Ferrocenes phosphine

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). 

Chelating ferrocene phosphine L18 was reported by Hartwig to efficiently catalyze the amination of most aryl chlorides with any type of primary aliphatic amine, imine, or hydrazine at 80-100 °C with NaOf-Bu in DME. Base sensitive aryl chlorides, or those containing acidic protons, may be aminated using LiHMDS as the stoichiometric base. Impressively, catalyst loadings as low as 0.005 mol% can be used. 

Kingston. J.E. Ashford. L. Beer. P.D. Drew. M.G.B. Anion recognition and sensing by neutral and charged transition metal co-ordinated ferrocene phosphine amide receptors. J. Chem. Soc.. Dalton Trans. 1999. 251-257. 

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

Polyphosphazenes with simple alkyl and aryl substituents directly attached to the backbone by P-C linkages can be prepared by the condensation polymerization of N-silylphosphoranimine precursors. These simple polymers can then be converted to a variety of functionalized polyphosphazenes by derivatization reactions. In this paper, the synthesis and characterization of some derivatives of poly(methylphenyl-phosphazene), [Me(Ph)P=N]and the copolymer, [Me(Ph)P=N]j [Me2P=N)y, are discussed. These polymers include grafted copolymers, water soluble carboxylated polymers, and polymers with silyl, vinyl, alcohol, ester, ferrocene, phosphine, thiophene, and/or fluoroalkyl groups. 

Asymmetric catalysis using chiral ligands, including cyclic phosphine or pyra-zole fragments covalent-bonded with ferrocene system 98PAC1477. 

Togni and co-workers have used the convergent methodology to link phosphine-containing chiral ferrocene ligands on the cyclophosphazene core to obtain dendrimeric structures of the type 37 (Fig. 21) (201). The reaction with the cyclophosphazene end occurs by the replacement of the P-Cl bond and by the formation of the P-0 bond. The dendrimers contain twelve and sixteen ferrocene moieties respectively. The phosphine units present can coordinate to Rh(I) to afford metallic dendrimers, which have been shown to be excellent catalysts for the enantioselective hydrogenation of dimethyl itaconate. The product... 

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 combination of [Rh(Cl(NBD)]2 and ligands 89, 90, 91, or 92 with diphenylsilane asymmetrically reduces aryl alkyl ketones, including acetophenones, in excellent yields and in 81 to 90% ee (Eq. 346).574 The best results are with ferrocene 91 and acetophenone in toluene.575 Other phosphine-substituted ferrocenes do not give comparable results. Rhodium(I) complexes of TADDOL-derived... 

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.

Kang et al.6 reported a practical synthesis of an air-stable ferrocenyl bis-(phosphine) (p5, p5 )-l,l,-bis-(diphenylphosphino)-2,2 -di-3-pentyl ferrocene ([5, 5]-FerroPhos, 10a) and its application in the rhodium(I)-catalyzed enan-tioselective hydrogenation of dehydroamino acid derivatives. 

Since the solubility of long-chain alkenes is higher in ionic liquids than in water, there is much interest in finding effective ionic liquid catalysts for the hydroformylation reaction. Bis-phosphines have proved to be particularly useful in hydroformylation reactions and a bis-phosphine with a charged cobaltocenium backbone, analogous to l,l/-bis(diphenylphosphino)ferrocene (dppf), has been developed specifically for use in ionic liquid hydroformylation reactions [26], In combination with [Rh(CO)2(acac)], the 1, I -bis(diphenylphosphino)cobaltocenium hexafluorophosphate ligand dissolved in [bmim][PF6] effectively catalyses the hydroformylation of 1-octene as shown in Scheme 8.11. 

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