טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSchuster Yael
SubjectPincer Click Ligands: Synthesis and Catalysis
DepartmentDepartment of Chemistry
Supervisor Professor Mark Gandelman
Full Thesis textFull thesis text - English Version


Abstract

Bidentate and tridentate chelating ligands represent an important class of compounds for the construction of transition metal catalysts. In particular, hetero-bidentate ligands, which have two different chelating atoms, have recently received a great amount of attention due their capacity to fine-tune the stereoelectronic properties of the reaction center. As compared to monodentate ligands, however, the synthesis of their poly-dentate counterparts is generally more complex and less efficient. It especially represents a substantial drawback for reactions which require rigorous ligand optimization.

We have developed a novel approach to the fast and efficient preparation of bi-and tridentate ligands. Our strategy utilizes a highly selective cycloaddition of the corresponding precursor azide and alkyne counterparts leading to their covalent assembly as multidentate ligands in solution. To the best of our knowledge, this is the first such approach to the preparation of pincer-type ligand libraries. Novel precursors incorporating alkyl phosphines were synthesized.

            Numerous late transition metal complexes based on these novel ligands have been prepared in both bidentate and tridentate-type coordination. Catalytic activity of the tridentate complexes was explored in the context of the Heck reaction and a highly active catalyst was found.

Several unique properties of these systems imparted by the triazole backbone were discovered. In particular, a coordination “switch” was identified from a bidentate to tridentate-type coordination. Additionally, the tridentate pincer complex was found to be capable of undergoing alkylation on a nitrogen of the triazole backbone to thereby transform the singly σ bonded C-metal bond to a mesoionic carbene-type coordination.

The results are discussed along with potential implications of these discoveries in the field of catalysis and organic chemistry.