1,3-Migration of a phenyl group in the conversion of (Me3Si)2(PhMe2Si)CSiMePhX into (Me3Si)2(Ph2MeSi)CSiMe2Y species

The finding that compounds of the type (Me₃Si)₂(PhMe₂Si)CSiMePhX react with electrophiles to give very predominantly rearranged products (Me₃Si)₂(Ph₂MeSi)CSiMe₂Y, which would be expected to be thermodynamically disfavoured, can be rationalized in terms of a mechanism in which the anchimerically-assisted departure of X⁻ gives the Ph-bridged cation [(Me₃Si)₂

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MePh]⁺ which is attacked by the nucleophile at the less hindered centre bearing two Me groups rather than that bearing one Me and one Ph group, with the outcome determined by kinetic rather than thermodynamic factors. Both (Me₃Si)₂(Ph₂MeSi)CSiMe₂Br and its isomer (Me₃Si)₂(PhMe₂Si)CSiMePhBr react with AgBF₄ in CH₂Cl₂ or Et₂O to give >95% of the fluoride (Me₃Si)₂(Ph₂MeSi)CSiMe₂F. Reaction of the bromide (Me₃Si)₂(PhMe₂Si)CSiMePhBr with AgO₂CCF₃ in Et₂O, and that of the hydride (Me₃Si)₂(PhMe₂Si)CSiMePhH with ICl in CCl₄, likewise give >95% of the rearranged (Me₃Si)₂(Ph₂MeSi)CSiMe₂O₂CCF₃ and (Me₃Si)₂(Ph₂MeSi)CSiMe₂Cl, respectively.     

Preparation, spectroscopic properties and thermal stabilities of organomercury compounds containing the bulky ligand (Me3Si)3C or (PhMe2Si)3C

Mercury compounds of the types HgR¹R (R¹ = C(SiMe₃)₃; R = Me, ⁱPr, Bu, ^tBu or Ph) and HgR²R(R² = C(SiMe₂Ph)₃; R = Me, Bu, CH₂Ph or Ph) have been prepared. Those containing R¹ were made by reactions of the bromides HgR¹Br with the Grignard reagents MgRX, and those containing R² by reaction of HgR²Cl with LiR or, for R = CH₂Ph, with Mg(CH₂Ph)Cl. Replacement of one R group in HgR₂ by the bulky R¹ or R² group leads to a large increase in thermal stability, a marked shift in the ¹⁹⁹Hg resonance to lower frequency and an increase in the coupling constant ¹J(¹³C---¹⁹⁹Hg) for the Hg---R bond. The compound HgR²Cl does not react further with LiR² in tetrahydrofuran, but with LiR¹ gives HgR¹R²; the arrangement of the SiMe₂Ph groups in the latter in solution in CH₂C12 at low temperature appears to be different from that in the solid.     

Syntheses and structures of [Me2Si{As(PBu)3}2] and [(CyP)3SiMe2] (Cy = cyclohexyl, C6H11)

The reaction of the anion [(^tBuP)₃As]⁻ (1) with Me₂SiCl₂ results in nucleophilic substitution of the Cl⁻ anions, giving the di- and mono-substituted products [Me₂Si{As(P^tBu)₃}₂] (3a) and [Me₂Si(Cl){As(P^tBu)₃}] (3b). Analogous reactions of the pre-isolated [(CyP)₄As]⁻ anion (2) (Cy = cyclohexyl) with Me₂SiCl₂ produced mixtures of products, from which no pure materials could be isolated. However, reaction of 2 [generated in situ from CyPHLi and As(NMe₂)₃] gives the heterocycle [(CyP)₃SiMe₂] (4). The X-ray structures of 3a and 4 are reported.     

Synthesis, molecular structure, and catalytic activity of borohydride complexes [(Me3Si)2NC(NPri)2]2Nd(BH4)2Li(thf)2 and [(Me3Si)2NC(NPri)2]2Sm(BH4)2Li(thf)2

The reactions of lanthanide tris(borohydrides) Ln(BH₄)₃(thf)₃ (Ln = Sm or Nd) with 2 equiv. of lithium N,N′-diisopropyl-N′-bis(trimethylsilyl)guanidinate in toluene produced the [(Me₃Si)₂NC(NPrⁱ)₂]Ln(BH₄)₂Li(thf)₂ complexes (Ln = Sm or Nd), which were isolated in 57 and 42% yields, respectively, by recrystallization from hexane. X-ray diffraction experiments and NMR and IR spectroscopic studies demonstrated that the reactions afford monomeric ate complexes, in which the lanthanide and lithium atoms are linked to each other by two bridging borohydride groups. The complexes exhibit catalytic activity in polymerization of methyl methacrylate. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 441–445, March, 2007.     

Synthesis and Characterization of N3P3(O2C12H8)2(OC6H4Si(CH3)3)(OC6H4Br) and Its Conversion to Nanostructured Si Material

A new silicated cyclotriphosphazene N₃P₃(O₂C₁₂H₈)₂(OC₆H₄Si(CH₃)₃)(OC₆H₄Br) 1 has been synthesized and characterized. The solid state pyrolysis of 1 in air gives a nanostructured SiP₂O₇ 3D network. The morphology of the network strongly depends on the temperature of the pyrolysis. Spinal-like columns and ring-shaped SiP₂O₇ are formed at 800 °C, while, at 600 °C, fused grains of about 300 nm were observed. Based on air TG and DSC thermal studies, we propose the mechanism of formation for the nanostructured network.     

Glass transition temperature modification of acrylic and dienic type copolymers of 4-chloromethyl styrene with incorporation of (Me3Si)3C- groups

The new functional styrenic monomer, 4-trisylmethyl styrene (TsiMS) [Tsi=trisyl=tris(trimethylsilyl)methyl], was synthesized by reacting 4-chloromethyl styrene (CMS) with trisyllithium (TsiLi) in tetrahydrofuran (THF) solvent in the presence of copper chloride (CuCl). Attempt for the free radical polymerization of TsiMS by α,α^′-azobis(isobutyronitrile) (AIBN) as an initiator at 70 ± 1 °C failed for several periods of times. This result showed that the trisyl group is a highly sterically hindered substituent and, subsequently, TsiMS becomes resistant for polymerization. Therefore, for preparation of new methacrylic, acrylic and dienic copolymers of TsiMS, we firstly synthesized the copolymers of CMS with different monomers such as methyl methacrylate (MMA), ethyl methacrylate (EMA), methyl acrylate (MA), ethyl acrylate (EA), n-butyl acrylate (BA) and isoprene (IP) by free radical polymerization method in toluene solution at 70 ± 1 °C using AIBN initiator to give the copolymers I-VI in good yields. The copolymer compositions were obtained using related ¹H NMR spectra and the polydispersity indices of the copolymers determined using gel permeation chromatography (GPC). The trisyl groups were then covalently attached to the obtained copolymers as side chains by reaction between excess of TsiLi and benzyl chloride bonds of CMS units, to give the copolymers - in 80-92% yields. All the resulted polymers were characterized by FT-IR, ¹H NMR and ¹³C NMR spectroscopic techniques. The solubility of all the copolymers was examined in various polar and non-polar solvents. The glass transition temperature (T_g) of all copolymers was determined by differential scanning calorimetry (DSC) apparatus. The T_g value of copolymers containing bulky trisyl groups was found to increase with incorporation of trisyl groups in polymer structures. The presence of trisyl groups in polymer side chains, create new macromolecules with novel modified properties.     

Perfluormethyl-element-liganden : XXXI. Ligandeneigenschaften von Me2PP(CF3)2 und Me2AsP(CF3)2

The coordinating properties of the trifluoromethyl elemental compounds Me₂PP(CF₃)₂ and Me₂AsP(CF₃)₂ have been studied by the synthesis and spectroscopic investigations (IR, NMR, MS) of their complexes cis-M(CO)₄L₂ (A), [(CO)₄ML]₂ (B) and [(CO)₅M]₂L (C) (M = Cr, Mo, W). Complexes of type A with L = Me₂PP(CF₃)₂ are obtained in good yield by reaction with M(CO)₄NBD (NBD = norbornadiene), whereas with L = Me₂AsP(CF₃)₂ the homobinuclear compounds B are formed. The attempt to prepare the cis-M(CO)₄[Me₂AsP(CF₃)₂]₂ complexes by treating M(CO)₄(Me₂AsH)₂ with P₂(CF₃)₄ is successful only for M = W. Binuclear compounds of type B or C, in general, can be prepared by stepwise reaction of the ligands with either M(CO)₄NBD or M(CO)₅THF.     

A mechanistic investigation of (Me3Si)3SiH oxidation

The interaction of (Me₃Si)₃SiH with O₂ is known to afford (Me₃SiO)₂Si(H)SiMe₃ in which the two oxygen atoms arise from the same oxygen molecule. In order to investigate the mechanism of this unusual reaction, the oxidation rates were measured in the temperature range 30-70 °C by following oxygen uptake in the presence and absence of hydroquinone as inhibitor. The rate constant for the spontaneous reaction of (Me₃Si)₃SiH with O₂ was determined at 70 °C to be ∼3.5 × 10⁻⁵ M⁻¹ s⁻¹. A sequence of the propagation steps is proposed by combining the previous and present experimental findings with some theoretical results obtained at the semiempirical level. These calculations showed that the silylperoxyl radical (Me₃Si)₃SiOO undergoes three consecutive unimolecular steps to give (Me₃SiO)₂Si()SiMe₃. Evidence has been obtained that the rate determining step is the rearrangement of silylperoxyl radical to a dioxirand-like pentacoordinated silyl radical. Our findings are of considerable importance for the understanding of the oxidation of hydrogen-terminated silicon surfaces.     

Crystal structure of the crowded silanol (Me3Si)3CSiPh2OH

The unit cell in a crystal of (Me₃Si)₃CSiPh₂OH contains two dimers, one of them centrosymmetric. There are no significant differences between the geometries of the molecules in the two types of dimers, in which the components appear to be held together by hydrogen bonding of the type Si---(H)O.…H--- O---Si. kw]Silicon; Crystal structure; Hydrogen bonding; silanol     

Monocyclische organotri- und -tetrastibane: synthese von [(Me3Si)2CHSb]n (n = 3, 4)

Reduction of (Me₃Si)₂CHSbCl₂ with Mg in tetrahydrofuran yields [(Me₃Si)₂CHSb]_n (n = 3, 4).     

Darstellung und chemie von Me2TlN(SiMe3)2 und Tl[N(SiMe3)2]3

The complexes [Rh(η³-C₃H₄R)(η⁵-C₅R′₅)L]⁺BF₄^- (R  1-Me, R′  H, Me; R  2-Me, R′  H) (L  C₅H₅N, Ph₃P, Ph₃As) have been prepared from Rh(η³-C₃H₄R)(η⁵-C₅R′₅)Cl and AGBF₄ in acetone, followed by reaction with the stoicheiometric quantity of L. The ¹H and ¹³C NMR spectra of the salts are reported and discussed.     

Reactions of the sterically hindered organosilicon diol (Me3Si)2C(SiMe2OH)2 and some of its derivatives

The diol R₂C(SiMe₂OH)₂ (R = Me₃Si) has been shown to react with: SO₂Cl₂ to give R₂ Me₂; SOCl₂ to give R₂C(SiMe₂Cl)₂; Me₃SiI or Me₃SiCl to give R₂C(SiMe₂OSiMe₃)₂; R′COCl; (R′ = Me or CF₃) to give R₂C(SiMe₂O₂CR′)-(SiMe₂Cl); (R′CO)₂O (R′ = Me or CF₃ to give R₂C(SiMe₂O₂CR′)₂; with MeOH containing acid to give R₂C(SiMe₂OMe)₂; with neutral MeOH to give R₂C-(SiMe₂OMe)₂ and probably R₂ Me₂; MeLi to give R₂C(SiMe₂OLi)₂ (and the latter to react with PhMeSiF₂ to give R₂ Me₂). The diacetate R₂C(SiMe₂O₂CMe)₂ reacts with CsF in MeCN to give R₂C(SiMe₂F)₂; it does not react with NaN₃ or KSCN in MeCN, but the bis(trifluoroacetate) reacts with these salts with KOCN to give R₂C(SiMe₂X)₂ (X = N₃, NCS, NCO).     

Alternative-liganden XIII. Koordinatives verhalten der chelatliganden Me2XGeMe2(CH2)2X′Me2 (Me = CH3; X, X′ = N, P, As)

In order to gain information about the coordinating properties of the chelating ligands Me₂XGeMe₂(CH₂)₂X′Me₂ (abbr. XGeCCX′) the chemical and spectroscopic results obtained during the synthesis of the M(CO)₄(XGeCCX′) complexes (M = Cr, Mo, W; X, X′ = N, P, As) are critically discussed and compared with the results for the analogous five-membered ring chelates M(CO)₄(KGeCX′).     

[Pb2(TNR)2(CHZ)2(H2O)2]4H2O的结构及热分解机理

The coordination compound of [Pb 2(TNR) 2(CHZ) 2(H 2O) 2]•4H 2O was prepared by using the aqueous solution of carbohydrazide, lead nitrate and sodium styphnate. The molecular structure of [Pb 2(TNR) 2(CHZ) 2(H 2O) 2]•4H 2O(C 7H 13 N 7O 12 Pb, Mr=594.43) was determined by using a single crystal diffraction analysis .The thermal decomposition mechanism of the title compound was studied by TGDTG, DSC and IR techniques. The crystal belongs to monoclinic with space group P2 1/n.The unit cell parameters are as follows: a=0.64700(10)nm, b=1.6074(3)nm, c=1.4883(3)nm,β=97.42(2)°,V=1.5349(5)nm3, Z=2, DC=2.572g•cm -3 ,μ(Mo, Kα)=11.080cm -1 , F(000)=1128. R=0.0422, Rw=0.0735. The binuclear lead coordination compound is bridged by two carbohydrazide molecules. The molecule has a symmetrical center. TNR 2- ,CHZ and H 2O coordinate with the central ions simultaneously.     

Condensation reaction through base assistance within (Ph2SiO)8[AlO(OH)]4

When the polycyclic alumosiloxane (Ph₂SiO)₈[AlO(OH)]₄, which may be isolated as the diethyl ether adduct (Ph₂SiO)₈[AlO(OH)]₄·4OEt₂, is allowed to react with the double N-methylpiperidine (nmp) adduct of monochloroalane, AlH₂Cl·2nmp (1) (crystal structure analysis), the polycycle (Ph₂SiO)₈[AlO(O)_0.5]₄·2nmp (2) is obtained. Compared to the starting material and apart from the coordinating bases, the compound formally has lost two water molecules. The structure of (Ph₂SiO)₈[AlO(O)_0.5]₄·2nmp (2) can be derived from (Ph₂SiO)₈[AlO(OH)]₄ by substituting the central Al₄(OH)₄ motif through an Al₄O₂ entity which consists of a central Al₂O₂ ring coordinated to two further aluminum atoms through almost trigonal planar oxygen atoms. Using tris(ethylene)diamine (ted) as base and reacting it with (Ph₂SiO)₈[Al(OH)]₄, we have been able to isolate and completely characterize an intermediate on the way to these formally condensed alumosiloxane polycycles like in (Ph₂SiO)₈[AlO(O)_0.5]₄·2nmp (2). It has the composition (Ph₂SiO)₈[AlO(O)_0.25]₄·(OH·ted)₂·(OH₂·ted) (3) and has, compared to the starting material, the same number of hydrogen, oxygen, aluminum and silicon atoms within the inner molecular framework. Nevertheless, its structure is very different: whereas half of the molecule is structurally similar to (Ph₂SiO)₈[AlO(OH)]₄, with OH-groups forming hydrogen bridges to the nitrogen atoms of ted and connecting two aluminum atoms, the other half contains a unique oxygen atom which is in an almost planar trigonal bonding mode to three aluminum atoms. Furthermore, this part of the molecule has an aluminum atom to which a water molecule is coordinated, one of the hydrogen atoms being involved in hydrogen bonding to a further tris(ethylene)diamine (ted). This structure gives some important insights in the possible mechanism of the “condensation reaction” within (Ph₂SiO)₈[AlO(OH)]₄.     

The preparation of NbH5(Me2PCH2CH2Me2)2 and NbHL2(Me2PCH2CH2PMe2)2 (L = CO or C2H4)

MMe₅(dmpe) (M = Nb or Ta, dmpe = Me₂PCH₂CH₂PMe₂) reacts with H₂ (500 atm) and dmpe in THF at 60°C to give MH₅(dmpe)_2? NbH₅(dmpe)₂ readily reacts with two mol of CO or ethylene (L) to give NbHL₂(dmpe)₂. The exchange of the hydride ligand with the ethylene protons in NbH(C₂H₄)₂(dmpe)₂ is not rapid on the ¹H NMR time scale (60 MHz) at 95°C.     

Synthesis and characterisation of trimethylsilyl phosphorohalidates: Me3SiOP(O)FX (X = Cl, Br) and (Me3SiO)2P2O3F2

Trimethylsilyl phosphorochloridofluoridate, Me₃SiOP(O)FCl, has been prepared by reaction of POFCl₂ with hexamethyldisiloxane or by treatment of bis(trimethylsilyl) phosphorofluoridate with phosphorus pentachloride. The compound could be purified by vacuum distillation and has been isolated in 55% yield. The ester Me₃SiOP(O)FBr is formed in an analogous reaction of POFBr₂ with (Me₃Si)₂O, however its susceptibility to spontaneous decomposition makes its isolation unfeasible. Condensation of Me₃SiOP(O)FCl with (Me₃SiO)₂P(O)F or heating of POFBr₂ with excess hexamethyldisiloxane gave bis(trimethylsilyl) diphosphorodifluoridate, (Me₃SiO)₂P₂O₃F₂, in 45-53% yield. The existence of both expected diastereoisomers was revealed by and NMR spectroscopy.     

Structures, energy bands and conductivities of (Me3NEt)[Pd(dmit) 2]2 and (NEt4)[Pd(dmit) 2]2

The electrical conductive molecular crystals (Me₃NEt)[Pd(dmit) ₂]₂ and (NEt₄)[Pd (dmit) ₂]₂ (dmit = 4,5-dimercapto-1,3-dithiole-2-thione) have been prepared, and their crystal structures and conductivity-temperature curves have been determined. The fact that the conductivity at room temperature of (Me₃NEt)[Pd(dmit) ₂]₂ (σ = 58 Ω^-1 cm^-1) is much higher than that of (Net₄)-[Pd(dmit)₂]₂ (σ = 2.2 Ω^-1.cm^-1) has been rationally explained by the results of energy band calculations. (MeNEt₃)[Pd(dmit)₂]₂ belongs to monoclinic system, P2₁/m space group and (Net₄)[Pd (dmit)₂]₂ belongs to triclinic system, space group. The structural conducting component of the crystals is the planar coordinative anion [Pd(dmit)₂]^0.5- which forms the face-to-face dimmer. [Pd(dmit)₂]^- ₂These dimers have been further constructed to be a kind of two-dimensional (2-D) conductive molecular sheet by means of S_S intermolecular interactions. The tiny difference of the above 2-D molecular sheets of the two title crystals has resulted in one order of magnitude difference of conductivities.     

Reactions of Ru3(CO)12 with Ene-yne and Alkoxy-silyl Functionalized Compounds. The Crystal Structure of (μ-H)Ru3(CO)9[μ3-η2-HC=N(CH2)3Si(OEt)3]

Ru₃(CO)₁₂ has been reacted with the compounds hex-1-en-3-yne [EtC≡CCH=CH₂], 2-methyl-hex-1-en-3-yne [EtC≡CC(=CH₂)CH₃] and with 3(ethoxy-silyl)propyl isocyanate [(EtO)₃Si(CH₂)₃NCO] and the compound tb [(EtO)₃Si(CH₂)₃NHC(=O)OCH₂C≡CCH₂OC(=O)NH(CH₂)₃Si(OEt)₃] in hydrocarbon solution. Some reactions in CH₃OH/KOH solution (followed by acidification) have also been performed. The main products of the reactions with ene-ynes are the clusters Ru₃(CO)₆(μ-CO)₂L₂ (L = C₆H₈, C₇H₁₀) and their demolition products, the “ferrole” Ru₂(CO)₆L₂ complexes. One of the isomers of Ru₃(CO)₆(μ-CO)₂L₂, and Ru₂(CO)₆L₂ (L = C₇H₁₀) have been reacted with vinyl-triethoxysilane [(EtO)₃SiCH=CH₂]: these reactions did not afford complexes containing new carbon–carbon bonds or triethoxy-silyl groups. Only polymerization of vinyl-triethoxysilane occurred. The reactions of Ru₃(CO)₁₂ with triethoxysilyl-propyl-isocyanate and tb (in the presence of Me₃NO) lead to the same products, that is the isomeric complexes (μ-H)Ru₃(CO)₉[C=N(H)(CH₂)₃Si(OEt)₃] with a “perpendicular” ligand (complex 3, as proposed on the basis of spectroscopic results) and (μ-H)Ru₃(CO)₉[HC=N(CH₂)₃Si(OEt)₃] with a “parallel” ligand (complex 4, as confirmed by a X-ray analysis). The reaction pathways leading to these products are discussed. Complex 4 has been reacted with tetraethyl orthosilicate and the resulting material has been characterized. These reactions are part of a study on the synthesis of inorganic-organometallic materials through sol–gel techniques. This paper is dedicated to Prof. Gunther Schmid in the occasion of his 70th birthday.