Alkali metal zincate reagents are attracting considerable attention at present in respect to their often special reactivity/selectivity in hydrogen-metal and halogen-metal interconversion reactions. Heteroleptic diorgano-amidozincates, typified by lithium di-tert-butyltetramethylpiperidinozincate, have proved to be especially useful reagents in such applications. In this paper the related sodium TMP-zincate, prepared as its TMEDA (N,N,N',N'-tetramethylethylenediamine) adduct, [TMEDA.Na(mu-tBu)(mu-TMP)Zn(tBu)], 1, is introduced. This new zincate was synthesized from a 1:1:1 mixture of tBu2Zn, NaTMP, and TMEDA in hexane solution, as a colorless crystalline solid in an isolated yield of 58%. It has been characterized in solution by 1H and 13C NMR spectroscopic studies. An X-ray crystallographic study reveals that 1 adopts a five-membered (NaNZnCC) ring system featuring a TMP bridge and an unusual, asymmetrical tBu bridge involving a Na...Me agostic contact. Probing the basicity of 1, reaction with benzene affords the new hetero(tri)leptic zincate [TMEDA.Na(mu-Ph)(mu-TMP)Zn(tBu)], 2, which has also been crystallographically characterized. Thus, in this hydrogen-metal exchange reaction 1 functions as an alkyl base, with the elimination of butane, as opposed to an amido base. Also reported are DFT calculations using B3LYP functionals and the 6-311G** basis set on model zincate systems, which intimate that the preference of 1 for tBu ligand transfer over TMP ligand transfer in the reaction toward benzene is due to favorable thermodynamic factors.

Transforming a carbon-hydrogen bond of an organic compound into a more useful, more reactive carbon-metal bond (so-called deprotonative metalation), which, in turn, can be treated with an electrophile to create a new carbon-carbon or carbon-heteroatom bond, is one of the most fundamental synthetic approaches that chemists employ to construct compounds. [1,2] Many of these reactions involve a special type of deprotonative metalation, in which an activating functional group is positioned adjacent to the hydrogen atom (strictly a proton) that is to be replaced by the metal cation.

Since the pioneering work of Schlenk nearly a century ago, alkali-metal-organic compounds (organolithium reagents, in particular) have served as frontline reagents in the battle to advance chemical synthesis. Metal-hydrogen exchange (metalation) in which a relatively inert carbon-hydrogen bond is transformed into a more labile carbon-alkali-metal bond, thus opening up a myriad of bond-forming possibilities at the carbon center, represents one of the oldest and still most important general uses of these centurial reagents. [1,2] Recently, however, new variations of these fundamental synthetic strategies have started to emerge in which the alkali metal, though still actively involved in the exchange reaction, takes on more of a secondary, supporting role, as the vanguard metals attacking the carbon centers are now either magnesium, zinc, or aluminum. On their own, these less electropositive metals generally form slow-reacting, ineffectual metalating agents, but combining them with an alkali-metal component appears to activate a special synergy that greatly enhances the power of the magnesiation, zincation, or alumination. Kondo et al. emphasized the importance of the "precomplexation of lithium TMP and tBu 2 Zn" (TMP = 2,2,6,6-tetramethylpiperidine) in the zincate reagent "[Li", which acts as a highly chemoselective base towards a series of functionalized aromatic and heteroaromatic compounds.[3] We recently extended this idea of alkali-metal-mediated zincation (AMMZ) to sodium through the N,N,N',N'-tetramethyl-1,2-ethanediamine (TMEDA)-chelated zincate [(tmeda)Na(m-tmp)(m-tBu)Zn(tBu)] (1), [4] which can effect the directed ortho-zincation of N,N-diisopropylbenzamide, [5] directed meta-zincation of N,N-dimethylanilines, [6] and the selective delivery of a tBu À nucleophile to the 6-position of benzophenone. [7] Herein, we report the first study in which AMMZ with 1 has been applied to a fused-ring aromatic hydrocarbon, using the simplest and most important compound of this type, naphthalene, as a case study. This investigation breaks new ground in establishing that AMMZ can provide 1) access to new zincated naphthalene molecules not directly accessible by mainstream organozinc reagents; 2) an improved method for metalation of naphthalene; 3) a degree of stoichiometric control, which enables di-and monometalation applications; and 4) an unprecedented set of crystalline 2-monometalated and 2,6-dimetalated naphthalene products from which the first crystal structures of zincated (or any metalated in the 2,6-case) naphthalene compounds have been obtained.Scheme 1 summarizes the reactions between 1 and naphthalene that yielded crystalline products. Carried out under mild conditions (room temperature, stirring for 2 h), the equimolar experiment (pathway a) produced yellow [(tmeda)Na(m-tmp)(m-2-C 10 H 7 )Zn(tBu)] (2) in yields of typically 50 % of the isolated product.1 H and 13 C NMR spectra of a solution of an isolated sample 2 in C 6 D 6 reveal a pattern of seven and ten distinct resonances, respectively, in the aromat...

Benzene can be easily 1,4-dideprotonated stoichiometrically on reaction with two equivalents of a synergic mixture of tBu2Zn, NaTMP and TMEDA to give a unique 1,4-dizincated benzene product which has been characterised by X-ray crystallography and NMR spectroscopy as well as modelled theoretically by DFT computational studies; a related synergic dimagnesiation of benzene is also reported.

Lithium dialkyl tetramethylpiperidino zincates of the general formula "[LiR 2 Zn(tmp)]" (tmp = 2,2,6,6-tetramethylpiperidine) represent an important subfamily of organozincate reagent. Established only in 1999 through the pioneering work on "[LitBu 2 Zn(tmp)]" by Kondo et al., [1] "tmp zincates" have found application as highly chemo-and/or regioselective bases for the metalation of alkyl benzoates and related aza aromatic compounds, bromopyridines, and various halobenzenes. [2,3] Recent reports [4] have highlighted the poverty of structural information available on lithium zincates in general. Tmp zincates are no exception in this regard, with a 13 C NMR spectroscopic study of "[LitBu 2 Zn(tmp)]" in solution [1] providing the only morsel of structural evidence