Chemistry at the Alkyne–Carbene Intersection: A Metallacyclobutene−η³‑Vinylcarbene Equilibration

Synthesis of a sterically congested metallacyclobutene complex has led to the first observation of metallacyclobutene−η³-vinylcarbene equilibration. The structure of the η³-vinylcarbene complex was elucidated by spectroscopy, HRMS, and ab initio computations. The vinylcarbene complex was trapped by reactions with ethyl diazoacetate and (C₅H₅)­Co­(PPh₃)₂ to give cobalt–diene and dicobalt complexes, respectively.