BPMEN

Que and coworkers reported on a similar monomeric iron complex, formed with the BPMEN ligand but without acetic acid [128]. This complex was able to epoxidize cyclooctene in reasonably good yield (75%), but at the same time a small amount of the ris-diol (9 %) was formed. This feature observed with this class of complexes has been further studied and more selective catalysts have been prepared. Even though poor levels of conversion are often obtained with the current... 

Scheme 1 BPMEN and TPA ligands for the iron-catalyzed epoxidation of olefins...

In addition, also nonheme iron catalysts containing BPMEN 1 and TPA 2 as ligands are known to activate hydrogen peroxide for the epoxidation of olefins (Scheme 1) [20-26]. More recently, especially Que and coworkers were able to improve the catalyst productivity to nearly quantitative conversion of the alkene by using an acetonitrile/acetic acid solution [27-29]. The carboxylic acid is required to increase the efficiency of the reaction and the epoxide/diol product ratio. The competitive dihydroxylation reaction suggested the participation of different active species in these oxidations (Scheme 2). 

Scheme 2 Epoxidation of cyclooctene catalyzed by Fe(BPMEN) and Fe(TPA) complexes...

A linear tetradentate ligand, bpmen [N,N -dimethyl-N,N -bis(2-pyridylmethyl)-l,2-diaminoethane] was reported to allow stereospecific alkane hydroxylation [36, 40], The same holds true for the [Fen(TPA)(CH3CN)2]2+ [TPA = tris(2-pyridylmethyl) amine] catalyst family (Figure 3.3) [35],... 

In a seminal contribution [42a], Que and coworkers revealed insight into the reaction mechanisms of epoxidation and dihydroxylation using the pentadentate TPA and bpmen ligands. Some of those compounds had earlier shown remarkable... 

In a second study, Rybak-Akimova and coworkers investigated the catalytic properties of the dinuclear complex, [ Fe (BPMEN) 2(n-0)(n-0H)] " [39]. This complex is a catalyst comparable to its mononuclear iron(II) version, 6. The addition of a single equivalent of fluoride resulted in the opening of the... 

S. Taktak, S. V. Kryatov, T. E. Haas, E. V. Rybak-Akimova, Diiron(lll) oxo-bridged complexes with bpmen and additional monodentate or bidentate ligands Synthesis and reactivity in olefin epoxidation with H2O2, / Mol. Catal. A Chem. 259 (2006) 24. 

A similar architectural feature is shared by doubly carboxylate bridged di-iron(II) compounds [Fe2(/u-OAc)2(BPMEN)2] + (4) and [Fc2(M-02CPh)2(02CPh)2(C5H5N)4] (5) (Scheme 7),i in which coordinatively saturated iron(II) centers are supported by A-rich ligand sets. 

Excellent oxidant-to-product conversion (70 % based on H2O2 in 30 min) and highly stereospecific alkane hydroxylation was observed in the oxidation reaction catalyzed by [Fe(bpmen)(CH3CN)2](C104)2 45). The oxidation of cis-... 

Steric effect is very crudal in the selectivity of ds-diol [79]. While the (6-Me2-BPMEN)Fe(OTf)2 produces ds-l,2-cylcooctanediol as the major product (Table 1.5, entry 4), the 5-methyl analog performs as an epoxidation catalyst (Table 1.5, entry 5). In the presence of acetic add, the nonsubstituted (B PM EN) Fe(SbF6)2, also referred to as (MEP)Fe(SbF6)2, self-assembled to a dimer as a stmdural mimic of methane monooxygenase (MMO) [80]. It catalyzes the epoxidation of a range of aliphatic alkenes. Even the relatively nonreactive substrate, 1-decene, can be oxidized to the corresponding epoxide in 85% yield in 5 min. 

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