Ruthenium(II) complexes of monodonor ligands: efficient reagents for asymmetric ketone hydrogenation

[Chemical reaction: See text] A series of BINOL-derived ligands have been prepared and incorporated into ruthenium(II) complexes containing a diamine ligand. The complexes have proven to be excellent catalysts for the asymmetric hydrogenation of ketones, giving reduction products with enantiomeric excesses of up to 99%.     

CHLOROPHYLL ONE-ELECTRON PHOTOCHEMISTRY-II. PHOTOSENSITIZATION BY CHLOROPHYLL,PHEOPHYTIN AND BACTERIOCHLOROPHYLL OF A ONE-ELECTRON TRANSFER REACTION BETWEEN ETHANOL AND QUINONE*

Abstract— Chlorophyll, pheophytin and bacteriochlorophyll sensitize a one-electron transfer in the presence of quinones in ethanol, to produce a ternary complex of ground state porphyrin analog, alcohol cation radical and semiquinone anion radical as the primary photo-product at low temperature. A similar photo-oxidation of alcohol to produce a binary complex is caused by direct excitation of quin-one in the absence of chlorophyll. The mechanisms of these reactions and their implications for photosynthesis are discussed.     

Regioselective ortho lithiation of halopyridines

Regioselective ortho lithiation of 2-, 3-, and 4-halopyridines is achieved with lithium diisopropylamide (?78°, tetrahydrofuran) to afford, upon quenching with electrophilic reagents, 2,3- and 3,4-disubstituted pyridines in good to excellent yield.     

A fast computer algorithm for finding the permanent of adjacency matrices

A fast computer algorithm is described which brings computation of the permanents of sparse matrices, specifically, chemical adjacency matrices, within the reach of a desktop computer. Examples and results are presented, along with a discussion of the relationship of the permanent to the Kekulé structure count. Also presented is a C-language implementation which was deliberately written for ease of translation into other high-level languages.     

Gradients of the Exchange-repulsion Energy in the General Effective Fragment Potential Method

Formulae for calculating the analytic gradients of the exchange-repulsion energy in the general effective fragment potential (EFP2) method are derived and implemented using a direct differentiation approach. The timings for the exchange repulsion gradient evaluations are approximately three times longer than the energy evaluations, orders of magnitude faster than a previous implementation. Since the direct differentiation approach is not approximate, the gradients can be used with confidence in molecular dynamics and Monte Carlo simulations with the EFP2 method.     

Quantitative determination of selected compounds in a Kentucky 1R4F reference cigarette smoke by multidimensional gas chromatography and selected ion monitoring-mass spectrometry

Eight compounds from a Kentucky 1R4F reference cigarette smoke condensate have been determined by selected ion monitoring-mass spectrometry (SIM-MS) to confirm the validity of multidimensional gas chromatography (MDGC) as a quantitative tool in complex mixture analyses. Four electrostatically precipitated smoke condensate samples of 100 cigarettes each are dissolved individually in 25 mL of 2-propanol. The 2-propanol contains two methyl esters (C8 and C14) and seven deuterium-labeled compounds used as internal standards (IS). Analysis of the compounds of interest, pyridine; acetamide; acrylamide; phenol; o-, m-, and p-cresol; and quinoline, is accomplished by using two heartcuts. Heartcut times of the MDGC analysis are selected such that at least one IS is transferred with each group of compounds being analyzed. This study shows that the MDGC technique previously developed and described can be used for quantitative analyses. A comparison is made between the two types of internal standards. The results obtained for both types of internal standards agree within 20% of each other, on the average, with higher standard deviations for approximately 60% of the compounds where methyl esters are used as internal standards.     

Synthesis of an isomer of the germacranolide isoaristolactone

Photocycloadditlon of (+)-isoplperltenone and cyclobutene-1-carboxylic acid gives an adduct which upon reduction with NaCNBH₃ followed by thermolysis yields an isomer of isoaristolactone in an overall yield of 26%.     

Rhodium(I) catalyst supported on polymer crystal surfaces: Further hydrogenation studies

Catalysts bound to polymers in the form of crosslinked beads have been demonstrated to have a number of advantages over homogeneous catalysts. However, there are several problems that exist due to the polymer support being in the form of a bead. The rate of reaction depends on the presence of solvents that adequately swell the bead in order to allow access to the catalytic sites. Differences in polarity and reactant size can inhibit diffusion into the bead. Recently a new system has been developed whereby tris(triphenyl phosphine) chlororhodium (I) (Wilkinson's catalyst) is bound to the surface of polyethylene single crystals. Polyethylene single crystals have a very high surface to volume ratio allowing for greater ease of reaction compared to a bead system. In a previous paper we showed that there is a dramatic increase in catalytic activity and that the reaction rate increased as the polarity of solvent was increased, even in ethanol where the homogeneous catalyst is not soluble and the polystyrene bead support would not swell. In this letter we are describing the activity of hydrogenation of olefins contained in both large and/or polar molecules. The results demonstrate the advantages of supported catalysts on polyethylene single crystals rather than on polymer beads.     

Some diels—alder reactions of η1-bonded cyclopentadienylmetal compounds

Bis(cyclopentadienyl)mercury readily undergoes Diels—Alder reactions with RCCR (R = CO₂Me or CF₃), CF₃CFCFCF₃, CF₃CFCF₂, (CF₃)₂CC(CN)₂, C₂(CN)₄ and Ph$\text{NCONNC}$O to give stable adducts characterised by¹H, ¹⁹F and ¹³C NMR, spectroscopy. Similar reactions of CF₃CCCF₃ and CF₃CFCFCF₃ with the cyclopentadiene derivatives Me₃MC₅H₅ and (Me₃M)₂C₅H₄ (M = Si, Sn) are also described.     

VECTORIAL ELECTRON TRANSPORT ACROSS LIPID VESICLE MEMBRANES DRIVEN BY TWO PHOTOREACTIONS. I. ETHYLENEDIAMINETETRAACETIC ACID AS AN ELECTRON DONOR via FLAVIN TRIPLET STATE IN THE INNER COMPARTMENT AND CYTOCHROME c AS AN ELECTRON ACCEPTOR FROM CHLOROPHYLL TRIPLET STATE IN THE OUTER COMPARTMENT

Negatively charged vesicle suspensions containing chlorophyll a (chl) dissolved in the lipid bilayer, flavin mononucleotide (FMN) and/or ethylenediaminetetraacetic acid (EDTA) enclosed in the inner compartment as electron sources and oxidized cytochrome c (cyt c[ox]) in the outer compartment as an electron acceptor have been studied using laser flash photolysis and steady-state irradiation methods. Cytochrome c initially quenches the chl triplet state (³chl) generating the chlorophyll cation radical (chi⁺′) in the membrane. Reverse electron transfer from cyt c(red) to chl^+. subsequently occurs in a kinetically biphasic reaction, with rate constants of 430 pT 30 and 21.9 pT 1.7 s^?1 for the fast and slow phases, respectively. In the absence of FMN, reduction of chl⁺′ by EDTA in the inner compartment can be observed during steady-state irradiation but not in a laser flash photolysis experiment. This is due to a low reaction yield, which is probably limited by the repulsive electrostatic interaction between EDTA and the negatively charged membrane. When FMN was enclosed together with EDTA in the inner Compartment, the reaction yield of vectorial electron transfer across the bilayer from EDTA to cyt c(oX) was increased by a factor of six during steadystate white light irradiation. Laser flash photolysis and steady-state irradiation experiments using red and blue light excitation have demonstrated that the enhancement mechanism involves the formation of fully reduced FMN by blue light-sensitized photooxidation of EDTA via the flavin triplet state, occumng simultaneously with red lightsensitized electron transfer to cyt c via the chlorophyll triplet state.