Doctor of Philosophy, The Ohio State University, 2023, Chemistry

Energy demands from increasing population are expected to double by 2050 and more than triple by the end of 2100. The urgent need for renewable and carbon-free energy sources demands scientists to pursue alternative ways to replace petroleum, coal, and natural gas as energy sources. Solar fuels have the potential to serve as an outstanding source of energy, since the energy from sunlight that reaches the Earth every hour is 173,000 terawatts. One key factor required to utilize solar fuels is to increase the ability of the light-harvesting process and the chemical bond-forming reactivity of photocatalysts. This dissertation demonstrates the design and characterization of dirhodium Rh2(II,II) complexes for photocatalysis with red light and the effect of ligand modification on the electronic structure and steric hindrance on the systems, as well as their ability for solar energy storage through the production of hydrogen, a clean fuel. In Chapter 4, a series of three dirhodium complexes with varying electron donating abilities of the formamidinate ligands were synthesized with general formula cis–[Rh2(DPhB)2(bncn)2](BF4)2 (DPhB = diphenyl-formamidinate, bncn = benzo[c]cinnoline). These complexes were found to act as single-molecule photocatalysts for H2 production in the presence of 0.1 M p-toluenesulfonic acid and the sacrificial electron donor BNAH (1-benzyl-1,4-dihydronicotinamide). The most efficient catalyst in this series is able to achieve turnover numbers (TONs) up to 250 upon 24 h irradiation with red light. The one-component catalytic system does not require any other catalyst, electron relay, or light absorber. Upon excitation, these complexes are able to store two electrons on each molecule after two stepwise reductive quenching steps by BNAH and provide protonation sites for the catalysis to generate H2 to proceed. These properties are essential for the complexes to act as single-molecule photocatalysts. The substitution of the bridging ligands affects (open full item for complete abstract)

Committee: Claudia Turro (Advisor); Yiying Wu (Committee Member); Christine Thomas (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2020, Chemistry

Formic acid, HCOOH, is an important product that results from the 2e−/2H+ reduction of CO2, since it has applications in fields that include the preservative and textile industries and it can also serve as a fuel that is carbon neutral. Partial paddlewheel dirhodium complexes represent a robust platform to develop CO2 reduction catalysts, as these complexes possess multiple low energy metal- and ligand-centered unoccupied frontier molecular orbitals to store redox equivalents. Therefore, the present work focuses on the design of a series of partial paddlewheel Rh2II,II complexes to better understand the steric and electronic requirements imposed by the ligand environment around the Rh2II,II core on CO2 reduction catalysis. Two Rh2II,II complexes were synthesized which contain the deprotonated 6-hydroxy-2-methylpyridine (mhp–) as the bridging ligand in cis–H,T–[Rh2(mhp)2(L)2]2+, with L = 1,10-phenanthroline (phen; Rh2-phen2) and dipyrido[3,2-f:2′,3′- h]quinoxaline (dpq; Rh2-dpq2) as chelating diimine ligands. Although Rh2-phen2 and Rh2-dpq2 feature similar molecular structures, selective electrocatalytic conversion of CO2 to HCOOH was achieved only with the former, resulting in 60 ± 5 x 10−6 mol of HCOOH and 4.3 ± 0.4 x 10−6 mol of H2, whereas Rh2-dpq2 resulted in only 7 ± 0.3 x 10−6 mol of H2. Mechanistic studies point to an axial Rh2II,I−H hydride as an intermediate with both complexes, however, H/D kinetic isotope effect (KIE) experiments suggest the insertion of CO2 in to the Rh2II,I−H bond takes place only in Rh2-phen2. In addition, the reduction of the dpq ligands in Rh2-dpq2 is followed by protonation of the ligand pyrazine nitrogen atoms, making the electrons provided by the dpq-centered reduction(s) unavailable for catalytic events taking place at the dirhodium core. The protonation of the reduced dpq ligands is also expected to affect the hydricity of the Rh2-H intermediate, thus affecting the subsequent CO2 insertion step. A second series of Rh2II,II com (open full item for complete abstract)

Committee: Claudia Turro (Advisor); James Cowan (Committee Member); Hannah Shafaat (Committee Member) Subjects: Chemistry

Doctor of Philosophy, The Ohio State University, 2017, Chemistry

Cancer is a disease that affects the lives of millions of people across the word. Current FDA approved treatments are not targeted enough to only treat the cancer without producing systematic toxicity and severe side effects, clearly showing that drugs that are more selective for cancer are needed. Photodynamic therapy (PDT) and photochemotherapy (PCT) were developed as a means to better target cancer only. Both PDT and PCT utilize a laser light source to activate a sensitizer at the location of the cancer, this allows for spatiotemporal control. Between the two therapies, three mechanisms of action can be attained: singlet oxygen production, ligand exchange for the ability to bind to biomolecules, or redox chemistry with DNA or biomolecules. Other ways to target cancer are also being explored through selective DNA mismatch detection. The work herein will focus on developing Rh2(II,II) complexes as potential PCT agents as well as targeted mismatch DNA detectors. Cis-H,H-[Rh2(OCCH3NH)2(LL)(CH3CN)4]2+ (LL = dppz, 1 and dppn, 2) were synthesized and characterized. Irradiation of complexes 1 and 2 followed by 1H NMR showed that the photoproducts Cis-H,H-[Rh2(OCCH3NH)2(CH3CNeq)(D2Oeq)(DD)]2+ (DD = dppz, 5a and dppn, 6a) were produced as 1 equivalence of CH3CN was exchanged for a D2O molecule. Complex 2 was found to have a 0.0033(1) photo-aquation quantum yield when measured with 450 nm irradiation. This was found to be an order of magnitude smaller compared to complex 1, which was measured to be of 0.040(3) with 450 nm irradiation. The lower photo-aquation quantum yield of 2 arises from the fact that it has other pathways to deactivate because it can also produce 1O2. Quantification of 1O2 production for 2 was determined to be 0.22(7), which is still better than the FDA approved Photofrin®. Thermal denaturation and relative viscosity studies with complex 2 show a p-stacking interaction with double-stranded DNA consist with intercalation, but titrations done with the (open full item for complete abstract)

Committee: Claudia Turro (Advisor) Subjects: Chemistry

Master of Science, The Ohio State University, 2007, Chemistry

The ability of Rh2(μ-O2CCH3)4 (1), cis-[Rh2(μ-O2CCH3)2(CH3CN)6]2+ (2), cis-[Rh2(µ-O2CCH3)2(dppz)(η1-O2CCH3)(CH3OH)]+ (dppz = dipyrido[3,2-a:2',3'-c]phenazine) (3), and cis-[Rh2(µ-O2CCH3)2(bpy)(dppz)]2+ (bpy = 2,2'-bipyridine) (4) to transverse a membrane bilayer was determined through quenching of DNA-bound SYBR Green I (SG) encapsulated within the interior of a vesicle. For comparison, quenching studies were performed with the known DNA binders ethidium bromide (EtBr), methyl viologen (MV2+), Hoechst 33258 and 2-methyl-antrhacene (2-Me-An). Emission quenching experiments were performed with DNA-bound SG (SG-DNA) free solution to determine the ability of the known DNA-binding compounds and the dirhodium series to affect the luminescence of the dye. The known minor groove binder Hoechst 3328 produced the most quenching of SG-DNA, likely due to displacement of the dye from the duplex. Within the dirhodium series, the degree of quenching correlates to the DNA binding constant of each complex. Complex 3, with the largest kb, produced the greatest quenching of SG-DNA. Each of the complexes in the dirhodium series can quench SG-DNA emission through various mechanisms, including displacement, energy transfer, and charge transfer. In each case, close proximity to the SG-DNA emissive species is a requirement. Therefore, a correlation between the association of each complex in the series with SG-DNA and its quenching ability is not unexpected. When SG-DNA was encapsulated in POPC vesicles, compounds added to the outside of the vesicles can only quench the SG-DNA emission if they are able to penetrate the bilayer membrane. The vesicles with encapsulated DNA-bound SG, SG-DNA@POPC, were incubated for 4 hours and the emission was monitored at 520 nm. Quenching was retained for the known DNA-binders, EtBr and Hoechst 33258. In the dirhodium series, complexes 1, 2, and 4 maintained at least some of their quenching ability, showing that these complexes are able to transverse the l (open full item for complete abstract)

Committee: Claudia Turro (Advisor) Subjects: Chemistry, Inorganic

Master of Science, Miami University, 2006, Chemistry and Biochemistry

There is a drive to understand how nature performs various catalytic reactions using minimal energy, in particular the activation of nitrogen. The work described here focuses on two types of models to study metal-substrate interactions: paddlewheel complexes (PCs) and metal organic frameworks (MOFs). PCs consist of a dimetal center and four bidentate ligands, and their unsaturated metal centers make them ideal candidates for catalysis. Hetero-bimetallic PCs are rare, but using a Ni-based intermediate allows the synthesis of a PC with an Fe—Ni center. Dirhodium homo-bimetallic PCs were synthesized as well, with a chiral asymmetric ligand that binds through two differently sized atoms (N and S), forcing PCs into the catalytically active D 2geometry. MOFs are also discussed, explaining how tuning the structure through metal choice, ligand design, and solvent manipulation allows for the synthesis of stable compounds with interesting properties,such as fluorescence and functionalized channels with potential for catalysis.

Committee: Hongcai Zhou (Advisor) Subjects: