ABSTRACT Modifications of the Small Molecule Maltol and Photoactivity when Coordinated to Transition Metals Britain C. Bruner, Ph.D. Advisor: Patrick J. Farmer, Ph.D. The family of hetero-substituted maltol chelators, thiomaltol (Htma), dithiomaltol (Httma), and 3-hydroxypyridine-4-thione (Hopto) have been used to generate complexes with Ru(II), Pt(II), Ti(IV), and P(III) that exhibit unique photochemical and photophysical properties. Photo-excitation into ligand-based absorption bands of + complexes [Ru(bpy)2(ttma)] and Zn(ttma)2 engendered electron transfer reactions. Both complexes exhibit long-lived triplet emissions in the near IR spectral region. + Photochemical experiments with [Ru(bpy)2(ttma)] formed alcohol and aldehyde products upon photolysis in presence of mild oxidants that do not oxidize in the dark, 3+ 2+ such as methyl viologen, [Ru(NH3)6] and [Co(NH3)5Cl] . A family of new Pt(II) bipyridyl complexes are reported using the maltol-derived ligands as electron-donors. The [Pt(bpy)L]+ complexes display intense and long-lived luminescences due to Ligand- to-Ligand Charge Transfer (LLCT) states; these luminescences are quenched by electron acceptors such as methylviologen and O2. These compounds are also efficient at singlet 1 oxygen ( O2) generation and quenching. Likewise, a family of Ti(IV) complexes with maltol-derived chelators has been synthesized to model the use in dye-sensitized solar cell applications. Lastly, several novel six-coordinate phosphorous complexes with the chelators of the formula P(L)2X2 were synthesized, which also exhibit room temperature emissions. These several families of photo-active complexes represent a useful palette of dyes for photochemical applications. Modifications of the Small Molecule Maltol and Photoactivity when Coordinated to Transition Metals by Britain C. Bruner, B.A. A Dissertation Approved by the Department of Chemistry and Biochemistry Patrick J. Farmer, Ph.D., Chairperson Submitted to the Graduate Faculty of Baylor University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Approved by the Dissertation Committee Patrick J. Farmer, Ph.D., Chairperson Kevin Klausmeyer, Ph.D. Caleb D. Martin, Ph.D. Kevin L. Shuford, Ph.D. Zhenrong Zhang, Ph.D. Accepted by the Graduate School August 2014 J. Larry Lyon, Ph.D., Dean Page bearing signatures is kept on file in the Graduate School. Copyright © 2014 by Britain C. Bruner All rights reserved TABLE OF CONTENTS List of Figures .................................................................................................................... vi List of Schemes ................................................................................................................... x List of Tables ..................................................................................................................... xi Acknowledgments............................................................................................................ xiii Chapter One ........................................................................................................................ 1 References ................................................................................................................. 11 Chapter Two...................................................................................................................... 16 Introduction ............................................................................................................... 16 Experimental ............................................................................................................. 18 Results ....................................................................................................................... 25 Discussion ................................................................................................................. 38 Conclusions ............................................................................................................... 43 References ................................................................................................................. 44 Chapter Three.................................................................................................................... 47 Introduction. .............................................................................................................. 47 Experimental ............................................................................................................. 49 Results ....................................................................................................................... 57 Discussion ................................................................................................................. 72 Conclusions ............................................................................................................... 84 References ................................................................................................................. 86 Chapter Four ..................................................................................................................... 89 Introduction ............................................................................................................... 89 Experimental ............................................................................................................. 92 Results ....................................................................................................................... 95 Discussion ............................................................................................................... 104 Conclusions ............................................................................................................. 109 References ............................................................................................................... 111 Chapter Five .................................................................................................................... 113 Introduction ............................................................................................................. 113 Experimental ........................................................................................................... 114 Results ..................................................................................................................... 118 Discussion ............................................................................................................... 131 Conclusion .............................................................................................................. 132 References ............................................................................................................... 134 Bibliography ................................................................................................................... 141 v LIST OF FIGURES Figure 1.1 1H NMR stack plot of maltol, thiomaltol, dithiomaltol, Hopto, deferiprone .... 3 Figure 1.2 Room temperature UV-visible absorption spectra (normalized) of thiolated, maltol-derived ligands in CH3CN ...................................................................... 5 Figure 1.3 Solid state structures of trismaltolato Fe(III) and tristhiomaltolato Fe(III) ....... 7 Figure 2.1 Crystal structure of Httma ............................................................................... 26 Figure 2.2 Crystal structure of [Zn(ttma)] 2, 2-4 ............................................................... 26 Figure 2.3 Cyclic voltammograms of 2-1, 2-4, and Httma .............................................. 29 + Figure 2.4 Comparison of normalized UV-vis spectra of [Ru(bpy)2ttma] , Zn(ttma)2 and -1 -1 Ru(bpy)3 molar extinction coefficient (M cm ). Inset: of Httma over same range ................................................................................................................ 30 Figure 2.5 Normalized absorption and emission spectra for compound 2-4 in CH3CN. .. 31 Figure 2.6 Normalized absorption and emission spectra for 2-4 in CH3OH. ................... 31 Figure 2.7 ESI-MS spectrum of a sample generated by photoexcitation of an anaerobic + 2+ solution of [Ru(bpy)2(ttma)] and MV in CH3CN/CH3OH followed the + addition of 0.1 M NaOH. The species formed is [Ru(bpy)2(ttma-aldehyde)] (m/z = 584). ..................................................................................................... 32 Figure 2.8 LCMS analysis of product solution after photolysis of 2-1 for in presence of Ru(NH3)6Cl3 .................................................................................................... 34 + Figure 2.9 Internal standard calibration curve for determining percent [Ru(bpy)2ttma] + and percent [Ru(bpy)2ttma-aldehyde] . Peak area ratio is equal to the ratio of + the sample to internal standard, [Ru(bpy)3] ................................................... 35 Figure 2.10 1H NMR spectra of complexes 2-1 – 2-4, free ligands Htma and Httma. ..... 35 Figure 2.11 MS analysis of soluble products obtained after photo-oxidations of 2-4 ...... 36 1 Figure 3.1 H NMR spectra (CD3CN) of 3-1 (top), 3-2 (middle) and 3-3 (bottom) ......... 58 Figure 3.2 Cyclic voltammograms of complexes 3-1, 3-2a and 3-3 ................................ 60 Figure 3.3 Room temperature UV-vis absorption of 3-1 & emission............................... 61 vi Figure 3.4 Room temperature UV-vis absorption of 3-2 & emission..............................