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

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, (M^sFluInd*)P[double bond, length as m-dash]PCl·(Et₂O)₂ (where M^sFluInd* is a sterically demanding hydrindacene substituent), for the first time. The structure and reactivity of (M^sFluInd*)P[double bond, length as m-dash]PCl were explored to compare the novel arylhalodiphosphene with compositionally related aryldiazonium chlorides, [RNN][Cl], and chloroiminophosphanes, RN[double bond, length as m-dash]PCl. The P-P bond of (M^sFluInd*)P[double bond, length as m-dash]PCl was cleaved via protonolysis to afford the parent phosphine, (M^sFluInd*)PH₂. Halogen-exchange reactions between (M^sFluInd*)P[double bond, length as m-dash]PCl and TMSX (TMS = trimethylsilyl, X = Br, I) afforded the related monomeric arylhalodiphosphenes, (M^sFluInd*)P[double bond, length as m-dash]PX (X = Br, I). Finally, the coordination complex, [(M^sFluInd*)P[double bond, length as m-dash]PCl·Ag][CF₃SO₃], was isolated by treatment of (M^sFluInd*)P[double bond, length as m-dash]PCl with AgCF₃SO₃. Periodic trends in the structure and bonding of (M^sFluInd*)P[double bond, length as m-dash]PX (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. (M^sFluInd*)P[double bond, length as m-dash]PX (X = Cl, Br, I) represent the first fully characterized, crystalline arylhalodiphosphenes and serve to advance the state of low-coordinate phosphorus chemistry.