Elongated Metal-Ligand Bonds Could Boost Catalysis

A multiply bonded diruthenium unit that forms multiple bonds with a terminal nitrogen ligand could serve as a general model for improving bimetallic catalysts, according to the scientists who discovered the complex (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200804397). John F. Berry of the University of Wisconsin, Madison, and colleagues created the highly unstable ruthenium nitrido complex (shown, phenyl groups omitted) by irradiating an azido compound, Ru₂(N,N′-diphenylformamidinate)₄N₃, with light. Spectroscopic analysis of the Ru=Ru≡N complex demonstrated that the Ru≡N bond is longer and weaker than analogous nitrido bonds in compounds with a single ruthenium center. The researchers note that the weaker bond is due to unprecedented electron delocalization throughout the Ru=Ru≡N unit. Berry says this type of tandem multiple bonding could become a general method for making the ligand more labile. The weak binding of the nitrido ligand in this compound suggests that similarly weak interactions occur in related dirhodium compounds, causing their catalytic activity to increase, he says. The discovery may therefore help decipher how dirhodium catalysts uniquely facilitate direct insertion of a carbene or nitrene into unreactive C–H bonds, Berry adds.