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

Abstract

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 σ p 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.

Highly Electrophilic, Catalytically Active and Redox‐Responsive Cobaltoceniumyl and Ferrocenyl Triazolylidene Coinage Metal Complexes

“…Standard Cu I catalyzed azide‐alkyne [3+2] cycloaddition reactions (CuAAC‐click‐chemistry) of azidoferrocene ( 1 ), ethynylferrocene ( 2 ), azidocobaltocenium hexafluoridophosphate ( 3 ) and ethynylcobaltocenium hexafluoridophosphate ( 4 ) afforded triazoles 5 – 7 in 63–84 % isolated yield (Scheme ). Note that a diferrocenylated triazole, made similarly by cycloaddition of azidoferrocene with ethynylferrocene, is not included, because its synthesis and further chemistry has already recently been published .…”

“…The triazoles 5 and 6 display one oxidation and two reduction steps (Figures and S62). In comparison to related compounds, the oxidation step is assigned to a ferrocenyl‐based Fe II to Fe III process, and the reduction steps to the cobaltoceniumyl‐based successive reduction of Co III , via Co II to Co I . Whereas the first reduction is reversible, the second reduction is quasi‐reversible, a fact that is likely related to the lability of the cobalt−Cp bond on reduction.…”

Cobaltocenylidene: A Mesoionic Metalloceno Carbene, Stabilized in a Gold(III) Complex

“…However, in our case, we had to use K[Au(CN) 2 ] as gold(I) substrate containing small cyanido ligands that allow unhindered access of the oxidizing reactant, thereby greatly facilitating the desired oxidative addition. That reaction is also supported by the polar solvent nitromethane, which turns out to be the only medium compatible with the highly reactive dicationic cobaltoceniumdiazonium salt . In addition, one equivalent of KCN was required to provide a fourth ligand for a neutral Au III species.…”

“…The highly reactive cobaltoceniumdiazonium bis(hexafluoridophosphate) ( 1 ) containing N 2 as the best leaving group turned out as the optimal CcC synthon. Attempted oxidative additions of the less reactive iodocobaltocenium hexafluoridophosphate with various d8 metal precursors of Rh + and Pt 2+ gave mostly no reaction at all or intractable product mixtures. We also note that our earlier attempts of CcC complex formation by thermal extrusion of CO 2 from late transition‐metal cobaltoceniumcarboxylato complexes by the Pesci reaction met with failure .…”

“…Unfortunately, Ni 0 /Rh I /Ir I carbonyl complexes and phosphinidene or selenium derivatives containing the CcC ligand are not accessible by an oxidative addition methodology. However, given the fact that cationic cobaltoceniumyl is a strong electron‐accepting aromatic moiety, it was proved to be possible to synthesize CcC–Se adduct ( 5 ) by an electrophilic aromatic substitution reaction of sodium selenide 20 with iodocobaltocenium iodide ( 4 ; Scheme ) . We note that similar electrophilic aromatic substitution reactions of N/O/S‐nucleophiles with nitro‐pentamethylcobaltocenium hexafluoridophosphate were recently published .…”