Ferrocene phosphine ligands

RX= Mel, I2, MejSiCI, PhsCO, B(OMe)3, PhjPCI, CyjPCI, (p-CF3C6H4P)2PCI, (p-AnljPCI Scheme 34 Ferrocene phosphine ligands 114... 

Phosphine ligands based on the ferrocene backbone are very efficient in many palladium-catalyzed reactions, e.g., cross-coupling reactions,248 Heck reaction,249 amination reaction,250 and enantioselective synthesis.251 A particularly interesting example of an unusual coordination mode of the l,l -bis(diphenylphosphino)ferrocene (dppf) ligand has been reported. Dicationic palladium(II) complexes, such as [(dppf)Pd(PPh3)]2+[BF4 ]2, were shown to contain a palladium-iron bond.252,253 Palladium-iron bonds occur also in monocationic methyl and acylpalladium(II) complexes.254 A palladium-iron interaction is favored by bulky alkyl substituents on phosphorus and a lower electron density at palladium. 

The linkers may be nitrogen and carbon, as in BoPhoz - that is, a ferrocene-type ligand, as has already been mentioned. An example of a phosphine-phos-phoramidite is provided by QuinaPhos (48) [292]. 

Fig. 25.1 Structures of Ugi s amine and the first ferrocene-based chiral phosphine ligands.

Sulphoxide removal using sulphoxide-lithium exchange is also effective. It was employed in tandem with a sulphoxide-directed stereoselective ortholithiation of the ferrocene 105 in the synthesis of the phosphine ligand 106 (Scheme 45). Ferrocene lithiation is discussed further in Section III. 

Twinphos A New Family of Chiral Ferrocene Te ra-Phosphine Ligands for Asymmetric Catalytic Transformations... 

A new family of chiral ligands for asymmetric homogeneous hydrogenation has been developed. The performance of mono- and bis-rhodium complexes of these chiral ferrocene tetraphosphine ligands in the hydrogenation of model substrates was surveyed in comparison to their ferrocene bis-phosphine analogs. 

Hartwig [9] et al. developed a novel ferrocene-based dialkyl-phosphine-ligand for this arylation 2-methoxy-4-methyl-phenol is arylated with 2-chloro-p-xylene in 81% yield [eq. (g)]. 

Numerous other bidentate phosphine ligands have also been tested in this reaction.[40] Interestingly, addition of water to the employed ionic liquids [C8Ciim][BF4] and [C4Ciim][Tf2N] led to increased ees and/or reaction rates compared to common organic solvents when ferrocene-based di-phosphines such as 4 and 5, shown in Figure 3.3, were used. 

A series of chiral chelate phosphine ligands, mainly based on the ferrocene backbone (Figure 6.9), have been tested in [C4Ciim][PF6] as catalysts for enantioselective allylic alkylation reactions and results are listed in Table 6.9.[134]... 

Bromothiophene has been coupled with phenylacetylene in a copper-free reaction to give a 96% yield of the product (Equation 33) <20030L4191>. A Pd(ll) complex containing the ferrocene-based phosphinimine-phosphine ligand 83 has proved very efficient for the reaction of 2-iodo- and 2-bromothiophene with phenylacetylene the coupling takes place under copper- and amine-free conditions (Equation 34) <2004TL4337>. 

Unmh and Christenson studied the unusual chelating phosphine ligand l,k-bis(diphenylphosphino)ferrocene and found several interesting effects on Rh-catalyzed hydroformylation. The effect of excess ligand on rate and selectivity is shown in Table 4. 

Optically active ferrocene derivatives, particularly ferrocenyl phosphines, have hitherto been utilized as chiral ligands for a wide range of asymmetric synthesis. We have now revealed that the ferrocene moiety can easily be incorporated in amino alcohol ligands instead of phosphinic ligands. The preparative methods for several types of ferrocenylamino alcohols were developed and they were successfully used to catalyze enantioselective addition of dialkylzinc to aldehydes with high enantio-selectivity. In particular, 1,2-disubstituted ferrocenyl amino alcohols with planar... 

Catalytic reactions have the advantage over the methods discussed so far in that the chiral catalyst need not be added in stoichiometric amounts, but only in very small quantities, which is important if not only the metal (very often a precious one) but also the chiral ligand are expensive. Among the ferrocenes, phosphines are by far the most important catalysts for stereoselective reactions, and are covered in Chapter 2 of this book. We will therefore focus here mainly on the catalytic applications of chiral ferrocenes not containing phosphine groups. Only recently, some progress has been made with such compounds, mainly with sulfides and selenides, and with amino alcohols in the side chain (for this topic, see Chapter 3 on the addition of dialkyl zinc to aldehydes). 

In Other variations, mercurated ferrocene was treated with olefins in the presence of Pd(II) salts to give vinyl ferrocene derivatives (9, 154). Aryl cobalt derivatives have also been used to produce the phenyl-palladium species 284-286). In another study it was found that even aryl phosphine ligands will transfer the aromatic to palladium 297). 

Phosphines ligands that have chirality from ferrocenes have been implemented in the iridium-catalyzed asymmetric hydrogenation of imine with moderate enantioselectivities for Novartis s manufacture of metolachlor. Electronic modifications of these ferrocenyl ligands have increased the enantioselectivity and catalyst reactivity for Lonza s asymmetric hydrogenation processes of biotin and 2-substituted piperazines, intermediates for several pharmaceutical drugs. 

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