Tetranuclear Titanium Nitride Cluster: Dinitrogen Cleavage Under Mild Conditions and Its Reactivity

Heating the readily available trinuclear Ti dinitrogen complex [{TiCp*(µ-Cl)}₃(µ₃-η¹: η²: η²-N₂)] 1(Cp* = η⁵-C₅Me₅), originally reported by C. Yélamos and J. Jover, in benzene at 80 °C leads to the cleavage of N≡N bond, forming a tetranuclear titanium nitride cluster [{TiCp*}₄Cl(µ-Cl)₃(µ₃-N)₂] 2. The structure of 2 was confirmed by single-crystal X-ray diffraction analysis. Kinetics study and density functional theory (DFT) calculations indicate that the energy barrier for the NN bond cleavage in the transformation from 1 to 2 is about 26 kcal mol^-1. Complex 2 exhibits reactivity toward various electrophiles, producing a range of nitrogen-containing compounds in the presence of air, while concurrently regenerating Ti(IV) salts. Furthermore, complex 2 reacts with pinacolborane, leading to the formation of N-B bond derivatives [{TiCp*(µ-NBPin)Cl}₂] 3. When complex 2-¹⁵N is treated with pyridine or 4-dimethylaminopyridine (DMAP), it dissociates to form a bent trinuclear Ti nitrido complex [{TiCp*}₃Cl₃(L)₂(µ-¹⁵N)₂] 4-L (L = py or DMAP).