Late first-row transition metal complexes of a tetradentate pyridinophane ligand: electronic properties and reactivity implications.

The synthesis and structural comparison are reported herein for a series of late first-row transition metal complexes using a macrocyclic pyridinophane ligand, N,N′-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane (tBuN4). The tBuN4 ligand enforces a distorted octahedral geometry in complexes [(tBuN4)MII(MeCN)2](OTf)2 (M = FeII, CoII, NiII, CuII), [(tBuN4)ZnII(MeCN)(OTf)](OTf), and [(tBuN4)FeIII(OMe)2](OTf), with elongated axial M–Namine distances compared to the equatorial M–Npy distances. The geometry of [(tBuN4)CuI(MeCN)](OTf) is pentacoordinate with weak axial interactions with the amine N-donors of tBuN4. Complexes [(tBuN4)M(MeCN)2](OTf)2 (M = Fe, Co) exhibit magnetic properties that are intermediate between those expected for high spin and low spin complexes. Electrochemical studies of (tBuN4)M complexes suggest that tBuN4 is suitable to stabilize CoI, NiI, CoIII, FeIII solvato-complexes, while the electrochemical oxidation of (tBuN4)NiCl2 complex leads to formation of a NiIII species, supporting the...