A specific route to enantiomerically pure asymmetric (eta(6)-arene)(eta(4)-1,5-cyclooctadiene)Ru(0) complexes

Chiral or achiral (arene)(COD)Ru complexes can be made by replacing the eta(6)-ligands of (eta(4)-1,5-COD)(eta(6)-1,3,5-cyclooctatriene)Ru (1) or (eta(4)-1,5-COD)(eta(6)-naphthalene)Ru (2) by a suitable arene. This well known reaction has been extended to mono- and dibromoarenes and we report a novel route to substituted (arene)(COD)Ru species, utilizing (bromoarene)-(COD)Ru as starting materials. These facilitate a rapid bromine-lithium exchange reaction with nBuLi at low temperatures and the Lithiated species react readily with alkyl chloro-formates as electrophiles. By using chiral electrophiles [alkyl = (-)-menthyl] enantiomerically pure or diastereomeric complexes containing CO(2)R* groups are formed, depending on the symmetry of the original complex. A diastereomeric 1:1 mixture was separated by recrystallization. All (arene)-(COD)Ru complexes tested so far are useful as catalysts for the hydrogenation of simple alkenes at room temperature.