On the Temperature Dependence of the I3C-NMR.-Spectra of Tetracarbonyl(q-(a-cyc1ooctene)iron and of (a-Cyclooctene SummaryReaction of (Z)-cyclooctene (1) with Fe2(CO)9 in pentane at 0" yielded tetracarbonyl(q-(Z)-cyc1ooctene)iron (2) as a yellow oil which can be stored over a longer period only at -78 '.It is shown that the title compounds (1 and 2, respectively) are fluxional. The activation parameters for the conformational C-atom site exchange of (Z)-cyclooctene (1) and tetracarbonyl (q-(Z)-cyc1ooctene)iron (2) (in CC12F2) have been determined between 113 K and 151 K for 1 and between 151 K and 205 K for 2, respectively, by a complete line shape analysis of the temperature dependent proton noise-decoupled 13C-NMR. signals of the olefinic C-atom. The kinetic data and activation parameters are given in Tables I and 2.

Intramolecular Exchange of Carbonyl Group Sites in Tetracarbonyliron Complexes of Ethylene and Simple (E)‐Configurated Olefins The activation parameters of the intramolecular exchange of carbonyl group sites in the tetracarbonyliron complexes 2–5 of ethylene, (E)‐2‐butene, (E)‐4‐octene and (E)‐cyclooctene, respectively have been determined between 180 and 115 K by a complete line shape analysis of the 13C‐NMR, signals of the CO‐groups. The temperature dependence of the rates (k (2), k (3), k (4) and k (5), respectively) of this intramolecular exchange process can be described by the following equations (Ea in J/mol): Further data are given in Tables 3 and 4. Furthermore, a good linear correlation between the energies of activation of the carbonyl exchange process in 1,2‐disubstituted olefins and the corresponding averaged wavenumbers ( (CO)) of the carbonyl stretching vibrations or of the corresponding chemical 13C‐shifts (δ (CO)) of the carbonyl group at fast exchange in the complexes seems to exist.

Die Titelkomplexe (I) und (II) wurden durch thermische oder photochemische Reaktion der entsprechenden Olefine mit Fe2(CO)9 bzw. Fe(CO)5 dargestellt.

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Die Aktivierungsparameter des intramolekularen Austauschs von Carbonylgruppen in den Titelkomplexen (I) wurde zwischen 180 und 115 Kdurch eine vollständige Linienformanalyse der 13C‐ NMR‐Signale bestimmt.