“Olefin metathesis” reactions of (η5-C5H5)NiRu3(μ-H)(CO)9-(μ4-η2)-(CCHBut) and related complexes

The complex (η⁵-C₅H₅)NiRu₃(μ-H)(CO)₉(μ₄-η²-CCHBu^t) (1a) reacts with olefins to give several organic products, including species derived from the coupling of the vinylidene ligand with an olefin-derived =CRR′ fragment, representing the first example of a (non catalytic) olefin metathesis reaction involving a metal cluster; other complexes structurally or chemically related to the compound 1a have also been treated with olefins and alkynes.     

The first nitrosyl derivatives of high nuclearity carbonyl clusters: Synthesis and X-ray analysis of the [(Ph3P)2N]+ salts of the anions [Os10C(CO)24(μ2-NO)]− and [Os10C(CO)23(NO)]−

The carbido dianion [Os₁₀C(CO)₂₄]^2? reacts with NOBF₄ in MeCN to give [OS₁₀C(CO)₂₄(μ₂-NO)]^? (1) in which the nitrosyl ligand adopts a novel bonding mode bridging the wingtips of a “butterfly” indentation of metal atoms. The anion 1 undergoes rearrangement and CO loss in solution to give [OS₁₀C(CO)₂₃(NO)]^? (2); the overall molecular geometry of 2 is close to that previously found for the dianion [Os₁₀C(CO)₂₄]^2? with the nitrosyl ligand bonded in a terminal fashion to the tetrahedral Os₁₀ metal skeleton. Crystals of the [(Ph₃P)₂N]⁺ salt of 1 are triclinic, space group P$\text{1}$, with a 20.389(4), b 14.670(3), c 12.333(3) Å, α 99.55(3), β 94.43(3), γ 103.03(3)°, Z = 2, refinement of atomic parameters using 2699 absorption corrected data converged at R = 0.0952. The [(Ph₃P)₂N]⁺ salt of 2 crystallises with one molecule of CH₂Cl₂ in the triclinic space group P$\text{1}$, with a 19.374(3), b 16.813(3), c 11.791(2) Å, α 85.00(3), β 101.81(3), γ 99.43(3)°, Z = 2, refinement of atomic parameters using 8736 absorption corrected data converged at R = 0.0943.     

Asymmetrical nitrogen-40;1 Geminal systems-261 N-chlorohydrazines3

The factors determining the kinetic and thermodynamic stabilities of N-chlorohydrazines are discussed. Acyclic N-chlorohydrazines exist only as trialkyldiazenium chlorides 3a,b. Chlorination of 2-acyl-1, 1-dimethylhydrazines 6a,b gave 1,4-diacyl-2,3-dimethylhexahydro-1,2,4,5-tetrazines 7a,b via hydrazyl radical intermediates, and chlorination of a 1-phenylpyrazolidin-5-one 8 gave phenylazoisovaleric esters 9a,b. Stable N-chlorohydrazines were obtained from bicyclic hydrazines; viz. the 2-chloro-1,2-diazabicyclo [2.2.2]octan-3-one 12 and 7-chloro-1,7-diazabicyclo[2.2.1]heptane 16. The restricted inversion of N(7) in 16 and its 1-methyl quaternary salt 21 were observed in the ¹³C-NMR spectra. The acyclic N-chloro-hydrazinium salt 25 was isolated.     

Potential energy curve of 1Σ+ Li+/He

The potential energy curve of the system Li⁺/He has been determined with moderately large basis sets for 0.5 ? r ? 10.0 a₀ both at the SCF level and including correlation. The present SCF results predict a deeper well (?0.00248 au) at a smaller r(3.66 a₀) compared with earlier calculations. Correlation deepens the well further (?0.00274 au), but pulls it inward slightly (3.63 a₀). In the repulsive part the calculated curve lies above the experimental one, especially at shorter distances. A similar behavior has been noted in the systems Li⁺/H₂, Li⁺/CO and Li⁺/N₂, suggesting that the experimental determinations may underestimate the interaction in this region by 10–20%.     

Photolysis of 3-oxo-δ5(10)-steroids in alcoholic solvents and in the solid phase

Irradiation of the β, γ-unsaturated ketone 1a in alcoholic solvents afforded the 1,2 and 1,3-acyl shift products 2a and 3 respectively. The cyclobutanone 3 underwent further photochemistry incorporating a molecule of solvent and affording the ring expanded cyclic acetal 6. Solid phase irradiation of 1a yielded 2a and 3 but 1b was photostable.     

An INDO-LMO and 13C NMR spectroscopic study of the C-H bonds in tetracyclo[3.2.0.02,7.04,6]heptane (quadricyclane) and tricyclo[3.1.0.02,4]hexane

Using an INDO approximation to Von Niessen's charge density localization method, the percent s character of the C atom hybrid orbitals engaged in C-H bonds is computed for a series of open-chain and cyclic saturated and unsaturated hydrocarbons. A semi-empirical linear relationship is found between these quantities and the experimental nuclear spin-spin coupling constants J_CH (standard deviation 4·98 Hz). The experimental values of J_CH were measured for quadricyclane (1) and tricyclo[3.1.0.0^2,4]hexane (2) and were shown to be in fair agreement with the theoretical predictions. An analogous relationship is also established between the percent s character of the involved C atom hybrid orbital and the C-H bond distance, the standard deviation being 0·0040Å. This relation is used in order to predict the different C-H bond lengths in the vibrational ground state of 1 and 2, for which equal CH distances were assumed in the analysis of electron diffraction experiments. The results indicate that molecular geometries can be refined with the use of semi-empirical correlations of the above mentioned type.     

The pheophytin a anion radical. 14N and 1H endor and triple resonance in liquid solution

From electrolytically generated phcophytin a anion radicals in solution, 12 proton and 2 nitrogen hyperfine coupling constants, including signs, were determined by ENDOR and TRIPLE resonance and interpreted by MO calculations. The data are compared with those from the anion radicals of chlorophyll a and the bacterial analogues bacteriopheophytin a and bacteriochlorophyll a.     

Radikalkomplexe vom typ Cp(CO)2MnXR. (X = S,Se)

CpMn(CO)₂ER (E = S, Se) compounds [1] belong to the rare radical derivatives of the CpMn(CO)₂ fragment. We describe herein the syntheses, electrochemistry, and organometallic reactions of CpMn(CO)₂SR ¹ (1a: R = t-C₄H₉, 1b: R = 2-adamantyl) and CpM(CO)₂SePh (2).     

1H,2H,19F and 31P NMR and ESR investigations of aryl-t-butyl nitroxides

Aspects of translocation of spin to fluorine and phosphorus are discussed. (2p–3d)_π overlap in phosphorus is insignificant. Spin polarization and (2p–3p)_π overlap are opposing spin transfer mechanisms for phosphorus. The³¹P NMR spectrum of the nitroxide from 7a shows some features which are not fully understood. Some gain in resolution of the NMR spectra can be achieved by deuteration, but it is considerably lower than predicted.     

Radiative lifetimes of the CO a′3Σ+, b3Σ+, c3Π, d3Δ and B1Σ+ states. Absolute emission cross sections for t

Radiative lifetimes have been measured for the CO a′³Σ⁺(ν′=4–9), b³Σ⁺(ν′= 0), c³Π(ν′=0), d³Δ(ν′=1–16) and B¹Σ⁺(ν′= 0) states. Our experimental values, arranged in the same order, are 7–10 μs, 56 ns, 16 ns, 3–7.5 μs, 34 ns. Some of these values disagree with the results of previous experiments. To our opinion this is due to an incomplete identification of the emission spectrum in regions where many bands may overlap, dependent on the applied spectral resolution. For the a′Σ⁺?a³Π and d³Δ?a³Π emissions effective cross sections for quenching by CO molecules are given. In connection with the identification of the spectrum, absolute emission cross sections for electrons incident on CO have been measured for the b³Σ⁺?a³Π and c³Π?a₃Π transitions. For an electron energy, corresponding to the maximum of the excitation function we find cross sections of 5.94 (?1.2) × 10^?18 cm² and 0.630 (? 0.13) × 10^?18 cm², respectively.     

Aufkl?rung der 1H- und 13C-NMR-spektren sowie der kristallstruktur unges?ttigter glycosylphosphonate und konformationsberechnungen an modellen1

By application of a modified LAOCN-3 program a complete elucidation of the ¹H NMR spectra of 2,3-unsaturated glycosyl phosphonates 1–5 could be achieved. The exactly determined ⁿJ(H, H) and novel ⁿJ(C, P) coupling constants are discussed, and permit a conclusive deduction of the conformations. The ¹³C NMR spectra of 1 to 6 can be fully interpreted. By a close inspection of chemical shifts as well as ¹J(C-H) and ⁿJ(C, P) coupling constants the conformational assignment is supported. For all the derivatives the correlations ¹J(C-1,H_e)>¹J(C-1, H_a) and ¹J(C-1, P_e) >¹J(C-1, P_a) can be used for the assignment of anomers. The crystal structure of 1 is in accordance with this assignment of anomers and displays an unexpected conformation. Calculations by MINDO-3 in resembling model compounds serve to elucidate such conformative effects.     

Hetero- and homo-nuclear bimetallic ruthenol complexes by dehydrogenative metallacyclization of Ru(CO)3(bi-1,7-cyclooctadienyl), preparation and x-ray structure of Fe(CO)3(C16H22), RuFe(CO)6(C16H22) and Ru2(CO)6(C16H20)

The reaction of M₃(CO)₁₂ (M = Ru, Fe) with excess bi-2,7-cyclooctadienyl (C₁₆H₂₂) 1 gave a mononuclear complex M(CO)₃(1,2,1′-2′-η⁴-C₁₆H₂₂), 2a (M = Ru) or 3a (M = Fe), in good yield. Treatment of 2a with Fe₃(CO)₁₂ or reaction of 3a with Ru₃(CO)₁₂ gave the heterobimetallic complex RuFe(CO)₆(C₁₀H₂₂) consisting of a ruthenacyclopentadiene unit coordinated to an Fe(CO)₃ fragment, as confirmed by ¹H NMR and X-ray studies. The corresponding homobimetallic complex Ru₂(CO)₆(C₁₆H₂₂) was obtained from the 1:1 reaction of 2a with Ru₃(CO)₁₂, while the direct reaction of 1 with Ru₃(CO)₁₂ gave Ru₂(CO)₆(C₁₆H₂₀) preferentially with a loss of two hydrogen atoms. The pathway for formation of these bimetallic complexes was interpreted as a dehydrogenative metallacyclization followed by hydrogen transfer.     

Synthesis of racemic and optically active Δ1- and Δ6-3,4-cis-tetrahydrocannabinols1

Three syntheses of the hitherto unknown (±)-Δ⁶-3,4-cis-THC 4a and the first total synthesis of optically active Δ¹- and Δ⁶-cis-THC's are described. These syntheses utilize a stereospecific intramolecular epoxide opening by phenolate anion; an acid catalyzed equilibration of Δ¹- and Δ⁶-cis-THC acetates; and a kinetically controlled dehydration. The use of HPLC, GLC and NMR for the separation and identification of closely related THC's is discussed.     

Stereochemical studies of 2-hydroxychromanones by 1H NMR spectroscopy

2-Hydroxychromanones (2a–2f) were synthesized by ring closing of 2-hydroxyacetophenones (1a, b) and 2-hyroxypropiophenones (1c–1f). In the case of 2-hydroxy-3-methyl-chromanones (2c–2f) a mixture of cis and trans isomers was obtained. The trans isomers are conformalionally homogeneous, the cis isomers exist in a conformational equilibrium. At room temperature the isomers are transformed into each other via opening of the heteroring. This process becomes faster in alkaline medium and the β-diketo form 4 can also be observed.     

Molecular structure of methyl 20-isopropyl-15(E)-hydroxyimino-5,9-dimethyl-18-oxahexacyclo [12.4.0.22,13.118,20.05,10.04,13]heneicosane-9-carboxylate

Methyl 20-isopropyl-15(E)-hydroxyimino-5,9-dimethyl-18-oxahexacyclo[12.4.0.2^2,13.1^18,20.0^5,10.0^4,13]-heneicosane-9-carboxylate is synthesized and its molecular structure is determined. Compound IIa of C₂₇H₄₁NO₄ crystallizes in the acentric P2₁ space group with the following unit cell parameters: a = 7.6511(7) ?,b = 12.0698(11) ?, c = 12.9182(12) ?, β = 95.257(2)°.     

Five-coordinate pentafluorobenzothiolate osmium(IV) complexes [Os(SC6F5)4(P(C6H4X-4)3)] (X = OCH3, CH3, F, Cl or CF3): Solid and solution structural characterization

The reactions of OsO₄ with excess of HSC₆F₅ and P(C₆H₄X-4)₃ in ethanol afford the five-coordinate compounds [Os(SC₆F₅)₄(P(C₆H₄X-4)₃)] where X = OCH₃ 1a and 1b, CH₃ 2a and 2b, F 3a and 3b, Cl 4a and 4b or CF₃ 5a and 5b. Single crystal X-ray diffraction studies of 1 to 5 exhibit a common pattern with an osmium center in a trigonal-bipyramidal coordination arrangement. The axial positions are occupied by mutually trans thiolate and phosphane ligands, while the remaining three equatorial positions are occupied by three thiolate ligands. The three pentafluorophenyl rings of the equatorial ligands are directed upwards, away from the axial phosphane ligand in the arrangement “3-up” (isomers a). On the other hand, ³¹P{¹H} and ¹⁹F NMR studies at room temperature reveal the presence of two isomers in solution: The “3-up” isomer (a) with the three C₆F₅-rings of the equatorial ligands directed towards the axial thiolate ligand, and the “2-up, 1-down” isomer (b) with two C₆F₅-rings of the equatorial ligands directed towards the axial thiolate and the C₆F₅-ring of the third equatorial ligand directed towards the axial phosphane. Bidimensional ¹⁹F–¹⁹F NMR studies encompass the two sub-spectra for the isomers a (“3-up”) and b (“2-up, 1-down”). Variable temperature ¹⁹F NMR experiments showed that these isomers are fluxional. Thus, the ¹⁹F NMR sub-spectra for the “2-up, 1-down” isomers (b) at room temperature indicate that the two S-C₆F₅ ligands in the 2-up equatorial positions have restricted rotation about their C–S bonds, but this rotation becomes free as the temperature increases. Room temperature ¹⁹F NMR spectra of 3 and 5 also indicate restricted rotation around the Os–P bonds in the “2-up, 1-down” isomers (b). In addition, as the temperature increases, the ¹⁹F NMR spectra tend to be consistent with an increased rate of the isomeric exchange. Variable temperature ³¹P{¹H} NMR studies also confirm that, as the temperature is increased, the a and b isomeric exchange becomes fast on the NMR time scale.     

CAS SCF Cl calculations for the 3Σ−g, 1Σ+g, 3Σ+u, and 5Δu states of Sc2

CAS SCF CI (SD) calculations have been carried out for the ³Σ^?_g, ¹Σ⁺_g, ³Σ⁺_u, and ⁵Δ_u states of Sc₂ using large gaussian basis sets. The ³Σ^?_g, ¹Σ⁺_g, and ³Σ⁺_u states arise from the ²D(4s² 3d¹) + ²D(4s² 3d¹) limit of Sc₂ and are found to be only weakly bound (D_c ≈ 0.06 eV and R_c ≈ 8.0a₀). The ⁵Δ_u state arises from the ²D(4s² 3d¹) + ⁴F(4s¹ 3d¹ 4p¹) atomic limit. This state is found to be strongly bound relative to its limits (D_c ≈ 0.8 eV and R_c ≈ 7.0a₀).     

Rotational analysis of the a3Π0+,1-X1Σ+ emission systems of GeH+

New emission systems have been observed from the helium afterglow reaction of GeH₄ in the 520–610 nm region. On the basis of the rotational analysis, they were assigned to the a ³Π_0⁺-X¹Σ⁺ and a³Π₁-X¹Σ⁺ subsystems of GeH⁺. Spectroscopic constants have been determined for the GeH⁺ (a³Π_0⁺, a³Π₁, X¹Σ⁺) states.     

Structures of cleomiscosins,coumarinolignoids of cleome viscosa seeds1

Structures of cleomiscosins A, B and C, three new coumarino-lignoids isolated from the seeds of Cleome viscosa Linné, have been established as 1a, 2a and 1f irrespectively, on the basis of spectral and chemical evidence. The compounds exhibited liver-protective properties.     

The energy balance and branching ratios associated with the chemiluminescent reaction Si(3P) + N2O(1Σ) → SiO*(a3Σ+, b3Π, A1Π) + N2(υ″ ⩾ 5) — possible formation of vibrationally excited N2

Silicon atoms react under single collision conditions with N₂O to yield chemiluminescent emission corresponding to the SiO a³Σ⁺?X¹Σ⁺ and b³Π?X¹Σ⁺ intercombination systems and the A¹Π?X¹Σ⁺ band system. A most striking feature of the SiN₂O reaction is the energy balance associated with the formation of SiO product molecules in the A¹Π and b³Π states. A significant energy discrepancy ( = 10000 cm^? = 1.24 eV) is found between the available energy to populate the highest energetically accessible excited-state quantum levels and the highest quantum level from which emission is observed. It is suggested that this discrepancy may result from the formation of vibrationally excited N₂ in a concerted fast SiN₂O reactive encounter. Emission from the SiO a³Σ⁺ (A¹Π) and b³Π(A¹Π, E¹Σ₀⁺) triplet-state manifold results primarily from intensity borrowing involving the indicated singlet states. Perturbation calculations indicate the magnitude of the mixing between the b³Π, A¹Π and E¹Σ₀⁺ states ranges between 0.5 and 2%. On the basis of these calculations, the branching ratio (excited triplet)/(excited singlet) is found to be well in excess of 500. An approximate vibrational population distribution is deduced for those molecules formed in the b³Π state. The present studies are correlated with those of previous workers in order to provide an explanation for diverse relaxation effects as well as observed changes in the ratio of a³Σ⁺ to b³Π emission as a function of pressure and experimental environment. Some of these effects are attributable to a strong coupling between the a³Σ⁺ and b³Π state. Based on the current results, there appears to be little correlation between either (1) the branching ratio for excited state formation or (2) the total absolute cross section for excited-state formation and (3) the measured quantum yield for the SiN₂O reaction. Implications for chemical laser development are considered.