Synthese,Struktur und Eigenschaften des Natriumsilanids tBu2PhSiNa – ein Zugang zu Di‐tert‐butyl‐phenylsilylsubstituierten Verbindungen

The Sodium Silanide t Bu₂PhSiNa: Synthesis, Properties, Structure Analysis – a Synthetic Pathway to Introduce the t Bu₂PhSi‐Ligand The sodium silanide tBu₂PhSiNa is easily obtained by the reaction of sodium metal with tBu₂PhSiBr at elevated temperatures in n‐heptane, THF or dibutylether. An X‐ray crystal structure analysis reveals, that the sodium silanide 3 contains chains of tBu₂PhSiNa units with η⁶ sodium–phenyl‐contacts. Oxidation of tBu₂PhSiNa with TCNE proceeds with formation of the disilane tBu₂PhSi–SiPhtBu₂.     

Darstellung,Charakterisierung und Reaktionsverhalten von Natrium‐ und Kaliumhydridosilylamiden R2(H)Si—N(M)R′ (M = Na,K) — Kristallstruktur von [(Me3C)2(H)Si—N(K)SiMe3]2·THF

Preparation, Characterization and Reaction Behaviour of Sodium and Potassium Hydridosilylamides R₂(H)Si—N(M)R′ (M = Na, K) — Crystal Structure of [(Me₃C)₂(H)Si—N(K)SiMe₃]₂ · THF The alkali metal hydridosilylamides R₂(H)Si—N(M)R′ 1a‐Na — 1d—Na and 1a‐K — 1d‐K ( a : R = Me, R′ = CMe₃; b : R = Me, R′ = SiMe₃; c : R = Me, R′ = Si(H)Me₂; d : R = CMe₃, R′= SiMe₃) have been prepared by reaction of the corresponding hydridosilylamines 1a — 1d with alkali metal M (M = Na, K) in presence of styrene or with alkali metal hydrides MH (M = Na, K). With NaNH₂ in toluene Me₂(H)Si—NHCMe₃ ( 1a ) reacted not under metalation but under nucleophilic substitution of the H(Si) atom to give Me₂(NaNH)Si—NHCMe₃ ( 5 ). In the reaction of Me₂(H)Si—NHSiMe₃ ( 1b ) with NaNH₂ intoluene a mixture of Me₂(NaNH)Si—NHSiMe₃ and Me₂(H)Si—N(Na)SiMe₃ ( 1b‐Na ) was obtained. The hydridosilylamides have been characterized spectroscopically. The spectroscopic data of these amides and of the corresponding lithium derivatives are discussed. The ²⁹Si‐NMR‐chemical shifts and the ²⁹Si—¹H coupling constants of homologous alkali metal hydridosilylamides R₂(H)Si—N(M)R′ (M = Li, Na, K) are depending on the alkali metal. With increasing of the ionic character of the M—N bond M = K > Na > Li the ²⁹Si‐NMR‐signals are shifted upfield and the ²⁹Si—¹H coupling constants except for compounds (Me₃C)(H)Si—N(M)SiMe₃ are decreased. The reaction behaviour of the amides 1a‐Na — 1c‐Na and 1a‐K — 1c‐K was investigated toward chlorotrimethylsilane in tetrahydrofuran (THF) and in n‐pentane. In THF the amides produced just like the analogous lithium amides the corresponding N‐silylation products Me₂(H)Si—N(SiMe₃)R′ ( 2a — 2c ) in high yields. The reaction of the sodium amides with chlorotrimethylsilane in nonpolar solvent n‐pentane produced from 1a‐Na the cyclodisilazane [Me₂Si—NCMe₃]₂ ( 8a ), from 1b‐Na and 1‐Na mixtures of cyclodisilazane [Me₂Si—NR′]₂ ( 8b , 8c ) and N‐silylation product 2b , 2c . In contrast to 1b‐Na and 1c‐Na and to the analogous lithium amides the reaction of 1b‐K and 1c‐K with chlorotrimethylsilane afforded the N‐silylation products Me₂(H)Si—N(SiMe₃)R′ ( 2b , 2c ) in high yields. The amide [(Me₃C)₂(H)Si—N(K)SiMe₃]₂·THF ( 9 ) crystallizes in the space group C2/c with Z = 4. The central part of the molecule is a planar four‐membered K₂N₂ ring. One potassium atom is coordinated by two nitrogen atoms and the other one by two nitrogen atoms and one oxygen atom. Furthermore K···H(Si) and K···CH₃ contacts exist in 9 . The K—N distances in the K₂N₂ ring differ marginally.     

The Reactions of Carbon Monoxide with Silyl and Silenyl Lithium – Synthesis and Isolation of the First Stable Tetra‐Silyl Di‐Ketyl Biradical and 1‐Silaallenolate Lithium

Reactions of carbon monoxide (CO) with tBu₂MeSiLi and (E)‐(tBu₂MeSi)(tBuMe₂Si)C=Si(SiMetBu₂)Li?2 THF ( 4 ) were studied both experimentally and computationally. Reaction of tBu₂MeSiLi with CO in hexane yields the first stable tetra‐silyl di‐ketyl biradical [(tBu₂MeSi)₂COLi]^.₂ ( 3 ). Reaction of 4 with CO yields selectively and quantitatively the first reported 1‐silaallenolate, (tBu₂MeSi)(tBuMe₂Si)C=C=Si(SiMetBu₂)OLi?THF ( 5 ). Both 3 and 5 were characterized by X‐ray crystallography and biradical 3 also by EPR spectroscopy. Silaallenolate 5 reacts with Me₃SiCl to produce siloxy substituted 1‐silaallene (tBu₂MeSi)(tBuMe₂Si)C=C=Si(SiMetBu₂)OSiMe₃. The reaction of 4 with CO provides a new route to 1‐silaallenes. The mechanisms of the reactions of tBuMe₂SiLi and of 4 with CO were studied by DFT calculations.     

Tuning Coordination in s‐Block Carbazol‐9‐yl Complexes

1,3,6,8‐Tetra‐tert‐butylcarbazol‐9‐yl and 1,8‐diaryl‐3,6‐di(tert‐butyl)carbazol‐9‐yl ligands have been utilized in the synthesis of potassium and magnesium complexes. The potassium complexes (1,3,6,8‐tBu₄carb)K(THF)₄ ( 1 ; carb=C₁₂H₄N), [(1,8‐Xyl₂‐3,6‐tBu₂carb)K(THF)]₂ ( 2 ; Xyl=3,5‐Me₂C₆H₃) and (1,8‐Mes₂‐3,6‐tBu₂carb)K(THF)₂ ( 3 ; Mes=2,4,6‐Me₃C₆H₂) were reacted with MgI₂ to give the Hauser bases 1,3,6,8‐tBu₄carbMgI(THF)₂ ( 4 ) and 1,8‐Ar₂‐3,6‐tBu₂carbMgI(THF) (Ar=Xyl 5 , Ar=Mes 6 ). Structural investigations of the potassium and magnesium derivatives highlight significant differences in the coordination motifs, which depend on the nature of the 1‐ and 8‐substituents: 1,8‐di(tert‐butyl)‐substituted ligands gave π‐type compounds ( 1 and 4 ), in which the carbazolyl ligand acts as a multi‐hapto donor, with the metal cations positioned below the coordination plane in a half‐sandwich conformation, whereas the use of 1,8‐diaryl substituted ligands gave σ‐type complexes ( 2 and 6 ). Space‐filling diagrams and percent buried volume calculations indicated that aryl‐substituted carbazolyl ligands offer a steric cleft better suited to stabilization of low‐coordinate magnesium complexes.     

Alkali Blues: Blue-Emissive Alkali Metal Pyrrolates

2-Iminopyrroles [H^tBuL, 4-tert-butyl phenyl(pyrrol-2-ylmethylene)amine] are non-fluorescent π systems. However, they display blue fluorescence after deprotonation with alkali metal bases in the solid state and in solution at room temperature. In the solid state, the alkali metal 2-imino pyrrolates, M(^tBuL), aggregate to dimers, [M(^tBuL)(NCR)]₂ (M=Li, R=CH₃, CH(CH₃)CNH₂), or polymers, [M(^tBuL)]_n (M=Na, K). In solution (solv=CH₃CN, DMSO, THF, and toluene), solvated, uncharged monomeric species M(^tBuL)(solv)_m with N,N′-chelated alkali metal ions are present. Due to the electron-rich pyrrolate and the electron-poor arylimino moiety, the M(^tBuL) chromophore possesses a low-energy intraligand charge-transfer (ILCT) excited state. The chelated alkali cations rigidify the chromophore, restricting intramolecular motions (RIM) by the chelation-enhanced fluorescence (CHEF) effect in solution and, consequently, switch-on a blue fluorescence emission.     

Pivaloylmetals (tBu‐COM: M=Li,MgX, K) as Equilibrium Components

Short‐lived pivaloylmetals, (H₃C)₃C‐COM, were established as the reactive intermediates arising through thermal heterolytic expulsion of O=CtBu₂ from the overcrowded metal alkoxides tBuC(=O)‐C(‐OM)tBu₂ (M=MgX, Li, K). In all three cases, this fission step is counteracted by a faster return process, as shown through the trapping of tBu‐COM by O=C(tBu)‐C(CD₃)₃ with formation of the deuterated starting alkoxides. If generated in the absence of trapping agents, all three tBu‐COM species “dimerize” to give the enediolates MO‐C(tBu)=C(tBu)‐OM along with O=CtBu₂ (2 equiv). A common‐component rate depression by surplus O=CtBu₂ proves the existence of some free tBu‐COM (separated from O=CtBu₂); but companion intermediates with the traits of an undissociated complex such as tBu‐COM & O=CtBu₂ had to be postulated. The slow fission step generating tBu‐COMgX in THF levels the overall rates of dimerization, ketone addition, and deuterium incorporation. Formed by much faster fission steps, both tBu‐COLi and tBu‐COK add very rapidly to ketones and dimerize somewhat slower (but still fairly fast, as shown through trapping of the emerging O=CtBu₂ by H₃CLi or PhCH₂K, respectively). At first sight surprisingly, the rapid fission, return, and dimerization steps combine to very slow overall decay rates of the precursor Li and K alkoxides in the absence of trapping agents: A detailed study revealed that the fast fission step, generating tBu‐COLi in THF, is followed by a kinetic partitioning that is heavily biased toward return and against the product‐forming dimerization. Both tBu‐COLi and tBu‐COK form tBu‐CH=O with HN(SiMe₃)₃, but only tBu‐COK is basic enough for being protonated by the precursor acyloin tBuC(=O)‐C(‐OH)tBu₂.     

Isolation and Characterization,Including by X‐ray Crystallography,of Contact and Solvent‐Separated Ion Pairs of Silenyl Lithium Species

Reaction of bromoacylsilane 1 (pink solution) with tBu₂MeSiLi (3.5 equiv) in a 4:1 hexane:THF solvent mixture at −78 °C to room temperature yields the solvent separated ion pair (SSIP) of silenyl lithium E‐[(tBuMe₂Si)(tBu₂MeSi)C=Si(SiMetBu₂)]⁻ [Li⋅4THF]⁺ 2 a (green–blue solution). Removal of the solvent and addition of benzene converts 2 a into the corresponding contact ion pair (CIP) 2 b (violet–red solution) with two THF molecules bonded to the lithium atom. The 2 a ⇌ 2 b interconversion is reversible upon THF⇌ benzene solvent change. Both 2 a and 2 b were characterized by X‐ray crystallography, NMR and UV/Vis spectroscopy, and theoretical calculations. The degree of dissociation of the Si−Li bond has a large effect on the visible spectrum (and thus color) and on the silenylic ²⁹Si NMR chemical shift, but a small effect on the molecular structure. This is the first report of the X‐ray molecular structure of both the SSIP and the CIP of any R₂E=E′RM species (E=C, Si; E′=C, Si; M=metal).     

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.     

The 9H‐9‐Borafluorene Dianion: A Surrogate for Elusive Diarylboryl Anion Nucleophiles

Double reduction of the THF adduct of 9H‐9‐borafluorene ( 1 ?THF) with excess alkali metal affords the dianion salts M₂[ 1 ] in essentially quantitative yields (M=Li–K). Even though the added charge is stabilized through π delocalization, [ 1 ]^2? acts as a formal boron nucleophile toward organoboron ( 1 ?THF) and tetrel halide electrophiles (MeCl, Et₃SiCl, Me₃SnCl) to form B?B/C/Si/Sn bonds. The substrate dependence of open‐shell versus closed‐shell pathways has been investigated.     

Reactions of tBu2P–PLi–PtBu2 with [(Et3P)2MCl2] (M = Ni,Pd, Pt). Synthesis and Properties of [(1,2‐η‐tBu2P=P–PtBu2)M(PEt3)Cl] (M=Ni,Pd)

^tBu₂P–PLi–P^tBu₂·2THF reacts with [cis‐(Et₃P)₂MCl₂] (M = Ni, Pd) yielding [(1,2‐η‐^tBu₂P=P–P^tBu₂)Ni(PEt₃)Cl] and [(1,2‐η‐^tBu₂P=P–P^tBu2)Pd(PEt₃)Cl], respectively. ^tBu₂P– PLi–P^tBu₂ undergoes an oxidation process and the ^tBu₂P–P–P^tBu₂ ligand adopts in the products the structure of a side‐on bonded 1,1‐di‐tert‐butyl‐2‐(di‐tert‐butylphosphino)diphosphenium cation with a short P–P bond. Surprisingly, the reaction of ^tBu₂P–PLi–P^tBu₂·2THF with [cis‐(Et₃P)₂PtCl₂] does not yield [(1,2‐η‐^tBu₂P=P–P^tBu₂)Pt(PEt₃)Cl].     

Syntheses of the Antimonides R2Sb− (R = Ph,Mes, tBu,tBu2Sb) and Sb73− by Reactions of Organoantimony Hydrides or cyclo‐(tBuSb)4 with Li,Na, K,or BuLi

Reactions of R₂SbH with BuLi at ?70 °C in tetrahydrofuran (thf) lead to [R₂SbLi(thf)₃] [R = Ph ( 1 ) or R = Mes ( 2 )]. The antimonides [tBu₂SbK(pmdeta)] ( 3 ) (pmdeta = pentamethyldiethylenetriamine), [Li(tmeda)₂][tBu₄Sb₃]·benzene ( 4 ) (tmeda = tetramethylethylenediamine), and [tBu₄Sb₃Na(tmeda, thf)] ( 5 ) result from the reduction of cyclo‐(tBuSb)₄ by Li, Na, or K with pmdeta or tmeda in thf. The primary stibanes RSbH₂ [R = Mes ( 6 ), 2‐(Me₂NCH₂)C₆H₂ ( 7 )] are synthesized by reactions of RSbCl₂ with LiAlH₄. PhSbH₂ reacts with BuLi, and tmeda in toluene to give [Sb₇Li₃(tmeda)₃]·toluene ( 8 ). [Sb₇Na₃(pmdeta)₃]·toluene ( 9 ) is obtained from PhSbH₂, Na in liqu. NH₃, pmdeta and toluene. Crystal structures are reported for 1 – 5 and 9 .     

Isolation and Characterization,Including by X‐ray Crystallography,of Contact and Solvent‐Separated Ion Pairs of Silenyl Lithium Species

Reaction of bromoacylsilane 1 (pink solution) with tBu₂MeSiLi (3.5 equiv) in a 4:1 hexane:THF solvent mixture at ?78 °C to room temperature yields the solvent separated ion pair (SSIP) of silenyl lithium E‐[(tBuMe₂Si)(tBu₂MeSi)C=Si(SiMetBu₂)]^? [Li?4THF]⁺ 2 a (green–blue solution). Removal of the solvent and addition of benzene converts 2 a into the corresponding contact ion pair (CIP) 2 b (violet–red solution) with two THF molecules bonded to the lithium atom. The 2 a ? 2 b interconversion is reversible upon THF? benzene solvent change. Both 2 a and 2 b were characterized by X‐ray crystallography, NMR and UV/Vis spectroscopy, and theoretical calculations. The degree of dissociation of the Si?Li bond has a large effect on the visible spectrum (and thus color) and on the silenylic ²⁹Si NMR chemical shift, but a small effect on the molecular structure. This is the first report of the X‐ray molecular structure of both the SSIP and the CIP of any R₂E=E′RM species (E=C, Si; E′=C, Si; M=metal).     

Synthese und Struktur von Sr6P8‐Polyedern in gemischten Phosphaniden/Phosphandiiden des Strontiums

Synthesis and Structures of Sr₆P₈ Polyhedra in Mixed Phosphanides/Phosphandiides of Strontium The strontiation of H₂PSiⁱPr₃ ( 1 ) with (THF)₂Sr[N(SiMe₃)₂]₂ in THF yields colorless tetrakis(tetrahydrofuran‐O)strontium bis(triisopropylsilylphosphanide) ( 3 ). The central alkaline earth metal atom has an octahedral environment with the phosphanide ligands in trans position. The homometalation in toluene leads to the elimination of 1 and THF. Cooling of this solution gives crystals of colorless tetrakis(tetrahydrofuran‐O)hexastrontium‐tetrakis(triisopropylsilylphosphanide)‐tetrakis(triisopropylsilylphosphandiide) ( 4 ). The equimolar reaction of H₂PSi^tBu₃ ( 2 ) with (THF)₂Sr[N(SiMe₃)₂]₂ in toluene yields in the first step heteroleptic dimeric {(Me₃Si)₂NSr(THF)₂[P(H)Si^tBu₃]}₂ ( 5 )₂. This compounds monomerizes in THF to (Me₃Si)₂N–Sr(THF)₄[P(H)Si^tBu₃] ( 6 ), which forms an equilibrium with the homoleptic dismutation products (THF)₂Sr[N(SiMe₃)₂]₂ and (THF)₄Sr[P(H)Si^tBu₃]₂ ( 7 ). Compound ( 5 )₂ undergoes a intramolecular strontiation and bis(tetrahydrofuran‐O)hexastrontium‐tetrakis[tri(tert‐butyl)silylphosphanide]‐tetrakis[tri(tert‐butyl)silylphosphandiide] ( 8 ) is isolated. The central Sr₆P₈‐polyhedra of 4 and 8 are very similar.     

Synthesis and Chloride Affinity of Sterically Demanding Ditopic Lithium Bis(pyrazol‐1‐yl)borates

The synthesis and full characterization of the sterically demanding ditopic lithium bis(pyrazol‐1‐yl)borates Li₂[p‐C₆H₄(B(Ph)pz^R₂)₂] is reported (pz^R = 3‐phenylpyrazol‐1‐yl ( 3 ^Ph), 3‐t‐butylpyrazol‐1‐yl ( 3 ^tBu)). Compound 3 ^Ph crystallizes from THF as THF‐adduct 3 ^Ph(THF)₄ which features a straight conformation with a long Li···Li distance of 12.68(1) Å. Compound 3 ^tBu was found to function as efficient and selective scavenger of chloride ions. In the presence of LiCl it forms anionic complexes [ 3 ^tBuCl]⁻ with a central Li‐Cl‐Li core (Li···Li = 3.75(1) Å).     

Oligophosphanid‐Anionen: Synthesen und Molekülstrukturen von [K2(PMDETA)2(P4Ph4)], [K2(PMDETA)(P4tBu4)]2 und [K(PMDETA)(THF){cyclo‐(P5tBu4)}] (PMDETA = NMe(CH2CH2NMe2)2)

Oligophosphanide Anions: Syntheses and Molecular Structures of [K₂(PMDETA)₂(P₄Ph₄)], [K₂(PMDETA)(P₄tBu₄)]₂ and [K(PMDETA)(THF){cyclo‐(P₅tBu₄)}] (PMDETA = NMe(CH₂CH₂NMe₂)₂) The alkali metal tetraphosphanediides [K₂(PMDETA)₂(P₄Ph₄)] ( 1 ) and [K₂(PMDETA)(P₄tBu₄)]₂ ( 2 ) [PMDETA = NMe(CH₂CH₂NMe₂)₂] were synthesized via reaction of PhPCl₂ or tBuPCl₂ with 2.5 equiv. potassium and characterized by X‐ray crystallography and ³¹P NMR spectroscopy. As in other ion contact complexes of the type M₂(P₄R₄) (M = alkali metal) the solid‐state structures are retained in solution. While 1 could be prepared in comparatively good yield (54 %), 2 was only isolated in very modest yield and with low purity as [K(PMDETA)(THF){cyclo‐(P₅tBu₄)}] ( 3 ) was formed as a side product in this case. 3 was also characterized by X‐ray crystallography and ³¹P NMR spectroscopy.     

Heterobimetallic s‐Block Hydrides by σ‐Bond Metathesis

Reactions between PhSiH₃ and alkali‐metal diamidoalkylmagnesiates ([M{N(SiMe₃)₂}₂MgBu], M=Li, Na, K) provide either selective alkyl metathesis or the formation of polyhydride aggregates contingent upon the identity of the Group 1 metal. In the case of [M{N(SiMe₃)₂}₂MgBu], this reactivity results in a structurally unprecedented dodecametallic decahydride cluster species.     

Synthese,spektroskopische Charakterisierung und Molekülstrukturen ausgewählter Lewis‐Basen‐Addukte der Alkalimetall‐tri(tert‐butyl)silylphosphanide

Synthesis, Spectroscopic Characterization, and Molecular Structures of Selected Lewis‐Base Adducts of the Alkali Metal Tri(tert‐butyl)silylphosphanides The metalation of tri(tert‐butyl)silylphosphane with butyllithium and the bis(trimethylsilyl)amides of sodium, potassium, and rubidium yields quantitatively the corresponding alkali metal tri(tert‐butyl)silylphosphanides, which crystallize after addition of appropriate Lewis‐bases as dimeric (DME)LiP(H)SitBu₃ ( 1 ), chain‐like (DME)NaP(H)SitBu₃ ( 2 ), monomeric ([18]Krone‐6)KP(H)SitBu₃ ( 3 ), and dimeric (TMEDA)_1.5RbP(H)SitBu₃ ( 4 ). The reaction of H₂PSitBu₃ with cesium bis(trimethylsilyl)amide at room temperature gives monocyclic and tetrameric cesium tri(tert‐butyl)silylphosphanide ( 5 ) with two additional coordinated CsN(SiMe₃)₂ molecules. At 80 °C this complex reacts with excess of phosphane to the tetrameric toluene adduct (η⁶‐Toluol)CsP(H)SitBu₃ ( 6 ) which contains a central Cs₄P₄‐heterocubane fragment. The constitution of these compounds was verified by X‐ray structure determinations.     

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.     

配合物(ArO)2Yb(NPh2)2K(THF)4(Ar=C6H2-t-Bu3-2,4,6)的合成、分子结构和催化行为

Reaction of anhydrous YbC13 with 2 equiv, of sodium 2,4,6-tri-tert-butylphenoxide (ArONa, Ar=C6H2-t-Bu3-2,4,6) and 2 equiv, of potassium diphenyl amide in THF afforded the first bis(aryloxo) amido-lanthanide complex of (ArO)2Yb(NPh2)2K(THF)4 (1). In 1, the ytterbium and potassium were bridged via diphenyl amido ligands.The ytterbium metal center was coordinated to two oxygen atoms of aryloxide ligands and two nitrogen atoms of diphenyl amido ligands in a conventional distorted tetrahedral fashion, while the potassium interacted in η^2-fashion with two phenyl rings of the diphenyl amido ligands besides four THF molecules. 1 displayed moderate catalytic activities for the polymerization of methyl methacrylate and acrylonitrile.     

1‐Azaallyl Complexes of NiII,PdII, and TiIII

The metal complexes [Ni{N(Ar)C(R)C(H)Ph}₂) ( 2 ) (Ar = 2,6‐Me₂C₆H₃, R = SiMe₃), [Ti(Cp₂){N(R)C(Bu^t)C(H)R}] ( 3 ), M{N(R)C(Bu^t)C(H)R}I [M = Ni ( 4 a ) or Pd ( 4 b )] and [M{N(R)C(Bu^t)C(H)R}I(PPh₃)] [M = Ni ( 5 a ) or Pd ( 5 b )] have been prepared from a suitable metal halide and lithium precursor of ( 2 ) or ( 3 ) or, alternatively from [M(LL)₂] (M = Ni, LL = cod; M = Pd, LL = dba) and the ketimine RN = C(Bu^t)CH(I)R ( 1 ). All compounds, except 4 were fully characterised, including the provision of X‐ray crystallographic data for complex 5 a .