Transition Metal Catalysis in Fluorous Media: Practical Application of a New Immobilization Principle to Rhodium-Catalyzed Hydroboration

摘要

Catalysis pervades the incessant quest for new or improved chemical transformations. Two of the most active frontiers entail 1) nontraditional reaction media, and 2) new catalyst-immobilization or recovery strategies to facilitate reuse. A conceptually new protocol, fluorous biphase catalysis, was developed in our laboratories. As detailed elsewhere, this involves modifying catalysts with fluoroalkyl groups or "pony tails" such as (CH_2)_y(CF, )_xCF_3 (x >= 5). These confer high affinities for fluorous media, and the (CH_2)_y spacers insulate the active sites from the electron-withdrawing fluorines. Many organic solvents give bilayers with fluorous solvents, with some systems becoming miscible above room temperature. As a result, reactions may be conducted under either biphasic ormonophasic conditions. Upon workup. appropriately deriva-tized catalysts remain immobilized in the fluorous layer.