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.