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A detailed kinetico-mechanistic investigation on the palladium C–H bond activation in azobenzenes and their monopalladated derivatives

Bjelopetrović, Alen; Barišić, Dajana; Duvnjak, Zrinka; Džajić, Ivan; Juribašić, Marina; Halasz, Ivan; Martinez, Manuel; Budimir, Ana; Babić, Darko; Ćurić, Manda (2020) A detailed kinetico-mechanistic investigation on the palladium C–H bond activation in azobenzenes and their monopalladated derivatives. Inorganic Chemistry, 59 (23). pp. 17123-17133. ISSN 0020-1669

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Palladium C–H bond activation in azobenzenes with R1 and R2 at para-positions of the phenyl rings (R1=N(Me)2, R2=H (L1); R1=N(Me)2, R2=Cl (L2); R1=N(Me)2, R2=I (L3); R1=–N(Me)2, R2=NO2 (L4); R1=H, R2=H (L5)) and their already monopalladated derivatives, using cis-[PdCl2(DMF)2] as precursor, has been studied in detail by in situ 1H NMR spectroscopy in N,N-dimethylformamide-d7 (DMF-d7) at room temperature; the same processes have been monitored in parallel via time-resolved UV-Vis spectroscopy in DMF at different temperatures and pressures. The final goal being to achieve, from a kinetico-mechanistic perspective, a complete insight of previously reported reactivity results. As expected, the results suggest the operation of an electrophilic substitution intimate mechanism for both the mono- and dipalladation reactions, occurring from the coordination compound and the monopalladated intermediates, respectively. The process involves a deprotonation of the C–H bond, which is assisted by the presence of a coordinated DMF molecule, that acts as a base. For the first time, NMR monitoring provides a direct evidence of all the intermediate stages, that is: i) coordination of the azo ligand to a PdII center, ii) formation of the monopalladated spe-cies, iii) coordination of the monopalladated species to another PdII unit, which finally result in the iv) formation of the dipalladated product. All of these species have been identified as intermediates in the dipalladation of azobenzenes, evidenced also by UV-Vis spectroscopy time-resolved monitoring; the data also confirms that the cyclopalladation of asymmetrically substituted azobenzenes occurs by two concurrent reaction paths. In order to identify the species observed by NMR and by UV-Vis spectroscopies, the final products, intermediates and the PdII precursor have been prepared and characterized by X-ray diffraction, IR and NMR spectroscopies. All attempts to isolate the intermediate monopalladated complexes attached to another PdII unit proved to be unsuccessful. DFT calculations have also been used in order to explain the isomerism ob-served for the isolated complexes, as well as to assign their NMR spectra.

Item Type: Article
Uncontrolled Keywords: azobenzene; C-H bond activation; kinetics; mechanism
Subjects: NATURAL SCIENCES > Chemistry > Physical Chemistry
NATURAL SCIENCES > Chemistry > Theoretical Chemistry
NATURAL SCIENCES > Chemistry > Inorganic Chemistry
Divisions: Division of Physical Chemistry
Project titleProject leaderProject codeProject type
Mehanokemijska aktivacija i funkcionalizacija veze C–H potaknuta paladijem i usmjerena ligandom-MECHEMFUNManda ĆurićIP-2019-04-9951HRZZ
Depositing User: Dajana Barišić
Date Deposited: 01 Dec 2021 14:01
DOI: 10.1021/acs.inorgchem.0c02418

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