Sulfonium cations as versatile strongly π-acidic ligands

More than a century old, sulfonium cations are still intriguing species in the landscape of organic chemistry. On one hand they have found broad applications in organic synthesis and materials science, but on the other hand, while isoelectronic to the ubiquitous tertiary phosphine ligands, their own coordination chemistry has been neglected for the last three decades. Here we report the synthesis and full characterization of the first Rh(i) and Pt(ii) complexes of sulfonium. Moreover, for the first time, coordination of an aromatic sulfonium has been established. A thorough computational analysis of the exceptionally short S-Rh bonds obtained attests to the strongly pi-accepting nature of sulfonium cations and places them among the best pi-acceptor ligands available today. Our calculations also show that embedding within a pincer framework enhances their pi-acidity even further. Therefore, in addition to the stability and modularity that these frameworks offer, our pincer complexes might open the way for sulfonium cations to become powerful tools in pi-acid catalysis.

Automated summary

This article reports the synthesis and characterization of complexes of sulfonium cations Rh(i) and Pt(ii), and establishes the coordination of aromatic sulfonium for the first time. The computational analysis shows that sulfonium cations have strong pi-accepting properties, and embedding them within a pincer framework enhances their pi-acidity. The article suggests that these pincer complexes may turn sulfonium cations into powerful tools for pi-acid catalysis.