On the Dynamic Behavior of Pacman PhosphanesA Case of Cooperativity and Redox Isomerism

In solution, the
Pacman chlorophosphane (2Cl) shows
fast exchange of the endo/exo-orientation
of the two P–Cl bonds in the molecule featuring cooperativity.
Experimental and quantum mechanical investigations of the inversion
on the phosphorus(III) centers reveal a crucial role of chloride ions
in the dynamic process. To confirm the results, the homologous Pacman
halogen-phosphanes 2X were prepared by halogen exchange
reactions (X = F, Br, and I). Besides accelerated dynamic behavior
for the heavier analogues, significant differences in the molecular
structure are caused by the halogen exchange reactions, including
the formation of an endo–endo substituted
Pacman fluorophosphane as well as dicationic species by phosphorus
halogen bond dissociation. The latter process can be regarded as redox
isomerism since two PIII atoms in 2X become
PV centers in the dications.