Synthesis of Novel 6‐(2‐Thienyl)‐2,2′‐Bipyridine Ligands Using “1,2,4‐Triazine” Methodology: an Unexpected Demethylation During the Aza‐Diels‐Alder Reaction with 2,5‐Norbornadiene

• Published in: ChemistrySelect (Weinheim) Vol. 9; no. 26
• Main Authors: Shtaitz, Yaroslav K., Ladin, Evgeny D., Valieva, Maria I., Kopchuk, Dmitry S., Nikonov, Igor L., Zyryanov, Grigory V., Khalymbadzha, Igor A., Fatykhov, Ramil F., Sharutin, Vladimir V.
• Format: Journal Article
• Language: English
• Published: 11-07-2024
• Subjects: Aza-Diels-Alder reaction; demethylation; platinum(II) complex; thienyl-2,2′-bipyridine; “1,2,4-triazine” methodology
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.202400941

New 2‐(di)methoxythienyl substituted ligands of the 2,2′‐bipyridine series containing various aromatic substituents at the C3 position were obtained in yields of up to 90 %. A “1,2,4‐triazine” methodology involving an SNH reaction in 1,2,4‐triazine followed by an aza‐Diels‐Alder reaction with 2,5‐norbornadiene was used to synthesize the target compounds. When the Diels‐Alder reaction was carried out in an autoclave, an unexpected demethylation reaction was observed, leading to the formation of oxo‐thienyl substituted products. A mechanism for the reaction that occurred has been proposed on the basis of identified byproducts. Preliminary studies on the photophysical and coordination properties of the obtained compounds were also carried out. In particular, the possibility of obtaining a platinum(II) complex with the demethylation product was demonstrated.
The synthesis of thiophene‐substituted bipyridines, ligands for platinum metals, was reported. The synthesis is based on the oxidative coupling of 3‐pyridyl‐1,2,4‐triazines with alkoxythiophene derivatives to give 5‐thienyl‐3‐pyridyl‐1,2,4‐triazines. Subsequent conversion of the 1,2,4‐triazine cycle to pyridine with norbornadiene gives the desired bipyridine ligand. In some cases, this reaction is accompanied by the demethylation of one of the alkoxy groups in the thiophene cycle. The photophysical properties of bipyridine ligands and their complexes with platinum were studied.