Ruthenium-chiral bisphosphine complexes

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. " ... 

The synthesis of P-chiral phosphines has been achieved throngh the use of ruthenium complexes supported by chiral ligands (Schemes 4.6 and 4.7) [23]. The chemistry was carried ont nnder mild conditions and afforded excellent yields and outstanding selectiv-ities for both mono- and bisphosphines as their borane addncts. A critical parameter in this chemistry was the selection of the base for the chemistry. While common metal alkoxides snch as NaOEt were unsuccessful, increasing the length of the carbon chain increased the solnbility of the alkoxide in organic solvents and promoted the reaction. 

---