LIGAND-EXCHANGE AND LIGAND MIGRATION REACTIONS INVOLVING DICYCLOPENTADIENYLNIOBIUM(III) CARBONYL DERIVATIVES

The methylniobocene carbonyl (C5H5)2Nb(CH3)(CO) shows an unexpected lack of reactivity with respect to ligand migration. Whereas (C5H5)2V(CH3) has been reported to react with CO to yield the acetyl derivative (C5H5)2V(OC-CH3)(CO) immediately, we find that the niobocene analogue (C5H5)2Nb(CH3) reacts with CO only to regenerate (C5H5)2Nb(CH3)(CO), from which it was obtained by photolysis. This resistance of the methylniobocene carbonyl derivative towards ligand migration is interpreted in terms of the bonding properties of the acetyl intermediate (C5H5)2Nb(OCCH3). © 1979.