Winter, Rainer F.
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The Effect of Remote Donor Substituents on the Properties of Alkoxy and Amino Fischer Carbene Complexes of Tungsten
Tungsten Fischer ethoxy‐ and dimethylaminocarbene complexes [W{C(X)(C6H4‐4‐R}(CO)5] (X = OEt: series a; or X = NMe2: series b) are synthesized from phenyl substrates containing remote tertiary amino substituents R’2N with R’ = Me (2), Ph (3) or C6H4Br‐4 (4). The π‐delocalization and carbene‐stabilizing effect of the distant tertiary amine donor substituent are investigated by NMR and IR spectroscopy, electrochemistry and quantum chemical calculations. A significant transfer of electron density from the remote 4‐R’2N substituent to the carbene C atom in the ethoxycarbene complexes is supported by NMR data and the solid‐state structure of 2a. This is strongly attenuated in the amino‐substituted carbene complex 2c and irrelevant in the dimethylaminocarbene complexes of series b, where the electron demand of the electrophilic carbene center is satisfied by the directly attached dimethylamino substituent. Quantum chemical calculations and IR spectroelectrochemistry on complexes 1a‐4a verify carbene‐centered reductions and a ligand based oxidation of complex 2b.
Redox-Rich Metallocene Tetrazene Complexes : Synthesis, Structure, Electrochemistry, and Catalysis
Thermal or photochemical metal-centered cycloaddition reactions of azidocobaltocenium hexafluoridophosphate or azidoferrocene with (cyclooctadiene)(cyclopentadienyl)cobalt(I) afforded the first metallocenyl-substituted tetrazene cyclopentadienyl cobalt complexes together with azocobaltocenium or azoferrocene as side products. The trimetallic CpCo compounds are highly conjugated, colored, and redox-active metallo-aromatic compounds, as shown by their spectroscopic, structural, and electrochemical properties. The CpCo-tetrazenido complex with two terminally appended cobaltocene units catalyzes electrochemical proton reduction from acetic acid at a mild overpotential (0.35 V). Replacing cobaltocene with ferrocene moieties rendered the complex inactive toward catalysis.
Synthesis and properties of Fischer carbene complexes of N,N -dimethylaniline and anisole π-coordinated to chromium tricarbonyl
Ferrocene- and Biferrocene-Containing Macrocycles towards Single-Molecule Electronics
Cyclic multiredox centered systems are currently of great interest, with new compounds being reported and developments made in understanding their behavior. Efficient, elegant, and high-yielding (for macrocyclic species) synthetic routes to two novel alkynyl-conjugated multiple ferrocene- and biferrocene-containing cyclic compounds are presented. The electronic interactions between the individual ferrocene units have been investigated through electrochemistry, spectroelectrochemistry, density functional theory (DFT), and crystallography to understand the effect of cyclization on the electronic properties and structure.
Roles played by carbene substituents during ligand transfer reactions between tungsten fischer carbene complexes and [Pt(COD)Cl2]
Mixed-Valent Ruthenocene–Vinylruthenium Conjugates : Valence Delocalization Despite Chemically Different Redox Sites
Cobaltocenylidene : A Mesoionic Metalloceno Carbene, Stabilized in a Gold(III) Complex
Oxidative addition of cobaltoceniumdiazonium bis(hexafluoridophosphate) with (pseudo)halide aurates gave gold(III) complexes containing zwitterionic cobaltoceniumide as a ligand. Its selenium derivative, cobaltoceniumselenolate, was obtained by an electrophilic aromatic substitution reaction of iodocobaltocenium iodide with Na2Se. Spectroscopic and structural data in combination with DFT calculations showed that this cobaltocenylidene species is a mesoionic carbene quite different from common N-heterocyclic carbenes. Its ligand properties (TEP, singlet-triplet gap, nucleophilicity, π-acidity, Brønsted basicity) are in part comparable to those of cyclic (amino)(alkyl/aryl)carbenes. Electrochemistry data showed that the mesoionic cobaltoceniumides are more electron-rich than their parent ferrocenes. The reversible reduction of the tricyanido gold complex appears 50 mV negative of the cobaltocenium/cobaltocene couple, whereas that of the selenide derivative is shifted cathodically by 550 mV.
Redox Isomeric Ferrocenyl Styrylruthenium Radical Cations with Diphenyl-Substituted β-Ketoenolato Ligands
Metallo‐Scorpionates : First Generation of Trimetallic, Homoleptic [Ru]–M–[Ru] Complexes (M = Fe, Co, Ni, Cu)
The first metallo‐scorpionate ligands, closely related to Trofimenko's scorpionates, are obtained by formal replacement of the hydrido‐boron moiety of hydrido‐tris(pyrazolyl)borate by an (arene)RuII fragment. Coordination to divalent and trivalent 3d‐transition metals (Fe, Co, Ni, Cu) gives access to a series of homoleptic, heterotrimetallic complexes containing linear metal chains bridged by pyrazole ligands. Synthetic aspects, spectroscopic, structural and electrochemical properties are reported and compared to those of standard scorpionate complexes.
Manipulation and Assessment of Charge and Spin Delocalization in Mixed-Valent Triarylamine–Vinylruthenium Conjugates
Triarylamine-vinylruthenium conjugates (4-RC6H4)2N{C6H4-4-CH═CHRu(CO)Cl(PiPr3)2}, with R = CHO (1-CHO), C(═O)Me (1-Ac), COOMe (1-E), and Me (1-Me), have been prepared and investigated in their neutral, mono- and dioxidized states by cyclic voltammetry, IR, and UV/vis/near-infrared spectroelectrochemistry, electron paramagnetic resonance spectroscopy, and quantum-chemical calculations. Electron-withdrawing substituents at the triarylamine moiety shift the charge and spin density toward the more electron-rich vinylruthenium site in comparison to the 4-OMe-substituted triarylamine-vinylruthenium conjugate 1-OMe. A more asymmetric charge distribution changes the intense vibrationally structured intervalence charge-transfer (IVCT) band of completely delocalized, mixed-valent (MV) 1-OMe+ to a weaker, highly asymmetric, nonsolvatochromic band with significantly smaller bandwidth at the low-energy side. The temperature dependence of the IVCT band of the formyl derivative 1-CHO+ proves that vibrational coupling of the IVCT transition to a symmetrical vibration is the underlying reason for band skewing. All of our results indicate that the MV radical cations remain electronically strongly coupled despite an increasingly stronger bias of the highest occupied molecular orbital to the vinylruthenium entity. Moreover, the dications of these complexes were found to be paramagnetic, which makes them rare examples of compounds that combine strong electronic coupling in the cationic MV state with paramagnetism of the dications.