent stereoconfrol (Scheme 171). An interesting example of hydride transfer from a cyclohexadiene ring to a pendant aldehyde followed by nucleophilic addition is seen in Scheme 172. 

N—Fe(IV)Por complexes. Oxo iron(IV) porphyrin cation radical complexes, [O—Fe(IV)Por ], are important intermediates in oxygen atom transfer reactions. Compound I of the enzymes catalase and peroxidase have this formulation, as does the active intermediate in the catalytic cycle of cytochrome P Q. Similar intermediates are invoked in the extensively investigated hydroxylations and epoxidations of hydrocarbon substrates cataly2ed by iron porphyrins in the presence of such oxidizing agents as iodosylbenzene, NaOCl, peroxides, and air. 

In most cases oxidation of uncharged borabenzene complexes produces cations which can only be observed electrochemically. The iron compounds 62 and 63 may serve as an example. Oxidation is fully reversible in rigorously dried CH2C12 but irreversible in more basic solvents such as THF and acetonitrile (62). Preparative oxidation with Ce(IV) salts cleanly produces monosubstituted ferricenium cations 64 (Scheme 10) (66). In contrast to the above mentioned boranediyl extrusions, the substituent at boron is retained here in the newly formed cyclopentadienyl ring. 

With the /. -methylene iron complex (/u.-C7H8)Fe2(CO)6, we encounter an apparent exception of this rule. Extensive H/D exchange occurs upon treatment of ihis compound with CF3CO2D, indicating formation of a rapidly equilibrating intermediate cationic species [R. Aumann, H. Wormann, and C. Kruger, Chem. Ber. 110, 1442 (1977)]. 

Fig. 14. Structures of a ethylene-bridged zirconium compound (above) and of a metal-stabilized cationic 1,3-propanediyl-bridged iron complex (below) including an ORTEP representation of the latter (223).

Cationic iron-alkene complexes also participate in an unusual cycloaddition process, wherein electron-deficient alkenes are attacked by nucleophilic o -allylic Fp complexes, generating stabilized carb-anions and cationic alkene-iron complexes. Attack of the carbanion on the alkene forming a five-membered ring completes this process (Scheme 13). Oxidative removal of the iron produces useful organic compounds.19-21... 

Iron complexes can also catalyze allylic amination [31,32]. Enders et al. have demonstrated the nucleophilic addition of various acyclic and cyclic amines to the optically active l-methoxycarbonyl-3-methyl-(T)3-allyl)-tetracarbonyliron cation 49 formed in high yield from reaction of 48 with iron carbonyls. Oxidative removal of the tetracarbonyliron group by reaction with CAN gives 50 with high optical purity and retention of the stereochemistry (Eq. (12)) [31]. The reaction proceeds well for the different amines, and has been used for the synthesis of a compound showing cytotoxic activity against diverse cell lines [31b]. 

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