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

The [RuII(D4-Por*)(CO)(MeOH)] (D4-H2Por* = tetrakis[(1S,4R,5R,8S)-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 (Cl2pyNO) 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 (kH/kD= 11 at 298 K) was observed for the catalytic ethylbenzene-d10oxidation. A mechanism involving rate-limiting hydrogen atom abstraction by reactive oxoruthenium species is postulated.