Room temperature stable E , Z -diphosphenes: their isomerization, coordination, and cycloaddition chemistry.

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[double bond, length as m-dash]CH-P[double bond, length as m-dash]P-CH[double bond, length as m-dash]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 the view that this E ↔ Z isomerization proceeds via P[double bond, length as m-dash]P bond rotation, reminiscent of the isomerization observed in alkenes. Furthermore, both E , Z -2b coordinate to an AuCl fragment affording the complex [AuCl(η 2 - Z -2b)] with the diphosphene ligand in Z -conformation, exclusively. In contrast, E , Z -2b undergo [2 + 4] and [2 + 1] cycloadditions 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.