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

The reaction of TaMe 3 Cl 2 with the rigid acridane-derived trisamine H 3 NNN yields the tantalum(V) complex [TaCl 2 (NNN cat )]. Subsequent reaction with dioxygen results in the full four-electron reduction of O 2 yielding the oxido-bridged bimetallic complex [{TaCl 2 (NNN sq )} 2 O]. This dinuclear complex features 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 O 2 activation was investigated by DFT calculations revealing initial binding of O 2 to the tantalum(V) center followed by complete O 2 scission to produce a terminal oxido-complex.