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
σ-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.