Mechanistic Investigations on Hydrogenation, Isomerization and Hydrosilylation Reactions Mediated by a Germyl-Rhodium System

We recently disclosed a dehydrogenative double C-H bond activation reaction in the unusual pincer-type rhodium-germyl complex [(Ar-Mes)(2)ClGeRh] (Ar-Mes=C6H3-2,6-(C6H2-2,4,6-Me-3)(2)). Herein we investigate the catalytic applications of this Rh/Ge system in several transformations, namely trans-semihydrogenation of internal alkynes, trans-isomerization of olefins and hydrosilylation of alkynes. We have compared the activity and selectivity of this catalyst against other common rhodium precursors, as well as related sterically hindered rhodium complexes, being the one with the germyl fragment superior in terms of selectivity towards E-isomers. To increase this selectivity, a tandem catalytic protocol that incorporates the use of a heterogeneous catalyst for the trans-semihydrogenation of internal alkynes has been devised. Kinetic mechanistic investigations provide important information regarding the individual catalytic cycles that comprise the overall trans-semihydrogenation of internal alkynes.

Automated summary

We investigated the catalytic applications of a pincer-type rhodium-germyl complex in several transformations, including semi-hydrogenation of internal alkynes, isomerization of olefins, and hydrosilylation of alkynes. The catalyst with the germyl fragment showed superior selectivity towards E-isomers compared to other rhodium precursors. To enhance this selectivity, a tandem catalytic protocol that incorporated the use of a heterogeneous catalyst for semi-hydrogenation of internal alkynes was developed.