By-Product-Free Siloxane-Bond Formation and Programmed One-Pot Oligosiloxane Synthesis

Siloxane bonds are usually synthesized by condensation reactions, such as hydrolysis/dehydration and cross-coupling reactions, in which the generation of by-products during bond formation can not be avoided. We have developed a one-pot sequence of iridium-catalyzed silyl ester hydrosilylation and boron-catalyzed rearrangement of the resulting disilyl acetals for the construction of siloxane bonds, in principle without the formation of any by-products. Moreover, the programmed synthesis of tri-, tetra-, and pentasiloxanes was possible in a single flask by combining the above sequence of iridium-catalyzed hydrosilylation and boron-catalyzed rearrangement with a boron-catalyzed cross-coupling reaction. The obtained oligosiloxanes are difficult to synthesize selectively by other known synthetic procedures.