Redox state switching of transition metals by deprotonation of the tridentate ligand 2,6-bis(imidazol-2-yl)pyridine

Abstract

The chemistry of the ligand 1, 2,6-bis(imidazol-2-yl)pyridine with manganese, cobalt, nickel and ruthenium has been investigated. The ligand binds as a meridional tridentate ligand as shown by the crystal structures of [Mn(1)₂](CF₃SO₃)₂·Et₂O and [Ru(1)₂](PF₆)₂·2CH₃CN·H₂O. The coordinated ligand is deprotonated in mildly basic solution, and this leads to a drop in the metal M(III)/M(II) reduction potential for cobalt and ruthenium of roughly 1.3 V. The crystal structure of Na₂(PPN)[Co(1 − 2H)₂]₂(OH)·MeOH·2H₂O confirms the deprotonation and shows sodium to bind to the deprotonated nitrogen atoms. No stabilisation of the M(III) oxidation state was observed for nickel and manganese.