Lewis Acid-Mediated β-Hydride Abstraction Reactions of Divalent M(C(SiHMe2)3)2THF2 (M = Ca, Yb)

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2009-10-01
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Yan, KaKing
Upton, Brianna
Ellern, Arkady
Sadow, Aaron
Sadow, Aaron
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Ames Laboratory
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Abstract

The divalent calcium and ytterbium compounds M(C(SiHMe2)3)2THF2 contain β-agostic SiH groups, as determined by spectroscopy and crystallography. Upon thermolysis, HC(SiHMe2)3is formed. However, the SiH groups are hydridic. The compounds M(C(SiHMe2)3)2THF2 react with 1 and 2 equiv of the Lewis acid B(C6F5)3 to form MC(SiHMe2)3HB(C6F5)3)THF2 and M(HB(C6F5)3)2THF2, respectively. These species contain the anion [HB(C6F5)3]− from hydride abstraction rather than [(Me2HSi)3CB(C6F5)3]− from alkyl abstraction. The 1,3-disilacyclobutane byproduct initially suggested β-elimination [as the dimer of the silene Me2Si═C(SiHMe2)2], but the other products and reaction stoichiometry rule out that pathway. Additionally, Yb(C(SiHMe2)3)2THF2 and the weak Lewis acid BPh3 react rapidly and also give the H-abstracted products. Despite the strong hydridic character of the SiH groups and the low-coordinate, Lewis acidic metal center in M(C(SiHMe2)3THF2 compounds, β-elimination is not an observed reaction pathway.

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<p>Reprinted (adapted) with permission from <em>Journal of the American Chemical Society</em> 131 (2009): 15110, doi: <a href="http://dx.doi.org/10.1021/ja9070865" target="_blank">10.1021/ja9070865</a>. Copyright 2009 American Chemical Society.</p>
Keywords
chemical equations, hydride abstraction, Lewis Acid, metal centers, reaction pathways, calcium, chemical reactions, crystallography, hysteresis motors, stoichiometry, Ytterbium, alkyl group, cyclobutane derivative, hydrogen, infrared spectroscopy, proton nuclear magnetic resonance
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