Intermetallic Interactions In A Series Of Multinuclear Late First-Row And Coinage Metal Complexes Supported By Pyridyldiimine-Derived Macrocyclic Ligands

Qiuran Wang, University of Pennsylvania

Abstract

The design of novel ligands that support multiple metal centers in close proximity to one another has gained increased attention in the past decade as a method of creating molecular models of heterogeneous surfaces and enzyme active sites. To this end, two multidentate macrocyclic ligands were developed. The ligands incorporated either two redox-active 1,1'-(4-(tert-butyl)pyridine-2,6-diyl)bis(ethan-1-imine) (PDI) or two redox-active (4-(tert-butyl)pyridine-2,6-diyl)dimethanimine (PDAI) moieties, linked through catenated chains of three CH2 groups that connect the imino nitrogen atoms. These structural elements provide both electronic and geometric flexibility to the multimetallic cores held by the ligands. In the first part of this dissertation, the study of the electronic flexibility of the ligands will be described. A series of bimetallic Fe, Co, and Ni complexes that span five cluster-electron counts (34 to 38 e– per cluster) supported by the PDI- and PDAI- derived macrocyclic ligands were synthesized and characterized. It was found that 1) the metal–metal bond order in the bimetallic core is tuned by adjusting the number of cluster electrons, and 2) the ligand oxidation state is tuned by a combination of an adjustment in the number of cluster electrons and an adjustment in the energy gap between metal d-manifolds and ligand π* orbitals. In the second part of this dissertation, a study of the geometric flexibility of the PDAI-derived ligand will be described, using a series of novel multinuclear Ag and Cu complexes. The ligand was shown to accommodate multimetallic coinage metal clusters that exhibit weak metallophilic interactions within cluster cores that range in nuclearity from 1 to 3. The geometric flexibility of the ligand allowed for 1) higher solution-phase symmetry than what is observed in the solid state for many of these complexes and 2) the atom-precise interconversion between [Cu2] and [Cu3] complexes. The work included in this dissertation demonstrates the electronic and geometric flexibility of these pyridyldiimine-derived macrocyclic ligands, and lays the fundamental knowledge for further studies on multimetallic complexes supported by these ligands.