CO substitution in the mixed-metal clusters PhCCo2Ni(CO)6Cp and PhCCo2Mo(CO)8Cp by (Z)-Ph2PCH=CHPPh2. X-ray diffraction structures and proof of ligand bridging in PhCCo2Ni(CO)4[(Z)-Ph2PCH=CHPPh2]Cp and PhCCo2Mo(CO)6[(Z)-Ph2PCH=CHPPh2]Cp

The heterometallic tetrahedrane clusters PhCCo₂Ni(CO)₆Cp (1) and PhCCo₂Mo(CO)₈Cp (3) react with the unsaturated diphosphine ligand (Z)-Ph₂PCH=CHPPh₂ at elevated temperature to afford the corresponding phosphine-substituted clusters PhCCo₂Ni(CO)₄[(Z)-Ph₂PCH=CHPPh₂]Cp (2) and PhCCo₂Mo(CO)₆[(Z)-Ph₂PCH=CHPPh₂]Cp (4). Clusters 2 and 4 have been isolated by column chromatography and characterized in solution by IR and NMR (¹H and ³¹P) spectroscopies, and the solid-state structures of these clusters have been determined by X-ray crystallography. PhCCo₂Ni(CO)₄[(Z)-Ph₂PCH=CHPPh₂]Cp crystallizes in the triclinic space group P-l, a = 10.8142(7), b = 10.8994(6), c = 17.661(2) Å, α = 82.870(6), β = 86.149(7), γ = 64.493(5)^°, V = 1864.0(2) ų, Z = 2, D _cacl = 1.495 g/cm³; R = 0.0409, R _w = 0.0424 for 3147 observed reflections with I > 3σ(I). PhCCo₂Mo(CO)₆[(Z)-Ph₂PCH=CHPPh₂]Cp, as the hexane solvent, crystallizes in the monoclinic space group P2₁/c, a = 12.706(4), b = 17.367(3), c = 21.639(7) Å, β = 106.48(3)^°, V = 4579(1) ų, Z = 4, D _cacl = 1.478 g/cm³; R = 0.0605, R _w = 0.0724 for 1330 observed reflections with I > 3σ(I). The solid-state structures of 2 and 4 confirm a bridging coordination mode for the (Z)-Ph₂PCH=CHPPh₂ ligand, with adjacent cobalt centers being ligated by the ancillary phosphine ligand. The structural highlights of these new mixed-metal clusters are discussed relative to the homometallic tetrahedrane cluster PhCCo₃(CO)₇[(Z)-Ph₂PCH=CHPPh₂].     

Surjectivity for Hamiltonian loop group spaces

Let G be a compact Lie group, and let LG denote the corresponding loop group. Let (X,) be a weakly symplectic Banach manifold. Consider a Hamiltonian action of LG on (X,), and assume that the moment map :XL ^* is proper. We consider the function ||²:X, and use a version of Morse theory to show that the inclusion map j:^-1(0)X induces a surjection j ^*:H _G ^*(X)H _G ^*(^-1(0)), in analogy with Kirwans surjectivity theorem in the finite-dimensional case. We also prove a version of this surjectivity theorem for quasi-Hamiltonian G-spaces.     

X-ray diffraction structure of (5S)-3,4-dichloro-5-menthoxy-2(5H)-furanone

The structure of (5S)-3,4-dichloro-5-menthoxy-2(5H)-furanone is reported. The title compound crystallizes in the monoclinic space group P2₁: a = 6.650(2) Å, b = 8.038(3) Å, c = 14.858(8) Å, = 97.01(3), V = 788.3(6) ų, Z = 2, R = 0.0718, R _w = 0.0795 for 735 observed reflections with I > 3 (I), and the absolute configuration at C-5 of the furanone ring is shown to be (S).     

Structure of the product formed via Cu(I)-promoted oxidative dimerization ofexo-8-ethynylpentacyclo[5.4.0.02,6.03,10.05.9]undecan-endo-8-ol

The structure consists of two acetyl-substituted PCU cages linked by a diyne fragment. The conformation about the linker is midway between staggered and eclipsed, and the acetyl groups are somewhat distorted due to the proximity to the bulky cage units.     

Mass transfer into near-critical extractants

One advantage which is often claimed for extraction operations carried out with near-critical extractants is that higher mass transfer rates may be obtained than with normal liquid extract. Although there is circumstantial evidence that this is the case, quantitative information is scarce.

On-going work at Birmingham which is directed towards the measurement of mass transfer rates into near-critical fluids and also the measurement of the associated phase equilibrium properties is described. Some new results are given, although the rate data presented are regarded as preliminary only. The extractant principally considered is carbon dioxide.     

The kinetics and thermochemistry of S2F10 pyrolysis

Data on the kinetics of S₂F₁₀ pyrolysis, which gives SF₄ + SF₆, have been reinterpreted to give a value for the equilibrium constant of S₂F₁₀ ? SF₄ + SF₆. This, together with statistical estimates of the entropy and heat capacity of S₂F₁₀, can be used to give for this reaction values of ΔH = 19.7 ± 1.0 kcal/mole and ΔS = 47.6 ± 2 gibbs/mole. ΔH(S₂F₁₀) = –494 kcal/mole. A compatible mechanism is shown to be S₂F₁₀ ? 2SF₅ (fast); 2SF₅ ? SF₆ + SF₄ (slow) with step 2 rate-determining. The overall, best first order rate constant is proposed as k_meas = 10^{17.42–43.0/θ} sec^?1 = K₁k₂, where θ = 2.303RT in kcal/mole. Independent measurements of δH and S° for the SF₅ radical, permits the evaluation of the equilibrium constant K₁ = 10^{8.92–(27.1 ± 6)/θ} l./mole-sec and yields k₂ = 10^{8.50–15.9/θ} l./mole-sec. The observed homogeneous catalysis by NO and CHCl ? CHCl can be explained in terms of a direct abstraction of F from S₂F₁₀ : C + S₂F₁₀ → CF + S₂F₉, followed by S₂F₉ → SF₅ + SF₄ and SF₅ + CF ? SF₆ + C (C ? NO or C₂H₂Cl₂).     

Crystal structures of three substituted pentacyclo[5.4.0.02,6.03,10.05,9]undecanes

The crystal structures of three compounds formed via ultimate nucleophilic attack of unsaturated hydrocarbon fragments are reported. Geometries of the bis(vinyl)-, mono(vinyl), and bis(ethynyl)-substituted PCU species are unexceptional. The crystal structures are dictated by the availability of intermolecular hydrogen bonding.