Cyclization of a 1,4-Diborabutadiene Ligand with Both Atoms of CO

A 1,4-dibora-1,3-butadiene iron complex was successfully synthesized through the stoichiometric reaction of an iron bis(borylene) complex with diphenylacetylene. This complex was treated with CO and PMe3, which led to the formation of an unusual six-membered B2C3O ylidic ring bound to both the PMe3 group and zerovalent iron center. The reaction is a very rare example of the incorporation of both atoms of CO into a ring system.