Dimitri M. Khramov

Diaminocarbene[3]ferrocenophanes and their transition-metal complexes.

N-heterocyclic carbenes (NHCs) form robust complexes with nearly every transition metal. In many instances, these complexes function as catalysts with superior activities and selectivities. The broad utility and application of NHCs can be traced to synthetic advancements which enable access to derivatives with novel N substituents and architectures. We envisioned that it would be possible to create a new class of carbene-based ligands with relatively wide N-C-N angles and redox-switchable functions by linking diaminocarbenes to 1,1’-disubstituted metallocenes. In view of the affinity of carbenes for transition metals, the use of such ligands may lead to new redox-active complexes with tunable electronic properties. Herein, we describe a novel carbene architecture that contains a 1,1’-disubstituted ferrocene moiety and demonstrate its ability to engage in unique electronic interactions with coordinated transition metals. The formamidinium salts 1a and 1b were synthesized in up to 95 % yield by the formylative cyclization of the respective 1,1’-dianilinoor 1,1’-dialkylaminoferrocene precursor upon treatment with trimethylorthoformate and HBF4. [8] Diagnostic formamidinium signals were found at d = 9.3 and 8.8 ppm ([D6]DMSO), respectively, in the H NMR spectra of these compounds. The solid-state structure of 1a reveals eclipsed cyclopentadienyl (Cp) ligands, which are tilted toward each other (f = 15.78) as a result of the tethering effect of the diaminocarbene fragment (Figure 1, left). This strain is manifested in a relatively large N-C-N angle of 129.6(3)8, a value that is comparable to those

Adapting N‐Heterocyclic Carbene/Azide Coupling Chemistry for Polymer Synthesis: Enabling Access to Aromatic Polytriazenes

A click by any other name: Coupling bis(N-heterocyclic carbene)s with bis(azide)s afforded a novel class of conjugated polytriazenes. These polymers were rendered electrically conductive upon doping, and fluorene-containing variants exhibited luminescence. This adaptation of N-heterocyclic carbene (NHC)/azide coupling chemistry to polymer synthesis reveals the potential of NHCs as building blocks for accessing polymers having useful electronic properties.

Synthesis and Study of Redox-Active Acyclic Triazenes: Toward Electrochromic Applications

Coupling of various 4-substituted phenyl azides with two distinct quinone-containing N-heterocyclic carbenes (NHCs) afforded the respective mono- and ditopic 1,3-disubstituted acyclic triazenes in moderate to excellent yields (38-92%). Depending on their pendant substituents (derived from the azides), the acyclic triazenes exhibited intense absorptions in the visible spectrum (359-428 nm), which were bathochromically shifted by up to Δλ=68 nm upon reduction of the quinone moiety on the component derived from the NHC. Cyclic voltammetry confirmed that the aforementioned redox processes were reversible, and a related set of UV-vis spectroelectrochemical experiments revealed that bulk electrolysis may also be used to switch reversibly the colors exhibited by these triazenes.

Triazene formation via reaction of imidazol-2-ylidenes with azides

Treatment of N-heterocyclic carbenes (as their free carbenes or generated in situ) with alkyl, aryl, acyl or tosyl azides afforded the respective substituted triazenes in excellent yields.