Rollover Cyclopalladation via Remote C‐H Bond Activation of Br‐Pyridinbenzothiazole: An Experimental Study

Abstract

Rollover palladacycles complexes containing pyridinebenzothiazole fragments were synthetized via remote C−H bond activation by PdCl2 in DMF. The structures of these compounds were proposed based on NMR analysis and high‐resolution mass spectrometry; in selected case of compound 1, its molecular structure was corroborated by single crystal X‐ray diffraction experiment. Upon solubilization in acetonitrile and using ESI‐QTOFMS, this complex was found as unusual tricoordinate cationic complex 1‐NCCH3 with acetonitrile attachment via Pd−Cl bond activation. Of note, synthesis success when PdCl2 was used as the starting material and mild heating (60 °C) of the reaction mixture was necessary to obtain the desired compound in a reasonable time (7 days). Evidence is provided that DMF solvent plays a key mechanistic role enabling the formation of organometallic rollover compounds; whereas using another solvent like DMSO, NCCH3 or acetone, a classic coordination complex is obtained.

Rollover Cyclometalation as a Valuable Tool for Regioselective C–H Bond Activation and Functionalization

“…Finally, one further ligand potentially able to coordinate in different ways, pyridinebenzothiazole, reacted with PdCl 2 in DMF under mild heating (60 °C), activated the pyridine C(3)–H bond to afford the rollover complex 106 . Notably, the DMF solvent seems to play a key role in the rollover process, because use of other solvents resulted only in classical coordination ( Figure 54 ) [ 103 ].…”

A rollover Ir(iii) complex of 2-(6-bromopyridin-2-yl)imidazo[1,2-a]pyridine

“…As we mention, part of our research has been addressed to understand the unusual reactivity of pyridine with Ir( iii ) giving the NHC-complexes; 17,18 bromo-pyridin derivative toward Pd( ii ) and Pt( ii ) complexes, where the bromine atom at pyridine ring regulates the coordination mode behaviour on the formation of platinum pincer complexes, seven-membered and rollover palladacycles. 33–37…”

“…32 As we mention, part of our research has been addressed to understand the unusual reactivity of pyridine with Ir(III) giving the NHC-complexes; 17,18 bromo-pyridin derivative toward Pd(II) and Pt(II) complexes, where the bromine atom at pyridine ring regulates the coordination mode behaviour on the formation of platinum pincer complexes, seven-membered and rollover palladacycles. [33][34][35][36][37] Herein, we report the first rollover cyclometallation reaction into the new 2-(6-bromo-pyridin-2-yl)imidazo [1,2-a]pyridine type ligand prompted by IrCl 3 , under mild reaction conditions, using dimethylformamide (DMF) as a solvent at 70 1C for a week under air. Additionally, we performed DFT calculations to propose a reaction mechanism that sheds some light on the reaction order of this C-H bond activation in the presence of Br-pyridine group.…”

A novel coordination mode of κ1-N-Br-pyridylbenz-(imida, oxa or othia)-zole to Pt(ii): synthesis, characterization, electrochemical and structural analysis

“…In 2018, we reported a direct synthesis on rollover palladacycles was achieved via C-H bond activation reaction in remote position on Br-pyridyl-benzothiazole (L PB2 ) by PdCl 2 , where the dimethylformamide plays an important role on the reaction pathway. 20 However, to the best of our knowledge, wellcharacterized transition metal complexes containing L PB ligands showing a N-k 1 -coordinated mode still relatively scarce in the literature. 7 Here in, we report our DFT calculations and experimental results on the reactivity of Br-Pyridylbenz-(imida, oxa or othia)-zole ligands toward platinum complexes.…”