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 Ag₂ SO₄ in toluene at 90 °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. α-, β-, and γ-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.