CARBON HYDROGEN, CARBON OXYGEN, AND CARBON CARBON BOND ACTIVATION BY AN ELECTROPHILIC RUTHENIUM COMPLEX

The ''Cp*Ru+'' fragment generated by protonation of [Cp*Ru(OMe)]2 with CF3SO3H reacts in CH2Cl2 or THF with cyclic C6 alkenes, dienes, alcohols, ketones, enones, and diones to yield coordinated aromatic derivatives after C-H, C-O, or C-C activation. The following transformations have been performed: cyclohexene and methylcyclohexene into benzene and toluene; 1,3- or 1.5-cyclooctadiene into 1,3,5-cyclooctatriene; cyclohexanol, cyclohexanone, or cyclohexenone into benzene; methylcyclohexenone into toluene; cyclohexanedione into phenol; 4,4-dimethylcyclohexenone and isophorone into 4-methylphenol and 3,5-dimethylphenol. The byproducts of these reactions are H2, H2O, CH4, and some C2H6- The conversions have been optimized and reach 100% for the three types of activation. The selectivity is better than 99% for C-H and C-O activation. In the case of gem-dimethyl enones, the formation of phenol derivatives is accompanied by the formation of their methyl ethers, but this problem can be circumvented. The mechanism of the reactions shows classical C-H activation and hydrogen-transfer processes to occur at the early stage of all the reactions. This is followed by H2 elimination possibly through an unstable dihydrogen intermediate, H2O elimination from a compound containing a coordinated OH group, or C-C bond breaking. The last process involves a radical pathway, as evidenced by the observation Of C2H6 in the gaseous phase.