ABSTRACTSYNTHESIS AND REACTIVITY STUDIES TOWARDS SMALL MOLECULE ACTIVATION OF PYRIDYLDIIMINE-DERIVED MACROCYCLIC DIIRON COMPLEXES Tianchang Liu Neil C. Tomson Multinuclear metallic cluster complexes have drawn lots of research interests given their promise in drawing analogies to surface species and metalloenzyme sites. In particular, cluster complexes supported by ligand scaffolds that are specifically designed to allow for fine-tuning steric and electronic environments during chemical transformations, have great potential in mediating challenging chemical transformations of inert small molecules but are still in its infancy. To this goal, a di-nucleating ligand scaffold was developed, which incorporates two redox-active 1,1’-(4-(tert-butyl)pyridine-2,6-diyl)bis(ethan-1-imine) (PDI) through catenated chains of three CH2 groups that connect the imino nitrogen atoms. This ligand presents high flexibility in accommodating the changes of geometric and electronic environment during certain chemical transformations. In this dissertation, we discuss the synthesis and reactivity studies towards small molecule substrates of a series of diiron complexes supported by this ligand scaffold. In Chapter 2, synthesis and characterization of diiron bridging dinitrogen complexes will be described, the acute Fe-CtN2-Fe bond angles is reminiscent of α-N2 as a key intermediate in Haber-Bosch process. In Chapter 3, preliminary reactivity studies of a diiron bridging dinitrogen complex ([Fe2N2]) towards various nitrogenous substrates will be described, characterization data of the reaction products suggest diverse N–H and N–N bond activation that shows promise in development of catalytic N–N bond cleavage and ammonia oxidation cycles. In Chapter 4, direct oxidative addition of alkyne-adjacent C(sp)–C(sp2/3) bonds will be described, affording thermodynamically favorable products with unique regioselectivity. The activation products are further shown to undergo hydrofunctionalization reactions to yield corresponding organic product and reforms [Fe2N2], thereby achieving synthetic cycles. Finally in Chapter 5, development of a stepwise C–C σ-bond metathesis process between diarylacetylene compounds will be described. C–C σ-bond oxidative addition, R-group exchange, and alkyne reductive elimination were identified as three elementary steps and achieved via stoichiometric studies. A stepwise C–C σ-bond metathesis process of diarylacetylene substrates was realized using a three-component system including [Fe2N2], Lewis acid and oxidant.