Highly Efficient Olefin Isomerization Catalyzed by Metal Hydrides Derived from Dirhodium(II) Carboxylates and Catecholborane

Dirhodium(ll) tetraacetate in combination with catecholborane catalyzes the isomerization of alkenes and dienes. Effective isomerization occurs at 80-135°C with the use of only 0.1 mol % rhodium acetate. With 2-methyl-1,5-hexadiene the disubstituted double bond is preferentially isomerized. In addition, hydrogen transfer hydrogenation occurs with 1,4-cyclohexadienes. The mechanism of these reactions is proposed to involve organoborane addition across a Rh-0 bond which activates the catalyst for isomerization and hydrogenation.