Cyclic Denitrogenation of N-Heterocycles Applying a Homogeneous Titanium Reagent

A transient titanium alkylidyne (PNP)Ti⋮CtBu (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-) offers an excellent opportunity to study an industrially important reaction such as the hydrodenitrogenation (HDN) of N-heterocycles present in crude oil. This type of molecule has allowed us to quantitatively remove the nitrogen, in a cyclic manner and under mild conditions, from heterocycles such as pyridine and picolines, resulting in formation of the corresponding arene and a titanium nitrogen-based product. Applying this complex for N-removal of pyridines avoids the use of drastic reaction conditions, over saturation of substrate (hydrogenation), and the use of hydrogen, all of which are common limitations in the HDN industrial setting. Isotopic labeling and mechanistic insights into both the C−N bond rupture and denitrogenation of N-heterocycles are also discussed in this report.