Dioxygen Splitting by a Tantalum(V) Complex Ligated by a Rigid, Redox Non-innocent Pincer Ligand

Reaction of TaMe3Cl2 with the rigid acridane-derived trisamine H3NNN (1) yields the tantalum(V) complex [TaCl2(NNNcat)] (2). Subsequent reaction with dioxygen results in the full four-electron reduction of O2 yielding the oxo-bridged bimetallic complex [{TaCl2(NNNsq)}2O] (5). This dinuclear complex exhibits an open-shell ground state due to partial ligand oxidation and was comprehensively characterized by single crystal X-ray diffraction, LIFDI mass spectrometry, NMR, EPR, IR and UV/VIS/NIR spectroscopy. The mechanism of O2 activation was investigated by DFT calculations revealing initial binding of O2 to the tantalum(V) center followed by complete O2 scission to produce a terminal oxo-complex.