Chemistry & Biochemistry Theses and Dissertations

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    ELECTRONIC MODIFICATION WITHIN THE WELL-ESTABLISHED CPAM FRAMEWORK AS A MEANS TOWARD INCREASED REACTIVITY
    (2017) Thompson, Richard; Sita, Lawrence R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Early transition metals (group IV-VI) supported by the pentamethylcyclopentadienyl-amidinate mixed ligand set (CPAM) have been found to enable a number of important chemical transformations including (living) coordinative polymerization of alpha-olefins, fixation of dinitrogen and group transfer chemistry involving oxo, imido and sulfido ligands to unsaturated organic substrates, including carbon dioxide. A great deal of the allure and success associated with these complexes is their modularity, particularly as it concerns the amidinate component which is tunable at both the N-bound substituents as well as the distal position. Accordingly, a great deal of work has established that by reducing the sterics in all three positions engendered higher reactivity. There exists, however, a practical “steric wall” such that the size of substituents can only be contracted so much. Tuning of the electronic character of these well-established systems could prove to be a novel and potent method for affecting reactivity of these complexes within an already well understood steric environment.
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    Structure, Reactivity and Solution Dynamics of the Sn94- Ion
    (2011) Kocak, Fatma Sanem; Eichhorn, Bryan W; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In this thesis, the nature of the Sn94- in solution and its reactivity with transition metal atoms and electrophiles have been studied. The Sn94- ion is a very strong Brønsted base that deprotonates en to form the Sn9H3- ion and is a potent ion sequestering agent that competes with 2,2,2-crypt for binding K+. The Sn9H3- ion has a pKa in a range of 32.2– 44 in dmso and can be reversibly interconverted to K3Sn9- through addition of K+ and base. Addition of K+ to Sn9H3- in the absence of base gives the proposed coupled Sn9–Sn96- dimer. The diamagnetic Sn9H3- ion was mischaracterized as the Sn93- paramagnetic radical in numerous publications since 1983. The Sn9H3- ion reacts with Ni(cod)2 and Pd(PPh3)4 complexes and give the M@Sn9H3- clusters (M= Ni, Pd). The Ni@Sn9H3- ion reacts with (arene)M(CO)3 complexes to form is the Ni@Sn9M(CO)34- ion. Endohedral d–10 atoms do not affect the pKa's of the hydrido clusters, whereas coordination of M(CO)3 group (M= Cr, Mo) significantly increases the acidity. The M@Sn9SnCy33- ions, where M= Ni and Pd, have been prepared with two different synthetic routes from Ni@Sn9H3- and Sn9SnCy33- ions, respectively. The Ni@Sn9H3- ion reacts with Cy3SnCl and gives the Ni@Sn9SnCy33- ion. The Sn9SnCy33- ion reacts with Pd(PPh3)4 and gives the Pd@Sn9SnCy33- cluster. The Pd@Sn9PdSnCy33- ion has been prepared from a new type of reaction, where the Pd metal is oxidatively inserted into the exo-bond of Pd@Sn9—SnCy33-. Two new fused deltahedral clusters have been prepared from Sn94-, Ge94-, Pd(PPh3)4, and Ni(cod)2 precursors to give the Pd2@Sn184-, the largest-known deltahedral cluster to-date, and Ni@Sn8(μ–Ge)Ni@Sn84-, the first example of an endohedral heteroatom cluster. 119Sn, 1H, 13C NMR studies show these clusters to be highly dynamic. The Sn9SnR33- ions (R= Cy and nBu) and M@Sn9R3- ions (M= Ni, Pd and R= H, SnCy3) exhibit fast intramolecular exchange of the all 9-Sn atoms, while the exo-substituent groups scramble around the clusters. The Sn9–iPr3- ion has non-mobile alkyl substituent, which removes the exo-bonded Sn atom from exchanging with the remaining 8-Sn atoms of the cluster.