Silole derivatives

Disubstituted silole derivatives are synthesized by the palladium-catalyzed reaction of (trialkylstannyl)di-methylsilane with terminal alkynes (Equation (107)).266 The mechanism is supposed to involve a palladium silylene complex, which is generated via /3-hydride elimination from LJ3d(SiMe2H)(SnBu3) (Scheme 62). Successive incorporation of two alkyne molecules into the complex followed by reductive elimination gives rise to the silole products. 

H. Murata, Z.H. Kafafi, and M. Uchida, Efficient organic light-emitting diodes with undoped active layers based on silole derivatives, Appl. Phys. Lett., 80 189-191 (2002). 

Treatment of 3,4-diethynylsilole 29 with 2 equivalents of lithium diisopropylamide, followed by the reaction of the resulting dilithio compound with 1,2-dichlorotetramethyl-, 1,2-dichlorotetraethyl- or 1,2-dibutyl- 1,2-dichlorodimethyldisilane produces the cyclic silole derivatives 11843 (Scheme 29). 

Peroxides, alkylaluminum reactions, 3, 267 Peroxyseleninic acids, as catalysts, 9, 491 Perphenylated 1,1-dichloro silol, in silol derivative preparation, 3, 435... 

FIGURE 10. ORTEP drawing of silole derivative 35. Reprinted with permission from Reference 22. Copyright 2000 American Chemical Society... 

Considering the peculiar contribution of the central silicon atom to the --electronic structure of silole derivatives through a -n conjugation, other Group 14 metalloles are also of interest. To elucidate the effects of the central Group 14 elements, we have prepared a series of 2,5-dithienyl-substituted Group 14 metalloles, cyclopentadiene 30, siloles 26m and 27, germole 31 and stannole 32, and compared their photophysical... 

Intramolecular hydrosilylation of the alkynes 122 and 124 catalyzed with AICI3 proceeds at low temperature and gives after 1 h the silole derivatives 123 and 125 in moderate yields <2000JOC8919>. 

Condensed silole derivatives such as 217 (l,6-dihydro-l,6-disilapentalenes) can be prepared by 1,1-ethylboration of disilatriynes with terminal groups R = SiMe3, SnMe3 <1998JOM(562)207, 1999JOM(577)82>. 

Recent application of the nickel-catalyzed reaction with diyne 91 provides new effective access to functionalized silole derivatives 92, which are further utilized for the synthesis of silole-thiophene co-polymers (Eq.47) [84]. 

As compared with hole-transporting materials, fewer electron-transporting materials have been reported. A well-known green emitter, Alq3, has been used as a good electron transporter. Other reported electron-transporting materials include oxadiazole derivatives, a dendrimer-type oxadiazole, a triazole derivative, tris(phe-nylquinoxaline), silole derivatives, benzimidazole derivative, and boron-containing compounds (Table 7.3). 

However, it has been found that some organic compounds that are non-emissive or only weakly emissive in solution become highly emissive upon formation of aggregates, or in the solid state. In 2001, Tang and coworkers reported that a non-fluorescent silole derivative 1 in solution showed intense emission upon formation of aggregates (Scheme 1). 

We have shown herein several new synthetic methods for the silole-based 7t-conjugated compounds and their possible applications to organic LEDs. The potential of the silole derivatives as new electron-transporting and emissive materials is very high. For their practical application, however, the synthesis of tailor-made silole compounds based on a more precise molecular design would be essential. We are now in a position to access them. 

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