Carbonyl scrambling

Temperature-dependent 13C-NMR carbonyl signals of the [Cr(CO)4-(f/4-diene)] complexes 3a-3f, indicate an easy mutual conversion of the four [Cr(CO),(13CO)(iy4-dicne)] isotopomers a, d, e, and f (10,23). For this interconversion the barriers of activation were found to be between 39 and 47 lcJ/mol for complexes with acyclic diene ligands (Table II). Only in the case of tetracarbonyl-f/4-l,3-cyclohexadienechromium(0) (3g) is the carbonyl scrambling fast, even at 190 K. 

Activation Parameters for Carbonyl Scrambling in [M(CO)4(i 4-diene)] Complexes... 

A similar model has been proposed for the so-called carbonyl scrambling mechanism in molecules like Co4(CO)i2, Rh4(CO)i2,... 

Di- and polynuclear metal carbonyl compounds have a general tendency to engage in a type of fiuxional behavior called carbonyl scrambling. This type of behavior arises because of some of the inherent properties of metal to CO bonding. As shown in Fig. 1-13, the energy of a binuclear system consisting of two metal atoms... 

Rearrangements in polynuclear transition metal clusters " Carbonyl scrambling and rearrangement ... 

Although these molecules have been widely studied, the calculation of accurate relative energies and the mechanism for carbonyl scrambling remain open... 

Carbonyl scrambling is a well-recognized phenomenon in complexes containing metal-metal bonds (I, 33, 34, 70, 85). Although carbonyl ligands are often interchanged between metals, situations exist, particularly in clusters, in which a metal tricarbonyl fragment appears to rotate. The fluxional behavior of the (diene)Fe(CO)3, (triene)Mo(CO)s, and... 

Whereas the ortho isomer easily transforms into the meta isomer in agreement with the above-mentioned model, the para isomer is obtained only under more drastic conditions and only in a small amount ([3-86] see also Refs. [3-88] and [3-89]). A similar model has been proposed [3-90] for the so-called carbonyl scrambling mechanism in molecules like Co4(CX))(2, Rh4(CO),2, and It4(CO),2. 

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