Bernard Henner

Pyrolysis of poly[(silylene)diacetylenes]: Direct evidence between their morphology and thermal behavior

The pyrolysis of poly[(silylene)diacetylenes] under argon to 1400°C gives β-SiC-containing ceramics in high yields (63–87%). All the solid residues contain a large amount of free carbon depending upon the nature of the substituents at silicon, i.e., saturated or unsaturated. Furthermore, the total amount of silicon present in the precursor remains in the final residue. The polymer-to-ceramic conversion has been studied by means of thermal analyses (TGA, TDA and DSC). The polymers primarily undergo low-temperature crosspolymerization through the triple bonds without weight loss which leads to a highly crosslinked carbon network. The mineralization occurs in the temperature range 450–800°C. The crosslinking step can be related to the morphology of the poly[(silylene)diacetylenes]. As shown clearly by X-ray powder diffraction and transmission electron microscopy studies, steric requirement of the side-groups bonded to silicon (methyl versus ethyl, phenyl and trimethylsilyl) greatly influences the degree of crystallinity of the above polymers. The relationship between this structural observation and the crosspolymerization rate is discussed.

Oligomers with silicon and transition metal groups: Thermolysis of poly[1,1′-bis(diorganosilylethynyl) ferrocenes] and poly[{(diorganosilylene) diacetylene}dicobalthexacarbonyls] to give iron silicide- and cobalt silicide-based ceramics

Abstract The pyrolysis of transition-metal-containing organosilicon-diacetylene oligomers was performed in order to prepare multiphase ceramics. Poly[1,1′-bis(diorganosilylethynyl)ferrocenes] ( 2 ) were pyrolysed, under argon, up to 1350°C to give Fe x Si y C z phases with good yields, owing to the incorporation of the cyclopentadiene groups in the carbon matrix and the participation of nearly all silicon and iron in the ceramic residue. The pyrolysis of poly[{(diorganosilylene) diacetylene} dicobalt hexacarbonyls] ( 3 ) at 1350°C gave Co 2 Si and graphite-like carbon. Evolution of part of the carbon monoxide of 3 in the early stage of the pyrolysis (100°C) showed that the cross-linking of the diacetylene units was induced by reactive cobalt species. Furthermore, at higher temperatures (200–500°C), cobalt clusters catalysed the ceramic formation. Co 2 Si was shown to result from the reaction of SiC with Co above 1000°C, both formed during the pyrolysis process. Finally, at 1100°C, a carboreduction reaction led to the elimination of the oxygen incorporated in the carbon matrix during the cross-linking process.

Hypervalent silicon hydrides: evidence for their intermediacy in the exchange reactions of di- and tri-hydrogenosilanes catalysed by hydrides(NaH,KH and LiAlH4)

Di- and tri-hydrogenosilanes, RR′SiH2 and RSiH3 (R = aryl, allyl or benzyl; R′ ue5fb aryl or alkyl), readily undergo exchange reactions, involving siliconue5f8carbon bonds and silicon-hydrogen bonds, in the presence of hydrides (LiAlH4, KH and NaH) as catalysts. These results are discussed in terms of five-coordinate silicon hydrides as intermediates in the reaction.

Organogermanium polymers: Pyrolysis chemistry of poly[(germylene)diacetylenes]

Abstract The pyrolysis of poly[(germylene)diacetylenes] and poly{[lgermylene)diacetylene][(silylene)diacetylenes]} was studied under argon. The ceramic residues were obtained in good yield (66–82%) due to cross-linking through the triple bonds at relatively low temperatures (150–250°C) which gave a carbon sp 2 matrix with disubstituted organogermyl and/or silyl groups. The ceramic residues contained a high amount of carbon (40–61%) and all the germanium was recovered as metallic germanium above 500°C. Pyrolysis of poly[(germylene) diacetylenes] under ammonia gave germanium nitride after cross-linking and nitridation between 400 and 600°C.

Hypervalent silicon hydrides: evidence of their intermediacy in the reaction of optically active 1-NpPhMeSiH(D) with hydrides

Abstract Racemisation of optically active 1-NpPhMeSi★H(D) takes place rapidly in the presence of hydrides (KH, LiAlH4, or LiAlD4) in THF at room temperature. Under more drastic conditions, i.e. 50°C for 24 h, (+)-1-NpPhMeSiH gave the racemic (±)-1-NpPhMeSi− anion. The results are discussed in terms of initial addition of H− to silicon to generate a pentavalent organosilicon anion.

Synthesis and characterization of magnetic organic-inorganic nanocomposites based on the [Mn2O12{CH2C(CH3)COO}16(H2O)4] building block

The new methacrylate-substituted manganese carboxylate cluster [Mn12O12{CH2C(CH3)COO}16(H2O)4] having single molecule magnetic (SMM) properties was synthesized and fully characterized by X-ray crystallography, LDI-TOF, fast atom bombardment (FAB) analyses and magnetic measurements. This cluster, containing sixteen polymerizable functionalities, was used as a cross-linker in the radical copolymerization with methyl methacrylate monomer in order to obtain hybrid cross-linked copolymers. The obtained nanocomposites were studied by infrared spectroscopy, magnetic measurements, thermogravimetric analysis, differential scanning calorimetry and transmission electronic microscopy. All these methods, along with the study of the swelling properties, reveal that the intact manganese cluster is enwrapped and covalently bonded to the polymer matrix, allowing to improve its chemical and thermal stability. The resulting nanocomposite materials have SMM properties.

Organosilicon polymers: pyrolysis of poly[(silanylene)diethynylene]s

Abstract The pyrolysis of Si(CH 3 ) 2 Cue5fcCCue5fcC n in a stream of argon to 1400°C gives a SiC-containing ceramic in high yield (85%). TDA, TGA-mass spectrometry and solid state 13 C NMR studies are reported, and show that: (1) a low-temperature cross-linking process involving the diacetylenic units occurs at about 300°C below the mineralisation stage and (2) the weight decrease between 400°C and 800°C arises only from loss of H 2 , CH 4 and C 2 H 4 . Pyrolysis under NH 3 leads to Si 3 N 4 with loss of the carbon.

(Z)-1-methoxy-4-(diphenylphosphino) but-1-ene-3-yne: A versatile synthon for unsymmetrically substituted (diphenylphosphino) diacetylene derivatives

Abstract An efficient synthesis of Ph 2 P-C≡C-C≡C-Li, 1 , was found, starting from commercially available ( Z )-1-methoxybut-1-ene-3-yne and its diphenylphosphino derivative 2 . The lithio compound 1 was condensed with electrophiles to give Ph 2 P-C≡C-C≡C—Σ (Σ = SiR 3 , SnR 3 , B(N i Pr) 2 ) 3 . Compound 2 was easily transformed into the phosphonium salt 6 and the phosphine oxide 7 using MeI and H 2 O 2 respectively. Derivatives 3 (Σ = SiMe 3 , SnMe 3 ) are reactive at phosphorus and at the Σ group; complexation with W(CO) 5 THF gave the expected derivatives W(CO) 5 Ph 2 P-C≡C-C≡C—Σ (Σ = SiMe 3 , SnMe 3 ), 10 , and in the case of Σ = SnMe 3 , coupling reaction between Ph 2 P-C≡-C-C≡C-SnMe 3 , 3c , and ( η 5 -IC 5 H 4 )Mn(CO) 3 in the presence of PdCl 2 (CH 3 CN) 2 as a catalyst gave the complex 11 , Ph 2 P-C≡C-C≡C-( η 5 -C 5 H 4 )Mn(CO) 3 .

Problème du cation siliconium IV. Mécanisme de la coupure métal—carbone dans les dérivés β-fonctionnels du silicium et du germanium

Abstract Brominations of triphenylallylsilane, methylphenyl-1-naphthylallylsilane, 2(1-naphthyl)-2-allyl-1,2,3,4-tetrahydro-2-silanaphthalene and triphenylallylgermane have been studied in carbon tetrachloride, acetic acid and methanol as solvents. Either cleavage of the M-allyl bond (M = Si, Ge) or addition on the double bond (M = Si) takes place according to the nucleophilicity of the solvent. Cleavage of the M-carbon bond has also been studied with Ph 3 SiCH 2 CH 2 Cl and Ph 3 GeCH 2 CH 2 Cl. The nucleophilicity of the solvent and steric effects are main factors controlling these reactions. Mechanisms are advanced for each reaction.

DIETHYL ETHYNYLPHOSPHONATE: A VERSATILE SYNTHON FOR THE PREPARATION OF 1-ALKYNYL- AND 1,3-BUTADIY NE-1,4-DIYLPHOSPHONATES

Abstract The cross-coupling reaction between diethyl ethynylphosphonate (1) and several aromatic iodides under the Sonogashira conditions (Cl2Pd(PPh3)2/CuI/Et3N) gives only minute amounts of the expected 1-alkynylphosphonates. Yields of about 20% are achieved upon using Pd(OAc)2/2PPh3/Et3N in place of the previous catalytic system. Side-reactions involving 1 and the mine are shown to be responsible for these low yields. Metalation of 1 with EtMgBr and t-BuLi has been carried out and the M-C≡C-P(O)(OEt)2 (M = MgBr, Li) derivatives have been characterized via reaction with Me3SiCl or Ph3iCl. The easy access to the organolithium compound has made possible the synthesis of the zinc analog (M = ZnCl) which reacts with aromatic iodides (C6H5I, p-MeOC6H41, p-O2NC6H4I, p-1C6H4I, 2-iodothiophene), in the presence of Pd(PPh3)4, to give diethyl 1-alkynylphosphonates in reasonable yields. Oxidative dimerization of 1 under the Hay conditions (CuCl/TMEDA:acetone/air) gives the symmetrical diacetylenic diphosphonate (EtO)2(O)P-C≡C-C≡C-P(O)(OEt)2 in high yield.