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(SiMe2OR)3M] (M-3), where M = Li, Na, K and R = CH2CH3(M-3b), CH(CH3)2(M-3c), CH2CH(CH3)2(M-3d), CH2CH2OSCH3(M-3g), CH2CH2N(CH3)2(M-3h), have been synthesized and their structures fully characterized. Compounds M-3were prepared from reactions of the corresponding alkali-metal alkoxides, R′OM (R′ = But, Bui; M = Li, Na, K) with the silanes Si(SiMe2OR)4(2a–h), where R = CH2CH3(b), CH(CH3)2(c), CH2CH(CH3)2(d), CH2CH2OSCH3(g), CH2CH2N(CH3)2(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,grevealed two major structural motifs in the solid state: infinite chain type and monomeric zwitterions. The reaction of Si(SiMe2OCH2CH3)3Li (Li-3b) with BPh3in THF gave the zwitterionic Lewis acid–base complex Ph3BSi(SiMe2OCH2CH3)3Li·THF (Li-5b). Reactions of W(CO)6with Li-3b–dand Na-3b,cresulted in the formation of the zwitterionic silyl tungstenate complexes (CO)5WSi[SiMe2OCH2CH3]3Li (Li-6b), (CO)5WSi[SiMe2OCH(CH3)2]3Li (Li-6c), (CO)5WSi[SiMe2OCH2CH(CH3)2)]3Li (Li-6d), (CO)5WSi(SiMe2OCH2CH3)3Na (Na-6b), and (CO)5WSi[SiMe2OCH(CH3)2]3Na (Na-6c), respectively. The solid-state structures of Li-5band Na-6bwere determined by X-ray crystallography.