Ferrocenes, helical

Cyclopentadiene, b.p. 40°, is obtained by heating commercial 85% dicyclopentadiene (e.g., from Matheson, Coleman and Bell Company, Norwood, Ohio) under a short column (M in. diameter X 8-12 in. length) filled with glass helices. The distilled cyclopentadiene is collected in a receiver which is maintained at Dry Ice temperature until the cyclopentadiene is used. Methylcyclopentadiene and other substituted cyclopentadienes such as indene may also be employed for the synthesis of the correspondingly substituted ferrocenes. In these cases, the reaction of the hydrocarbon with sodium is much slower than with cyclopentadiene, and refluxing for several hours is required to complete the reaction. 

The first helicene synthesized, which was bridged by a ferrocene unit, is based on the pentahelicene skeleton At its terminal phenylene rings, cyclopentadienyl units were condensed. The di-lithium salt of this compound with iron(III)chloride yielded the helical ferrocene 142 with an uninterrupted conjugation between the two cyclopentadienyl rings (Fig. 55). The cyclopentadienyl moieties are clamped by the iron atom in an angle deviating 19.4° from parallelity. 

Takahashi and co-workers have performed the living polymerization of ferrocene derivatives to obtain helical, chiral polyisocyanides 183.244 Using 100 equivalents of the monomer and a 20-hour reaction time, polymers with number-average molecular weights ranging between 9800 and 22,000 and PDI = 1.15 were obtained in 90% yield. 

Niwa M, Matsui M, Koide K, Higashi N. Enantioselective adsorption of ferrocene-modified glutamic acids on helical poly(L-glutamic acid) self-assemblies at gold electrodes. J Mater Chem 1997 7 2191-2192. 

Introduction of the tricarbonylchromium group into cyclophane chemistry has great potential for the preparation of planar- (or helical-)chiral compounds. Besides structure/chiroptics relationships, carrying out stereoselective reactions is of major importance. Recently, inclusion of ferrocenes and benzene-Cr(CO)3 into the cavity of a cyclodextrine was achieved and this makes the connection to supramolecular chemistry [183]. 

Electron transfer (ET) reactions along a sequential redox potential field occur effectively over a long distance in biological systems [123]. These redox centers are surrounded by highly ordered polypeptides, which are considered to control the three-dimensional environment of redox centers and the direction of the ET [124]. Self-assembled monolayers (SAMs) of helical ferrocene-contained peptides have been focused on to investigate the ET reaction. 

We have prepared and characterized a range of complexes of the new redox active Fctpy ligand, including [Fe(Fctpy)2][PF6]2 (blue), [Cu(Fctpy)2][PF6]2 (red) and [Ru(Fctpy)2][PF6]2- Each of these complexes shows two oxidation processes one is associated with the ferrocene substituent (+0.20, +0.30 and +0.22V respectively) and the other with the other metal centre (Fe, +0.8 IV, Co, -0.18V and Ru, +0.90V). These data have allowed us to define a Hammet redox active terminators into oligomers and into multiple helical systems. 

Scheme 19 Synthesis of optically active helical ferrocene (M)-(—)-92 [84]...

Optically active dibenzo[c,g]phenanthrene (Af)-(—)-91 bearing two fused cyclopentadienyl rings was synthesized by the photodehydrocyclization method with chirality being controlled during the cyclization process [84]. The optically active helical ferrocene (Af)-(—)-92 was obtained by treatment of (M)-(—)-91 with tcrt-butyllithium followed by FeCl2-2THF (Scheme 19). 

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