Stabilization of the Pd–NHC framework with 1,2,4-triazol-5-ylidene ligands toward decomposition in alkaline media

Stabilization of the Pd–NHC framework with 1,2,4-triazol-5-ylidene ligands toward decomposition in alkaline media Full article

Journal

Inorganic Chemistry Frontiers
ISSN: 2052-1553 , E-ISSN: 2052-1545

Output data

Year: 2021, Volume: 8, Number: 13, Pages: 3382-3401 Pages count : 20 DOI: 10.1039/d1qi00453k

Authors

Chernenko Andrey Yu. ¹ , Astakhov Alexander V. ¹ , Kutyrev Vadim V. ¹ , Gordeev Evgeniy G. ² , Burykina Julia V. ² , Minyaev Mikhail E. ² , Khrustalev Victor N. ² , Chernyshev Victor M. ¹ , Ananikov Valentine P. ^1,2

Affiliations

1	Platov South-Russian State Polytechnic University (NPI), Prosvescheniya 132, Novocherkassk, Russia
2	Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky Prospect 47, Moscow, Russia

Complexes of Pd(II) with NHC ligands can suffer facile decomposition in the presence of alkali metal hydroxides, alkoxydes and other strong oxygen-containing bases via the reductive elimination of the NHC and Pd-coordinated base anion, the so-called O–NHC coupling. O–NHC coupling can represent a serious problem for the stability of Pd/NHC catalytic systems in numerous practically important reactions conducted in the presence of bases. In the present study, a new approach to stabilizing the Pd–NHC bond against cleavage by strong bases was developed. The approach relies on the installation of an NH–acidic RNH substituent at position 3 of the triazole ring of the 1,2,4-triazol-5-ylidene ligand. A series of new Pd/NHCs containing RNH substituents (R = Ac, Ph, alkyl) in triazole NHC ligands were synthesized. These complexes undergo reversible deprotonation of the RNH group in strong alkaline media and demonstrate superior stability of the Pd–NHC bond, significantly higher than complexes of similar structure without the RNH group. DFT calculations revealed that the anionic Pd/NHC complex containing an N-deprotonated acetamido group (R = Ac) is more kinetically stable against O–NHC coupling and less prone to lose NHC via heterolytic dissociation of the Pd–NHC bond than the neutral complex. The new complexes with RNH-functionalized NHC ligands were tested as precatalysts in the Suzuki–Miyaura coupling of p-tolyl bromide with phenylboronic acid in the presence of KOH and revealed more than 2 times higher TONs than similar complexes without the RNH group or ligandless Pd system.

Chernenko A.Y. , Astakhov A.V. , Kutyrev V.V. , Gordeev E.G. , Burykina J.V. , Minyaev M.E. , Khrustalev V.N. , Chernyshev V.M. , Ananikov V.P.
Stabilization of the Pd–NHC framework with 1,2,4-triazol-5-ylidene ligands toward decomposition in alkaline media
Inorganic Chemistry Frontiers. 2021. V.8. N13. P.3382-3401. DOI: 10.1039/d1qi00453k WOS Scopus OpenAlex

≡ Web of science:	WOS:000660115800001
≡ Scopus:	2-s2.0-85109073011
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