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

Abstract

RhI(PPh 3 ) 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 [RhI(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.