Publication

Chiral Cyclopentadienyl Ruthenium (II) Complexes

David Kossler
2017
EPFL thesis
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

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Related concepts (19)
Homogeneous catalysis
In chemistry, homogeneous catalysis is catalysis where the catalyst is in same phase as reactants, principally by a soluble catalyst a in solution. In contrast, heterogeneous catalysis describes processes where the catalysts and substrate are in distinct phases, typically solid-gas, respectively. The term is used almost exclusively to describe solutions and implies catalysis by organometallic compounds. Homogeneous catalysis is an established technology that continues to evolve.
Rhodocene
Rhodocene is a chemical compound with the formula . Each molecule contains an atom of rhodium bound between two planar aromatic systems of five carbon atoms known as cyclopentadienyl rings in a sandwich arrangement. It is an organometallic compound as it has (haptic) covalent rhodium–carbon bonds. The radical is found above or when trapped by cooling to liquid nitrogen temperatures (). At room temperature, pairs of these radicals join via their cyclopentadienyl rings to form a dimer, a yellow solid.
Wilkinson's catalyst
Wilkinson's catalyst is the common name for chlorido­tris(triphenylphosphine)­rhodium(I), a coordination complex of rhodium with the formula [RhCl(PPh3)3], where 'Ph' denotes a phenyl group). It is a red-brown colored solid that is soluble in hydrocarbon solvents such as benzene, and more so in tetrahydrofuran or chlorinated solvents such as dichloromethane. The compound is widely used as a catalyst for hydrogenation of alkenes. It is named after chemist and Nobel laureate Sir Geoffrey Wilkinson, who first popularized its use.
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