Reversible Intramolecular Coupling of the Terminal Borylene and a Carbonyl Ligand of [Cp(CO)2MnBtBu]

Cyclic complex 2 with bridging carbonyl ligands was synthesized from a facile and reversible intermolecular carbonyl–borylene ligand coupling reaction at room temperature. Complex 2 exhibits an unprecedented coordination mode for boron–metal complexes, which is also reflected in its remarkable 11B NMR chemical shift of −57.2 ppm. Findings from spectroscopic, X‐ray, and computational studies are presented, along with a proposed mechanism.