Ligand Rotation with Carbonyl Rearrangement

COUPLING OF tt-LIGAND ROTATION WITH CARBONYL REARRANGEMENT 

The constraints of axial-equatorial preferences of the ligands presumably has a great influence on the apparent coupling of olefin rotation to pseudorotation of the carbonyls. Osborn et al. (113) investigated this feature by considering the nonrigidity of Fe(CO)3(CeH5CH2NC)(maleic anhydride). Equilibration of the two unequal sets of 2 1 carbonyl 

General consistency with pseudorotation should not be taken for granted. As shown in Fig. 7, careful examination of the carbonyl resonances observed in (methyl acrylate)Fe(CO)4 show that all the resonances do not broaden to the same degree at the onset of averaging 61, 78). Solvent variations do not alter this effect, and it is therefore unlikely to arise from averaging with an intermediate (see Section II). The Berry pseudorotation mechanism demands that each of the four carbonyl ligands move to a different environment hence, all should broaden to the same extent. This anomalous result can be accommo- 

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 

Fluxional Behavior of Diene and Triene Metal Tricarbonyls 

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V. Coupling of TT-Ligand Rotation with Carbonyl Rearrangement. .. 231... 

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