Zwitterionic Alkali-Metal Silanides of Tripodal Ligand Geometry: Synthesis, Structure, and Lewis Acid-Base Chemistry.

A unique family of zwitterionic alkali-metal silanides of general formula [Si(SiMeOR)M] (M-3), where M = Li, Na, K and R = CHCH (M-3b), CH(CH) (M-3c), CHCH(CH) (M-3d), CHCHOSCH (M-3g), CHCHN(CH) (M-3h), have been synthesized and their structures fully characterized. Compounds M-3 were prepared from reactions of the corresponding alkali-metal alkoxides, R'OM (R' = Bu, Bu; M = Li, Na, K) with the silanes Si(SiMeOR) (2a-h), where R = CHCH (b), CH(CH) (c), CHCH(CH) (d), CHCHOSCH (g), CHCHN(CH) (h), via selective Si-Si bond cleavage. Analysis of the X-ray data of Li-3a-e,g, Li-h, Li-4, Na-3a-c,e,f,h, and K-3b,d,e,g revealed two major structural motifs in the solid state: infinite chain type and monomeric zwitterions. The reaction of Si(SiMeOCHCH)Li (Li-3b) with BPh in THF gave the zwitterionic Lewis acid-base complex PhBSi(SiMeOCHCH)Li·THF (Li-5b). Reactions of W(CO) with Li-3b-d and Na-3b,c resulted in the formation of the zwitterionic silyl tungstenate complexes (CO)WSi[SiMeOCHCH]Li (Li-6b), (CO)WSi[SiMeOCH(CH)]Li (Li-6c), (CO)WSi[SiMeOCHCH(CH))]Li (Li-6d), (CO)WSi(SiMeOCHCH)Na (Na-6b), and (CO)WSi[SiMeOCH(CH)]Na (Na-6c), respectively. The solid-state structures of Li-5b and Na-6b were determined by X-ray crystallography.