Ferrocenes bridged

B. Redox, Optical, and Photoisomerization Properties of Azo-Bridged Ferrocene Oligomers... 

The electrochemistry of some single-atom bridged ferrocene dimers gives a separation of two le waves. The carbon atoms in CROH and C = 0 can communicate between ferrocene units in 32 and 33 (101). Diferrocenyl sulfide, 34, shows significant AE° values, 0.29-0.33 V, indicating the presence of strong internuclear interactions (102,103). 

Azo-bridged ferrocene oligomers also show a marked dependence on the redox potentials and IT-band characteristics of the solvent, as is usual for class II mixed valence complexes 21,22). As for the conjugated ferrocene dimers, 2 and 241 the effects of solvents on the electron-exchange rates were analyzed on the basis of the Marcus-Hush theory, in which the t/max of the IT band depends on (l/Dop — 1 /Ds), where Dop and Ds are the solvent s optical and static dielectric constants, respectively (155-157). However, a detailed analysis of the solvent effect on z/max of the IT band of the azo-bridged ferrocene oligomers, 252,64+, and 642+, indicates that the i/max shift is dependent not only on the parameters in the Marcus-Hush theory but also on the nature of the solvent as donor or acceptor (92). 

Strong MLCT bands appear in the neutral form of azo-bridged ferrocene oligomers, as noted above. The absorption of the MLCT band at 534 nm diminishes, and a new band appears and increases at 672 nm with the oxidation to 25+. The new band can be assigned to a ligand-to-... 

The intramolecular insertion of a sulphonyl nitrene into a side-chain methyl group to give 36 and 37 has already been mentioned, as has the intramolecular cyclization of ferrocenylsulphonyl azide to give the bridged ferrocene derivative (17). 

Substantial differences in the electrochemical behaviour have been observed for trifer-rocenes bridged by methylene (compound 80) and by dimethylsilyl (compound 81) units (Scheme 21). Cyclic voltammetry experiments reveal that 80 exhibits three reversible redox processes175, whereas for 81 only two redox events are observed176. The three reversible waves in the carbon-bridged ferrocene (80) are in the ratio 1 1 1 and can be assigned to successive redox events at each iron center, as described in Scheme 21. The two reversible waves in the silicon-bridged ferrocene (81) are in the ratio 2 1 and are consistent with oxidation of alternate ferrocene units, with subsequent oxidation of the intervening iron site (see Scheme 21). 

Photolysis of ferrocenylsulfonyl azide in hydrocarbon solvents using 3500 A radiation yields the novel bridged ferrocene derivative (43).42 Methylation of 43 with dimethyl sulfate and sodium hydroxide gave the A7-inethyl derivative. The trithia system (44) has been reported48 from the reaction of l,l -dilithioferrocene with sulfur. 

Strained silyl-bridged ferrocenes add to Pt°. This is the key reaction in the Pt catalyzed ring-opening polymerization of these ansa-ferrocenes 87... 

Bridged ferrocenes, or ferrocenophanes, have been known for many years. These compounds, in which the two Cp rings are linked by carbon and/or heteroatom chains, are... 

Bridged Ferrocene Derivatives Conformational Energy Surfaces of [3]-, [4], and (4,- -Ferrocenophanes. 

A chiral C2-symmetric bridged ferrocene was constructed from a synthetic ligand containing two cyclopentadiene units (Fig. 4-12d). The key step in the synthesis of the ligand is a diastereoselective Diels — Alder reaction of anthracene with bis[(S)-l-ethoxycarbonylethyl]fumarate. When oxidized to the ferrocinium salt, the ferrocene derivative has Lewis acid properties and catalyzes Diels — Alder reactions with some enantioselectivity [85]. 

The bifunctional ferrocene derivative fc(SH)2 has been tested as a component in the synthesis of macromolecules [84, 93, 94]. However, the reaction (1 1) of fc(SH)2 with norbornadiene (in the presence of AIBN) leads to oligomers containing only disulfide-bridged ferrocene units in the main chain [93,95] the diolefin appears solely in the form of norbornenyl or nortricyclyl terminations (Scheme 5-18). The preferred formation of disulfide linkages can be explained by the stability of the ferrocenyl thiyl radicals (Fc-S ), which live long enough to terminate the chain growth by radical combination [94]. 

The binuclear prototypes of the chalcogen-bridges ferrocenes, Fc-E-Fcand Fc-EE-Fc (E = S, Se, Te), are well-established compounds (Scheme 5-49) [95, 102]. 

Scheme 5-51. Disulfide-bridged ferrocene derivatives by ring-opening in l,2,3-trithia-[3]ferroceno-phane, fc(S3) [95].

Further possible applications of the rigidity of sulfonylnitrenes to the synthesis of strange compounds are illustrated by the preparation of the bridged ferrocene 408 (Eq. 140).471 This compound, which may be regarded as a heterocyclic molecule, is formed by photolysis in benzene, whereas thermolysis in the same solvent gives intermolecular insertion products... 

A C2-symmetric bridged ferrocene catalyzes the methacrolein-cyclopentadiene Diels-Alder reaction in 10% ee Gibis K-L, Helmchen G, Huttner, G, Zsolnai L (1993) J Organomet Chem 445 181... 

Linear, saturated, polymers obtained by radical initiation of 1,1 -divinylferrocene hive the Mossbauer parameters (6, 0.23 mm s l LEq, 2.29 mm s l) expected for cyclopolymer8 with three-carbon bridged ferrocene units in the main chain. However, cationic initiation yields polymers which exhibit differences from the radical polymers in Mossbauer (, 0.27 mm s 7 Eq, 2.40 ntn s 7) and other spectroscopic studies. The cationic polymers may contain a bicyclic unit or a ladder structure in the chain. 

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