[Rh-Pd] Ionic Gel-Soaked Bimetallic Catalyst

Key words

bimetallic catalysts - hydrosilylation - Hiyama cross-coupling

Significance

The [Rh-Pd] ionic gel-soaked bimetallic catalyst for the one-pot hydrosilylation/Hiyama cross-coupling reactions was described. Thus, the reaction of Merrifield resin 1 with Et₃N, followed by the anion exchange of 2 with NaI afforded the polyionic iodide gel 3. The polyionic iodide gel 3 was treated with RhCl(PPh₃)₃ and Pd(OAc)₂ to provide the [Rh-Pd] bimetallic catalyst 4. The one-pot synthesis of E-disubstituted alkene via hydrosilylation/Hiyama cross-coupling reaction was carried out in dioxane in the presence of 4 and subsequent addition of TBAF to give the corresponding E-alkenes in 50-95% yield.

Comment

It is noteworthy that the Sonogashira coupling side products were not obtained, even without sequential addition of coupling partners in the present procedure. The high chemoselectivity is attributed to a slower Sonogashira coupling in polyionic gel in the absence of copper co-catalysts. For the reaction of phenyl acetylene with phenyl iodide, the catalyst can be recycled three times without loss of the catalytic activity and stereoselectivity (>99% yield and E/Z > 99:1 for 1st-3rd cycles); however, the product yield decreased in the 4th cycle (78% yield and E/Z > 99:1).