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

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.