Ruthenium BINAP analogues

The modified BINAP catalyst 5 has been used for the hydrogenation of a number of analogues of substrate 1 (substrates 32-35, Fig. 30.8 Table 30.6), though again, enantioselectivities were modest [4]. Substrate 31 has also been hydrogenated with a ruthenium-BINAP-hydride cluster with low selectivity (11% ee) [27]. 

Since the diphosphine is appreciably more electron-rich than is BINAP, the major ruthenium complex is a more active hydrogenation catalyst than the parent. Increased electron-rich ligation may be the reason for the success of heterocyclic analogues of BINAP in which the binaphthalene is replaced by a bi(ben-zothiophene) or biindolyl the resulting Ru complexes are effective both in terms of enantioselectivity and reactivity [139]. Readers of the related Chapter 6.1 on the asymmetric hydrogenation of carbonyl compounds will encounter the Ru complexes of ligands in the DUPHOS family, where the ease of modification of the alkyl substituents of the phospholane enhances the power of the system, since it permits the easy optimization of ee for any substrate [140]. 

A ruthenium complex with the dendrimer BINAP ligand obtained from aromatic polyethers 55 catalyzed hydrogenation of 2-[p-(2-methylpropyl)phe-nyl] acrylic acid to ibuprofen at an optical selectivity of 99% in a methanol-toluene solution the activity of the dendrimer complex was twice as high as that of a low molecular weight analogue [138],... 

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