Iron complexes olefin

Alkenes in (alkene)dicarbonyl(T -cyclopentadienyl)iron(l+) cations react with carbon nucleophiles to form new C —C bonds (M. Rosenblum, 1974 A.J. Pearson, 1987). Tricarbon-yi(ri -cycIohexadienyI)iron(l-h) cations, prepared from the T] -l,3-cyclohexadiene complexes by hydride abstraction with tritylium cations, react similarly to give 5-substituted 1,3-cyclo-hexadienes, and neutral tricarbonyl(n -l,3-cyciohexadiene)iron complexes can be coupled with olefins by hydrogen transfer at > 140°C. These reactions proceed regio- and stereospecifically in the successive cyanide addition and spirocyclization at an optically pure N-allyl-N-phenyl-1,3-cyclohexadiene-l-carboxamide iron complex (A.J. Pearson, 1989). 

The following compounds have been obtained from thiete 1,1-dioxide Substituted cycloheptatrienes, benzyl o-toluenethiosulfinate, pyrazoles, - naphthothiete 1,1-dioxides, and 3-subst1tuted thietane 1,1-dioxides.It is a dienophile in Diels-Alder reactions and undergoes cycloadditions with enamines, dienamines, and ynamines. Thiete 1,1-dioxide is a source of the novel intermediate, vinylsulfene (CH2=CHCH=SQ2). which undergoes cyclo-additions to strained olefinic double bonds, reacts with phenol to give allyl sulfonate derivatives or cyclizes unimolecularly to give an unsaturated sultene. - Platinum and iron complexes of thiete 1,1-dioxide have been reported. 

Iron hydride complexes can be synthesized by many routes. Some typical methods are listed in Scheme 2. Protonation of an anionic iron complex or substitution of hydride for one electron donor ligands, such as halides, affords hydride complexes. NaBH4 and L1A1H4 are generally used as the hydride source for the latter transformation. Oxidative addition of H2 and E-H to a low valent and unsaturated iron complex gives a hydride complex. Furthermore, p-hydride abstraction from an alkyl iron complex affords a hydride complex with olefin coordination. The last two reactions are frequently involved in catalytic cycles. 

Table 1 Olefin hydrogenation reactions catalyzed by iron complexes...

As an alternative method for the C-C bond formation, oligomerization and polymerization reactions of olefins catalyzed by a bis(imino)pyridine iron complex are also well known (Scheme 40) [121-124]. 

Scheme 40 Olefin polymerization catalyzed by a bis(imino)pyridine iron complex...

The corresponding iron-catalyzed oligomerization of ethylene was developed by Gibson and coworkers [125]. A combination of an iron precatalyst with MAO (methyl aluminoxane) yields a catalyst that affords ethylene oligomers (>99% linear ot-olefin mixtures). The activity of ketimine iron complexes (R = Me) is higher than that of the aldimine analogs (R = H) and also the a-value of the oligomer is better (Scheme 41). 

A head-to-head dimerization of a-olefin catalyzed by a bis(imino)pyridine iron complex has been reported by Small and Marcucci [126]. This reaction delivers linear internal olefins (up to 80% linearity) from a-oleftns. The linearity of products, however, depends on the catalyst structure and the reaction conditions. 

Abstract In this review, recent developments of iron-catalyzed oxidations of olefins (epoxidation), alkanes, arenes, and alcohols are summarized. Special focus is given on the ligand systems and the catalytic performance of the iron complexes. In addition, the mechanistic involvement of high-valent iron-oxo species is discussed. 

Scheme 6 Chiral iron complexes for the asymmetric epoxidation of olefins...

Diastereoselective intermolecular nitrile oxide—olefin cycloaddition has been used in an enantioselective synthesis of the C(7)-C(24) segment 433 of the 24-membered natural lactone, macrolactin A 434 (471, 472). Two (carbonyl)iron moieties are instrumental for the stereoselective preparation of the C(8)-C(ii) E,Z-diene and the C(i5) and C(24) sp3 stereocenters. Also it is important to note that the (carbonyl)iron complexation serves to protect the C(8)-C(ii) and C(i6)-C(i9) diene groups during the reductive hydrolysis of an isoxazoline ring. 

Better results for the porphyrin complex-catalyzed asymmetric epoxidation of prochiral olefins were achieved by Naruta et al.98 using iron complexes of chiral binaphthalene or bitetralin-linked porphyrin 128 as chiral catalysts. As shown in Scheme 4-45, asymmetric epoxidation of styrene or its analogs provided the product with good ee. Even better results were obtained with substrates bearing electron-withdrawing substituents. 

The key feature of efficient metathesis catalysts seems to be their ability to form, before the [2 + 2] cycloaddition step, a n complex with the alkene (Figure 1.7). Comparison of catalyst 1 with the iron complex 3 shows that the latter, although cationic, will not be able to bind to an olefin, because this would give rise to a complex with 20 valence electrons. A similar argument can be used... 

Although the reaction responsible for the generation of the hydride is not specified, it is assumed that it arises from a disproportionation of iron carbonyl complexes. The hydride presumably adds after ir-complexing to form the c-bonded complex which then splits out the metal hydride in either direction. The ir-complexed olefin may then be displaced by another olefin or undergo another hydride addition-elimination sequence. The second path involves olefin complexing with the deficient Fe(CO)3 species and formation of a jr-allyliron hydride intermediate ... 

Perfluoroethylene was first thought to react with iron carbonyl to give the iron(O) olefin complex [Fe(CO)3(C2F4)2] 213). It has since been shown that the product is a heterocyclic derivative of iron(II) (structure XII) 150, 214) and not a true olefin complex. 

In order to produce a high initial rate we suggest that the iron complex must produce radicals by attacking a reactant, and the thiol is the most likely one. This proposal is supported by the recent demonstration by Wallace (25) that ferric octanoate readily reacts with thiols at ambient temperature to give RS radicals which are effectively captured by an olefin, provided the ratio of thiol to iron concentrations is not greater than 10. 

In the cases of the olefin-bridged, iron complexes (OC)3Fe(olen)Fe(CO)3 (olen = cyclooctatetraene, l,l -di-2,4-cyclohexadienyl, 1, l -di-2,4-cyclo-heptadienyl), we have again shown that reaction with NaN(SiMes)2 leads exclusively to the corresponding monocyano complexes [(OC)[Pg.41]

All these reactions proceed most likely by initial activation of the iron(0) species by a ligand exchange with the activating additives, such as amines, benzonitrile or DMF (Fig. 7). Thus generated mononuclear iron complexes bearing a labile ligand are activated to form coordinatively unsaturated iron complexes 37A. These species reduce the polyhalo compounds to radicals 38A, which add to olefins 30 or 33. 

Olefin aziridination catalysts derived from other transition metals continue to be developed. Simple non-heme iron complexes have been reported to serve as effective... 

Insights have also been provided by the first examples of biomimetic iron complexes that catalyze olefin cis-... 

While a great number of tricarbonyl( -diene)iron complexes have been reported and their reactivity investigated, much less is known of the corresponding heterodiene complexes. In recent years, synthesis of several tricar-bonyl(heterodiene)iron systems involving r] coordination of the heterodiene unit has been achieved. Among the tetracarbonyl(/ -olefin)iron complexes prepared by Weiss was tetracarbonyl(cinnamaldehyde)iron, which converts on heating to the //-bonded tricarbonyl(cinnamaldehyde)iron. The preparation and synthetic utility of (benzylideneacetone)tricarbonyl iron, an analogous complex of an ar,/9-unsaturated ketone, are reported here. 

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