84 / 2023-09-22 21:41:54

Room Temperature Stable E,Z-Diphosphenes: Isomerization, Coordination and Cycloaddition Study

diphosphene,phosphorus,N-heterocyclic carbenes,isomerization,diagonal relationship

Phosphorus in Synthetic Chemistry > 2) Phosphorus compounds as ligands

E,Z-isomers display distinct physical properties and chemical reactivities. However, investigations on heavy main group elements remain limited. In this work, we present the isolation and X-ray crystallographic characterization of N-heterocyclic vinyl (NHV) substituted diphosphenes as both E- and Z-isomers (L=CH-P=P-CH=L, E,Z-2b; L = N-heterocyclic carbene). E-2b is thermodynamically more stable and undergoes reversible photo-stimulated isomerization to Z-2b. The less stable Z-isomer Z-2b can be thermally reverted to E-2b. Theoretical studies support that this E ↔ Z isomerization proceeds via P=P bond rotation, reminiscent of the isomerization observed in alkenes. Furthermore, both E,Z-2b coordinate to an AuCl fragment affording the complex [AuCl(η²-Z-2b)] with the diphosphene ligand in Z-conformation, exclusively. On the contrary, E,Z-2b undergo [2+4] and [2+1] cycloaddtions with dienes or diazo compounds, respectively, yielding identical cycloaddition products in which the phosphorus bound NHV groups are in trans–position to each other. DFT calculations provide insight into the E/Z-isomerisation and stereoselective formation of Au(I) complexes and cycloaddition products.