Unraveling Terminal Cobalt–Antimony Double Bond: Breaking New Ground in Heavy Pnictogen Multiple Bonds

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ABSTRACT Terminal pnictinidene complexes featuring heavy group 15 elements (Sb, Bi) doubly bonded to transition metals remain exceptionally elusive compared to their lighter congeners. Herein, we demonstrate that N‐heterocyclic carbenes (NHCs) can effectively cleave the Sb═Sb double bond of distibenes to yield monomeric, zwitterionic stibinide species. Subsequent transfer of the antimony moiety to a cobalt center generates a terminal cobalt–stibinidene complex. Structural analysis reveals a very short Co─Sb bond distance, which is corroborated by Wiberg and Mayer bond indices as well as frontier molecular orbital and natural bond orbital analyses, providing compelling evidence for an unprecedented covalent Co═Sb double bond. In addition, we demonstrate that this compound reacts with an alkyne in a (2π+2π) cycloaddition and with phenyl azide to form a three‐membered ring, providing initial insight into its reactivity and drawing parallels with reactivity patterns established for lighter phosphinidene analogs. This work establishes a rational route to stabilize heavy‐element multiple bonds via a controlled and operationally‐simple distibene cleavage.

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