Oxidation of propene and 1-butene byMethylococcus capsulatus andMethylosinus trichosporium

Summary Methane-grown cells ofMethylococcus capsulatus andMethylosinus trichosporium readily oxidized propene and various isomers of butene to their respective epoxides. When examined in a proton NMR spectrum using tris([3-trifluoromethylhydroxymethylene]-d-camphorato), europium III derivative as an optically active chemical shift reagent, the products propylene oxide and 1,2-epoxybutane were found to contain equal amounts of both isomers. Methane-grown cells of both bacteria had considerable levels of reducing equivalents to catalyze the epoxidation of gaseous olefins. Cells depleted of reductants catalyzed the oxidation in the presence of low levels of methanol or formaldehyde with a stoichiometry of about 2:1. The rates of epoxidation of propene and 1-butene in a continuous reactor were 2–3-times that of a batch-wise reaction; the epoxidation activity, however, was lost within 3 h. The inactivation was attributed to the reactivity of the accumulated epoxides in the reactor. Propene and 1-butene oxidation by both bacteria were drastically inhibited by the respective products. Thus, the major problem in the application of microorganisms for production of epoxides from gaseous olefins is the rapid separation of the reactive products.     

Vanadyl tetradentate Schiff base complexes as catalyst for C-H bond activation of olefins with tert-butylhydroperoxide: Synthesis, characterization and structure

Three N₂O₂ tetradentate Schiff base ligands (H₂L^1-3) were prepared by reaction of 1,2-propylenediamine and appropriate aldehyde and ketone and characterized by FT-IR, ¹H and ¹³C NMR. The vanadyl complexes were synthesized by treating an ethanolic solution of the appropriate ligand and one equivalent of VO(acac)₂ to yield VOL^1-3. These oxovanadium (IV) complexes were characterized on the basis of their FT-IR, UV-Vis spectroscopy and elemental analysis. The crystal structure of VOL³ has been determined. The metal center in VOL³ is a deformed tetragonal pyramidal N₂O₃ coordination sphere. These complexes are used as catalyst for the selective epoxidation of olefins. High selectivity of epoxidation for cyclooctene observed from oxidation data. The catalytic activity increases as the number of electron-donor groups increases, and the catalytic selectivity is varied by changing the substituents on the ligands. The catalytic system described here is an efficient and inexpensive method for the oxidation of olefins, with the advantages of high activity, selectivity, re-usability and short reaction time.     

Model compounds for polymeric redox-switchable hemilabile ligands

The syntheses and characterization of two new tetradentate hemilabile ligands 1,2-bis(2-diphenylphosphinoethoxy)benzene (5) and 2,2′-bis(2-diphenylphosphinoethoxy)-1,1′-binaphthalene (10) are reported. Ligands 5 and 10 were synthesized as models to test the suitability of specific phosphinoether coordination environments for complexing Rh(I) in high surface area thiophene-based, redox-active polymeric systems. Ligands 5 and 10 react with the product formed from the reaction between (bicyclo[2.2.1]hepta-2,5-diene)rhodium(I) chloride dimer and AgBF₄ to form [η²-(1,2-bis(2-diphenylphosphinoethoxy)benzene) η⁴-norbornadiene rhodium(I)] tetrafluoroborate (6) and [η²-(2,2′-bis(2-diphenylphosphinoethoxy)-1,1′-binaphthalene) η4-norbornadiene rhodium(I)] tetrafluoroborate (11), respectively. Complexes 6 and 11 react with H₂ in CD₂Cl₂ to form the two new square-planar cis-phosphine, cis-ether Rh(I) complexes 7 and 12, respectively. Compound 7, which could be characterized on the basis of its ³¹P NMR spectrum, is extremely reactive and decomposes in CD₂Cl₂. In THF compounds 6 and 11 react with H₂ to form the dihydride, bis-THF adducts 8 and 16, respectively, which upon removal of solvent form 7 and 12, respectively. Compound 12 is a stable, isolable complex that reacts with acetonitrile to form a cis-phosphine, cis-acetonitrile adduct 15. Removal of solvent from 15 leads to the quantitative reformation of 12. Compound 12 does not react to a detectable extent with gross excesses of benzene or even thiophene, demonstrating the suitability of this ligand environment for implementation into a thiophene-based polymeric system. Compound 12 does catalyze the hydrogenation of cyclohexene to form cyclohexane, and mechanistic implications of such a transformation are discussed.     

Pseudomonas C12B, an SDS degrading strain, harbours a plasmid coding for degradation of medium chain length n-alkanes

Pseudomonas C12B is able to degrade alkyl sulfates, alkylbenzene sulfonates, and linear alkanes and alkenes. Mitomycin C curing experiments and conjugation experiments demonstrated that the ability to utilize n-alkanes (C₉–C₁₂) and n-alkenes (C₁₀ and C₁₂) of medium chain length was plasmid-encoded. The plasmid was designated pDEC. Its size was estimated at several hundreds kb according to mobility in agarose gels. The plasmid did not confer resistance to the antibiotics tested. Analysis of alkylsulfatases P1 and P2 in original and cured strains confirmed that both enzymes are encoded by the chromosome. The ability of Pseudomonas C12B to utilize alkylbenzene sulfonates also appears to be encoded by the chromosome. pDEC could be transferred only to cured derivatives of Pseudomonas C12B, but not to strains of P. aeruginosa, P. putida, or Acinetobacter sp. Cured derivatives of Pseudomonas C12B could not serve as hosts for the broad host range plasmid CAM–OCT. The enzyme system encoded by the putative dec genes present on plasmid pDEC differs from the system coded by the alk genes of plasmid OCT in the size range of hydrocarbons preferentially used.     

Catalytic air oxidation of olefins using molybdenum dioxo complexes with dissymmetric tridentate O,N,S-donor Schiff base ligands derived from o-hydroxyacetophenone and S-benzyldithiocarbazate or S-methyldithiocarbazate

We report the homogeneous catalytic air oxidation of 1-hexene, cyclohexene and styrene using cis-[MoO₂(hap-SBDTC)(solv)] (1b) and cis-[MoO₂(hap-SMDTC)(solv)] (2b), where hap-SBDTC and hap-SMDTC are Schiff bases derived from o-hydroxyacetophenone (hap) and S-benzyldithiocarbazate (SBDTC) or S-methyldithiocarbazate (SMDTC), respectively. Both hap-SBDTC and hap-SMDTC are dissymmetric tridentate O,N,S-donor Schiff base ligands. The catalytic tests were performed in DMF solvent at 60 °C under 1 atm O₂.The olefin conversion was determined using gas chromatography. The percentage conversion of the above-mentioned substrates at the end of 6 h was in the range 86-98%. The final oxidation products were found to be 1-hexanal for 1-hexene, styrene epoxide and phenyl acetaldehyde (81:19) for styrene and cyclohexene epoxide and 2-cyclohexen-1-ol (85:15) in the case of cyclohexene. The oxidation reaction typically followed pseudo-order kinetics; however, a two-stage first order reaction is evident with complex 2b. This is attributed to less steric and electron-donating methyl substitution on S in 2b that possibly imparted a higher reactivity accompanying the formation of an intermediate in a relatively faster reaction step prior to the formation of final oxidation products. A reaction mechanism that explains the experimental results is proposed.     

Structural characterizations of some adducts of silver(I) nitrate and perchlorate with some cyclic di- (or tri-) ene organic ligands

Single crystal X-ray structural characterizations of some adducts of silver(I) nitrate and perchlorate with assorted organic poly-ene ligands (nbd = norbornadiene, bicyclo[2.2.1]hepta-2,5-diene; cod = 1,5-cyclooctadiene; cdt ≡ trans,trans,cis-cyclododeca-1,5,9-triene) are reported, all being polymeric in form (with the exception of mononuclear ionic AgClO₄:cod (1:2)), with chains comprised of alternating silver and nitrate/perchlorate components substituted or linked by unsaturated donors which complete the coordination spheres of the silver atoms. In AgNO₃:nbd (2:1) (a redetermination), pairs of silver/nitrate strands are linked in a one-dimensional polymer by the nbd ligands. In AgNO₃:nbd (1:1)_∞, meandering silver/nitrate strands containing pairs of independent silver and nitrate units in a crystallographic mirror plane are linked to either side with parallel planes by nbd ligands. In AgNO₃:cod (1:1)_∞, the cod ligands ‘chelate’ to the silver atoms in a silver/nitrate chain. In AgNO₃:cdt (1:2)_∞, pairs of ‘unidentate’ cdt ligands are pendant from a silver/nitrate chain, while in the (1:1)_∞ adduct, the cdt ligands bridge pairs of silver atoms from an adjacent chain forming a two-dimensional web. A common form of the bridging nitrate group in the above is as an O,O′-NO₃-O′,O″ bis-chelate, the pair of the bis-oxygen chelates having a common oxygen atom.