Hydrocarbon chemistry : by G.A. Olah (C. Eaborn). J. Organomet. Chem., 334 (1987) C49-C50.

Sequential displacement of both N₂ ligands from cis-[Mo(N₂)₂(PMe₂Ph)₄] by CNMe occurs by a dissociative (I_d) mechanism (k₂/k₁～5,k₁ 0.020 min^?1 at 273 K) via the intermediate cis-[Mo(N₂)(CNMe)(PMe)₂Ph)₄] For t-BuNC substitution, the only detected intermediate appears to be [Mo(CNBu-t)(PMe₂Ph)₄] and no intermediate was detected in reactions of trans-[Mo(N₂)₂(Ph₂PCH₂CH₂PPh₂)₂] with CNMe. N₂ appears to be labilised by cis-ligands in the order t-BuNC > CNMe > N₂ > NCR.     

Determination of the ionization quantum yield and thermalization distance of photoelectrons created by v.u.v. photoionization in pure liquid alkanes and tetramethylsilane

The photocurrents, in liquid n-hexane, n-pentane, cyclohexane, cyclopentane, 2-2-4 trimethylpentane, 2-2 dimethylbutane, neopentane and tetramethylsilane, produced by v.u.v. irradiation, are measured at electric fields from 2 to 35 kV cm^-1. Assuming the one- and three-dimensional Onsager probabilities are respected, the values of the attenuation parameter of the photon flow B₁, the quantum yield for the production of an ion-pair θ_i, and the attenuation parameter of the photoelectron flow B₃ can be deduced. These values are compared with those provided by other injection methods. Both the validity of these values and the theoretical models are discussed. The discussion is extended to other parameters: V₀, μ₀ and K_J, all correlated to emission and propagation mechanisms in non-polar liquids.     

Transition metal clusters : edited by B.F.G. Johnson, John Wiley and Sons, Inc. Chichester/New York/Brisbane/Toronto, 1980, 681 pages, $ 96.50.

The complexes cis-[V(CO)₄LL] (where LL is a ditertiary phosphine), V(CO)₅PPh₃ and {V(CO)₅}₂-μ-{p-C₆H₄(PPh₂)₂} were prepared by oxidation of the corresponding anionic compounds with tropylium tetrafluoroborate. IR and selected ESR data are presented.     

Advances in inorganic chemistry and radiochemistry,vol. 18: Edited by H.J. Emeléus and A.G. Sharpe,Academic Press,New York/San Francisco/London, 1976, vii + 414 pages, $35.50.

The catinic complex trans-[FeCl(CCHPh)(depe)₂]⁺ (depe = bis(diethylphosphino)ethane has been prepared by interaction of trans-[FeCl₂(depe)₂] with penylacetylene in methanol solution in the presence of NaX (X = BPh₄ or PF₆.     

The cationic polymerization of fluoral—III. Thermodynamics of polymerization in solution

The equilibrium between fluoral in dichloromethane solution and live condensed liquid polyfluoral has been investigated between 22 and 43°C. Equilibrium monomer concentrations gave: ΔH_ac°(298 K) = -50-8 ± 2·3 kJ mol^?1 and ΔS_sc° (298 K) = -142·7 ± 7·4 J K^-1 mol^-1. With the aid of calibration and monomer vaporization data, thermodynamic values for the polymerization of liquid monomer to liquid polymer were also calculated: ΔH_tc° (298 K) = -47 ± 3 kJ mol^-1 and ΔS_1e° (298 K) = -97 ± 10 J K^-1 mol^-1.     

Chemicals from Synthesis Gas : By Robert A. Sheldon (Series: Catalysis by Metal Complexes) D. Reidel Publishing Company,Dordrecht, The Netherlands, 1983, xx + 216 pages,Dfl. 110.00, US$ 48.00. ISBN 90-277-1489-4.

Photolysis of cis-HMn(CO)₄PPh₃ in the presence of H₂ and 1-alkene results in catalytic hydrogenation and isomerization of the alkene. The isomerization leads to cis- and trans-2-alkene in the presence or absence of H₂. Catalytic hydrogenation also occurs when cis-CH₃Mn(CO)₄PPh₃ is irradiated in the presence of H₂; use of D₂ leads exclusively to CH₃D. The possible mechanism of the hydrogenation is discussed.     

Raman and i.r. studies of phase transitions in (CH3)3NHClO4

(CH₃)₃NHClO₄ belongs to the monoclinic system with space group P2₁/m (C²_2h) at 300 K. Raman and i.r. spectra (20-5000cm⁻¹) of single crystals and polycrystalline samples of (CH₃)₃NHClO₄ and its N-deuterated derivative were investigated in the temperature range 90-500 K. A systematic temperature-dependence study of the frequencies and band-widths show the existence of phase transitions at 397 and 480 K. The main features of the spectra, particularly in the ambient temperature phase, are assigned with the aid of factor group analysis. The spectral changes indicate that both cations and anions undergo quasiisotropic motion in phases II and I and self-diffusion in phase I.     

Pyrolysis of polypropylene: II. Kinetics of degradation

The kinetic law dα/dr=k(1-α)[1-(1-α)^2b]^1,2 proposed for the pyrolysis of polystyrene is shown to be valid for the pyrolysis of polypropylene taking into account only the percentage of isotactic polymer.As the experimental activation energy of 265 kJ mol^?1 is of the same order of magnitude the as the theoretical energy calculated by the equation E = 1 2 (E_ir-E_r)-E_r it can be concluded that the decomposition mechanism is governed by a depolymerization reaction as the principal products obtained are compounds with 3n carbon atoms.     

The unattainability of a unified E.M.F. series for molten salts the relation between the temperature coefficient of isothermal cells and the thermoelectric coefficients of thermocells

It is shown that the e.m.f. of a cell (T₁) A¦AX¦BX¦B (T₂) can not be split unambiguously into a combination of an isothermal cell A¦AX¦BX¦B either at T₁ or at T₂ and a thermocell either B¦BX¦B or A¦BX¦A between T₂ and T₁. The difference Δ in e.m.f. of both possible combinations is equal to FΔ/(T₂ - T₁) = ^*S(X^? in AX) - ^*S(X^? in BX).In examples given for molten silver and cuprous halides this difference in transported entropies is 1–2 cal mol^?1 K^?1 or Δ equal to 17.5–35 mV for T₂ - T₁ = 400 K. It is impossible to obtain unambiguously a unified e.m.f. series. The same qualitative conclusion is reached on the basis of the second law of thermodynamics from a discussion of an irreversible cyclic process involving the four cells mentioned.     

Progress in NMR spectroscopy,Volume 11 : edited by J.W. Emsley,J. Feeney and J.R. Sutcliffe,Pergamon Press,Oxford, 1978, vii + 298 pages; $ 40.00 (£ 20)

Protonolysis of the complexes trans-[Pt(PEt₃)₂(R)(Me)] (R = C₆H₅ ; m-MeC₆H₄ ; o-MeC₆H₄ ; m-FC₆H₄ ; p-FC₆H₄ ; m-CF₃C₆H₄ and C₆F₅) by hydrogen chloride in methanol/water ($\text{90}\text{10}$ v/v) selectively cleaves the alkyl group yielding trans-[Pt(PEt₃)₂(R)Cl] and methane. A kinetic study of these reactions suggests that the primary step involves a proton transfer to the carbonmetal σ-bond with release of CH₄ in a three-center transition state.     

Insertion vs. site epimerization with singly-bridged and doubly-bridged metallocene polymerization catalysts

A statistical model has been employed to determine the unidirectional site epimerization probability, ε, during propylene polymerization with the following C₁-symmetric metallocene precatalysts activated with MAO (MAO = methylaluminoxane): doubly-bridged rac-(1,2-SiMe₂)₂{η⁵-C₅H₂-4-(CHMe(CMe₃))}{η⁵-C₅H-3,5-(CHMe₂)₂}ZrCl₂ (1) and (1,2-SiMe₂)₂{η⁵-C₅H₂-4-(1R,2S,5R-menthyl)}{η⁵-C₅H-3,5-(CHMe₂)₂}ZrCl₂ (2); and singly-bridged Me₂C(3-(2-adamantyl)-C₅H₃)(C₁₃H₈)ZrCl₂ (3) and Me₂Si(3-(2-adamantyl)-C₅H₃)(C₁₃H₈)ZrCl₂ (4). For 1/MAO a steep tacticity dependence on monomer concentration was found, as ε increased from 0.114 to 0.909 as [C₃H₆] decreased from 12.5 M to 0.5 M; similarly, ε increased for 2/MAO from 0.177 to 0.709. For 3/MAO, ε was moderately responsive to an increase in polymerization temperature, as ε increased from 0.000 to 0.485 from T_p = 0-90 °C ([C₃H₆] = 1.1 M). Similarly, ε increased for 4/MAO from 0.709 to 0.913 from T_p = 0-40 °C; at higher temperatures, bidirectional site epimerization was implicated.     

Derivatographic studies on transition metal complexes XV. Thermal isomerization of trans-[CrBr2pn2]Br.H2O in solid phase

The thermal trans-to-cis isomerization of [CrBr₂pn₂]Br·H₂O in a solid phase was studied by means of both derivatography and isothermal measurement. It was found that trans-[CrBr₂pn₂]Br·H₂O undergoes isomerization to the cis-complex by about 10% with complete dehydration followed by isomerization of the residual trans complex in the anhydrous state. It was characteristic of the complex, trans-[CrBr₂pn₂]Br·H₂O, that the thermal dehydration was remarkably rapid in comparison with that of the trans-[CoCl₂pn ₂](H₅O₂)Cl₂ and the isomerization of the cis complex occurred even in the anhydrous state though it did not in the corresponding cobalt(III) complex trans-[CoBr₂pn₂](H₅O₂)Br₂ in an analogous state.     

Catalytic synthesis of 1,4-hexadiene by a nickel-based catalyst. Factors controlling activity and selectivity

The nature of the phosphine ligand and the aluminum cocatalyst strongly affect activity and stereoselectivity in the Al/Ni/P type (e.g. R_nAlX_3−n + NiX₂ · 2 PR₃ or Ni⁰[L] + R₃P) catalyst system to synthesize trans- and cis-1,4-hexadiene from ethylene and butadiene.     

The triplet state of photosynthetic pigments. I. Pheophytins

ZFS constants (in cm^?1) and decay rate constants for the lowest triplet state of pheophytins have been determined by ESR: pheophytin a: D = 341 ± 3,E = 33 ± 3, K_T = 1050 s^?1; pheophytin b: D = 358 ± 8, E = 46 ± 5, K_T = 630 s^?1; bacteriopheophytin: D = 256 ± 4, E = 54 ± 5/37 ± 5, K_T ≈ 4000 s^?1. In addition values for the decay rate constants and relative populating rates of the individual spin levels have been obtained; these numbers turn out to be appreciably different from those for the corresponding chlorophylls. For the series pheophytin a, b and bacteriopheophytin we find parallel behaviour with the corresponding chlorophylls. The effects of side group substitution and pyrrole ring reduction on the ZFS constant D can be understood by including configuration interaction between the excited states using the 4-orbital model. The change of the mean triplet decay constant K_T upon side group substitution and pyrrole ring reduction follows an energy gap law. Substitution of the central Mg-ion by two protons, however, causes K_T to increase; this is attributed to the introduction of an extra promoting mode - of the NH-group - and/or to the presence of low lying nπ^* states in pheophytins.     

Directional metal-hydrogen bonding in interstitial hydrides. III. Structural study of ErCo3Dx (0?x?4.3)

The ErCo₃-D₂ system has been studied by in situ neutron powder diffraction (NPD) at 60 °C and 0-16 bar deuterium pressure. Two deuteride phases were identified, β-ErCo₃D_1.07−1.38 and γ-ErCo₃D_3.7−4.3. They were structurally characterized at the compositions β-ErCo₃D_1.37 and γ-ErCo₃D_3.7 by high-resolution neutron and synchrotron powder diffraction. In contrast to the analogous nickel systems RNi₃-D₂ (R=Er, Ho; see part I, J. Alloys and Compds. 404-406 (2005) 89-94, and part II, J. Alloys and Compds. 2005, in press), their structures preserve the symmetry of the parent alloy (PuNi₃-type, space group R-3m). Deuterium occupies mainly AB₂ building blocks in the β-phase, and AB₂ and AB₅ building blocks in the γ-phase. In the AB₂ building blocks cobalt is surrounded by an average of 3.8 (β-ErCo₃D_1.37) and 4.4 D-atoms (γ-ErCo₃D_3.7) in disordered distorted octahedral configurations (point symmetry −3), in contrast to nickel that is surrounded by ∼3 (β₁- and β₂-RNi₃D_x, R=Er, Ho) and ∼4 (γ-ErNi₃D_3.7) D-atoms in disordered trigonal (pyramidal) and tetrahedral configurations, respectively (point symmetry 3). These results indicate that the D-atom distributions in this homologous series depend on the nature of the transition element rather than on geometric factors, and that directional bonding effects similar to those in non-metallic complex transition metal hydrides also prevail in metallic interstitial metal hydrides.     

H.T. Clarke,A handbook of organic analysis,qualitative and quantitative, (Fifth Edition), Edward Arnold,London (1975), Revised by B. Haynes,with E.C. Brick and G.G. Shone,pp. x + 291, price £12.00 (clothbound), 4.95 (paperback)

Ab initio calculations at minimal (STO-3G) and extended (4-31G) basis levels have been carried out for the cyclopropylcarbinyl radical using the unrestricted Hartree-Fock procedure. It is found that the ordering of the long-range proton isotropic hyperfine coupling constants are opposite to the results obtained from semi-empirical INDO calculations. The coupling constants for the extended basis set are a_exo = ?1.71 G, a_endo = ?4.25 G, a_β= 11.41 G, a_α1 = ?66.01 G and a_α2 = ?64.73 G.     

Chlorures vinyliques : I. Lithiation directe; radicaux vinyliques

Reaction of E- and Z-4-chlorohept-3-enes (R_ZCl and R_ECl with lithium gives reduction products in addition to the organolithium compound. This reduction occurs with partial inversion of the double bond while retention of configuration takes place when the n-butyllithium exchange reaction is used.A partial inversion also occurs when _Z- and _E-4-bromohept-3-enes (R_ZBr and R_EBr) are formed from exchange with the corresponding vinylic organolithium and dibromoethane.A vinylic radical is postulated to explain the lack of stereospecificity during the formation of the

Li bond in the reaction with lithium.     

Polyhydroxylated pyrrolizidines. Part 8. Enantiospecific synthesis of looking-glass analogues of hyacinthacine A5 from DADP

(1R,2S,3S,5R,7aR)-1,2-Dihydroxy-3-hydroxymethyl-5-methylpyrrolizidine[(−)-3-epihyacinthacine A₅, 1a] and (1S,2R,3R,5S 7aS)-1,2-dihydroxy-3-hydroxymethylpyrrolizidine[(+)-3-epihyacinthacine A₅, 1b] have been synthesized either by Wittig's or Horner-Wadsworth-Emmond's (HWE's) methodology using aldehydes 4 and 9, both prepared from (2S,3S,4R,5R)-3,4-dibenzyloxy-2′-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine (2, partially protected DADP), and the appropriate ylides, followed by cyclization through an internal reductive amination process of the resulting α,β-unsaturated ketones 5 and 10, respectively, and total deprotection.     

A new approach to the synthesis of oligomers. Application to the synthesis of p-phenylene thioether wires

Oligothioethers 4-RC₆H₄(SC₆H₄-4)_nX (n = 1-3; X = Br, I; R = NO₂; X = Br; R = MeO. n = 1 and 2; X = I; R = MeO. n = 4; X = Br; R = NO₂) have been prepared through a process involving (i) palladium-catalyzed C-S coupling between 4-RC₆H₄(SC₆H₄-4)_n−1I and 4-BrC₆H₄SH to give 4-RC₆H₄(SC₆H₄-4)_nBr and (ii) copper-catalyzed replacement of Br by I.     

The use of CO2 gas as an in-situ dosimeter for d.c. and microwave pulse-radiolysis conductivity experiments

Carbon dioxide gas at a few hundred torr pressure is proposed as a convenient, in-situ dosimetric and test medium for d.c. and microwave pulse radiolysis conductivity experiments. The dose in gray is related to the (pressure independent) conductivity by D_g=2.89 × 10² σ_CO2 where σ_CO2 is the radiation induced conductivity in units of ω^-1m^-1. The measurement of σ_CO2 and the parameters required for extrapolation to other gaseous and condensed media are discussed. The time required for electron thermalization in CO₂ gas at atmospheric pressure is determined to be approximately 100 ps.