2003 Alcan Award Lecture — Roles of the adjacent metals in the coupling of methylene groups promoted by heterobinuclear complexes of Group 8 and 9 metals

2005 ◽  
Vol 83 (8) ◽  
pp. 1043-1055 ◽  
Author(s):  
Martin Cowie
Keyword(s):  
Ambient Temperature ◽  
Key Words ◽  
Fischer Tropsch ◽  
Methyl Group ◽  
Methylene Groups ◽  
Ru Species ◽  
Methylene Group ◽  
Coupling Sequence

The reactivities of the heterobinuclear complexes, [MM′(CO)4(dppm)2][X] (MM′ = RhOs, RhRu, IrRu; dppm = µ-Ph2PCH2PPh2; X– = BF4–, CF3SO3–) with diazomethane are reported. The RhOs species reacts to give three products of methylene-group incorporation, depending on the temperature; at –80 °C the methylene bridged product, [RhOs(CO)4(µ-CH2)(dppm)2][X], is formed exclusively, at ambient temperature only [RhOs(η1-C3H5)(CH3)(CO)3(dppm)2][X], having the allyl group bound to Rh and the methyl group bound to Os, is obtained, while at intermediate temperatures [RhOs(η1:η1-C4H8)(CO)3(dppm)2][X], having the butanediyl fragment chelating on Os, is generated. Based on labeling studies a mechanism is proposed rationalizing formation of the different products. Under the same range of conditions the Rh/Ru and Ir/Ru species yield only the methylene bridged products, [MM′(CO)4(µ-CH2)(dppm)2][X] (MM′ = RhRu, IrRu). A rationalization for the different reactivities observed and a description of the roles of the different metals in coupling of the methylene groups are presented. Attempts to model key intermediates in the methylene coupling sequence promoted by the Rh/Os complexes, through coupling of methylene groups with ethylene or alkynes, are described. Key words: heterobinuclear, rhodium/osmium, rhodium/ruthenium, iridium/ruthenium, methylene coupling, Fischer–Tropsch, alkyne insertions, bimetallic cooperativity.

Mechanistic studies of the reactions of 2-methylpropene with deuterium over supported metal catalysts

1989 ◽  
Vol 424 (1866) ◽  
pp. 39-56 ◽  
Keyword(s):  
Mass Spectrometry ◽  
Gas Chromatography ◽  
Metal Catalysts ◽  
Supported Metal Catalysts ◽  
Mechanistic Studies ◽  
Dissociative Mechanism ◽  
Methyl Group ◽  
Methylene Groups ◽  
Methylene Group ◽  
Supported Metal

Deuterium NMR spectroscopy, gas chromatography and mass spectrometry have been used to examine the products from the reaction of 2-methylpropene with deuterium over supported metal catalysts. The detailed information, so obtained, about the number, location and grouping of deuterium atoms in both the exchanged alkenes and the 2-methylpropanes formed by addition provided evidence about possible mechanisms. With palladium, exchange was faster than addition and the deuterium atoms were randomly distributed in the alkene, probably through a π-allyl dissociative mechanism. With platinum and rhodium, exchange occurred preferentially in the methylene groups of the alkene and the results indicated a dissociative mechanism involving adsorbed vinyl intermediates together with some intramolecular double-bond movement through a π-allyl type of species. Relatively little exchange occurred with iridium. The activities of the metals for production of alkane at 235 K were Rh > Ir > Pd > Pt but the spread was only a factor of about 20. With all metals except palladium further exchange occurred during the addition process, but this was mainly concentrated in one methyl group. This behaviour was explained in terms of mechanisms that permitted additional exchange of the methylene group of the alkene to take place during the addition process.

scholarly journals Stereochemistry of the incorporation of valine methyl groups into methylene groups in cephalosporin C.

1984 ◽  
Vol 222 (3) ◽  
pp. 777-788 ◽  
Author(s):  
C P Pang ◽  
R L White ◽  
E P Abraham ◽  
D H G Crout ◽  
M Lutstorf ◽  
...  
Keyword(s):  
Side Chain ◽  
Methyl Groups ◽  
Cephalosporin C ◽  
Cephalosporium Acremonium ◽  
Methyl Group ◽  
Methylene Groups ◽  
Methylene Group

‘Chiral methyl valines’, i.e. samples of valine labelled stereospecifically in the methyl groups with 2H and 3H, were incorporated into cephalosporin C by a suspension of washed cells of Cephalosporium acremonium. Analysis by 3H n.m.r. of the cephalosporin C produced showed that the conversion of the 3-pro-S-methyl group of valine into the acetoxymethyl side-chain was a highly stereospecific process. By contrast, conversion of the 3-pro-R-methyl group into the endocyclic methylene group of the dihydrothiazine ring was shown to proceed by a non-stereospecific process.

Remarkable kinetic stability of α-thiocarbamoyl substituted 4-methoxybenzylcations

1998 ◽  
Vol 76 (12) ◽  
pp. 1910-1915 ◽  
Author(s):  
Robert A McClelland ◽  
Victoria E Licence ◽  
John P Richard ◽  
Kathleen B Williams ◽  
Shrong-Shi Lin
Keyword(s):  
Key Words ◽  
Strong Interaction ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Visible Absorption ◽  
Methyl Group ◽  
Thioamide Group ◽  
Azide Ion ◽  
Uv Visible ◽  
Leaving Groups

4-Methoxybenzyl cations bearing α-(N,N-dimethylcarbamoyl) and α-(N,N-dimethylthiocarbamoyl) substituents have been generated photochemically upon irradiation of precursors with pentafluorobenzoate or 4-methoxybenzoate leaving groups. The ions have been observed with flash photolysis in 40:60 acetonitrile:water and in 50:50 methanol:water, and rate constants were measured for their decay in solvent alone and for their capture by azide ion. The cations so studied and their lifetimes in 40% acetonitrile are 6, ArC+H-CONMe2, 0.6 μs; 2, ArC+H-CSNMe2, 7 ms; and 4, ArC+(CH3)-CSMe2, 6 ms, where Ar = 4-MeOC6H4. The cation 4 reacts with solvent by elimination of a proton from the α-methyl group, and the rate constant for solvent addition must be less than 1 s-1. The CSNMe2 substituted cations are 105-107-fold longer lived than analogs where the thioamide group has been replaced with an α-methyl. The UV-visible absorption spectra of these two cations also show significant differences from those of typical 4-methoxybenzyl cations. Thus, both the lifetimes and spectra point to a strong interaction of the benzylic centre with the thioamide group. Key words: flash photolysis, thiocarbamoyl stabilized carbocation, photosolvolysis.

Assesment of Vibrational Coupling at Solid-SAM Junctions

2011 ◽  
Author(s):  
Christopher B. Saltonstall ◽  
John C. Duda ◽  
Patrick E. Hopkins ◽  
Pamela M. Norris
Keyword(s):  
Thermal Conductance ◽  
Chemical Properties ◽  
Self Assembled Monolayers ◽  
Vibrational Coupling ◽  
Thermal Boundary Conductance ◽  
Hartree Fock ◽  
Assembled Monolayers ◽  
Methylene Groups ◽  
Methylene Group ◽  
And Chemical Properties

Self-assembled monolayers (SAMs) have recently garnered much interest due to their unique electrical and chemical properties. The limited literature detailing SAM thermal properties has suggested that thermal boundary conductance (TBC) at solid-SAM junctions is not only low, but also insensitive to changes in SAM length as the number of methylene groups (-CH2-) along alkanedithiol chains is varied from 8 to 10. The present study investigates the vibrational spectra of alkanedithiol SAMs as a function of the number of methylene groups forming the molecule backbone via Hartree-Fock methods and the subsequent effects on TBC calculated using a diffuse scattering model. In particular, the vibrational overlap between the alkanedithiol and Au is studied. It is found that despite the addition of 9 new vibrational modes per added methylene group, only one of those modes is elastically accessible to Au. It is believed that this “vibrational inaccessibility” is the cause of the insensitivity of thermal conductance to molecule length.

The reactions of [Pd2Cl2(μ-PP)2] (PP = dppm, dmpm) with Et2NC≡CNEt2 in methylene chloride solution: X-ray crystal structures of [Pd2Cl2(μ-CH2)(μ-dppm)2] and hexakis(diethylamino)benzene, C6(NEt2)6

1996 ◽  
Vol 74 (11) ◽  
pp. 2331-2339 ◽  
Author(s):  
Sean R. Klopfenstein ◽  
Constanze Kluwe ◽  
Kristin Kirschbaum ◽  
Julian A. Davies
Keyword(s):  
Key Words ◽  
Crystal Structures ◽  
Chloride Solution ◽  
Methylene Chloride ◽  
X Ray ◽  
Methylene Chloride Solution ◽  
Methylene Group

The binuciear palladium(I) complex, [Pd2Cl2(μ-dppm)2] (dppm = bis(diphenylphosphino)methane), has been shown to react with bis(diethylamino)acetylene, Et2NC≡CNEt2, in methylene chloride solution to yield two isolable products, the known methylene-bridged complex, [Pd2Cl2(μ-CH2)(μ-dppm)2], and hexakis(diethylamino)benzene, C6(NEt2)6, both of which have been characterized crystallographically. The source of the bridging methylene group in [Pd2Cl2(μ-CH2)(μ-dppm)2] has been shown to be the methylene chloride solvent. A mechanism that accounts for the formation of the two isolable products is proposed. The complex, [Pd2Cl2(μdmpm)2] (dmpm = bis(dimethylphosphino)methane), was similarly found to react with Et2NC≡NEt2 in methylene chloride solution to yield [Pd2Cl2(μ-CH2)(μ-dmpm)2], which was identified spectroscopically. Key words: acetylene, palladium, cyclooligomerization, aminoacetylene, hexakis(diethylamino)benzene.

scholarly journals N′-[(E)-2-Hydroxybenzylidene]-2-(6-methoxynaphthalen-2-yl)propanohydrazide: a redetermination

IUCrData ◽  
2016 ◽  
Vol 1 (4) ◽  
Author(s):  
Shaaban K. Mohamed ◽  
Joel T. Mague ◽  
Mehmet Akkurt ◽  
Alaa F. Mohamed ◽  
Mustafa R. Albayati
Keyword(s):  
Hydrogen Bonds ◽  
Ambient Temperature ◽  
Title Compound ◽  
Asymmetric Unit ◽  
Methyl Group ◽  
Π Interactions ◽  
Compound C ◽  
Additional Input ◽  
Independent Molecules

The structure of the title compound, C21H20N2O3, was originally determined at ambient temperature [Wuet al.(2007).Inorg. Chim. Acta,360, 3069–3074]. In this determination, with data collected at 150 K, the asymmetric unit comprises two independent molecules (1 and 2) that differ considerably in their conformations. In particular, the methyl group at the mid-point of molecule 2 is disordered over two sites. This was modelled with restraints so that the geometries of the two components are comparable and the disorder components refined to an occupancy ratio of 0.750 (6):0.250 (6). Intramolecular O—H...N and intermolecular N—H...O hydrogen bonds stabilize the structure with significant additional input from C—H...π interactions.

scholarly journals Synthesis of Some Biologically Important 3-Oxacepham Derivatives

1970 ◽  
Vol 5 (1) ◽  
pp. 47-51 ◽  
Author(s):  
Mohammad Rafiqul Islam ◽  
Mohammad Nurnabi ◽  
AM Sarwaruddin Chowdhury ◽  
Mohammad Mehdi Masud
Keyword(s):  
Key Words ◽  
Full Text ◽  
Crystallographic Analysis ◽  
High Yield ◽  
Methyl Group ◽  
X Ray ◽  
Tert Butyl ◽  
Relative Stereochemistry

The 6H-oxathiazines 1a-e having imine moiety underwent [2+2] cycloaddition with phenoxyacetylchloride in the presence of Et3N to give β-lactam derivatives 2a-e in high yield. The X-ray crystallographic analysis revealed the relative stereochemistry that the substituents at C-2 and C-4 were cis configurated. The subtituents at C-6 and C-7 were also cis to each other. However, the 6H-oxathiazines 1f-i containing tert-butyl or methyl group at C-4 did not undergo the cycloaddition. Key words: Azetedinone, β-lactam, oxacepham, cycloaddition, imine, ketene, oxathiazine. Dhaka Univ. J. Pharm. Sci. Vol.5(1-2) 2006 The full text is of this article is available at the Dhaka Univ. J. Pharm. Sci. website

Stereoselectivity of C(3) methylation and aldol condensation of camphor and derivatives

1991 ◽  
Vol 69 (3) ◽  
pp. 558-566 ◽  
Author(s):  
J. H. Hutchinson ◽  
D. L. F. Li ◽  
T. Money ◽  
M. Palme ◽  
M. R. Agharahimi ◽  
...  
Keyword(s):  
Key Words ◽  
Aldol Condensation ◽  
Hydrogen Atoms ◽  
Methyl Group

The stereoselectivity of methylation and aldol condensation of camphor and derivatives is determined by the presence or absence of a C(7) syn-methyl group and (or) C(5) and C(6) endo-hydrogen atoms. Key words: camphor, C(3) methylation, C(3) aldol.

Methylsteroids. VII. Factors Affecting the Hydrolysis of 7α- and 11β-Acetoxylanostanes

1961 ◽  
Vol 14 (1) ◽  
pp. 48
Author(s):  
CS Barnes ◽  
BD Beilby
Keyword(s):  
Carbonyl Group ◽  
Carbonyl Groups ◽  
Factors Affecting ◽  
Steric Crowding ◽  
Methylene Groups ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of ◽  
Methylene Group

Doubly bonded methylene groups have been introduced into 7α- and 11β-acetoxylanostanes and the rate of hydrolysis compared with compounds having a hydroxy or carbonyl group at the same position as the methylene group. It was found that methylene groups facilitate hydrolysis of the hindered acetoxy groups in the same way, but not to the same extent, as carbonyl groups. It is concluded that the facilitation in each case results from a conformational disturbance, but that there is some other factor involved in carbonyl facilitation. It was not possible to demonstrate a similar effect resulting from steric crowding of substituents.

PERIODATE–PERMANGANATE OXIDATIONS: II. DETERMINATION OF TERMINAL METHYLENE GROUPS

1955 ◽  
Vol 33 (11) ◽  
pp. 1710-1713 ◽  
Author(s):  
R. U. Lemieux ◽  
E. Von Rudloff
Keyword(s):  
Quantitative Yield ◽  
Permanganate Oxidation ◽  
Initial Stage ◽  
Methylene Groups ◽  
Methylene Group

The periodate–permanganate oxidation of a terminal methylene group can be made to produce formaldehyde in high although not quantitative yield. Since the yields compare favorably with those obtained by ozonolysis, the reagent can serve as the basis for a convenient micromethod for the estimation of terminal methylene groups. The less than theoretical yields of formaldehyde are believed mainly due to the conversion of the olefin in part to α-hydroxyaldehyde in the initial stage of the reaction.

Sign in / Sign up

Export Citation Format

Share Document