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-3 were 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,g revealed two major structural motifs in the solid state: infinite chain type and monomeric zwitterions. The reaction of Si(SiMe2OCH2CH3)3Li (Li-3b) with BPh3 in THF gave the zwitterionic Lewis acid-base complex Ph3BSi(SiMe2OCH2CH3)3Li·THF (Li-5b). Reactions of W(CO)6 with Li-3b-d and Na-3b,c resulted 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-5b and Na-6b were determined by X-ray crystallography.

Synthesis, structure, and reactivity of zwitterionic divalent rare-earth metal silanides.

The synthesis and structures of the first zwitterionic divalent rare-earth metal silanides of the formula [Si(SiMe2OMe)3-κ(3)]2M (M-3), where M = Eu, Yb, and Sm, are reported. M-3 compounds feature spirocyclic bicyclooctane structures in which the central rare-earth metal ions are being octahedrally coordinated by six methoxy groups. The reaction of Yb-3 with BPh3 and W(CO)6 respectively generated the trinuclear zwitterions [Ph3BSi(SiMe2OMe)3-κ(3)]2Yb (Yb-4) and [(CO)5WSi(SiMe2OMe)3-κ(3)]2Yb (Yb-5) in good yield.

Dissolution of cotton cellulose in 1:1 mixtures of 1-butyl-3-methylimidazolium methylphosphonate and 1-alkylimidazole co-solvents.

During the past decade, ionic liquids (ILs) have attracted increasing attention as efficient, novel solvents for dissolving cellulose. In this study, 1-butyl-3-methylimdazolium methylphosphonate ([C4C1im][(OMe)(H)PO2]) was used in the dissolution of cotton cellulose and the role of 1-methylimidazole, 1-ethylimidazole, 1-propylimidazole, and 1-butylimidazole as co-solvents was investigated. The progress of the dissolution was monitored using polarized light microscopy (PLM) and the regenerated cellulose was characterized using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The effect of 1-alkylimidazoles as co-solvents in cellulose dissolution was examined in terms of the basicity (hydrogen-bond acceptor capability), conductivity, viscosity, and ionicity of the IL and IL/co-solvent mixtures. These studies showed that the addition of 1-alkylimidazole co-solvents enhances cellulose dissolution by the IL and that the role of these co-solvents is mainly to increase mass transport by reducing the viscosity of the mixtures.