Bisphosphine/diamine-based

In some cases, the use of base can be incompatible with substrates or can add an imde-sirable variable to running a process. This base can be avoided by starting with the complexes [Ru(bisphosphine)(diamine)(H)(BH )]. ... 

Great care must be taken not to generalize these effects, as the addition of primary diamines to ruthenium bisphosphine complexes generates a very active catalyst for ketone hydrogenation after the addition of base (see Chapter 32). 

A class of chiral bisphosphines that has not received much attention is aminophosphines (e.g., 7 and 8) known as PNNP.7 The chirality is derived from a 1,2-diamine. One advantage of aminophosphines is that they can be easily prepared by the reaction of a chiral amine and Ph2PCl in the presence of a base.70 However, the rhodium-catalyzed reductions must be performed with care because the P-N bonds are easily hydrolyzed or solvoly/cd.177... 

The ability to catalyze the asymmetric hydrogenation of aliphatic ketones provides an opportunity to extend the scope of these reactions to the dynamic kinetic resolution of ketones that contain a stereocenter in the enolizable a-position. The catalysts containing bisphosphine and diamine ligands are activated by base, and the base used to activate the metal catalyst can also catalyze the racemization of the ketone. An example of such a process is shown in Equation 15.76. ... 

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. " ... 

Benzophenone, although an achiral molecule, has been shown to exist in two different enantiomeric forms in the solid state [39]. Mikami s and Ding s groups [40] independently reported the use of achiral benzophenone-based bisphosphine hgands in combination with enantiopure chiral diamines to generate Noyori-type Ru(II) catalysts for the asymmetric hydrogenation of ketones. A library of Ru(II) catalysts was set up by combining the achiral benzophenone-based bisphosphines 25a-d (Scheme 5.14) and enantiopure 1,2-diamines 21a-i with the Ru salt. 

Scheme 5.14 Ru(ll) complexes containing achiral benzophenone-based bisphosphine ligands and enantiopure 1,2-diamines for asymmetric hydrogenation of ketone.

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