ETA-4-COMPLEXES OF 4,7-DIHYDROACEPENTALENE - FACILE DEGENERATE HAPTOTROPIC REARRANGEMENT OF (ETA-5-CYCLOPENTADIENYL)(ETA-4-4,7-DIHYDROACEPENTALENE)COBALT(I) IN CONTRAST TO ITS TRICARBONYLIRON COUNTERPART

The (cyclopentadienyl)cobalt(I) complex 4 of the 4,7-dihydroacepentalene not-equal not-equal) derivative 2b has been prepared by the reaction of the ligand with (cyclopentadienyl)bis(ethene)cobalt(I). NOE experiments indicate a complexation at the convex face of the polyolefinic ligand. H-1-NMR spectra establish a degenerate haptotropic rearrangement with CpCo migration from one diene unit to the adjacent one. The activation energy of this process is estimated to be 15 kcal/mol. An X-ray crystal structure determination of (eta-4-4,7-dihydroacepentalene)tricar-bonyliron derivative 3a shows a distorted coordination of Fe(CO)3 at the convex face of the ligand, too.