Sol‐Gel‐Process in the Ammono‐System – a Novel Access to Silicon Based Nitrides

Controlled coammonolysis of elementalkylamides in aprotic organic solvents at low temperatures have been shown to result in the formation of polyazanes. The synthetic procedure developed may be addressed as “sol‐gel‐route in the ammono system”. Pyrolysis of these novel polymer precursors gave access to multinary nitrides. For the model systems Si(NHMe)₄/B(NMe₂)₃, Si(NHMe)₄/Ti(NMe₂)₄, and Si(NHMe)₄/Ta(NMe₂)₅ polymeric boro‐, titano and tantalosilazanes were obtained. Pyrolysis in ammonia at 1000 °C yielded amorphous silicon boron nitride, silicon titanium nitride and silicon tantalum nitride powders; further heating of the nitride powders at 1500 °C in nitrogen atmosphere led to the formation of partly crystalline composites of α‐Si₃N₄ and amorphous silicon boron nitride for the Si/B/N system, a composite of finely dispersed TiN and amorphous silicon titanium nitride for the Si/Ti/N system, and crystalline TaN and amorphous silicon nitride for the Si/Ta/N system. Furthermore, the structure and pyrolysis chemistry of the polymeric intermediates, as well as the morphology of the pyrolysis products, were studied by NMR, MAS‐NMR, FT‐IR, DTA‐TG‐MS, XRD, SEM, EDX and elemental analyses.     

Synthese und Charakterisierung von [Zn{Si(NMe2)2(NHCMe3)(NCMe3)}‐(μ‐NC5H4)]2, einem molekularen Einkomponentenvorläufer zur Darstellung von ZnSiN2

Synthesis and Characterization of [Zn{Si(NMe₂)₂(NHCMe₃)(NCMe₃)}(μ‐NC₅H₄)]₂, a Molecular Single Source Precursor for ZnSiN₂ For an application as single source precursor for ZnSiN₂ the siladiazazinca cyclo butane [Zn{Si(NMe₂)₂(NHCMe₃)(NCMe₃)}(μ‐NC₅H₄)]₂has been synthesised for the first time from Si(NMe₂)₂(NLi t‐Butyl)₂ and ZnCl₂(NC₅H₅)₂. It has been characterized by single crystal structure analysis (P1, a = 870.5(3) pm, b = 903.8(3) pm, c = 1530.6(4) pm, α = 96.982(5)°, β = 106.501(5)°, γ = 104.729(5)°). The CP‐MAS‐NMR data for the nuclei ¹³C, ¹⁵N and ²⁹Si are reported. ZnSiN₂ was prepared by thermal decomposition of the precursor molecule and characterized by elemental analysis, EDX, IR spectroscopy and thermal analysis. The crystal structure was determined (X‐ray powder diffraction data, profile matching: P6₃mc, a = 315.33(1) pm, c = 508.07(2) pm, R_B = 4.87). The thermal behaviour of the precursor molecule, the preparation of polymers by linking with NH₃ and the decomposition of the polymers in an argon or NH₃ stream were investigated.     

Rivalry under Pressure: The Coexistence of Ambient‐Pressure Motifs and Close‐Packing in Silicon Phosphorus Nitride Imide SiP2N4NH

Non‐metal nitrides such as BN, Si₃N₄, and P₃N₅ meet numerous demands on high‐performance materials, and their high‐pressure polymorphs exhibit outstanding mechanical properties. Herein, we present the silicon phosphorus nitride imide SiP₂N₄NH featuring sixfold coordinated Si. Using the multi‐anvil technique, SiP₂N₄NH was obtained by high‐pressure high‐temperature synthesis at 8 GPa and 1100 °C with in situ formed HCl acting as a mineralizer. Its structure was elucidated by a combination of single‐crystal X‐ray diffraction and solid‐state NMR measurements. Moreover, SiP₂N₄NH was characterized by energy‐dispersive X‐ray spectroscopy and (temperature‐dependent) powder X‐ray diffraction. The highly condensed Si/P/N framework features PN₄ tetrahedra as well as the rare motif of SiN₆ octahedra, and is discussed in the context of ambient‐pressure motifs competing with close‐packing of nitride anions, representing a missing link in the high‐pressure chemistry of non‐metal nitrides.     

1,1‐Ethylboration of alkyn‐1‐yl‐chloro(methyl)silanes: alkenes with chloro(methyl)silyl and diethylboryl groups in cis positions

The 1,1‐ethylboration of alkyn‐1‐yl‐chloro(methyl)silanes, Me₂Si(Cl)? C?C? R ( 1 ) and Me(H)Si(Cl)? C?C? R ( 2 ) [R = Bu ( 2a ), CH₂NMe₂ ( 2b )] requires harsh reaction conditions (up to 20 days in boiling triethylborane), and leads to alkenes in which the boryl and silyl groups occupy cis ((E)‐isomers: 3a , 3b , 5a , 5b ) or trans positions ((Z)‐isomers in smaller quantities: 4b and 6b ). The alkenes are destabilized in the presence of SiH(Cl) and CH₂NMe₂ units ( 5b , 6b ). NMR data indicate hyper‐coordinated silicon by intramolecular N? Si coordination in 3b and 5b , by which, at the same time, weak Si? Cl? B bridges are favoured. Copyright © 2005 John Wiley & Sons, Ltd.     

A Silyliumylidene Cation Stabilized by an Amidinate Ligand and 4‐Dimethylaminopyridine

The synthesis and reactivity of a silyliumylidene cation stabilized by an amidinate ligand and 4‐dimethylaminopyridine (DMAP) are described. The reaction of the amidinate silicon(I) dimer [ L Si:]₂ ( 1 ; L =PhC(NtBu)₂) with one equivalent of N‐trimethylsilyl‐4‐dimethylaminopyridinium triflate [4‐NMe₂C₅H₄NSiMe₃]OTf and two equivalents of DMAP in THF afforded [ L Si(DMAP)]OTf ( 2 ). The ambiphilic character of 2 is demonstrated from its reactivity. Treatment of 2 with 1 in THF afforded the disilylenylsilylium triflate [ L′ ₂( L )Si]OTf ( 3 ; L′ = L Si:) with the displacement of DMAP. The reaction of 2 with [K{HB(iBu)₃}] and elemental sulfur in THF afforded the silylsilylene [ L SiSi(H){(NtBu)₂C(H)Ph}] ( 4 ) and the base‐stabilized silanethionium triflate [ L Si(S)DMAP]OTf ( 5 ), respectively. Compounds 2 , 3 , and 5 have been characterized by X‐ray crystallography.     

The Synthesis of Functionalised Diaryltetraynes and Their Transport Properties in Single‐Molecule Junctions

The synthesis and characterisation is described of six diaryltetrayne derivatives [Ar‐(C?C)₄‐Ar] with Ar=4‐NO₂‐C₆H₄‐ ( NO₂4 ), 4‐NH(Me)C₆H₄‐ ( NHMe4 ), 4‐NMe₂C₆H₄‐ ( NMe₂4 ), 4‐NH₂‐(2,6‐dimethyl)C₆H₄‐ ( DMeNH₂4 ), 5‐indolyl ( IN4 ) and 5‐benzothienyl ( BTh4 ). X‐ray molecular structures are reported for NO₂4 , NHMe4 , DMeNH₂4 , IN4 and BTh4 . The stability of the tetraynes has been assessed under ambient laboratory conditions (20 °C, daylight and in air): NO₂4 and BTh4 are stable for at least six months without observable decomposition, whereas NHMe4 , NMe₂4 , DMeNH₂4 and IN4 decompose within a few hours or days. The derivative DMeNH₂4 , with ortho‐methyl groups partially shielding the tetrayne backbone, is considerably more stable than the parent compound with Ar=4‐NH₂C₆H₄ ( NH₂4 ). The ability of the stable tetraynes to anchor in Au|molecule|Au junctions is reported. Scanning‐tunnelling‐microscopy break junction (STM‐BJ) and mechanically controllable break junction (MCBJ) techniques are employed to investigate single‐molecule conductance characteristics.     

Synthesis,Structure, and Fluxionality of Strained Hypercoordinate Silicon‐Bridged [1]Ferrocenophanes

The first hypercoordinate sila[1]ferrocenophanes [fcSiMe(2‐C₆H₄CH₂NMe₂)] ( 5 a ) and [fcSi(CH₂Cl)(2‐C₆H₄CH₂NMe₂)] ( 5 b ) (fc=(η⁵‐C₅H₄)Fe(η⁵‐C₅H₄)) were synthesized by low‐temperature (?78 °C) reactions of Li[2‐C₆H₄CH₂NMe₂] with the appropriate chlorinated sila[1]ferrocenophanes ([fcSiMeCl] ( 1 a ) and [fcSi(CH₂Cl)Cl] ( 1 d ), respectively). Single‐crystal Xray diffraction studies revealed pseudo‐trigonal bipyramidal structures for both 5 a and 5 b , with one of the shortest reported Si???N distances for an sp³‐hybridized nitrogen atom interacting with a tetraorganosilane detected for 5 a (2.776(2) Å). Elongated Si? C_ipso bonds trans to the donating NMe₂ arms (1.919(2) and 1.909(2) Å for 5 a and 5 b , respectively) were observed relative to both the non‐trans bonds ( 5 a : 1.891(2); 5 b : 1.879(2) Å) and the Si? C_ipso bonds of the non‐hypercoordinate analogues ([fcSiMePh] ( 1 b ): 1.879(4), 1.880(4) Å; [fcSi(CH₂Cl)Ph] ( 1 e ): 1.881(2), 1.884(2)). Solution‐state fluxionality of 5 a and 5 b , suggestive of reversible coordination of the NMe₂ group to silicon, was demonstrated by means of variable‐temperature NMR studies. The ΔG^≠ of the fluxional processes for 5 a and 5 b in CD₂Cl₂ were estimated to be 35.0 and 37.6 kJ mol^?1, respectively (35.8 and 38.3 kJ mol^?1 in [D₈]toluene). The quaternization of 5 a and 5 b by MeOTf, to give [fcSiMe(2‐C₆H₄CH₂NMe₃)][OTf] ( 7 a‐ OTf) and [fcSi(CH₂Cl)(2‐C₆H₄CH₂NMe₃)][OTf] ( 7 b‐ OTf), respectively, supported the reversibility of NMe₂ coordination at the silicon center as the source of fluxionality for 5 a and 5 b . Surprisingly, low room‐temperature stability was detected for 5 b due to its tendency to intramolecularly cyclize and form the spirocyclic [fcSi(cyclo‐CH₂NMe₂CH₂C₆H₄)]Cl ( 9 ‐Cl). This process was observed in both solution and the solid state, and isolation and Xray characterization of 9 ‐Cl was achieved. The model compound, [Fc₂Si(2‐C₆H₄CH₂NMe₂)₂] ( 8 ), synthesized through reaction of [Fc₂SiCl₂] with two equivalents of Li[2‐C₆H₄CH₂NMe₂] at ?78 °C, showed a lack of hypercoordination in both the solid state and in solution (down to ?80 °C). This suggests that either the reduced steric hindrance around Si or the unique electronics of the strained sila[1]ferrocenophanes is necessary for hypercoordination to occur.     

N(B(NMe2)2)(Si(NMe2)3)(Ti(NMe2)3), [N(Si(NMe2)3)(Ti(NMe2)2)]2 und N(SiMe3)(Si(NMe2)3)(Ti(NMe2)3) — Synthese und Charakterisierung neuer molekularer Einkomponentenvorläufer für nitridische und carbonitridische Keramiken

N(B(NMe₂)₂)(Si(NMe₂)₃) (Ti(NMe₂)₃), [N(Si(NMe₂)₃)(Ti(NMe₂)₂)]₂ und N(SiMe₃)(Si(NMe₂)₃)(Ti(NMe₂)₃) — Synthesis and Characterization of New Molecular Single-source Precursors for Nitride and Carbonitride Ceramics Synthesis and spectroscopic data of the title compounds are reported. [N(Si(NMe₂)₃)(Ti(NMe₂)₂)]₂ crystallizes in the space group P1 , a = 8.406(7), b = 10.673(8), c = 10.872(6) Å, α = 68.45(4)°, β = 71.72(4)°, γ = 78.11(7)°, 2 877 diffractometer data (F_o ? 2σF_o), R = 0.051. The compound is characterized by a planar four-membered Ti₂N₂-ring with exocyclic tris(dimethylamino)silyl substituents attached to the nitrogen atoms of the ring.     

Low‐Temperature Atomic Layer Deposition of MoS2 Films

Wet chemical screening reveals the very high reactivity of Mo(NMe₂)₄ with H₂S for the low‐temperature synthesis of MoS₂. This observation motivated an investigation of Mo(NMe₂)₄ as a volatile precursor for the atomic layer deposition (ALD) of MoS₂ thin films. Herein we report that Mo(NMe₂)₄ enables MoS₂ film growth at record low temperatures—as low as 60 °C. The as‐deposited films are amorphous but can be readily crystallized by annealing. Importantly, the low ALD growth temperature is compatible with photolithographic and lift‐off patterning for the straightforward fabrication of diverse device structures.     

Zur Umsetzung von Kupfer(I)‐ und Kupfer(II)‐Salzen mit P(C6H4CH2NMe2‐2)3 ‐ die Festkörperstrukturen von {[P(C6H4CH2NMe2‐2)3]CuOClO3}ClO4, {[P(C6H4CH2NMe2‐2)3]Cu}ClO4, [P(C6H4CH2NMe2‐2)3]CuONO2 und [P(C6H4CH2NMe2‐2)2(C6H4CH2NMe2H+NO3‐‐2)]CuONO2

Reaction Behaviour of Copper(I) and Copper(II) Salts Towards P(C₆H₄CH₂NMe₂‐2)₃ ‐ the Solid‐State Structures of {[P(C₆H₄CH₂NMe₂‐2)₃]CuOClO₃}ClO₄, {[P(C₆H₄CH₂NMe₂‐2)₃]Cu}ClO₄, [P(C₆H₄CH₂NMe₂‐2)₃]CuONO₂ and [P(C₆H₄CH₂NMe₂‐2)₂(C₆H₄CH₂NMe₂H⁺NO₃^‐‐2)]CuONO₂ The reaction behaviour of P(C₆H₄CH₂NMe₂‐2)₃ ( 1 ) towards different copper(II) and copper(I) salts of the type CuX₂ ( 2a : X = BF₄, 2b : X = PF₆, 2c : X = ClO₄, 2d : X = NO₃, 2e : X = Cl, 2f : X = Br, 13 : X = O₂CMe) and CuX ( 5a : X = ClO₄, 5b : X = NO₃, 5c : X = Cl, 5d : X = Br) is discussed. Depending on X, the transition metal complexes [P(C₆H₄CH₂NMe₂‐2)₃Cu]X₂ ( 3a : X = BF₄, 3b : X = PF₆), {[P(C₆H₄CH₂NMe₂‐2)₃]CuX}X ( 4 : X = ClO₄, 11a : X = Cl, 11b : X = Br, 14 : X = O₂CMe), {[P(C₆H₄CH₂NMe₂‐2)₃]Cu}ClO₄ ( 6 ), [P(C₆H₄CH₂NMe₂‐2)₃]CuX ( 7a : X = Cl, 7b : X = Br, 10 : X = ONO₂), [P(C₆H₄CH₂NMe₂‐2)₂(C₆H₄CH₂NMe₂H⁺NO₃^‐‐2)]CuONO₂ ( 9 ) and [P(C₆H₄CH₂NMe₂‐2)₃]CuCl}CuCl₂ ( 12 ) are accessible. While in 3a , 3b and 6 the phosphane 1 preferentially acts as tetrapodale ligand, in all other species only the phosphorus atom and two of the three C₆H₄CH₂NMe₂ side‐arms are datively‐bound to the appropriate copper ion. In solution a dynamic behaviour of the latter species is observed. Due to the coordination ability of X in 3a , 3b and 6 non‐coordinating anions X^‐ are present. However, in 4 one of the two perchlorate ions forms a dative oxygen‐copper bond and the second perchlorate ion acts as counter ion to {[P(C₆H₄CH₂NMe₂‐2)₃]CuOClO₃}⁺. In 7 , 9 and 10 the fragments X (X = Cl, Br, ONO₂) form a σ‐bond with the copper(I) ion. The acetate moiety in 14 acts as chelating ligand as it could be shown by IR‐spectroscopic studies. All newly synthesised cationic and neutral copper(I) and copper(II) complexes are representing stable species. Redox processes are involved in the formation of 9 and 12 by reacting 1 with 2 . The solid‐state structures of 4 , 6 , 9 and 10 are reported. In the latter complexes the copper(II) ( 4 ) or copper(I) ion ( 6 , 9 , 10 ) possesses the coordination number 4. This is achieved by the formation of a phosphorus‐ and two nitrogen‐copper‐ ( 4 , 9 , 10 ) or three ( 6 ) nitrogen‐copper dative bonds and a coordinating ( 4 ) or σ‐binding ( 9 , 10 ) ligand X. In 6 all three nitrogen and the phosphorus atoms are coordinatively bound to copper, while X acts as non‐coordinating counter‐ion. Based on this, the respective copper ion occupies a distorted tetrahedral coordination sphere. While in 4 and 10 a free, neutral Me₂NCH₂ side‐arm is present, which rapidly exchanges in solution with the coordinatively‐bound Me₂NCH₂ fragments, this unit is protonated in 10 . NO₃^‐ acts as counter ion to the CH₂NMe₂H⁺ moiety. In all structural characterized complexes 6‐membered boat‐like CuPNC₃ cycles are present.     

Diverse Reactivity of an Electrophilic Phosphasilene towards Anionic Nucleophiles: Substitution or Metal–Amino Exchange

The reaction of MesLi (Mes=2,4,6‐trimethylphenyl) with the electrophilic phosphasilene R₂(NMe₂)Si‐RSi=PNMe₂ ( 2 , R=Tip=2,4,6‐triisopropylphenyl) cleanly affords R₂(NMe₂)Si‐RSi=PMes and thus provides the first example of a substitution reaction at an unperturbed Si=P bond. In toluene, the reaction of 2 with lithium disilenide, R₂Si=Si(R)Li ( 1 ), apparently proceeds via an initial nucleophilic substitution step as well (as suggested by DFT calculations), but affords a saturated bicyclo[1.1.0]butane analogue as the final product, which was further characterized as its Fe(CO)₄ complex. In contrast, in 1,2‐dimethoxyethane the reaction of 1 with 2 results in an unprecedented metal–amino exchange reaction.     

Synthese,Röntgenstrukturanalyse und Multikern‐NMR‐spektroskopische Untersuchung einiger intramolekular stickstoffstabilisierter Bor‐, Aluminium‐ und Galliumorganyle

Synthesis, X‐Ray Structure, and Multinuclear NMR Investigation of some intramolecularly Nitrogen stabilized Organoboron, ‐aluminum, and ‐gallium Compounds The intramolecularly nitrogen stabilized organoaluminum‐ and organoboron compounds Me₂Al(CH₂)₃NMe₂ ( 1 ), Me₂AlC₁₀H₆‐8‐NMe₂ ( 2 ), ⁱPr₂Al(CH₂)₃NEt₂ ( 3 ), (CH₂)₅Al(CH₂)₃NMe₂ ( 4 ), and (CH₂)₅B(CH₂)₃NMe₂ ( 5 ) are synthesized from Me₂AlCl and the corresponding organolithium compounds and from AlCl₃ or BCl₃, the lithium alkyl and ⁱPrMgCl or BrMg(CH₂)₅MgBr, respectively. AlCl₃ and GaCl₃ react with Li(CH₂)₃NMe₂ or LiCH₂CHMeCH₂NMe₂ forming Cl₂AlCH₂CHMeCH₂NMe₂ ( 6 ), Cl₂Al(CH₂)₃NMe₂ ( 8 ), and Cl₂Ga(CH₂)₃NMe₂ ( 9 ). The reaction of 6 and of 8 or 9 with BrMg(CH₂)₅MgBr and BrMg(CH₂)₆MgBr, respectively, yields (CH₂)₅AlCH₂CHMeCH₂NMe₂ ( 7 ), (CH₂)₆Al(CH₂)₃NMe₂ ( 10 ), and (CH₂)₆Ga(CH₂)₃NMe₂ ( 11 ). MeAlCl₂, made by the redistribution reaction of AlCl₃ with Me₂AlCl, reacts with 2 equivalents of Li(CH₂)₃NMe₂ yielding MeAl[(CH₂)₃NMe₂]₂ ( 12 ) and with MeN[(CH₂)₃MgCl]₂ under formation of MeAl[(CH₂)₃]₂NMe ( 13 ). MeAlCl₂, MeGaCl₂, or GaCl₃ accordingly react with one equivalent of organolithium reagent to give the intramolecularly nitrogen stabilized organoaluminum and organogallium chlorides MeClAl(CH₂)₃NMe₂ ( 14 ), MeClGa(CH₂)₃NMe₂ ( 15 ), MeClGaC₆H₄‐2‐CH₂NMe₂ ( 16 ) as well as Cl₂GaC₆H₄‐2‐CHMeNMe₂ ( 17 ). The compounds were characterized by elemental analyses, mass spectroscopy, ¹H, ¹¹B, ¹³C and ²⁷Al NMR investigations. Single crystal X‐ray structure analyses of 1 , 2 , 4 , 5 and 17 reveal the monomeric molecular structures with intramolecular nitrogen coordination.     

Solid‐State NMR and DFT Studies on the Formation of Well‐Defined Silica‐Supported Tantallaaziridines: From Synthesis to Catalytic Application

Single‐site, well‐defined, silica‐supported tantallaaziridine intermediates [≡Si‐O‐Ta(η²‐NRCH₂)(NMe₂)₂] [R=Me ( 2 ), Ph ( 3 )] were prepared from silica‐supported tetrakis(dimethylamido)tantalum [≡Si‐O‐Ta(NMe₂)₄] ( 1 ) and fully characterized by FTIR spectroscopy, elemental analysis, and ¹H,¹³C HETCOR and DQ TQ solid‐state (SS) NMR spectroscopy. The formation mechanism, by β‐H abstraction, was investigated by SS NMR spectroscopy and supported by DFT calculations. The C?H activation of the dimethylamide ligand is favored for R=Ph. The results from catalytic testing in the hydroaminoalkylation of alkenes were consistent with the N‐alkyl aryl amine substrates being more efficient than N‐dialkyl amines.     

Synthesis and characterization of novel chelated dimethylamino lithium alkoxides: molecular structures of [1‐LiOC(C6H11)2‐2‐NMe2C6H4]2 and [1‐LiOCPh2CH2‐2‐NMe2C6H4]2

From the reaction of 1‐HOCPh₂‐2‐NMe₂C₆H₄ ( 1 ), 1‐HOC(C₆H₁₁)₂‐2‐NMe₂C₆H₄ ( 2 ) and 1‐HOCPh₂CH₂‐2‐NMe₂C₆H₄ ( 3 ) with n‐BuLi in diethyl ether, the solvent‐free chelated dimethylamino lithium alkoxides [1‐LiOCPh₂‐2‐NMe₂C₆H₄]₂ ( 4 ), [1‐LiOC(C₆H₁₁)₂‐2‐NMe₂C₆H₄]₂ ( 5 ) and [1‐LiOCPh₂CH₂‐2‐NMe₂C₆H₄]₂ ( 6 ) were obtained. The lithium alkoxides 4 – 6 were characterized by ¹H, ⁷Li, and ¹³C NMR spectroscopy. Crystal structure determinations of 5 and 6 were carried out. Compounds 5 and 6 are examples of structurally characterized solvent‐free chelated dimethylamino lithium alkoxides and 6 is a rare example of this type containing a seven‐membered ring. Copyright © 2002 John Wiley & Sons, Ltd.     

Solid‐state conformations of linear depsipeptide amides with an alternating sequence of α,α‐disubstituted α‐amino acid and α‐hydroxy acid

Depsipeptides and cyclodepsipeptides are analogues of the corresponding peptides in which one or more amide groups are replaced by ester functions. Reports of crystal structures of linear depsipeptides are rare. The crystal structures and conformational analyses of four depsipeptides with an alternating sequence of an α,α‐disubstituted α‐amino acid and an α‐hydroxy acid are reported. The molecules in the linear hexadepsipeptide amide in (S)‐Pms‐Acp‐(S)‐Pms‐Acp‐(S)‐Pms‐Acp‐NMe₂ acetonitrile solvate, C₄₇H₅₈N₄O₉·C₂H₃N, ( 3b ), as well as in the related linear tetradepsipeptide amide (S)‐Pms‐Aib‐(S)‐Pms‐Aib‐NMe₂, C₂₈H₃₇N₃O₆, ( 5a ), the diastereoisomeric mixture (S,R)‐Pms‐Acp‐(R,S)‐Pms‐Acp‐NMe₂/(R,S)‐Pms‐Acp‐(R,S)‐Pms‐Acp‐NMe₂ (1:1), C₃₂H₄₁N₃O₆, ( 5b ), and (R,S)‐Mns‐Acp‐(S,R)‐Mns‐Acp‐NMe₂, C₃₀H₃₇N₃O₆, ( 5c ) (Pms is phenyllactic acid, Acp is 1‐aminocyclopentanecarboxylic acid and Mns is mandelic acid), generally adopt a β‐turn conformation in the solid state, which is stabilized by intramolecular N—H…O hydrogen bonds. Whereas β‐turns of type I (or I′) are formed in the cases of ( 3b ), ( 5a ) and ( 5b ), which contain phenyllactic acid, the torsion angles for ( 5c ), which incorporates mandelic acid, indicate a β‐turn in between type I and type III. Intermolecular N—H…O and O—H…O hydrogen bonds link the molecules of ( 3a ) and ( 5b ) into extended chains, and those of ( 5a ) and ( 5c ) into two‐dimensional networks.     

Gemischte Sandwichkomplexe der 4 f‐Elemente: Enantiomerenreine Cyclooctatetraenyl‐Cyclopentadienyl‐Komplexe des Samariums und Lutetiums mit donorfunktionalisierten Cyclopentadienylliganden

Organometallic Compounds of the Lanthanides. 139 Mixed Sandwich Complexes of the 4 f Elements: Enantiomerically Pure Cyclooctatetraenyl Cyclopentadienyl Complexes of Samarium and Lutetium with Donor‐Functionalized Cyclopentadienyl Ligands The reactions of [K{(S)‐C₅H₄CH₂CH(Me)OMe}], [K{(S)‐C₅H₄CH₂CH(Me)NMe₂}] and [K{(S)‐C₅H₄CH(Ph)CH₂NMe₂}] with the cyclooctatetraenyl lanthanide chlorides [(η⁸‐C₈H₈)Ln(μ‐Cl)(THF)]₂ (Ln = Sm, Lu) yield the mixed cyclooctatetraenyl cyclopentadienyl lanthanide complexes [(η⁸‐C₈H₈)Sm{(S)‐η⁵ : η¹‐C₅H₄CH₂CH(Me)OMe}] ( 1 a ), [(η⁸‐C₈H₈)Ln{(S)‐η⁵ : η¹‐C₅H₄CH₂CH(Me)NMe₂}] (Ln = Sm ( 2 a ), Lu ( 2 b )) and [(η⁸‐C₈H₈)Ln{(S)‐η⁵ : η¹‐C₅H₄CH(Ph)CH₂NMe₂}] (Ln = Sm ( 3 a ), Lu ( 3 b )). For comparison, the achiral compounds [(η⁸‐C₈H₈)Ln{η⁵ : η¹‐C₅H₄CH₂CH₂NMe₂}] (Ln = Sm ( 4 a ), Lu ( 4 b )) are synthesized in an analogous manner. ¹H‐, ¹³C‐NMR‐, and mass spectra of all new compounds as well as the X‐ray crystal structures of 3 b and 4 b are discussed.     

Synthesen und Charakteristika von Heterobimetallorganika des Siliciums mit dem 2‐(Dimethylaminomethyl)ferrocenyl‐Liganden FcN (η5‐C5H5)Fe[η5‐C5H3(CH2NMe2)]—

Syntheses and characteristics of the heterobimetalorganics of the silicon with the 2‐(dimethylaminomethyl)ferrocenyl ligand FcN (η⁵‐C₅H₅)Fe[η⁵‐C₅H₃(CH₂NMe₂)]^— The heterobimetallic lithiumorganyl [2‐(dimethylaminomethyl)ferrocenyl] lithium, LiFcN, reacts with silicon(IV)‐chlorid, SiCl₄, under the formation of heterobimetallic silicon(IV) organyl [(FcN)₃SiCl] ( 1 ). The heterobimetallic organosilanol [(FcN)₃SiOH] ( 2 ) is formed at hydrolysis of 1 . A detailed characterization of the defined compounds 1 and 2 was carried out by NMR‐ rsp. mass‐spectrometry and by crystal X‐ray analysis of 2 .     

Well‐Defined Single‐Site Monohydride Silica‐Supported Zirconium from Azazirconacyclopropane

The silica‐supported azazirconacyclopropane ?SiOZr(HNMe₂)(η²‐NMeCH₂)(NMe₂) ( 1 ) leads exclusively under hydrogenolysis conditions (H₂, 150 °C) to the single‐site monopodal monohydride silica‐supported zirconium species ?SiOZr(HNMe₂)(NMe₂)₂H ( 2 ). Reactivity studies by contacting compound 2 with ethylene, hydrogen/ethylene, propene, or hydrogen/propene, at a temperature of 200 °C revealed alkene hydrogenation.     

CH Bond Activation during and after the Reactions of a Metallacyclic Amide with Silanes: Formation of a μ‐Alkylidene Hydride Complex,Its H–D Exchange,and β‐H Abstraction by a Hydride Ligand

Metallacyclic complex [(Me₂N)₃Ta(η²‐CH₂SiMe₂NSiMe₃)] ( 3 ) undergoes C?H activation in its reaction with H₃SiPh to afford a Ta/μ‐alkylidene/hydride complex, [(Me₂N)₂{(Me₃Si)₂N}Ta(μ‐H)₂(μ‐C‐η²‐CHSiMe₂NSiMe₃)Ta(NMe₂)₂] ( 4 ). Deuterium‐labeling studies with [D₃]SiPh show H–D exchange between the Ta?D ?Ta unit and all methyl groups in [(Me₂N)₂{(Me₃Si)₂N}Ta(μ‐D)₂(μ‐C‐η²‐CHSiMe₂NSiMe₃)Ta(NMe₂)₂] ([D₂]‐ 4 ) to give the partially deuterated complex [D_n]‐ 4 . In addition, 4 undergoes β‐H abstraction between a hydride and an NMe₂ ligand and forms a new complex [(Me₂N){(Me₃Si)₂N}Ta(μ‐H)(μ‐N‐η²‐C,N‐CH₂NMe)(μ‐C‐η²‐C,N‐CHSiMe₂NSiMe₃)Ta(NMe₂)₂] ( 5 ) with a cyclometalated, η²‐imine ligand. These results indicate that there are two simultaneous processes in [D_n]‐ 4 : 1) H–D exchange through σ‐bond metathesis, and 2) H?D elimination through β‐H abstraction (to give [D_n]‐ 5 ). Both 4 and 5 have been characterized by single‐crystal X‐ray diffraction studies.     

Spectroscopic Properties of Amine‐substituted Analogues of Firefly Luciferin and Oxyluciferin

Spectroscopic and photophysical properties of firefly luciferin and oxyluciferin analogues with an amine substituent (NH₂, NHMe and NMe₂) at the C6' position were studied based on absorption and fluorescence measurements. Their π‐electronic properties were investigated by DFT and TD‐DFT calculations. These compounds showed fluorescence solvatochromism with good quantum yields. An increase in the electron‐donating strength of the substituent led to the bathochromic shift of the fluorescence maximum. The fluorescence maxima of the luciferin analogues and the corresponding oxyluciferin analogues in a solvent were well correlated with each other. Based on the obtained data, the polarity of a luciferase active site was explained. As a result, the maximum wavelength of bioluminescence for a luciferin analogue was readily predicted by measuring the photoluminescence of the luciferin analogue in place of that of the corresponding oxyluciferin analogue.