Metal—metal bonding in dinuclear complexes of platinum(I). The crystal and molecular structure of carbonyl(chloro)-bis-μ-[bis(diphenylphosphino)methane]diplatinum hexafluorophosphate

The structure of [Pt₂Cl(CO) (μ-Ph₂PCH₂PPh₂)₂] [PF₆] was determined by $\text{X}$-ray methods and refined to $\text{R}$ = 0.082, using diffractometric intensities of 5646 independent reflections. The crystals are monoclinic, space group $\text{P}$2₁/$\text{n}$, $\text{a}$ = 12.919(3), $\text{b}$ = 15.576(6), $\text{c}$ = 25.151(5)Å, β = 94.82(3)°, $\text{Z}$ = 4. They are built of octahedral hexafluorophosphate anions and dinuclear platinum(I) cations. The latter contain PtCl and PtCO fragments linked to one another by a PtPt σ-bond and by two bridging bis(diphenylphosphino)methane ligands. The platinum atoms are in square planar environments and the dihedral angle between the two coordination planes is 40.1°. Selected bond lengths are: PtPt 2.620(1), PtCl 2.384(5), PtC 1.89(3) and PtP 2.291(5) – 2.308(5)Å.     

An approach to the enantiocontrolled synthesis of pseudomonic acids via a novel mono—claisen rearrangement

A short, efficient approach to a key chiral intermediate for the synthesis of pseudomonic acids A and C is delineated.Pseudomonic acids A($\text{1a}$), B($\text{1b}$), and C($\text{2}$) are members of a novel of “C-glycopyranoside” antimicrobial agents which have recently attracted synthetic attetion.² Presently, we wish to report a short efficient stratedy towards the total synthesis of opticaly active pseudomonic acids. The sequence is highlighted by a novel controlled mono-Claisen rearrangement and a highly regioselective π-allylpalladium mediated displacement.Diacetyl-(L)-arabinal ($\text{3}$)³ was converted to the bis-ketenesilylacetal $\text{4}$ and warmed to 60°C according to the Ireland ester-enolate Claisen rearrangement method.⁴ Over a period of ≈5h, smooth conversion to a major rearranged product $\text{5}$ was observed by 300 MHz NMR. The identity of $\text{5}$ was confirmed by direct desilylation and methylation (KF, KHCO₃, H₂O, HMPA, CH₃I). After flash chromatography, compound $\text{7}$ was isolated in 55% overall yield from $\text{3}$. Careful inspection of the crude methylation product revealed the presence of ≈5% doubly rearranged product $\text{6}$.The rearrangement of $\text{4}$ to $\text{5}$ is a unique example of a selective mono-Claisen rearrangement in which the rate of a second similar Claisen rearrangement ($\text{5}$ → $\text{6}$) is much slower under the reaction conditions. Although the reasons for this interesting selectivity are unclear at this time,⁵ in practice, the mono-Claisen rearrangement obviates the need for selective differentiation of the two hydroxyl groups, a difficult task at best, in this case.Palladium mediated allylic acetate displacement provided an ideal method for introduction of a second chemodifferentiated side chain with allylic retention and retention of stereochemistry. Alkylation of $\text{7}$ with sodiothylmalonate using 5 mole % Pd(O)dppe₂⁶ was unusually facile (<45 min, 25°C, THF). After semi-preparative HPLC, essentially a single regio- and stereoisomer was isolated in 96% yield.⁷ Structure $\text{8}$ was confirmed by extensive ¹H-NMR decoupling, as well as an off-resonance ¹³C-NMR experiment. In particular, H₁ (δ 4.53) was coupled vicinally to H₆ and H₆′ (5 Hz, 8 Hz) and H₂ (1.5 Hz), and allylically to H₃ (2 Hz). In contrast, H₄ (δ 2.78) was coupled to H₇ (10 Hz), H_5e and H_5a (1.8 Hz, 4 Hz), H₃ (5 Hz), and H₂ (<1 Hz). In addition, H₁ and H₄ exhibited a small long range coupling constant (J = <1 Hz). The coupling constants rule out

regioisomer $\text{9}$ and are fully consistent with the indicated conformation, which minimizes 1,3-diaxial-like interactions.Finally, catalytic osmylation of $\text{8}{}^8$ gave a single cis-diol $\text{10}$ in nearly quantitative yield. Appending of suitably functionalized side chains to provide an enantiocontrolled synthesis of pseudomonic acids A($\text{1a}$) and C($\text{2}$) is in progress.^9,10     

Reactions of cyclo-octatetraene and its derivatives - X: 1,2,3,8-Tetraphenylcyclo-octatetraene and 2,3,4,5-tetraphenylcyclo-octa-1,3,5-triene

The reaction of tetracyclone $\text{1b}$ with the cyclo-octatetraene-dimethyl acetylenedicarboxylate adduct $\text{2}$ at $\text{ca}$. 110° produces, in addition to the $\text{exo}$[4+2] Π cycloadduct $\text{3b}$ (49%), 1,2,3,8-tetraphenylcyclo-octatraene $\text{5}$ (11%), together with the diketone $\text{11}$ (5%). In a similar reaction with the esterified cyclo-octatetraene-maleic anhydride adduct $\text{13a}$, the major product $\text{14}$ (82%) is accompanied by the cyclohexa-1,3-diene $\text{15}$ and the dihydrosemibullvalene derivative $\text{16}$. Thermolysis of $\text{3b}$ at $\text{ca}$. 145° leads to the cyclobutene $\text{12}$., which on catalytic hydrogonation followed by decarbonylation at 180°–190° gives 2,3,4,5-tetraphenylcyclo-octa-1,3,5-triene $\text{19}$. Attempted thermal conversion of $\text{19}$ into a dihydrosemibullvalene failed.     

Organothiometallate - alkyne addition products. The crystal and molecular structure of [(η5-C5H5)W{C(CO2Me)C(CO2Me)C(O)SMe} (CO)2]

The title compound is the final product of the reaction between dimethylacetylene dicarboxylate and [(η⁵-C₅H₅)W(SMe) (CO)₃ ]. Its molecular structure has been established by an $\text{x}$-ray analysis based on 3301 diffractometric intensities. The crystals are monoclinic, space group $\text{P}$2₁/$\text{a}$, with four molecules in a cell of dimensions $\text{a}$ = 10.323(2), $\text{b}$ = 16.016(2), $\text{c}$ = 10.437(2)», β = 103.56(2)°. After least-squares refinement $\text{R}$ = 0.036. The tungsten co-ordination is square-pyramidal, the apical site being occupied by the centroid of the cyclopentadienyl ring. The basal co-ordination sites contain two carbonyl groups and also the sulphur and σ-bonded carbon atoms of a chelating carbothiolic methyl ester ligand derived from the incoming alkyne and CO and SMe groups of the original complex. The W-S and σ-W-C bond lengths are 2.440(2) and 2.194(7)».     

Rare earth ions in a hexagonal field IV

Energy levels and eigenfunctions of rare earth ions in a crystal field of hexagonal symmetry have been obtained using a Hamiltonian of the form $\text{H}$ = B°₂O°₂ + B°₄O°₄. Results are presented for all J values appearing in the rare earth series. The order of the energy levels has been determined for all relative values of the second and fourth order crystal field intensity parameters, B°₂ and B°₄. This, of course, includes information for the commercially significant RCo₅ compounds, for which the second order term is dominant. The eigenfunctions are pure M states with permanent magnetic moments ± Mg μ_B. The moments are unchanged by a field applied along the c axis.     

Molecular and electronic structure of the dehydroalanine derivatives: The cyclic dipeptide of dehydrophenylalanine

The molecular structure of the cyclic dipeptide of dehydrophenylalanine [3,6-bis(phenylmethylene)-piperazine-2,5-dione] has been determined from three dimensional X-ray data. C₁₈H₁₄ N₂O₂ is monoclinic, space group C2/$\text{c}$, with Z = 12 in a cell of dimensions $\text{a}$=4Ø.774(1), $\text{b}$=6.237(2), $\text{c}$=17.731(3) Å, β=107.76(5)°. Molecules are approximately planar as far as the piperazinedione ring is concerned, and they are linked in two series of hydrogen-bonded ribbons. The vapour phase He(I) and He(II) photoelectron spectra are also presented. Their assignment is proposed by comparison with related molecules and supported by semiempirical quantum mechanical calculations. Analogies and differences with respect to the photoelectron results of the cyclic dipeptide of dehydroalanine and corresponding acyclic compounds are discussed.     

An outline of the stucture of 7Bi2O3 · 2WO3 and its solid solutions

This paper gives an outline of the structure of a solid solution based on 7Bi₂O₃ · 2WO₃. The experimental results using X-ray diffraction methods (precession and powder) showed that 7Bi₂O₃ · 2WO₃ crystallizes in the space group $\text{I4}{}_1\text{a}$ with a = 12.5143(5)Å and c = 11.2248(6) Å. The number of formula weights per unit cell is 40, when the formula is considered to be of the oxygen-deficient fluorite-type Bi_0.875W_0.125O_1.6875. The compound has a substructure based on a defect fluorite-type pseudocubic subcell with $\text{a′ ? 5.6}$ Å. The axial relations between the supercell and subcell are $\text{a ? √a′}$ and $\text{c ? 2a′}$. The solid solution was formed over a limited range of WO₃ content between 21.3 mole% and 26.3 mole% at 700°C. The ordering of metal atoms is discussed and an ideal crystal structure is proposed.     

The structure of some transition metal fluorides

The structures of the solid fluorides MF₂, MF₃, MF₄ and MF₅, in which M has the coordination number 6 and belongs to the 3$\text{d}$, 4$\text{d}$- and 5$\text{d}$-periods and the Vb to VIII groups, can be divided into 3 types: (a) cubic close packing ($\text{ccp}$) of F with an MFM bridging angle of 180°; (b) hexagonal close packing ($\text{hcp}$) with an MFM-bonding angle of 132°; (c) intermediate packing between (a) and (b). The linear bridging is assumed to be a consequence of π-back bonding (or charge transfer) between $\text{p}$F-orbitals and $\text{d}$-orbitals of the metal. If such bonding is not possible then $\text{hcp}$ with the bridging angle of 132° will result. Weaker π-interactions give the intermediates (c).     

Crystal structures and magnetic properties of BaTiF5 and CaTiF5

Single crystals of BaTiF₅ and CaTiF₅ were obtained by the Czochralski and Bridgman techniques, respectively. The crystal structures were determined by X-ray diffraction; BaTiF₅: $\text{14}\text{m}\text{, a = 15.091(5)}$Å, c = 7.670(3)Å; CaTiF₅: $\text{I2}\text{c}\text{, a = 9.080(4)}$Å, b = 6.614Å, c = 7.696(3)Å, β = 115.16(3)°. Both structures are characterized by the presence of either branched or straight chains of TiF₆ octahedra. BaTiF₅ contains the unusual dimeric unit (Ti₂F₁₀)^4?. Magnetic susceptibility measurements were performed on both compounds in the temperature range 4.2 to 300 K, however, no evidence for magnetic interactions between the Ti³⁺ moments were observed.     

The crystal structure of N-sodiohexamethyldisilazane,Na[N{Si(CH3)3}2]

The crystal structure of Na[N{Si(CH₃)₃}₂] has been determined from single-crystal x-ray diffraction data collected by counter methods. N-sodiohexamethyldisilazane crystallizes in the mono-clinic space group p21/n with unit cell parameters $\text{a}$ = 9.426(3), $\text{b}$ = 6.921(3), c = 17.974(5)Å, β = 93.83(2)°, and ?_calc = 1.04 g cm^?3 for z = 4 formula units. Least-squares refinement gave a final conventional R value of 0.034 for 1244 independent observed reflections. In the solid state the compound exists in a polymeric arrangement with an average Na-N distance of 2.355(4)Å. The methyl group are configured such that the angle of rotation of the trimethylsilyl moiety about the Si-N bond is 30° from the eclipsed position. The Si-N bond length is 1.690(5)Å, and the Si-N-Si bond angle is 125.6(1)°.     

Solid state reactions to CdTeMoO6 and its structural characterization

CdTeMoO₆ has been obtained by solid state reactions of CdMoO₄ with orth. TeO₂ at 425°C, with tetr. TeO₂ at 470°C, and with H₆TeO₆ at 490°C. Its crystal structure belongs to the tetragonal system (space group $\text{P4}\text{n}$ or $\text{P4}\text{nmm}$ with unit cell dimensions a = 5.279(2) Å, c = 9.056(2) Å. The specificity of this compound in the allylic oxidation reactions should be strictly related to its structural features, among which the presence of cis MoO₂ groups could be very important.     

Phase behavior of Li2WO4 at high pressures and temperatures

The phase diagram of Li₂WO₄, previously studied by Yamaoka et al. (J. Solid State Chem.6, 280 (1973)) has been revised. Li₂WO₄ II is stable at atmospheric pressure below ～310°C. This phase appears to be a modified spinel, and is tetragonal, a, c = 11.941, 8.409Å, Z = 16, space group $\text{I4}{}_1\text{amd}$. The melting curve of phenacite-type Li₂WO₄ I rises with pressure with a slope of 0.9°C/kbar to the III/I/liquid triple point at 3.1 kbar, 743°C, beyond which the melting curve of orthorhombic Li₂WO₄ III rises steeply with pressure (initial slope 31°C/kbar). The Li₂WO₄$\text{I}\text{III}$ transition line at 3 kbar is almost independent of temperature, i.e., the $\text{I}\text{III}$ transition entropy is zero. Li₂WO₄ II is 21.3% denser than Li₂WO₄ I at ambient conditions.     

New defect vanadium dioxide phases

Two new monoclinic V₂O₄ phases were prepared at high pressure from the regular monoclinic (M₁) form of V₂O₄. The unit cell dimensions for the unmodified monoclinic (M₂) phase are: a = 9.083, b = 5.763, c = 4.532 Å, and β = 91.30°. The space group $\text{C 2}\text{m}$ is consistent with the crystallographic data. The new vanadium dioxide exhibited a structural transition and an abrupt, reversible change in resistivity (approx. 4 orders of magnitude) at 66°C similar to that observed in M₁-type V₂O₄. This new form of V₂O₄ is believed to be stabilized by chemical and structural defects. Controlled substitution of V⁵⁺ for V⁴⁺ in the structure led to yet another monoclinic (M₃) phase. This phase is closely related to the M₂ phase. The M₃ unit cell dimensions are: a = 4.506, b = 2.899, c = 4.617 Å, and β = 91.79°, having the space group $\text{P 2}\text{m}$. The substitution of V³⁺ yielded only monoclinic (M₁) derivatives. The modified products have varied semiconductor to metal transition temperatures which depend on the type and amount of substitution and defect structure.     

Reaction of 5,5-diphenyl-2-thiohydantoin with 1,2-dibromoethane.crystal and molecular structures of 2,3-dihydro-6,6-diphenylimi-dazo-[2,1-b]-thiazol-5(6h)-one and 2,3-dihydro-5,5-diphenylimi-dazo-[2,-1-b]-thiazol-6(5h)-one and their reactivity

The crystal and molecular structures of the title isomeric compounds $\text{1}$ and $\text{2}$, obtained by intramolecular N,S--dialkylation of 5,5-diphenyl-2-thiohydantoin with 1,2-dibro-moethane, have been determined from X-ray diffractometer data. 2,3-Dihydro-6,6-diphenylimidazo-[2,1-b]-thiazol-5(6H)-one $\text{1}$ crystallizes in space group P2₁2₁2₁ with a=11.376(3), b=12,255(5), c=8.434(3) Å and Z=4. Crystals of $\text{2}$, containing one molecule of benzene, are monoclinic,space group P2₁/c with a=11.539(6), b=10.242(3), c=16.353(5) Å, β=95.45(5)° and Z=4. In both cases a planar geometry of the two fused five-membered heterocyclic rings was found. The selected bond lengths in $\text{1}$ and $\text{2}$, as well as those analogous imidazothiazinones $\text{3}$ and $\text{4}$, were used to calculate E_HOSE (Harmonic Oscillation Stabilization Energy). The problem of stability and chemical reactivity of compounds $\text{1}$ to $\text{4}$ is also discussed.     

Reactions of triphenylarsine oxide with aqueous hydrogen fluoride: Crystal structure of bis(triphenylarsine oxide)hydrogen(I) tetrafluoroborate

Fluorination of triphenylarsine oxide by aqueous hydrogen fluoride (1–40%) in the absence of glass readily gives triphenylarsine difluoride. When the reaction with dilute (1%) aqueous hydrogen fluoride is carried out in borosilicate glass apparatus, the glass participates in the reaction resulting in the formation of the crystalline 2:1 adduct 2Ph₃AsO·HBF₄. Crystals of this compound are monoclinic, $\text{P}$2₁/$\text{c}$, $\text{a}$ = 12.926(4), $\text{b}$ = 17.819(6), $\text{c}$ = 14.994(4) Å, β = 98.97(3)°, Z = 4. The structure contains cations [(Ph₃AsO)₂H]⁺ in which $\text{O}\text{?}$O is 2.44(2)Å, and anions BF₄^?.     

Mössbauer spectra,magnetic and electrical behavior of Ba1+xFe2S4 phases

The Mössbauer spectra, and magnetic and electrical properties of Ba_1+xFe₂S₄ infinitely adaptive phases with 0.074 ≤ x ≤ 0.142 and of BaFe₂S₄ were studied. The properties are highly anisotropic because of the presence in the structure of one-dimensional infinite chains of edge sharing FeS₄ tetrahedra. BaFe₂S₄ is a semiconductor, E_g = 0.66 eV; magnetic susceptibility can be fit by a one-dimensional Heisenberg model with spin $\text{5}\text{2}$ and $\text{J}\text{k}\text{= ?30°}\text{K}$. The Ba_1+xFe₂S₄ phases have Curie-Weiss behavior with an effective moment of about 2 B.M. The moment increases with x. These phases are metallic. The Mössbauer isomer shift varies linearly with valence, increasing with increasing x. The single quadrupole split absorption line characteristic of these compounds disappears at about 270°K and a complex spectrum consisting of overlapping hyperfine patterns appears at lower temperatures. Magnetic short-range ordering is responsible for this behavior although the susceptibility in this temperature range does not reflect this effect.     

Comparative reactions between aziridines and F2, COF2, CF3OF

In CFCl₃, aziridines $\text{I}$ react with F₂(6 %/N₂,  20°C), COF₂ (20 %/N₂,  40°C) and CF₃OF [1] (20 %/N₂,  40°C).Substitution products are obtained : l-(aziridine)carbonyl fluorides $\text{II}$ and l-Fluoroaziridines $\text{III}$

In (Et)₂O, aziridines $\text{I}$ react with COF₂ (20 %/N₂, 10°C) and we have the carbonyl fluorides $\text{IV}$.

Products IV can be thermally decomposed into β fluoro isocyanates.In CFCl₃, N substituted aziridines $\text{V}$ react with F₂(6%/N₂, 20°C) and with CF₃OF [2] (20%/N₂, 40°C). No reaction is observed with COF₂in our conditions (5% to 25%/N₂, 80°C to + 40°C).Addition products are obtained : N Fluoro amines β fluorinated $\text{VI}$, N Fluoro and NN difluoro amines β trifluoro methoxylated $\text{VII}$ and $\text{VIII}$.

with R = SO₂Ø, COØNO₂, Cl.     

High-pressure/high-temperature phase relations and vibrational spectra of CsSbF6

CsSbF₆(II) under ambient conditions is trigonal, space group $\text{D}{}_{\mathrm{3d}}{}^5\text{-R}\text{3}\text{m}$. At 187.8°C it undergoes a phase transition with an enthalpy change of 5.267 ± 0.316 kJ mole^?1, to phase CsSbF₆(I). CsSbF₆ decomposes with loss of fluorine at atmospheric pressure at high temperatures, but under pressure the decomposition is prevented and a melting point of 310°C at atmospheric pressure can be inferred. The $\text{II}\text{I}$ phase boundary and melting curve were studied as functions of pressure. The infrared and Raman spectra of CsSbF₆(II) were studied in the temperature range of ?256 to 20°C, at ambient pressure. The crystal chemistry of the CsSbF₆ and its relationship with other related compounds is discussed.     

Etude à haute pression des tétramétaphosphates du type M2P4O12 (M = Ni,Mg, Cu,Co, Fe,Mn, Cd). Données cristallographiques sur tous les composés M2P4O12

Fe₂P₄O₁₂ has been prepared and identified as an isotype of the other M^II₂P₄O₁₂ tetrametaphosphates (M^II = Ni, Mg, Cu, Co, Mn, Cd). Its monoclinic unit cell:

$\text{a=11.952,b=8.359,c=9.932}\text{A}\text{?}$

$\text{β=118°76}$

contains 4 formula units. The space group is $\text{C2}\text{c}$. For tetrametaphosphates with M^II = Ni, Mg, Cu, Co, and Mn we found a new denser phase induced at 80 kbar and 1000°C. In the case of Fe₂P₄O₁₂ the unit cell of this new form is

$\text{a=9.777,b=8.994,c=4.968}\text{A}\text{?}$

$\text{β=107°22}$

with Z = 2 and two possible space groups Cc or $\text{2C}\text{c}$. This dense phase exists at ordinary pressure for the zinc salt.