Alkyl and aryl derivatives of π-cyclopentadienyl compounds of chromium, molybdenum, tungsten, and iron

Publisher Summary This chapter describes the chemisorption on supported-metal samples, chemisorption on acidic oxides, spectra of adsorbed water and surface hydroxyl groups on nonacidic oxides, infrared spectra of physically adsorbed molecules, the pressed-salt method for obtaining spectra of adsorbed molecules, and spectra of molecules adsorbed on unsupported metals. Not only is the infrared method applicable to studies of both chemisorptions and physical adsorption systems, but it also provides a means of distinguishing between chemisorption and physical adsorption. The infrared spectra of physically adsorbed molecules are similar to the spectra of the gaseous, liquid, or dissolved states. While, minor differences in band positions may be observed during physical adsorption, these differences are of the same magnitude as the differences between the various unadsorbed states. No new bands are observed in the spectra of physically adsorbed molecules which cannot be attributed to vibrations, which provide infrared or Raman bands in the liquid state.

The Infrared Spectra of Adsorbed Molecules

In1938,whileOttoRoelenwasstudyingtheFischer-Tropsch reaction, which converts H2/CO into alkanes and alkenes, and was trying to improve the yields by recycling ethylene, the cobalt catalyst deposited on a ThO2/SiO2 support produced some propanal. Fortunately, Roelen focused on this unexpected reaction and discovered that cobalt was able to catalyze specifically the hydrocarbonylation of ethylene.1-3 It was rapidly established that this reaction, which has been extended to various alkenes, was occurring in the organic phase: homogeneous catalysis was born.

Cobalt-catalyzed hydroformylation of alkenes: generation and recycling of the carbonyl species, and catalytic cycle.

In this paper, the effect of the presence of humidity and molecular oxygen on the low temperature oxidation of carbon monoxide on a Co3O4 powder surface was studied. The interaction between the probe molecules and the Co3O4 surface was investigated by means of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and quadrupolar mass spectrometry (QMS). Carbon monoxide interacts with the Co3O4 surface and is converted to carbon dioxide at rather low temperature (T≥323 K); the formation of carbonate species is also evident. The reactivity of Co3O4 is strongly depressed by humidity: as a matter of fact, in steam conditions carbon monoxide oxidation is significant at temperatures higher than 523 K. Moreover, the formation of carbonate species is more evident than in dry conditions. The Co3O4 powder surface interacts with oxygen molecules at T≥323 K to originate several activated surface oxygen species. The activation with oxygen does not appear to facilitate significantly the formation of carbon dioxide.

Low temperature oxidation of carbon monoxide: the influence of water and oxygen on the reactivity of a Co3O4 powder surface

A normal coordinate treatment on the chelate ring of bis‐(acetylacetonato)‐Cu(II) gives calculated frequencies in good agreement with the observed ones in the 1700 and 350 cm—1 range obtained with NaCl, KBr, and CsBr optics. In order to assign the observed bands and to see the coupling between various vibrational modes, the L matrices and the potential energy distribution, Lii2Fi were calculated for all the in‐plane vibrations. The results reveal that (1) the band at 1580 cm—1 previously assigned to asym. CO stretching is asym. CC stretching, (2) the bands at 684 and 654 cm—1 formerly suggested to be metal‐oxygen stretching modes are metal‐oxygen stretching vibrations coupled with ring deformation and CCH3 bending modes, respectively, and (3) a new band found at 455 cm—1 is the sym. Cu–O stretching mode. By comparing the force constants of the Cu–O stretching vibration with those of metal‐nitrogen and metal‐carbon bonds of other compounds, it is suggested that the Cu–O bond in this compound has double bon...

S. L. Shufler

Papers

Spectra and Structures of Cobalt Carbonyls1