|M.Sc Student||Rabin Nira|
|Subject||Indenyl-Click Ligands: Combinatorial Synthesis and|
|Department||Department of Chemistry||Supervisor||Professor Mark Gandelman|
|Full Thesis text|
Over the past two decades, tremendous progress has been made in the functionalization of carbon-hydrogen bonds. Formally, it requires insertion of a transition metal (usually Ru, Ir, Rh or Pd) across a strong C-H bond followed by generation of a new C-R bond.
Murai demonstrated that cyclopentadienyl-ruthenium species are able to catalyze olefin hydroarylation with benzaldehyde and other functionalized arenes. In all these cases, aromatic ring contains a hemi-labile coordination substituent and the functionalization takes place ortho- to it. Interestingly, the C-H activation doesn’t happen with the Cp-Ru based complexes in the absence of such substituent on the aromatic ring. It is believed that this substituent plays a role of a directing group which brings a metal to the close proximity of the activated C-H bond.
Brookhart, however, showed that analogous Cp-Rh species are able to reversibly activate C-H bond of simple benzene, but the productive functionalization takes place only when arenes substituted with carbonyl "on-off-coordinating" group were utilized. The reason for that is stabilization of the intermediate species by coordination to rhodium center and prevention by that the reversible redundant β-H elimination.
We anticipate that this "stabilizing" group should not necessary be on the organic substrate itself. We suggest that Cp-ligand decorated with the carbonyl unit or similar hemi-labile group can also stabilize the reactive intermediate after Rh-H insertion in double bond.
In this work, we describe the synthesis of new versatile family of indenyl-click ligands that have a hemi-labile triazole group. Triazole unit attracts us due to ability of facile constructing of versatile libraries with tunable properties by click reaction between the appropriate azides and alkynes. In addition, triazole is not strong ligand and possesses hemi-labile coordination behavior under appropriate conditions.
A library of the indenyl-triazole-based ligands was synthesized, starting from the appropriate indenyl-azide or indenyl-alkyne precursors. Novel rhodium and iridium complexes were synthesized based on these ligands, and fully characterized by NMR techniques. In addition, crystallographic confirmation for the molecular structure of Rh-biscarbonyl based complex was obtained.
As a proof of concept, number of reactions was performed to check the coordination of the triazole moiety to the metal center. For example, iodination reaction of a rhodium(I)-bis-ethylene complex results in a formation of rhodium(III)-diiodo 16ē-complex, which allowed for coordination of the triazole nitrogen to the rhodium center. An evidence for the coordination is based on NMR characterization of the new complex and its chemical reactions.