Cyclohexene complexes, with iron

We studied the oxidation of cyclohexene at 70°C in the presence of cyclopentadienylcarbonyl complexes of several transition metals. As with the acetylacetonates, the metal center was the determining factor in the product distribution. The decomposition of cyclohexenyl hydroperoxide by the metal complexes in cyclohexene gave insight into the nature of the reaction. With iron and molybdenum complexes the product profile from hydroperoxide decomposition paralleled that observed in olefin oxidation. When vanadium complexes were used, this was not the case. Variance in product distribution between the cyclopentadienylcarbonyl metal-promoted oxidations as a function of the metal center were more pronounced than with the acetylacetonates. Results are summarized in Table V. 

Dienes form very stable complexes with a variety of metal caibonyls, particularly Fe(CO)s, and the neutral V-diene metal carbonyl complexes are quite resistant to normal reactions of dienes (e.g. hydrogenation, Diels-Alder). However, they are subject to nucleophilic attack by a variety of nonstabilized carbanions. Treatment of -cyclohexadiene iron tricarbonyl with nonstabilized carbanions, followed by protonolysis of the resulting complex, produced isomeric mixtures of alkylated cyclohexenes (Scheme 15).24 With acyclic dienes, this alkylation was shown to be reversible, with kinetic alkylation occurring at an internal position of the complexed dienes but rearranging to the terminal position under thermodynamic conditions (Scheme 16).2S By trapping the kinetic product with an electrophile, overall carbo-... 

We have prepared the Fe Pc/ zeolite catalyst and used in the aerobic oxidation of 1-octene and cyclohexene. Zeohte-encapsulated iron phthalocyanine proved to be an active and stable catalyst in the oxidation of hydroquinone and in the triple catdytic oxidation of 1-octene and cyclohexene. Product distribution, selectivity and yield were similar to those obtained with free iron phthalocyanine. No decrease in catalytic activity was observed during the catalytic reaction. The zeohte-encapsulated complex is easier to handle than the non-supported one, it can be removed from the reaction mixture by simple filtration and it can be reused in several subsequent catalytic runs with similar catalytic activity. 

Udenfriend suggested a simple non-enzymatic system as a possible model of monooxygenase [44]. It involves an iron(II) complex with EDTA and ascorbic acid and is capable of hydroxylating aromatic compounds. Later, Hamilton found that this system was able to hydroxylate cyclohexane (however, with very low yield) and epoxidize cyclohexene [45]. Afterwards, a number of similar systems were proposed. For example, Ullrich found two models which are more effective than the Udenfriend system. One of them includes a Sn(II) phosphate complex... 

A quite original approach to selective oxidations using H2O2 is based on polymeric membranes. In one case the polymer (polydimethyl siloxane) is filled with a zeolite which encapsulates an iron complex, i.e. the homogenous catalyst is inunobilized in the membrane. The organic phase and the aqueous phase are fed at opposite sides of the membrane. This system has been used for the oxidation of cyclohexane to cyclohexanol and cyclohexanone, and the products were kept in the organic phase. In addition, Buonomenna used polymeric membranes for the oxidation of benzyl alcohol to benzaldehyde and for the oxidation of cyclohexene, both with H2O2. 

Epoxy alcohols are the normal products of the [VO(acac)2]+(Me2C(CN)N a -catalysed oxidation of cyclic olefins by dioxygen however, cyclo-octene is oxidized exclusively to cyclo-octene oxide. The oxidation of sulphides and alkenes by peroxides with a [V(0)(acac)2] catalyst have been compared and the nature of the monoperoxovanadium(v) intermediate investigated. Complexation of a Cr(CO)3 unit to aromatic hydrocarbons enhances the benzylic positions towards attack by superoxide ion, e.g., diphenylmethane is readily converted into benzophenone. Metal porphyrin complexes ML4 continue to attract attention both as reversible oxygen-carriers (M = Fe) and oxidation catalysts (M = Mn, Fe, or Co ). For example [Mn (=0 IPh)(TPP)Cl] is believed to be involved in the oxidation of cyclohexene to cyclohexanol by PhIO in the presence of [Mn(TPP)]+ and a ferryl intermediate [Fe (0)L4] has been proposed in the oxygenation of triphenylphosphine with iron(ii) porphyrin. [M(TPP)]X (M=Mn, X = OAc M=Fe, X=C1 M = Co, X=Br) catalyses the epoxidation of styrene and cyclohexene with NaOCl under phase-transfer conditions. ... 

Interestingly, [Ee(F20-TPP)C(Ph)CO2Et] and [Fe(p2o-TPP)CPh2] can react with cyclohexene, THF, and cumene, leading to C-H insertion products (Table 3) [22]. The carbenoid insertion reactions were found to occur at allylic C-H bond of cyclohexene, benzylic C-H bond of cumene, and ot C-H bond of THF. This is the first example of isolated iron carbene complex to undergo intermolecular carbenoid insertion to saturated C-H bonds. 

Cyclohexene oxidation in the presence of the vanadium complex, [C5H5V(CO)4], gave a product distribution which differed greatly from that observed with either the iron or the molybdenum complex. The major product, l,2-epoxy-3-hydroxycyclohexane, IX, was not formed with the iron or molybdenum complexes. The epoxy alcohol, IX, represented... 

A remarkable solvent effect on the chemoselectivity was discovered by Agarwala and Bandyopadhyay (Scheme 3.24, B) [114]. When cyclohexene la was oxidized with tBuOOH in the presence of an electronegative substituted iron(III) porphyrin complex in CH2Cl2-MeOH, epoxide 4a was the predominant product (69% yield) in addition to alcohol 2a and ketone 3a as byproducts in 20% and 11% yields,... 

Roelfes et al. prepared a non-heme iron(II) complex 26 from pentadentate ligand N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine 25 (Scheme 3.32) [126]. In the presence of H202, complex 26 reacted to a low-spin Fe(III)OOH intermediate, which was cleaved homolytically to an oxo Fe(IV) species and a hydroxy radical. Both species are capable of oxidizing various organic substrates via a radical pathway (Scheme 3.32). Under the catalysis of complex 26, cyclohexene la was oxidized with excess H202 to a mixture of products 2a, 3a and 4a. The TON was found to be solvent dependent, with higher TON in acetonitrile than in acetone (Scheme 3.32). In no case were isolated yields given and, furthermore, the allylic oxidation is limited to cyclohexene la. 

When metal ion complexed amino radicals are produced by the reaction of A -chloro amines with reducing metal salts in the presence of alkenes, /6-halo amines are produced12-39 41. The reaction of 1-chloropiperidine with cyclohexene, iron(II) sulfate and iron(III) chloride in methanol afforded mainly the d.s-adduct of 2. The diastereoselectivity is attributed to coordination of the unprotonated amino group with the iron(III) salt, which is mainly responsible for the chlorine atom transfer. With A-chlorodimethylarnine and 4-chloromorpholine lower yields are obtained. 

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