Open Access Dissertation
Date of Award
A series of redox non-innocent bis(aldimino)pyridine ligands were synthesized. These were then reacted with nickel(II) salts to form Ni[NNN]X2 complexes. Cyclic voltammograms of these nickel(II) complexes suggest that more reduced states can be achieved. Reduction of these nickel(II) complexes lead to distorted square planar complexes with the halide bent ~20° out of the plane. EPR suggests that spin density is located on the metal as g-values of >2.01 were obtained. This differs from previously reported analogous bis(ketimino)pyridine complexes, which show a ligand-based radical and nickel(II). DFT confirms that as the Npyr-Ni-X angle decreases, spin density on the nickel increases. Because of the imino proton as opposed to the imino methyl group, the halide can distort out of the plane and put the spin density on the nickel. Reaction with PhSSPh leads to the formation of (Ni(SPh)2)11. This is the first example of nickel(I) reductively splitting PhSSPh to form this product. Reaction with CS2 results in free ligand, suggesting that CS2 replaces [NNN]. No reactivity with CO2 was observed.
[NNN] was reacted with Ni(COD)2. [NNN]a formed a mixture of Ni[NNN](COD) and Ni[NNN]2. [NNN]b forms only Ni[NNN]2. In both cases, [NNN] ligand binds in a bidentate fashion to the nickel. Because of this, we moved to reduction of Ni[NNN]X. Reduction of Ni[NNN]X led to the formation of a dimer, (Ni[NNN])2. Each nickel is bound in a bidentate fashion to one ligand and bound through the imine bond of the other ligand. Reactivity with CS2 again leads to the formation of free ligand and an unknown paramagnetic nickel solid. This complex does not react with CO2.
Based on the CV data of Ni[NNN]X2, there are three-quasi-reversible reduction waves. In order to access the (Ni[NNN])1- state, we turned to electrochemistry. Cyclic voltammetry of Ni[NNN]X2 in the presence of CO2 shows an increase in catalytic current. Bulk electrolysis experiments show a low (<3%) Faradaic yield for CO and a high (89%) Faradaic yield for H2.
Reed, Blake, "Synthesis And Heteroallene Reactivity Of Bis(aldimino)pyridine Nickel Complexes In Four Different Oxidation States" (2016). Wayne State University Dissertations. 1580.