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

The trilithium triamide [HC{SiMe2NLi(2-FC6H4)}(3)] (2) was obtained by treatment of HC{SiMe2NH(2-FC6H4)}(3) (1) with 3 M equivalents of n-butyllithium in n-pentane. Upon reaction of 2 with 1 M equivalent of SnCl2 in toluene at elevated temperature, the amidostannate [HC{SiMe2N(2-FC6H4)}(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) Angstrom 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(Lil-C3) = 2.545 and 2.516 Angstrom 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). (C) 2002 Elsevier Science B.V. All rights reserved.