Versatile Conversion of N‐Heterocyclic Silylene to Silyl Metal Compounds by Insertion of Divalent Silicon into Metal–Carbon and Metal–Hydrogen Bonds

The facile one‐pot reaction of the stable N‐heterocyclic silylene LSi: 1 (L?(ArN)C(?CH₂) CH?C(Me)(NAr), Ar=2,6‐iPr₂C₆H₃) with Me₂Zn, Me₃Al, H₃Al‐NMe₃, and MeLi has been investigated. The silicon(II) atom in 1 is capable of insertion into the corresponding M? C and Al? H bonds under very mild reaction conditions. Thus, Me₂Zn furnishes the bis(silyl) zinc complex LSi(Me)ZnSi(Me)L 2 as the sole product, irrespective of the molar ratio of the starting materials applied. Moreover, the reactions of 1 with Me₃Al, H₃Al‐NMe₃, and MeLi lead directly to the 1,1‐addition products LSi(Me)(Al(thf)Me₂) 3 , LSi(H)(AlH₂(NMe₃)) 4 , and LSi(Me)Li(thf)₃ 5 , respectively. All new compounds 2 – 5 were fully characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses, and single‐crystal X‐ray diffraction analyses.     

Phenoxyaluminium compounds : VII. Reactions of organoaluminium compounds with hindered phenols

Reactions of Me₃Al, i-Bu₃Al, Me₂AlCl and Me₂AlCCMe with 2,6-di-t-butyl-4-methylphenol have been studied at different molar ratios of the reactants.It is found that in the reaction with the phenol, trimethylaluminium forms monomeric methylaluminium diphenoxide; triisobutylaluminium gives both monomeric mono- and di-phenoxyaluminium (depending on molar ratios of the reactants) and dimethylchloroaluminium forms dimeric methylphenoxyaluminium chloride.It is found that methylpropynylaluminium phenoxide is unstable and disproportionates in hydrocarbon solutions.The mechanisms of some of these reactions are suggested.     

Substitutionsreaktionen der Bis(trimethylelement)carbodiimide des Siliciums und Germaniums mit Metallchloriden und Dimethylmetallchloriden des Sb,Al, Ga und In

Substitution Reactions of Bis(trimethylelement)carbodiimides of Silicon and Germanium with Metal Chlorides and Dimethylmetalchlorides of Sb, Al, Ga, and In The reaction of Me₃Ge? N?C?N? GeMe₃ (Me?CH₃) with SbCl₅ in a 1 : 1 molar ratio forms dimeric Cl₄SbNCNGeMe₃ in high yields. The corresponding compounds (X₂MNCNSiMe₃)_2–3 (with X?Cl, Me and M = Al, Ga), formed by reactions of X₂MCl and Me₃SiNCNSiMe₃, are less stable and tend to condensations, eliminating Me₃SiX. The carbodiimide derivates (Me₂MNCNEMe₃)_2–3 (with E = Si, Ge) are also available in aprotic solvents from polymeric LiNCNEMe₃ and Me₂MCl (M = Al, Ga, In). According to the IR and Raman spectra the low associated substitution products consists of cyclic ring skeletons and asymmetric > N? C?N? EMe₃ units with cyanamide conformation.     

Darstellung,Eigenschaften und Molekülstrukturen von Dimethylmetallalkoxiden und ‐amiden des Aluminiums und Galliums

Preparation, Properties, and Molecular Structures of Dimethylmetal Alkoxides and Amides of Aluminium and Gallium Dimethylaluminium‐ ( 1 ) and Dimethylgallium‐o‐methoxyphenyl‐1‐ethoxide ( 2 ) were obtained by reaction of Me₃Al and Me₃Ga respectively with o‐Methoxyphenyl‐1‐ethanol in n‐pentane. Dimethylaluminium‐ ( 3 ) and dimethylgallium‐o‐methoxyphenyl‐2‐ethylamide ( 4 ) were prepared by treatment of Me₂AlCl and Me₂GaCl respectively with Lithium‐o‐methoxyphenyl‐2‐ethylamide. Trimethylgallium‐o‐methoxyphenylmethylamine‐Adduct ( 5 ) was isolated using reaction of Me₃Ga with the corresponding amine. The compounds were characterised by ¹H‐, ¹³C‐, and ²⁷Al n.m.r. spectroscopy. The molecular structures of 2 and 5 were determined by X‐ray diffraction. Compounds 1 – 4 form brigded dimeric molecules. The bond distances of the central Ga₂O₂ ring in 2 correspond to those of compounds of similar structure.     

The conversion of alkynes into substituted cyclopropanes effected by CH2I2-R3Al (R = Me, Et, i-Bu)

The reaction of mono- and disubstituted alkynes with CH₂I₂-R₃Al (R = Me, Et, i-Bu) was studied. It was found that the reaction of alkynes with CH₂I₂ in the presence of Me₃Al gives β-iodoethyl-substituted cyclopropanes. The use of Et₃Al or i-Bu₃Al affords exclusively cyclopropylic organoaluminum compounds.     

Phenoxyaluminium compounds: VI. Complex and reaction mechanism of methylaluminium compounds with anisole

The reactions of anisole with organoaluminium compounds Me_nAlX_3−n have been investigated.The formation of a complex is the first reaction step, followed by cleavage and elimination of the gases MeX and small amounts of hydrocarbons. The yield of the gases and the cleavage rate decreases in the order: AlCl₃ >/ MeAlCl₂ > Me₂AlCl > Me₃Al and Me₂AlI > Me₂AlCl > Me₂AlBr. For most of the investigated reactions a marked decrease in gas evolution was observed after a short period of time. This is explained by the formation of an almost inactive mixed dimer (I) which at the

reaction temperature is more stable than the Me₂(Cl)Al : O(Me)Ph complex. It is suggested that dimer I is formed after the intramolecular reaction of the 2 : 1 complex II after elimination of MeX.

     

Stereo- and regioselective routes to allylic silanes

The Ni- or Pd-catalyzed reaction of alkenyl iodides with Me₃SiCH₂Mgcl provides various types of allytrimethylsilanes in excellent yields in a highly stereo- and regioselective manner, while the Zr-catalyzed carboalumination of Me₃SiCH₂CCH followed by replacement of Al with carbon groups by known reactions produces allylsilanes represented by $\text{2}$.     

N,N,N′,N′-Tetramethylethylendiamin-di(tert-butyl)aluminium-Kationen — Molekülstruktur des [(Me3C)2Al · TMEDA]⊕[(Me3C)2AlBr2]⊖

(N,N,N′,N′ -tetramethylethylendiamine) di(tert-butyl)aluminium Cations — Molecular Structure of [(Me₃C)₂Al(TMEDA)]^⊕[(Me₃C)₂AlBr₂]^? Dimeric di(tert-butyl)aluminium halides (Me₃C)₂AlX (X = Cl, Br) react with N,N,N′,N′ -tetramethylethylendiamine (TMEDA) to give three compounds: the salt-like [(Me₃C)₂Al(TMEDA)]^⊕[(Me₃C)₂AlX₂]^? 1 , characterized by crystal structure determination, and [(Me₃C)₂Al(TMEDA)]^⊕X^? 3 both with chelating amine, and the more covalent, pentane soluble (Me₃C)₂AlX(TMEDA) 2 with TMEDA bound by only one nitrogen atom. The reaction resembles the symmetrical and unsymmetrical cleavage of diborane(6). 3 (X = Cl) is also formed by treatment of 1 with boiling n-hexane in the presence of TMEDA over a period of 24 hours, while for X = Br the more covalent 2 is the main product under similar conditions. In solution 2 decomposes slowly yielding different products in dependency of the solvent: in benzene 3 and in n-pentane 1 are formed.     

Halogenid‐Ionen als Katalysator: Metallzentrierte C–C‐Bindungsknüpfung ausgehend von Acetontril

Halide Ions as Catalyst: Metalcentered C–C Bond Formation Proceeded from Acetonitril AlMe₃ reacts at 20 ?C in acetonitrile to the complex [Me₃Al(NCMe)] ( 1 ). By addition of cesium halides (X^– = F^–, Cl^–, Br^–) a trimerisation to the heterocycle [Me₂Al{HNC(Me)}₂C(CN)] ( 2 ) has been observed. The reaction might be carried out under catalytic conditions (1–2 mol% CsX). The gallium complex [Me₂Ga{HNC(Me)}₂ · C(CN)] ( 3 ), generated under similar reaction conditions, can be converted to the silylated compound [Me₂Ga{Me₃SiNC(Me)}₂C(CN)] ( 4 ) by successive treatment with two equivalents n‐butyllithium and Me₃SiCl. 3 reacts under hydrolysis conditions (1 M hydrochloric acid) to the iminium salt [{H₂NC(Me)}₂C(CN)]Cl ( 5 ). A mixture of H₂O, Ph₂PCl and 3 in THF/toluene leads in a unusual conversion to the diphospane derivative [Ph₂P–P(O)(Me₂GaCl)] ( 6 ). 1 , 2 , 4 , 5 and 6 have been characterized by NMR, IR and MS techniques. X‐ray structure analyses were performed with 1 , 2 , 4 and 6 · 0.5 toluene. According this 1 possesses an almost linear axis AlNCC [Al1–N1–C3: 179,5(2)?; N1–C3–C4: 179,7(4)?]. 2 is an AlN₂C₃ six‐membered heterocycle with two iminium fuctions. One N–H group is responsible for a intermolecular chain‐formation through hydrogen bridges to an adjacent nitrile group along the direction [010]. The basic structural motif of the heterocycle 3 has been maintained after silylation to 4 . In 6 · 0.5 toluene an unit Me₂GaCl, originated from 3 , is coordinated to the oxygen atom of the diphosphane oxide Ph₂P–P(O)Ph₂.     

Ring-opening of 2,3-epoxy-1-propanol with R3Al: Unprecedented regiochemical switching simply achieved by changing alkyl substituents of aluminium reagent

Several control experiments were designed to optimize the reaction of 2,3-epoxy-1-propanol with R₃Al (R = Me, Et or ⁱBu) and to probe for the nature of aluminium-bound alkyl groups that influence the reactivity and selectivity. The reported studies revealed that the Et₃Al mediated reaction leads to the C-2 product in contrast to the well-known C-3 substitution promoted by Me₃Al.     

Studien zur Reaktion von [Me2AlP(SiMe3)2]2 mit basenstabilisierten Organogalliumchloriden und ‐hydriden

Investigations on the Reactivity of [Me₂AlP(SiMe₃)₂]₂ with Base‐stabilized Organogalliumhalides and ‐hydrides [Me₂AlP(SiMe₃)₂]₂ ( 1 ) reacts with dmap?Ga(Cl)Me₂, dmap?Ga(Me)Cl₂, dmap?GaCl₃ and dmap?Ga(H)Me₂ with Al‐P bond cleavage and subsequent formation of heterocyclic [Me₂GaP(SiMe₃)₂]₂ ( 2 ) as well as dmap?AlMe_xCl_3?x (x = 3 8 ; 2 3 ; 1 4 ; 0 5 ). The reaction between equimolar amounts of dmap?Al(Me₂)P(SiMe₃)₂ and dmap?Ga(t‐Bu₂)Cl yield dmap?Ga(t‐Bu₂)P(SiMe₃)₂ ( 6 ) and dmap?AlMe₂Cl ( 3 ). 2 – 8 were characterized by NMR spectroscopy, 2 and 6 also by single crystal X‐ray diffraction.     

The reversible adduct formation of group III trialkyls with relatively involatile phosphines; X-ray crystal structures of (Me3M)2·(Ph2PCH2)2 (M = Al,Ga, In) and (Me3Al)3·(Ph2PCH2CH2)2PPh

The following adducts of Group III trialkyls with phosphines have been prepared, either by direct reaction in hydrocarbon solution or by displacement of ether from the metal trialkyl etherate: Me₃M·PPh₃ (M = Ga, In); Me₃In·P(2-MeC₆H₄)₃; (R₃M)₂·(Ph₂PCH₂)₂ (R = Me, M = Al, Ga, In; R = Et, M = Ga, In; R = Buⁱ, M = Al); (Me₃M)₃·(Ph₂PCH₂CH₂)₂PPh (M = Al, Ga, In) and (Me₃M)₄·(Ph₂PCH₂CH₂PPhCH₂)₂ (M = Al, Ga, In). The compounds were analysed by ¹H and ³¹P NMR spectra of (Me₃M)₂·(Ph₂PCH₂)₂ (M = Ga, In) showed little change between 193 K and room temperature. Thermal dissociation of the adducts in vacuo gave the free metal trialkyl with no detectable contamination by the respective phosphine. Crystals of (Me₃M)₂·(Ph₂PCH₂)₂ (M = Al, Ga, In) are iso-structural and the molecules contain two distorted tetrahedral metals bridged by the (Ph₂PCH₂)₂; the MP distances are 2.544(4), 2.546(4) and 2.755(4) Å, respectively. The X-ray crystal structure of (Me₃Al)₃·(Ph₂PCH₂CH₂)₂PPh shows the molecule to contain distorted tetrahedral aluminium atoms bonded to each of the three phosphorus atoms, with AlP distances of 2.536(9) and 2.510(9) Å for the terminal and central moieties, respectively; the unit cell contains two such molecules plus one benzene molecule (the crystallizing solvent).     

Darstellung,Eigenschaften und Molekülstrukturen von Dimethylaminomethylferrocenyl‐Verbindungen ausgewählter Elemente der Gruppen 13 und 14

Preparation, Properties, and Molecular Structures of Dimethylaminomethyl Ferrocenyl Compounds of selected Elements of Group 13 and 14 Dimethylmetalchlorides of gallium and indium react with dimethylaminomethylferrocenyllithium (FcNLi) to give the corresponding dimethylmetaldimethylaminomethylferrocenes 1 and 2 [Me₂MFcN; M=Ga, In]. In a similar manner dialkylmetaldichlorides of germanium and tin yield the expected chlordialkylmetaldimethylaminomethylferrocenes 3 – 5 [R₂(Cl)MFcN; M=Ge; R = Me ( 3 ), M=Sn; R=Me ( 4 ), Ph ( 5 )]. In a reaction of Me₃Al and Me₂AlCl with dimethylaminomethylferrocene the formation of the 1 : 1 adducts 7 and 8 could be observed. All compounds were characterised by ¹H and ¹³C nmr spectroscopy. The molecular structures of 1 , 3 , 4 and 7 were determined. 3 and 4 build in contrast to 1 monomeric molecules with chelat rings as a result of the M–N coordination. Compound 7 consist of monomeric molecules with 4 coordinated Al atoms.     

Competitive Reaction Pathways for the Gas‐Phase Reactivity of [Me2AlNH2]3

Reaction energy profiles for [Me₂AlNH₂]₃ have been computationally explored by using density functional theory. Both intra‐ and intermolecular methane elimination reactions, as well as Al?N bond‐breaking pathways, were considered. The results show that the energy required for Al?N bond breaking in cyclic [Me₂AlNH₂]₃ is of the same order of magnitude as the activation energies for the first (limiting) step of methane elimination (for both mono‐ and bimolecular mechanisms). Thus, dissociative and associative reaction pathways are competitive. Low‐temperature/high‐pressure conditions will favor the bimolecular pathway, whereas at high temperatures, either intramolecular methane elimination or Al?N bond‐breaking dissociative pathways will be operational.     

Synthese eines funktionalen Aluminiumalkinids,Me3C‐C≡C‐AlBr2, und dessen Reaktionen mit der sperrigen Lithiumverbindung LiCH(SiMe3)2

Synthesis of a Functional Aluminium Alkynide, Me₃C‐C≡C‐AlBr₂, and its Reactions with the Bulky Lithium Compound LiCH(SiMe₃)₂ Treatment of aluminium tribromide with the lithium alkynide (Li)C≡C‐CMe₃ afforded the aluminium alkynide Me₃C‐C≡C‐AlBr₂ ( 1 ) in an almost quantitative yield. 1 crystallizes with trimeric formula units possessing Al₃C₃ heterocycles and the anionic carbon atoms of the alkynido groups in the bridging positions. A dynamic equilibrium was determined in solution which probably comprises trimeric and dimeric formula units. Reaction of 1 with one equivalent of LiCH(SiMe₃)₂ yielded the compound [Me₃C‐C≡C‐Al(Br)‐CH(SiMe₃)₂]₂ ( 2 ), which is a dimer via Al‐C‐Al bridges. Two equivalents of the lithium compound gave a mixture of four main‐products, which could be identified as 2 , Li[Me₃C‐C≡C‐Al{CH(SiMe₃)₂}₃] ( 3 ), Me₃C‐C≡C‐Al[CH(SiMe₃)₂]₂ ( 4 ), and Al[CH(SiMe₃)₂]₃. The lithium atom of 3 is coordinated by the C≡C triple bond and an inner carbon atom of one bis(trimethylsilyl)methyl group. Further interactions were observed to C‐H bonds of methyl groups.     

Die Reaktion des [(Me3Si)2CH]2Al?CH2?Al [CH(SiMe3)2]2 mit Neopentyllithium: Bildung des {[(Me3Si)2CH]2Al?CH2?Al [CH(SiMe3)2]2CH2CMe3}⊖ [Li(TMEDA)2]⊕

Reaction of [(Me₃Si)₂CH]₂Al? CH₂? Al [CH(SiMe₃)₂]₂ with Neopentyllithium: Formation of {[(Me₃Si)₂CH]₂Al? CH₂? Al [CH(SiMe₃)₂]₂CH₂CMe₃} ? [Li(TMEDA)₂]⊕ The recently synthesized methylene bridged dialuminium compound [(Me₃Si)₂CH]₂Al? CH₂? Al [CH(SiMe₃)₂]₂ reacts with neopentyl lithium in the presence of TMEDA to give the stable {[(Me₃Si)₂CH]₂Al? CH₂? Al [CH(SiMe₃)₂]₂CH₂ · CMe₃}? [Li(TMEDA)₂]⊕ decomposing at 115°C. The aluminium atoms therein are not additionally bridged, but the new substituent is occupying a terminal position as detected by crystal structure determination. A compound is formed containing a saturated, fourfold coordinated neighbouring a formally unsaturated, threefold coordinated aluminium atom. Due to high sterical restrictions the Al? C bonds are lengthened up to 209.0(3) pm at the alanate site and the Al? C? Al angle in the methylene bridge is extraordinarily enlarged to 144.4(2)°.     

Die Hydroaluminierung von 1,1,4,4‐Tetramethyl‐2,3‐diazabutadien mit Dialkylaluminiumhydriden – Synthese von Dialkylaluminiumhydrazoniden

The Hydroalumination of 1,1,4,4‐Tetramethyl‐2,3‐diazabutadiene by Dialkylaluminium Hydrides – Synthesis of Dialkylaluminium Hydrazonides 1,1,4,4‐Tetramethyl‐2,3‐diazabutadiene reacted with dimethylaluminium hydride by hydroalumination of only one C=N double bond. The hydrazone derivative [Me₂Al–N(CHMe₂)–N=CMe₂]₂ ( 1 ) was formed which gave a dimer possessing a six‐membered Al₂N₄ heterocycle. The hydroalumination of both C=N double bonds was not observed. Also an excess of di(tert‐butyl)‐ or bis(trimethylsilylmethyl)aluminium hydride afforded only the product of a single hydroalumination step, a second dialkylaluminium hydride molecule was attached via a coordinative interaction between its central aluminium atom and the nitrogen atom of the C=N double bond and in addition via a 3 c‐2 e Al–H–Al bond. Compounds [(Me₃C)₂Al][(Me₃C)₂AlH]N(CHMe₂)NCMe₂ ( 2 ) and [(Me₃SiCH₂)₂Al][(Me₃SiCH₂)₂AlH]N(CHMe₂)NCMe₂ ( 3 ) were formed which have five‐membered Al₂N₂H heterocycles. Thermolysis of 2 gave by C–H activation compound [(Me₃C)₂Al]₂[CH₂C(Me)=N–]₂ ( 4 ) in trace amounts which possesses two anellated AlN₂C₂ rings with a common N–N bond. In contrast, the thermal decomposition of 3 yielded by the cleavage of the N–N bond a dimeric dialkylaluminium methylideneamide ( 5 ) which has two intact C=N double bonds. Up to now our attempts to insert a C=N double bond into an Al–C bond remained unsuccessful, and only the formation of an adduct [(Me₃C)₃Al(–N=CMe₂)₂] ( 6 ) was observed upon treatment of tri(tert‐butyl)aluminium with the diazabutadiene derivative.     

A Janus‐Headed Lewis Superacid: Simple Access to,and First Application of Me3Si‐F‐Al(ORF)3

Upon reaction of gaseous Me₃SiF with the in situ prepared Lewis acid Al(OR^F)₃, the stable ion‐like silylium compound Me₃Si‐F‐Al(OR^F)₃ 1 forms. The Janus‐headed 1 is a readily available smart Lewis acid that differentiates between hard and soft nucleophiles, but also polymerizes isobutene effectively. Thus, in reactions of 1 with soft nucleophiles (Nu), such as phosphanes, the silylium side interacts in an orbital‐controlled manner, with formation of [Me₃Si?Nu]⁺ and the weakly coordinating [F?Al(OR^F)₃]^– or [(^FRO)₃Al‐F‐Al(OR^F)₃]^– anions. If exchanged for hard nucleophiles, such as primary alcohols, the aluminum side reacts in a charge‐controlled manner, with release of FSiMe₃ gas and formation of the adduct R(H)O?Al(OR^F)₃. Compound 1 very effectively initiates polymerization of 8 to 21 mL of liquid C₄H₈ in 50 mL of CH₂Cl₂ already at temperatures between ?57 and ?30 °C with initiator loads as low as 10 mg in a few seconds with 100 % yield but broad polydispersities.     

Spectroscopic Studies of Synthetic Methylaluminoxane: Structure of Methylaluminoxane Activators

Hydrolysis of trimethylaluminum (Me₃Al) in polar solvents can be monitored by electrospray ionization mass spectrometry (ESI-MS) using the donor additive octamethyltrisiloxane [(Me₃SiO)₂SiMe₂, OMTS]. Using hydrated salts, hydrolytic methylaluminoxane (h-MAO) features different anion distributions, depending on the conditions of synthesis, and different activator contents as measured by NMR spectroscopy. Non-hydrolytic MAO was prepared using trimethylboroxine. The properties of this material, which contains incorporated boron, differ significantly from h-MAO. In the case of MAO prepared by direct hydrolysis, oligomeric anions are observed to rapidly form, and then more slowly evolve into a mixture dominated by an anion with m/z 1375 with formula [(MeAlO)₁₆(Me₃Al)₆Me]⁻. Theoretical calculations predict that sheet structures with composition (MeAlO)_n(Me₃Al)_m are favoured over other motifs for MAO in the size range suggested by the ESI-MS experiments. A possible precursor to the m/z 1375 anion is a local minimum based on the free energy released upon hydrolysis of Me₃Al.     

Trimethylstannyl- und Dimethylstannyl-substituierte Pyrrole – Synthesen,Spektren und Strukturen

Trimethylstannyl- and Dimethylstannyl-substituted Pyrroles – Synthesis, Spectra, and Structures Monomeric trimethylstannyl pyrroles, Me₃Sn? R (Me = CH₃ and R = ? NC₄H₄, ? NC₄H₂Me₂-2,5, ? NC₄Me₄-2,3,4,5, ? C₄H₃NMe-1), are synthesized by metathesis reactions from Me₃SnCl with 1(N)- and 2(C)-lithium pyrroles, respectively. An almost similar procedure gives monomeric dimethylstannylbis(pyrroles), Me₂SnR₂ ( 1 a – 3 a ), from Me₂SnCl₂ and 1-Li-pyrrolides (1 : 2 molar ratio) in good yields. Lithiated 1,2,5-trimethylpyrrole and Me₃SnCl forms the compound Me₃Sn? CH₂? C₄H₂Me(-5)NMe ( 8 ), the reaction of Me₂SnCl₂ with 2-lithium-1-methylpyrrole gives oligomeric [Me₂Sn? C₄H₂NMe? ]_x, ( 6 a ). The mass-, NMR, and vibrational spectra have been measured and discussed. The results of the X-ray structure determinations of Me₃Sn? NC₄H₄ ( 1 ) and Me₂Sn(? NC₄Me₄)₂ ( 3 a ) are compared with the structures of the known dimethylmetal pyrroles of Al, Ga, and In.