Ocasio-Delgado, Yessenia

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    Synthesis, mechanisms and electrochemical studies of [60]fullerene transition metal carbonyl complexes
    (2005) Ocasio-Delgado, Yessenia; Cortés-Figueroa, José E.; College of Arts and Sciencies - Sciences; López-Quiñones, Gustavo E.; Meléndez-Martínez, Enrique; Department of Chemistry; Quintana-Cheeseborough, Anibal
    In this work the ligand exchange reactions on (η²-C₆₀)(η²-phen)Mo(CO)₃ (phen = 1,10-phenanthroline) and the electrochemical profiles of [60]fullerene and various [60]fullerene-transition metal complexes (metal = Cr, Mo, W) were investigated. The Lewis bases (=L) triphenylphosphine (PPh₃) and tricyclohexyl phosphine (P(Cy)₃) displace [60]fullerene (C₆₀) from the complex fac(η²-C₆₀)(η²-phen)Mo(CO)₃ producing fac-(η²-L)(η²-phen)Mo(CO)₃. The progress of the reactions was followed observing the decrease of the absorbance values at 440 nm and by monitoring the stretching carbonyl region from 1700 to 2100 cm⁻¹. The plots of absorbance vs. time were biexponential, indicative of a biphasic behavior, for reactions under flooding conditions where [L]>> [(η²-C₆₀)(η²-phen)Mo(CO)₃]. The plot of absorbance vs. time consisted of two consecutive segments: the first segment of the plot was a decrease of absorbance with time followed by a second segment where the absorbance increased with time. The first segment of the biphasic plot was ascribed to the solvent-assisted displacement of C₆₀ from (η²-C₆₀)(η²-phen)Mo(CO)₃ and the second segment to decomposition of the complex fac-(η²-L)(η²-phen)Mo(CO)₃ produced in the first of the two consecutive reactions. The rate constant values corresponding to the first segment of the biphasic plot are independent of the chemical nature of L, the molar concentration of L, and the molar concentration of C₆₀ but dependent on the chemical nature of the solvent. Cyclic voltammetry of [60]fullerene and [60]fullerene metal complexes suggest a decrease of the C-C double bond character between the carbons in neighboring six-membered rings on [60]fullerene. The determination of the reduction waves on fullerene and complexes were limited by the solvent electrochemical window. The more negative reduction potentials in the fullerene metal complexes relative to the uncoordinated fullerene, suggest a metal “walking” on the fullerene surface.