Evaluating cis‐2,6‐Dimethylpiperidide (cis‐DMP) as a Base Component in Lithium‐Mediated Zincation Chemistry

Most recent advances in metallation chemistry have centred on the bulky secondary amide 2,2,6,6‐tetramethylpiperidide (TMP) within mixed metal, often ate, compositions. However, the precursor amine TMP(H) is rather expensive so a cheaper substitute would be welcome. Thus this study was aimed towards developing cheaper non‐TMP based mixed‐metal bases and, as cis‐2,6‐dimethylpiperidide (cis‐DMP) was chosen as the alternative amide, developing cis‐DMP zincate chemistry which has received meagre attention compared to that of its methyl‐rich counterpart TMP. A new lithium diethylzincate, [(TMEDA)LiZn(cis‐DMP)Et₂] (TMEDA=N,N,N′,N′‐tetramethylethylenediamine) has been synthesised by co‐complexation of Li(cis‐DMP), Et₂Zn and TMEDA, and characterised by NMR (including DOSY) spectroscopy and X‐ray crystallography, which revealed a dinuclear contact ion pair arrangement. By using N,N‐diisopropylbenzamide as a test aromatic substrate, the deprotonative reactivity of [(TMEDA)LiZn(cis‐DMP)Et₂] has been probed and contrasted with that of the known but previously uninvestigated di‐tert‐butylzincate, [(TMEDA)LiZn(cis‐DMP)tBu₂]. The former was found to be the superior base (for example, producing the ortho‐deuteriated product in respective yields of 78 % and 48 % following D₂O quenching of zincated benzamide intermediates). An 88 % yield of 2‐iodo‐N,N‐diisopropylbenzamide was obtained on reaction of two equivalents of the diethylzincate with the benzamide followed by iodination. Comparisons are also drawn using 1,1,1,3,3,3‐hexamethyldisilazide (HMDS), diisopropylamide and TMP as the amide component in the lithium amide, Et₂Zn and TMEDA system. Under certain conditions, the cis‐DMP base system was found to give improved results in comparison to HMDS and diisopropylamide (DA), and comparable results to a TMP system. Two novel complexes isolated from reactions of the di‐tert‐butylzincate and crystallographically characterised, namely the pre‐metallation complex [{(iPr)₂N(Ph)C?O}LiZn(cis‐DMP)tBu₂] and the post‐metallation complex [(TMEDA)Li(cis‐DMP){2‐[1‐C(=O)N(iPr)₂]C₆H₄}Zn(tBu)], shed valuable light on the structures and mechanisms involved in these alkali‐metal‐mediated zincation reactions. Aspects of these reactions are also modelled by DFT calculations.     

Developing a Hetero‐Alkali‐Metal Chemistry of 2,2,6,6‐Tetramethylpiperidide (TMP): Stoichiometric and Structural Diversity within a Series of Lithium/Sodium,Lithium/Potassium and Sodium/Potassium TMP Compounds

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 C? H 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)₂Li], 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)₂M] (M=Li, Na) have also been isolated as closed structures with a distinctly asymmetric central MN₂K 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.     

Structurally Defined Potassium‐Mediated Zincation of Pyridine and 4‐R‐Substituted Pyridines (R=Et,iPr, tBu,Ph, and Me2N) by Using Dialkyl–TMP–Zincate Bases

Two potassium–dialkyl–TMP–zincate bases [(pmdeta)K(μ‐Et)(μ‐tmp)Zn(Et)] ( 1 ) (PMDETA=N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine, TMP=2,2,6,6‐tetramethylpiperidide), and [(pmdeta)K(μ‐nBu)(μ‐tmp)Zn(nBu)] ( 2 ), have been synthesized by a simple co‐complexation procedure. Treatment of 1 with a series of substituted 4‐R‐pyridines (R=Me₂N, H, Et, iPr, tBu, and Ph) gave 2‐zincated products of the general formula [{2‐Zn(Et)₂‐μ‐4‐R‐C₅H₃N}₂ ? 2{K(pmdeta)}] ( 3 – 8 , respectively) in isolated crystalline yields of 53, 16, 7, 23, 67, and 51 %, respectively; the treatment of 2 with 4‐tBu‐pyridine gave [{2‐Zn(nBu)₂‐μ‐4‐tBu‐C₅H₃N}₂ ? 2{K(pmdeta)}] ( 9 ) in an isolated crystalline yield of 58 %. Single‐crystal X‐ray crystallographic and NMR spectroscopic characterization of 3 – 9 revealed a novel structural motif consisting of a dianionic dihydroanthracene‐like tricyclic ring system with a central diazadicarbadizinca (ZnCN)₂ ring, face‐capped on either side by PMDETA‐wrapped K⁺ cations. All the new metalated pyridine complexes share this dimeric arrangement. As determined by NMR spectroscopic investigations of the reaction filtrates, those solutions producing 3 , 7 , 8 , and 9 appear to be essentially clean reactions, in contrast to those producing 4 , 5 , and 6 , which also contain laterally zincated coproducts. In all of these metalation reactions, the potassium–zincate base acts as an amido transfer agent with a subsequent ligand‐exchange mechanism (amido replacing alkyl) inhibited by the coordinative saturation, and thus, low Lewis acidity of the 4‐coordinate Zn centers in these dimeric molecules. Studies on analogous trialkyl–zincate reagents in the absence and presence of stoichiometric or substoichiometric amounts of TMP(H) established the importance of Zn? N bonds for efficient zincation.     

Homoleptic Zincate‐Promoted Room‐Temperature Halogen–Metal Exchange of Bromopyridines

Homoleptic lithium tri‐ and tetraalkyl zincates were reacted with a set of bromopyridines. Efficient and chemoselective bromine–metal exchanges were realized at room temperature with a substoichiometric amount of nBu₄ZnLi₂?TMEDA reagent (1/3 equiv; TMEDA=N,N,N′,N′‐tetramethylethylenediamine). This reactivity contrasted with that of tBu₄ZnLi₂?TMEDA, which was inefficient below one equivalent. DFT calculations allowed us to rationalize the formation of N???Li stabilized polypyridyl zincates in the reaction. The one‐pot difunctionalization of dibromopyridines was also realized using the reagent stoichiometrically. The direct creation of C? Zn bonds in bromopyridines enabled us to perform efficient Negishi‐type cross‐couplings.     

[P,P‐Di‐tert‐butyl‐N‐trimethylsilyl‐P‐(trimethylsilylamino)phosphine imidato‐κ2N,N′]bis(pyridine‐κN)lithium(I)

In the title compound, [Li(C₁₄H₃₆N₂PSi₂)(C₅H₅N)₂], the bulky chelating monoanionic P,P‐di‐tert‐butyl‐N‐trimethylsilyl‐P‐(trimethylsilylamino)phosphine imidate ligand and two pyridine ligands bind to Li in a pseudo‐tetrahedral arrangement with twofold symmetry. The Li—N_phosphine distance is 2.048 (5) Å, while the Li?P distance is 2.520 (6) Å.     

fac‐Tri­carbonyl(4,4′‐di­methyl‐2,2′‐bi­pyridine)­tri­phenyl­tin(II)­rhenium(I)

The title organometallic compound, fac‐tri­carbonyl‐2κ³C‐(4,4′‐di­methyl‐2,2′‐bi­pyridine)‐2κ²N,N′‐tri­phenyl‐1κ³C¹‐tin(II)­rhenium(I)(Sn—Re), [ReSn(C₆H₅)₃(C₁₂H₁₂N₂)(CO)₃], con­tains three unique π–π stacking interactions. The result is an infinite chain of uninterrupted alternating intra‐ and intermolecular offset π–π stacking interactions throughout the crystal lattice. This extended π–π stacking arrangement, and an additional isolated intramolecular π–π interaction between the remaining 4,4′‐di­methyl‐2,2′‐bi­pyridine ring and a second phenyl group, impose geometric constraints on the Re and Sn atoms, yielding distorted octahedral and tetrahedral coordinations, respectively, for the metal centers.     

Imino‐Bridged Bisphosphaalkenes (2,4‐Diphospha‐3‐azapentadienes)

Deprotonation of aminophosphaalkenes (RMe₂Si)₂C?PN(H)(R′) (R=Me, iPr; R′=tBu, 1‐adamantyl (1‐Ada), 2,4,6‐tBu₃C₆H₂ (Mes*)) followed by reactions of the corresponding Li salts Li[(RMe₂Si)₂C?P(M)(R′)] with one equivalent of the corresponding P‐chlorophosphaalkenes (RMe₂Si)₂C?PCl provides bisphosphaalkenes (2,4‐diphospha‐3‐azapentadienes) [(RMe₂Si)₂C?P]₂NR′. The thermally unstable tert‐butyliminobisphosphaalkene [(Me₃Si)₂C?P]₂NtBu ( 4 a ) undergoes isomerisation reactions by Me₃Si‐group migration that lead to mixtures of four‐membered heterocyles, but in the presence of an excess amount of (Me₃Si)₂C?PCl, 4 a furnishes an azatriphosphabicyclohexene C₃(SiMe₃)₅P₃NtBu ( 5 ) that gave red single crystals. Compound 5 contains a diphosphirane ring condensed with an azatriphospholene system that exhibits an endocylic P?C double bond and an exocyclic ylidic P⁽⁺⁾? C^(?)(SiMe₃)₂ unit. Using the bulkier iPrMe₂Si substituents at three‐coordinated carbon leads to slightly enhanced thermal stability of 2,4‐diphospha‐3‐azapentadienes [(iPrMe₂Si)₂C?P]₂NR′ (R′=tBu: 4 b ; R′=1‐Ada: 8 ). According to a low‐temperature crystal‐structure determination, 8 adopts a non‐planar structure with two distinctly differently oriented P?C sites, but ³¹P NMR spectra in solution exhibit singlet signals. ³¹P NMR spectra also reveal that bulky Mes* groups (Mes*=2,4,6‐tBu₃C₆H₂) at the central imino function lead to mixtures of symmetric and unsymmetric rotamers, thus implying hindered rotation around the P? N bonds in persistent compounds [(RMe₂Si)₂C?P]₂NMes* ( 11 a , 11 b ). DFT calculations for the parent molecule [(H₃Si)₂C?P]₂NCH₃ suggest that the non‐planar distortion of compound 8 will have steric grounds.     

N‐Benzyl‐2′‐iodo­cinnamanilide and N‐benzyl‐2′‐iodo‐4′‐methyl‐2‐phenyl­cinnamanilide

The aromatic ring of the cinnamic moiety in N‐benzyl‐2′‐iodo­cinnamanilide, C₂₂H₁₈INO, (I), and N‐benzyl‐2′‐iodo‐4′‐methyl‐2‐phenyl­cinnamanilide, C₂₉H₂₄INO, (II), makes a dihedral angle with the iodo­phenyl ring of 72.1 (2) and 81.0 (2)° in (I) and (II), respectively. In (I), mol­ecules exist as discrete components, while in (II), they form infinite chains along the b axis, through I?O non‐bonded interactions.     

The high‐anti conformation of 8‐aza‐1,3‐dide­aza‐2′‐deoxy­adenosine

In the title compound, 4‐amino‐1‐(2‐deoxy‐β‐d ‐erythro‐pento­furan­osyl)‐1H‐benzotriazole, C₁₁H₁₄N₄O₃, the conformation of the N‐glycosidic bond is in the high‐anti range [χ = ?77.1 (4)°] and the 2′‐deoxy­ribo­furan­ose moiety adopts a 2′‐­endo (²E) sugar puckering. The 5′‐hydroxyl group is disordered and has conformations ap with γ = 171.1 (3)° [occupation of 61.4 (3)%] and +sc with γ = 52.4 (6)° [occupation of 38.6 (3)%]. The nucleobases are stacked in the crystal state.     

Four N7‐alkoxybenzyl‐substituted 4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐diones: hydrogen‐bonded supramolecular structures in zero,one, two or three dimensions

3‐tert‐Butyl‐7‐(4‐methoxybenzyl)‐4′,4′‐dimethyl‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione, C₃₁H₃₇N₃O₃, (I), 3‐tert‐butyl‐7‐(2,3‐dimethoxybenzyl)‐4′,4′‐dimethyl‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione, C₃₂H₃₉N₃O₄, (II), 3‐tert‐butyl‐4′,4′‐dimethyl‐7‐(3,4‐methylenedioxybenzyl)‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione, C₃₁H₃₅N₃O₄, (III), and 3‐tert‐butyl‐4′,4′‐dimethyl‐1‐phenyl‐7‐(3,4,5‐trimethoxybenzyl)‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione ethanol 0.67‐solvate, C₃₃H₄₁N₃O₅·0.67C₂H₆O, (IV), all contain reduced pyridine rings having half‐chair conformations. The molecules of (I) and (II) are linked into centrosymmetric dimers and simple chains, respectively, by C—H...O hydrogen bonds, augmented only in (I) by a C—H...π hydrogen bond. The molecules of (III) are linked by a combination of C—H...O and C—H...π hydrogen bonds into a chain of edge‐fused centrosymmetric rings, further linked by weak hydrogen bonds into supramolecular arrays in two or three dimensions. The heterocyclic molecules in (IV) are linked by two independent C—H...O hydrogen bonds into sheets, from which the partial‐occupancy ethanol molecules are pendent. The significance of this study lies in its finding of a very wide range of supramolecular aggregation modes dependent on rather modest changes in the peripheral substituents remote from the main hydrogen‐bond acceptor sites.     

Reduced 3,4′‐bipyrazoles from a simple pyrazole precursor: synthetic sequence,molecular structures and supramolecular assembly

The reaction of 5‐chloro‐3‐methyl‐1‐phenyl‐1H‐pyrazole‐4‐carbaldehyde and N‐benzylmethylamine under microwave irradiation gives 5‐[benzyl(methyl)amino]‐3‐methyl‐1‐phenyl‐1H‐pyrazole‐4‐carbaldehyde, C₁₉H₁₉N₃O, (I). Subsequent reactions under basic conditions, between (I) and a range of acetophenones, yield the corresponding chalcones. These undergo cyclocondensation reactions with hydrazine to produce reduced bipyrazoles which can be N‐formylated with formic acid or N‐acetylated with acetic anhydride. The structures of (I) and of representative examples from this reaction sequence are reported, namely the chalcone (E )‐3‐{5‐[benzyl(methyl)amino]‐3‐methyl‐1‐phenyl‐1H‐pyrazol‐4‐yl}‐1‐(4‐bromophenyl)prop‐2‐en‐1‐one, C₂₇H₂₄BrN₃O, (II), the N‐formyl derivative (3RS )‐5′‐[benzyl(methyl)amino]‐3′‐methyl‐1′,5‐diphenyl‐3,4‐dihydro‐1′H ,2H‐[3,4′‐bipyrazole]‐2‐carbaldehyde, C₂₈H₂₇N₅O, (III), and the N‐acetyl derivative (3RS )‐2‐acetyl‐5′‐[benzyl(methyl)amino]‐5‐(4‐methoxyphenyl)‐3′‐methyl‐1′‐phenyl‐3,4‐dihydro‐1′H ,2H‐[3,4′‐bipyrazole], which crystallizes as the ethanol 0.945‐solvate, C₃₀H₃₁N₅O₂·0.945C₂H₆O, (IV). There is significant delocalization of charge from the benzyl(methyl)amino substituent onto the carbonyl group in (I), but not in (II). In each of (III) and (IV), the reduced pyrazole ring is modestly puckered into an envelope conformation. The molecules of (I) are linked by a combination of C—H…N and C—H…π(arene) hydrogen bonds to form a simple chain of rings; those of (III) are linked by a combination of C—H…O and C—H…N hydrogen bonds to form sheets of R ²₂(8) and R ⁶₆(42) rings, and those of (IV) are linked by a combination of O—H…N and C—H…O hydrogen bonds to form a ribbon of edge‐fused R ²₄(16) and R ⁴₄(24) rings.     

Monodentate and bridging behaviour of the sulfur‐containing ligand 4′‐[4‐(methylsulfanyl)phenyl]‐4,2′:6′,4′′‐terpyridine in two discrete zinc(II) complexes with acetylacetonate

The Zn complexes bis(acetylacetonato‐κ²O,O′)bis{4′‐[4‐(methylsulfanyl)phenyl]‐4,2′:6′,4′′‐terpyridine‐κN¹}zinc(II), [Zn(C₅H₇O₂)₂(C₂₂H₁₇N₃S)₂], (I), and {μ‐4′‐[4‐(methylsulfanyl)phenyl]‐4,2′:6′,4′′‐terpyridine‐κ²N¹:N^1′′}bis[bis(acetylacetonato‐κ²O,O′)zinc(II)], [Zn₂(C₅H₇O₂)₄(C₂₂H₁₇N₃S)], (II), are discrete entities with different nuclearities. Compound (I) consists of two centrosymmetrically related monodentate 4′‐[4‐(methylsulfanyl)phenyl]‐4,2′:6′,4′′‐terpyridine (L1) ligands binding to one Zn^II atom sitting on an inversion centre and two centrosymmetrically related chelating acetylacetonate (acac) groups which bind via carbonyl O‐atom donors, giving an N₂O₄ octahedral environment for Zn^II. Compound (II), however, consists of a bis‐monodentate L1 ligand bridging two Zn^II atoms from two different Zn(acac)₂ fragments. Intra‐ and intermolecular interactions are weak, mainly of the C—H...π and π–π types, mediating similar layered structures. In contrast to related structures in the literature, sulfur‐mediated nonbonding interactions in (II) do not seem to have any significant influence on the supramolecular structure.     

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(^tBu)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‐μ₄‐oxido‐bis(tetramethylethylenediamine‐κ²N,N′)bis(μ₂‐2,2,6,6‐tetramethylpiperidin‐1‐ido‐κ²N:N)disodiumtetrazinc hexane 0.59‐solvate, [Na₂Zn₄(C₄H₉)₄(C₉H₁₈N)₂O₂(C₆H₁₆N₂)₂]·0.59C₆H₁₄. 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.     

Reaction of N‐Heterocyclic Silylenes with Thioketone: Formation of Silicon–Sulfur Three (Si‐C‐S)‐ and Five (Si‐C‐C‐C‐S)‐Membered Ring Systems

Three‐ and five‐membered rings that bear the (Si‐C‐S ) and (Si‐C‐C‐C‐S ) unit have been synthesized by the reactions of L SiCl ( 1 ; L =PhC(NtBu)₂) and L′ Si ( 2 ; L′ =CH{(C?CH₂)(CMe)(2,6‐iPr₂C₆H₃N)₂}) with the thioketone 4,4′‐bis(dimethylamino)thiobenzophenone. Treatment of 4,4′‐bis(dimethylamino)thiobenzophenone with L SiCl at room temperature furnished the [1+2]‐cycloaddition product silathiacyclopropane 3 . However, reaction of 4,4′‐bis(dimethylamino)thiobenzophenone with L′ Si at low temperature afforded a [1+4]‐cycloaddition to yield the five‐membered ring product 4 . Compounds 3 and 4 were characterized by NMR spectroscopy, EIMS, and elemental analysis. The molecular structures of 3 and 4 were unambiguously established by single‐crystal X‐ray structural analysis. The room‐temperature reaction of 4,4′‐bis(dimethylamino)thiobenzophenone with L′ Si resulted in products 4 and 5 , in which 4 is the dearomatized product and 5 is formed under the 1,3‐migration of a hydrogen atom from the aromatic phenyl ring to the carbon atom of the C? S unit. Furthermore, the optimized structures of probable products were investigated by using DFT calculations.     

LiTMP Trans‐Metal‐Trapping of Fluorinated Aromatic Molecules: A Comparative Study of Aluminum and Gallium Carbanion Traps

Fluoroaromatic scaffolds pose a challenge to lithiation due to low stability of lithiated intermediates. Here we apply trans‐metal‐trapping (TMT) to a series of key fluorinated aromatics. In TMT, LiTMP performs the metalation, while an organometallic trap intercepts the emergent carbanion. This study contrasts the trapping abilities of i Bu₂AlTMP and Ga(CH₂SiMe₃)₃, structurally mapping their TMT reactions and probing relative stabilities of metalated fluoroaromatic intermediates by NMR studies. Results show the installed Al−C(aryl) bonds are more prone to decomposition by benzyne formation and Li‐F liberation, than the Ga−C(aryl) species. The latter are thus better for onward reactivity as demonstrated in cross‐coupling reactions with benzoyl chloride that produce ketones.     

Concealed Cyclotrimeric Polymorph of Lithium 2,2,6,6‐Tetramethylpiperidide Unconcealed: X‐Ray Crystallographic and NMR Spectroscopic Studies

Lithium 2,2,6,6‐tetramethylpiperidide (LiTMP), one of the most important polar organometallic reagents both in its own right and as a key component of ate compositions, has long been known for its classic cyclotetrameric (LiTMP)₄ solid‐state structure. Made by a new approach through transmetalation of Zn(TMP)₂ with tBuLi in n‐hexane solution, a crystalline polymorph of LiTMP has been uncovered. X‐ray crystallographic studies at 123(2) K revealed this polymorph crystallises in the hexagonal space group P6₃/m and exhibited a discrete cyclotrimeric (C_3h) structure with a strictly planar (LiN)₃ ring containing three symmetrically equivalent TMP chair‐shaped ligands. The molecular structure of (LiTMP)₄ was redetermined at 123(2) K, because its original crystallographic characterisation was done at ambient temperature. This improved redetermination confirmed a monoclinic C2/c space group with the planar (LiN)₄ ring possessing pseudo (non‐crystallographic) C_4h symmetry. Investigation of both metalation and transmetalation routes to LiTMP under different conditions established that polymorph formation did not depend on the route employed but rather the temperature of crystallisation. Low‐temperature (freezer at ?35 °C) cooling of the reaction solution favoured (LiTMP)₃; whereas high‐temperature (bench) storage favoured (LiTMP)₄. Routine ¹H and ¹³C NMR spectroscopic studies in a variety of solvents showed that (LiTMP)₃ and (LiTMP)₄ exist in equilibrium, whereas ¹H DOSY NMR studies gave diffusion coefficient results consistent with their relative sizes.     

Reactivity of ortho‐Substituted Aryl–Palladium Complexes towards Carbodiimides,Isothiocyanates, Nitriles,and Cyanamides

Complexes [Pd(C₆H₃XH‐2‐R′‐5)Y(N^N)] (X=O, NH; Y=Br, I; R′=H, NO₂; N^N=N,N,N′,N′‐tetramethylethylenediamine (tmeda), 2,2′‐bipyridine (bpy), 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine (dtbbpy)) react with RN?C?E (E=NR, S) or RC≡N (R=alkyl, aryl, NR′′₂) and TlOTf (OTf=CF₃SO₃) to give, respectively, 1) products of the insertion of the C?E group into the C? Pd bond, protonation of the N atom, and coordination of X to Pd, [Pd{κ²‐X,E‐(XC₆H₃{EC(NHR)}‐2‐R′‐4)}(N^N)]OTf or [Pd(κ²‐X,N‐{ZC₆H₃(NH?CR)‐2‐R′‐4})(N^N)]OTf, or products of the coordination of carbodiimides and OH addition, [Pd{κ²‐C,N‐(C₆H₄{OC(NR)}NHR‐2)}(bpy)]OTf; or 2) products of the insertion of the C≡N group to Pd and N‐protonation, [Pd(κ²‐X,N‐{XC₆H₃(NH?CR)‐2‐R′‐4})(N^N)]OTf.     

Deprotonative Metalation of Functionalized Aromatics Using Mixed Lithium–Cadmium,Lithium–Indium,and Lithium–Zinc Species

In situ mixtures of CdCl₂?TMEDA (0.5 equiv; TMEDA=N,N,N′,N′‐tetramethylethylenediamine) or InCl₃ (0.33 equiv) with [Li(tmp)] (tmp=2,2,6,6‐tetramethylpiperidino; 1.5 or 1.3 equiv, respectively) were compared with the previously described mixture of ZnCl₂?TMEDA (0.5 equiv) and [Li(tmp)] (1.5 equiv) for their ability to deprotonate anisole, benzothiazole, and pyrimidine. [(tmp)₃CdLi] proved to be the best base when used in tetrahydrofuran at room temperature, as demonstrated by subsequent trapping with iodine. The Cd–Li base then proved suitable for the metalation of a large range of aromatics including benzenes bearing reactive functional groups (CONEt₂, CO₂Me, CN, COPh) or heavy halogens (Br, I), and heterocycles (from the furan, thiophene, pyrrole, oxazole, thiazole, pyridine, and diazine series). Five‐membered heterocycles benefiting from doubly activated positions were similarly dideprotonated at room temperature. The aromatic lithium cadmates thus obtained were involved in palladium‐catalyzed cross‐coupling reactions or simply quenched with acid chlorides.     

Synthesis, Characterization and Biological Activity of Diorganotin（IV） Complexes of N-（3,5-Dibromosalicylidene）-α-amino Acid

The diorganotin（Ⅳ） complexes of N-（3,5-dibromosalicylidene）-α-amino acid, R2Sn（2-O-3,5-Br2C6H2CH= NCHRCOO）（where R=H, Me, i-Pr, Bz; R＇=n-Bu, Cy）, were synthesized by the reactions of diorganotin dichlorides with in situ formed potassium salt of N-（3,5-dibromosalicylidene）-α-amino acid and characterized by elemental analysis, IR and NMR （^1H, ^13C and ^119Sn） spectra. The crystal structures of n-Bu2Sn（2-O-3,5-Br2C6H2CH= NCHRCOO）（R=i-Pr, Bz） and Cy2Sn（2-O-3,5-Br2C6H2CH=NCHRCOO）（R=Me, Bz） were determined by X-ray single crystal diffraction and showed that the tin atoms are in a distorted trigonal bipyramidal geometry to form five- and six-membered chelate rings with the tridentate ligand. Bioassay results indicated that the compounds possess better in vitro antitumour activity against three human tumour cell lines, HeLa, CoLo205 and MCF-7, than cis-platin and moderate anti-bacterial activity against two bacteria, E. coli and S. aureus.     

Two N‐ortho‐nitro­benzene­sulfonyl α,α‐disubstituted amino acid adducts

The carboxy group of 2‐methyl‐N‐[(2‐nitrophenyl)sulfonyl]­alanine, C₁₀H₁₂N₂O₆S, forms centrosymmetric hydrogen‐bonded dimers with an O?O distance of 2.629 (2) Å and an intramolecular N—H?O(nitro) hydrogen bond N?O distance of 2.823 (2) Å. 1‐[(2‐Nitro­phenyl)­sulfonyl­amino]­cyclo­hexane­carboxyl­ic acid, C₁₃H₁₆N₂O₆S, has Z′ = 2 and forms similar interactions.