React by Insertions of Olefins into Monohydride Intermediates

Catalysts that React by Insertions of Olefins into Monohydride Intermediates 

One of the classic catalysts that reacts through a pathway involving the insertion of olefins into monohydride intermediates is [Rh(H)(PPh3)3(CO)]. The reactions of terminal olefins occur imder mild conditions (Equation 15.24). The pronounced substrate selectivity of this catalyst is illustrated by its lack of reactivity with cyclohexene. This complex catalyzes the isomerization of internal olefins, but it does not catalyze their hydrogenation. Other unsaturated fimctionalities, such as aldehydes, nitriles, and esters, are stable to this catalyst under these mild conditions. 

Ruthenium catalysts are now widely used for olefin hydrogenation, and many examples of enantioselective ruthenium-catalyzed hydrogenation are discussed in Section 15.7. Here, before addressing the issues of stereoselectivity, the elementary steps of ruthenium-catalyzed hydrogenation are discussed. These catalysts react through monohydride species containing a second anionic ligand. 

Mechanism of Hydrogenation of Olefins and Ketones by RuyK -OAc) and [RuLjCljlj 

Ruthenium catalysts became widely used for hydrogenation when Noyori showed that complexes of the formula RuLjfK -OAc), in which = BINAP, catalyze the asymmetric hydrogenation of a variety of functionalized alkenes, and many related complexes have now been studied as catalysts for asymmetric hydrogenation. Halpem conducted detailed 

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