Iron catalysts oxidative coupling

BINOL and its derivatives have been utilized as versatile chiral sources for asymmetric catalysis, and efficient catalysts for their syntheses are, ultimately, required in many chemical fields [39-42]. The oxidative coupling of 2-naphthols is a direct synthesis of BINOL derivatives [43, 44], and some transition metals such as copper [45, 46], iron [46, 47] and manganese [48] are known as active metals for the reaction. However, few studies on homogeneous metal complexes have been reported for the asymmetric coupling of 2-naphthols [49-56]. The chiral self-dimerized V dimers on Si02 is the first heterogeneous catalyst for the asymmetric oxidative coupling of 2-naphthol. 

The unique versatility of ruthenium as an oxidation catalyst continues to provide a stimulus for research on a variety of oxidative transformations. Its juxtaposition in the periodic table and close similarity to the biological redox elements, iron and manganese, coupled with the accessibility of various high-valent oxo species by reaction of lower-valent complexes with dioxygen make ruthenium an ideal candidate for suprabiotic catalysis. 

Unfortunately, these requirements have not yet fully been met for any catalytic reaction, although for some simple catalytic reactions reasonable approaches are known. Such reactions are the oxidation of CO over a supported Rh catalyst [46,47], ammonia synthesis over iron [48, 49], and the HCN synthesis over a Pt gauze catalyst. More recently Wolf [50] carried out a micro-kinetic analysis of the primary reaction steps in the oxidative coupling of methane and also related the rate... 

Intermolecular dehydrogenative oxidative homocouplings of (hetero)arenes turned out to be among the most important methods for the synthesis of symmetrically substituted biaryls [122]. A recent illustrative example is oxidative coupling reactions of 2-naphthols, which were accomplished in an asymmetric fashion employing an inexpensive iron catalyst (Scheme 9.47) [123]. 

Interestingly, coupling of phenols and jS-ketoesters under iron-catalysed oxidative conditions leads selectively to the formation of substituted benzofurans. Notably, the iron catalyst acts as a transition-metal catalyst in the oxidative coupling step and as Lewis acid in the condensation step. The presence of water coordinated to the catalyst and/or protic solvents accelerates the process, likely favouring the (final) tautomerisation step (Scheme 13.12). ... 

It has been established that Fe(II) complexes such as 74 and 75 are active catalysts in iron-catalyzed cross-couplings of alkyl halides (Figure 1.3) [347, 348]. The couplings probably involve a Fe(I)-Fe(III) cycle, in which radical intermediates in the coupling step can be excluded, although they might be involved in the oxidative addition step [349, 350]. 

The cw-dicarboxylic acid is also obtained in 27 % yield from butadiene and carbon dioxide, using ( j" -butadiene)-tris(trimethylphosphane) (o)iron as the catalyst. The insertion of carbon dioxide occurs into the Fe-C a bond of the initially formed metallacycle to give 30. Treatment of 30 with FeCls gives rise to an oxidative coupling reaction affording the... 

This chapter deseribes the spectacular and fast development of CDC reactions using iron catalysts involving the oxidative coupling of various sp, sp and sp C-H bonds (Scheme 4.1). 

Guo et al. [24] reported iron-catalyzed tandem oxidative coupling and annulation of phenols and p-keto esters, furnishing polysubstituted benzofurans 38 (Scheme 5.20). The combination of FeClj 6HjO and (t-BuO) offers an efficient catalytic oxidative system. The iron catalyst demonstrates dichotomous catalytic behavior in this transformation, which is a transition metal catalyst in the oxidative coupling step and a Lewis acid in the condensation. 

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