A series of dialkali metal complexes, [(HMe2Si)2C=C(SiMe2H)2]2- [M+(ligand)(n)]2 (M = Li, Na, K, Rb, Cs), were prepared by the reaction of tetrakis(dimethylsilylethylene) with alkali metals. These complexes exhibit Si-H alkali metal agostic interactions and have been characterized by spectroscopic and structural methods. Spectroscopic evidence for the interaction of the hydrogen on the silicon atom with alkali metals include (1) an unusually small value of the silicon-hydrogen coupling constant (1J(Si-H)) in NMR spectra and (2) low-energy Si-H stretching frequency in the infrared spectra. The smallest cation, Li+, can interact with SiH most strongly.
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