Lithium fluoroarylsilylamides and their structural features
Résumé
In order to probe the role of Li⋯F interactions toward the stabilisation of low-coordinate lithium complexes, the four fluoroarylsilylamides [LiN(SiMe 3 )(2-C 6 H 4 F)] ( 1-Li ), [LiN(SiMe 3 )(2,6-C 6 H 3 F 2 )] ( 2-Li ), [LiN(SiMe 3 )(C 6 F 5 )] ( 3-Li ), and [LiN(SiMe 2 H)(2-C 6 H 4 F)] ( 4-Li ) have been synthesised in high yields by deprotonation of the parent amines with n BuLi. They have been comprehensively characterised by multinuclear NMR spectroscopy, and complete assignments were achieved with the help of 2D NMR data. The molecular solid-state structures of [( 2-Li ) 2 ] ∞ , [ 3-Li · Et 2 O ] 2 , and [ 4-Li ] 8 were determined by single-crystal X-ray diffraction. They feature unusual coordination patterns, notably for the formation of the polymeric [( 2-Li ) 2 ] ∞ and a unique octagonal, crown-like [ 4-Li ] 8 . In both structures, the role of Li⋯F non-covalent interactions was the key toward the building of the final architecture. It is shown that Li–F and C–F interatomic distances, along with | 1 J C,F | coupling constants, can be used as qualitative tools for the evaluation of the presence and relative strength of Li⋯F contacts.
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