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.     

Synthesis and Structures of New Oxidation/ Cycloaddition Products of λ3‐Cyclodiphosphazanes

Reaction of the cyclodiphosphazane [(OC₄H₈N)P(μ‐N‐t‐Bu)₂P(HN‐t‐Bu)] ( 1 ) with an equimolar quantity of diisopropyl azodicarboxylate afforded the phosphinimine product [(OC₄H₈N)P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂ ‐i‐Pr)NHCO₂‐i‐Pr] ( 6 ) having a P^III‐N‐P^V skeleton. Similar products [(t‐BuNH)P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂Et)NHCO₂Et] ( 7 ) and [(CO₂‐i‐Pr)HNN(CO₂‐i‐Pr)](t‐BuN=P(μ‐N‐t‐Bu)₂POCH₂CMe₂CH₂O[P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂‐i‐Pr)NH(CO₂‐i‐Pr)] ( 8 ) were spectroscopically characterized in the reaction of [(t‐BuNH)P‐N‐t‐Bu]₂ ( 2 ) and [(t‐BuNH)P(μ‐N‐t‐Bu)₂POCH₂CMe₂CH₂OP(μ‐N‐t‐Bu)₂P(NH‐t‐Bu)] ( 3 ) with diethyl‐ and diisopropyl azodicarboxylate, respectively. By contrast, the reaction of [(μ‐t‐BuN)P]₂[O‐6‐t‐Bu‐4‐Me‐C₆H₂]₂CH₂ ( 4 ) and [(C₅H₁₀N)P‐μ‐N‐t‐Bu]₂ ( 5 ) with diisopropyl azodicarboxylate afforded the mono‐ and bis‐oxidized compounds [(O)P(μ‐N‐t‐Bu)₂P][O‐6‐t‐Bu‐4‐Me‐C₆H₂]₂CH₂ ( 9 ) and [(C₅H₁₀N)(O)P‐μ‐N‐t‐Bu]₂ ( 10 ), respectively. Oxidative addition of o‐chloranil to 7 and its DIAD analogue [(t‐BuNH)P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂‐i‐Pr)NHCO₂‐i‐Pr] ( 11 ) afforded [(C₆Cl₄‐1, 2‐O₂)(t‐BuNH)P(μ‐N‐t‐Bu)₂P=N‐t‐Bu)(N(CO₂R)NHCO₂R] [R = Et ( 12 ) and i‐Pr ( 13 )] containing tetra‐ and pentacoordinate P^V atoms in the cyclodiphosphazane ring. The structures of 6 , 9 , 12 and 13 have been confirmed by X‐ray structure determination. For comparison, the X‐ray structure of the double cycloaddition product [(C₆Cl₄‐1, 2‐O₂)(t‐BuNH)PN‐t‐Bu]₂ ( 14 ), obtained from the reaction of 2 with two mole equivalents of o‐chloranil is also reported.     

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.     

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.     

Preparation and Characterization of Aluminum Alkoxides and their Application to Ring‐Opening Polymerization of ϵ‐Caprolactones

The reaction of 2‐methoxybenzyl alcohol with one molar equiv of R₂AIX in diethyl ether at 0°C gives [(2‐MeOC₆H₄CH₂‐μ‐O)AlRX]₂ ( 1 : R = Et, X = Cl, 2 : R = X = Et). In addition, 2,4‐di‐tert‐butylphenol reacts with ⁱBu₃Al affording a four‐coordinated aluminum compound [(μ‐2,4‐^tBu₂‐C₆H₄O)Al(ⁱBu)₂]₂ ( 4 ). Single crystal X‐ray structure analysis of 4 shows a C_2h‐symmetry with a planar Al₂O₂ core. Ring‐opening polymerization (ROP) of caprolactones initiated by 1, 4 and [(μ‐OCH₂C₆H₄OMe)Al(ⁱBu)₂]₂ ( 3 ) is performed and polyesters with narrow molecular weight distributions were obtained from the “living” ROP of caprolactones. ¹H NMR spectroscopic studies of PCL reveal that the initiator of 1 and 3 is through the Al‐OAr function, but the initiator of 4 is through the Al‐ ⁱBu group.     

Bisaminophosphane – Synthese,Struktur und Reaktivität

Bisaminophosphanes – Synthesis, Structure, and Reactivity Different pathways for the synthesis of bis(alkylamino)phosphanes RP(N(H)R′)₂ are described. t‐BuP(N(H)‐ Dipp)₂ (Dipp = 2,6‐i‐Pr₂–C₆H₃) was structurally characterized by single crystal X‐ray diffraction. The reactivity of the compounds was examplarily investigated using t‐BuP(N(H)t‐Bu)₂. Its reaction with Me₃Al and R₂AlH (R = Me, Et, i‐Bu) in 1 : 1 and 1 : 2 stoichiometrie yield monosubstituted compounds of the type t‐BuP(N(H)t‐Bu)(N(AlR₂)t‐Bu).     

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.     

Copper–Carbene Intermediates in the Copper‐Catalyzed Functionalization of OH Bonds

Copper–carbene [Tp^xCu?C(Ph)(CO₂Et)] and copper–diazo adducts [Tp^xCu{η¹‐N₂C(Ph)(CO₂Et)}] have been detected and characterized in the context of the catalytic functionalization of O?H bonds through carbene insertion by using N₂?C(Ph)(CO₂Et) as the carbene source. These are the first examples of these type of complexes in which the copper center bears a tridentate ligand and displays a tetrahedral geometry. The relevance of these complexes in the catalytic cycle has been assessed by NMR spectroscopy, and kinetic studies have demonstrated that the N‐bound diazo adduct is a dormant species and is not en route to the formation of the copper–carbene intermediate.     

Structural Diversity in Alkali Metal and Alkali Metal Magnesiate Chemistry of the Bulky 2,6‐Diisopropyl‐N‐(trimethylsilyl)anilino Ligand

Bulky amido ligands are precious in s‐block chemistry, since they can implant complementary strong basic and weak nucleophilic properties within compounds. Recent work has shown the pivotal importance of the base structure with enhancement of basicity and extraordinary regioselectivities possible for cyclic alkali metal magnesiates containing mixed n‐butyl/amido ligand sets. This work advances alkali metal and alkali metal magnesiate chemistry of the bulky arylsilyl amido ligand [N(SiMe₃)(Dipp)]^? (Dipp=2,6‐iPr₂‐C₆H₃). Infinite chain structures of the parent sodium and potassium amides are disclosed, adding to the few known crystallographically characterised unsolvated s‐block metal amides. Solvation by N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) or N,N,N′,N′‐tetramethylethylenediamine (TMEDA) gives molecular variants of the lithium and sodium amides; whereas for potassium, PMDETA gives a molecular structure, TMEDA affords a novel, hemi‐solvated infinite chain. Crystal structures of the first magnesiate examples of this amide in [MMg{N(SiMe₃)(Dipp)}₂(μ‐nBu)]_∞ (M=Na or K) are also revealed, though these breakdown to their homometallic components in donor solvents as revealed through NMR and DOSY studies.     

Crystal Structures,Magnetic Properties and Catecholase‐Like Activities of μ‐Alkoxo‐μ‐Carboxylato Double Bridged Dinuclear and Tetranuclear Copper(II) Complexes

One μ‐alkoxo‐μ‐carboxylato bridged dinuclear copper(II) complex, [Cu₂(L¹)(μ‐C₆H₅CO₂)] ( 1 )(H₃L¹ = 1,3‐bis(salicylideneamino)‐2‐propanol)), and two μ‐alkoxo‐μ‐dicarboxylato doubly‐bridged tetranuclear copper(II) complexes, [Cu₄(L¹)₂(μ‐C₈H₁₀O₄)(DMF)₂]·H₂O ( 2 ) and [Cu₄(L²)₂(μ‐C₅H₆O₄]·2H₂O·2CH₃CN ( 3 ) (H₃L² = 1,3‐bis(5‐bromo‐salicylideneamino)‐2‐propanol)) have been prepared and characterized. The single crystal X‐ray analysis shows that the structure of complex 1 is dimeric with two adjacent copper(II) atoms bridged by μ‐alkoxo‐μ‐carboxylato ligands where the Cu···Cu distances and Cu‐O(alkoxo)‐Cu angles are 3.5 11 Å and 132.8°, respectively. Complexes 2 and 3 consist of a μ‐alkoxo‐μ‐dicarboxylato doubly‐bridged tetranuclear Cu(II) complex with mean Cu‐Cu distances and Cu‐O‐Cu angles of 3.092 Å and 104.2° for 2 and 3.486 Å and 129.9° for 3 , respectively. Magnetic measurements reveal that 1 is strong antiferromagnetically coupled with 2J =‐210 cm^?1 while 2 and 3 exhibit ferromagnetic coupling with 2J = 126 cm^?1 and 82 cm^?1 (averaged), respectively. The 2J values of 1–3 are correlated to dihedral angles and the Cu‐O‐Cu angles. Dependence of the pH at 25 °C on the reaction rate of oxidation of 3,5‐di‐tert‐butylcatechol (3,5‐DTBC) to the corresponding quinone (3,5‐DTBQ) catalyzed by 1–3 was studied. Complexes 1–3 exhibit catecholase‐like active at above pH 8 and 25 °C for oxidation of 3,5‐di‐tert‐butylcatechol.     

Synthesis and X‐ray Structures of the Polycyclic Dimers {[PhB(μ‐NtBu)2AsN(tBu)H]LiI}2 and [PhB(μ‐NtBu)2AsN(tBu)Li]2

The metathesis of [PhB(μ‐NtBu)₂]AsCl and tBuN(H)Li in 1:1 molar ratio in diethyl ether produced the amido derivative [PhB(μ‐NtBu)₂AsN(tBu)H] ( 1 ) in good yield. The lithiation of 1 with one equivalent of nBuLi afforded the lithium salt [PhB(μ‐NtBu)₂AsN(tBu)Li] ( 2a ). Both 1 and 2a were characterized by multinuclear NMR spectroscopy. The crystal structure of 2a is comprised of a U‐shaped, centrosymmetric dimer in which the monomeric [PhB(μ‐NtBu)₂AsN(tBu)]^?Li⁺ units are linked by Li‐N interactions to give a six‐rung ladder. Oxidation of 2a with one‐half equivalent of I₂ in diethyl ether resulted in hydrogen abstraction from the solvent to give the dimeric lithium iodide adduct {[PhB(μ‐NtBu)₂AsN(tBu)H]LiI}₂ ( 1 ·LiI) with a central Li₂I₂ ring.     

Surprisingly Different Reaction Behavior of Alkali and Alkaline Earth Metal Bis(trimethylsilyl)amides toward Bulky N‐(2‐Pyridylethyl)‐N′‐(2,6‐diisopropylphenyl)pivalamidine

N‐(2,6‐Diisopropylphenyl)‐N′‐(2‐pyridylethyl)pivalamidine (Dipp‐N=C(tBu)‐N(H)‐C₂H₄‐Py) ( 1 ), reacts with metalation reagents of lithium, magnesium, calcium, and strontium to give the corresponding pivalamidinates [(tmeda)Li{Dipp‐N=C(tBu)‐N‐C₂H₄‐Py}] ( 6 ), [Mg{Dipp‐N=C(tBu)‐N‐C₂H₄‐Py}₂] ( 3 ), and heteroleptic [{(Me₃Si)₂N}Ae{Dipp‐N=C(tBu)‐N‐C₂H₄‐Py}], with Ae being Ca ( 2 a ) and Sr ( 2 b ). In contrast to this straightforward deprotonation of the amidine units, the reaction of 1 with the bis(trimethylsilyl)amides of sodium or potassium unexpectedly leads to a β‐metalation and an immediate deamidation reaction yielding [(thf)₂Na{Dipp‐N=C(tBu)‐N(H)}] ( 4 a ) or [(thf)₂K{Dipp‐N=C(tBu)‐N(H)}] ( 4 b ), respectively, as well as 2‐vinylpyridine in both cases. The lithium derivative shows a similar reaction behavior to the alkaline earth metal congeners, underlining the diagonal relationship in the periodic table. Protonation of 4 a or the metathesis reaction of 4 b with CaI₂ in tetrahydrofuran yields N‐(2,6‐diisopropylphenyl)pivalamidine (Dipp‐N=C(tBu)‐NH₂) ( 5 ), or [(thf)₄Ca{Dipp‐N=C(tBu)‐N(H)}₂] ( 7 ), respectively. The reaction of AN(SiMe₃)₂ (A=Na, K) with less bulky formamidine Dipp‐N=C(H)‐N(H)‐C₂H₄‐Py ( 8 ) leads to deprotonation of the amidine functionality, and [(thf)Na{Dipp‐N=C(H)‐N‐C₂H₄‐Py}]₂ ( 9 a ) or [(thf)K{Dipp‐N=C(H)‐N‐C₂H₄‐Py}]₂ ( 9 b ), respectively, are isolated as dinuclear complexes. From these experiments it is obvious, that β‐metalation/deamidation of N‐(2‐pyridylethyl)amidines requires bases with soft metal ions and also steric pressure. The isomeric forms of all compounds are verified by single‐crystal X‐ray structure analysis and are maintained in solution.     

catena‐Poly[potassium [copper(II)‐μ‐isothiocyanato‐μ‐N‐salicylidene‐β‐alaninato(2–)]]

The title polymeric compound, catena‐poly­[dipotassium [bis­[μ‐N‐salicyl­idene‐β‐alaninato(2−)]‐κ⁴O,N,O′:O′′;κ⁴O′′:O,N,O′‐dicopper(II)]‐di‐μ‐iso­thio­cyanato‐κ²N:S;κ²S:N], {K[Cu(NCS)(C₁₀H₉NO₃)]}_n, consists of [iso­thio­cyanato(N‐salicyl­idene‐β‐alaninato)copper(II)]⁻ anions connected through the two three‐atom thio­cyanate (μ‐NCS) and the two anti,anti‐μ‐­carboxyl­ate bridges into infinite one‐dimensional polymeric anions, with coulombically interacting K⁺ counter‐ions with coordination number 7 constrained between the chains. The Cu^II atoms adopt a distorted tetragonal–bipyramidal coordination, with three donor atoms of the tridentate Schiff base and one N atom of the bridging μ‐NCS ligand in the basal plane. The first axial position is occupied by a thio­cyanate S atom of a symmetry‐related μ‐NCS ligand at an apical distance of 2.9770 (8) Å, and the second position is occupied by an O atom of a bridging carboxyl­ate group from an adjacent coordination unit at a distance of 2.639 (2) Å.     

Heterobi‐ and ‐trimetallic Ion Pairs of Zirconocene‐Based Isoselective Olefin Polymerization Catalysts with AlMe3

The reactivity towards AlMe₃ of discrete cationic ansa‐zirconocenes 2 a,b that are ubiquitously used in isoselective propylene polymerization and based on [{Ph(H)C(3,6‐tBu₂‐Flu)(3‐tBu‐5‐Et‐Cp)}ZrMe₂)] {Cp‐Flu} and rac‐[{Me₂Si‐(2‐Me‐4‐Ph‐Ind)₂}ZrMe₂] {SBI} was scrutinized. The first example of a structurally characterized Group 4 metallocene AlMe₃ adduct ( 3 b ) is reported. In the presence of excess AlMe₃, the {SBI}‐based AlMe₃ adduct 3 b undergoes a slow decomposition via C? H activation in a bridging methyl unit to yield a new species ( 4 b ) with a trimetallic {Zr(μ‐CH₂)(μ‐Me)AlMe(μ‐Me)AlMe₂} core. EXSY NMR data for the process 2 b ? 3 b → 4 b suggest very rapid and reversible binding of an additional AlMe₃ molecule onto AlMe₃ adduct 3 b . The resulting heterotrimetallic species intermediates exchange of methyl groups between different metal centers and slowly undergoes the C? H activation reaction towards 4 b .     

New Insights into Cinchonine–Aluminium Complexes and Their Application as Chiral Building Blocks: Unprecedented Ligand‐Exchange Processes in the Presence of ZnR2 Compounds

Previous studies have demonstrated that [(CN)₂AlCl] and [R₂Al(μ‐CN)]₂ (CN=deprotonated cinchonine) complexes can effectively act as chiral, semirigid, N,N‐ditopic metalloligands for Zn‐containing nodes, and provide viable means for constructing new, homochiral, heterometallic, coordination polymers of zigzag and helical topologies. These findings have prompted further investigations on the organometallic analogues of the formula [(CN)₂AlR], anticipating their utility as N,N‐metalloligands for ZnR₂ units. Surprisingly, reactions of [(CN)₂AlMe]‐type metalloligands with ZnR₂ compounds (R=Me or Et) revealed unprecedented ligand‐exchange processes, including zinc‐to‐aluminium and aluminium‐to‐zinc transmetalations of alkyl groups. The molecular and crystal structure of the resulting compounds was determined by X‐ray diffraction analysis. From the reaction of [(CN)₂AlMe] with ZnMe₂ a new pseudopolymorphic form of a noncovalent porous material based on [Me₂Al(μ‐CN)]₂ molecules was isolated. Strikingly, the analogous reaction involving ZnEt₂ led to the generation of a new chiral 4N‐tetratopic heterometalloligand [(CN)EtAl(μ‐CN)₂ZnEt]. The latter unit was successfully connected by alkyl‐exchanged ZnMe₂ nodes to give an original homochiral heterometallic {[(CN)EtAl(μ‐CN)₂ZnEt]ZnMe₂}_n coordination polymer adopting a snake 1D motif. The outcome of the revealed reactions indicates the complicated multistep reaction route that involves redistribution of cinchonine and alkyl ligands among the Al and Zn centers, and a general reaction scheme is proposed. The results are in strong contrast with the previously studied inorganic–organic [(CN)₂AlCl/ZnCl₂] system, which exclusively affords a helical coordination polymer based on ZnCl₂ nodes and (CN)₂AlCl metalloligands and lacks the exchange of CN ligands.     

Adding a Structural Context to the Deprotometalation and Trans‐Metal Trapping Chemistry of Phenyl‐Substituted Benzotriazole

Organometallic bases are becoming increasingly complex, because mixing components can lead to bases superior to single‐component bases. To better understand this superiority, it is useful to study metalated intermediate structures prior to quenching. This study is on 1‐phenyl‐1H‐benzotriazole, which was previously deprotonated by an in situ ZnCl₂ ? TMEDA/LiTMP (TMEDA=N,N,N′,N′‐tetramethylethylenediamine; TMP=2,2,6,6‐tetramethylpiperidide) mixture and then iodinated. Herein, reaction with LiTMP exposes the deficiency of the single‐component base as the crystalline product obtained was [{4‐R‐1‐(2‐lithiophenyl)‐1H‐benzotriazole ? 3THF}₂], [R=2‐C₆H₄(Ph)NLi], in which ring opening of benzotriazole and N₂ extrusion had occurred. Supporting lithiation by adding iBu₂Al(TMP) induces trans‐metal trapping, in which C?Li bonds transform into C?Al bonds to stabilise the metalated intermediate. X‐ray diffraction studies revealed homodimeric [(4‐R′‐1‐phenyl‐1H‐benzotriazole)₂], [R′=(iBu)₂Al(μ‐TMP)Li], and its heterodimeric isomer [(4‐R′‐1‐phenyl‐1H‐benzotriazole){2‐R′‐1‐phenyl‐1H‐benzotriazole}], whose structure and slow conformational dynamics were probed by solution NMR spectroscopy.     

New Ga/N‐based Active Lewis Pairs,Trifunctional Ga–Ga Compounds,Reactions with Cyanamide and Dual Insertion of Isocyanate

Hydrogallation of Me₃Si–C≡C–NR'₂ with R₂Ga–H (R = tBu, CH₂tBu, iBu) yielded Ga/N‐based active Lewis pairs, R₂Ga–C(SiMe₃)=C(H)–NR'₂ ( 7 ). The Ga and N atoms adopt cis‐positions at the C=C bonds and show weak Ga–N interactions. tBu₂GaH and Me₃Si–C≡C–N(C₂H₄)₂NMe afforded under exposure of daylight the trifunctional digallium(II) compound [MeN(C₂H₄)₂N](H)C=C(SiMe₃)Ga(tBu)–Ga(tBu)C(SiMe₃)=C(H)[N(C₂H₄)₂NMe] ( 8 ), which results from elimination of isobutene and H₂ and Ga–Ga bond formation. 8 was selectively obtained from the ynamine and [tBu(H)Ga–Ga(H)tBu]₂[HGatBu₂]₂. 7a (R = tBu; NR'₂ = 2,6‐Me₂NC₅H₈) and H₈C₄N–C≡N afforded the adduct tBu₂Ga‐C(SiMe₃)=C(H)(2,6‐Me₂NC₅H₈) · N≡C–NC₄H₈ ( 11 ) with the nitrile bound to gallium. The analogous ALP with harder Al atoms yielded an adduct of the nitrile dimer or oligomers of the nitrile at room temperature. The reaction of 7a with Ph–N=C=O led to the insertion of two NCO groups into the Ga–C_vinyl bond to yield a GaOCNCN heterocycle with Ga bound to O and N atoms ( 12 ).     

A new double‐cube nitride complex containing titanium and potassium

The reaction of the imide–nitride complex [{Ti(η⁵‐C₅Me₅)(μ‐NH)}₃(μ₃‐N)] with potassium iodide in pyridine at room temperature affords the adduct di‐μ‐iodido‐1:1′κ⁴I‐bis{tri‐μ₃‐imido‐1:2:3κ³N;1:2:4κ³N;1:3:4κ³N‐μ₃‐nitrido‐2:3:4κ³N‐tris[2,3,4(η⁵)‐pentamethylcyclopentadienyl](pyridine‐1κN)‐tetrahedro‐potassiumtrititanium(IV)}, [K₂Ti₆(C₁₀H₁₅)₆I₂N₂(NH)₆(C₅H₅N)₂] or [(C₅H₅N)(μ‐I)K{(μ₃‐NH)₃Ti₃(η⁵‐C₅Me₅)₃(μ₃‐N)}]₂. The crystal structure contains two [KTi₃N₄] cube‐type units held together by two bridging I atoms. There is a centre of inversion located in the middle of this unprecedented discrete K₂I₂ unit. The geometry around K is best described as distorted trigonal prismatic, with three imide groups, two bridging I atoms and one pyridine ligand.     

Synthese und Molekülstruktur von [{Cp′(μ‐η1 : η5‐C5H3Me)Mo(μ‐AlRH)}2] (Cp′ = C5H4Me,R = iBu,Et)

Synthesis and Molecular Structure of [{Cp′(μ‐η¹ : η⁵‐C₅H₃Me)Mo(μ‐AlRH)}₂] (Cp′ = C₅H₄Me, R = ⁱBu, Et) [Cp′₂MoH₂] reacts with HAlR₂ to give [{Cp′(μ‐η¹ : η⁵‐C₅H₃Me)Mo(μ‐AlRH)}₂] (Cp′ = C₅H₄Me, R = ⁱBu ( 1 ), Et ( 2 )). Crystal structure determinations were carried out on [Cp′₂MoH₂] and 1 . 1 exhibits a direct Mo–Al bond (2.636(2) Å).     

Chiral Lithiated Allylic α‐Sulfonyl Carbanions: Experimental and Computational Study of Their Structure,Configurational Stability,and Enantioselective Synthesis

X‐ray crystal structure analysis of the lithiated allylic α‐sulfonyl carbanions [CH₂?CHC(Me)SO₂Ph]Li ? diglyme, [cC₆H₈SO₂tBu]Li ? PMDETA and [cC₇H₁₀SO₂tBu]Li ? PMDETA showed dimeric and monomeric CIPs, having nearly planar anionic C atoms, only O?Li bonds, almost planar allylic units with strong C?C bond length alternation and the s‐trans conformation around C1?C2. They adopt a C1?S conformation, which is similar to the one generally found for alkyl and aryl substituted α‐sulfonyl carbanions. Cryoscopy of [EtCH?CHC(Et)SO₂tBu]Li in THF at 164 K revealed an equilibrium between monomers and dimers in a ratio of 83:17, which is similar to the one found by low temperature NMR spectroscopy. According to NMR spectroscopy the lone‐pair orbital at C1 strongly interacts with the C?C double bond. Low temperature ⁶Li,¹H NOE experiments of [EtCH?CHC(Et)SO₂tBu]Li in THF point to an equilibrium between monomeric CIPs having only O?Li bonds and CIPs having both O?Li and C1?Li bonds. Ab initio calculation of [MeCH?CHC(Me)SO₂Me]Li ? (Me₂O)₂ gave three isomeric CIPs having the s‐trans conformation and three isomeric CIPs having the s‐cis conformation around the C1?C2 bond. All s‐trans isomers are more stable than the s‐cis isomers. At all levels of theory the s‐trans isomer having O?Li and C1?Li bonds is the most stable one followed by the isomer which has two O?Li bonds. The allylic unit of the C,O,Li isomer shows strong bond length alternation and the C1 atom is in contrast to the O,Li isomer significantly pyramidalized. According to NBO analysis of the s‐trans and s‐cis isomers, the interaction of the lone pair at C1 with the π* orbital of the CC double bond is energetically much more favorable than that with the “empty” orbitals at the Li atom. The C1?S and C1?C2 conformations are determined by the stereoelectronic effects n_C–σ_SR* interaction and allylic conjugation. ¹H DNMR spectroscopy of racemic [EtCH?CHC(Et)SO₂tBu]Li, [iPrCH?CHC(iPr)SO₂tBu]Li and [EtCH?C(Me)C(Et)SO₂tBu]Li in [D₈]THF gave estimated barriers of enantiomerization of ΔG^≠=13.2 kcal mol^?1 (270 K), 14.2 kcal mol^?1 (291 K) and 14.2 kcal mol^?1 (295 K), respectively. Deprotonation of sulfone (R)‐EtCH?CHCH(Et)SO₂tBu (94 % ee) with nBuLi in THF at ?105 °C occurred with a calculated enantioselectivity of 93 % ee and gave carbanion (M)‐[EtCH?CHC(Et)SO₂tBu]Li, the deuteration and alkylation of which with CF₃CO₂D and MeOCH₂I, respectively, proceeded with high enantioselectivities. Time‐dependent deuteration of the enantioenriched carbanion (M)‐[EtCH?CHC(Et)SO₂tBu]Li in THF gave a racemization barrier of ΔG^≠=12.5 kcal mol^?1 (168 K), which translates to a calculated half‐time of racemization of t_1/2=12 min at ?105 °C.