Chiral Cyclopentadienyl Ruthenium (II) Complexes

Abstract

Cyclopentadienyl ruthenium(II) complexes are an important class of homogenous catalysts. They engage in a multitude of different transformations, for example cycloisomerizations. Due to a lack of suitable chiral cyclopentadienyl ligands, no efficient enantioselective version of the cationic CpRu(MeCN)3PF6 catalyst had been developed in the past, despite synthetic needs and potential. This thesis describes a general synthesis of efficient chiral CpxRu(II) catalysts. An atropchiral C2-symmetric biaryl ligand scaffold proved to be the most suitable and allows for fine-tuning of the corresponding complexes. The synthesis of the best performing ligand has been reduced to six steps form (R)-BINOL by implementing a C–H activation strategy. The cationic catalyst I enabled the highly enantioselective cyclization of yne-enone II to 4H-pyrans III. A tremendous counterion effect on the reaction outcome was observed. In situ formation of neutral CpxRu(II) species IV gave rise to a complementary set of catalysts, competent for an enantioselective formal [2+2] reaction of strained alkenes V and internal alkynes VI. Cyclobutenes VII were rapidly formed under mild conditions. Both propiolates and alkynyltriazenes were suitable substrates, enabling rich follow-up chemistry via derivatization of the products