CC Triple Bond Research Articles

Properties and reactivity of lanthanide (Eu and Yb) catalysts dispersed on SiO2

Lanthanide metals (Ln : Eu and Yb) dissolved in liquid ammonia react with SiO2 to form active Ln/SiO2 catalysts. The behaviour of lanthanides present on SiO2 varies markedly with the level of lanthanide loading. For low loadings, lanthanide catalysts immobilized on SiO2, formed by the preferential reaction of lanthanides with surface hydroxyl groups on SiO2 and which Fourier-transform infrared studies have shown have the structure Si—O—Ln—NH2, exhibited selective hydrogenation properties, discriminating between conjugated and non-conjugated dienes. This was further confirmed by using polyvinyl alcohol (PVA) with uniform hydroxyl groups as a model compound. The lanthanide-bound PVA exhibited similar catalytic properties and the turnover frequencies of Ln/PVA were very close to those of Ln/SiO2. For high loadings of lanthanide, Ln/SiO2 additionally showed selective hydrogenation of alkynes; only internal CC triple bonds were reduced in marked contrast to terminal CC bonds. The active catalysts were those in which the lanthanide used, in excess compared with the surface hydroxyl groups on SiO2, was highly dispersed on the support in an active metallic form, leading to the selective hydrogenation of alkynes.

Synthesis and absorption/emission spectroscopic properties of bis(phenylethynyl)benzenes and 9,10-bis(phenylethynyl)anthracenes

A series of bis(phenylethynyl)benzenes 3 and 9,10-bis(phenylethynyl)anthracenes 4 was synthesized by bromination–dehydrobromination reaction or newly developed direct CC triple bond formation reaction from styrylstilbenes 1 or distyrylanthracenes 2. Subsequently systematic investigations were carried out on their absorption and fluorescence spectra, and their chemiluminescence properties. The following points are apparent; (a) a linear relationship between ν and Hammett's σp of compounds 3 and 4 was observed, (b) a significant relationship between the Stokes' shift of 4 and σp was observed and (c) in the series of compounds 4 the electron-donating ability of the substituents has a pronounced effect on the chemiluminescence properties.

Polarisabilities of triply bonded molecules: The 14- and 26-electron systems CN −, N 2, HCN, C 2H 2, C 2N 2, HC 3N and C 4H 2

Dipole moments and polarisabilities are calculated by correlated methods for a series of linear molecules containing NN, CN and CC triple bonds. A compact polarised basis gives near-Hartree-Fock anisotropic polarisabilities with largest component along the molecular axis and roughly additive behaviour with increasing chain length. Correlation corrections to the polarisability are insignificant for these systems.

ChemInform Abstract: Mn(I)‐Induced 1,6‐Demethanation Across the CC Triple Bond of Linear Alkynes in the Gas Phase. A Case for the Generation of Manganese Cycloalkynes?

AbstractComplexes of Mn(alkynes)+, generated in the gas phase, are found to exhibit a reactivity which is even richer than that of analogous Fe species.

ChemInform Abstract: The Chemistry of Hydroisocyanic Acid. Part 3. Reaction of M(CO)5CNH (M = Cr, Mo, W) and (FeCp(diphos)CNH)BF4 with Activated CC Double and Triple Bonds.

ChemInform Abstract: The Chemistry of Hydroisocyanic Acid. Part 3. Reaction of M(CO)5CNH (M = Cr, Mo, W) and (FeCp(diphos)CNH)BF4 with Activated CC Double and Triple Bonds.

Carbon–carbon triple bond cleavage at room temperature with nonacarbonyldi-iron: synthesis of [Fe3(CO)9(µ3-CMe)(µ3-CNEt2)

An aminoalkyne CC triple bond has been cleaved at room temperature in the presence of [Fe2(CO)9] using a sodium diphenylketyl catalyst; a di-µ3-carbyne cluster is formed.

ChemInform Abstract: Synthesis and X‐Ray Structure of the First Cluster‐Stabilized Phosphaallene, (μ3‐η2‐tBuP(C=CH(C6H5)))FeCo2(CO)9.

AbstractComlexation of the CC triple bond in (III), prepared from (I) and (II), by reaction with Co2(CO)8 yields the complex (IV), which on refluxing in hexane gives two complexes: the major product (V), in which the P atom has lost the phenylethynyl group and one hydrogen, and the title product (VI) (in low yield), which crystallizes in the space group Pbca with Z = 8. Phenylacetylene is detected in the reaction media, but it is shown that (VI) does not result from the reaction of (V) with the alkyne.

The linear relationship between the one-bond spin—spin coupling constants 1JCC and the product of the electronegativities Ex·Ey of substituents at the CC triple bond

Abstract The linear equation connecting the one-bond spin–spin coupling constants between carbon nuclei, J CC , and the product of the electronegativities of substituents at the CC triple bond is derived using a large number of data for variously substituted acetylenes. The equation 1 J CC = 23.23 E x · E y + 15.45 provides a means for estimation of unknown 1 J CC s and for calculation (and/or verification) of electronegativities of substituents. The equation allows one to estimate a total range of about 350 Hz for 1 J CC s. The smallest value (30 Hz) is predicted for dicaesium acetylide, Cs 2 C 2 , and the largest one for difluoroacetylene, F 2 C 2 (383 Hz). The electronegativities of tin and lead, which constituted a subject of long-lasting controversy in the literature, calculated using the equation are equal to 1.74 and 1.64, respectively.

Cyclooctyne — a sterically strained molecule with an unusual CC triple bond geometry

The molecular structure of cyclooctyne has been reinvestigated by the gas electron diffraction method. Experimentally observed and theoretically calculated 1 J CC NMR coupling constants for model compounds have been incorporated in the study, MMZ calculations for cyclooctyne have been carried out. The ED and NMR results are in agreement with a cyclooctyne molecular model involving a very distorted CCCC fragment (∠ CCCC: 154.5°, θ(CCCC): ca. 40°).

Selective hydrogenation of the CC-triple bond in PhCCPh by tris(triphenylphosphine)cobalt activated NaBH 4; deuterium tracing experiments

Sodium borohydride does not on its own react with diphenylacetylene, but becomes an active hydrogenation agent in the presence of (Ph 3P) 3CoCl. Unlike systems involving other catalysts, e.g. cobalt halides in ethanol, this is a selective reagent for hydrogenation in which an alkyne is selectively hydrogenated to cis and trans alkenes. The role of NaBH 4 in this hydrogenation and isomerization has been studied by deuterium labelling. A brief comparison is made with other active catalysts in this system like (Ph 3P) 3CoBH 4.

Singlet cyclobutyne: a relative minimum on the C4H4 potential-energy hypersurface?

The lowest singlet and triplet electronic states of cyclobutyne have been investigated by using the nonempirical molecular electronic structure theory. Initially, singlet cyclobutyne was studied with use of two-configuration self-consistent-field (TCSCF) methods and triplet cyclobutyne with single-configuration SCF theory. Three standard basis sets, of double-xi (DZ) through double-xi plus polarization (DZ + P) caliber, were employed, the largest being designated C(9s5p1d/4s2p1d), H(4s1p/2s1p). Geometrical structures and harmonic vibrational frequencies were determined with use of analytic gradient techniques. From purely geometrical considerations, the short carbon-carbon bond in singlet cyclobutyne may be labeled a weak (or long) triple bond, with r/sub e/(C double bond C) = 1.258 A. For triplet cyclobutyne a much longer carbon-carbon distance (1.323 A) is predicted, consistent with the sort of C double bond C double bond expected for this diradical species. The triple-bond CC harmonic stretching frequency for singlet cyclobutyne is predicted to be 1911 cm/sup -1/, while the analoguous stretching frequency for the triplet diradical species is 1779 cm/sup -1/. Vibrational analyses demonstrate that (at the levels of theory considered) both singlet and triplet cyclobutyne are relative minima on the C/sub 4/H/sub 4/ potential-energy hypersurface. For the former, the lowest frequency predicted at the DZ+d TCSCF levelmore » of theory is 276 cm/sup -1/, corresponding to the ring-puckering mode. These remarks notwithstanding, it is to be emphasized that singlet cyclobutyne is a highly energetic species, predicted to lie approx. 78 kcal above vinyl acetylene, HC double bond C - CH double bond CH/sub 2/, the absolute minimum among C/sub 4/H/sub 4/ molecules. Finally, singlet cyclobutyne is predicted to lie 13 kcal below its triplet diradical.« less

ChemInform Abstract: NUCLEOPHILIC ADDITION TO A TRIPLE BOND: PRELIMINARY AB INITIO STUDY

Preliminary ab initio, calculations (minimal basis set STO-3 G) suggest that the preferred direction of approach of a nucleophilic centre towards a CC triple bond makes an obtuse angle (∼120°) with this bond. The stereoelectronic requirements for nucleophilic addition to triple bonds and to ketones are thus rather similar.

Nucleophilic Addition to a Triple Bond; Preliminary ab initio study

AbstractPreliminary ab initio, calculations (minimal basis set STO‐3 G) suggest that the preferred direction of approach of a nucleophilic centre towards a CC triple bond makes an obtuse angle (∼120°) with this bond. The stereoelectronic requirements for nucleophilic addition to triple bonds and to ketones are thus rather similar.

13C- und 199Sn-NMR untersuchungen an alkinylstannanen

Chemical shifts δ( 13C), δ( 119Sn) and coupling constants J( 119Sn 13C) for alkynylstannanes of the type R 4- n Sn(CCR′) n ( n = 1–4) are reported. The values of 1J( 119Sn 13C) and 2J( 119SnC 13C) depend upon the nature of the substituent R′. 1J( 119Sn 13C) in Sn(CCCH 3) 4 is 1168 Hz, much larger than a value predicted in the literature of ca. 700 Hz. The comparison of δ( 119Sn) for (CH 3) 2Sn(CCR′) 2 and 1,1,4,4-tetramethyl-1-stannacyclohexadi-2,5-ene suggests that the δ( 119Sn) of alkynylstannanes are determined only to a small extent by the diamagnetic anisotropic effect of the CC-triple bond.

Electron transfer through a carbon–carbon triple bond: kinetics and mechanisms of the reductions of µ(carboxyacetylenecarboxylato-OO′)-di-µ-hydroxo-bis[triamminecobalt(III)] and related complexes by chromium(II) and vanadium(II)

Four polynuclear cobalt(III)ammine complexes with bridging carboxylic acids containing a carbon–carbon triple-bond have been prepared and characterized. The kinetics of the reduction of the µ-(carboxyacetylemecarboxylato-OO′)-di-µ-hydroxo-bis[triamminecobalt(III)] complex, (I), by CrII has been studied in perchloric acid media. Reduction of the first CoIII is rate determining and dependent on [H+]. It is shown that both the protonated and unprotonated form of complex (I) are reduced by an inner-sphere mechanism with attack of the first Cr2+ at the uncomplexed remote carbonyl oxygen and transfer of an electron through the ligand. The detection of a binuclear chromium(III) complex incorporating the organic ligand as a product of the reaction is strong evidence that the second CoIII is reduced via an inner-sphere mechanism too, most probably by attack of a second Cr2+ at the carbonyl oxygen adjacent to co-ordinated CoIII. The assignments are supported by reactivity patterns observed for the reductions of similar complexes: di-µ-hydroxo-µ-(methoxycarbonylacetylenecarboxylato-OO′)-bis-[triamminecobalt(III)], (II), reacts with Cr2+ by an inner-sphere mechanism with remote attack, but the rate of reduction is independent of [H+]; V2+ reacts via an outer-sphere mechanism. The reductions of complexes µ-(acetylenedicarboxylato-O1O1′ : O2O2′)-bis{di-µ-hydroxo-bis[triamminecobalt(III)]}, (III), and di-µ-hydroxo-µ-(propiolato-OO′)-bis[triamminecobalt(III)], (IV), by Cr2+ and V2+ occur by outer-sphere mechanisms, respectively, because a suitable ‘lead-in’ functional group for the reductants is not available. No evidence for direct interactions of the reductants with the CC triple-bonds has been found.

1,3‐Anionic Cycloadditions of Organolithium Compounds: An Initial Survey. New synthetic methods (4)

AbstractIn the field of [3 + 2]‐cycloaddition reactions, 1,3‐anionic cycloadditions have now joined 1,3‐dipolar cycloadditions as a second reaction type of major general importance. The cycloaddition in question has been found to occur with 2‐azaallyllithium compounds, allyllithium compounds (with an electron acceptor located on C2), and 1,3‐diphenylpropargyllithium. Compounds with CC, CN, NN, and CS double bonds and those with CC and CN triple bonds were found to be 1,3‐anionophilic. 1,3‐Anionic cycloaddition opens new routes to 1‐aza‐, 1,2‐diaza‐, 1,3‐diaza‐, 1,2,4‐triaza‐, and 1‐thia‐3‐azacyclopentane derivatives, to pyrroles and imidazoles, as well as (and this appears to be of special importance) to cyclopentane derivatives. Currently available data attribute stereospecificity to the 1,3‐anionic cycloadditions, which occupy an interesting intermediate position between 1,3‐dipolar cycloadditions and transition‐metal‐catalyzed cyclizations. A two‐step mechanism has been demonstrated in one case.

Reactivity of vinyl sulphonic esters. Part XVI. Solvolytic reactivity of β-halogenovinyl derivatives

The solvolytic reactivity of trans-(I) and cis-(II)β-halogenovinyl 2,4,6-trinitrobenzenesulphonates, R2(Hal)C:C(O3SAr)R1[(I; Hal = Cl, Br, or I, R1,R2= alkyl or aryl), (II; Hal = Cl or Br, R1,R2= aryl)], has been investigated in acetic acid and in nitromethane–methanol. The kinetics and products indicate that the solvolysis in both solvents proceeds by SN1 and SN1–E1 mechanisms in the case of some β-iodovinyl derivatives. The reactivity of esters (I) strongly depends on the nature of the halogen and follows the order IBr > Cl. The trans-esters (I; R1,R2= aryl) are more reactive than the corresponding cis-isomers when Hal = Br [k(I)/k(II)= 10–15] and almost equally reactive when Hal = Cl. The substitution products from (I; Hal = I) retain the trans-geometry, whereas the substitutions of esters (I) and (II)(R1,R2= aryl), when Hal = Br or Cl, are not stereospecific. Anchimeric assistance due to iodine and, to a much lesser extent, to bromine are suggested to be involved. The results are also discussed in terms of bridged versus open geometry for the intermediate vinyl cations and compared with those for electrophilic additions of halogens to the CC triple bond.

Molecular packing modes. Part VIII. Crystal and molecular structures of but-3-ynoic acid

The title compound crystallises in space group Pca21 with two molecules in the asymmetric unit, the cell having dimensions a= 8·060, b= 4·195, c= 25·433 A. The phases were determined from a diffractometer data by a multi-solution method and the structure refined by a least-squares procedure to R 0·067 for 968 independent reflections. The bond lengths are CC 1·175, 1·179; C–C 1·455, 1·453; C–CO2H 1·484, 1·506; CO 1·221, 1·214; C–OH 1·307, 1·259 A. The C(:O)·C·C⋮C system is syn-planar.The molecules are hydrogen-bonded (O–H ⋯ 2·69 and 2·65 A) in pseudo-centrosymmetric pairs. In the crystal there are no intermolecular ethynyl-H ⋯ OC interactions; rather, the acetylenic; C–H bond points at the CC triple bond, [H ⋯ C⋮C(midpoint) 3·0 A]. The C(sp3)–H ⋯ bond is directed towards the carbonyl oxygen (C–H ⋯ O 3·45, and H ⋯ O 2·6 A).But-3-ynoic acid also appears in a pseudo-orthorhombic form showing order-disorder. The relationship of the two forms is discussed.

Additions to the Activated CC Triple Bond

AbstractThe possibilities of additions to the activated CC triple bond are discussed with the aid of a number of examples. The additions of donors that contain no active hydrogen are generally initiated via a dipolar primary complex, which can undergo stabilization by rearrangement, cyclization, or addition reactions. Preparative aspects of these reactions are also discussed. They offer routes for the preparation of heterocycles, particularly pyrrole and thiophene derivatives.

Microwave Spectrum, Structure, and Dipole Moment of Silyl Acetylene

The microwave spectrum of silyl acetylene has been investigated in the region 8–36 kMc. The rotational constants for the isotopic species H3Si28C12≡C12H, H3Si29C12≡C12H, H3Si30C12≡C12H, H3Si28C13≡C12H, H3Si28C12≡C13H have been determined to be 4828.66, 4775.65, 4725.65, 4803.98, 4662.34 Mc/sec, respectively. From these data the structural parameters rSiC=1.826 Å and rCC=1.208 are determined. If rCH is assumed to be 1.056 Å then rSiH=1.455 Å, <HSiH=110.3°. The length of the SiC bond is definitely shortened by its location adjacent to the CC triple bond and there may be some lengthening of the CC bond. Measurement of the Stark effect leads to a dipole moment of 0.316 D.