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ABSTRACT: Undercover agent: Masquerading as a simple donor-acceptor complex (1), sodium amide substoichiometrically activates tBu2 Zn for the challenging 1,6-addition of a tert-butyl group to benzophenone. In contrast, the nonactivated tBu2 Zn is ineffectual.
Angewandte Chemie International Edition 06/2013; · 13.45 Impact Factor
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ABSTRACT: Designed to extend the synthetically important alkali-metal diisopropylamide [N(i)Pr(2); DA] class of compounds, the first example of a hetero-alkali-metallic complex of DA has been prepared as a partial TMEDA solvate. Revealed by an X-ray crystallographic study, its structure exists as a discrete lithium-rich trinuclear Li(2)KN(3) heterocycle, with TMEDA only solvating the largest of the alkali-metals, with the two-coordinate lithium atoms being close to linearity [161.9(2)°]. A variety of NMR spectroscopic studies, including variable temperature and DOSY NMR experiments, suggests that this new form of LDA maintains its integrity in non-polar hydrocarbon solution. This complex thus represents a rare example of a KDA molecule which is soluble in non-polar medium without the need for excessive amounts of solubilizing Lewis donor being added.
Dalton Transactions 01/2013; · 3.84 Impact Factor
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ABSTRACT: Five novel neutral homometallic complexes which contain the anthracen-9-olate anion have been prepared and characterised by treating anthrone with an organometallic base to induce aromatisation. Three of these complexes [(donor)·M(OC(14)H(9))](2) () are dimeric and contain sodium, lithium and potassium respectively. For and the donor is N,N,N',N'-tetramethylethylenediamine (TMEDA) whilst for it is N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA). When bimetallic reagents such as [(TMEDA)·Na(μ-(t)Bu)(μ-TMP)Zn((t)Bu)] are employed, only the alkali-metal-containing species is isolated (e.g., in this case). Providing a contrast, complexes [(TMEDA)·Mg(OC(14)H(9))(n)Bu] and [(TMEDA)·Zn(OC(14)H(9))Et] are monomeric. The alkali metal complexes were prepared by reacting anthrone with one molar equivalent of either n-butylsodium, n-butyllithium or (trimethylsilyl)methylpotassium in the presence of the required donor solvent. For and , equimolar quantities of di-n-butylmagnesium and diethylzinc, respectively, were reacted with anthrone in the presence of TMEDA. The solid-state structures and the arene solution structures of have been determined by X-ray crystallography and NMR spectroscopy respectively.
Dalton Transactions 12/2012; · 3.84 Impact Factor
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ABSTRACT: The title compound, [Na(CHNSi)(CHN)] , was found to consist of dimeric [Na(NSiMe)] units with crystallographically imposed centrosymmetry based upon four-membered NaNNaN rings. The dimers are bridged by ,,','-tetra-methyl-ethylenediamine ligands, which act in an unusual extended non-chelating coordination mode. This gives a one-dimensional coordination polymer that extends parallel to the -axis direction.
Acta Crystallographica Section E Structure Reports Online 12/2012; 68(Pt 12):m1468. · 0.35 Impact Factor
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ABSTRACT: The title compound, [Na 2 (C 6 H 18 NSi 2) 2 (C 6 H 16 N 2)] n , was found to consist of dimeric [Na(NSiMe 3) 2 ] units with crystal-lographically imposed centrosymmetry based upon four-membered NaNNaN rings. The dimers are bridged by N,N,N 0 ,N 0 -tetramethylethylenediamine ligands, which act in an unusual extended non-chelating coordination mode. This gives a one-dimensional coordination polymer that extends parallel to the a-axis direction.
Acta Crystallographica Section E Structure Reports Online 11/2012; E68:m1468. · 0.35 Impact Factor
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ABSTRACT: New coordination complexes of the neutral tripodal tetra-amine Me(6)TREN with tBu(3)Ga or tBu(2)Zn have been synthesised and studied with their molecular structures revealing, for the first time, coordination to metal centres via an η(1) or η(2) mode, adding to previously reported η(3) and η(4) ligated examples.
Dalton Transactions 07/2012; 41(34):10141-4. · 3.84 Impact Factor
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ABSTRACT: 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.
Angewandte Chemie International Edition 06/2012; 51(28):6934-7. · 13.45 Impact Factor
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ABSTRACT: Sodium TMP-zincate, [(TMEDA)Na(TMP)((t)Bu)Zn((t)Bu)], can deproto-zincate N-Boc pyrrolidine at ambient temperature in hexane solution, whereas in toluene the captured α-carbanion of the heterocycle attacks the solvent setting off a cascade of reactions that ultimately produce a pyrrolidine-substituted enolate.
Chemical Communications 04/2012; 48(43):5265-7. · 6.17 Impact Factor
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ABSTRACT: As the aluminate base [LiAl(TMP)(2)(iBu)(2)] 1 displays halogen tolerance towards substituted aromatics, 4-halo-anisoles have been ortho-aluminated and electrophilically quenched to form synthetically useful multi-heterohalogenated anisoles, with the Al intermediates along the route structurally defined.
Chemical Communications 03/2012; 48(39):4674-6. · 6.17 Impact Factor
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Chemical Communications (London) 01/2012;
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ABSTRACT: Gaining a deeper understanding of the modus operandi of heterometallic lithium aluminate bases towards deprotonative metallation of substituted aromatic substrates, we have studied the reactions and their aftermath between our recently developed bis-amido base '(i)Bu(2)Al(μ-TMP)(2)Li'3 and 3-halogenated anisoles. Ortho-metallation of 3-iodoanisole with 3 results in a delicately poised heterometallic intermediate whose breakdown into homometallic species and benzyne cannot be suppressed, even at low temperature or in a non-polar solvent (hexane). Homometallic components [LiI·TMP(H)](4) (5) and (i)Bu(2)Al(TMP)·THF (6) have been isolated while the reactive benzyne intermediate has been trapped via Diels-Alder cyclization with 1,3-diphenylisobenzofuran yielding 1-methoxy-9-10-diphenyl-9-10-epoxyanthracene (7). In polar THF solution, nucleophilic addition of LiTMP across the benzyne functionality followed by electrophilic quenching with iodine yields the trisubstituted aromatic species 1-(2-iodo-3-methoxyphenyl)-2,2,6,6-tetramethylpiperidide (8). Compounds 5-8 have been characterized by single-crystal X-ray diffraction in the solid state and multinuclear NMR spectroscopy in solution. By considering these collated results, a plausible reaction mechanism has been proposed for the breakdown of the aforementioned intermediate bimetallic framework. Interestingly, the metallation reaction can be controlled by changing to 3-chloroanisole with an excess of base 3, as evidenced by electrophilically trapping the deprotonated aromatic with iodine to give 2-iodo-3-chloroanisole (9).
Dalton Transactions 12/2011; 41(6):1832-9. · 3.84 Impact Factor
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ABSTRACT: Towards a systematic development of the zinc chemistry of the important five-membered nitrogen heterocycle pyrrole, this work reports the synthesis and characterisation of five crystalline zinc-pyrrolyl complexes. Pyrrolyl in this context means where conversion of the N-H bond to an N-zinc bond has occurred. Two neutral complexes, [(t)BuZn(NC(4)H(4))(TMEDA)·HNC(4)H(4)] 1 and [Zn(NC(4)H(4))(2)(TMEDA)] 2, containing one and two pyrrolyl ligands, respectively, were synthesised by reacting di-t-butylzinc with different amounts of pyrrole in the presence of TMEDA (TMEDA is N,N,N',N'-tetramethylethylenediamine). X-ray crystallographic studies established that both adopt mononuclear structures with the salient feature of the former the presence of an additional parent protonated pyrrole molecule which engages its anionic counterpart in N-H…πC-C interactions. Employing a similar synthetic approach but adding n-butylsodium to the reaction mixture in attempts to form ate derivatives delivered three distinct sodium zincate (anionic zinc) compounds in [{(THF)(2)·NaZn(THF)(NC(4)H(4))(3)}(∞)] 3, [{(TMEDA)·Na}(2)Zn(NC(4)H(4))(4)] 4, and [{(PMDETA)·Na}(2)Zn(NC(4)H(4))(4)] 5 (PMDETA is N,N,N',N'',N''-pentamethyldiethylenetriamine). From their crystal structures, the 1 : 1, Na:Zn complex 3 can be classified as a lower-order zincate having three pyrrolyl ligands bound to zinc in a polymeric chain arrangement, while the 2 : 1, Na:Zn complexes 4 and 5 are molecular higher-order zincates having Zn centres fully saturated by four pyrrolyl ligands. Discussion of the structures of 1-5 focuses on the interplay of σ-bonding and π-bonding between the pyrrolyl ligands and the metal centres. Revealingly, the zinc-free sodiopyrrole complex [{(PMDETA)·Na(NC(4)H(4))}(2)] 6, made and characterised for comparison, shows that on its own sodium prefers the former type of bonding, but is forced to switch to the latter type when combined with the stronger Lewis acid zinc in the zincate compositions. Complexes 1-6 have also been characterised in solution by NMR spectroscopy.
Dalton Transactions 11/2011; 40(44):11945-54. · 3.84 Impact Factor
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Angewandte Chemie International Edition 09/2011; 50(41):9668-71. · 13.45 Impact Factor
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ABSTRACT: The surprising transformation of the saturated diamine (iPr)NHCH(2)CH(2)NH(iPr) to the unsaturated diazaethene [(iPr)NCH═CHN(iPr)](2-) via the synergic mixture nBuM, (tBu)(2)Zn and TMEDA (where M = Li, Na; TMEDA = N,N,N',N'-tetramethylethylenediamine) has been investigated by multinuclear NMR spectroscopic studies and DFT calculations. Several pertinent intermediary and related compounds (TMEDA)Li[(iPr)NCH(2)CH(2)NH(iPr)]Zn(tBu)(2) (3), (TMEDA)Li[(iPr)NCH(2)CH(2)CH(2)N(iPr)]Zn(tBu) (5), {(THF)Li[(iPr)NCH(2)CH(2)N(iPr)]Zn(tBu)}(2) (6), and {(TMEDA)Na[(iPr)NCH(2)CH(2)N(iPr)]Zn(tBu)}(2) (11), characterized by single-crystal X-ray diffraction, are discussed in relation to their role in the formation of (TMEDA)M[(iPr)NCH═CHN(iPr)]Zn(tBu) (M = Li, 1; Na, 10). In addition, the dilithio zincate molecular hydride [(TMEDA)Li](2)[(iPr)NCH(2)CH(2)N(iPr)]Zn(tBu)H 7 has been synthesized from the reaction of (TMEDA)Li[(iPr)NCH(2)CH(2)NH(iPr)]Zn(tBu)(2)3 with nBuLi(TMEDA) and also characterized by both X-ray crystallographic and NMR spectroscopic studies. The retention of the Li-H bond of 7 in solution was confirmed by (7)Li-(1)H HSQC experiments. Also, the (7)Li NMR spectrum of 7 in C(6)D(6) solution allowed for the rare observation of a scalar (1)J(Li-H) coupling constant of 13.3 Hz. Possible mechanisms for the transformation from diamine to diazaethene, a process involving the formal breakage of four bonds, have been determined computationally using density functional theory. The dominant mechanism, starting from (TMEDA)Li[(iPr)NCH(2)CH(2)N(iPr)]Zn(tBu) (4), involves the formation of a hydride intermediate and leads directly to the observed diazaethene product. In addition the existence of 7 in equilibrium with 4 through the dynamic association and dissociation of a (TMEDA)LiH ligand, also provides a secondary mechanism for the formation of the diazaethene. The two reaction pathways (i.e., starting from 4 or 7) are quite distinct and provide excellent examples in which the two distinct metals in the system are able to interact synergically to catalyze this otherwise challenging transformation.
Journal of the American Chemical Society 08/2011; 133(34):13706-17. · 9.91 Impact Factor
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Berichte der deutschen chemischen Gesellschaft 08/2011; 2011(30):4675 - 4679. · 2.94 Impact Factor
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Angewandte Chemie International Edition 08/2011; 50(34):7776-80. · 13.45 Impact Factor
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ABSTRACT: Molecular salt cellars: The addition of substoichiometric quantities of lithium halides to the lithium hexamethyldisilazide was studied. Surprisingly, a novel class of mixed amido-halide macrocyclic complexes, namely metal anionic crowns (MACs) was revealed (see picture: Li pink, N yellow, Cl green, Si orange, C black).
Angewandte Chemie International Edition 07/2011; 50(36):8375-8. · 13.45 Impact Factor
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ABSTRACT: Studied extensively in solution and in the solid state, Li(TMP) (TMP=2,2,6,6-tetramethylpiperidide) is an important utility reagent popular as a strongly basic, weakly nucleophilic tool for CH metallation. Recently, there has been a surge in interest in mixed metal derivatives containing the bulky TMP anion. Herein, we start to develop hetero (alkali metal) TMP chemistry by reporting the N,N,N',N'-tetramethylethylenediamine (TMEDA)-hemisolvated sodium-lithium cycloheterodimer [(tmeda)Na(μ-tmp)(2) Li], and its TMEDA-free variant [{Na(μ-tmp)Li(μ-tmp)}(∞) ], which provides a rare example of a crystallographically authenticated polymeric alkali metal amide. Experimental observations suggest that the former is a kinetic intermediate en route to the latter thermodynamic product. Furthermore, a third modification, the mixed potassium-lithium-rich cycloheterotrimer [(tmeda)K(μ-tmp)Li(μ-tmp)Li(μ-tmp)], has also been synthesised and crystallographically characterised. On moving to the bulkier tridentate donor N,N,N',N'',N''-pentamethyldiethylenediamine (PMDETA), the additional ligation forces the sodium-lithium and potassium-dilithium ring species to open giving the acyclic arc-shaped complexes [(pmdeta)Na(μ-tmp)Li(tmp)] and [(pmdeta)K(μ-tmp)Li(μ-tmp)Li(tmp)], respectively. Completing the series, the potassium-lithium and potassium-sodium derivatives [(pmdeta)K(μ-tmp)(2) M] (M=Li, Na) have also been isolated as closed structures with a distinctly asymmetric central MN(2) K ring. Collectively, these seven new bimetallic compounds display five distinct structural motifs, four of which have never hitherto been witnessed in TMP chemistry and three of which are unprecedented in the vast structural library of alkali metal amide chemistry.
Chemistry 07/2011; 17(32):8820-31. · 5.93 Impact Factor
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Angewandte Chemie International Edition 07/2011; 50(40):9242-3. · 13.45 Impact Factor
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ABSTRACT: 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.
Acta crystallographica. Section C, Crystal structure communications 07/2011; 67(Pt 7):m252-4. · 0.78 Impact Factor
