Monosubstituted Acetylenes Research Articles

Platinum and Palladium Complexes with Metal–Silicon Bonds. New Bonding, Structures, and Chemical Properties

Abstract Studies on the Pt and Pd complexes with Si-containing ligands by the authors are reviewed. trans-[Pt(SiHPh2)2(PMe3)2], the first Pt(II) complex with two silyl ligands at trans positions, is equilibrated with the thermodynamically more stable cis isomer in solution. The reaction of dimethyl acetylenedicarboxylate (Z–C≡C–Z, Z=COOMe) with [Pt(SiHPh2)2(PMe3)2] produces 3-sila-1-propenylplatinum complex, cis-[Pt(CZ=CZSiHPh2)(SiHPh2)(PMe3)2], and 4-sila-3-platinacyclobutene, , depending on the reaction conditions. The former product is turned into the latter, accompanied by elimination of H2SiPh2. The spectroscopic data of cis-[Pt(CZ=CZSiHPh2)(SiHPh2)(PMe3)2] as well as the crystallographic structure of the 3-sila-1-propenylplatinum with a chelating bisphosphine, [Pt(CZ=CZSiHPh2)(SiHPh2)(dmpe)] (dmpe = 1,2-bis(dimethylphosphino)ethane), indicate intramolecular interaction of the γ-Si–H hydrogen of the ligand with the Pt center. The 4-sila-3-platinacyclobutene reacts with mono-substituted alkynes to produce various 5-sila-2-platina-1,4-cyclohexadienes via insertion of the C≡C bond into the Pt–Si bond of the four-membered ring. [Pt(SiHPh2)2(PMe3)2] reacts with nitriles to cause double addition of the Si–H bonds to the C≡N triple bond, yielding (R = Me and Ph). The reactions of H2SiPh2 and H2SiPhMe with [PdEt2(PMe3)2] afford dinuclear Pd complexes with bridging silyl ligands, [{Pd(PMe3)}{Pd(PMe3)n}(μ-HSiPhR)2] (R = Me and Ph; n = 1 and 2). Pd–Pt heterobimetallic complexes with bridging diphenylsilyl ligands, [{Pd(PR3)}{Pt(PR3)n}(μ-HSiPh2)2] (R = Et and Cy (cyclohexyl); n = 1 and 2), are obtained from the reactions of bis(silyl)platinum(II) complexes with palladium(0)–phosphine complexes. The heterobimetallic complex with PEt3 ligands reacts with t-butyl isocyanide to afford a new disilaplatinacyclopentane, . Heating of [Pt(SiHPh2)2(PMe3)2] at 80 °C in solution produces a trinuclear Pt complex with bridging diphenylsilylene ligands, [{Pt(PMe3)}3(μ-SiPh2)3], which was characterized by X-ray crystallography, NMR spectroscopy, and theoretical calculations.

Polymerization of substituted acetylenes by various rhodium catalysts: Comparison of catalyst activity and effect of additives

AbstractThis research deals with comparison of the activity of various Rh catalysts in the polymerization of monosubstituted acetylenes and the effect of various amines used in conjunction with [Rh(nbd)Cl]2 in the polymerization of phenylacetylene. A zwitterionic Rh complex, Rh+(nbd)[(η6‐C6H5)B−(C6H5)3] (3), was able to polymerize phenylacetylene (5a), t‐butylacetylene (5b), N‐propargylhexanamide (5c) and n‐hexyl propiolate (5d), and displayed higher activity than the other catalysts examined, that is [Rh(nbd)Cl]2 (1), [Rh(cod)(O‐o‐cresol)]2 (2), and Rh‐vinyl complex (4). Monomers 5a and 5c polymerized virtually quantitatively or in fair yields with all these catalysts, while monomer 5b was polymerizable only with catalyts 3 and 4. Monomer 5d did not polymerize in high yields with these Rh complexes. The catalytic activity tended to decrease in the order of 3 > 4 > 2 > 1. Although polymerization of 5a did not proceed at all in toluene with [Rh(nbd)Cl]2 alone, it smoothly polymerized in the presence of various amines as cocatalysts. The polymerization rate as well as the molecular weight of polymer depended on the basicity and steric bulkiness of amines. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4530–4536, 2005

Electrical and morphological characterization of poly(monosubstituted)acetylene based membranes: application as humidity and organic vapors sensors

Electrical and morphological characterization of poly(monosubstituted)acetylene based membranes: application as humidity and organic vapors sensors

Synthesis and Properties of Polymers from Monosubstituted Acetylene Derivatives Bearing Ferroelectric Liquid Crystalline Groups

Novel liquid crystalline polyacetylene derivatives were developed as advanced LC conjugated polymers with quick response to an electric field used as external force. In practice, we synthesized ferroelectric LC conjugated polymers by introducing fluorine-containing chiral LC groups into side chains of polyacetylenes. Phase-transition behaviors of these polymers were examined by differential scanning calorimetry and polarizing optical microscopy. Mesophases as well as higher order structures were evaluated with X-ray diffraction measurements. The polymers synthesized showed chiral nematic (N*), twist grain boundary smectic A (TGBA*), and chiral smectic (SmC*) phases in the heating and cooling processes. Observation of the SmC* phase allows us to expect that the polymer should exhibit ferroelectricity.

NMR chemical shifts. Substituted acetylenes.

The MPW1PW91/6-311+G(2d,p) and MP2/6-311+G(2d,p) GIAO nuclear shieldings for a series of monosubstituted acetylenes have been calculated using the MP2/6-311G(2d,p) geometries. Axially symmetric substituents such as fluorine may lead to large changes in the isotropic shielding but have little effect on the tensor component (zz) about the C[triple bond]C bond axis. On the other hand, substituents such as vinyl and aldehyde groups lead to essentially no difference in the isotropic shielding but are calculated to give a large zz paramagnetic shift to the terminal carbon of the acetylene group, without having much effect on the inner carbon. The tensor components of the chemical shifts for trimethylsilylacetylene, methoxyacetylene, and propiolaldehyde have been measured and are in reasonable agreement with the calculations. The downfield shift at the terminal carbon of propiolaldehyde along with a small upfield shift at the adjacent carbon has been found to result from the coupling of the in-plane pi MO of the acetylene with the pi* orbital that has a node near the central carbon. The tensor components for acetonitrile also have been measured, and the shielding of cyano and acetylenic carbons are compared.

Ketene-acetylene [2 + 2] cycloadditions: cyclobutenone and/or oxete formation?

The [2 + 2] cycloaddition of monosubstituted acetylenes to ketene has been studied by ab initio(G2(MP2,SVP) and DFT (B3LYP/6-31Gd)) methods. The activation barrier decreases with increasing electron-donating ability of the acetylene substituent, and it can be roughly correlated with the energy of the acetylene HOMO. The addition to the C[double bond, length as m-dash]C bond of ketene (giving cyclobutenones) is preferred for the less electron-rich acetylenes, but for the most electron rich ones (X = NH(2) and NMe(2)) the addition to the C[double bond, length as m-dash]O bond (giving oxetes) becomes competitive, with activation barriers as low as ca. 45 (30) kJ mol(-1) for the two computational methods used. The cyclobutenones and oxetes can undergo ring opening to vinylketenes and acylallenes, respectively. Furthermore, the latter two compounds can interconvert by a 1,3-shift of the substituent X. The acylallenes become thermodynamically more stable than the vinylketenes for [small pi]-(lone pair) donating substituents X, and the 1,3-shift barrier also decreases, to ca. 130 kJ mol(-1) for X = NMe(2). In contrast, the 1,3-shifts of CH(3) and H have very high barriers.

Vibrational and electronic contributions to the polarizability and first hyperpolarizability of monosubstituted acetylene: Theoretical study

AbstractThe two contributions, vibrational and electronic, to the electrical properties polarizability and first hyperpolarizability of monosubstituted acetylene HCCX (with X = F, Cl, Br, OH, SH, BH2, NH2, CH3, and SiH3) have been evaluated using the self‐consistent field wave functions within the double‐harmonic oscillator approximation. The results show that both contributions to the electrical properties are sensitive to the nature of the substituent: electronegativity, atomic volume, and X‐weight. In some cases, X = NH2, SiH3, and SH, the nonlinear optical response is essentially due to, and only to, the vibrational response β of the molecule. A complete study is made upon two tracks, upon the intrinsic properties of X and upon the IR and Raman spectra as well as the sum‐over‐modes expression. We also calculated the electrical properties at the AUG‐cc‐pVDZ basis set and at geometric parameters optimized at different levels of theory (B3LYP and MP2). © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

The Electrostatic Potential at Atomic Sites as a Reactivity Index in the Hydrogen Bond Formation

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis, Structure and Chemical Transformations of Ethynylgermatranes

AbstractEthynylgermatranes have been prepared from monosubstituted acetylenes by a three‐step synthesis without isolation of the hydrolytically unstable intermediate chlorogermanes and ethoxygermanes. Boiling an equimolar mixture of tetrachlorogermane Cl4Ge, acetylene RC≡CH and triethylamine in hexane leads to germylation of the Csp−H bond and the formation of ethynyl‐substituted trichlorogermanes. Subsequent alkoxylation of chlorogermanes by ethanol in the presence of triethylamine affords triethoxygermanes that then take part in transalkoxylation with triethanolamine to give ethynylgermatranes. The molecular structures of all ethynylgermatranes and the hexacarbonyldicobalt complex of 1‐heptynylgermatrane have been determined by X‐ray crystallography. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The electrostatic potential at atomic sites as a reactivity index in the hydrogen bond formation

The paper reviews results from computational studies by molecular orbital and density functional theories on several series of hydrogen bonded complexes. These studies aim at quantifying the reactivity of molecules for the complexation process. Excellent linear relationships are found between the electrostatic potential values at the sites of the electron donor and electron accepting atoms and the energy of hydrogen bond formation (Δ E). The series studied are: (a) complexes of R–CHO and R–CN molecules with hydrogen fluoride; (b) complexes of mono-substituted acetylene derivatives with ammonia; (c) (HCN) n hydrogen bonded cluster for n=2–7. All 22 studied complexes of carbonyl and nitrile compounds with hydrogen fluoride fall in the same dependence between the energy of hydrogen bond formation and the electrostatic potential at the atomic site of the carbonyl oxygen and nitrile nitrogen atoms, with linear regression correlation coefficient r=0.979. In the case of complexes of mono-substituted acetylene and diacetylene derivatives with NH 3, the correlation coefficient for the dependence between the electrostatic potential at the acidic hydrogen atom and Δ E equals 0.996. For the series of hydrogen bonded (HCN) n clusters, the correlation coefficient for the relationship between the electrostatic potential at the end nitrogen atom and Δ E is r=0.9996. Similarly, the analogous relationship with the electrostatic potential at the end hydrogen atom has a regression coefficient equal to 0.9994. The dependencies found are theoretically substantiated by applying the Morokuma energy decomposition scheme. The results show that the molecular electrostatic potential at atomic sites can be successfully used to predict the ability of molecules to form hydrogen bonds.

π‐conjugated columnar polyacetylenes prepared with Rh complex catalysts

AbstractHighly stereospecific polymerization of monosubstituted acetylenes was carried out using the Rh complex, [Rh(norbornadiene)Cl]2 catalysts. The resulting polyacetylenes were characterized in detail by 1HNMR, ESR, laser Raman, diffuse reflective UV, and wide angle X‐ray diffraction methods. The data showed that the Rh complex were the preferred catalyst to selectively yield the corresponding cis‐transoid polymers even at room temperature when alcohol, triethylamine or water was used as the polymerization solvent. Additionally, the resulting cis polyacetylenes were found to have a helical form whose polymer is amorphous or composed of pseudohexagonal structures called π‐conjugated columnar as self‐assembly or super structure. Further compression of the amorphous cis polymers resulted in cis to trans isomerization at room temperature under vacuum, breaking rotationally the cis C=C bonds giving π‐radicals called solitons as the origin of a polymer magnet. On the other hand, the π‐conjugated columnar was also found to show an extremely longer wavelength absorption compared with that of the amorphous one, although the absorption maximum was shifted to a shorter wavelength when the columnar was destroyed by the compression. Therefore, the formation of the π‐conjugated columnar can be considered as a new and quite useful control method concerning color of such conjugated polymers, i.e., a new concept concerning the color of conjugated polymers.

Polyacetylenes Bearing Mesogenic Side Groups: Synthesis and Properties, 2

AbstractWe report on the synthesis of novel liquid crystalline polyacetylenes derived from monosubstituted acetylene monomers. In the monomers A1OBP‐Acn obtained from 3‐bromo‐1‐propyne, the acetylenic moiety is linked through a very short spacer to a biphenyl mesogenic core. Several linear acyl groups of different length are introduced as tail groups. Most of the monomers show liquid crystalline behavior. Polymerizations are carried out in solution with typical metathesis catalysts based on Mo and W and yield polyacetylenes with fairly high molecular weight (MW), soluble in common organic solvents. Polymers PA1OBP‐Acn are fully characterized in terms of molecular structure, by GPC, FT‐IR, NMR and UV/VIS techniques, and of thermal and morphological behavior, by TGA, DSC, POM and X‐ray diffraction experiments. THF solutions of the polymers show a quite relevant photoluminescence with a broadened maximum located around 450 nm.POM analysis on monomer A1OBP‐Ac6: crystal transformation on heating at 76 °C.imagePOM analysis on monomer A1OBP‐Ac6: crystal transformation on heating at 76 °C.

First X-ray Characterization and Theoretical Study of π-Alkyne, Alkynyl-Hydride, and Vinylidene Isomers for the Same Transition Metal Fragment [Cp*Ru(PEt3)2]+

The reaction of the chloro-complex [CpRuCl(PEt(3))(2)] with acetylene gas in methanol gave the pi-alkyne complex [CpRu(eta(2)-HCtbd1;CH)(PEt(3))(2)][BPh(4)] (1), which has been structurally characterized by X-ray analysis. The alkyne complex undergoes spontaneous isomerization even at low temperature, yielding the metastable alkynyl-hydride complex [CpRu(H)(Ctbd1;CH)(PEt(3))(2)][BPh(4)] (2), as the result of the oxidative addition of the alkyne C-H bond. This compound has also been structurally characterized despite it tautomerizes spontaneously into the stable primary vinylidene [CpRu(=C=CH(2))(PEt(3))(2)][BPh(4)] (3). This species has been alternatively prepared by a two-step deprotonation/protonation synthesis from the pi-alkyne complex. Moreover, the reaction of the initial chloro-complex with monosubstituted alkynes HCtbd1;CR (R = SiMe(3), Ph, COOMe, (t)Bu) has been studied without detection of pi-alkyne intermediates. Instead of this, alkynyl-hydride complexes were obtained in good yields. They also rearrange to the corresponding substituted vinylidenes. In the case of R = SiMe(3), the isomerization takes place followed by desilylation, yielding the primary vinylidene complex. X-ray crystal structures of the vinylidene complexes [CpRu(=C=CH(2))(PEt(3))(2)][BPh(4)] (3) and [CpRu(=C=CHCOOMe)(PEt(3))(2)][BPh(4)] (10) have also been determined. Both, full ab initio and quantum mechanics/molecular mechanics (QM/MM) calculations were carried out, respectively, on the model system [CpRu(C(2)H(2))(PH(3))(2)](+) (A) and the real complex [CpRu(C(2)H(2))(PEt(3))(2)](+) (B) to analyze the steric and electronic influence of ligands on the structures and relative energies of the three C(2)H(2) isomers. QM/MM calculations have been employed to evaluate the role of the steric effects of real ligands, whereas full ab initio energy calculations on the optimized QM/MM model have allowed recovering the electronic effects of ligands. Additional pure quantum mechanics calculations on [CpRu(C(2)H(2))(PH(3))(2)](+) (C) and [CpRu(C(2)H(2))(PMe(3))(2)](+) (D) model systems have been performed to analyze in more detail the effects of different ligands. Calculations have shown that the steric effects induced by the presence of bulky substituents in phosphine ligand are responsible for experimentally observed alkyne distortion and for relative destabilization of the alkyne isomer. Moreover, increasing the phosphine basicity and sigma donor capabilities of ligands causes a relative stabilization of an alkynyl-hydride isomer. The combination of both steric and electronic effects, makes alkyne and alkynyl-hydride isomers to be close in energy, leading to the isolation of both complexes.

The anharmonic resonances in the infrared spectrum of 12C13CH2

The vibration-rotation spectrum of 13C mono-substituted acetylene, 12C13CH2, has been recorded in the region between 1100 and 3500 cm−1 at instrumental (4 × 10−3 cm−1) or Doppler limited (6–8 × 10−3cm−1) resolution. Hot and cold bands involving the stretchings v1, v2 and v3 and the stretching-bending combination bands with ν2 = 1, ν4 ⩽ 1 and ν5 ⩽ 2 have been observed and analysed. The anharmonic resonances within the dyads ν1/(v2 + 2ν5) and ν3/(ν2 + ν4 +ν5), which strongly perturb the spectrum of 13C2H2 and 12C2H2, respectively, have been analysed. From the simultaneous treatment of all the assigned transitions a set of deperturbed molecular parameters, containing also the coupling coefficients K1,255 and K3,245, was derived. They fully characterize the ro-Vibrational pattern of the observed stretching and stretching-bending combination states and provide an accurate description of the anharmonic resonances in the molecule.

Electrostatic Potential at Atomic Sites as a Reactivity Descriptor for Hydrogen Bonding. Complexes of Monosubstituted Acetylenes and Ammonia

The applicability of molecular electrostatic potential values at atomic sites as a reactivity descriptor for the process of hydrogen bonding is assessed for a series of complexes involving acetylene and diacetylene derivatives as proton donors and ammonia as a model proton acceptor. The acetylenic compounds studied were of the type R−C⋮C−H, where R represents H, F, Cl, CH3, CH2F, CHF2, CF3, CH2Cl, CHCl2, CCl3, CN, H−C⋮C, F−C⋮C, Cl−C⋮C. Density functional theory computations at the B3LYP/6-31G(d,p) level were employed. An excellent linear relation between the molecular electrostatic potential at the acetylenic hydrogen atom in the isolated acetylenes with the energy of hydrogen-bond formation is found. It is concluded that the value of the electrostatic potential at the acidic hydrogen atomic site can be used as a reactivity descriptor for the hydrogen bonding ability of the molecules studied.

Cyclotrimerization of phenylacetylene and living polymerization of tert-butylacetylene by Mo 2(O 2CCH 3) 4–Lewis acid systems

Mo 2(O 2CCH 3) 4-LA catalysts (LA = TiCl 4, SnCl 4, GeCl 4, EtAlCl 2) induce monosubstituted acetylene (phenylacetylene and tert-butylacetylene) to cyclotrimerize and/or to polymerize. The catalytic ability of these catalyst as well as the structure of polymers formed strongly depends on the Lewis acid and solvent. The systems with TiCl 4 and GeCl 4 trimerize phenylacetylene with high selectivity. The system with TiCl 4 also cyclotrimerizes tert-butylacetylene, but SnCl 4 and GeCl 4 systems polymerize tert-butylacetylene with 100% conversion. In the latter system the polymerization of tert-butylacetylene follows a living mechanism.

The Infrared Spectrum of 12C13CH2: The Bending States up to v4+v5=4

The vibration–rotation spectra of 13C monosubstituted acetylene, 12C13CH2, have been recorded in the region between 450 and 3200 cm−1 with an effective resolution ranging from 0.004 to 0.006 cm−1. A total of about 5300 rovibrational transitions have been assigned to 53 bands involving the bending states up to vt=v4+v5=4, allowing the characterization of the ground state and of 30 vibrationally excited states. All the bands involving states up to vt=3 have been analyzed simultaneously by adopting a model Hamiltonian which takes into account the vibration and rotation l-type resonances. The derived spectroscopic parameters reproduce the transition wavenumbers with a RMS value of the order of the experimental uncertainty. Using the same model larger discrepancies between observed and calculated values have been obtained for transitions involving states with vt=4. These could be satisfactorily reproduced by only adopting, in addition to the previously determined parameters which were constrained in the analysis, a set of effective constants for each vibrational manifold.

Z-scan measurements of third-order optical non-linearities in poly(phenylacetylenes)

Poly(phenylacetylene) (PPA) and poly( p-methoxyphenylacetylene) (PMOPPA) were synthesized by catalytic polymerization of monosubstituted alkynes and were fully characterized by conventional techniques. Linear and third-order non-linear optical properties of polymers solutions were investigated at λ=780 nm using a Z-scan set-up equipped with a femtosecond laser source at different operating regimes. A high repetition rate (76 MHz) regime was used to measure the linear and non-linear absorption coefficients by means of thermo-optical effects. Values of the linear and non-linear absorption coefficients were α=4.9×10 −3 cm −1 and β=1.1×10 −11 cm W −1 for PPA and α=2×10 −2 cm −1 and β=2.1×10 −10 cm W −1 for PMOPPA. Very low repetition rate (14 Hz) excitation was used to evidence the purely-optical non-linear refractive indexes, that were γ=6×10 −18 cm 2 W −1 and γ=11×10 −18 cm 2 W −1, respectively, for PPA and PMOPPA.

Induced chiral helical effect on the main chain of aliphatic polyacetylenes

11-Dodecyn-1-ol as an achiral, aliphatic, monosubstituted acetylene was copolymerized with cholesteryl 3-butynyl carbonate as a chiral, aliphatic, monosubstituted acetylene with Rh(nbd)[B(C 6 H 5 ) 4 ] (nbd = norbornadiene) in tetrahydrofuran. The main chain of the obtained copolymers seemed to be mainly composed of the cis-type structure. The backbone π-π * transition of these copolymers showed significant circular dichroism (CD), indicating an excess of one-handed helical conformation. These CD signals were varied with the contents of the cholesteryl units in the copolymers.

Bithienylsilanes: unexpected structure and reactivity

5-(2,2′-Bithienyl)hydrosilanes were prepared by reaction of bithienyl lithium with chlorodimethylsilane, dichloromethylsilane and trichlorosilane. It was shown that 5-(2,2′-bithienyl)dimethylsilane possesses higher reactivity in the hydrosilylation reaction of monosubstituted acetylene derivatives compared with (2-thienyl)dimethylsilane. The elongation of the π-conjugated chain leads to increasing selectivity of the hydrosilylation reaction. An unusual structure for bis[5-(2,2′-bithienyl)]methylsilane has been established by X-ray analysis.