Coordination chemistry of molybdenum relevant to hydrodenitrogenation: Reactivity of Mo(PMe3)6 towards 6-membered heterocyclic aromatic nitrogen compounds involving C–H bond cleavage and η6-coordination

The reactivity of Mo(PMe3)6 towards 6-membered heterocyclic aromatic nitrogen compounds, namely pyridine, pyrazine, pyrimidine and triazine, has been investigated as part of an effort to define the coordination chemistry of molybdenum relevant to hydrodenitrogenation. For example, Mo(PMe3)6 reacts with pyridine to yield initially (η2-N,C-pyridyl)Mo(PMe3)4H, an uncommon example of an η2-pyridyl–hydride complex. The formation of (η2-N,C-pyridyl)Mo(PMe3)4H is reversible and treatment with PMe3 regenerates Mo(PMe3)6 and pyridine. At elevated temperatures, (η2-N,C-pyridyl)Mo(PMe3)4H dissociates PMe3 and converts to the η6-pyridine complex (η6-pyridine)Mo(PMe3)3. Pyrazine, pyrimidine and 1,3,5-triazine likewise react with Mo(PMe3)6 to yield (η2-N,C-pyrazinyl)Mo(PMe3)4H, (η2-N,C-pyrimidinyl)Mo(PMe3)4H and (η2-N,C-triazinyl)Mo(PMe3)4H, respectively. At elevated temperatures (η2-N,C-pyrazinyl)Mo(PMe3)4H and (η2-N,C-pyrimidinyl)Mo(PMe3)4H dissociate PMe3 and convert to (η6-pyrazine)Mo(PMe3)3 and (η6-pyrimidine)Mo(PMe3)3 in which the heterocycle coordinates to molybdenum in an unprecedented η6-manner.

Mo(PMe3)6 reacts with 6-membered heterocyclic aromatic nitrogen compounds (NHetH = pyridine, pyrazine, pyrimidine, and triazine) to yield (η2-NHet)Mo(PMe3)4H resulting from cleavage of a C–H bond adjacent to the nitrogen atom. The C–H bond cleavage is reversible and (η2-NHet)Mo(PMe3)4H converts to (η6-NHetH)Mo(PMe3)3 upon heating for NHetH = pyridine, pyrazine, and pyrimidine.Figure optionsDownload as PowerPoint slide