Lewis acid-mediated beta-hydride abstraction reactions of divalent M(C(SiHMe(2))(3))(2)THF(2) (M = Ca, Yb)

KaKing Yan; Brianna M Upton; Arkady Ellern; Aaron D Sadow

doi:10.1021/ja9070865

Lewis acid-mediated beta-hydride abstraction reactions of divalent M(C(SiHMe(2))(3))(2)THF(2) (M = Ca, Yb)

J Am Chem Soc. 2009 Oct 28;131(42):15110-1. doi: 10.1021/ja9070865.

Authors

KaKing Yan¹, Brianna M Upton, Arkady Ellern, Aaron D Sadow

Affiliation

¹ Department of Chemistry and U.S. Department of Energy Ames Laboratory, Iowa State University, Ames, Iowa 50011-3111, USA.

PMID: 19795868
DOI: 10.1021/ja9070865

Abstract

The divalent calcium and ytterbium compounds M(C(SiHMe(2))(3))(2)THF(2) contain beta-agostic SiH groups, as determined by spectroscopy and crystallography. Upon thermolysis, HC(SiHMe(2))(3) is formed. However, the SiH groups are hydridic. The compounds M(C(SiHMe(2))(3))(2)THF(2) react with 1 and 2 equiv of the Lewis acid B(C(6)F(5))(3) to form MC(SiHMe(2))(3)HB(C(6)F(5))(3))THF(2) and M(HB(C(6)F(5))(3))(2)THF(2), respectively. These species contain the anion [HB(C(6)F(5))(3)](-) from hydride abstraction rather than [(Me(2)HSi)(3)CB(C(6)F(5))(3)](-) from alkyl abstraction. The 1,3-disilacyclobutane byproduct initially suggested beta-elimination [as the dimer of the silene Me(2)Si horizontal lineC(SiHMe(2))(2)], but the other products and reaction stoichiometry rule out that pathway. Additionally, Yb(C(SiHMe(2))(3))(2)THF(2) and the weak Lewis acid BPh(3) 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(SiHMe(2))(3)THF(2) compounds, beta-elimination is not an observed reaction pathway.