In continuation of our exploration of metallocenium chemistry we report here on innovative ways toward monofunctionalized rhodocenium salts applying half-sandwich capping reactions of cyclopentadienyl rhodium(III) halide synthons with cyclopentadienyl ylides containing pyridine, phosphine or dinitrogen leaving groups, followed by Zincke and Sandmeyer reactions. Thereby amino, diazonio, bromo, azido and iodo rhodocenium salts containing valuable functional groups are accessible for the first time. Target compounds were characterized by spectroscopic ( 1 H/ 13 C/ 103 Rh-NMR, IR, HR-MS), structural (single crystal XRD) and electrochemical (CV) methods and their properties were compared to those of isoelectronic cobaltocenium compounds. These new functionalized rhodocenium complexes significantly expand the so far extremely limited chemical space of rhodocenium salts with promising options for the future development in the area of rhodocenium chemistry.
The natural vitamin B 12 -derivatives are intriguing complexes of cobalt that entrap the metal within the strikingly skewed and ring-contracted corrin ligand. Here, we describe the synthesis of the Rh(III)-corrin acetylrhodibalamin (AcRhbl) from biotechnologically produced metal-free hydrogenobyric acid and analyze the effect of the replacement of the cobalt-center of the organometallic vitamin B 12 -derivative acetylcobalamin (AcCbl) with its group-IX homologue rhodium, to give AcRhbl. The structures of AcCbl and AcRhbl were thoroughly analyzed in aqueous solution, in crystals and by in silico methods, in order to gain detailed insights into the structural adaptations to the two homologous metals. Indeed, the common, nucleotide-appended corrin-ligand in these two metal corrins features extensive structural similarity. Thus, the rhodium-corrin AcRhbl joins the small group of B 12 -mimics classified as 'antivitamins B 12 ', isostructural metal analogues of the natural cobalt-corrins that hold significant potential in biological and biomedical applications as selective inhibitors of key cellular processes.
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