Remote Multiproton Storage within a Pyrrolide-Pincer-Type Ligand.

A chemically non-innocent pyrrole-based trianionic (ONO)(3-) pincer ligand within [(pyr-ONO)TiCl(thf)2 ] (2) can access the dianionic [(3H-pyr-ONO)TiCl2 (thf)] (1-THF) and monoanionic [(3H,4H-pyr-ONO)TiCl2 (OEt2 )][B{3,5-(CF3 )2 C6 H3 }4 ] (3-Et2 O) states through remote protonation of the pyrrole γ-C π-bonds. The homoleptic [(3H-pyr-ONO)2 Zr] (4) was synthesized and characterized by X-ray diffraction and NMR spectroscopy in solution. The protonation of 4 by [H(OEt2 )2 ][B{C6 H3 (CF3 )2 }4 ] yields [(3H,4H-pyr-ONO)(3H-pyr-ONO)Zr][B{3,5-(CF3 )2 C6 H3 }4 ] (5), thus demonstrating the storage of three protons.