Catalytic N-H Bond Activation and Breaking by a Well-Defined Co1IIO4 Site of a Heterogeneous Catalyst

Catalytic N-H bond activation and breaking by well-defined molecular complexes or their heterogeneous analogues is considered to be a challenge in chemical science. Metal(0) nanoparticles catalytically decompose NH3; they are, however, ill defined and contain a range of contiguous metal sites with varying coordination numbers and catalytic properties. So far, no well-defined/molecular Mn+-containing materials have been demonstrated to break strong N-H bonds catalytically, especially in NH3, the molecule with the strongest N-H bonds. Recently, noncatalytic activation of NH3 with the liberation of molecular H-2 on an organometallic molybdenum complex was demonstrated. Herein, we show the catalytic activation and breaking of N-H bonds on a singly dispersed, well-defined, and highly thermally resistant (even under reducing environments) (Co1O4)-O-II site of a heterogeneous catalyst for organic (ethylamine) and inorganic (NH3, with the formation of N-2 and H-2) molecules. The single-site material serves as a viable precursor to ultrasmall (2.7 nm and less) silica-supported cobalt nanoparticles; thus, we directly compare the activity of isolated cationic cobalt sites with small cobalt nanoparticles. Density functional theory (DFT) calculations suggest a unique mechanism involving breaking of the N-H bonds in NH3 and N-N coupling steps taking place on a Co1O4 site with the formation of N2H4, which then decomposes to H-2 and N2H2; N2H2 subsequently decomposes to H-2 and N-2. In contrast, Co1N4 sites are not catalytically active, which implies that the ligand environment around a single atom of a heterogeneous catalyst largely controls reactivity. This may open a new chapter for the design of well-defined heterogeneous materials for N-H bond-activation reactions.