Stereodivergent Syntheses of (Z)- and (E)-Alkenylsilanes via Hydrosilylation of Terminal Alkynes Catalyzed by Rhodium(I) Iodide Complexes and Application to Silicon-Containing Polymer Syntheses

RhI(PPh₃)₃ or [RhI(cod)]₂ (cod = 1,5-cyclooctadiene) as a catalyst delivers both (Z)- and (E)-alkenylsilanes in the stereodivergent hydrosilylation of terminal alkynes with heteroatom-substituted organosilane reagents. Treatment of the rhodium catalyst and the silane reagent followed by addition of terminal alkyne at room temperature leads to (Z)-silanes, while addition of the silane and the alkyne to the rhodium catalyst in one portion and heating at 60°C affords (E)-silanes highly selectively. The obtained (E)- and (Z)-alkenylsilanes bearing heteroatom substituents on the silicon atom are subjected to the palladium-catalyzed cross-coupling reaction with aryl halides to form a carbon-carbon bond with retention of stereochemistry. The stereodivergent hydrosilylations are applied to the polyaddition with bifunctional alkynes (1,3- and 1,4-diethynylbenzene) and silanes (1,3- or 1,4-bis(dimethylsilyl)benzene), giving silicon-containing polymers, poly(aryleneethenylenesilylene)s, in highly stereocontrolled manners. A fluorine-containing silicon reagent bearing a 3,3,3-trifluoropropyl group is also subjected to the polymerization, in which [Rhl(cod)]₂ is found to be an efficient catalyst. Measurement of UV-vis absorption/emission spectra and several thermal analyses of the polymers are also conducted.