Elementary Arrhenius Parameters in the CO-for-Ethylene Dissociative Substitution of Cr(CO)5(C2H4)
摘要:
Gas-phase samples of Cr(CO)(5)(C2H4) are prepared in situ by laser irradiation of quantitative mixtures of Cr(CO)(6), CO, and C2H4 In the presence of CO and C2H4, Cr(CO)(5)(C2H4) decays thermally to re-form Cr(CO)(6) by the mechanism of dissociative substitution. Systematic study of the rate of this reaction as a function of partial pressures of CO and C2H4 yields the elementary high-pressure limiting thermal rate constant for unimolecular dissociation of Cr(CO)(5)(C2H4) (k(1)) and the relative rate constant for recombination of Cr(CO)(5) with CO and C2H4 (k(2)/k(3)) Measurements of k(1) and k(2)/k(3) extended over a range of precisely controlled temperatures determine Arrhenius parameters reflecting energetic and statistical properties of these elementary rate processes.
Pulsed laser photolysis of chromium hexacarbonyl in the gas phase
作者:W. H. Breckenridge、G. M. Stewart
DOI:10.1021/ja00263a002
日期:1986.2
Spectres d'absorption dus a des especes Cr(CO) 5 et Cr(CO 5 )Q (avec Q=Cr(CO) 6 ; N 2 ; NH 3 ; methanol; acetone; ethylene et silane). Formation d'un produit inconnu par reaction de deux molecules Cr(CO) 5
Specters d'absorption dus a des especes Cr(CO) 5 和 Cr(CO 5 )Q (avec Q=Cr(CO) 6 ;N 2 ;NH 3 ;甲醇;丙酮;乙烯和硅烷)。Formation d'un produit inconnu par reaction de deux 分子Cr(CO) 5
Preparative-scale organometallic chemistry in supercritical fluids; isolation of [Cr(CO)5(C2H4)] as a stable solid at room temperature
作者:James A. Banister、Steven M. Howdle、Martyn Poliakoff
DOI:10.1039/c39930001814
日期:——
A miniature flow reactor has been developed for photochemical reactions in supercritical fluids; [Cr(CO)5(C2H4)] is isolated, for the first time, by the UV photolysis of [Cr(CO)6] in supercritical C2H4 at room temp, with a yield of ca. 40 mg per hour at ca. 80% purity as estimated by IR spectroscopy.
Ethene complexes of chromium; the generation and characterisation of [Cr(CO)5(C2H4)] and cis- and trans-[Cr(CO)4(C2H4)2] and their relative stabilities in liquid xenon solution
作者:Marion F. Gregory、Sarah A. Jackson、Martyn Poliakoff、James J. Turner
DOI:10.1039/c39860001175
日期:——
The unstable complexes [Cr(CO)5(C2H4)] and cis- and trans-[Cr(CO)4(C2H4)2] are generated by photolysis of [Cr(CO)6] in C2H4-doped liquidxenon and are characterised by i.r. spectroscopy; these complexes are all unstable, even at -78 °C with the cis-[Cr(CO)4(C2H4)2] complex being the least stable, decomposing with an enthalpy of activation, ΔH‡, of ∼60 kJ mol–1.
不稳定络合物[Cr(CO)5(C 2 H 4)]和顺式和反式-[Cr(CO)4(C 2 H 4)2 ]是通过在C中光解[Cr(CO)6 ]生成的2 H 4掺杂的液态氙,通过红外光谱进行表征;这些配合物都是不稳定的,即使在-78°C时,顺式-[Cr(CO)4(C 2 H 4)2 ]配合物的稳定性也最差,分解时的活化焓为ΔH ‡约60。千摩尔–1。
Grevels, Friedrich-Wilhelm; Jacke, Juergen; Klotzbuecher, Werner E., Pure and Applied Chemistry, 1988, vol. 60, p. 1017 - 1024
作者:Grevels, Friedrich-Wilhelm、Jacke, Juergen、Klotzbuecher, Werner E.、Oezkar, Saim、Skibbe, Volker
DOI:——
日期:——
Organometallic Stability and Structure: Elementary Rates of Unimolecular Decomposition in Chromium Olefin Carbonyls
作者:Bruce McNamara、Marcy H. Towns、Edward R. Grant
DOI:10.1021/ja00154a027
日期:1995.12
Time-resolved infrared absorption has been applied to obtain elementary rates of unimolecular decomposition in the gas phase for the chromium carbonyl complexes of ethylene, propylene, l-butene, cis-2-butene, trans-2-butene, and isobutene. Observed rates fit a trend of declining stability with increasing alkyl substitution. Arrhenius parameters, derived from the temperature dependence of the elementary unimolecular decay rate, establish that the source of this stability trend lies not in decreasing bond strengths-activation energies are essentially constant for the series-but rather in a substantial increase in the A factor for the larger leaving olefins. This effect is explained in terms of sterically constrained torsional and C-C-C skeletal bending vibrations that are released as the molecule dissociates, adding to the statistical driving force that favors decomposition. This suggestion is confirmed by a simplified RRKM unimolecular rate theory model that quantitatively reproduces the observed rates.