Catalytic Si-Si/Si-O dehydrocoupling of 1,1-dihydrotetraphenylsilole to optoelectronic polysiloles with colloidal silver nanoparticles

The combinative Si-Si/Si-O dehydrocoupling at ambient air atmosphere of 1,1-dihydrotetraphenylsilole 1 with 2 mol% of AgNO3 and Ag2SO4 in toluene at 90 degrees C produces optoelectronic polysiloles 2 in high yield. The complexes such as Cp2Co, Cp2Ni, Cp2ZrCl2/Red-Al, and AgCl were found to be ineffective for the dehydrocoupling of 1. The polysiloles mainly have Si-Si bonds along with the small portion of Si-O bonds in the polymer backbone chain. Interestingly, the Si-O linkage increased with increasing the concentration of catalyst AgNO3, implying that while Ag(0) species catalyze the Si-Si dehydrocoupling, Ag(I) species catalyze the Si-O dehydrocoupling along with the simultaneous oxidation of NO3 ion to NO2. The silver complexes transformed to colloidal silver nanoparticles during the catalytic reaction. The Si-Si/Si-O dehydrocoupling of 1 with AgNO3 even at dry nitrogen atmosphere is occurred, supporting that the oxidation of NO3- ion to NO2 is only the possible oxygen source, but not from the adventitious moisture in air. sigma-, beta-, and gamma-Cyclodextrins considerably deteriorated the dehydrocoupling of 1 probably due to both the formation of insoluble inclusion complexes in toluene and the encapsulation of SiH2 moiety. The resulting silole polymer 2 emits green light at 520 nm and is electroluminescent at 520 nm.