Vinylidene Groups Research Articles

The chemistry of iron-tris(dimethylphosphinomethyl)methylsilane complexes: crystal structure of the compound [{Fe((Me 2PCH 2) 3SiMe)} 2(μ-H) 2(μ-CCH 2)] with a vinylidene group which is derived from ethylene

The ability of the tri-tertiary-phosphine tris(dimethylphosphinomethyl)methylsilane (tmps) to act as a ligand in a variety of iron compounds has been explored. Tmps reacts with [Fe(η-C 6H 6)(PMe 3) 2] giving [Fe(η 4-C 6H 6)(tmps)]. The η 4-C 6H 6 ligand of this compound is readily displaced by carbon monoxide, cyclopentadiene, cyclohexa-1,3-diene, disubstituted acetylenes or ethylene giving [Fe(tmps)(CO) 2], [Fe(η-C 5H 5)H(η 2-tmps)], [Fe(η-C 6H 8)(tmps)], [Fe(η-RCCR)(tmps)] (R,R′  Ph, Ph; Me, Me; Me, Et; Et, Et or Me 3Si, Me 3Si) or [{Fe(tmps)(μ-H)} 2(μ-CCH 2)], respectively. The formation of the μ-vinylidene compound directly from ethylene is noteworthy. The crystal structure of the μ-vinylidene compound has been determined. The new compounds [Fe(η 5-C 6H 7)(tmps)]PF 6, [Fe(η-C 6H 6)(tmps)][BF 4] 2, [(tmps)Fe(μ-Cl) 3Fe(tmps)]Cl, [(tmps)Fe(μ-Cl) 3Fe(tmps)]BPh 4, [Fe(η-C 5H 5)(tmps)]-PF 6, [Fe(η-C 4H 6)(tmps)], [Fe(η-C 6H 5CH 2CH 2Ph)(tmps)], [Fe(η 5-2-PhCH 2CH 2C 6H 6)(tmps)]PF 6 are also described.

Structure of products of the initial stage of chlorination of natural rubber

The structure of the products of the initial stage of chlorination of natural rubber was studied by ozonolysis and IR spectroscopy. Specimens of uniform composition containing up to one atom of chlorine per monomer unit were obtained in a stop-flow setup. On the basis of data on unsaturation and the contents of methyl and vinylidene groups in the specimens under study it was concluded that cyclization occurs during the initial stage of chlorination and the probable paths involving the formation of cyclic structures are considered.

Chemistry of vinylidene complexes. 6. Electrochemical reduction and UV spectra of vinylidene derivatives of cymantrene and complexes with an Mn-Pt bond

1. A comparative polarographic study of the phenylvinylidene compounds Cp(CO)2Mn=C= CHPh (I), Cp2(CO)4Mn2(Μ-C=CHPh) (II), and Cp (CO)2MnPt (Μ-CHPh)LL' (III–IX), where L and L′ may be P(OR)3 or CO, has shown that the coordination of the Mn=C bond to a second metal atom results in transposition of the electrophilic center from the α-C atom of the vinylidene group in I to the Mn atoms in II and the Pt atom in III–IX. 2. A correlation between the potential for the electrochemical reduction of the complexes Cp(CO)2MnPt(Μ-C=CHPh)LL' and the energy of the σ → σ* transition of the metal-metal bond in their UV spectra has been established. 3. The attachment of the donor substituents L and L′ to the Pt atoms in compounds III–IX results in an increase in the strength of the Mn-Pt bond. The donor interaction between the Pt atom and the semibridging carbonyl group causes the opposite effect.

ChemInform Abstract: Synthesis of O‐Heterocycles with an Exocyclic Vinylidene Group by Means of Organo Silicium Compounds.

AbstractThe silanes (Ia) and (Ib) react with the aldehydes (IIa) to give the title compounds (III).

ChemInform Abstract: The Conformation of 2‐Cyclopropylpropene and 1,1‐Dicyclopropyl Ethylene by Means of ab initio SCF Calculations.

Abstract The geometrical structure of 2-cyclopropylpropene and 1,1-dicyclopropyl ethylene has been determined by means of the ab initio SCF gradient method. The most stable conformation of 2-cyclopropylpropene has a gauche structure and the internal rotation angle between the cyclopropyl ring and the vinyl group is calculated to be 62°. The most stable conformation of 1,1-dicyclopropyl ethylene also has a gauche structure and the internal rotation angles between one of two cyclopropyl rings and the vinylidene group are 64°.

Radiation effects in polymers at high pressure

It has been established that high pressure increase the reaction rate of alkyl macroradicals in polyethylene due to the decrease of the height and narrowing of the reaction potential barrier. The enhancement of free valence migration at high pressure changes the accumulation rate for the main products of polyethylene radiolysis—the radiation yield of the crosslinking increases about 10 times, the yield of vinylidene groups decay increases, too. High pressure crosslinking of polyethylene proceeds by the chain mechanism.

Environmental degradation of stabilized LDPE. Initial step

The environmental degradation of a stabilized low density polyethylene film was studied. The polymer degradation has started in the first 2400 h of exposure. Irregular changes in tensile strength and elongation at break up to exposure times of 7080 h are observed. A constant reduction of the mechanical properties studied begins at 7080 h of exposure. The relative optical density of the carbonyl and vinyl groups increases regularly during the whole exposure time, while a small change in the relative optical density of the vinylidene groups is observed. The thermal oxidation strength decreases after 7080 h of exposure. The crystallinity remains steady. Reflection infra-red-Fourier Transform measurements indicate that the oxidation reaction proceeds at the same rate on both sides of the film.

The conformation of 2-cyclopropylpropene and 1,1-dicyclopropyl ethylene by means of ab initio SCF calculations

The geometrical structure of 2-cyclopropylpropene and 1,1-dicyclopropyl ethylene has been determined by means of the ab initio SCF gradient method. The most stable conformation of 2-cyclopropylpropene has a gauche structure and the internal rotation angle between the cyclopropyl ring and the vinyl group is calculated to be 62°. The most stable conformation of 1,1-dicyclopropyl ethylene also has a gauche structure and the internal rotation angles between one of two cyclopropyl rings and the vinylidene group are 64°.

Novel benzeneosmium complexes containing alkynyl, vinyl and vinylidene groups as ligands

The complex C6H6Os(CCHPh)(PPri3) has been prepared from [C6H6Osl2]2via alkynyl(iodo)-, vinyl(hydrido)-, and vinyl(halogeno)-osmium compounds as precursors; it reacts with sulphur, selenium, and CuCl by electrophilic addition to the OsC bond.

Simulation of tubular low‐density polyethylene

AbstractThe simulation of tubular, high‐pressure low‐density polyethylene reactors is performed using a comprehensive kinetic scheme which includes branching reactions as well as reactions leading to vinyl and vinylidene group formation. The variation of the physical properties of the reaction mass with position has been accounted for. In addition to predicting the conversions of the monomer and initiator, the temperature, and the number‐average molecular weight, this study enables the computation of the polydispersity index and the concentration of vinyl, vinylidene, and methyl groups as a function of position. These have important implications in terms of product properties. Detailed simulations have shown that the steady‐state approximation can be used for obtaining the concentrations of the initiator and the polymer radicals. In addition, some simple closure conditions have been established. The effect of multiple intermediate feeds is also investigated and it is found that under certain operating conditions the reactor performance becomes inherently unstable.

Octene-1 linear low density polyethylene photooxidation

Low-temperature thermooxidation and photooxidation at long wavelengths ( λ > 300 nm) of octene-1 linear low density polyethylene have been examined. It is shown that both oxidations proceed according to mechanisms which are very similar to those thought to occur in free radical low density polyethylene presenting a low content of vinylidene unsaturation. Hydroperoxidation in the α-position to the vinylidene groups gives rise to isolated hydroperoxide groups that absorb at 3550 cm −1 and are stable at 85°C. A parallel hydroperoxidation occurs on the saturated chain affording hydrogen-bonded hydroperoxides which are fairly unstable at 85°C. In photooxidation at long wavelengths both hydroperoxides are produced and readily photolysed. Variations in the number of branch points which provoke large variations in density have no significant influence on the photooxidation rate.

Ambidentate Behavior of Mononuclear Vinylidenerhodium Complexes—Novel CC Coupling of a Methyl to a Vinylidene Group

Ambidentate Behavior of Mononuclear Vinylidenerhodium Complexes—Novel CC Coupling of a Methyl to a Vinylidene Group

Primary hydroperoxidation in photooxidation of polyolefins and polyamides

Special attention is focussed on the various hydroperoxides which appear as primary products in the photooxidation of polyolefins and polyamides. In polyethylene, hydroperoxidation in α position to the vinylidene group affords monomeric hydroperoxides (absorbing at 3550 cm −1), thermostable up to 85°C and easily photolyzed. Hydroperoxidation on the saturated chain affords hydrogen-bonded hydroperoxides which are fairly unstable at 85°C under vacuum. The polyethylene hydroperoxides are not able to induce significantly new oxidation processes. Isolated and associated hydroperoxides also exhibit very different behaviour in an ethylene-propylene-norbornene-ethylidene terpolymer. In polyamides (PA 11, PA 12, PA 6), hydroperoxidation α to the nitrogen atom is predominant. Hydroperoxides are revealed only by chemical titration at room temperature. Thermally unstable above 60°C, photounstable at λ < 300 nm, they decompose into imides and hydroxylated groups α to the nitrogen. Up to now, the photoinductive ability of the hydroperoxides cannot be completely excluded.

ChemInform Abstract: SPECTROSCOPIC STUDIES ON C2 HYDROCARBON FRAGMENTS. PART 1. VIBRATIONAL STUDIES OF CLUSTER‐BOUND VINYL AND VINYLIDENE LIGANDS

Vibrational assignments of the vinyl and vinylidene groups in [Os3(CO)10(µ-H)(µ-η2-CHCH2)](1) and [Os3(CO)9(µ-H)2(µ3-η2-CCH2)](3) respectively have been made on the basis of normal co-ordinate analyses of the Os3(C2Hn)(n= 2 or 3) fragments and [2H] substitution. π-Co-ordination caused the lowering of the principal ν(CC) vibration to 1 311 and 1 331 cm–1 in (1) and (3) respectively. The vinyl group frequencies could largely be transferred to assign partially the spectrum of another vinyl complex [Ru2(CO)3(η5-C5H5)2(µ-η2-CHCH2)]BF4(2) with the same co-ordination mode. The vinylidene frequencies in (3) were quite distinct from those of another complex, [Ru2(CO)3(η5-C5H5)2(µ-CCH2)](4) which has a different co-ordination mode; a band at 1 586 cm–1 in (4) is assigned as consisting largely of the ν(CC) mode. Analysis was also made of the Os(µ-H) group in (1) and showed strong mixing between the symmetric ν(Os–H) and out-of-plane bend giving rise to the i.r. active vibrations at 1 285 and 710 cm–1; the asymmetric ν(Os–H) stretch occurs at 1 394 cm–1.

Spectroscopic studies on C2 hydrocarbon fragments. Part 1. Vibrational studies of cluster-bound vinyl and vinylidene ligands

Vibrational assignments of the vinyl and vinylidene groups in [Os3(CO)10(µ-H)(µ-η2-CHCH2)](1) and [Os3(CO)9(µ-H)2(µ3-η2-CCH2)](3) respectively have been made on the basis of normal co-ordinate analyses of the Os3(C2Hn)(n= 2 or 3) fragments and [2H] substitution. π-Co-ordination caused the lowering of the principal ν(CC) vibration to 1 311 and 1 331 cm–1 in (1) and (3) respectively. The vinyl group frequencies could largely be transferred to assign partially the spectrum of another vinyl complex [Ru2(CO)3(η5-C5H5)2(µ-η2-CHCH2)]BF4(2) with the same co-ordination mode. The vinylidene frequencies in (3) were quite distinct from those of another complex, [Ru2(CO)3(η5-C5H5)2(µ-CCH2)](4) which has a different co-ordination mode; a band at 1 586 cm–1 in (4) is assigned as consisting largely of the ν(CC) mode. Analysis was also made of the Os(µ-H) group in (1) and showed strong mixing between the symmetric ν(Os–H) and out-of-plane bend giving rise to the i.r. active vibrations at 1 285 and 710 cm–1; the asymmetric ν(Os–H) stretch occurs at 1 394 cm–1.

Infrared absorption spectra of hydrogen complexes in type I diamonds

The 3107 cm −1 peak has been observed in the infrared absorption spectra of all but one of some 50 type I diamonds examined. Evidence is presented which strongly supports the interpretation of this peak as being due to a carbon-hydrogen bond stretching mode. Reasons are given for believing that the hydrogen responsible for this, and the associated 1405 cm −1 line, is present as a constituent of the vinylidene group( > C = CH 2). Several new peaks, of fairly general occurrence, are reported in the wavenumber range 3400 cm −1 to 2750 cm −1. Some of these lines, seen only when the specimens exhibit at least partial type Ib character, are almost certainly due to nitrogen-hydrogen bond stretching. Others, found in type Ia and/or partially type Ib specimens may be due to C-H or N-H stretching in different local environments. Our observations show that hydrogen is as ubiquitous an impurity in diamond as nitrogen. Possible sites within the crystals for these hydrogenous groups are discussed.

The role of hydroperoxides in photooxidation of polyolefins, polyamides and polyurethane elastomers

Abstract

An intermediate-spin iron(III) porphyrin complex with a vinylidene group inserted into a iron-nitrogen bond: paramagnetic susceptibility, EPR, and Moessbauer properties

An intermediate-spin iron(III) porphyrin complex with a vinylidene group inserted into a iron-nitrogen bond: paramagnetic susceptibility, EPR, and Moessbauer properties

An iron(III)-porphyrin complex with a vinylidene group inserted into an iron-nitrogen bond: relevance to the structure of the active oxygen complex of catalase

An iron(III)-porphyrin complex with a vinylidene group inserted into an iron-nitrogen bond: relevance to the structure of the active oxygen complex of catalase

Conjugate additions of functionalized carbanions to the vinylidene groups of [M(CO) 4{(Ph 2P) 2CCH 2}] (M = W, Mo or Cr)

Treatment of complexes of the type [M(CO) 4{(Ph 2P) 2CCH 2}] (M = W, Mo or Cr) with functionalized lithium reagents, LiR, followed by hydrolysis gives complexes of the type [M(CO) 4{PH 2P) 2CHCH 2R}] in high yields; R = C 6H 4Me-4, C 6H 4OMe-2, C 6H 3(OMe) 2-2,6, C 6H 4OH-2, C 6H 4(COOH)-2, CH 2COPh or CH 2COMe. IR, and 31P and 1H NMR data are given.