Lithium fluoroarylsilylamides and their structural features

Abstract

In order to probe the role of Li⋯F interactions toward the stabilisation of low-coordinate lithium complexes, the four fluoroarylsilylamides [LiN(SiMe3)(2-C6H4F)] (1-Li), [LiN(SiMe3)(2,6-C6H3F2)] (2-Li), [LiN(SiMe3)(C6F5)] (3-Li), and [LiN(SiMe2H)(2-C6H4F)] (4-Li) have been synthesised in high yields by deprotonation of the parent amines with nBuLi. 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.

Keywords

• lithium
• fluoroarylsilylamides
• li⋯f interaction
• x-ray structures
• nmr spectroscopy