Mercaptopyridine-Functionalized MIC-Pd(II)-PEPPSI Complexes: Synthesis and Hemilability Effect in Catalytic Applications

• Published in: Organometallics 2023-10, Vol.42 (19), p.2893-2901
• Main Authors: Patricio-Rangel, Emmanuel B., González-Silva, Karen, Mendoza-Espinosa, Daniel
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.3c00325

Palladium­(II)-PEPPSI-type complexes bearing 2- or 4-mercaptopyridine-functionalized 1,2,3-triazolylidenes (4 and 5, respectively) have been prepared and fully characterized. Complexes 4 and 5 show high catalytic activity in the Suzuki–Miyaura coupling of aryl chlorides with ortho-substituted boronic acids under mild reaction conditions. The effect of the mercaptopyridine substituent in the preparation of cyclometalated derivatives was investigated by the treatment of 4 and 5 with an excess of AgSbF6. The dehalogenation process allows the preparation of the dicationic complex 7, in which the nitrogen atom of the 2-mercaptopyridine coordinates the palladium center, forming a seven-membered ring. The isolation of the respective derivative with the 4-mercaptopyridine was unsuccessful. Complex 7 efficiently catalyzes the intermolecular hydroamination between anilines and terminal alkynes without the need for additives and shows good group tolerance. A key feature for the successful catalytic hydroamination relies on the hemilability of the 2-mercaptopyridine wingtip confined to the proximity of the alkynophilic metal active site, which favors a series of proton transfers, the process which is not possible when complexes 4 or 5 are employed as catalysts.