Luminescent Transition Metal Complexes Based on N-Heterocyclic and N^C-Chelate 4-Coordinate Organoboryl Ligands

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Wang, Nan
luminescent transition metal complexes
The objective of this thesis is to examine the photophysical and structural properties of Ru(II)/Re(I) based bimetallic complexes based on p-[N-2-(2’-pyridyl)benzimidazolyl]-[N-2-(2’-pyridyl)indolyl]-benzene (L1) ligand, as well as the photophysical and photochemical properties of N^C-chelate 4-coordinate organoboron compounds that contain a metal acetylide group. Ligand L1 was synthesized and fully characterized. Due to the incorporation of two distinct chelating sites, an N^N-chelate site and an N^C-chelate site, L1 has been found to be very effective in selective binding to two different metal ions. Two new heterobimetallic complexes Ru(II)-Pt(II) and Ru(II)-Pd(II) using L1 as the bridging ligand were prepared and fully characterized. All Ru(II)-containing complexes have been found to be luminescent. The Pt(II) unit appears to enhance phosphorescent efficiency of the Ru(II) unit while the Pd(II) unit has little influence. Using L1 as the bridging unit, two new Re(I) based heterobimetallic complexes Re(I)-Pt(II) and Re(I)-Pd(II) were also successfully synthesized. Results indicate that there is communication between the two different metal centers. The preliminary results indicated that the mononuclear Re(I) complex based on L1 is a promising candidate for the electrocatalytic CO2 reduction. Pd(II) and Pt(II) complexes were synthesized with an atropisomeric bis-pyridyl chelate ligand bis{3,3’-[N-Ph-2-(2’-py) indolyl]} (L4). To examine the potential use of the trans-chelate L4 ligand in oxidative coupling reactions catalyzed by Pd(II) compounds, acetoxylation of arenes by PhI(OAc)2 using PhI(OAc)2/L4 (2:1) as the catalyst was examined and found to accelerate the reaction, but lower the overall yield. Finally, to examine the impact of metal ions on photochromic properties of N^C-chelate organoboron compounds, three metal acetylide compounds that contain a photo-active N^C-chelate BMes2 unit (B(ppy)Mes2) were prepared and fully characterized. The studies indicated that by taking advantage of different heavy metals the photoisomerization quantum efficiency of the boron chromophores can be readily tuned through the adjustment of 3LC state localized on the chelate backbone or the involvement of MLCT state in the lowest energy electronic transition.
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