In this talk I will discuss the geometric and electronic structures of Group 13 complexes containing redox-active ligands. As a first example, square planar Al(III) and Ga(III) complexes containing the bis(imino)pyridine ligand (I2P) will be presented. Delocalization of ligand p-symmetry electrons over both the ligand and the metal centers will be discussed as the origin of the electronic preference for the square planar geometry, along with experimental evidence for ring current effects observed in the proton NMR spectrum. Previous observations of ring current effects in square planar complexes have included transition metal ions. The ability of these complexes to generate ligand-based hydride intermediates from two electrons and one proton enables electrocatalytic H2 evolution from protons under 1 atm Ar, or NH3 evolution from N2 under 1 atm of N2, at -1.16 V vs. SCE, in THF solution. A second example to be discussed are octahedral complexes of Al, Ga, and In(III) which each contain two I2P ligands and have the form [(I2P)2M]n, where M = Al(III), Ga(III), or In(III), and n spans 3- up to 2+ depending on the charge of each I2P ligand. The charge series can be accessed using cyclic voltammetry or chemically. Analysis of the CV’s and the near infra-red (NIR) spectra associated with the octahedral complexes indicates that the mixed-valent members of the charge series, [(I2P0)(I2P-)M]2+, [(I2P-)(I2P2-)M], and [(I2P2-)(I2P3-)M]2- have completely delocalized electronic structures, where the Al and Ga complexes satisfy the description of Class III mixed-valency and In complexes are Class II/III. This work demonstrates that main group elements paired with redox-active ligands can mediate strong electronic coupling that implies metal-ligand covalency.

Unusual geometric and electronic structures and reactivity in redox active ligand complexes of group 13

2019 Spring National Meeting

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