Preorganization within a pyrazolato-bridged bis-β-diketiminato dinickel frame as a key tool to access terminal sulfides and synergistically stabilized intermediates for acetyl-CoA synthase mimetic thioester formation

by Valeria Tagliavini
Doctoral thesis
Date of Examination:2024-07-22
Date of issue:2025-05-21
Advisor:Prof. Dr. Franc Meyer
Referee:Prof. Dr. Franc Meyer
Referee:Prof. Dr. Sven Schneider
Referee:Prof. Dr. Manuel Alcarazo
Persistent Address: http://dx.doi.org/10.53846/goediss-11272

 

 

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Abstract

English

Bimetallic complexes are frequently employed in natural enzymes and in applications such as imaging, targeting, and catalysis, in order to exploit the synergy between two metal centers or to combine different functionalities. Herein, a dinickel complex supported by a pyrazolate-bridged bis-β-diketiminate ligand framework was employed to enable metal cooperativity and stabilize reactive intermediates. In particular, this complex was shown to accommodate a unique sulfido radical moiety, whose spectroscopic signatures have been elucidated. Stepwise transformations following sulfur activation allowed the construction of a thermodynamic square scheme, providing the S–H bond dissociation free energy of the corresponding hydrosulfido congener. Moreover, this bimetallic platform was shown to support an acetyl-CoA synthase mimetic cycle, in which a methyl complex stabilized by agostic interactions reacts with CO to yield a side-on acetyl complex. Upon reaction with thiols, a thioester was ultimately released. The intermediates and mechanism were investigated in detail. Finally, the scope of the ligand framework was extended to heterobimetallic [NiFe] and [NiMg] complexes.
Keywords: nickel; bimetallic complexes; nacnac; small molecule activation; sulfido radical; acetyl-CoA synthase; agostic interacions; PCET; heterobimetallic complexes
 
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