Catalytic enantioselective oxidation of aromatic hydrocarbons with D4-symmetric chiral ruthenium porphyrin catalysts

The [Ru-II(D-4-Por*)(CO)(McOH)] (D-4-H(2)Por*=tetrakis[(1S,4R,5R,SS)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracen-9-yl]porphyrin) complex 1 is an effective catalyst for asymmetric hydroxylation of aromatic hydrocarbons with 2,6-dichloropyridine N-oxide (Cl(2)pyNO) as terminal oxidant. Up to 76% ee was achieved for the catalytic hydroxylation of 4-ethyltoluene, 1,1-diethylindan and benzylcyclopropane. Both electron-donating and -withdrawing substituents were found to accelerate the catalytic oxidation reaction, and a large primary H/D kinetic isotope effect (k(H)/k(D) = 11 at 298 K) was observed for the catalytic ethylbenzene-d(10) oxidation. A mechanism involving rate-limiting hydrogen atom abstraction by reactive oxoruthenium species is postulated. (c) 2005 Elsevier Ltd. All rights reserved.