26319-33-5Relevant articles and documents
Boxhoorn, G.,Stufkens, D. J.,Oskam, A.
, p. 215 - 226 (1979)
Excimer Laser Photolysis of Group 6 Metal Carbonyls in the Gas Phase
Ishikawa, Yo-ichi,Brown, Carl E.,Hackett, Peter A.,Rayner, David M.
, p. 2404 - 2413 (1990)
The excimer laser photolysis of Mo(CO)6 in the gas phase has been studied at 351, 308, 248, and 222 nm with laser-based, time-resolved infrared absorption spectroscopy.Results have also been obtained on the 308- and 222-nm photolysis of Cr(CO)6 and on the 222-nm photolysis of W(CO)6, complementing earlier studies and presenting a complete picture of group 6 metal carbonyl ultraviolet photodecomposition.Infrared spectra in the range 1700-2033 cm-1 have been assigned for the coordinatively unsaturated species Mo(CO)5, Mo(CO)4, and Mo(CO)3.As in the case of Cr and W,their gas-phase structures are the same as found in low-temperature matrices.Rates for the reaction of these species with CO and Mo(CO)6 have been determined and are fast, within ca 1/10th gas kinetic.Overall, the behavior of Mo(CO)6 is similar to the other group 6 carbonyls.The photolysis wavelength dependence of the fragmentation patterns in the group 6 carbonyls shows no correlation with initially excited electronic excited states of M(CO)6 but is consistent with a sequential dissociation proceeding entirely through ground electronic states of M(CO)x following rapid internal conversion of the initially populated state of M(CO)6.The relative fragment yields support earlier indications that in Cr(CO)6 the first M-CO bond dissociation energy, BDE6, is of the order of or smaller than the second (BDE5).The first case of buffer gas pressure dependence of the relative yields of M(CO)x and M(CO)x-1 fragments has been observed for x=5 following the 308-nm photolysis of Cr(CO)6.The form of the dependence can be modeled by unimolecular reaction theory with BDE6 = BDE5 = 36 kcal mol-1.
PHOTOFRAGMENTATION DYNAMICS OF Cr(CO)6 IN THE GAS PHASE.
Fletcher,Rosenfeld
, p. 6358 - 6359 (1983)
CO laser absorption spectroscopy has been used to study the dissociation dynamics of Cr(CO)//6 following photoactivation. Results suggest that the excited state prepared at 249 nm yields CO both by rapid predissociation, with an efficiency phi //S less than equivalent to 0. 36, and by intersystem crossing to a long-lived triplet, with an efficiency phi //T greater than equivalent to 0. 64. The triplet state thus formed undergoes serial decarbonylation yielding Cr(CO)//5 and Cr(CO)//4. Refs.
Organometallic stability and structure: Elementary rates of unimolecular decomposition in chromium olefin carbonyls
McNamara, Bruce,Towns, Marcy H.,Grant, Edward R.
, p. 12254 - 12261 (2007/10/03)
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, 1-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.
Gas-phase ligand substitution reactions with the 17-electron transition-metal complexes (OC)4Fe.-, (OC)5Cr.-, and (OC)4MnH.-
McDonald, Richard N.,Schell, Philip L.
, p. 1820 - 1827 (2008/10/08)
Three transition-metal complex negative ions, (OC)4Fe.-, (OC)5Cr.-, and (OC)4MnH.-, were generated and studied in ligand substitution reactions with a variety of neutral ligand substrates. Only (OC)4Fe.- reacted with PF3 and gave sequentially the product ions (OC)4-xFe(PF3)x.- where x = 1-3. The three metal complex negative ions formed ligand substitution product anions with NO; the reaction with (OC)4MnH.- also produced some of the corresponding adduct anion. With SO2, (OC)4Fe.- gave only ligand substitution, (OC)5Cr.- formed a mixture of the adduct and the product of ligand substitution, and (OC)4MnH.- produced only the adduct. Both the NO and SO2 reactions were believed to occur by the associative mechanism with the SO2 reactions proceeding via Lewis acid-base complexes. Only (NC)2C=C(CN)2 (TCNE) of the seven olefins examined reacted with the metal complex negative ions forming the product of electron transfer (TCNE.-) as well as the product ions of ligand substitution. The reactions of all three metal complex negative ions with (CF3)2C=O and of (OC)5Cr.- with biacetyl were considered to involve initial electron transfer within the orbiting collision complex. The reaction of (OC)4MnH.- with O2 produced various oxidation products, the most noteworthy being HCO2- as a major product anion. This latter result is considered to be evidence for the migratory insertion reaction, OC-Mn-H ? Mn-CHO, in the adduct formed from (OC)4MnH.- with O2.
