Structural Chemistry of Lithium Hydrazides

Abstract
Deprotonation of NH protons, of four diorgano‐, organo(trimethylsilyl)‐ and bis(trimethylsilyl)hydrazines by n‐butyllithium in hexane led to the following lithium hydrazides: [Et‐(Li)N‐N(H)Et]6, (1)6, [Me3Si(Li)N‐N(Li)SiMe3]4, (2)4, [Me3Si‐(Li)N‐N(Li)SiMe3 · (Me3Si)2N‐N(Li)SiMe3]2 (3)2, and [Ph‐(Li)N‐N(Li)SiMe3]4, (4)4, respectively. The structure determination by X‐ray methods at low temperature reveals butterfly‐shaped Li2N2 structural monomeric units which associate through “laddering” to the observed oligomers thereby generating penta‐ and hexacoordinated Li centers. N‐N bonds lengths of up to 1.556 Å suggest that negative charge accumulates at the nitrogen atoms of (1)6, (2)4, and (3)2. An amazing structure shows the red compound 4 where two Li ions are π‐sandwiched between two phenyl groups each. The compound can be looked at as a new type of a lithium lithiate complex, Li2[Li6N8Ph4(SiMe3)4], but short N‐C and N‐N bonds in the Li6N8 core indicate that its negative charge is transferred to the phenyl groups.

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