Strukturen zweifach metallierter Derivate von 3, 3‐Dimethyl‐1, 5‐bis(trimethylsilyl)‐1, 5‐diaza‐pentan mit Lithium und Aluminium sowie zweier Donor‐substituierter Digallane

Structural Characterization of Bis(metallated) Derivatives of 3, 3‐Dimethyl‐1, 5‐bis(trimethylsilyl)‐1, 5‐diaza‐pentane with Lithium and Aluminum and of two Donor‐substituted Digallanes The diaminopropane derivative Me₂C[CH₂N(H)SiMe₃]₂ is metallated with n‐butyllithium and lithium tetrahydridoaluminate to obtain Me₂C[CH₂N(Li)SiMe₃]₂ and Me₂C[CH₂N(Li)SiMe₃][CH₂N(AlH₂)SiMe₃], respectively. Both compounds exhibit a central eight‐membered ring, Li₄N₄ or Li₂Al₂N₄. Me₂C[CH₂N(Li)SiMe₃]₂ reacts with Ga₂Cl₄ · 2dioxane under formation of the corresponding tetra(amino)digallane. This is monomeric, in contrast to a dimeric tetraalkoxy‐substituted digallane, Ga₄O^tBu₈. All compounds were characterized by single crystal X‐ray crystallography.     

Spiro Compounds of Tin,Selenium and Tellurium Containing 1,3,2‐Diazaelement‐[3]ferrocenophane Units

The reactions of 1,1′‐bis[Li(trimethylsilyl)amino]ferrocene ( 2a ) with selenium‐ or tellurium tetrahalides gave the 1,1′,3,3′‐tetrakis(trimethylsilyl)‐1,1′,3,3′‐tetraaza‐2‐selene‐ and 2‐tellura‐2,2′‐spirobi[3]ferrocenophanes 5 and 6 , respectively. The analogous reaction with tin dichloride afforded the corresponding 2‐stanna‐2,2′‐spirobi[3]ferrocenophane ( 9 ) rather than the expected stannylene 8 . The reaction of 2,2‐dichloro‐1,3‐bis(trimethylsilyl)‐1,3,2‐diazastanna‐[3]ferrocenophane ( 10 ) with the dilithio reagent 2b also gave the spirotin compound 9 , of which the molecular structure was determined by X‐ray analysis. The formation of the products and their solution‐state structures was deduced from multinuclear magnetic resonance spectroscopic studies (¹H, ¹³C, ¹⁵N, ²⁹Si, ⁷⁷Se, ¹²⁵Te, ¹¹⁹Sn NMR spectroscopy).     

Chirale 1,3,2‐Oxazaborolidine aus chiralen 2,3‐Dihydro‐1H‐1,3,2‐diazaborolen und Diphenylketen

Chiral 1,3,2‐Oxazaborolidines from the Reaction of Chiral 2,3‐Dihydro‐1H‐1,3,2‐diazaboroles and Diphenylketene Reaction of equimolar amounts of diphenylketene with 1,3‐di‐tert‐butyl‐2‐isobutyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborole ( 1 ) regioselectively afforded 1,3,2‐oxazaborolidine ( 2 ). The employment of a series of chiral diazaboroles ( 3a : X = nBu; b: iBu; c: CH₂SiMe₃; d: NHtBu) led to the formation of the diastereoisomeric oxazaborolidines ( 4a – d ) with diastereomeric excesses de, which increase with the steric demand of X from de = 55 % (X = nBu) to de ≥ 95 % (X = NHtBu). Under comparable conditions the treatment of the enantiomerically pure diazaborole ( 6 ) with the ketene yielded oxazaborolidine ( 7 ) with a de‐value of only 52 %. The new compounds, with exception of 2 and 4d , are thermolabile solids, which were characterized mainly by spectroscopy (¹H‐, ¹¹B{¹H}‐, ¹³C{¹H}‐NMR, MS). The X‐ray structure analysis of 2 revealed a slightly puckered five‐membered heterocycle with a long B–O bond.     

Synthese und Reaktivität von 2‐Brom‐1,3‐diethyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborol Molekülstruktur von Bis(1,3‐diethyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborol‐2‐yl)

Synthesis and Reactivity of 2‐Bromo‐1,3‐diethyl‐2,3‐dihydro‐1 H ‐1,3,2‐benzodiazaborole Molecular Structure of Bis(1,3‐diethyl‐2,3‐dihydro‐1 H ‐1,3,2‐benzodiazaborol‐2‐yl The reaction of a slurry of calcium hydride in toluene with N,N′‐diethyl‐o‐phenylenediamine ( 1 ) and boron tribromide affords 2‐bromo‐1,3‐diethyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborol ( 2 ) as a colorless oil. Compound 2 is converted into 2‐cyano‐1,3‐diethyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborole ( 3 ) by treatment with silver cyanide in acetonitrile. Reaction of 2 with an equimolar amount of methyllithium affords 1,3‐diethyl‐2‐methyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborole ( 4 ). 1,3,2‐Benzodiazaborole is smoothly reduced by a potassium‐sodium alloy to yield bis(1,3‐diethyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborol‐2‐yl] ( 7 ), which crystallizes from n‐pentane as colorless needles. Compound 7 is also obtained from the reaction of 2 and LiSnMe₃ instead of the expected 2‐trimethylstannyl‐1,3,2‐benzodiazaborole. N,N′‐Bis(1,3‐diethyl‐2,3‐dihydro‐1 H‐1,3,2‐benzodiazaborol‐2‐ yl)‐1,2‐diamino‐ethane ( 6 ) results from the reaction of 2 with Li(en)C≡CH as the only boron containing product. Compounds 2 – 4 , 6 and 7 are characterized by means of elemental analyses and spectroscopy (IR, ¹H‐, ¹¹B{¹H}‐, ¹³C{¹H}‐NMR, MS). The molecular structure of 7 was elucidated by X‐ray diffraction analysis.     

Die Kristallstruktur von [Li · 11/3 H2O · C7H8][{(CH3)3Si}3C–GaI3], ein stabiles Hydrat des Lithium‐Tris(trimethylsilyl)methyl‐triiodogallats

The Crystal Structure of [Li · 1¹/₃ H₂O · C₇H₈][{(CH₃)₃Si}₃C–GaI₃], a Stable Hydrate of Lithium Tris(trimethylsilyl)methyl Triiodogallate Water‐free Li[Tsi–GaI₃], prepared from gallium triiodide and base‐free Tsi–Li (Tsi = –C(SiMe₃)₃) in toluene, which has been recrystallized several times from humid toluene, c‐hexane, benzene and toluene again gives the water‐containing title compound. According to the X‐ray structure determination this product crystallizes in the monoclinic space group P2₁/c and consists of three‐membered units of [Tsi–GaI₃]^–‐anions forming an asymmetric triangle and a related chain of three Li cations, four fold but dissimilar coordinated by the oxygen atoms of 4 water molecules, the iodligands of different anions and a h²‐bonded toluene molecule, respectively.     

meso‐Bis{η5‐1‐[1‐(dimethylamino)ethenyl]‐3‐(trimethylsilyl)cyclopentadienyl}iron(II) and the cobalt(II) analogue

The two title crystalline compounds, viz.meso‐bis{η⁵‐1‐[1‐(dimethylamino)ethenyl]‐3‐(trimethylsilyl)cyclopentadienyl}iron(II), [Fe(C₁₂H₂₀NSi)₂], (II), and meso‐bis{η⁵‐1‐[1‐(dimethylamino)ethenyl]‐3‐(trimethylsilyl)cyclopentadienyl}cobalt(II), [Co(C₁₂H₂₀NSi)₂], (III), were obtained by the reaction of lithium 1‐[1‐(dimethylamino)ethenyl]‐3‐(trimethylsilyl)cyclopentadienide with FeCl₂ and CoCl₂, respectively. For (II), the trimethylsilyl‐ and dimethylaminoethenyl‐substituted cyclopentadienyl (Cp) rings present a nearly eclipsed conformation, and the two pairs of trimethylsilyl and dimethylaminoethenyl substituents on the Cp rings are arranged in an interlocked fashion. In the case of (III), the same substituted Cp rings are perfectly staggered leading to a crystallographically centrosymmetric molecular structure, and the two trimethylsilyl and two dimethylaminoethenyl substituents are oriented in opposite directions, respectively, with the trimethylsilyl group of one Cp ring and the dimethylaminoethenyl group of the other Cp ring arranged more closely than in (II).     

1,3‐Bis(trimethylsilyl)‐1,3,2‐diazaphospha‐[3]ferrocenophanes

The 2‐tert‐butyl, 2‐phenoxy, and 2‐diethylamino derivatives of 1,3‐bis(trimethylsilyl)‐1,3,2‐diazaphospha‐[3]ferrocenophane were prepared, and the molecular structure of the latter was determined by X‐ray diffraction. The phosphines could be oxidized by their slow reactions with sulfur or selenium, and the molecular structures of three sulfides and one selenide were determined. In contrast, the synthesis of oxides was less straightforward. All new compounds were characterized in solution by multinuclear magnetic resonance methods (1D and 2D ¹H, ¹³C, ¹⁵N, ²⁹Si, ³¹P, and ⁷⁷Se NMR spectroscopy).     

Synthese eines hexanuklearen Calcium–Phosphor‐Käfigs über heteroleptische Calcium‐amid‐phosphanid‐Vorstufen

Synthesis of a Hexanuclear Calcium–Phosphorus‐Cage The metalation of tri(tert‐butyl)silylphosphane with calcium bis[bis(trimethylsilyl)amide] yields the dimer {(Me₃Si)₂N–Ca(THF)[μ‐P(H)Si^tBu₃]}₂ ( 1 ). In THF monomerization occurs and dismutation reactions lead to the homoleptic compounds, namely (THF)₂Ca[N(SiMe₃)₂]₂ and (THF)₄Ca[P(H)Si^tBu₃]₂. In toluene, 1 undergoes dismutation reactions, bis(tetrahydrofuran)calcium bis[bis(trimethylsilyl)amide] is regained and [(Me₃Si)₂N–Ca(THF)]₂Ca[P(H)Si^tBu₃]₄ ( 2 ) precipitates. At raised temperatures, 2 undergoes a homometallic metalation with the loss of two equivalents of HN(SiMe₃)₂ and dimerizes. The thus formed cage compound (THF)₂Ca₆[PSi^tBu₃]₄[P(H)Si^tBu₃]₄ ( 3 ) with a central Ca₄P₄ heterocubane moiety crystallizes upon cooling of the toluene solution. The molecular structures of 2 and 3 were determined.     

Ferrocenophanes with Interannular Nitrogen–Gallium Bridges. 1,3,2‐Diazagalla‐[3]Ferrocenophanes and an 1‐Aza‐3‐Azonia‐2‐Gallata‐[3]Ferrocenophane. Synthesis and Structure

1,1′‐Bis(trimethylsilylamino)ferrocene reacts with trimethyl‐ and triethylgallium to give the μ‐[ferrocene‐1,1′‐diyl‐bis(trimethylsilylamido)]tetraalkyldigallanes. These were converted into the 1,3‐bis(trimethylsilyl)‐2‐alkyl‐2‐pyridine‐1,3,2‐diazagalla‐[3]ferrocenophanes, of which the ethyl derivative was characterized by X‐ray structural analysis. Treatment of gallium trichloride with N,N′‐dilithio‐1,1′‐bis(trimethylsilylamino)ferrocene affords μ‐[ferrocene‐1,1′‐diyl‐bis(trimethylsilylamido)]tetrachlorodigallane along with bis(trimethylsilyl)‐2,2‐dichloro‐1‐aza‐3‐azonia‐2‐gallata‐[3]ferrocenophane as a side product, and both were structurally characterized by X‐ray analysis. The solution‐state structures of the new gallium compounds and aspects of their molecular dynamics in solution were studied by NMR spectroscopy (¹H, ¹³C, ²⁹Si NMR).     

Synthesis of ferrocene‐containing N‐aryloxo β‐ketoiminate lanthanide complexes and polymerization of ε‐caprolactone

The synthesis, characterization and ε‐caprolactone polymerization behavior of lanthanide amido complexes stabilized by ferrocene‐containing N‐aryloxo functionalized β‐ketoiminate ligand FcCOCH₂C(Me)N(2‐HO‐5‐Bu^t‐C₆H₃) (LH₂, Fc = ferrocenyl) are described. The lanthanide amido complexes [LLnN(SiMe₃)₂(THF)]₂ [Ln = Nd ( 1 ), Sm ( 2 ), Yb ( 3 ), Y ( 4 )] were synthesized in good yields by the amine elimination reactions of LH₂ with Ln[N(SiMe₃)₂]₃(µ‐Cl)Li(THF)₃ in a 1:1 molar ratio in THF. These complexes were characterized by IR spectroscopy and elemental analysis, and ¹H NMR spectroscopy was added for the analysis of complex 4 . The definitive molecular structures of complexes 1 and 3 were determined by X‐ray diffraction studies. Complexes 1 – 4 can initiate the ring‐opening polymerization of ε‐caprolactone with moderate activity. Copyright © 2011 John Wiley & Sons, Ltd.     

Formation of an Imino‐Stabilized Cyclic Tin(II) Cation from an Amino(imino)stannylene

The novel amino(imino)stannylene 1 was prepared by conversion of HNIPr (NIPr=bis(2,6‐diisopropylphenyl)imidazolin‐2‐imino) with one equivalent of Lappert’s tin reagent (Sn[N(SiMe₃)₂]₂). Treatment of 1 with DMAP (4‐dimethylaminopyridine) yields its Lewis acid–base adduct 2 . The reaction of 1 with one equivalent of trimethylsilyl azide results in replacement of the amino group at the tin center by an N₃ substituent with concomitant elimination of N(SiMe₃)₃ to afford dimeric [N₃SnNIPr]₂ ( 3 ). Remarkably, the reaction of 1 with B(C₆F₅)₃ produces the novel tin(II) monocation 4 ⁺[MeB(C₆F₅)₃]^? comprising a four‐membered stannacycle through methyl‐abstraction from the trimethylsilyl group.     

Syntheses,Crystal Structure and Reactivity of Tin(II) Bis[N‐(diphenylphosphanyl)(2‐pyridylmethyl)amide]

Metallation of N‐(diphenylphosphanyl)(2‐pyridylmethyl)amine with n‐butyllithium in toluene yields lithium N‐(diphenylphosphanyl)(2‐pyridylmethyl)amide ( 1 ), which crystallizes as a tetramer. Transamination of N‐(diphenylphosphanyl)(2‐pyridylmethyl)amine with an equimolar amount of Sn[N(SiMe₃)₂]₂ leads to the formation of monomeric bis(trimethylsilyl)amido tin(II) N‐(diphenylphosphanyl)(2‐pyridylmethyl)amide ( 2 ). The addition of another equivalent of N‐(diphenylphosphanyl)(2‐pyridylmethyl)amine gives homoleptic tin(II) bis[N‐(diphenylphosphanyl)(2‐pyridylmethyl)amide] ( 3 ). In these complexes the N‐(diphenylphosphanyl)(2‐pyridylmethyl)amido groups act as bidentate bases through the nitrogen bases. At elevated temperatures HN(SiMe₃)₂ is liberated from bis(trimethylsilyl)amido tin(II) N‐(diphenylphosphanyl)(2‐pyridylmethyl)amide ( 2 ) yielding mononuclear tin(II) 1,2‐dipyridyl‐1,2‐bis(diphenylphosphanylamido)ethane ( 4 ) through a C–C coupling reaction. The three‐coordinate tin(II) atoms of 2 and 4 adopt trigonal pyramidal coordination spheres.     

ZrIV‐ und TaV‐Komplexe mit methanoverbrückten Bis(aryloxy)‐Liganden

Zr^IV and Ta^V Complexes with Methano‐Bridged Bis(aryloxy) Ligands The bis(aryloxy) ligand precursor compounds bis(2‐trimethylsiloxy‐5‐tbutylphenyl)methane (L–SiMe₃) and its bromoderivative (2‐trimethylsiloxy‐3‐bromo‐5‐tbutylphenyl)(2′‐trimethylsiloxy‐5′‐tbutylphenyl)methane (L^Br–SiMe₃) are prepared in analogy to the corresponding calixarenes in excellent yields. X‐ray structure analysis for L^Br–SiMe₃: space group P2₁/c, a = 12.462(7), b = 10.466(6), c = 23.315(14) Å, β = 105.02(4)°, V = 2937(3) ų, Z = 4. L–SiMe₃ and L^Br–SiMe₃ react with Zr^IV and Ta^V chlorides in very good yields forming di‐ and trinuclear complexes. From the reaction of CpZrCl₃ with L^Br–SiMe₃ in the ratio of 3 : 2 a Zr₃ complex ( 7 ) is obtained, with one L^Br ligand only, which Zr atoms are bridged by a μ₃‐oxygen. The X‐ray structure analysis of 7 (space group R 3, a = 33.23(6), c = 24.47(8) Å, V = 23405(128) ų, Z = 18) additionally reveals that one phenolato oxygen atom of the L^Br ligand is terminally bound to a distorted tetragonal‐pyramidal coordinated Zr atom, while the second phenolato oxygen atom of the L^Br ligand forms a bridge to another Zr atom with a distorted octahedral coordination. The third Zr atom is also found in a distorted octahedral coordination mode. The reactions of L–SiMe₃ and L^Br–SiMe₃ with CpTaCl₄ and TaCl₅ yield dinuclear Ta complexes with a bridging bis(aryloxy) ligand. NMR spectroscopic data point out that the coordination of the bis(aryloxy) ligands in the Ta complexes very much resembles that in the Zr₃‐complex with one terminal and one bridging phenolato oxygen atom. The Zr₃ and the Ta complexes L^BrTa₂Cp₂Cl₆ and LTa₂Cl₈ were tested with respect to their catalytic properties in olefin polymerisation reactions in the presence of MAO.     

2,4‐Disila‐1,3,5‐oxadiazin,Cyclodisilazan‐Carbonsäure‐silylamid und ‐silylester

The lithium salts of the Me₃Si‐ as well as Me₃Si‐ and Me₂SiF‐substituted Cyclotrisilazanes I and II react with tert‐butylacylchloride under ring contraction and formation of the cyclodisilazane‐silylester, Me₃SiN(SiMe₂–N)₂SiMe₂–O–CO–CMe₃ ( 1 ). The lithium salt of the fluorodi‐methylsilyl‐substituted cyclotrisilazan III forms with benzoylchloride primarily in the analogous reaction the carboxy‐silyl‐amide, Me₂SiF(N–SiMe₂)₂SiMe₂–NH–CO–C₆H₅⁺ ( 2 ), which can be converted with III and benzoylchloride into the cyclodisilazane‐silylester, Me₂SiF(NSiMe₂)₂SiMe₂–O–CO–C₆H₅, ( 3 ). A silylester substituted six‐membered disila‐oxadiazine ( 4 ) is the result of the reaction of the lithiated cyclotrisilazane, (Me₂SiNH)₂, (Me₂SiNLi) with tert‐butyl‐acylchloride. The reaction includes anionic ring contraction and can be rationilized by a process analogous to keto‐enol‐tautomerism. Dilithiated octamethyl‐cyclotetrasilazane, (Me₂SiNHMe₂SiNLi)₂, reacts with tert‐butyl‐acylchloride or benzoylchloride in a molar ratio 1:2 to yield symmetrically acylestersubstituted cyclodisilazanes, (RCO–O–SiMe₂–NSiMe₂)₂, R = C₆H₅ ( 5 ), CMe₃ ( 6 ). The reaction mechanisms are discussed and the crystal structures of 2 and 6 are reported.     

Carbenhomologe Verbindungen von Germanium,Zinn und Blei mit 2‐substituierten N‐Pyrrolyl‐Liganden

Carbene Homologues of Germanium, Tin, and Lead with 2‐substituted N ‐Pyrrolyl Ligands A series of germylenes, stannylenes, and plumbylenes could be prepared by reacting the appropriate bis(trimethylsilyl)amino‐substituted carbene homologue E[N(SiMe₃)₂]₂ (E = Ge, Sn, and Pb) with an α‐carbonyl substituted pyrrole derivative under elimination of bis(trimethylsilyl)amine. The isolated compounds have been analysed spectroscopically, and the resulting NMR and IR data were contrasted with parameters obtained from quantumchemical calculations. The good agreement between experimental and theoretical results gives us the opportunity to discuss the vibrations in more detail, particularly those in which the group 14 element is involved. X‐ray crystal structure analyses obtained for five examples show the title compounds essentially to be monomers with primary E–N bonds and, in addition to that, coordinative E ← O contacts.     

Synthese,Struktur, Elektrochemie und optische Eigenschaften von alkinylfunktionalisierten 1,3,2‐Diazaborolen und 1,3,2‐Diazaborolidinen

Syntheses, Structures, Electrochemistry and Optical Properties of Alkyne‐Functionalized 1,3,2‐Diazaboroles and 1,3,2‐Diazaborolidenes The reaction of 2‐bromo‐1,3‐ditert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborole ( 3 ) with lithiated tert‐butyl‐acetylene and lithiated phenylacetylene affords the 2‐alkynyl‐functionalized 1,3,2‐diazaboroles 4 and 5 as a thermolabile colorless oil ( 4 ) or a solid ( 5 ). Similarly 2‐bromo‐1,3‐diethyl‐2,3‐dihydro‐1H‐1,3,2‐benzodiazaborole ( 6 ) was converted into the crystalline 2‐alkynyl‐benzo‐1,3,2‐diazaboroles 7 and 8 by treatment with LiC≡C–tBu or LiC≡CPh, respectively. 2‐Ethynyl‐1,3‐ditert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborole ( 2 ) was metalated with tert‐butyl‐lithium and subsequently coupled with 2‐bromo‐1,3,‐ditert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborole ( 3 ) to afford bis(1,3‐ditert‐butyl‐2,3‐dihydro‐1H‐1,3,2‐diazaborol‐2‐yl)acetylene ( 9 ) as thermolabile colorless crystals. Analogously coupling of the lithiated species with 6 or with 2‐bromo‐1,3‐ditert‐butyl‐1,3,2‐diazaborolidine ( 11 ) gave the unsymmetrically substituted acetylenes 10 or 12 , respectively, as colorless solids. Compounds 4 , 5 , 7 – 10 and 12 are characterized by elemental analyses and spectroscopy (IR, ¹H‐, ¹¹B{¹H}, ¹³C{¹H}‐NMR, MS). The molecular structures of 5 , 8 and 9 were elucidated by X‐ray diffraction analyses.     

Alkali Metal and Alkaline Earth Metal Complexes with the Bis(borane‐diphenylphosphanyl)amido Ligand – Synthesis,Structures, and Catalysis for Ring‐Opening Polymerization of ϵ‐Caprolactone

The syntheses of lithium and alkaline earth metal complexes with the bis(borane‐diphenylphosphanyl)amido ligand ( 1 ‐ H ) of molecular formulas [{κ²‐N(PPh₂(BH₃))₂}Li(THF)₂] ( 2 ) and [{κ³‐N(PPh₂(BH₃))₂}₂M(THF)₂] [(M = Ca ( 3 ), Sr ( 4 ), Ba ( 5 )] are reported. The lithium complex 2 was obtained by treatment of bis(borane‐diphenylphosphanyl)amine ( 1 ‐ H ) with lithium bis(trimethylsilyl)amide in a 1:1 molar ratio via the silylamine elimination method. The corresponding homoleptic alkaline earth metal complexes 3 – 5 were prepared by two synthetic routes – first, the treatment of metal bis(trimethylsilyl)amide and protio ligand 1 ‐ H via the elimination of silylamine, and second, through salt metathesis reaction involving respective metal diiodides and lithium salt 2 . The molecular structures of lithium complex 2 and barium complex 5 were established by single‐crystal X‐ray diffraction analysis. In the solid‐state structure of 2 , the lithium ion is ligated by amido nitrogen atoms and hydrogen atoms of the BH₃ group in κ²‐coordination of the ligand 1 resulting in a distorted tetrahedral geometry around the lithium ion. However, in complex 5 , κ³‐coordination of the ligand 1 was observed, and the barium ion adopted a distorted octahedral arrangement. The metal complex 5 was tested as catalyst for the ring opening polymerization of ?‐caprolactone. High activity for the barium complex 5 towards ring opening polymerization (ROP) of ?‐caprolactone with a narrow polydispersity index was observed. Additionally, first‐principle calculations to investigate the structure and coordination properties of alkaline earth metal complexes 3 – 5 as a comparative study between the experimental and theoretical findings were described.     

Dinuclear Dysprosium and Ytterbium Complexes Incorporating N,N‐Bis(pyrrolyl‐α‐methyl)‐N‐methylamine Ligand: Syntheses and Structures

Reaction of DyCl₃ with two equivalents of NaN(SiMe₃)₂ in THF yielded {Dy(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ ( 1 ). X‐ray crystal structure analysis revealed that 1 is a centrosymmetric dimer with asymmetrically bridging chloride ligands. The metal coordination arrangement can be best described as distorted trigonal bipyramid. The bond lengths of Ln–Cl and Ln–N showed a decreasing trend with the contraction of the size of Ln³⁺. Treatment of N,N‐bis(pyrrolyl‐α‐methyl)‐N‐methylamine (H₂dpma) with 1 and known compound {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂, respectively, led to the formations of [Dy(μ‐Cl)(dpma)(THF)₂]₂ ( 2 ) and {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ ( 3 ). Compounds 2 and 3 were fully characterized by single‐crystal X‐ray crystallography, elemental analysis, and ¹H NMR spectroscopy. Structure determination indicated that 2 and 3 exhibit as centrosymmetric dimers with asymmetrically bridging chloride ligands. One pot reactions involving LnCl₃ (Ln = Dy and Yb), LiN(SiMe₃)₂, and H₂dpma were explored and desired products 2 and 3 were not yielded, which indicated that 1 and {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ are the demanding precursors to synthesize Dysprosium and Ytterbium complexes supported by dpma^2– ligand. Compounds 2 and 3 are the first reported lanthanide complexes chelated by dpma^2– ligand.     

1,2‐Diaza‐3‐silacyclopent‐5‐ene – Synthese und Reaktionen

1,2‐Diaza‐3‐silacyclopent‐5‐ene – Synthesis and Reactions The dilithium salt of bis(tert‐butyl‐trimethylsilylmethylen)ketazine ( 1 ) forms an imine‐enamine salt. 1 reacts with halosilanes in a molar ratio of 1:1 to give 1,2‐diaza‐3‐silacyclopent‐5‐enes. Me₃SiCH=CCMe₃ [N(SiR,R′)‐N=C‐C]HSiMe₃ ( 2 ‐ 7 ). ( 2 : R,R′ = Cl; 3 : R = CH₃, R′ = Ph; 4 : R = F, R′ = CMe₃; 5 : R = F, R′ = Ph; 6 : R = F, R′ = N(SiMe₃)₂; 7 : R = F, R′ = N(CMe₃)SiMe₃). In the reaction of 1 with tetrafluorosilane the spirocyclus 8 is isolated. The five‐membered ring compounds 2 ‐ 7 and compound 9 substituted on the silicon‐fluoro‐ and (tert‐butyltrimethylsilyl) are acid at the C(4)‐atom and therefore can be lithiated. Experiments to prepare lithium salts of 4 with MeLi, n‐BuLi and PhLi gave LiF and the substitution‐products 10 ‐ 12 . 9 forms a lithium salt which reacts with ClSiMe₃ to give LiCl and the SiMe₃ ring system ( 13 ) substituted at the C(4)‐atom. The ring compounds 3 ‐ 7 and 10 ‐ 12 form isomers, the formation is discussed. Results of the crystal structure and analyses of 8 , 10 , 12 , and 13 are presented.     

The Reaction of Transient 1,1‐Bis(trimethylsilyl)silenes with Tris(trimethylsilyl)silyllithium – Synthesis and Structure of Sterically Congested 1‐Trimethylsilylalkylpolysilanes

Tris(trimethylsilyl)silyllithium ( 3 ) reacted with aldehydes and ketones (molar ratio 2 : 1) according to a modified Peterson mechanism under formation of transient silenes, which were immediately trapped by excess 3 to give the organolithium derivatives (Me₃Si)₃SiSi(SiMe₃)₂C(Li)R¹R² ( 7 ). Hydrolysis of 7 afforded the alkylpolysilanes (Me₃Si)₃SiSi(SiMe₃)₂CHR¹R² ( 8 ). Depending on the substituents R¹ and R², 7 proved to be rather unstable in THF solution and underwent a rapid rearrangement, involving a 1,3‐Si,C‐trimethylsilyl migration, resulting in the formation of the lithium silanides (Me₃Si)₂Si(Li)Si(SiMe₃)₂C(SiMe₃)R¹R² ( 9 ), which were hydrolized during the aqueous workup to give the H‐silanes (Me₃Si)₂Si(H)Si(SiMe₃)₂C(SiMe₃)R¹R² ( 10 ). Reaction of 9 with chlorotrimethylsilane produced the 1‐trimethylsilylalkylpolysilanes (Me₃Si)₃SiSi(SiMe₃)₂C(SiMe₃)R¹R² ( 11 ). The structures of the products described were elucidated by comprehensive spectral analyses. The results of X‐ray crystal structure analyses, performed for 8 l (R¹ = H, R² = 2,4,6‐(MeO)₃C₆H₂), 10 d (R¹ = H, R² = Mes) and 11 d (R¹ = H, R² = Mes) are discussed and confirm the expected extreme sterical congestion of the molecules.