Synthesis of Annelated Phospholes through Intramolecular C?H Activation by Monovalent Phosphorus

Electrophilic terminal phosphinidene complexes Ar‐Ar‐P‐W(CO)₅] (Ar‐Ar: biaryl or an analogue thereof) undergo a spontaneous insertion of the phosphorus atom into the vicinal C? H bonds to give annelated phospholes. Twelve examples are described, including biphenyl, thienyl, pyrrolyl, and benzofuryl groups as biaryl moieties. The activation energy of the insertion reaction is quite low (about 2 kcal mol^?1).