Ferrocenes/ferrocenyls

Chiral ferrocenes have received niucli attenlion as ligands in metal-calalyzed reactions [39], bul tiieir use in copper cliemislry has been very limited [40, 41]. Hie ferrocene moiety offers die possibility of utilizing botli central and planar cliirality in die ligand. By analogy witli tlie copper arenetiiiolales described above, ferrocenyl copper complex 33 iSclieme 8.20) is extremely inleresling. 

Potassium cyanide, reaction with N,N-dimethylaminomethyl ferrocene methiodide to yield ferrocenyl-acetonitrile, 40, 45... 

The lithium benzamidinates Li[PhC(NR)2] (R = Cy, Pr ) and Li[2,4,6-(Cp3)3C6H2C(NCy)2] have been prepared analogously. Reaction of FcLi (Fc = ferrocenyl) with 1,3-dicyclohexylcarbodiimide ( = DCC, Scheme 6), followed by addition of water, afforded the ferrocene-substituted amidine Fc(NCy)NHCy in 50% yield. The amidine is readily deprotonated by LLN(SiMe3)2 or NaN(SiMe3)2 to yield the alkali metal amidinates, Li[FcC(NCy)2l and Na[FcC(NCy)2l in high yields. ... 

Recently a novel chiral ferrocene-based amidinato ligand and its rhodium complexes have been described. The chiral N,N -bis(ferrocenyl)-substituted formamidine (N,N -bis[(S)-2- (lR)-l-(diphenylphosphino)ethyl ferrocen-l-yl]for-mamidine was prepared from commercially available (IR)-l-(dimethylamino) ethyl ferrocene by a multistep procedure in an overall yield of 29%. Deprotonation of the ligand with -butyllithium followed by addition of [RhCl2(COD)2] as illustrated in Scheme 167 yielded the corresponding (formamidinato)rhodium(l)... 

F. la-c. Cyclic voltammograms of dissolved and stance confined ferrcx ne in a< tonitrile/0.1 M TBAP. a. 4 X 10 M dissolved ferrocene at Pt. b. 4-ferrocenyl-phenylacetamid monolayer bound to Pt (ref. ). c. Poly-vinylferrocene dip coated on Pt,r = 1 x lO raolcm. Straight arrows indicate diffusional events. Curved arrows electron transfer events (from ref. ). 

The synthesis of the unsymmetrical imidazolium salt 11 bearing a planar-chiral ferrocene was described by Bolm starting from (Rp)-[2-(trimethysilyl)-ferrocenyl] methanol 12 which afforded the salt in good yield after reaction with Ar,M-carbonyl diimidazole and methylation (Scheme 9) [18]. 

Due to the pronounced electron donating character of ferrocene, ot-ferrocenyl carbocations 3 possess a remarkable stability and can therefore be isolated as salts [16]. They can also be described by a fulvene-type resonance structure 3 (Fig. 4) in which the Fe center and the ot-center are significantly shifted toward each other as revealed by crystal stmcture analysis, indicating a bonding interaction [17]. 

Palladacycles are defined as compounds with a Pd-C CT-bond with the Pd being stabilized by one or two neutral donor atoms, typically forming 5- or 6-membered rings [51]. Ferrocenyl palladacycles constitute a particularly attractive catalyst class partly due to the element of planar chirality. The first diastereoselective cyclopallada-tion of a chiral ferrocene derivative was reported in 1979 by Sokolov [52, 53]. 

Third, metallocene units, such as ferrocene or ruthenocene, have been linked to phosphazene cyclic trimers or tetramers and these were polymerized and substituted to give polymers of the type mentioned previously (41). Polyphosphazenes with ferrocenyl groups can be doped with iodine to form weak semiconductors. Polymer chains that bear both ruthenocenyl and ferrocenyl side groups are prospective electrode mediator systems. 

In 3, the amino functional group is two methylene units removed from the ferrocene nucleus. It appears from the instantaneous and quantitative formation of h from 3 that this feature minimizes steric effects and also enables 3 to undergo the Schotten-Baumann reaction readily without the classical a-metallocenylcarbenium ion effects providing any constraints. The IR spectrum of showed the characteristic N-H stretch at 3320 cm" (s), the amide 1 (carbonyl) stretch at 1625 an - -(s), the amide II (N—H) stretch at 1540 cm (s), and the amide III band at 1310 cm 1(m). In addition, characteristic absorptions of the ferrocenyl group were evident at 1100 and 1000 cm l (indicating an unsubstituted cyclopentadienyl ring) and at 800 cm"l. 

Macrocycles attached to redox responsive groups such as ferrocene (78) can give selective transition metal ion receptors. The X-ray structure reveals a five-coordinate zinc with distorted square-pyramidal geometry bound to the four macrocycle nitrogens and an iodide. In the solid state the two ferrocenyl groups are positioned on the same side of the ligand with distances to the metal center of 5.347(7) and 6.120(8) A and these distances can be related to the redox behavior.689... 

As will be discussed later, it is possible a4> that the thermolysis involves a metal-nitrene complex whereas the photolysis involves the free nitrene. The product distribution is not affected by the presence of a photosensitizer, but since ferrocene itself is both an efficient triplet quencher as well as a sensitizer 26,27) jt is very difficult to probe the spin state of ferrocenyl nitrene at the moment of reaction. The cycli-zation appears to be a singlet reaction since the yield of 27 in benzene solution is essentially unaffected by oxygen or the presence of hydro-quinone a5>. 

---