1603-73-2Relevant articles and documents
Scherf,Brown
, p. 1613,1617 (1961)
Migratory Insertion of Carbenes into Au(III)-C Bonds
Zhukhovitskiy, Aleksandr V.,Kobylianskii, Ilia J.,Wu, Chung-Yeh,Toste, F. Dean
supporting information, p. 466 - 474 (2018/03/21)
Migratory insertion of carbon-based species into transition-metal-carbon bonds is a mechanistic manifold of vast significance: it underlies the Fischer-Tropsch process, Mizoroki-Heck reaction, Ziegler-Natta and analogous late-transition-metal-catalyzed olefin polymerizations, and a number of carbonylative methods for the synthesis of ketones and esters, among others. Although this type of reactivity is well-precedented for most transition metals, gold constitutes a notable exception, with virtually no well-characterized examples known to date. Yet, the complementary reactivity of gold to numerous other transition metals would offer new synthetic opportunities for migratory insertion of carbon-based species into gold-carbon bonds. Here we report the discovery of well-defined Au(III) complexes that participate in rapid migratory insertion of carbenes derived from silyl- or carbonyl-stabilized diazoalkanes into Au-C bonds at temperatures ≥ -40 °C. Through a combined theoretical and experimental approach, key kinetic, thermodynamic, and structural details of this reaction manifold were elucidated. This study paves the way for homogeneous gold-catalyzed processes incorporating carbene migratory insertion steps.
Keto-enol tautomerism and hydration of 9-acylfluorenes
Harcourt, Myles P.,O'Ferrall, Rory A. More
, p. 1415 - 1426 (2007/10/02)
Keto-enol tautomeric constants and ionisation constants heve been measured for the keto and enol tautomeers of 9-formyl-, 9-acetyl- and 9-benzoyl-fluorene in aqueous solution at 25 deg C.Values of pKE(KE=/ and pKE=-log KE) are -1.22, 2.28 and 1.91, respectively, and the corresponding pKas for enolate anion formation are 6.19, 9.94 and 9.44 for the keto tautomers and 7.41, 7,66 and 7.53 for the enols.The measurements demonstrate the effectiveness of the fluorenyl group in increassing enol stability and ketone acidity.For 9-formyfluorene, for which the enol is the stable tautomer, KE is increased by a factor of more than 107 and the acidity of the keto tautomer by more than 109 relative to acetaldehyde (pKE=6.17, pKa=16.73).For 9-acetyl- and 9-benzoyl-fluorenes tautomeric constants were determined kinetically by combining rate constants for ketonisation measured spectrophotometrically following quenching of their enolate anions in carboxylic acid buffers with rate constants for enolisation measured by halogen trapping under the same conditions.For 9-formylfluorene rate constants for enolisation were measured by generating its unstable aldehyde tautomer from an ethanethiol hemithioacetal by reaction with iodine.Combining these rate constants with rate constants for ketonisation from trapping the aldehyde with bisulfite ion gave the tautomeric constant.In aqueous solution the aldehyde tautomer of 9-formyfluorene is appreciably hydrated and an equilibrium constant Kh=/=5.6 was derived from measurements of the (slower) equilibration of enol and hydrate following enolisation in acetic acid buffers.In aqueous solution therefore the enol (71percent) and hydrate (24percent) are the principal species. log k-pH profiles for enolisation, ketonisation and hydration reactions are reported.Intrinsic reactivities of the three enolate anions towards protonation by H3O+ and carboxylic acids are comapred within and extended Broensted plot of log k versus ΔpK with mearurements by Kresge for the corresponding enolate anions derived from fluorene-9-carboxylic acid and its methyl, methylthio and methylthione esters.Surprisingly, not only are the thio and thione esters less acidic than the oxygen ester, but intrinsically less reactive.
