Cyclopentadienyl/dithiolene

Magnetic Properties of Radical, Crystalline Mixed Cyclopentadienyl/Dithiolene Complexes... 

Cyclopentadienyl dithiolene complexes such as CpCo(S2C2R2) and Cp2Ti-(S2C2R2) have been shown to catalyze the isomerization of quadricyclane to norbomadiene (Eq. 9) (133). The catalytic activity is closely related to the reduction potential of the complexes Complexes with higher E /2 are more active. This result suggests that the reaction involves a certain degree of charge transfer between quadricyclane and the dithiolene complex. 

The photocatalyst used for these conversions can be generated in situ, by photolysis of a zinc dithiolene salt by preformed catalysts , or by particles supported within surfactant vesicles The idea of employing semiconductor surfaces as environments for the enhanced coupling of radicals had previous support in the photochemical coupling of cyclopentadienyl radicals formed by excitation of the corresponding anions at single crystal electrodes... 

Two classes of material will be described here - the metal dithiolenes and rare earth metallocenes. In the metal dithiolenes a strong, low energy pi-pi transistion occurs in the near IR (9.10). This can be tuned from about 700 nm to 1400 nm by altering the metal ion, substituents or charge state of the dithiolene. The dithiolenes are particularly attractive because of their optical stability which has been exploited in their use as laser Q-switch materials. In the rare earth complexes the near IR band is provided by/-/transistions of the rare earth ion rather than the cyclopentadienyl ring structure various nonlinear optical phenomena have been observed in glasses incorporating similar ions. Previous studies have shown that dicyclopentadienyl complexes such as ferrocene have off-resonant nonlinearities similar to nitrobenzene or carbon disulphide (11-13)... 

For both classes of materials initial trial compounds were selected for their potential at 1064 nm, these included Yb -cyclopentadienyl and dithiolenes with absorption bands from 700-950 nm. However the results observed here may be extended to useful wavelengths by appropriate selection of derivatives. 

A large number of cyclopentadienyl (Cp) complexes, both neutral and charged, has been prepared. Most of the complexes reported are for early to mid-transition metals. Rich redox and chemical reactivity has been reported (126). Extensive work on the Cp dithiolene complexes has been carried out by Sugimori et al. (127) and has recently been reviewed. A few representative examples are discussed below. 

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