Tertiary Arsine Ligands for Pd-Catalyzed Direct Arylation

Catalysts for direct arylations have been extensively studied for the efficient synthesis of (hetero)biaryl compounds. Phosphine ligands are pivotal in this field, and electron-deficient phosphine ligands are advantageous for direct arylation. Due to its relatively weak sigma-donation ability, arsenic is considered an ideal candidate for designing electron-deficient ligands. However, no studies have explored the relationship between the structure of the arsine ligands and their catalytic activity for direct arylation. In this study, we synthesized 27 arsine ligands with varying electron-donating and steric properties. Tris(o-trifluorotolyl)arsine, an electron-deficient and bulky ligand, exhibited the highest efficiency in a model reaction between 2-propylthiophene and 4-bromobenzotrifluoride. Both experimental and computational studies revealed the mechanism of direct arylation using arsine ligands. This is the first comprehensive investigation of an arsine-ligated catalytic direct arylation.