Intensity of bands of the C≡C stretching modes in the IR spectra and conjugation in silylacetylenes

A comparative study of the integrated extinction coefficients (A) of the C≡C stretching bands in the IR spectra of acetylene derivatives Me₃SiC≡CR, HC≡CR, and Me₃CC≡CR was carried out. The resonance interactions of substituents with a triple bond are the main cause of the changes in the values ofA. The total resonance effect of the Me₃Si fragment involves both acceptor (d, π-conjugation) and donor (σ, π-conjugation) components; d, π-conjugation dominates in the silylacetylenes studied. Theσ _R ⁰ resonance constant of the Me₃Si substituent in compounds Me₃SiC≡CR is 0.17±0.02. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 76–80. January 1997.     

Electronic effects of Me3SiOCR2 substituents in acetylene derivatives

The σR⁰ and σ_p parameters of Me₃SiOCR₂ and HOCR₂ substituents at the triple bond were determined using the IR spectra of individual acetylene derivatives and their H-complexes. These parameters vary as the effective charge on the atoms of the C≡C fragment of terminal acetylenic alcohols and their trimethylsilyl ethers changes due to intermolecular interaction. The most reliable values of σR⁰ and σ_p parameters (−0.02 and −0.03, respectively) for the Me₃SiOCH₂ substituent were established; they indicate a sharp decrease in σ,π-conjugation of the Me₃SiOCH₂ substituent with the triple bond as compared to the Me₃SiCH₂ substituent. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1759–1762, September, 1998.     

The conjugation and effective charges of the atoms at the triple bond in germylacetylenes

The integrated extinction coefficients (A) of the C≡C stretching modes in the IR spectra of 12 germylacetylenes Me₃GeC≡CR are determined by the resonance interactions of substituents with the triple bond. TheA ^1/2 values change linearly with change in the difference between the effective π-electron charges on the atoms at the triple bond and σ⁰ _R constants of organic substituents R. The average value of the σ⁰ _R constant of the Me₃Ge substituent in the compounds studied is +0.06. The resonance acceptor effect of the Me₃Ge substituent toward the triple bond (d,π-conjugation) is stronger than the donor effect (σ,π-conjugation). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1569–1574, August, 1998.     

Synthesis and mesomorphism of diacetylene-bridged triphenylene discotic liquid crystal dimers

Connecting two discotic mesogens via a spacer not only stabilizes the columnar mesophase but also leads to the formation of glass columnar phase, and therefore improves the physical properties of discotic liquid crystals as organic semiconductor. Here, we report the synthesis of eight diacetylene-bridged triphenylene discotic liquid crystal dimers, [C18H6(OCnH2n+1)4(OMe)O2C-C8H16-C≡≡ C-]2, 3(n), (n = 4-8), [C18H6(OC6H13)5O2C-C8H16-C≡≡ C-]2, 6 and [C18H6(OC6H13)5O-(CH2)m-C≡≡ C-]2, 8(m), (m = 1, 3) by Eglinto...     

Molecular Structures of Acetylene Derivatives of Tin. VIII Trimethylstannylacetylene: Use of Results of Quantum-Chemical Calculations and Spectroscopic Measurements in Analysis of Gas-Phase Electron Diffraction Data

Structural analysis of electron diffraction data on trimethylstannylacetylene, (CH₃)₃SnCCH (1), obtained in the previous investigation (the nozzle temperature being 22°C), has been performed with consideration of nonlinear kinematic effects at the first-order level of perturbation theory (h1). The geometry and force field of 1 have been calculated by the RHF and MP2 (frozen core) methods. The effective core potential in SBK form and the optimized 31G* valence basis set have been applied in the case of Sn atom. The 6-311G** basis set have been used for carbon and hydrogen atoms. Vibrational spectra of the light and two deuterated isotopomers of 1 have been interpreted using the C _3v equilibrium molecular symmetry. For this purpose, the procedure of scaling the quantum-chemical force field by fitting the calculated frequencies to the experimental ones has been employed. The root-mean-square (RMS) vibrational amplitudes and shrinkage corrections used in the electron diffraction analysis have been calculated from the scaled quantum-chemical force field. It has been shown that flexibility of the linear fragment in 1 decreases considerably compared to that of the symmetrically substituted acetylene fragment in the (CH₃)₃SnCCSn(CH₃)₃ molecule (2). Using these data, we refined the geometrical parameters of 1 in terms of a static C _3v symmetry molecular model. The following r _h1 values have been obtained (the bond distances are given in Å and the valence angles in degrees): Sn—C_Me 2.147(7), Sn—C2.096(17), CC 1.237(11), C_Me—H (av.) 1.091(4), C_Me—Sn-C107.1(7), Sn—C_Me—H (av.) 113.4(6). The values in parentheses are experimental total errors including least-squares standard deviation values and scale uncertainties. The structural parameters of linear fragments in both ethynyl derivatives of Sn 1 and 2 are found to be virtually equal.     

Chemistry of chromium bis-acetylide complexes

Abstract  

Stable paramagnetic Cr(II) and Cr(III) bis(alkynyl) complexes of the type [trans(RC≡C)₂Cr(dmpe)₂] ⁿ⁺ (R = Ph, SiMe₃, SiEt₃, C≡C–SiMe₃ n = 0, 1) were prepared and characterised by NMR, cyclic voltammetry, EPR, magnetic measurements, and X-ray single-crystal diffraction studies.     

A Density Functional Investigation on C2Aun+ (n?=?1, 3, 5) and C2Aun (n?=?2, 4, 6): from Gold Terminals, Gold Bridges, to Gold Triangles

A systematic density functional theory investigation on C₂Au _n ⁺ (n = 1,3,5) and C₂Au _n (n = 2,4,6) indicates that gold atoms serve as terminals (–Au) in the chain-like C_s C₂Au⁺ (C=C–Au⁺) and D_∞h C₂Au₂ (Au–C≡C–Au) and as bridges (–Au–) in the side-on coordinated C_2v C₂Au₃ ⁺ ([Au–C≡C–Au]Au⁺) and C_s C₂HAu₂ ⁺([H–C≡C–Au]Au⁺). However, when the number of gold atoms reaches four, they form stable gold triangles (–Au₃) in the head-on coordinated C_2v C₂Au₄ (Au–C≡C–Au₃) and the side-on coordinated C_2v C₂Au₅ ⁺ ([Au–C≡C–Au]Au₃ ⁺). Similar –Au₃ triangular units exist in the head-on coordinated C_2v C₂HAu₃ (H–C≡C–Au₃) and D_2d C₂Au₆ (Au₃–C≡C–Au₃). The existence of stable –Au₃ triangular units in small dicarbon aurides is significant and intriguing. The high stability of Au₃ triangles originates from the fact that an equilateral D_3h Au₃ ⁺ cation possesses a completely delocalized three-center-two-electron (3c–2e) σ bond and therefore is σ-aromatic in nature. The extension from H/Au analogy to H/Au₃ analogy established in this work may have important implications in designing new gold-containing catalysts and nano-materials.     

Unusual coupling of diynes and CO on an Ru3-cluster: Crystal structure of RU3{μ3-CPhCC(O)C(SiMe3)C(C≡CSiMe3)CCPH}(μ-dppm)(μ-CO)(CO)6

Among several products isolated in the reaction between Ru₃(μ₃-PhC₂C≡CPh)(μ-dppm)(CO)₈ and Me₃SiCэCCэCSiMe₃ was the Ru₃{μ₃-CPhCC(O)C(SiMe₃)C(C≡CSiMe₃)CCPh)(μ-ddpm)(CO)₇ complex formally obtained by coupling of the two diynes and a CO molecule on the Ru₃ framework. Other products were Ru₄(μ₄-PhC₂C≡CPh)(μ≡dppm)(CO)₁₀ and the already known complex Ru₃{μ₃-PhCCHCC(C₆H₄}(μ-dppm)(CO)₈. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1012–1016, May, 1998.     

A quantum-chemical and gas phase electron diffraction study of the structure of formylphosphine and acetyldimethylphosphine

The equilibrium geometry and energy and structural changes accompanying inversion motion in the phosphorus fragment and acyl group internal rotation in the H₂PCHO and Me₂PCMeO molecules were calculated by the MP2(full) method using basis sets from 6–31G(d, p) to 6–311G(3df, 2p). The structure of Me₂PCMeO was determined by electron diffraction using the dynamic model of acyl group internal rotation based on the quantum-chemical potential function of torsional motion. Acylphosphines have amide-type equilibrium conformations with acyl groups rotated through ∼100° from their orientation in the C=O/PX₂ anti- form, where X = H, Me (C ₁ symmetry). Considerable pyramidality of the phosphorus fragment distinguishes the equilibrium structures of acylphosphines from amides with a planar molecular frame (C _s symmetry). The r _h1 geometric parameters of the Me₂PCMeO molecule determined by electron diffraction closely agree with quantum-chemical estimates for the equilibrium configuration.     

Gas phase electron diffraction analysis andab initio calculations of the molecular structure of 3,3-dimethyl-1-oxa-3-silacyclopentane

3,3-Dimethyl-1-oxa-3-silacyclopentane was synthesized, and its molecular structure was determined by gas phase electron diffractometry using ab initio calculations (GAUSSIAN-92, RHF method, 6-31G^* basis set). The six models derived from the gas phase electron diffraction analysis equally adequately (R≈3%) describe experimental data, whereas quantum chemical calculations lead to only one (O-envelope) conformer. The stereochemical data and the results of ab initio calculations confirm that the O-envelope is the best conformation; its geometrical parameters are as follows (bond lengths r_a in Å, and angles in degrees; total error in parentheses in units of the least significant digit): r(Si-C_cyc) 1.891(3) and 1.904; r(Si-C_Me) 1.877 and 1.879; r(C-C) 1.556(7); r(C-O) 1.431(3) and 1.445; r(C_cyc-H) 1.11(2); r(C_Me-H) 1.10(2); ϕ(O−C−C−Si) −33.0(14); ∠C_cycSiC_cyc 92.2(5); −33.0(14); ∠C_MeSiC_Me 107.2(8); ∠SiCC 102.6(6); ∠CCO 109.9(11); ∠HC_cycH 110.5(47); ∠SiC_MeH 111.6(14). Method for the synthesis of 3,3-dimethyl-1-oxa-3-silacyclopentane is given, and generalized notation for five-membered ring confor-mations is suggested. Moscow State University. Tromse University, Norway. Irkutsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 4, pp. 689–707, July–August, 1996. Translated by L. Smolina     

Synthesis and photophysical properties of luminescent mononuclear and dinuclear gold(I) complexes with ethynyl-substituted phenanthrolines

A novel asymmetric dinuclear gold(I) complex with 3,6-diethynylphenanthroline, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, has been synthesized from Au(PPh₃)Cl (PPh₃ = triphenylphosphine) and 3,6-diethynyl-1,10-phenanthroline. The asymmetrical dinuclear gold(I) complex, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, demonstrated a weak phosphorescence assignable to the metal-perturbed ³ π–π* transition in the long wavelength region compared to an intense emission of the symmetrical dinuclear complex with 3,8-diethynylphenanthroline, 3,8-bis{(PPh₃)–Au–C≡C}₂-phen. A similar tendency of phosphorescent bands for the mononuclear gold(I) complexes with 5-ethynylphenanthroline, 5-{(PPh₃)–Au–C≡C}-phen, and 3-ethynylphenanthroline, 3-{(PPh₃)–Au–C≡C}-phen was observed. The absorption bands assignable to the π–π*(C≡Cphen) transition and phosphorescent emission assignable to the metal-perturbed ³ π–π* transition for these four gold(I) complexes were reasonably consistent with the results calculated by DFT and TD-DFT.     

Molecular Structure and Conformational Composition of 1-[(Methylthio)methyl]-2-nitrobenzene (MTMNB): A Theoretical and Experimental Study

The conformational composition of gaseous MTMNB and the molecular structures of the rotational forms have been studied by electron diffraction at 130^∘C aided by results from ab initio and density functional theory calculations. The conformational potential energy surface has been investigated by using the B3LYP/6-31G(d,p) method. As a result, six minimum-energy conformers have been identified. Geometries of all conformers were optimized using MP2/6-31G(d,p), B3LYP/6-31G(d,p), and B3LYP/cc-pVTZ methods. These calculations resulted in accurate geometries, relative energies, and harmonic vibrational frequencies for all conformers. The B3LYP/cc-pVTZ energies were then used to calculate the Boltzmann distribution of conformers. The best fit of the electron diffraction data to calculated values was obtained for the six conformer model, in agreement with the theoretical predictions. Average parameter values (r_a in angstroms, angle α in degrees, and estimated total errors given in parentheses) weighted for the mixture of six conformers are r(C–C) = 1.507(5), r(C–C)_{ring, av} = 1.397(3), r(C–S)_av = 1.814(4), r(C–N) = 1.495(4), r(N–O)_av = 1.223(3), ∠(C–C–C)_ring = 116.0–122.5, ∠ C6–C4–C7 = 118.2(4), ∠ C–C–S = 113.6(6), ∠ C–S–C = 98.5(12), ∠ N–C–C4 = 121.9(3), ∠(O–N–C)_av = 116.8(3), ∠ O–N–O = 127.0(4). Torsional angles could not be refined. Theoretical B3LYP/cc-pVTZ torsional angles for the rotation about C–N bond, φ_C−N, were found to be 30.5–36.5^∘ for different conformers. As to internal rotation about C–C and C–S bonds, values of φ_C−C = 68–118^∘ and φ_C−S = 66–71^∘ were obtained for the three most stable conformers with gauche orientation with respect to these bonds. Some conclusions of this work were presented in a short communication in Russ. J. Phys. Chem. 2005, 79, 1701.     

DFT evaluation of the electronic structures and spectroscopic properties of the self-assembled [Pt2M4(C ≡ CH)8] (M=Cu, Ag) clusters

Electronic structures and spectroscopic properties of self-assembled [Pt₂M₄(C≡CH)₈] (M=Cu, Ag) clusters have been studied by the TD-DFT (time-dependent density functional theory) calculations with the polarizable continuum model (PCM). The ground- and excited-state structures were optimized by the DFT (density functional theory) methods. The calculated structures and spectroscopic properties are in agreement with the corresponding experimental results. The [Pt₂Ag₄(C≡CH)₈] clusters have two stable ground state geometries (D ₄ and D _4h symmetry). The calculated Pt-M distances suggest only very weak interactions. The Cu-Cu distances are larger than the van der Waals radii of two Cu atoms and the Ag-Ag distances are analogous with the sum of van der Waals radii of two Ag atoms. Upon excitation, the interaction of Pt⋯M, Ag⋯Ag is strengthened, while the Cu⋯Cu distances are shortened but they are still larger than the sum of van der Waals radii of two Cu atoms. The lowest-energy absorptions are at 450, 365 and 375 nm and the emissions are at 611, 431 and 435 nm for [Pt₂Cu₄(C≡CH)₈], [Pt₂Ag₄(C≡CH)₈] (A) and (B), respectively. The transitions are all perturbed by the Cu or Ag composition through the UV-Vis spectra region; therefore, there are not pure ILCT or M_PtLCT characteristics (ILCT: intraligand charge transfer; MLCT: metal-to-ligand charge transfer) in absorptions of heteropolynuclear [Pt₂M₄(C≡CH)₈] clusters. Since the emissions and the lowest-absorptions have different transition characteristics for each complex, the emissions should not come from the lowest-energy absorptions. Because the M⋯M interactions in the excited state of [Pt₂Ag₄(C≡CH)₈] are augmented, the emissions of [Pt₂Ag₄(C≡CH)₈] clusters bear prominent ILCT character, which is the reason why the emission wavelengths of [Pt₂Ag₄(C≡CH)₈] have a small hypsochromic shift relative to the emission wavelength of homoleptic [Pt(C≡CH)₄]²⁻ precursor.     

The saddle point of the nucleophilic substitution reaction Cl− + CH3Cl: results of large-scale coupled cluster calculations

On the basis of large-scale coupled cluster calculations including connectedz triple substitutions in a perturbative way, the geometrical parameters of the D _{3 h} saddle point of the Walden inversion reaction Cl⁻ + CH₃Cl′→ ClCH₃ + Cl′⁻ are predicted to be R _s (C—Cl) = 2.301 ? and r _s (C—H) = 1.069 ?. The barrier height with respect to the reactants is recommended to be 11.5 ± 1.0 kJ mol⁻¹. Connected triple substitutions lower the barrier height by almost a factor of 2, but have very little influence on the geometric structure of the saddle point. Received: 26 June 1998 / Accepted: 15 July 1998 / Published online: 28 September 1998     

New polyunsaturated organosilicon dendrimers

Spherical dendrimer of regular structure with the spatial characteristic S = 5, tetrakis[tris-(trimethylsilylethynyl)silyl-2-vinyldimethylsilylethynyl]silane, and the unsymmetrical binuclear dendrimer containing simultaneously groups (−CH₂CH₂−), (−CH=CH−), (−C≡C−) and combining the branches of the zero order (G0) and of the second generation (G2), 2-tris(trimethyl-silylethynyl)silyl-1-tris[tris(trimethylsilylethynyl)silylvinyldimethylsilylethynyl]silylethane were isolated from the reaction of hydrosilylation of tetrakis (dimethylethynylsilylethynyl)silane and vinyltris(dimethylethynylsilylethynyl)silane with trichlorosilane and a subsequent treatment of the reaction products with trimethylsilylethynylmagnesium bromide. NMR spectra of the synthesized compounds were studied.     

Gold(I) complexes containing ionic phosphine ligands with a cobaltocenium backbone

The reaction of [(η⁵-R₂PC₅H₄)₂Co][PF₆] with (Me₂S)AuCl (1:2) resulted in {[(η⁵-R₂PC₅H₄)₂Co](AuCl)₂}[PF₆] (R = Ph, Cy, or ⁱ Pr). With a 1:1 ratio of [(η⁵-R₂PC₅H₄)Co(η⁵-C₅H₅)][PF₆] to (Me₂S)AuCl, yellow crystalline {[(η⁵-R₂PC₅H₄)Co(η⁵-C₅H₅)](AuCl)}[PF₆] was produced. The reaction of {[(η⁵-Cy₂PC₅H₄)Co(η⁵-C₅H₅)](AuCl)}[PF₆] with phenyl acetylene gave {[(η⁵-Cy₂PC₅H₄)Co(η⁵-C₅H₅)][Au(C≡C–Ph)]}[PF₆], while the reaction of {[(η⁵-Cy₂PC₅H₄)₂Co](AuCl)₂}[PF₆] with phenyl acetylene produced the unusual ionic complex {[(η⁵-Cy₂PC₅H₄)₂Co][Au(C≡C–Ph)]₂}[Au(C≡C–Ph)₂]. The structure of this complex has been characterized by X-ray crystallography, and a possible pathway for its formation is suggested. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis of ferrocenylacetylide derivatives of gold-ruthenium and gold-osmium clusters. Crystal structures of M3(AuPPh3)(C≡CFc)(CO)9 (M=Ru or Os; Fc is ferrocenyl)

The synthesis and crystal structures of the clusters M₃(AuPPh₃)(C≡CFc)(CO)₉ (M=Ru,3a; or M=Os,3b) are described. Compound3a was synthesized by deprotonation of Ru₃H(C≡CFc)(CO)₉ under the action of KOH/EtOH followed by treatment of the anionic complex [Ru₃(C≡CFc)(CO)₉]⁻ with chloro(triphenylphosphine)gold. Compound3b was prepared by the reaction of Os₃(CO)₁₀(NCMe)₂ with FcC≡CAuPPh₃, which was synthesized by the reaction of FcC≡CNa with ClAuPPh₃. The pentanuclear cluster Ru₄(AuPPh₃)(C≡CFc)(CO)₁₂ (4a), which was prepared by the reaction of3a with Ru₃(CO)₁₂, was characterized by spectral methods. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1295–1299, July, 2000.     

Radical addition reactions: factors determining the transition-state geometry

Interatomic distances in the reaction centers of the addition reactions of (i) H^· to the C=C, C=O, N≡C, and C≡C bonds, (ii) ^·CH₃ radical to the C=C, C=O, and C≡C bonds, and (iii) alkyl, aminyl, and alkoxyl radicals to olefin C=C bonds were determined using a new semiempirical method for calculating transition-state geometries of radical reactions. For all reactions of the type X^· + Y=Z → X— Y—Z^· the r ^# _X...Y distance in the transition state is a linear function of the enthalpy of reaction. Parameters of this dependence were determined for seventeen classes of radical addition reactions. The bond elongation, Δr ^# _X...Y, in the transition state decreases as the triplet repulsion, electronegativity difference between the atoms X and Y in the reaction center, and the force constant of the attacked multiple bond increase. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 894–902, April, 2005.     

Preparation and Structures of Several Complexes Containing Carbon-Rich Ligands Attached to Polynuclear Metal Carbonyls

Several new gold-containing cluster complexes have been prepared from the reactions of gold alkynyl complexes, L _n M-C _x -Au(PPh₃), (x = 3, 4, 6) with Ru₃(CO)₁₀(NCMe)₂. The bis-cluster complex 1,4-{AuRu₃(CO)₉(PPh₃)(μ₃-C₂)}₂C₆H₄ was obtained from Ru₃(CO)₁₀(NCMe)₂ and 1,4-{(Ph₃P)Au(C≡C)}₂C₆H₄. The complexes Ru₃(μ-H){μ₃-C₂C≡C[Ru(PP)Cp′]}(CO)₉ [PP = (PPh₃)₂, Cp′ = Cp; PP = dppe, Cp′ = Cp*] were also obtained as minor by-products and synthesised independently from Ru(C≡CC≡CH)(PP)Cp′. A reaction between Co₃{μ₃-CC≡CC≡CAu(PPh₃)}(μ-dppm)(CO)₇ and Ru₃(CO)₁₂ afforded {(Ph₃P)(OC)₉AuRu₃}C≡CC≡CC{Co₃(μ-dppm)(CO)₇} 7. Related complexes AuRu₃{μ₃-C₂C≡[M(CO)₂Tp]}(CO)₉(PPh₃) (M = Mo 8, W 9) were obtained from {Tp(OC)₂M}≡CC≡C{Au(PPh₃)}, while the mixed metal cluster complexes MoM₂(C₂Me)(CO)₈Tp (M = Ru 13, Fe 14) were obtained from M(≡CC≡CSiMe₃)(CO)₂Tp (M = Mo, W) with Fe₂(CO)₉ and Ru₃(CO)₁₂, respectively. Reactions of the Mo carbyne complex with Co₂(LL)(CO)₆ [LL = (CO)₂, μ-dppm] or nickelocene afforded complexes 15–17 in which Co₂ and Ni₂ fragments, respectively, had coordinated to the C≡C triple bond. XRD structural determinations of 7, 8, 14, 16 and {Tp(OC)₂W}≡CC≡CC≡{Co₃(μ-dppm)(CO)₇} (18-W) are reported. In memoriam: F. Albert Cotton (1930–2007).     

Chemistry of chromium bis-acetylide complexes

Abstract  Stable paramagnetic Cr(II) and Cr(III) bis(alkynyl) complexes of the type [trans(RC≡C)₂Cr(dmpe)₂] ⁿ⁺ (R = Ph, SiMe₃, SiEt₃, C≡C–SiMe₃ n = 0, 1) were prepared and characterised by NMR, cyclic voltammetry, EPR, magnetic measurements, and X-ray single-crystal diffraction studies. Graphical Abstract