Trimerization and cyclization of reactive P-functionalities confined within OCO pincers

Generation and reactivity of an elusive base-stabilised phosphinidene

Reduction of phosphorus dichloride 6, supported by the diaryloxyphenyl group (OCO) featuring two bulky phenoxy wingtips, by PMe₃, generates a reactive intermediate that behaves as a base-stabilized phosphinidene (OCO)P (5). Warming up a solution of this species in toluene to room temperature results in trimerization to give the isolable cyclic triphosphine [(OCO)P]₃, whereas in situ trapping with 2,3-dimethylbutadiene-1,3 afforded a 3,4-dimethylphospholene-3. Investigation of the reduction of 6 by the phosphine PMe₃ by NMR led to the observation of a persistent species between -10 °C and 10 °C. A DFT study of this process suggests that this compound cannot be the proposed phosphinidene 5, and is more likely the diphosphine (OCO)ClP-PCl(OCO) (12). Attempted reduction of 5 by the bulky carbene IPr resulted in unusual electrophilic substitution in the carbene olefin backbone by the chlorophosphinyl group.