Iron catalysis cross-coupling

Keywords Allylic substitution Catalysis Cross-coupling Cycloaddition Cycloisomerisation DNIC Ferrate Hydrogenase Iron... 

The application of transition metal catalysis provided new opportunities to introduce diverse functionality to the diazepine ring system. Iron-catalyzed cross-coupling of Grignard reagents with the imidoyl chloride 40 provided a convenient and efficient method for substituting the heterocyclic ring (Scheme 9) <20060L1771>. 

Figure 1.3 Active catalysis in iron-catalyzed cross-couplings of alkyl halides.

Scheme 28 Domino iron catalysis for cross-coupling of alkyl and aryl halides [90]...

B. Iron Catalysis in the Cross Coupling of Alkenyl Halides and Grignard Reagents Grignard reagents are cross coupled stereospecifically with alkenyl halides such as 1-bromopropene in the presence of catalytic amounts of iron complexes.(27)... 

Iron, cobalt and manganese are effective catalysts for cross coupling and other reactions. They were studied in the very early days of transition-metal catalysis and are now being resurrected." ... 

Nakamura s group reported the first efficient cross-coupling reaction between primary and secondary allq l sulfonates using arylzinc reagents achieved under iron catalysis (Scheme 13.23). This contribution displays... 

A large number of cross-dehydrogenative couplings using iron catalysis under oxidative conditions have been reported [89,90]. The coupling of sp -sp, sp -sp, and sp -sp bonds has been achieved. These reactions proceed through iron-mediated electron-transfer processes and are outside the scope of this review. 

The use of palladium, and to a minor extent nickel, catalysts (the Negishi cross-coupling cf. Chapter 3 of this book), is prevalent and stiU attracts most of the research interest. In recent years, however, some other variants involving, for instance, cobalt or iron catalysis have emerged. 

The metal-catalyzed cross-coupling of aryl-, heteroaryl-, and alkenyhnagnesium derivatives is a broad-scope transformation that has found many synthetic applications C(sp )-C(sp ) couplings are by far the most common. Catalysts by nickel, palladium, and iron complexes is most widespread, but the emerging fields of cobalt and manganese catalysis can also provide useful alternatives. 

Because iron is a cheap, abundant, non-toxic, and environmentally benign metal, it has attracted a lot of attention in catalysis over the last few years. In particular, iron-based catalytic systems showed great promise for the formation of carbon-carbon bonds via cross-coupling reactions. In most cases, however, simple inorganic salts or coordination compounds of Fe and Fe are employed as catalyst precursors. Recourse to NFIC ligands to fine-tune the catalytic properties of iron active centres is still scarce in organic synthesis and was documented for only a handful of reactions. Other important transformations mediated by NHC Fe species were found in the related fields of biocatalysis and organometallic synthesis, and will be discussed first. 

To date, catalytic applications of NHC-Fe systems are still scarce and do not reflect the full potential of this cheap, abundant and non-toxic metal that shows great promise for the formation of carbon-carbon bonds via cross-coupling reactions. Recourse to ill-defined species generated in situ and difficulties in understanding the intimate nature of reaction mechanisms do not ease the development of organo iron catalysis. Support from the related field of iron biocatalysis and recent discoveries in organometallic chemistry are expected to provide help and inspiration for further advances. 

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