C-H activation with heterogenous N-Heterocyclic palladium complexes: Synthesis and Evaluation of ligand-directed catalysis

Abstract

C-H activation with transition metal catalysts is one the most intense areas of research today
and new advancements aid in the production of bulk chemicals, simplifying synthetic routes
and transforming inert substrates into functionalized ones. By attempting to synthesize two N-
heterocyclic palladium complexes (1 and 2, complex 3 is received) heterogenous, ligand-
directed halogenation of substrates 4 and 5 is evaluated to for activity, selectivity, time-profile
recyclability, and heterogenity. Complex 1 was synthesized in low yield and further
purification must be done going forward. The intermediate silver complex of complex 2 was
synthesized. The bromination of substrate 5 was completely selective in low yield and more
selective than the homogenous variant. Further, the time-profile indicated a single reaction
pathway. The iodination and bromination of substrate 4 showed complete selectivity in
moderate yield and better selectivity than the homogenous equivalent. The iodination was
found to be recyclable up to 5 runs.

Popular Abstract

Chemical catalysis is a hugely important tool used not only by our bodies in different biological processes but also by the synthetic chemist to perform transformations that would otherwise be impossible or very difficult. One important class of catalysts employ a transition metal, such as palladium, bound to a N-heterocyclic (NHC) ligand. The NHC ligand allows the chemist to modify the properties of the catalyst so that it can be used for a wide variety of purposes. Such catalysts can, moreover, be noncovalently bound to a support, such as graphene or carbon nanotubes, which makes the catalyst heterogenous and easily separable from the reaction mixture after the reaction is complete. By using these catalysts, the hope is that selective (only targeting one bond) and high-yielding conversion of C-H bonds into C-X (X usually N, O, C, halogen) can be achieved. C-H activation, as this is called, is a tricky but highly useful part of synthetic chemistry.

This diploma work aims to synthesize two NHC-palladium catalysts and support them onto reduced graphene oxide (rGO). Further, a third presynthesized NHC-palladium complex will be supported on rGO and used in a number of catalytic reactions. The results show that one of these catalysts was succesfully synthesized, with some impurities, while strides were made on the path to synthesize the other. The third catalyst was used for a number of C-H activation reactions where a ligand on the substrate directs the C-H activation. The results show that when the catalyst was supported onto rGO the catalysis gave a lower yielding but much more selective conversion. Further, a time-profile of the catalysis was constructed, which showed typical behaviour. Finally, the recyclability of one of the catalytic reactions was performed and was shown to be effective up to 4 cycles.

• author: Redzic, Dino
• supervisor: Maitham Majeed
• organization: Department of Chemistry; Centre for Analysis and Synthesis
• course: KOK820 20171
• year: 2017
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: organometallic chemistry, organic chemistry, ligand-directed catalysis
• language: English
• id: 8927706
• date added to LUP: 2024-02-28 12:46:22
• date last changed: 2024-02-28 12:46:22