141753-80-2Relevant academic research and scientific papers
Homogeneous models for hydrodenitrogenation catalysis
Weller, Keith J.,Fox, Peter A.,Gray, Steven D.,Wigley, David E.
, p. 3139 - 3163 (2008/10/09)
Hydrodenitrogenation (HDN) catalysis is the process of removing nitrogen from petroleum feed-stocks in the form of NH3 to provide more processable and environmentally compatible liquid fuels. In practice, HDN is carried out simultaneously with other catal
Carbon-nitrogen bond cleavage in an η2(N,C)-pyridine complex induced by intramolecular metal-to-ligand alkyl migration: Models for hydrodenitrogenation catalysis
Gray, Steven D.,Weller, Keith J.,Brack, Michael A.,Briggs, Paula M.,Wigley, David E.
, p. 10678 - 10693 (2007/10/03)
The reaction of the η2(N,C)-pyridine complex [η2(N,C)-2,4,6-NC5tBu3H 2]Ta(OAr)2Cl (1, Ar = 2,6-C6H3iPr2) with LiBEt3H affords the C-N bond scission product Ta(=NCtBu=CHCtBu=CHCHtBu)(OAr)2 (2). The reactions of [η2(N,C)-2,4,6-NC5tBu3H 2]Ta(OAr)2Cl (1) with carbon nucleophiles RLi or RMgX provide the alkyl derivatives [η2(N,C)-2,4,6-NC5tBu3H 2]Ta(OAr)2R [R = Me (3), Et (4), nPr (5), nBu (6), and CH2SiMe3 (7)]. Complexes 3-6 represent the kinetic products of the reaction since upon their thermolysis, alkyl migration from metal to ligand occurs and the C-N bond cleavage compounds Ta(=NCtBu=CHCtBu=CHCtBuR)(OAr)2 [R = Me (8), Et (9), nPr (10), nBu (11)] are formed. Kinetic and mechanistic studies of the 3→8 rearrangement reveal that methyl migration is strictly intramolecular. Further studies Of Ta(=NCtBu=CHCtBu=CHCtBuMe)(OAr)2 (8) reveal that this complex subsequently rearranges to afford the eight-membered metallacycle Ta(=NCtBu=CHCtBu=CHCtBuHCH 2)(OAr)2 (12), which further decomposes to givejhe metallapyridine dimer [Ta(μ-NCtBu=CHCtBu=CH)(OAr)2]2 (13) and tBuCH=CH2. Synthetic and mechanistic studies on the 8 → 12 → 13 rearrangement reveal the source of the tBuCH=CH2 through labeling experiments, allow the isolation of an adduct of 12, viz. Ta(=NCtBu=CHCtBu=CHCtBu- HCH2)(OAr)2·2NCMe (12-NCMe), and suggest a mechanistic scheme to account for these rearrangements. Complexes 2, 4, and 13 have been structurally characterized. Ta(=NCtBu=CHCtBu=CHCHtBu)(OAr)2 (2) crystallizes in the monoclinic space group P21In (No. 14) and displays a highly localized metallacyclic structure with an imido nitrogen linkage characterized by a Ta-N-C angle of 145.7(6)°. [η2(N,C)-2,4,6-NC5tBu3H 2]Ta(OAr)2Et (4) crystallizes in the monoclinic space group P21In (No. 14) and is characterized by an interruption of aromaticity to the heterocyclic ring through a 1,3-diene-like π electron localization. Metallapyridine [Ta(μ-NCtBu=CHCtBu=CH)(OAr)2]2 (13) crystallizes in the triclinic space group P1? (No. 2) and reveals an extremely crowded structure with a π localized, formal [μ-NCtBu=CHCtBu=CH]3- μ-imido ligand. The reactions of this model system delineate one process by which heterocyclic C-N bonds are cleaved and offer new insight as to how nitrogen heterocycles may be further degraded after C-N bond cleavage in hydrodenitrogenation catalysis.
