Structure, Reactivity and Solution Dynamics of the Sn94- Ion

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Kocak, Fatma Sanem
Eichhorn, Bryan W
In this thesis, the nature of the Sn<sub>9</sub><super>4-</super> in solution and its reactivity with transition metal atoms and electrophiles have been studied. The Sn<sub>9</sub><super>4-</super> ion is a very strong Brønsted base that deprotonates en to form the Sn<sub>9</sub>H<super>3-</super> ion and is a potent ion sequestering agent that competes with 2,2,2-crypt for binding K<super>+</super>. The Sn<sub>9</sub>H<super>3-</super> ion has a pK<sub>a</sub> in a range of 32.2&ndash; 44 in dmso and can be reversibly interconverted to K<sub>3</sub>Sn<sub>9</sub><super>-</super> through addition of K<super>+</super> and base. Addition of K<super>+</super> to Sn<sub>9</sub>H<super>3-</super> in the absence of base gives the proposed coupled Sn<sub>9</sub>&ndash;Sn<sub>9</sub><super>6-</super> dimer. The diamagnetic Sn<sub>9</sub>H<super>3-</super> ion was mischaracterized as the Sn<sub>9</sub><super>3-</super> paramagnetic radical in numerous publications since 1983. The Sn<sub>9</sub>H<super>3-</super> ion reacts with Ni(cod)<sub>2</sub> and Pd(PPh<sub>3</sub>)<sub>4</sub> complexes and give the M@Sn<sub>9</sub>H<super>3-</super> clusters (M= Ni, Pd). The Ni@Sn<sub>9</sub>H<super>3-</super> ion reacts with (arene)M(CO)<sub>3</sub> complexes to form is the Ni@Sn<sub>9</sub>M(CO)<sub>3</sub><super>4-</super> ion. Endohedral d&ndash;10 atoms do not affect the pK<sub>a</sub>'s of the hydrido clusters, whereas coordination of M(CO)<sub>3</sub> group (M= Cr, Mo) significantly increases the acidity. The M@Sn<sub>9</sub>SnCy<sub>3</sub><super>3-</super> ions, where M= Ni and Pd, have been prepared with two different synthetic routes from Ni@Sn<sub>9</sub>H<super>3-</super> and Sn<sub>9</sub>SnCy<sub>3</sub><super>3-</super> ions, respectively. The Ni@Sn<sub>9</sub>H<super>3-</super> ion reacts with Cy<sub>3</sub>SnCl and gives the Ni@Sn<sub>9</sub>SnCy<sub>3</sub><super>3-</super> ion. The Sn<sub>9</sub>SnCy<sub>3</sub><super>3-</super> ion reacts with Pd(PPh<sub>3</sub>)<sub>4</sub> and gives the Pd@Sn<sub>9</sub>SnCy<sub>3</sub><super>3-</super> cluster. The Pd@Sn<sub>9</sub>PdSnCy<sub>3</sub><super>3-</super> ion has been prepared from a new type of reaction, where the Pd metal is oxidatively inserted into the exo-bond of Pd@Sn<sub>9</sub>&mdash;SnCy<sub>3</sub><super>3-</super>. Two new fused deltahedral clusters have been prepared from Sn<sub>9</sub><super>4-</super>, Ge<sub>9</sub><super>4-</super>, Pd(PPh<sub>3</sub>)<sub>4</sub>, and Ni(cod)<sub>2</sub> precursors to give the Pd<sub>2</sub>@Sn<sub>18</sub><super>4-</super>, the largest-known deltahedral cluster to-date, and Ni@Sn<sub>8</sub>(&mu;&ndash;Ge)Ni@Sn<sub>8</sub><super>4-</super>, the first example of an endohedral heteroatom cluster. <super>119</super>Sn, <super>1</super>H, <super>13</super>C NMR studies show these clusters to be highly dynamic. The Sn<sub>9</sub>SnR<sub>3</sub><super>3-</super> ions (R= Cy and <super>n</super>Bu) and M@Sn<sub>9</sub>R<super>3-</super> ions (M= Ni, Pd and R= H, SnCy<sub>3</sub>) exhibit fast intramolecular exchange of the all 9-Sn atoms, while the exo-substituent groups scramble around the clusters. The Sn<sub>9</sub>&ndash;<super>i</super>Pr<super>3-</super> ion has non-mobile alkyl substituent, which removes the exo-bonded Sn atom from exchanging with the remaining 8-Sn atoms of the cluster.