Structural Chemistry of Lithium Hydrazides

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 , [Me 3 Si(Li)N‐N(Li)SiMe 3 ] 4 , ( 2 ) 4 , [Me 3 Si‐(Li)N‐N(Li)SiMe 3 · (Me 3 Si) 2 N‐N(Li)SiMe 3 ] 2 ( 3 ) 2 , and [Ph‐(Li)N‐N(Li)SiMe 3 ] 4 , ( 4 )4, respectively. The structure determination by X‐ray methods at low temperature reveals butterfly‐shaped Li 2 N 2 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, Li 2 [Li 6 N 8 Ph 4 (SiMe 3 ) 4 ], but short N‐C and N‐N bonds in the Li 6 N 8 core indicate that its negative charge is transferred to the phenyl groups.