Ferrocenyl amines

Hollis TK, Overman LE (1997) Cyclopalladated ferrocenyl amines as enantioselective catalysts for the rearrangement of allylic imidates to allylic amides. Tetrahedron Lett 38 8837-8840... 

Cohen F, Overman LE (1998) Planar-chiral cyclopalladated ferrocenyl amines and imines as enantioselective catalysts for allylic imidate rearrangements. Tetrahedron Asymmetry 9 3213-3222... 

The ligands discussed so far all contained C2 symmetry. An important new class of ligands having Ci symmetry was introduced by Togni [22] (see Figure 4.19). They can be easily made from an enantiomeric amine as the precursor in a few steps. Different substituents can be introduced at the phosphorus atoms. In addition to the chiral carbon atom the molecule has planar chirality as well. The chiral carbon atom is used to introduce the planar chirality, i.e. lithiation of the ferrocenyl amine takes place at a specific side of the amine at the ferrocene moiety. 

The ferrocenyl amine ligands 39 could be improved further by changing the Ar substituent (Scheme 8.24) [41b]. 

The asymmetric aza-Claisen rearrangement of allyl imidates, (86) (87), has been shown to be catalysed by homochiral cationic palladium(II) complexes, and a series of enantiopure cyclopalladated ferrocenyl amines and imines have been... 

Other aminoferrocene precursors are Af-ferrocenyl phthalimide, which can be converted to FC-NH2 by N2H4 H2O in boiling ethanol (82% yield) [16, 44], and ferrocenyl azide, FC-N3, which has been reduced with LiAlH4 (72% yield) (cf. Scheme 5-6) [45]. Ferrocenyl amine, FC-NH2, is generally formed among other products in the thermal or photochemical decomposition of FC-N3 [56] and in the thermolysis of ferrocenyl isocyanate, Fc-NCO [57], in solvents such as cyclohexane, cyclohexene and benzene, probably by reaction of the intermediate nitrene, [Fc-N], with the solvent [56, 57]. The reduction of nitroferrocene, FC-NO2, provides another route to aminoferrocene, FC-NH2 [58 — 61] however, FC-NO2 is not an easily accessible starting material. 

Ferrocenyl amine, FC-NH2, is a somewhat stronger base than aniline [51, 60, 65]. Its chemistry has been studied in detail alkylation and acylation — but not diazotation — proceed as expected. FC-NH2 is the parent compound for the... 

Scheme 5-23. Synthesis of the ferrocenyl amines Fc-NHa, FcaNH and NFcj [54], (a) Metallation (NaNH2 in toluene) (b) ferrocenylation (Fc-Br/CuBr/py) in toluene, 110°C (c) hydrolysis (10% aq. KOH, reflux) (d) hydrolysis (KOH/EtOH), reflux).

The ferrocenyl-amine (S)-172, upon treatment with n-BuLi and iododimethylarsine or chlorodiphenylarsine in diethyl ether, affords the arsines (S,RpJ-173 or (S,Rpe) 1 4 with... 

Zheng and coworkers introduced a series of chiral ferrocenyl amines into the... 

Ferrocenyl amine (30), which has two different donor sites, gives crystals when mixed with 10 and the related a, w-diiodoperfluoroalkanes (31) [12]. Melting points of these crystals are moderate (43-80°C). Two iodine atoms of 31 interact with both cyclopentadiene and amino nitrogen, separately (Scheme 1.10). 

The decomposition of ferrocenyl amines in oxalic acid solution gives iron oxalate 356>. 

Trisubstituted ferrocenes are also accessible via the palladated ferrocenyl-amines [6]. Individual compounds of these types will be described in the following sections. 

Asymmetric aldolization of a-isocyanoacetamide and fluorinated benzaldehydes has been realized with a gold(I) salt and a ferrocenyl amine-phosphine ligand. (Salen)-Ti complexes serve well in catalyzing the condensation of diketene with aldehydes. " A camphor lactam is an adequate chiral auxiliary as its derived imide undergoes asymmetric aldol reactions. 

Finally, the ferrocenyl complexes were decomposed photochemically and thermally. Thermolyses can be performed in this case because the decomposition temperature of the azide (96) (80 °C) is much lower than those employed for other diazirines and azides. The results obtained from photolyses and thermolyses do not differ significantly. Here again, a-CD causes the most drastic changes because of the complete encapsulation of the guest in a 1 2 complex (Scheme 10.27). In accord with the other reactions performed in a-CD, the main reaction pathway is hydrogen abstraction from the host. Upon thermolysis ferrocenyl amine (112) is obtained in a yield up to 60%. More remailcably, ferrocenyl nitrene (111) seems to react in very low yields with a-CD. However, the structure of the reaction product 113 has not been fully established yet and is quite unexpected because 113 is the result of a glucopyranose-furanose conversion. In contrast, the products obtained by thermolysis of ferrocenyl nitrene in the soUd state, namely... 

The resolution of a racemic mixture by diemical or biodimical methods is the main route to ferrocenes with planar chirality. In pionemng work in 1970, Ugi et al resolved the ferrocenyl amine 9 (Figure 8) and found that the amino group directs the ortho-deprotonation with a good diastereoselectivity. By this method many compounds were later prepared, including chiral ligands. 

In an exciting development. Beer and co-workers prepared a range of novel compounds incorporating copper(ll) bis(dithiocarbamate) units (Fig. 220). These include macrocyclic complexes based on terphenyl diamines (439-442) (326, 1468, 1469) and ferrocenyl amines (443) (1468), pyrrole-based metallo-cryptands (444) (492), cyclic amide complexes (445), and monometallic complexes with crown-ether substituents (446) (492), a number of which have been... 

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