Abstract
Investigation of the hydrodenitrogenation (HDN) of aromatic N-heterocycles such as pyridines and quinolines at the molecular level is of fundamental interest and practical importance, as this transformation is essential in the industrial petroleum refining on solid catalysts. Here, we report the HDN of pyridines and quinolines by a molecular trinuclear titanium polyhydride complex. Experimental and computational studies reveal that the denitrogenation of a pyridine or quinoline ring is easier than the ring-opening reaction at the trinuclear titanium hydride framework, which is in sharp contrast with what has been reported previously. Hydrolysis of the pyridine-derived nitrogen-free hydrocarbon skeleton at the titanium framework with H2O leads to recyclization to afford cyclopentadiene with the generation of ammonia, while treatment with HCl gives the corresponding linear hydrocarbon products and ammonium chloride. This work has provides insights into the mechanistic aspects of the hydrodenitrogenation of an aromatic N-heterocycle at the molecular level.
Highlights
Investigation of the hydrodenitrogenation (HDN) of aromatic N-heterocycles such as pyridines and quinolines at the molecular level is of fundamental interest and practical importance, as this transformation is essential in the industrial petroleum refining on solid catalysts
We have found that the nitrogen atom in a pyridine or quinoline ring can be extruded under mild conditions at the trinuclear titanium framework through reduction of a HC = N unit followed by cleavage of the two C−N bonds
The present hydrodenitrogenation of pyridines and quinolines by the trinuclear titanium hydride cluster 1 stands in sharp contrast with the previously reported reactions of transition metal hydride complexes with N-heterocycle compounds, in which the cleavage of a C−N bond was not observed[24,25,26,27,28,29,30,31,32,33,34,35,36,37]
Summary
Investigation of the hydrodenitrogenation (HDN) of aromatic N-heterocycles such as pyridines and quinolines at the molecular level is of fundamental interest and practical importance, as this transformation is essential in the industrial petroleum refining on solid catalysts. In view of the fact that the industrial HDN process might involve transition metal hydrides as the true active species, investigation of the reactions of molecular transition metal hydrides with aromatic N-heterocycles is especially of interest and importance, as this approach may provide a useful entry into homogeneous HDN systems Toward this end, a number of transition metal hydride complexes have been examined with aromatic N-heterocycles such as pyridines and quinolines, and various reaction patterns such as coordination, C−H activation, hydrogenation, hydroboration, and hydrosilylation have been observed[24,25,26,27,28,29,30,31,32,33,34,35,36,37]. Exhibit an unusually high activity for the activation of some very stable chemical benzene ring at bonds, such as cleaving room temperature[38,39,40,41,42]
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