Synthesis and electrochemistry property of new crowded multi-ferrocenyl substituted benzene derivatives

Multi-Ferrocene-Based Ligands: From Design to Applications

Despite the extensive literature on ferrocene chemistry, a comprehensive analysis of multiferrocene ligands is notably absent. Thus, this review presents an overview of multiferrocenyl-containing ligands, focusing on their synthesis, characterization, and applications in catalysis and sensing. These ligands offer unique properties, including redox activity and planar chirality, making them valuable in asymmetric catalysis and molecular electronics. The review covers the literature from the first synthesis of tris(ferrocenyl)phosphane in 1962 to current developments, including various ligand subsets, which contain at least two ferrocene units within their structure. Special attention is given to explaining the coordination chemistry, electrochemical behavior, and practical applications of these ligands. The aim of this undertaking is to fill gaps in knowledge and inspire further research by identifying areas for exploration. Notably, certain ligand families like TRAP (trans-spanning phosphane) ligands remain underexplored in terms of their electrochemical properties, highlighting opportunities for future investigation. Thus, this review provides a resource for researchers in the field, stimulating further advancements in multiferrocenyl ligand chemistry and its wide-ranging applications.

(Electrochemical) Properties and Computational Investigations of Ferrocenyl-substituted Fe3(μ3-PFc)2(CO)9 and Co4(μ4-PFc)2(CO)9 Clusters and Their Reduced Species

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).