Infrared Dynamics of Iron Carbonyl Diene Complexes

Abstract

The temperature dependence of the low-frequency C-O bands in the IR spectrum of [(η-norbornadiene)Fe(CO)], reminiscent of signal coalescence in dynamic NMR, was interpreted by Grevels (in 1987) as chemical exchange due to very fast rotation of the diene group. Since then, there has been both support and objection to this interpretation. We discuss these various claims involving both one- and two-dimensional IR and, largely on the basis of new density functional theory calculations, furnish support for Grevels' original interpretation.

Steric and electronic control of an ultrafast isomerization

“…4, S2 and S3). 1,[10][11][12][13][14][15][16][17][18][19] Owing to the similar line shape observed for complexes 1-3 ( Fig. S2 †) phosphine electronic effects appear to have little impact on the isomerization reaction.…”

Structure and Dynamics of Iron Pentacarbonyl

“…There is an excellent book on 2D-IR by Hamm and Zanni 17 and a summary by Thielges and colleagues. 18 The application to 39.9 k ax,eq 28.0 a Evaluated as the difference between the D 3h -symmetric minimum and the C 4v -symmetric transition state for Fe(CO) 5 and between the C s -symmetric minimum shown in Figure 6 metal carbonyls has been outlined by Kubarych and colleagues, 19 and a very recent review 20 summarizes the experiments on metal carbonyls that have been carried out over the past few years. The literature reveals that there is often a problem relating to the difficulty of distinguishing between the effects caused by chemical exchange and those caused by intramolecular vibrational redistribution (IVR) (see ref 20 for a discussion of this).…”

“…This point has been much discussed, and the details were summarized by us elsewhere. 20 The general conclusion is that the method is applicable, but one must be cautious when trying to extract accurate data. In fact, two educational publications 30,31 show advanced students how to obtain kinetic data from the coalescing ν(CO) bands of Fe(CO) 3 (COD).…”

“…Fortunately, for the iron tricarbonyl species, DFT calculations show that the ν(CO) vibrations are hardly affected as the barrier is climbed. 20 This point is raised here because it is important to consider such effects in the case of Fe(CO) 5 , and this will be discussed later.…”

“…DFT calculations 20 of the Fe(CO) 3 (diene) complexes (Figure 7) show that as the barrier is climbed, both lowfrequency bands (a′ and a″) hardly shift. This means that any extra intensity between peaks must be produced by exchange.…”