H Abstraction/O Rebound or 3+2 Cycloaddition: Dichotomy of C-H Bond Activation by Transition Metal Oxides

摘要

Hydrocarbons, especially light alkanes, are the primary constituents of natural gas and crude oil. Selective oxidation of hydrocarbons is of fundamental and technological interest. Metal-oxo complexes are well-known active oxidants in a broad range from metalloenzyme families to heterogeneous metal oxide catalysts and homogeneous oxidants . Although it is generally believed that the selective oxidation of alkanes involves the splitting of C-H bonds, the detail mechanisms of C-H bond activation remain obscure. In present work, we have explored the reaction mechanisms based on the parent system, i.e. CH_4 activation by MnO_4~-. Scheme 1 illustrates two possible reaction pathways for the initial C-H activation: (a) conceited [3+2] cycloaddition-like and (b) hydrogen abstraction followed by oxygen rebound.