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

A series of organometallic compounds containing the tris­(dimethylsilyl)­methyl
ligand are described. The potassium carbanions KC­(SiHMe2)3 and {KC­(SiHMe2)3TMEDA}2 are synthesized by deprotonation of the hydrocarbon HC­(SiHMe2)3 with potassium benzyl. {KC­(SiHMe2)3TMEDA}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(SiHMe2)3}2L (M = Ca, Yb; L =
2THF, TMEDA) are prepared from MI2 and 2 equiv
of KC­(SiHMe2)3. Low 1JSiH coupling constants in the NMR spectra, low-energy
νSiH 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(SiHMe2)3 ligand. The IR assignments of M­{C­(SiHMe2)3}2L (L = 2THF, TMEDA) are supported
by DFT calculations. The compounds M­{C­(SiHMe2)3}2L react with 1 or 2 equiv of B­(C6F5)3 to give the 1,3-disilacyclobutane {Me2SiC­(SiHMe2)2}2 and MC­(SiHMe2)3HB­(C6F5)3L or M­{HB­(C6F5)3}2L, respectively. In addition,
M­{C­(SiHMe2)3}2L compounds react with
BPh3 to give β-H abstracted products. The compounds
M­{C­(SiHMe2)3}2THF2 react
with SiMe3I to yield Me3SiH and disilacyclobutane
as the products of β-H abstraction, while M­{C­(SiHMe2)3}2TMEDA and Me3SiI form a mixture
of Me3SiH and the alkylation product Me3SiC­(SiHMe2)3 in a 1:3 ratio.