Olefin Metathesis, p-Cresol, and the Second Generation Grubbs Catalyst: Fitting the Pieces
p-Cresol as additive to the Grubbs second generation catalyst (GII) allows the cross-metathesis of acrylates with prop-1-en-1-ylbenzenes under conditions that only give the prop-1-en-1-ylbenzene self-metathesis product in the absence of cresol. NMR and IR spectroscopy, MALDI-TOF MS and XPS supported the formation of a ruthenium benzylidene with hydrogen bonds between p-cresol and the chloride ligands of GII. XPS furthermore confirmed p-cresol to increase the binding energies of the GII Ru 3d5/2, 3d3/2, 3p3/2 and 3p1/2 photoelectron lines, whereas 1H NMR spectroscopy indicated the carbene carbon and hydrogen to be shielded. It is thus postulated that p-cresol allows for more facile interaction between electron-deficient compounds and the ruthenium benzylidene by decreasing the electron density on the metal center and increasing the electron density on the carbene.
Swart, Marthinus R.,Twigge, Linette,Erasmus, Elizabeth,Marais, Charlene,Bezuidenhoudt, Barend C. B.
Spectroscopic characterisation of Grubbs 2nd generation catalyst and its p-cresol derivatives
p-Cresol derivatives of the Grubbs 2nd generation catalyst were prepared with either hydrogen bonds between p-cresol and the Cl-ligands or ligand exchange between the Grubbs 2nd generation catalyst and thallium p-cresolate to form Ru-O coordination bonds and TlCl. ATR FTIR and UV–Vis spectroscopic studies revealed a blue shift in certain bands, indicating that coordination occurred. X-ray Photoelectron Spectroscopy was recorded for each of the three Ru-complexes. The binding energy of the Ru 3d5/2, Ru 3p3/2 photoelectron line (found at ca. 281 and 462 eV, respectively) of the different complexes showed the influence of the inductive electronic effects of the p-cresol interaction with the complexes. The Cl 2p photoelectron lines indicated ionic and covalent environments, representing the TlCl and the Ru-Cl bonds, respectively. The atomic ratio between Ru:P:Cl:N:Tl confirmed the binding modes of p-cresol to the Grubbs 2nd generation catalyst.
The iodination of thallium(I) salts of phenols is examined and the results are compared with those of the selective ortho-iodinating reagent thallium(I) acetate-iodine.
Gambie, Richard C.,Larsen, David S.,Rutledge, Peter S.,Woodgate, Paul D.
p. 767 - 769
(2007/10/03)
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