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Metallated, beta-substituted phosphine-oligothiophenes Moorlag, Carolyn Patricia

Abstract

The synthesis and characterization of transition metal complexes combined with π-conjugated chains to yield hybrid metal-organic materials with new structural, chemical, and electronic properties are reported. β-Phosphinothiophene ligands (9, 11, 13-15, 21-22, 27) were prepared by metal-catalyzed coupling reactions, thienyl backbone conformations were determined by X-ray crystallography, and electronic properties were characterized by absorption and emission spectroscopy and electrochemical methods. Transition metal groups were attached in close proximity to π-conjugated thienyl chains, at pendent positions or directly to the conjugated backbone, and metal-thienyl interactions were investigated. Pd(II) (29-30) and Au(I) (33-34) complexes were prepared by reaction of the metal groups with bis(phosphino)thiophene ligands. The conformational and electronic properties of the complexes were characterized, and the conjugation of the oligothiophene chains was modified by metal attachment. Ru(II) complexes (41-46, 47-52) are formed from bis(bipyridine) Ru(II) groups and mono(phosphino)thiophenes. Metal-mediated acid-base reactions change the mode of direct attachment of Ru(II) with the oligothiophene chains, between P,S and P,C bonding modes, resulting in different structural and electronic properties, as observed by absorption and emission spectroscopy, electrochemical oxidation and reduction, X-ray crystallography, spectroelectrochemistry, and electron paramagnetic resonance spectroscopy. These two modes of metal bonding to the π-conjugated backbone constitute a reversible molecular switch. The incorporated bis(bipyridine) Ru(II) groups undergo charge-transfer transitions, and light absorption of 51 appears to remove charge from the pentathiophene chain, suggesting possible light-harvesting applications. Preliminary polymerization studies towards the preparation of polynuclear, metallated polythiophene poly-46 and a β-polysubstituted polythiophene derivative are reported. Long oligomers were observed by ¹H NMR spectroscopy and mass spectrometry, but further studies are required. [Chemical Diagrams]

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