A Class of Trinuclear Clusters with Carbonyl Bridging

The impetus for this work was the structure of a trinuclear complex with two carbonyl groups showing incipient triple bridging ‐ Cp2Rh3(CO)4−. Its structure, barrier to rotation of one Rh(CO)2− piece vs. the rest of the molecule, and the nature of the bridging carbonyl interaction are analyzed. Isolobal analogies form an interesting connection between this complex and a bridged isomer of the recently synthesized carbene complexes, Cp2Rh2(CO)2CR2, one isomer of Cp2Rh3(CO)3, and hypothetical carbyne complexes Cp2Rh2(CO)2CH+,−. A general bonding model for Cp2Rh2(μ‐CO)2X complexes is constructed. The model, rich in geometrical detail, allows minima for the bridging carbonyl groups bending toward and away from the bonded ligand X.