Rhodocenium Functionalization Enabled by Half‐Sandwich Capping, Zincke Reaction, Diazoniation and Sandmeyer Chemistry

Abstract

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.

Curious Case of Cobaltocenium Carbaldehyde

“…This finding is in line with calculated data, where analysis of the spin density indicates that the excess alpha electron is localized at the Co center (Table , Figure , calculation details in the Supporting Information). Comparable EPR spectra of cobaltocenes containing non-redox-active substituents have been reported in the literature …”

“…Standard organometallic methods and analytical equipment were used as published previously . The starting material cobaltocenium carboxylic acid hexafluoridophosphate ( 1 ) was prepared according to literature…”