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(Electrochemical) Properties and Computational Investigations of Ferrocenyl-substituted Fe33‑PFc)2(CO)9 and Co44‑PFc)2(CO)9 Clusters and Their Reduced Species

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journal contribution
posted on 23.04.2020, 14:35 by Marcus Korb, Xianming Liu, Sebastian Walz, Marco Rosenkranz, Evgenia Dmitrieva, Alexey A. Popov, Heinrich Lang
The formation of ferrocenyl-functionalized iron and cobalt carbonyl clusters is reported, based on a reaction of FcPCl2 (3) (Fc = Fe­(η5-C5H5)­(η5-C5H4)) with Fe2(CO)9 and Co2(CO)8, respectively. Therein, nido-Fe3(CO)9­(μ3-PFc)2 (4) and nido-Co4(CO)10­(μ3-PFc)2 (5) clusters were obtained as the first diferrocenyl-substituted carbonyl clusters with a symmetrical cluster core. Cluster 4 shows two reversible one-electron processes within the anodic region, based on Fc/Fc+ redox events, as well as two processes in the cathodic region. In situ IR and electron paramagnetic resonance (EPR) measurements of all electronic states confirmed an Fc-based oxidation and a core-based reduction. On the basis of the results of a single-crystal X-ray analysis of structures of 4 and 5, computational studies of the highest occupied molecular orbital–lowest unoccupied molecular orbital energies, the spin density, quantum theory of atom-in-molecule delocalization indices, and the atomic charges were performed to explain the experimental results. The latter revealed a reorganization of the cluster core upon reduction and the existence of weak P···P interactions in 4 and 5. Ferrocenyl-related redox processes, occurring reversibly in case of 4, were absent for 5, due to a different distribution of the HOMO energies. EPR measurements furthermore confirmed the core-based radical anion and the formation of a decomposition product at potentials lower than [M]2– (M = Fe, Co).