Cleavage of an Aromatic C-C Bond in Ferrocene by Insertion of an Iridium Nitrido Nitrogen Atom

The intermolecularcleavage of C-C bonds is arare event.Herein, we report on a late transition-metal terminal nitrido complex,which upon oxidation undergoes insertion of the nitrido nitrogen atominto the aromatic C-C bond of ferrocene. This reaction pathwas confirmed through N-15 and deuterium isotope labelingexperiments of the nitrido complex and ferrocenium, respectively.Cyclic voltammetry and UV/vis spectroscopy monitoring of the reactionrevealed that oxidation is the initial step, yielding the tentativeradical cationic nitrido complex, which is experimentally supportedby extended X and Q-band electron paramagnetic resonance (EPR) andENDOR, UV/vis, vT H-1 NMR, and vibrational spectroscopicdata. Density functional theory (DFT) and multireference calculationsof this highly reactive intermediate revealed an S = 1/2 ground state. The high reactivity can be traced to the increasedelectrophilicity in the oxidized complex. Based on high-level PNO-UCCSD-(T)calculations and UV/vis kinetic measurements, it is proposed thatthe reaction proceeds by initial electrophilic exo attack of the nitridonitrogen atom at the cyclopentadienyl ring and consecutive ring expansionto a pyridine ring.

Automated summary

The rare intermolecular cleavage of C-C bonds was observed in a study on a late transition-metal terminal nitrido complex, which undergoes insertion of the nitrido nitrogen atom into the aromatic C-C bond of ferrocene upon oxidation. The reaction path was confirmed using isotope labeling experiments and various spectroscopic techniques. The high reactivity of the oxidized complex can be attributed to its increased electrophilicity.