Mechanistic Investigation of the Synthesis of 5‐Arylthiol‐Substituted 2,1,3‐Benzofurazan Using Pd(Pro) 2 as Catalyst

Abstract Pd 0 is well known for catalyzing cross‐coupling reactions, but how this Pd 0 specie is obtained in the reaction medium remains unclear. Concepts such as “releasing the ligand from the catalyst” do not completely describe the full redox process, but they are generally accepted as an explanation for Pd 0 formation. Herein, we studied the transformation of Pd(Pro) 2 , a Pd(II) precatalyst, into Pd 0 using experimental methods and theoretical calculations via the C–S cross‐coupling reaction involving 5‐chlorobenzofurazan with various thiols. We found that the thiol hydrogen transfer (THT) process is responsible for the formation of Pd 0 from Pd(Pro) 2 . We also observed that the THT process was influenced by the p K a of the thiol group and enhanced by the addition of a base to the reaction system. Therefore, the base choice also plays a crucial role in Pd 0 formation. Furthermore, a wide variety of sulfured compounds derived from 5‐chlorobenzofurazan was obtained in moderate to high yields using a low catalytic loading of Pd(Pro) 2 with K 2 CO 3 over a short reaction time.