Browsing by Subject "Ligands."
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Item Chemistry, electrochemistry and electron transfer induced reactions of cobalt complexes with fluorinated ligands.(2008-03-03T17:20:55Z) Gunawardhana, Kihanduwage N.; Gipson, Stephen L. (Stephen Lloyd); Chemistry and Biochemistry.; Baylor University. Dept. of Chemistry and Biochemistry.The chemical or electrochemical reduction of the trifluoroacetyl complex CF3COCo(CO)3PPh3 involves a single electron transfer yielding trifluoromethyl radical and an anionic cobalt carbonyl complex. The mechanism is proposed to involve electron transfer followed by initial dissociation of either a carbonyl or phosphine ligand from the 19-electron [CF3COCo(CO)3PPh3 ]- anion. The resulting 17-electron intermediate undergoes subsequent one-electron reductive elimination of trifluoromethyl radical by homolytic cleavage of the carbon-carbon bond of the trifluoroacetyl group. The CF3· radical can be trapped by either benzophenone anion, forming the anion of [a]-(trifluoromethyl)benzhydrol, or Bu3SnH, yielding CF3H. The final organometallic product is an 18-electron anion, either [Co(CO)4]- or [Co(CO)3(PPh3)]-, depending upon which ligand is initially lost. The chemical or electrochemical reduction CF3Co(CO)3PPh3 is a two-electron process involving heterolytic cobalt-carbon bond cleavage to yield trifluoromethyl anion and cobalt carbonyl anions. The trifluoromethyl anion rapidly decomposes to fluoride and difluorocarbene. This carbene may dimerize to form C2F4. The unstable fluoro carbene can also be trapped by cyclohexene. The mechanism proposed for the reduction of C6F5Co(CO)3PPh3 involves a homolytic cobalt-carbon bond cleavage to form C6F5[bullet] radical. The resultant C6F5[bullet] radical abstracts hydrogen or deuterium from the solvent or trace amounts of water to produce C6F5H or C6F5D. With an excess of reducing agent this C6F5[bullet] radical can be further reduced to C6F5- anion before forming pentafluorobenzene by protonation. The inorganic fragment, the 18-electron [Co(CO)3PPh3]- anion, may participate in a ligand exchange reaction to form [Co(CO)4]-. In addition, interesting reactivity was observed between C6F5Co(CO)3PPh3 and tin hydrides, deuterides and chlorides without any reducing agents. We have demonstrated that ligand replacement reactions can be used for the synthesis of new cobalt-NHC complexes with fluorinated alkyl, acyl and aryl ligands. In addition, the X-ray crystal structure of CF3COCo(CO)3PPh3 was obtained to compare the bond lengths and bond angles with other related compounds. An unusual Co-C(acyl) bond length was observed for CF3COCo(CO)3PPh3. Considering the bond lengths of other alkyl and acyl complexes, it can generally be argued that the position of the alkyl/acyl equilibrium varies with the Co-C(alkyl/acyl) bond length.Item Luminescent supramolecular silver(I) coordination complexes of pyridyl-substituted phosphinites, phosphonites and amines.(2006-05-28T01:17:15Z) Feazell, Rodney P.; Klausmeyer, Kevin Kenneth, 1969-; Chemistry and Biochemistry.; Baylor University. Dept. of Chemistry and Biochemistry.Interest in the design and synthesis of supramolecular metal-organic coordination polymers has increased exponentially in the last decade. This attraction comes along with advances in crystallographic instrumentation that has made the collection and processing of crystal data sets faster and more automated than ever. As a result, our understanding of the intra- and intermolecular forces that exist within the confines of the crystalline lattice is at a historic high. In this work we use several new bi- and tridentate pyridyl-substituted phosphinite ligands as well as a series of isomeric aminomethylpyridines to construct discrete, one-, two, and three-dimensional metal-organic coordination architectures with salts of the silver(I) cation. These complexes were then analyzed and discussed in terms of the variables (metal/ligand ratio, anion, temperature, solvent) and forces (donor-metal bonding, hydrogen-bonding, π-stacking, dispersion forces) that cause the structural motifs that are observed. The luminescence of these complexes was also studied and was seen to be variable with changes in structure and metal environment.Item Synthesis and characterization of silver(I) salts with amino methyl pyridines containing phosphines: novel complex formation upon ratio, anion, or ligand changes.(2008-06-10T21:57:15Z) Amawi, Rema Mouawya.; Klausmeyer, Kevin Kenneth, 1969-; Chemistry and Biochemistry.; Baylor University. Dept. of Chemistry and Biochemistry.Phosphorus ligands are well recognized for stabilizing metal complexes in a variety of oxidation states and coordination geometries.1 Compounds with pyridyl containing phosphines have been investigated with carbinol groups in the past; this work studies the pyridyl amines. The focus of this research is to explore the different binding properties as the position of the nitrogen changes on the ligand, as well as changing the silver(I) salts binding to the ligand such as the BF₄⁻ , OTf⁻ and the tfa⁻ anions. The synthesis and characterization of two new ligands that are from the same family have been looked at, and the synthesis of novel silver(I) complexes involving these ligands have been explored. All of the compounds produced have been characterized by X-ray crystallography, NMR spectroscopy, fluorescence, and elemental analyses.