# Isolation of arylhalodiphosphenes: periodic trends in R–P[double bond, length as m-dash]P–X bonding (X = Cl, Br, I)

## TL;DR

Scientists have created and studied new phosphorus-based compounds called arylhalodiphosphenes, which are similar to commonly used nitrogen-based compounds in chemistry.

## Contribution

The first isolation and structural characterization of monomeric arylhalodiphosphenes with periodic trends in their bonding.

## Key findings

- A monomeric arylchlorodiphosphene was isolated and characterized for the first time.
- Halogen-exchange reactions produced related arylhalodiphosphenes with X = Br and I.
- The compounds exhibit a formal P–P double bond and polar covalent P–X bonds.

## Abstract

For over a century, aryldiazonium halides have served as widely used building blocks within synthetic chemistry. They are vital intermediates in converting simple anilines to high-value products, including those needed to prepare pharmaceuticals, dyes, and functional materials. Despite the prevalence of these nitrogen-based organic salts in laboratories, structurally related phosphorus-based salts remain scarce. Herein, we report the isolation and structural characterization of a monomeric arylchlorodiphosphene, (MsFluInd*)PPCl·(Et2O)2 (where MsFluInd* is a sterically demanding hydrindacene substituent), for the first time. The structure and reactivity of (MsFluInd*)PPCl were explored to compare the novel arylhalodiphosphene with compositionally related aryldiazonium chlorides, [RNN][Cl], and chloroiminophosphanes, RNPCl. The P–P bond of (MsFluInd*)PPCl was cleaved via protonolysis to afford the parent phosphine, (MsFluInd*)PH2. Halogen-exchange reactions between (MsFluInd*)PPCl and TMSX (TMS = trimethylsilyl, X = Br, I) afforded the related monomeric arylhalodiphosphenes, (MsFluInd*)PPX (X = Br, I). Finally, the coordination complex, [(MsFluInd*)PPCl·Ag][CF3SO3], was isolated by treatment of (MsFluInd*)PPCl with AgCF3SO3. Periodic trends in the structure and bonding of (MsFluInd*)PPX (X = Cl, Br, I) were investigated with spectroscopic, crystallographic, and computational methods. These studies confirm that the {PPX} moeity consists of a formal P–P double bond, and polar covalent P–X (X = Cl, Br, I) single bonds. (MsFluInd*)PPX (X = Cl, Br, I) represent the first fully characterized, crystalline arylhalodiphosphenes and serve to advance the state of low-coordinate phosphorus chemistry.

Aryldiazonium halides have served as important synthetic intermediates for over a century. Herein, we report the synthesis of compositionally related monomeric arylhalodiphosphenes.