A Multifunctional Pincer Ligand for Cobalt-Promoted Oxidation by N O.

The divalent cobalt complex of the diprotic pincer ligand bis-pyrazolylpyridine, (H L)CoCl , is dehydrohalogenated twice by LiN(SiMe ) in the presence of PEt to give monomeric S=1/2 LCo(PEt ) (1), fully characterized in the solid-state and solution as a square pyramidal monomer with a long axial Co-P bond. This 17-electron species reacts in time of mixing with N O to form L Co (μ-OPEt ) (2)+3 OPEt , the former the first example of phosphine oxide bridging two transition metals. The same products are formed from O , and divalent cobalt persists even in the presence of excess oxidant. Species (2) catalyzes oxygen atom transfer (OAT) for generation of O=PEt from PEt from either N O or O . Bridging and terminal cobalt oxo intermediates are suggested, and the electron donor power, and potential redox activity of the dianionic pincer ligand is emphasized.