Ferrocene optically active

The asymmetric cyclopalladation of dimethylaminomethylferrocene takes place in the presence of an optically active carboxylic acid (e.g, A -acetylvaline), giving the cyclopalladation product 478 in 78% ee, from which optically active ferrocene derivatives were prepared[434]. 

The enzyme p-ethylphenol methylene hydroxylase (EPMH), which is very similar to PCMH, can also be obtained from a special Pseudomonas putida strain. This enzyme catalyzes the oxidation of p-alkylphenols with alkyl chains from C2 to C8 to the optically active p-hydroxybenzylic alcohols. We used this enzyme in the same way as PCMH for continuous electroenzymatie oxidation of p-ethylphenol in the electrochemical enzyme membrane reactor with PEG-ferrocene 3 (MW 20 000) as high molecular weight water soluble mediator. During a five day experiment using a 16 mM concentration of p-ethylphenol, we obtained a turnover of the starting material of more than 90% to yield the (f )-l-(4 -hydroxyphenyl)ethanol with 93% optical purity and 99% enantiomeric excess (glc at a j -CD-phase) (Figure 14). The (S)-enantiomer was obtained by electroenzymatie oxidation using PCMH as production enzyme. 

The principal question addressed, is there any kind of chiral recognition in electron transfer reactions involving GO or HRP and enantiomerically pure metal complexes. The chirality of optically active metal complexes may be different. Examples include central carbon chirality, when a complex has a side chain with an asymmetric sp3 carbon (Chart 2A), planar chirality as in the case of asymmetrically 1,2-substituted ferrocenes (Chart 2B,C), and central metal chirality when an octahedral central metal itself generates and enantiomers (Chart 2D) (202). These three types are discussed in this section. 

Metallocenes have frequently been used as terminal moieties in dendrimer chemistry - as already demonstrated in previous sections. They are of interest primarily because of their potential application in catalysis [123]. An unusual metallodendrimer with peripheral ferrocene entities and optically active ferro-cenyldiphosphine ligands (josiphos ligands) was prepared by Togni et al. (Fig. 4.58) [124]. Adamantanetetracarboxlic acid was one of the core units employed. 

Fig. 4.58 Metallodendrimer with optically active ferrocene entities at its periphery (according to Togni et al.)...

Chiral moieties have been tethered onto MCM-41 surface in order to obtain optically active supported catalysts possessing the intrinsic texture brought by this particular support.2 >23 24 26 41-43 Thomas et al26,41 have developed a very interesting methodology to anchor a chiral ligand l,r-bis(diphenylphosphino)ferrocene to the inner walls of MCM-41 silica (Figure 1). 

Asymmetric selenoxide elimination via a diastereomeric chiral selenoxide as a key intermediate was also achieved by Uemura and co-workers [23]. They prepared new optically active diferrocenyl diselenides from the corresponding chiral ferrocenes and used the optically active ferrocenyl group as a chiral aryl moiety since an arylselenium moiety can easily be introduced into organic molecules. 

As chiral ligands for transition metal complex-catalyzed asymmetric reactions, a variety of novel chiral ferrocenylchalcogen compounds, which possess a planar chirality due to the 1,2-unsymmetrically disubstituted ferrocene structure, have been prepared from chiral ferrocenes (Scheme 1). Thus, chiral diferrocenyl dichalcogenides bearing an optically active dimethylaminoethyl or p-tolyl-sulfoxide moiety 1-10 were prepared by lithiation of the corresponding chiral ferrocenes, highly diastereoselectively, in moderate to high chemical yields. 

Results from these laboratories (79) likewise support the idea that the ring-metal bond of a ferrocene system is quite labile. Treatment of the optically active ketone (V) with refluxing nitromethane and AlClj brought recovery of the identical ketone... 

In the simplest case of a donor-acceptor (D-A) molecule, the nonlinear optical activity arises from the electric-field-induced mixing of electronic states such as D-A and D+-A . This makes the response (polarizability) of the molecule different according to the sense of the electric field, and a second-order hyperpolarizability fi coefficient) is observed. If D and A are connected by some bridge, its role in promoting the electronic interaction will be quite similar to the bridge role in mixed-valence complexes. Metal complexes can play the role of donor or acceptor groups. Recent examples have been described with ferrocene or ruthenium(pentaammine) groups [48], but they are either monometallic or too short to be considered in this review. 

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... 

Some other stereoselective rearrangements of anils were carried out using optically active ferrocene catalysts196 and silica gel197. 

These recent developments have reawakened interest in the fundamental chemistry of optically active ferrocenes [66]. 

Recent progress in material science, notably with the development of new materials exhibiting blue phases, has generated a renewed interest in the incorporation of the functional properties with the unique structure of frustrated phases. Synthesis of a monosubstituted ferrocene-based chiral Schiff s base derivative which exhibits TGBA and blue phases has been reported [17] (Fig. 9). Other metallomesogens leading to blue phases have been found for palladium complexes [18] (Fig. 10). Optically active materials incorporating... 

Siegel and Schmalz [79] reported a new approach to optically active ferrocenes with planar chiraHty, based on a Cu-catalyzed C-H insertion (Scheme 17). Both a five- and a six-membered ring could be formed in this way. Using a copper-bisoxazoline catalyst, good yields and ees in the range of 60-80% could be obtained, whereas chiral dirhodium catalysts proved to be ineffective in this case. 

The intermolecular asymmetric Heck reaction, a palladium-catalysed carbon-carbon bond forming process, is an efficient method for the preparation of optically active cyclic compounds.[1] Very recently, a new catalytic system has been developed based on palladium complexes having l-[4-(5)-tert-butyl-2-oxazolin-2-yl]-2-(5)-(diphenylphosphino)ferrocene (1) as the chiral ligand121 (Figure 5.2), which we have shown to be efficient catalysts for the enantioselective intermolecular Heck reaction of 2,3-dihydrofuran (2).[3] In contrast to complexes derived... 

Enantiopure diaryl methanols (1) are important intermediates for the synthesis of biologically active compounds.[1] Here, a synthetic approach which employs aromatic aldehydes and readily accessible and commercially available aryl boronic acids is reported.[2,3] The catalysis with planar chiral ferrocene (2)[4] yields a broad range of optically active diaryl methanols with excellent enantioselectivities. Upon addition of DiMPEG (dimethoxy polyethyleneglycol) to the reaction mixture the enantioselectivity is increased. 

Once it was demonstrated that it adds stereoselectively, the n-butyllithium/ ( —) -sparteine complex was used to prepare a series of optically active ferrocenes (36). Treatment of isopropyl ferrocene with a 2.5-molar excess of the lithiating complex followed by reaction with an electrophile... 

Certain substituted ferrocenes are also optically active and have been examined regarding this feature [33, 153, 155]. A central challenge for 10-15 years was the complete bridging of ferrocene (70), which culminated in the preparation of e.g. [4]superferrocenophane , which now offers the possibility of including an iron atom in the cage of a saturated hydrocarbon [157, 158]. Unfortunately studies of the hydrogenation of fcp revealed that reduction becomes more difficult when the number of bridges increases [159], This implies a participation of the iron atom in the reduction step to be probable [159],... 

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