# Structural effects of arsine ligands on C–H difunctionalization of thiophene

## TL;DR

This study shows that arsine ligands outperform phosphines in a specific chemical reaction involving thiophene, offering better stability and accessibility for catalyst design.

## Contribution

The study systematically explores and identifies optimal arsine ligands for C–H difunctionalization, revealing their superior steric and oxidative properties over phosphines.

## Key findings

- Arsines with moderate electron-donating abilities and sufficient steric accessibility are preferred in the reaction.
- Arsines show higher oxidative stability compared to phosphines under reaction conditions.
- The use of arsines expands the scope of transition metal catalysts beyond traditional phosphine limitations.

## Abstract

Despite their significant potential in organometallic chemistry, the utility of arsines as ligands in transition-metal catalysis remains underexplored relative to their phosphine counterparts. Although the Pd-catalyzed C–H difunctionalization of thiophene proceeds efficiently with triphenylarsine (AsPh3) but fails with conventional phosphine ligands, the synthetic utility of arsine ligands other than AsPh3 has not been explored. In this study, the steric and electronic requirements of the Pd-catalyzed C–H difunctionalization of thiophene are explored using 36 synthesized arsines and nine phosphines. Ligand parameterization reveals that arsines with moderate electron-donating abilities and sufficient steric accessibility were preferred. Notably, the identified steric demand is more readily met by arsines than by phosphines. Furthermore, arsines exhibit superior oxidative stability under reaction conditions that typically oxidize phosphines owing to the high oxophilicity of phosphorus. These experimental and computational findings demonstrate that the use of arsines can expand the scope of transition metal catalysts by enabling access to catalytic spaces that are less accessible with traditional phosphines.

This study highlights the advantages of arsine ligands over phosphines in Pd-catalyzed C–H difunctionalization. Analysis of 36 arsines shows higher steric accessibility and oxidative stability, enabling new catalyst designs beyond phosphine limits.