Multifaceted Inorganic Chemistry: Metal Oxide Materials for Use in Oxidation Catalysis & the Synthesis and Photophysics of Macrocyclic Transition Metal-Alkynyl Complexes
Abstract
The first chapter focuses on the synthesis and characterization of four new Cr(III)-bis-alkynyl complexes bearing the macrocyclic tetraaza ligand DMC (DMC = 5,12-dimethyl-1,4,8,11-tetraazacyclotetradecane). The complexes trans-[Cr(DMC)(C2R)2]X (R = Ph ([1.1 ]X), Fc ([1.2]X), X = Cl, ClO4; C2H ([1.3]X′); X′ = ClO 4, BPh4) and cis-[Cr(DMC)(C4TMS) 2]Cl ([1.4]Cl) were studied using UV-vis and FT-IR spectroscopies, and their identities were verified with ESI-MS and elemental analysis. The three trans-complexes, [1.1]Cl, [1.2](ClO 4), and [1.3](BPh4), were structurally characterized using single crystal X-ray diffraction, which revealed a pseudo-octahedral geometry around the Cr center with the nitrogen atoms occupying the equatorial plane and the alkynyl ligands residing in the apical positions. Spectroscopic analysis of [1.1]Cl, [1.3](BPh4) and [1.4]Cl shows highly structured d-d bands between 320 and 500 nm. All Cr(III) complexes reported herein are emissive, and detailed studies were performed for [1.1]Cl, [1.3](BPh 4) and [1.4]Cl, yielding both phosphorescence lifetimes (77 K) of 380 µs, 358 µs, and 160 µs, respectively, and room temperature quantum yields of 0.01% for complex [1.1]Cl and 0.15% for complex [1.4]Cl. Chapter 2 expands on the above investigation of Cr(III) complexes, incorporating fluorophore ligand substituents. Two Cr(III) bis-ethynylnaphthalene (C 2Np) complexes, trans-[Cr(HMC)(C2Np)2]Cl (2.1) and cis-[Cr(HMC)(C2Np)2]Cl ( 2.2), were prepared from the reactions between trans/cis-[Cr(HMC)Cl 2]Cl and lithium 1-ethynylnaphthalene (LiC2Np) in yields of 73.4% and 66.2%, respectively. Also investigated are CoIII(cyclam) complexes bearing both C2Np and C2ANT (ANT = anthryl), namely [Co(cyclam)(C2Ar)Cl]Cl (Ar = ANT(2.3), Np (2.4)), [Co(cyclam)(C2Np)(NCCH3)](OTf) 2 (2.5), and [Co(cyclam)(C2Np)2]OTf (2.6). Complexes 2.3 (72.2%) and 2.4 (67.4%) were prepared from the reaction between [Co(cyclam)Cl2]Cl and Me3SiC2ANT or Me3SiC2Np, respectively, in the presence of a weak base (triethylamine). The reaction of 2.4 with excess silver triflate in CH3CN yielded complex 2.5 (77.7%), which was reacted with HC2Np in the presence of a weak base to form complex 2.6 in 39.2% yield. Single X-ray diffraction studies of 2.1, 2.3, 2.4, and 2.6 revealed a pseudo-octahedral geometry around the Cr(III) or Co(III) center, with the tetraaza-macrocyclic ligand occupying the equatorial plane and the alkynyl- and/or chloro-ligand occupying the apical positions. As observed in chapter one, the absorption spectra of complexes 2.1 and 2.2 display structured d-d bands between 400 and 550 nm, which is absent in the spectra of the Co(III) complexes 2.3-2.6. Contrasting emission behaviors were observed: the Cr(III) complexes display metal-centered phosphorescence while the Co(III) species exhibit ligand based fluorescence. Time-delayed phosphorescence measurements revealed lifetimes of 447 µs and 97 µs for 2.1 and 2.2 at 77 K, respectively, and a room temperature lifetime of 218 µs for 2.1. Chapter 3 discusses the use of different metal oxide materials for oxidation catalysis and is organized in three parts. First, the polyoxometalate [Mo 2O11]2- is investigated for its ability to catalyze the oxygenation of methyl phenyl sulfide (MPS), finding excellent activity for both sulfoxide and sulfone when employing hydrogen peroxide, with complete consumption of MPS within 2 h. Decreased rates and a preference for the formation of sulfoxide were found when using tert-butyl hydrogen peroxide (TBHP). Next, supported RuO2 nanoparticulates are utilized for water oxidation. Several different ways of preparing these supported RuO 2 nanoparticulates are discussed and evaluated for efficiency, finding that preparing RuO2 nanoparticulates via hydrothermal methods and passively diffusing them into an SBA-15 support yields the highest activity for water oxidation under both chemical and photochemical reaction conditions. Lastly, the activity of hematite (α-Fe2O3) was evaluated for the photo-oxidation of aniline to azobenzene. Both supported and unsupported hematite nanoparticulates were analyzed, finding a preference in the use of unsupported hematite likely due to the light scattering effect of the support preventing effective light utilization by the hematite catalyst.
Degree
Ph.D.
Advisors
Ren, Purdue University.
Subject Area
Inorganic chemistry
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