Monofunctionalized Cobaltocenium Compounds by Dediazoniation Reactions of Cobaltoceniumdiazonium Bis(hexafluorophosphate)

Monofunctionalized
cobaltocenium salts are obtained for the first time from cobaltoceniumdiazonium
bis­(hexafluorophosphate) with various nucleophiles via Sandmeyer-type
and related reactions. For successful conversions, reaction conditions
are quite critical: either standard solution chemistry in nitromethane
or solvent-free ball milling proved necessary, depending on the type
of reactant. By this synthetic approach valuable synthons such as
iodocobaltocenium and azidocobaltocenium salts are accessible that
open up new vistas in cobaltocenium chemistry. Spectroscopic characterization
by NMR, IR, HRMS, and single-crystal structure analysis as well as
the results of electrochemical studies are reported. Derivatives with
two reversible reductions show the expected relation of the half-wave
potentials with the Hammett substituent parameter σp of the respective substituent with a slightly larger slope for the
first reduction. The carboxylic acid (reductive deprotonation of the
−COOH functionality), the iodo (protodehalogenation), and the
azido derivatives undergo irreversible subsequent reactions after
primary reduction.