Lithium cation solvation in the ligand periphery of an ortho-fluorophenyl substituted tripodal triaminostannate

Abstract

The trilithium triamide [HC{SiMe 2NLi(2-FC 6H 4)} 3] ( 2) was obtained by treatment of HC{SiMe 2NH(2-FC 6H 4)} 3 ( 1) with 3 M equivalents of n-butyllithium in n-pentane. Upon reaction of 2 with 1 M equivalent of SnCl 2 in toluene at elevated temperature, the amidostannate [HC{SiMe 2N(2-FC 6H 4)} 3 SnLi] ( 3) was formed for which an X-ray diffraction study established the intramolecular coordination of the lithium cation by two of the peripheral ortho-fluoro groups. The mean LiF bond distances found in 3 are 1.986(8) and 1.982(9) Å for the two independent molecules in the asymmetric unit. This exposed position of the lithium, bonded to two amido N atoms and the two fluorine atoms, leads to a very close contact with the adjacent methyl-group [d(Li1C3)=2.545 and 2.516 Å for the two independent molecules in the unit cell] which effectively occupies a vacant coordination site of the lithium centre. This disposition of the alkyl group at close proximity of the Li centre is probably due to the unusual cation coordination geometry (distorted square-planar instead of tetrahedral) imposed by the rigid caged structure of the triamidoatannate(II).