Dizincation of a 2-substituted thiophene: constructing a cage with a [16]crown-4 zincocyclic core.

Metal detector: a bowl-shaped nanomolecule (see picture; S yellow, C gray, Zn blue) containing an unprecedented 16-atom [ZnC(3)](4) "anti-crown" ring has been unearthed by isolating a dizincated 2-substituted thiophene intermediate that would normally be hidden in tandem functionalization methodology.

Meta-metallation of N,N-dimethylaniline: Contrasting direct sodium-mediated zincation with indirect sodiation-dialkylzinc co-complexation.

Previously we reported that direct zincation of N,N-dimethylaniline by the mixed-metal zincate reagent 1 ((TMEDA)Na(TMP)(t-Bu)Zn(t-Bu)) surprisingly led to meta-metallation (zincation) of the aniline, as manifested in the crystalline complex 2 ((TMEDA)Na(TMP)(m-C(6)H(4)-NMe(2))Zn(t-Bu)), and that iodination of these isolated crystals produced the meta-isomer N,N-dimethyl-3-iodoaniline quantitatively. Completing the study here we find that treating the reaction solution with iodine produces a 72% conversion and results in a mixture of regioisomers of N,N-dimethyliodoaniline, with the meta-isomer still the major product (ortho:meta:para ratio, 6:73:21), as determined by NMR. In contrast to this bimetallic method, sodiation of N,N-dimethylaniline with n-BuNa produced the dimeric, ortho-sodiated complex 3 (((TMEDA)Na(o-C(6)H(4)-NMe(2)))(2)), as characterised by X-ray crystallography and NMR. No regioisomers were observed in the reaction solution. Introducing t-Bu(2)Zn to this reaction solution afforded a cocrystalline product in the solid-state, composed of the bis-anilide 4 ((TMEDA)Na(o-C(6)H(4)-NMe(2))(2)Zn(t-Bu)) and the Me(2)N-C cleavage product 5 ({(TMEDA)(2)Na}(+){(t-Bu(2)Zn)(2)(µ-NMe(2))}(-)), which was characterised by X-ray crystallography. NMR studies of the reaction mixture that produces 4 and 5 revealed one additional species, but the mixture as a whole contained only ortho-species and a trace amount of para-species as established by iodine quenching. In an indirect variation of the bimetallic reaction, TMP(H) was added at room temperature to the reaction mixture that afforded 4 and 5. This gave the crystalline product 6 ((TMEDA)Na(TMP)(o-C(6)H(4)-NMe(2))Zn(t-Bu)), the ortho-isomer of the meta-complex 2, as determined from X-ray crystallographic and NMR data. Monitoring the regioselectivity of the reaction by iodination revealed a 16.6:1.6:1.0 ortho:meta:para ratio. Interestingly, when the TMP(H) containing solution was heated under reflux for 18 hours more meta-isomer was produced (corresponding ratio 3.7:4.2:1.0). It is likely that this change has its origin in a retro reaction that produces the original base 1 as an intermediate. Theoretical calculations at the DFT level using the B3LYP method and the 6-311G** basis set were used to probe the energetics of both monometallic and bimetallic systems. In accord with the experimental results, it was found that ortho-metallation was favoured by sodiation; whereas meta- (closely followed by para-) metallation was favoured by direct sodium-mediated zincation.

A µ4-oxide-containing a dimeric variant of a sodium dialkyl(amido)zincate reagent.

Post-metallation derivatives of the sodium dialkyl(amido)zincate reagent (TMEDA)Na(µ-TMP)Zn((t)Bu)(2) (TMEDA is N,N,N',N'-tetramethylethylenediamine and TMP is 2,2,6,6-tetramethylpiperidide) have been of structural interest due to the insight they give into aromatic metallation mechanisms. Here, the aromatic substrate is formally replaced with [ZnO](2) to give tetra-tert-butyldi-µ(4)-oxido-bis(tetramethylethylenediamine-κ(2)N,N')bis(µ(2)-2,2,6,6-tetramethylpiperidin-1-ido-κ(2)N:N)disodiumtetrazinc hexane 0.59-solvate, [Na(2)Zn(4)(C(4)H(9))(4)(C(9)H(18)N)(2)O(2)(C(6)H(16)N(2))(2)]·0.59C(6)H(14). The crystallographically centrosymmetric complex retains many of the structural features of its parent monomer but has an unusual dimeric structure, with a central planar Zn-O-Zn-O ring joined to two orthogonal near-planar Zn-O-Na-N rings through the distorted tetrahedral geometries of the oxide ions.

Structural elaboration of the surprising ortho-zincation of benzyl methyl ether.

Breaking with convention, the reaction of the sodium zincate, [(TMEDA)Na(mu-TMP)(mu-(t)Bu)Zn((t)Bu)] with benzyl methyl ether (PhCH(2)OMe) produces exclusively an ortho-zincated intermediate [(TMEDA)Na(mu-TMP)(mu-C(6)H(4)CH(2)OMe)Zn((t)Bu)] instead of the expected "thermodynamic" alpha-metallated product.

Structural variations within group 1 (Li-Cs)+ (2,2,6,6-tetramethyl-1-piperidinyloxy)- complexes made via metallic reduction of the nitroxyl radical.

Treatment of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) with a group 1 metal (Li, Na, K, Rb, or Cs), resulted in the reduction of this important radical to the TEMPO(-) anion--the first examples of elemental-metal single electron reduction of the radical to its anionic form. The synthesis and characterization of seven alkali metal TEMPO(-) complexes are reported. A variety of structural motifs are encountered depending on the choice of metal and/or solvent. (THF)(2) x [Li(+)(TEMPO(-))](4) 1 crystallized from THF as a cyclic (Li(4)O(4)) molecule. Two Li centers are stabilized by coordination to a THF molecule; the others by intramolecular coordination to N(TEMPO) atoms. [(THF) x Na(+)(TEMPO(-))](4) 2 exists as a distorted cubane where each Na center is coordinated to a THF molecule. No appreciable Na-N(TEMPO) coordination is observed. [(THF)(2) x Na(+)(3)(TEMPO(-))(2)(OH)](2) 3 was serendipitously prepared and exists as a distorted bis(cubane). It is envisaged that 3 is formed from 2 by insertion of a (Na-OH)(2) double bridge into its framework. [Na(+)(4)(mu(3)-TEMPO(-))(2)(mu(2)-TEMPO(-))(2)(TMEDA)(2)] 4, adopts a four-runged ladder structure, whereby the two outer Na centers are coordinated to TMEDA, in addition to two mu(2)-O and a N atom. The inner metal atoms are bound to three mu(3)-O atoms and a N atom. [(THF) x K(+)(TEMPO(-))](4) 5 resembles the motif found for 2; however, presumably because of the larger size of the metal, K-N(TEMPO) interactions are present in 5. The asymmetric unit of [(TMEDA) x Rb(+)(2)(TEMPO(-))(2)](2) 6 comprises a Rb(4)O(4) cubane with half a molecule of TMEDA coordinated to each metal. From a supramolecular perspective, 6 exists as a polymeric array of cubane units connected by TMEDA bridges. Completing the series, [Cs(+)(TEMPO)](infinity) 7 crystallizes from hexane to form a donor-free polymeric complex. Complexes 1, 2, and 4-7 are soluble in D(8)-THF solution, and their NMR spectra are reported. The solution structures in donor solvent appear virtually identical.