Catalytic hydrogenation of propene over polymer supported rhodium complexes

Hydrogenation of propene and other substrates has been studied in flow and batch reactors using various rhodium catalysts. The results show that in some cases rhodium metal is probably formed, but only if solvent is present. A possible explanation is given.     

Complexes of silver(III) with oxoanions

Silver(III) has a half-life at pH 11 of several hundred seconds in aqueous solutions in the presence of 0.1–1.0 M concentrations of certain basic oxoanions (Oxo) (phosphate, carbonate, borate, pyrophosphate, and arsenate). This compares with a lifetime of a few seconds at pH 11 in the absence of these oxoanions. UV-visible spectra and kinetic data for these solutions are interpreted as evidence for the following equilibria in the pH range 9–13.Ag(OH)₄^?1 + H₂O ? Ag(OH)₃H₂O + OH^? (1)Ag(OH)₄^?1 + Oxo ? Ag(OH)₃Oxo + OH^? (2)Ag(OH)₃Oxo + H₂O ? Ag(OH)₂(Oxo)H₂O + OH^? (3) Values of K₃ lie in the range 10^?3 < K₃ <10⁴ M for the systems studied. K₂ is estimated to be ～10² for phosphate and slightly smaller for the other systems. Ag(OH)₄^? undergoes an unusual reaction with pyrophosphate at pH ～ 8 to form a novel silver(II) complex, [Ag(P₂O₇)₂]^6?, for which EPR and electronic absorption spectral parameters are reported.     

The chemistry of sulfines. 9. A novel synthesis of α-chloroalkyl alkanethiosulfonate esters

Sulfines react with sulfinyl chlorides giving α-chloroalkyl alkanethiosulfonate esters and with thionyl chloride giving α-chloroalkanesulfenyl chlorides, both in good yields.     

Sesquiterpenoids of vetiver oil—I: The structures of zizanoic acid and related constituents

Two sesquiterpene car?ylic acids, zizanoic and epizizanoic acids, were isolated from the essential oil of vetiver and were assigned the structures1a and2a on the basis of chemical degradation. Although khusimol and zizaene (tricyclovetivene) had been assigned structures previously, the current work revealed that these sesquiterpenoids also belong to the zizaane group and that the formulae should be revised as1b and1c, respectively.     

Studies of organosulfur compounds : X. Preparation of some trimethylmetal(IVb) esters of dithio acids and their spectral properties

Some trimethylmetal(IVb) esters of dithio acids have been prepared by treatment of the secondary or tertiary amine salts of dithio acids with chlorotrimethylsilane, -germane, or -tin, and their IR, UV and NMR spectra recorded.     

Azole chemistry : XI. 3-Dimethylsila-2H-imidazo[1,2-a]benzimidazoles

2-Aminobenzimidazole, and its 5,6-dichloro, 5,6-dimethyl, and 5,6-dinitro derivatives react with bromomethyldimethylchlorosilane in anhydrous tetrahydrofuran at room temperature to give the new heterocycles, 3-dimethylsila-2H-imidazo [1,2-a]benzimidazoles, in good yields. The spectral properties of these heterocycles are discussed.     

Dynamic 19F NMR studies The torsional barrier in pentafluorobenzaldehyde,its conjugate acid and protonated pentafluoroacetophenone

An upper limit of the barrier to internal rotation around the phenyl-carbonyl bond in pentalfluorobenzaldehyde dissolved in a freon mixture has been estimated from low temperature ₁₉F NMR study. Protonation of this compound increases drastically the free energy of activation ΔG≠. Complete lineshape analysis leads to ΔG≠ (273 K) = 60.4 kJ/mol, comparable to the value obtained for protonated benzaldehyde. This result, as well as those obtained by CNDO/2 calculations support the conclusions that protonated pentafluorobenzaldehyde is planar in the ground state. This is not the case for protonated pentafluoroacetophenone in which the lower barrier height when compared to protonated acetophenon has been related to the steric strain and dipole repulsion.     

Niobium and tantalum mesityl complexes and the role of the mesityl ligand in α- and γ-hydrogen abstraction reactions

The Ta and Nb complexes M(Mes)_nX_5?n (Mes = Mesityl; XCl or Br; n = 1, 2 or 3) and several derivatives can be prepared in high yield. They are considerably more stable than their phenyl analogues. 1H NMR data indicate that a mesityl ligand most likely occupies an equatorial site in a trigonal bipyramidal molecule but cannot rotate freely because its ortho methyl groups cannot pass by the axial chloride ligands. TaMes(CH₂CMe₃)X3 reacts with PMe₃ ( L) to give the known alkylidene complexes, Ta(CHCMe₃)L2X3, but TaMes(CH₃)X₃ reacts with PMe₃ to give the benzylidene complexes, Ta(CHC₆H₃Me₂)L₂X₃ (by γ-abstraction from the mesityl ligand), instead of the hoped for analogous methylene complex.     

Reaction of ethylene with the unsaturated cluster complex H2Os3 (CO)10

Treatment of H₂Os₃(CO)₁₀ with excess ethylene forms ethane and a hydridovinyl cluster complex HOs₃(CO)₁₀(CHCH₂), which rearranges in refluxing octane to the vinylidene complex H₂Os₃(CO)₉(CCH₂).     

ortho-Effects on carbon monoxide insertion in benzyl-molybdenum complexes

The formation of phosphine-substituted acylmolybdenums [(η⁵-C₅H₅)-(CO)₂(PPh₃)Mo(COR)], from reactions between substituted benzylmolybdenum complexes and triphenylphosphine in acetonitrile, is enhanced by the presence of a single bulky substituent in the ortho-position. However di-substitution (for i-Pr, Cl and OMe) causes a pronounced lowering of reactivity. The results are interpreted in terms of the steric demands of the reaction.     

Transition metal complexes of azo compounds V. Complexation and cleavage of the NN bond of diazirines by iron carbonyls

3,3-Dimethyldiazirine and 3,3-pentamethylenediazirine, R₂CN₂, react with enneacarbonyldiiron initially via N-tetracarbonyl intermediates to give dark blue μ-1,2-diazirine-bis(tetracarbonyliron) complexes and small amounts of an Fe₃(CO)₉-cluster of the diazirine. Depending upon the solvent, further reaction may take place by splitting of the NN bond to yield orange (R₂CN)Fe₂(CO)₆(NCR₂) and red (R₂CN)Fe₂(CO)₆(NCO), which contain bridging ketiminato and isocyanato groups. Formation of the latter complexes probably involves “nitrenic” intermediates. A general scheme is proposed for the reactions of the cis-azo group of cyclic azo compounds with iron carbonyls which permits estimation of the product ratio as a function of the ring size of the parent azo ligand. (R₂CN)Fe₂(CO)₆(NCO) adds methanol at room temperature to give (R₂CN)Fe₂(CO)₆(NHCO₂Me).     

Cationic iron complexes containing the η2-Butatriene ligand

Cationic iron complexes of the type Fp(alkene)⁺ (Fp =η⁵-C₅ H₅ (CO)₂ Fe) containing an unsubstitutedη²-butatriene ligand are synthesized and characterized by spectroscopic and analytical data.     

Transition metal promoted alkylations of unsaturated alcohols: the methylation and ethylation of 3-buten-1-ol using titanium tetrachloride-organoaluminum systems

The ethylation and methylation of the olefinic linkage in 3-buten 1-ol by incorporating the alkenol into a titanium-organoaluminum system was studied under a variety of conditions. Systems were derived from titanium tetrachloride and the organoaluminum compounds Al(C₂H₅)₃, Al(C₂H₅)₂Cl, Al(CH₃)₃, and Al(CH₃)₂Cl. With diethylaluminum chloride the major products obtained were 1-hexanol, 3-methyl-1-pentanol, trans-3-hexen-1-ol, and 1-butan I. Triethylaluminum gave no alkylation products. Dimethylaluminum chloride and trimethylaluminum gave product distributions similar to the analogous diethylaluminum chloride system.     

Metalloidalmethyl substituent effects by 13C and 19F NMR : electron release in the neutral ground state.

¹³C and ¹⁹F chemical shift studies of a series of CH₂M(CH₃)₃ and CH₂M(C₆H₅)₃ (M  Si, Ge, Sn, Pb) - substituted aryl derivatives (phenyl; 1-naphthyl; 2-naphthyl) have established unambiguously that the order of hyperconjugative electron release in the neutral ground state is Pb>Sn>Ge>Si. This order is clearly at variance with the commonly accepted order(Pb>Sn>Ge>Si) based on studies of electron deficient substrates. The phenomenon is discussed in terms of current theories on σ-π interactions. In addition, substituent parameters (σ_I and σ_R^o) for the PB(CH₃)₃ group have been derived utilizing new data from the fluorophenyl tag. These new constants are compared with those previously reported.     

Structural studies on osmium carbonyl hydrides: XXXI. Crystal and molecular structure of CpWOs3(CO)9(μ-H)(μ-O)(μ-CHCH2C6H4Me), a hydrido-alkylidene produced by hydrogenation of a μ3-alkylidyne

The complex CpWOs₃(CO)₉(μ-H)(μ-O)(μ-CHCH₂C₆H₄Me), previously prepared by hydrogenation of CpWOs₃(CO)₉(μ-O)(μ₃-CCH₂C₆H₄Me), has been subjected to a single-crystal X-ray diffraction study. The complex crystallizes in the non-centrosymmetric monoclinic space group Cc(C_s⁴; No. 9) with a 14.1510(27), b 13.9257(22), c 13.3179(19) Å, β 92.023(13)°, V 2622.8(7) ų and D(calcd) 3.06 g cm^?3 for Z = 4 and mol. wt. 1206.8. Single-crystal X-ray diffraction data were collected with a Syntex P2₁ automated four-circle diffractometer and the structure was refined to R 3.5% for all 2476 independent observations (Mo-K_α radiation, 2θ = 4.5–40.0°) and R 3.4% for those 2430 data with | F₀| > 3.0σ(| F₀|). The molecule contains a tetrahedral WOs₃ core associated with 60 valence electrons. Each osmium atom is associated with three terminal carbonyl ligands and the tungsten atom is linked to an η⁵-C₅H₅ ligand. In addition, the μ-oxo ligand is involved in a WO: → Os bridge (in which WO(B) 1.737(17), Os(3)← :O(B) 2.167(16) Å and WO(B)Os(3) 96.0(7)°), the μ-hydride ligand spans the Os(1)Os(3) linkage and the μ-CHCH₂C₆H₄Me ligand bridges the WOs(2) linkage (WC(1) 2.068(26) and Os(2)C(1) 2.281(26) Å).     

Transition metal promoted reactions of unsaturated hydrocarbons : III. Insertion of 1,2-dienes into allylic palladium bonds

Addition of strained olefins, based on norbornene, norbornadiene,benzonorbornadiene or bicyclo [2.2.2] octene skeletons to π-allylic(hexafluoroacetylacetonato) palladium(II) complexes [(π-All)Pd(Hfacac)], gives “enyl” products derived from “insertion” of the olefin into the least substituted terminal allylicpalladium bond. The reaction involves an initial rapid and reversible formation of (gs-allyl)(π-olefin)Pd(Hfacac). The rate-determining step involves migration of a σ-allylic carbon atom from Pd to the coordinated olefin in a concerted cis—exo addition of Pd---C across the double bond. Remote electronegative substituents on the olefin do not affect the coordinative ability of the olefin towards Pd. They do however inhibit the migration of the σ-allylic ligand to the coordinated olefin. This observation is interpreted in terms of a small degree of polarization of the π-olefin—Pd bond in the transition state for the σ-allyl migration.