Multiple bonding versus cage formation in organophosphorus compounds: the gas-phase structures of tricyclo-P3(CBut)2Cl and PC–But determined by electron diffraction and computational methods

Abstract

The gas-phase structures of tricyclo-P₃(CBu^t)₂Cl and PC–Bu^t have been determined by electron diffraction and associated quantum chemical calculations. Efforts to obtain detailed solid-state data for tricyclo-P₃(CBu^t)₂Cl have been thwarted by inability to prepare suitable crystalline material. Additional calculations for another tricyclic isomer of P₃(CBu^t)₂Cl and for two phosphorus-containing cyclopentadiene derivatives with pseudo-planar five-membered rings show that the experimentally observed isomer is more stable by at least 52 kJ mol⁻¹. Calculations for the equivalent structures with P atoms replaced by CH fragments have demonstrated that a ring structure is more favourable by over 200 kJ mol⁻¹ compared to each of two cage structures.