Intermolecular β-Hydrogen Abstraction in Ytterbium, Calcium, and Potassium Tris(dimethylsilyl)methyl Compounds

Abstract

A series of organometallic compounds containing the tris(dimethylsilyl)methyl ligand are described. The potassium carbanions KC(SiHMe 2 ) 3 and {KC(SiHMe 2 ) 3 TMEDA} 2 are synthesized by deprotonation of the hydrocarbon HC(SiHMe 2 ) 3 with potassium benzyl. {KC(SiHMe 2 ) 3 TMEDA} 2 crystallizes as a dimer with two types of three-center–two-electron K–H–Si interactions: side-on coordination of SiH (∠K–H–Si = 102(2)°) and more obtuse K–H–Si structures (∠K–H–Si ≈ 150°). The divalent calcium and ytterbium compounds M{C(SiHMe 2 ) 3 } 2 L (M = Ca, Yb; L = 2THF, TMEDA) are prepared from MI 2 and 2 equiv of KC(SiHMe 2 ) 3 . Low 1 J SiH coupling constants in the NMR spectra, low-energy ν SiH bands in the IR spectra, and short M–Si distances and small M–C–Si angles in the crystal structures suggest β-agostic interactions on each C(SiHMe 2 ) 3 ligand. The IR assignments of M{C(SiHMe 2 ) 3 } 2 L (L = 2THF, TMEDA) are supported by DFT calculations. The compounds M{C(SiHMe 2 ) 3 } 2 L react with 1 or 2 equiv of B(C 6 F 5 ) 3 to give the 1,3-disilacyclobutane {Me 2 SiC(SiHMe 2 ) 2 } 2 and MC(SiHMe 2 ) 3 HB(C 6 F 5 ) 3 L or M{HB(C 6 F 5 ) 3 } 2 L, respectively. In addition, M{C(SiHMe 2 ) 3 } 2 L compounds react with BPh 3 to give β-H abstracted products. The compounds M{C(SiHMe 2 ) 3 } 2 THF 2 react with SiMe 3 I to yield Me 3 SiH and disilacyclobutane as the products of β-H abstraction, while M{C(SiHMe 2 ) 3 } 2 TMEDA and Me 3 SiI form a mixture of Me 3 SiH and the alkylation product Me 3 SiC(SiHMe 2 ) 3 in a 1:3 ratio.