Unusual Coordination to the Group 14 Elements: An Analysis of the Effect of Substituents on the Lewis Acidity of these Elements
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It is well known that the Lewis acidity of the group 14 elements increases going down the group. In addition, it is known that electronegative substituents increase the Lewis acidity of the metal. Therefore, this study focuses on the group 14 elements that are surprisingly acting as Lewis acids without electronegative substituents. The objective of this study was to probe the factors facilitating or hindering Lewis acidity of the group 14 elements. Triphenyl oxinates of the group 14 atoms were synthesized. This study shows an increase in coordination in the potentially bidentate oxinates Ph3MOx from M = Si to M = Pb, with the heavier elements of the group having dative bonds strong enough to produce slow fluxionality among geometric isomers as observed by NMR spectroscopy. With silicon and germanium, however, NMR central atom shifts and coupling constants, as well as 15N chemical shifts, show that these oxinates are four coordinate with no Lewis interactions. The hypercoordination in the tin and lead analogs, however, indicates that electronegative groups are not necessary to observe Lewis acidic behavior with these elements.
Franklin and Marshall College Archives, Undergraduate Honors Thesis 2010
- F&M Theses Collection