Chemistry of oxaphosphirane complexes

Metal-catalyzed valence isomerization of a methylene(thioxo)phosphorane to a thiaphosphirane

We explored coordination chemistry associated with valence isomerization between a methylene(thioxo)phosphorane (MTP) and a thiaphosphirane. For this purpose, we developed the selective synthesis of a MTP by eliminating chlorodimethylphenylsilane from the corresponding chlorophosphine sulfide. Treatment of the MTP with an equivalent amount of pentafluorophenylgold(I) complex resulted in the formation of a thiaphosphirane gold(I) complex, which likely proceeds via an η2-P,C-MTP gold complex. The MTP undergoes a valence isomerization catalyzed by copper(I) chloride to furnish a transition metal-free thiaphosphirane. Computational studies proposed a plausible mechanism involving a Cu-assisted cyclization reaction.

The quest for unligated oxaphosphiranes with phosphorus in different coordination numbers

After more than 160 years of oxirane (epoxide) chemistry, the first derivative of a phosphorus analogue, namely oxaphosphirane, has been synthesized. Reactions with borane sulfane, a peroxy compound and elemental sulfur, as well as tetra-chloro-ortho-benzoquinone (TOB) reveal a significant destabilization upon increasing the coordination number at phosphorus from σ³ to σ⁴, thus somehow supporting previous reports on such fleeting species. Theoretical studies provide insight into ring strain energy, ring/ring interconversion and the oxidation pathways.

Azaphosphiridines: challenges and perspectives

This mini-review describes a broad spectrum of synthetic strategies to access mono- and polycyclic azaphosphiridines; properties and theoretical calculations of free and metal-ligated are discussed. These species are characterized by a highly strained (saturated) CPN ring with three differently polarized endocyclic bonds. The latter causes a high reactivity of aza-phosphiridine complexes towards ring expansion and exchange reactions. Increasing the ring strain leads to masked FLP behaviour, i.e., small molecule activation was observed. New perspectives in homogenous catalysis are also offered, e.g., a pool of novel chiral P-heterocyclic ligands, ready to be explored, if the challenge to unligate them is solved.