UC Irvine

Within the active sites of metalloenzymes the timely transfer of protons and electrons to the appropriate location enables chemical transformations under ambient conditions. Redox activity and non-covalent interactions have been found to play pivotal roles in tuning the active site for functionality and selectively. Because of their biological significance, redox activity and non-covalent interactions have been incorporated in synthetic systems to impart electronic and structural features necessary to develop small molecules towards the goal of concerted proton electron transfer (CPET) which require multiple electrons. Key to a metalloenzyme’s function is control over the primary and secondary coordination spheres. The primary sphere is defined as the ligands bound directly to the metal center, whereas the secondary sphere consists of the noncovalent interactions within the local environment. Recent advances have demonstrated the importance of hydrogen bonds (H-bonds) within metalloenzyme active sites and small molecule model complexes. This dissertation describes the use of a tridentate, redox active ligand with hydrogen-bond (H-bond) acceptors and steric bulk to prepare first row transition metal complexes. This ligand precursor, H3ibaps, (N,N’-(azanediyl bis(2,1-phenylene)) bis(2,4,6-triisopropyl-benzene-sulfonamide) was previously reported to prepare [FeII(ibaps)(bpy)]─ and [GaIII(ibaps)(bpy)]─ complexes with enhanced electronic properties. Additionally, the H-bond accepting ability of the sulfonamido groups was demonstrated in the previously reported [NiII(ibaps)(OH2)]─ complex. This work describes three routes to enhance the redox activity of a metal complex for multielectron processes: 1) use of a redox active ligand in Cu complexes, 2) formation of multinuclear species, 3) introduction of a metal capable of multiple oxidation events. Chapter 1 provides context within the field of redox active ligand complexes and Cu-complexes capable of reactivity toward substrates as well as those with intramolecular H-bonds. Chapter 2 describes the synthesis and characterization of a series of [CuII(ibapscat)(L)]─ complexes where L = DBU (1,8-diazabicyclo(5.4.0)unde-7-ene), TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene), and TMG (1,1,3,3-tetramethylguanidine), and water. Each complex was observed to undergo two oxidations by cyclic voltammetry (CV). Chapters 3 and 4 describe the chemical oxidation of all four Cu-complexes by one electron and two electrons, respectively. These three chapters (2 – 4) describe mononuclear Cu-complexes designed to achieve high oxidation levels through the use of a redox active ligand. The electronic structure as a function of structural properties is investigated using a variety of spectroscopic techniques. The second route to enhancing redox properties of metal complexes mentioned above, is through formation of multinuclear species as pursued in Appendix A which describes a trinuclear [CuII(ibapscat)(OAc)]2─ complex. The third route for pursuing high valent species is through the use of a metal ion that is not limited to three oxidation states as is the case for Cu(III/II/I). Appendix B describes a series of [MnII(ibapscat)(L)]─ complexes where L = phen (1,10-phenanthroline), bpy (2,2’-bipyridine), terpy (2,2’:6’,2”-terpyridine), and water, for this purpose.