Hydrogenation of unfunctionalized olefins

Ligand S/C ratio Reaction conditions Percent ee of product (confign.) References 

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Substrate 2 has also been used as a test substrate HPLC separation methods exist for 2, while ee-value determination of 1 is more difficult [6, 17]. Reflecting the general recent interest in the hydrogenation of unfunctionalized olefins, the past few years have seen the publication of a number of results for this substrate [15, 18-26]. The highest enantioselectivities were achieved using catalysts 12b [22] and 14a [26],... 

Recently, a breakthrough in the hydrogenation of unfunctionalized olefins was made [51]. For the first time, high enantioselectivities with purely alkyl-substituted alkenes such as 72-74 could be achieved using pyridine-phosphinite catalysts 75 and 76. 

Scheme 36.4 Lib raries of P,N- and C,N-ligands in the Ir-catalyzed enantioselective hydrogenation of unfunctionalized olefins.

Figure 10. Buchwald s catalyst system for the enantio-selective hydrogenation of unfunctionalized olefins such as 52 and 53.

Scheme 15. Ir-Catalysed hydrogenation of unfunctionalized olefins and imines using PHOX-ligands.

Historically, reaction of simple olefins in the presence of chiral phosphine-Rh complexes in 1968 marked the first examples of homogeneous asymmetric hydrogenation [6], However, only a few successful results have been reported for asymmetric hydrogenation of unfunctionalized olefins. Some examples with late and early transition-metal complexes are illustrated in Schemes 1.27-28 and Schemes 1.29-30, respectively. 

Scheme 2 PHOX-based Ir complex as catalyst in the hydrogenation of unfunctionalized olefins...

Other catalysts such as rhodium phosphane complexes are much less effective in the hydrogenation of unfunctionalized olefins. The best results have been obtained with 2-phenyl-l-butene using a polymeric phosphinite ligand derived from cellulose113, (S,S)-1,2-bis-(diphenylphosphinoxy)cyclopentane114, or BDPP24 (50-60% ee). 

Asymmetric hydrogenation of unfunctionalized olefins, enamines, and imines... 

The synthesized zwitterionic iridium complexes containing various chiral P, N ligands with imidazoline or oxazoline were used as precatalysts for the asymmetric hydrogenation of unfunctionalized olefins. The cationic complexes with fluorinated borates as anions were superior catalysts in dichloromethane, whereas the iridium betaines were good catalysts in pure hydrocarbons. ... 

Figure 15.7. A selection of P,N ligands used for the asymmetric hydrogenation of unfunctionalized olefins.

Three classes of catalysts have been studied for the asymmetric hydrogenation of imines. One class of catalyst is generated from late transition metal precursors and bisphosphines. These catalysts have typically been generated from rhodium and iridium precursors. A second class of catalyst is based on the chiral titanocene and zirconocene systems presented in the previous section on the asymmetric hydrogenation of unfunctionalized olefins. The third class of catalyst is used for the transfer hydrogenation of imines and consists of ruthenium or rhodium complexes containing diamine, amino tosylamide, or amino alcohol ligands. " ... 

Brandt, R Hedbei, C. Andersson, P. G. New mechanistic insights into the iridium-phosphanooxazoline-catalyzed hydrogenation of unfunctionalized olefins A DPT and kinetic study. Chem. 2003, 9,339-347. 

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