Cyclooctatetraene Research Articles

Semi-empirical molecular orbital conformational study of benzannelated cyclooctatetraenes and related compounds, and x-ray crystal structure of benzocyclooctatetraene

Semi-empirical molecular orbital conformational analyses of benzocyclooctatetraene, 1, dibenzo [ a, c] cyclooctatetraene, 2, dibenzo [ a, e] cyclooctatetraene, 3, tribenzo[ a, c, e] - cyclooctatetraene; 4, tetrabenzo[ a, c, e, g] cyclooctatetraene, 5, octafluorocyclooctatetraene, 6A, and cyclooctatetraene, 6B, have been done at the MNDO and MINDO/3 (excluding 4 and 5) levels of approximation. Comparison of these results with the X-ray structural data for 1 (as determined in the present work) and the other benzannelated cyclooctatetraenes showed that, while MNDO is vastly superior to MINDO/3, both fail to account for the subtle effects of benzannelation on the conformation of the cyclooctatetraene ring. The experimental data indicate that the tub conformation of cyclooctatetraene is only slightly perturbed by the successive fusion of one and two non-adjacent benzene rings, but steric repulsion between adjacent annelated benzene rings, when present, predominates and gives rise to more folded configurations. Compound 1 crystallizes in space group P2 1 n with a = 11.856(2), b = 6.327(1), c = 12.470(3) A ̊ , β = 110.03(2)° , and Z = 4. The structure has been solved by direct methods and refined to R = 0.049 for 1435 observed Mo- K α diffractometer data.

An experimental and theoretical study of the low temperature E.S.R. of the cyclooctatetraene and tetramethylcyclooctatetraene anion radicals-in single crystal environments

Experimental and theoretical investigations are reported of the E.S.R. spectroscopy of cyclooctatetraene (COT) and 1,3,5,7-tetramethylcyclooctatetraene (TMCOT) monoanion radicals oriented in single crystals of dialkali metal cyclooctatetraene diglyme (M 2COT · dg), where M= K, Rb or Cs, and dipotassium 1,3,5,7-tetramethylcyclooctatetraene bis(diglyme) (K2TMCOT · 2dg), respectively. Theoretical calculations are presented which explain why, as previously found experimentally, the equilibrium position of the COT monoanion in single crystals of M2COT · dg at low temperatures is rotated about its D 8 symmetry axis by an angle of 22·5° relative to the equilibrium position of the COT dianion. Also presented are calculations of the ion-pair association energies (due to the electrostatic interactions of the nearest neighbour alkali metal ions and COT monoanion) which show that (a) the orbital degeneracy of the free, unperturbed COT monoanion is removed and (b) the lowest energy state of the COT monoanion (in agree...

Transition metal chemistry of octafluorocyclooctatetraene

The organometallic chemistry of cyclooctatetraene (COT) has been particularly rich and varied in terms of the types of structure and dynamic behavior which have been observed. Our studies of the interactions of octafluorocyclooctatetraene (OFCOT) with transition metal centers have yielded novel structural types not encountered in the chemistry of COT. The transition metal oxidative addition chemistry of OFCOT will be described, and new metal-promoted transannular CC bond forming reactions to yield fluorocarbon skeletons based on the perfluorobicyclo[4.2.0]octatriene and perfluorosemibullvalene valence isomers of OFCOT will be outlined. Notably these structural classes of valence isomer have proven to be resistant to synthesis and isolation from free OFCOT. The x-ray crystal and molecular structures of a number of these complexes will be discussed.

Dibenzo[def,pqr]tetraphenylene (bi-4,5-phenanthrylene)

C28H16 , M r = 352.44, monoclinic, Cc, a = 30.492(4), b = 7.405(4), c = 16.362 (4)A, fl = 105.30 (1) °, U = 3563.5 A 3, Z = 8, D x = 1.314 Mg m -3, ~(Mo K~t) = 0.069 mm -1. The structure was solved by incorporating trio relations into the starting set for multisolution direct methods, and refined to R = 0.048 for 3947 unique observed reflexions. The molecule shows a distorted tub conformation. The phenanthrene moieties are twisted considerably. The racemate consists of helical PP and MM enantiomers. Introduction. Cyclooctatetraene and its derivatives show non-planar tub conformations (Fray & Saxton, 1978). Tetraphenylene, a tetrabenzocyclooctatetraene, has the same geometry (Irngartinger & Reibel, 1981). Some bridged tetraphenylene derivatives have been synthesized and non-planar conformations postulated from spectroscopic data (Hellwinkel & Haas, 1979; Hellwinkel, Reiff & Nykodym, 1977). We determined the structure of dibenzo(def, pqrltetraphenylene (I), a bi-4,5-phenanthrylene (Thulin & Wennerstr6m, 1977), to establish the molecular conformation.

Tert-Butyl-substituted cyclooctatetraenes

Reaction of cyclooctatetraene (COT) with tert-butyllithium provides a convenient synthesis of tert-butylcyclooctatetraene, 4. As a byproduct of the reaction mixture, 1,4-di-tert-butylcyclooctatriene has been isolated and converted to 1,4-di-tert-butylcyclooctatetraene, 5, by deprotonation with potassium amide and oxidation with iodine. An independent synthesis of 5 was developed from 9-oxabicyclo(6.1.0)octa-2,4,6-triene (cyclooctatetraene oxide), 9. The highly substituted compound 1,3,5,7-tetra-tert-butylcyclooctatetraene (6) has been prepared in 24% overall yield in four steps. The acetylenic ketone 27, prepared from (tert-butylethynyl)copper and pivaloyl chloride, undergoes condensation with dimethyl malonate to give the pyrone ester 28. This ester undergoes facile hydrolysis and decarboxylation in hot concentrated sulfuric acid to yield 4,6-di-tert-butyl-2H-pyran-2-one (22) which is converted to 6 in one step by photolysis in dilute solution.

Calculation of gain coefficients for vapour phase dyes

The gain coefficient for four vapour phase organic dyes has been calculated under laser and (for POPOP, flashlamp) pumped conditions and compared with various experimental results for POPOP vapour under nitrogen laser excitation. As quenching of the POPOP vapour triplet state by vapour phase 1,3,5,7 cyclooctatetraene (COT) has been observed with a known rate constant this has been applied to the calculation of the gain coefficient of POPOP/COT vapour mixtures.

η2Complexes of cyclic polyolefins: crystal structure of [Mn(CO)2(η2-C8H8)(η-C5H5)

Treatment of [Mn(CO)2(thf)(η-C5H5)](thf = tetrahydrofuran) with cyclo-octatetraene produces [Mn(CO)2(η2-C8H8)(η-C5H5)], whose structure was determined by X-ray diffraction. Crystals are monoclinic, space group P21/c, with four molecules in a unit cell of dimensions a= 10.813(7), b= 6.606(4), c= 17.164(9)A, β= 94.68(5)°. The structure was solved by conventional techniques and refined by least squares to R 0.034 for 2 787 independent diffracted intensities. The molecule contains an η2-cyclo-octatetraene ligand which possesses mirror symmetry and present the convex face of a tub conformation towards the cyclopentadienyl ring. Nuclear magnetic resonance spectra show that the complex is non-fluxional below the temperature (ca. 75 °C) at which it decomposes to the dimanganese µ-cyclo-octatetraene complex [{Mn(CO)2(η-C5H5)}2(µ-C8H8)]. The η2-cyclo-octatetraene is readily displaced by phosphine ligands. Analogous η2-olefin complexes of manganese are obtained from cycloheptatriene and cyclo-octa-1,3,6-triene.

The photochemical synthesis of (cyclooctatetraene) W(CO)4

Photolysis of W(CO)o in the presence of cyclooctatetraene in hexane obtains sequential displacement of CO resulting in the formation of dihapto, tetrahapto and hexahapto complexes of cyclooctatetrae ne with tungsten. A simple preparation of η4-cyclooctatetraenetetracarbonyltungsten is described.

The crystal and molecular structure of tetrabenzocyclodecan-1,6-dione

The crystals belong to the orthorhombic space group C222, with a = 9.226, b = 12.092, c = 16.513 Å, Z = 4. A single crystal X-ray diffraction analysis has shown that the title compound, in which all carbon atoms are sp2 hybridized, exists with the ten membered ring in a slightly twisted tub conformation. The 13C nmr spectrum is also reported.

Olefinic and acetylenic compounds.v. the regiospecific synthesis of 1,5- disubstituted-cyclooctatetraene derivatives.

The Thermally controlled addition of methylpropiolate or cyanoacetyle-ne to 1-methoxycarbonyl-or 1-cyano-quadricyclanone leads in a regiospecific way to the corresponding 1,5-disubstituted cyclooctatetraenes.

Book Review: The Chemistry of Cyclo‐octatetraene and Its Derivatives. By G. I. Fray and R. G. Saxton

Book Review: The Chemistry of Cyclo‐octatetraene and Its Derivatives. By G. I. Fray and R. G. Saxton

IR spectra of the cyclooctatetraene dianion prepared by matrix reactions with alkali metals

The IR absorption spectra of pure dipotassium and disodium salts ofthe cyclooctatetraene (COT) dianion formed by matrix reaction with alkali metals were measured. It is shown that the absorotion band in the 1300 cm −1 region should be assigned to the v(CC) stretching vibration of the COT 2− dianion. A dependence of the frequency of the out-of-plane bendingϱ(CH) vibrationon the nature of the cation is established.

The negative effect of cyclooctatetraene on small coaxial flashlamp-pumped dye lasers

The negative effect of cyclooctatetraene (COT) on the efficiency of a dye laser using a small-bore (ID = 5 mm) and fast-rise-time (80 ns, 10 to 90 percent of maximum) coaxial flashlamp pump was investigated.

ChemInform Abstract: ELECTROCHEMICAL REDUCTION OF SYM‐DIBENZOCYCLOOCTATETRAENE, SYM‐DIBENZO‐1,5‐CYCLOOCTADIENE‐3,7‐DIYNE, AND SYM‐DIBENZO‐1,3,5‐CYCLOOCTATRIEN‐7‐YNE

AbstractDie reversiblen Halbstufenpotentiale der drei Titelverbindungen, die Geschwindigkeiten des heterogenen Elektronentransfers und die Transferkoeffizienten werden mit Hilfe von ′cyclischen Voltammogrammen und Digital‐Simulationen von Voltammogrammen bestimmt, und die Kinetik der chemischen Folgereaktionen wird untersucht.

Electrochemical reduction of sym-dibenzocyclooctatetraene, sym-dibenzo-1,5-cyclooctadiene-3,7-diyne, and sym-dibenzo-1,3,5-cyclooctatrien-7-yne

A study of the electroreduction of sym-dibenzocyclooctatetraene (DBCOT), sym-dibenzo1,5-cyclooctadiene-3,7diyne (DBCOD) and sym-dibenzo-l,3,5-cyclooctatrien-7-yne (DBCOM) in DMF-TBAP solutions was carried out to investigate the effects of differences in the structure of the central eight-membered ring on the electrochemical behavior. The reversible half-wave potentials ( E , 1 2 9 , heterogeneous electron-transfer rate constants ( k s ) , transfer coefficients, and pseudo-firstorder rate constants of the following chemical reactions were determined by cyclic voltammetric-digital simulation techniques. The results are consistent with reduction of tub-shaped DBCOT to a planar radical anion and dianion and of planar or almost planar DBCOM and DBCOD to planar radical anions. Estimates of the energy of the conformational change were obtained by comparison of E 119 to calculated energies of the lowest unoccupied molecular orbital and from the k , values. The electrochemical behavior of cyclooctatetraene (COT) and related compounds and the electron spin resonance (ESR) of the associated radical anions have been the subjects of numerous investigations.2-8 The general picture which emerges is that reduction of the tub-shaped COT produces a planar or nearly planar radical anion (COT.-); the large change in molecular geometry leads to a high activation energy and hence slow electron-transfer rates. The second reduction step to the dianion involves only small changes in geometry and hence more rapid electron transfer. A more detailed explanation of the experimental results requires taking account of solvation changes, ion pairing effects, and following protonation reactions. Recently, Wong, Garratt, and Sondheimerg reported the synthesis of sym-dibenzo-l,5-cyclooctadiene-3,7-diyne (DBCOD) and sym-dibenzo1,3,5-cyclooctatrien-7-yne (DBCOM). The central eight-membered ring in these com-

A magnetic resonance study of the monoanions of cyclooctatetraene and 1,3,5,7-tetramethyl cyclooctatetraene, produced in single crystals of K2C8H8· diglyme, Rb2C8H8· diglyme and K2(CH3)4C8H4· (diglyme)2

Single-crystal E.S.R. studies of the monoanions of cyclooctatetraene (COT) and tetramethyl cyclooctatetraene (TMCOT) produced by X-irradiation of M2COT·diglyme (Dg) (M=K, Rb) and K2TMCOT·2Dg, respectively, are reported. The experimental g tensors of these anions are compared with the principal values calculated for the free COT anion. From the hyperfine interactions at room temperature it could be concluded that the COT anion rapidly rotates around its eightfold axis. The spectra at 20 K (where the rotation is slow on the E.S.R. time scale) reveal an alternating spin density of 20 per cent at the eight carbon atoms. An interpretation for this is given in terms of crystal-field interactions and vibronic coupling. From the temperature behaviour of the E.S.R. spectrum of the TMCOT anions it is shown that the frequency of the methyl group rotation falls below the hyperfine splitting frequencies between 50 K and 20 K. From the analysis of the hyperfine splitting at different temperatures it can be concluded th...

Photodegradation mechanisms in laser dyes: A laser irradiated ESR study

The photodegradation mechanisms in xanthene dye-laser solutions are investigated at 77 K by the direct detection of a decrease in the concentration of dye molecules in the lowest excited triplet state (T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> state) and of free radicals produced after degradation using an ESR technique under UV (3511 + 3638 Å) or 5145-Å laser irradiations. It is shown that the ESR spectral shape of the radicals induced by an UV laser beam is quite different from that of those induced by a 5145-Å beam. For those radicals, the irradiation time and power dependences, the effects of dye and solvent molecular structures and the role of the T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> state by the addition of cyclooctatetraene (COT) quenchers are examined in some detail. As a result the two following laser-induced photochemical reactions are proposed: in UV laser- or flashlamp-pumped dye lasers, the C-H bond rupture of a solvent molecule due to the energy transfer of a dye molecule in a higher excited triplet state, which is produced by a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T-T</tex> absorption of a dye molecule in the T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> state, results in a radical and a leuco compound of the dye. On the other hand, in the case of the 5145-Å laser excitation, a partially reversible change of a dye molecule in the T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> state produced by only a one-photon absorption results in another radical which depends on the chromophoric structure of the dye.

Hydrocarbon complexes of iron, ruthenium, and osmium. Part VIII. Isolation of η-(1,1,1-tricarbonyl-1-metallainden-1-yl) tricarbonylmetal-(M–M)[M = iron, ruthenium, or osmium] complexes: crystal and molecular structure of η-(1,1,1-tricarbony-1-osmainden-1-yl)tricarbonylosmium (Os–Os)

Treatment of [Os(MMe3)2(CO)4](M = Si or Ge) or [{Os(SiMe3)(CO)4}2] with cyclo-octatetraene (COT) gives primarily the 1,2,3,3a,6a-η-1,4,5,6-tetrahydropentalenyl complexes [Os(MMe3)(CO)2(C8H9)], with minor formation of [Os2(CO)6(C8H10)] and of complexes of unidentified dimers of COT, [Os(CO)2(C16 H16)] and [Os(CO)3(C16 H16)]. The latter is also formed on heating [Os3(CO)12] with COT in octane. Under u.v. irradiation a moderate yield of [Os(CO)3(C8H8)] is obtained from [{Os(SiMe3)(CO)4}2] and COT. Dimethyl(tetracarbonyl) osmium and cyclo-octatetraene afford a complicated mixture from which η-(1,1,1-tricarbonyl-1-osmainden-1-yl)tricarbonylosmium (Os–Os), [Os2(CO)6(C8H6)], was obtained and characterised by X-ray diffraction. Crystals are triclinic(P) with two molecules per unit cell [a= 7.973(4), b= 10.684(4), c= 9.191(3)A, α= 89.16(3), β= 99.28(3), γ= 91.75(3)°]. The structure was solved by conventional heavy-atom methods from 2 152 independent reflections and refined to R= 0.053 (R′= 0.064). One osmium atom has been incorporated with the eight carbon atoms of the original cyclo-octatetraene ring to form a planar osmaindenyl system. The second osmium atom is bonded to the first [Os–Os = 2.754(2)A] and is also η4-bonded to the four carbon atoms of the 5-membered ring, thereby achieving octahedral co-ordination.Debromination of 1,4-dibromocyclo-octatetraene with [Fe2(CO)9] or [Fe(CO)4]2– affords benzocyclobutadiene-(tricarbonyl)iron. In refluxing hydrocarbons. [Fe2(CO)9] or [Ru3(CO)12] and 1,4-dibromocyclo-octacetraene yield the metallainden-1-yl complexes [M2(CO)6(C8H6)](M = Fe or Ru).

The addition of dimethylsilylene to cyclooctatetraene

The addition of dimethylsilylene to cyclooctatetraene

ChemInform Abstract: CRYSTAL AND MOLECULAR STRUCTURE OF NONAMETHYLCYCLOTETRAPHOSPHONITRILIUM PENTACARBONYLIODOCHROMATE(0)

Crystals of the title compound are triclinic, a= 14·632(21), b= 10·364(10), c= 10·765(9)A, α= 89·65(9), β= 106·98(13), γ= 63·72(7)°, Z= 2, space group P. The structure was determined from diffractometer data by Patterson and electron-density maps, and was refined by full-matrix least-squares methods to R 0·053 for 2112 observed reflexions. The anion has approximate C4v symmetry. Mean Cr–C bond lengths cis to I are 1·893 A and the trans Cr–C bond length is 1·859 A. Mean C–O is 1·135, and the Cr–I 2·790 A. The phosphonitrilic ring has an unusual distorted tub conformation, probably as a result of steric requirements. Bond length inequalities in the phosphonitrilic ring are discussed and compared with the P–N bond lengths in the [N4P4Me8H+]ion.