Synthesis and Characterization of a Metallacyclic Framework with Three Fused Five‐membered Rings

Polycyclic complexes containing a bridgehead transition metal are interesting species because the transition metal is shared by all the rings simultaneously. In this study, we present a novel osmium–bridgehead system with three fused five‐membered rings. This novel framework can be viewed as a 10‐atom carbon chain coordinating to the osmium center. In sharp contrast to the nonplanar organic analogue, this unique metallacycle exhibits good planarity, which was unambiguously verified by means of X‐ray diffraction. Interestingly, preliminary DFT calculations show that the aromaticity in the three 5MRs of these osmatricycles can be easily tuned by the ligand substitution. Finally, the broad UV/Vis absorption spectra of these novel polycyclic complexes were also reported. Missing link: A metallacyclic framework with three fused five‐membered rings (5MRs) was constructed (dotted box) from a 10‐atom carbon chain coordinating with a transition metal in the equatorial plane. This structure can be viewed as the missing link between a metallapentalyne, metallapentalene‐fused 3MR, metallapentalene‐fused 4MR, and metallapentalene‐fused 6MR.