Posts Tagged ‘metal’
Wednesday, April 17th, 2013
This is another in the occasional series of “what a neat molecule”. In this case, more of a “what a neat idea”. The s-triazine below, when coordinated to eg ZnI2, forms what is called a metal-organic-framework, or MOF. A recent article[1] shows how such frameworks can be used to help solve a long-standing problem in structure determination, how to get a crystal structure on a compound that does not crystallise on its own.
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References
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Y. Inokuma, S. Yoshioka, J. Ariyoshi, T. Arai, Y. Hitora, K. Takada, S. Matsunaga, K. Rissanen, and M. Fujita, "X-ray analysis on the nanogram to microgram scale using porous complexes", Nature, vol. 495, pp. 461-466, 2013. http://dx.doi.org/10.1038/nature11990
Tags:chair, Interesting chemistry, marine natural product, metal, radiation, X-ray
Posted in Uncategorised | 2 Comments »
Saturday, March 16th, 2013
Functionalisation of a (hetero)aromatic ring by selectively (directedly) removing protons using the metal lithium is a relative mechanistic newcomer, compared to the pantheon of knowledge on aromatic electrophilic substitution. Investigating the mechanism using quantum calculations poses some interesting challenges, ones I have not previously discussed on this blog.
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Tags:carbon-metal bond, Hypervalency, Interesting chemistry, lithiation, metal, metal alkyls, metal lithium, pericyclic, Reaction Mechanism, Tutorial material
Posted in Uncategorised | 2 Comments »
Wednesday, January 16th, 2013
If you search e.g. Scifinder for N,O-diphenyl hydroxylamine (RN 24928-98-1) there is just one literature citation, to a 1962 patent. Nothing else; not even a calculation (an increasing proportion of the molecules reported in Chemical Abstracts have now only ever been subjected to calculation, not synthesis). A search of Reaxys also offers only one hit[1] reporting one unsuccessful attempt in 1963 to prepare this compound. Again, nothing else. Yet show this structure to most organic chemists, and I venture to suggest few would immediately predict this (unless they are experts on benzidine rearrangements).‡
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References
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J.R. Cox, and M.F. Dunn, "The chemistry of O,N-diarylhydroxlamines - I", Tetrahedron Letters, vol. 4, pp. 985-989, 1963. http://dx.doi.org/10.1016/S0040-4039(01)90757-9
Tags:energy, Historical, Interesting chemistry, metal, pericyclic, Reaction Mechanism
Posted in Uncategorised | 7 Comments »
Friday, January 4th, 2013
Tags:basic search, Cambridge, CF 3, conformational analysis, gauche, Interesting chemistry, metal, search takes, similar, Tutorial material
Posted in crystal_structure_mining | 8 Comments »
Monday, December 24th, 2012
tpap[1], as it is affectionately known, is a ruthenium-based oxidant of primary alcohols to aldehydes discovered by Griffith and Ley. Whereas ruthenium tetroxide (RuO4) is a voracious oxidant[2], its radical anion countered by a tetra-propylammonium cation is considered a more moderate animal[3]. In this post, I want to try to use quantum mechanically derived energies as a pathfinder for exploring what might be going on (or a reality-check if you like).
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References
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S.V. Ley, J. Norman, W.P. Griffith, and S.P. Marsden, "Tetrapropylammonium Perruthenate, Pr4N+RuO4
-, TPAP: A Catalytic Oxidant for Organic Synthesis", Synthesis, vol. 1994, pp. 639-666, 1994. http://dx.doi.org/10.1055/s-1994-25538
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D.G. Lee, U.A. Spitzer, J. Cleland, and M.E. Olson, "The oxidation of cyclobutanol by ruthenium tetroxide and sodium ruthenate", Canadian Journal of Chemistry, vol. 54, pp. 2124-2126, 1976. http://dx.doi.org/10.1139/v76-304
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D.G. Lee, Z. Wang, and W.D. Chandler, "Autocatalysis during the reduction of tetra-n-propylammonium perruthenate by 2-propanol", The Journal of Organic Chemistry, vol. 57, pp. 3276-3277, 1992. http://dx.doi.org/10.1021/jo00038a009
Tags:catalysis, energy, free energy, Interesting chemistry, low energy elimination, metal, react freq, Reaction Mechanism, RuO4+ ethanol, triplet state energy, Tutorial material
Posted in Uncategorised | 2 Comments »
Sunday, November 4th, 2012
The text books say that cyclohexenone A will react with a Grignard reagent by delivery of an alkyl (anion) to the carbon of the carbonyl (1,2-addition) but if dimethyl lithium cuprate is used, a conjugate 1,4-addition proceeds, to give the product B shown below. The standard explanation is that the alkyl copper is a “soft” nucleophile attacking the soft conjugate carbon, whereas the alkyl magnesium is a “hard” nucleophile attacking the hard carbonyl carbon. Is this the best explanation?
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Tags:metal, Reaction Mechanism, simulation, Tutorial material
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Wednesday, October 17th, 2012
Every once in a while, one encounters a molecule which instantly makes an interesting point. Thus Ruthenium is ten electrons short of completing an 18-electron shell, and it can form a complex with benzene on one face and a ligand known as trimethylenemethane on the other[1].
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References
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G.E. Herberich, and T.P. Spaniol, "Trimethylenemethane complexes of ruthenium via the trimethylenemethane dianion", Journal of the Chemical Society, Chemical Communications, pp. 1457, 1991. http://dx.doi.org/10.1039/C39910001457
Tags:Interesting chemistry, Iron complex, metal, Postscript
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Monday, October 1st, 2012
Alkene metathesis is part of a new generation of synthetic reaction in which a double C=C bond is formed from appropriate reactants where no bond initially exists (another example is the Wittig reaction), with the involvement† of a 4-membered-ring metallacyclobutane ring 1 (again, very similar to the Wittig). I thought it might make a good addition to my collection of reaction mechanisms and so as the first step I set about locating the transition state (TS or TS’) for the reaction, using in this case a model for Grubbs’ catalyst. I have located a fair few transition states in my time, and was frankly not expecting a surprise. This is the story that showed otherwise …
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Tags:free ligand site, Interesting chemistry, metal, metal coordination, Reaction Mechanism
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Saturday, September 3rd, 2011
The (hopefully tongue-in-cheek) title Mindless chemistry was given to an article reporting[1] an automated stochastic search procedure for locating all possible minima with a given composition using high-level quantum mechanical calculations. “Many new structures, often with nonintuitive geometries, were found”. Well, another approach is to follow unexpected hunches. One such was described in the previous post, and here I follow it to one logical conclusion.
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References
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P.P. Bera, K.W. Sattelmeyer, M. Saunders, H.F. Schaefer, and P.V.R. Schleyer, "Mindless Chemistry", The Journal of Physical Chemistry A, vol. 110, pp. 4287-4290, 2006. http://dx.doi.org/10.1021/jp057107z
Tags:automated stochastic search procedure, free energy, Interesting chemistry, metal, scientist, Tutorial material
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Monday, April 25th, 2011
In discussing ferrocene in the previous post, I mentioned Irving Langmuir’s 1921 postulate that filled valence shells in what he called complete molecules would have magic numbers of 2, 8, 18 or 32 electrons (deriving from the sum of terms in 2[1+3+5+7]). The first two dominate organic chemistry of course, whilst the third is illustrated by the transition series, ferrocene being an example of such. The fourth case is very much rarer, only one example ever having been suggested[1], it deriving from the actinides. In this post, I thought I would augment ferrocene (an 18-electron example) with beryllocene (an 8-electron example) and then speculate about 32-electron metallocenes.
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References
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J. Dognon, C. Clavaguéra, and P. Pyykkö, "Towards a 32‐Electron Principle: Pu@Pb12 and Related Systems", Angewandte Chemie International Edition, vol. 46, pp. 1427-1430, 2007. http://dx.doi.org/10.1002/anie.200604198
Tags:8-electron rule, beryllocene, Cambridge, Interesting chemistry, Irving Langmuir, metal, pence, uranocene
Posted in Uncategorised | 11 Comments »
