The zinc-hydrogen exchange reaction has undergone a remarkable transformation in recent times from obscurity to a novel alternative, and in many cases the preferred option, to long-established lithiation methods for generating aromatic organometallic intermediates suitable for subsequent functionalization. Simple zinc reagents (alkyls, amides), as kinetically sluggish bases, are generally useless for such applications. Installing high metalation power within a zinc reagent usually requires a more complex composition, in which reactivity is boosted through cooperative effects between its different components. Modified from their magnesiating "turbo-Grignard" reagents, Knochels three-component systems [(TMP) 2 Zn·2MgCl 2 ·2 LiCl] [1] and [{iPr(tBu)N} 2 Zn· 2MgCl 2 ·2 LiCl][2] are excellent complex zincators for both aromatic and heteroaromatic substrates (TMP is 2,2,6,6-tetramethylpiperidide). Formally a two-component lithium amide-zinc alkyl mixed complex, "[LiZn(TMP)(tBu) 2 ]" introduced by Kondo and Uchiyama, is also a potent chemo-and regioselective zincator for similar substrates.[3]Our own group has contributed the related sodium TMPzincate [(TMEDA)·Na(m-TMP)(m-tBu)Zn(tBu)] [4] (1), which depending on the organic substrate can execute regioselective ortho-, meta-, or dizincation in reactions that have been structurally defined.[5]Here we report the first investigation of the surprising reactivity of 1 towards an aryl halide, namely chlorobenzene. Fully characterized by X-ray crystallography and NMR spectroscopy, the unexpected final product isolated from this reaction is the remarkable zwitterionic benzannulated bicyclic zinc complex [{1-Zn(tBu)} À -{2-N(Me)(CH 2 )CH 2 -CH 2 NMe 2 } + -C 6 H 4 ] (2). Formation of 2 can be rationalized by a novel four-step ortho-zincation, zincate (or sodium chloride) elimination, azazincation-addition, amine a-zincation sequence. An intermediate along this path formed prior to the final step (amine a-zincation), [{1-Zn(tBu) 2 } À -{2-N(Me) 2 CH 2 CH 2 NMe 2 } + -C 6 H 4 ] (Int), has also been isolated from the reaction and crystallographically characterized.In the few previous studies of reactions of aryl halides and TMP-zincates, [6] no experimental evidence has been collected on the chemistry taking place between the limits of the starting materials and the zinc-free quenched products. Therefore, to shed light on the critical metal (and bimetal) activity stage of these reactions, our primary objective was to get inside these limits by isolating and characterizing representative zinc-containing intermediates. This was realized through the synthesis of 2, which were isolated as small colorless block crystals in 20.7 % yield from the equimolar reaction of 1 and chlorobenzene in hexane solution.Since it was reported earlier [6] that reaction of [LiZn-(TMP)(tBu) 2 ] with haloarenes followed by electrophilic trapping produced polyfunctional haloarenes (i.e., with retention of the original halogen substituent), we expected 2 to be an ortho-zincated chlorobenzene derivative. Sur...