Fluorescence quantum yields of trans-stilbene-d0 and -d2 in n-hexane and n-tetradecane: medium and deuterium isotope effects on decay processes
摘要:
Fluorescence quantum yields of trans-stilbene-d0, t-d0, and -alpha,alpha'-d2, t-d2, in n-hexane and in n-tetradecane are reported as a function of temperature. Together with literature lifetimes these are used to define radiative, k(f), and radiationless, k(tp), decay rate constants of trans-stilbene. The index of refraction dependence of k(f) is given by k(f) = k(f)0n(x), where x = 1.65 +/- 0.08 and k(f)0 = 3.75 x 10(8) s-1, the known radiative rate constant for jet-cooled isolated trans-stilbene in the gas phase. Inclusion of the n-dependence of k(f) gives identical k(tp)'s from fluorescence lifetime and quantum yield data. This eliminates small but opposite systematic errors in derived activation parameters for torsional relaxation that were previously based on fluorescence quantum yields or lifetimes, separately, by assuming a constant k(f). Substitution of vinyl hydrogens with deuteria leads to a 50-60% increase in the fluorescence quantum yields. The dependence of k(tpd0)/k(tpd2) on T indicates that deuteration increases DELTAH(tp) by as much as 0.19 +/- 0.11 kcal/mol in n-hexane and that a more significant increase of 0.32 +/- 0.10 kcal/mol applies in n-tetradecane.
Ruthenium‐Catalyzed
<i>E</i>
‐Selective Partial Hydrogenation of Alkynes under Transfer‐Hydrogenation Conditions using Paraformaldehyde as Hydrogen Source
作者:Marcus N. A. Fetzer、Ghazal Tavakoli、Axel Klein、Martin H. G. Prechtl
DOI:10.1002/cctc.202001411
日期:2021.3.5
E‐alkenes were synthesized with up to 100 % E/Z selectivity via ruthenium‐catalyzed partial hydrogenation of different aliphatic and aromatic alkynes under transfer‐hydrogenation conditions. Paraformaldehyde as a safe, cheap and easily available solid hydrogen carrier was used for the first time as hydrogen source in the presence of water for transfer‐hydrogenation of alkynes. Optimization reactions showed
By using a readily available, air‐ and moisture‐stable dihydrido–Ru complex, a variety of Zolefins are accessible under transfer‐hydrogenation conditions with formic acid as the hydrogen source in excellent yields and Z/E selectivities.
Stereodivergent Alkyne Reduction by using Water as the Hydrogen Source
作者:Santhosh Rao、Kandikere Ramaiah Prabhu
DOI:10.1002/chem.201803147
日期:2018.9.18
homogeneous Pd‐catalyzed stereodivergent reduction of alkynes to Z and E alkenes by using H2O as the H2 source is presented. Mediated by a diboron reagent, the transfer hydrogenation has been accomplished to yield the desired geometrical isomer by rational ligand selection. The switchable stereoselectivity achieved using simple phosphine ligands is generally excellent. D2O has also been used as a D2 source
Synthesis and transformations of metallacycles. 31. Catalysts based on cobalt complexes in reactions of trialkyl- and alkylhaloalanes with olefins, allenes, and acetylenes
作者:A. G. Ibragimov、L. O. Khafizova、G. N. Gil"fanova、L. R. Yakupova、A. L. Borisova、U. M. Dzhemilev
DOI:10.1023/b:rucb.0000012366.05437.af
日期:2003.11
Cobalt-containing complexes capable of catalyzing reactions of trialkyl- and alkylhaloalanes (RnAlCl3–n) with olefins, allenes, and acetylenes were synthesized. The reactions afford cyclic and acyclic organoaluminum compounds.
Copper-catalysed, diboron-mediated <i>cis</i>-dideuterated semihydrogenation of alkynes with heavy water
作者:Xiaowei Han、Jiefeng Hu、Cheng Chen、Yu Yuan、Zhuangzhi Shi
DOI:10.1039/c9cc03213d
日期:——
efficiently mediate the transfer of two D atoms from heavy water directly onto alkynes through copper-catalysed cis-selective semihydrogenation. Avoiding the use of costly and flammable D2 gas, this safe and practical process can proceed with excellent chemoselectivity and stereoselectivity. Utilizing the present method as the key step, the formal asymmetrictotalsynthesis of d2-deuterium-labeled cis-combretastatin