Synthetic, spectral and catalytic activity studies of ruthenium bipyridine and terpyridine complexes:: Implications in the mechanism of the ruthenium(pyridine-2,6-bisoxazoline)(pyridine-2,6-dicarboxylate)-catalyzed asymmetric epoxidation of olefins utilizing H2O2

Various Ru(L-1)(L-2) (1) complexes (L-1 = 2,2'-bipyridines, 2,2':6',2-terpyridines, 6-(4S)-4-phenyl-4,5-dihydro-oxazol-2-yi-2,2'-bipyridinyl or 2,2'-bipyridinyl-6-carboxylate; L-2 = pyridine-2,6-dicarboxylate, pyridine-2-carboxylate or 2,2'-bipyridinyl-6-carboxylate) have been synthesized (or in situ generated) and tested on epoxidation of olefins utilizing 30% aqueous H2O2. The complexes containing pyridine-2,6-dicarboxylate show extraordinarily high catalytic activity. Based on the stereoselective performance of chiral ruthenium complexes containing non-racemic 2,2'-bipyridines including 6-[(4S)-4-phenyl-4,5-dihydro-oxazol-2-yl]-[2,2']bipyridinyl new insights on the reaction intermediates and reaction pathway of the ruthenium-catalyzed enantioselective epoxidation are proposed. In addition, a simplified protocol for epoxidation of olefins using urea hydrogen peroxide complex as oxidizing agent has been developed. (c) 2006 Elsevier B.V. All rights reserved.