The modulation of membrane fluidity by hydrogenation processes. III. The hydrogenation of biomembranes of spinach chloroplasts and a study of the effect of this on photosynthetic electron transport

A method is reported for the in situ modification of the lipids of isolated spinach chloroplast membranes. The technique is based on a direct hydrogenation of the lipid double bonds in the presence of the catalyst, chlorotris(triphenylphosphine)rhodium (I). The pattern of hydrogenation achieved suggests that the catalyst distributes amongst all of the membranes. The polyunsaturated lipids within the membranes are hydrogenated at a faster rate and at an earlier stage than are the monoenoic lipids.Whilst addition of the catalyst to the chloroplast causes an initial 10–20% decrease in Hill activity, saturation of up to 40% of the double bonds present can be accomplished without causing further significant alterations in photosynthetic electron transport processes or marked morphological changes of the chloroplast structure as observed in the electron microscope.     

The use of tri-O-acetyl-D-glucal and -D-galactal in the synthesis of 3-acetamido-2,3-dideoxyhexopyranoses and -hexopyranosides

Addition of hydrazoic acid to alpha,beta-unsaturated aldehydes derived from tri-O-acetyl-D-glucal and -D-galactal gave 3-azido-2,3-dideoxyhexopyranoses. These were converted into 1,4,6-tri-O-acetyl-3-azido-2,3-dideoxyhexopyranoses as well as methyl and ethyl glycosides. Hydrogenation of the proamine group in 3-azido-2,3-dideoxy derivatives provided different 3-amino and 3-acetamido sugars. The configuration and conformation of all products were established on the basis of the 1H and 13 C NMR, IR and polarimetric data.     

The hydrogenation and hydroformylation of alkenes as catalyzed by polymer-anchored rhodium trichloride under water gas shift reaction conditions

The ‘heterogenized’ water gas shift catalyst Rh/P4VP, prepared from the reaction of RhCl₃ with poly(4-vinylpyridine), is also active for hydrogenation and hydroformylation of 1-hexene and cyclohexene in aqueous ethoxyethanol under mild shift reaction conditions (typically 0.9 atm. P_CO at 100°C). The catalytic activities for these systems were studied as functions of several experimental variables. Hydroformylation rates increased with the P_CO but exhibited saturation behavior in the 1.5 atm. range. Rates for cyclohexane and hexane production were inhibited by CO at higher pressures. Cyclohexene hydroformylation and hydrogenation turnover frequencies were independent of the polymer-loading (50–150 μM RhCl₃/1.0 g P4VP) indicating that the active species are of the same nuclearity as the principal species present. The temperature dependence did not follow simple Arrhenius behavior, but appeared segmented. These data are discussed in terms of possible mechanisms.     

Unexpected reductions of glycosyl spacer-armed phthalimides

An unusual reductive ring-opening reaction in the title compounds, of the phthalimide group with sodium hydride in anhydrous DMF is observed for the first time and the presumed mechanism is described in detail. An unexpected hydrogenation of the phthalimide group was also observed.     

Heterogenised Rh(I), Ir(I) metal complexes with chiral triaza donor ligands: a cooperative effect between support and complex

Rhodium and iridium complexes of the chiral triaza ligands, {N,N^′-bis{[(2S)-(1-benzylpyrrolidinyl)]methyl}amine (2), N,N^′-bis{[(2S)-(1-benzylpyrrolidinyl)]methyl}-N-propylamine (3), N,N^′-bis{[(2S)-(1-benzylpyrrolidinyl)]methyl}-N-[3-(triethoxysilyl)propyl]amine (4)}, are described. All ligands form one to one [ML] species with the above metal ions. The structures of these complexes were elucidated by analytical and spectroscopic data (elemental analysis, mass spectroscopy, IR, ¹H and ¹³C NMR). The fixation of the preformed triethoxysilyl-rhodium and iridium complexes, on mesoporous solids (MCM-41, SBA-15), and their use, under heterogeneous conditions, for the hydrogenation reactions are reported. The catalytic activity and selectivity of heterogenised complexes are higher to that observed under homogeneous conditions, as a consequence of the complex- and/or reagents-to-support interaction. The stable covalent bond between support and complex allows the recovery and recycling of the heterogenised catalysts for a number of cycles, moreover atomic absorption analysis of the reaction solutions shows that there is not any metal leaching into the solutions.     

Unprecedented rhodium-mediated catalytic transfer hydrogenation of a phosphonate functionalized olefin in ecofriendly media

RhCl₃ · xH₂O catalyst-mediated hydrogenation reactions of vinyl phosphonic diethyl ester H₂CCH-P(O)(OEt)₂ (1) have been investigated. Results demonstrate that the hydrogenation of H₂CCH-P(O)(OEt)₂ (1) to CH₃CH₂-P(O)(OEt)(OH) (2) proceeds in the presence of RhCl₃ · xH₂O catalyst, without any external hydrogen source and ancillary ligands, to near qualitative yields in ethanol and water media. ³¹P, ¹³C and ¹H NMR and deuterium-labeling experiments provide evidence for the non-concerted mechanistic pathway associated with the hydrogenation of 1 to 2.     

Biotransformation of sesquiterpenoids having α,β-unsaturated carbonyl groups with cultured plant cells of Marchantia polymorpha

The biotransformation of sesquiterpenoids having an α,β-unsaturated carbonyl group, such as α-santonin (1), lancerodiol p-hydroxybenzoate (2), 8,9-dehydronootkatone (3), and nootkatone (4), with cultured suspension cells of Marchantia polymorpha was investigated. It was found that the CC double bond of 1 and 2 was hydrogenated to give 1,2-dihydro-α-santonin (5) and 3,4-dihydrolancerodiol p-hydroxybenzoate (6), respectively, while the allylic position of the CC double bond of 3 and 4 was hydroxylated to give 13-hydroxy-8,9-dehydronootkatone (7) and 9-hydroxynootkatone (8), respectively.     

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.     

Catalytic activity of dihydride ruthenium complexes in the hydrogenation of nitrogen containing heterocycles

The catalytic activity of the dihydride ruthenium complexes, RuH₂(CO)₂(PⁿBu₃)₂, RuH₂(CO)₂(PPh₃)₂ and RuH₂(PPh₃)₄, in the hydrogenation of nitrogen containing heterocycles has been tested by analyzing the influence of reaction parameters such as temperature, hydrogen pressure, catalyst concentration, on the rate and regioselectivity of the reaction.RuH₂(PPh₃)₄ shows a better catalytic activity with an 86.7% conversion of quinoline after 24 h at 100 °C under a hydrogen pressure of 25 bar, while RuH₂(CO)₂(PPh₃)₂ and RuH₂(CO)₂(PⁿBu₃)₂ in the same conditions give a conversion of 37.1% and 35.6%, respectively. These results are confirmed by the reaction rate of the hydrogenation of quinoline, since the K_c in the presence of RuH₂(PPh₃)₄ (1.46 × 10⁻⁵ s⁻¹) is higher than others (6.37 × 10⁻⁶ s⁻¹ for RuH₂(CO)₂(PPh₃)₂ and 6.36 × 10⁻⁶ s⁻¹ for RuH₂(CO)₂(PⁿBu₃)₂).Noteworthy is the selectivity of these catalytic systems in the hydrogenation of quinoline: in all tests the three catalysts lead to 1,2,3,4-tetrahydroquinoline as the major product, furthermore this compound is the only formed in the presence of RuH₂(CO)₂(PPh₃)₂. The selectivity is affected by the presence of an acid (CH₃COOH) or a base (NⁿBu₃) in the reaction media.The complex RuH₂(PPh₃)₄ is catalytically active, even if in a minor extent, in the hydrogenation of isoquinoline, pyridine and 2-methylpyridine.The basicity of the substrate and steric hindrance around the nitrogen atom show a great influence on the conversion.The results obtained suggest that the catalytic system activates a heterocyclic ring through the coordination of the heteroatom to the metal centre of the complexes.