Ligand fluxionality and the formation of cationic iron carbonyl clusters

Abstract

M+/M2+ ratio is 3.7. The collision-induced dissociation data are interpreted as evidence that the Cr-Cr bond strength is directly influenced by the M/L ratio. That is, the metal-metal bond strength follows the order Cr2(C0)6+ < Cr2(C0)s+ < Cr2(C0)4+. The CID data have also been obtained for the Cr3(CO),+ 0, = 6, 7) ionic cluster fragments and the M+/M3+ ratio is 1/12 for y = 6 and 1 /IO for y = 7; whereas the M2+/M3+ ratio is 1 /6 for y = 6 and 1 /5 for y = 7, suggesting a very strong metal-metal interaction for the chromium trimer center. The general utility of the collision-induced dissociation experiment for probing the metal-metal bond order is now being examined on larger Crcontaining clusters as well as clusters containing Fe, Co, and Ni. Conclusions The reactivities of Cr2(CO),+ 0, = 4, 5, 6) with small neutral molecules do not parallel that observed for reactions with Cr(CO),. That is, reaction rates for Cr2(CO),+ ions with Cr(CO), differ considerably and the reactivity can be explained by an electron deficiency argument, but the variations in reaction rate for the Cr2(CO),+ ions with the small neutral molecules are rather small, e.g., 10-40%. In each case the ion-molecule reaction efficiency (determined by comparing theoretical collision frequency with the experimental reaction rate) is quite high and approaches unity. The CO ligands of Cr2(C0)4+ and Cr2(C0)s+ are quite labile and readily undergo thermoneutral ligand exchange with I3CO, whereas the Co ligands of Cr2(C0)6+ are nonlabile and do not