Redox-active multinuclear Pd(II) complexes with bis- and tris-mesoionic carbenes

Synthesis of a ligand platform to generate di- and tri-mesoionic carbenes is reported together with their multinuclear Pd(II) complexes. Complete structural characterization and preliminary electrochemical data are presented

examples of monometallic, homobimetallic and heterobimetallic complexes

Mononuclear PtII and the first dinuclear PtII complexes along with a cyclometalated heterobimetallic IrIII/PdII complex bearing mesoionic carbene donor ligands are presented starting from the same bis-triazolium salt. The mononuclear PtII complex possesses a free triazole moiety which is generated from the corresponding triazolium salt through an N-demethylation reaction, whereas the mononuclear IrIII complex features an unreacted triazolium unit

Structural Characterization and Catalytic Hydrosilylation Reactions

Two series of different Cu(I)-complexes of “click” derived mesoionic carbenes are reported. Halide complexes of the type (MIC)CuI (with MIC = 1,4-(2,6-diisopropyl)-phenyl-3-methyl-1,2,3-triazol-5-ylidene (for 1b), 1-benzyl-3-methyl-4-phenyl-1,2,3-triazol-5-ylidene (for 1c)) and cationic complexes of the general formula [Cu(MIC)2]X (with MIC =1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene, X = CuI2− (for 2á), 1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene, X = BF4− (for 2a), 1,4-(2,6-diisopropyl)phenyl-3-methyl-1,2,3-triazol-5-ylidene, X = BF4− (for 2b), 1-benzyl-3-methyl-4-phenyl-1,2,3-triazol-5-ylidene, X = BF4− (for 2c)) have been prepared from CuI or [Cu(CH3CN)4](BF4) and the corresponding ligands, respectively. All complexes were characterized by elemental analysis and standard spectroscopic methods. Complexes 2á and 1b were studied by single-crystal X-ray diffraction analysis. Structural analysis revealed 2á to adopt a cationic form as [Cu(MIC)2](CuI2) and comparison of the NMR spectra of 2á and 2a confirmed this conformation in solution. In contrast, after crystallization complex 1b was found to adopt the desired neutral form. All complexes were tested for the reduction of cyclohexanone under hydrosilylation condition at elevated temperatures. These complexes were found to be efficient catalysts for this reaction. 2c was also found to catalyze this reaction at room temperature. Mechanistic studies have been carried out as well

Triply cyclometalated trinuclear iridium(III) and trinuclear palladium(II) complexes with a tri-mesoionic carbene ligand

The first example of a triply cyclometalated homopolynuclear tri-IrIII complex with additional carbene donors is presented. Cooperative catalysis and the interplay between homogenous and heterogeneous catalyses are discussed for the tri-IrIII complex and a related non-cyclometalated tri-PdII complex

(Electro)catalytic C-C bond formation reaction with a redox-active cobalt complex

Cooperativity between cobalt and non-innocent ligands in electron transfer processes has been utilized for (electro)catalytic C–C bond formation reactions

Probing bistability in FeII and CoII complexes with an unsymmetrically substituted quinonoid ligand

The generation of molecular platforms, the properties of which can be influenced by a variety of external perturbations, is an important goal in the field of functional molecular materials. We present here the synthesis of a new quinonoid ligand platform containing an [O,O,O,N] donor set. The ligand is derived from a chloranilic acid core by using the [NR] (nitrogen atom with a substituent R) for [O] isoelectronic substitution. Mononuclear FeII and CoII complexes have been synthesized with this new ligand. Results obtained from single crystal X-ray crystallography, NMR spectroscopy, (spectro)electrochemistry, SQUID magnetometry, multi-frequency EPR spectroscopy and FIR spectroscopy are used to elucidate the electronic and geometric structures of the complexes. Furthermore, we show here that the spin state of the FeII complex can be influenced by temperature, pressure and light and the CoII complex displays redox-induced spin-state switching. Bistability is observed in the solid-state as well as in solution for the FeII complex. The new ligand presented here, owing to the [NR] group present in it, will likely have more adaptability while investigating switching phenomena compared to its [O,O,O,O] analogues. Thus, such classes of ligands as well as the results obtained on the reversible changes in physical properties of the metal complexes are likely to contribute to the generation of multifunctional molecular materials

Copper(I) Complexes of Mesoionic Carbene: Structural Characterization and Catalytic Hydrosilylation Reactions

Two series of different Cu(I)-complexes of “click” derived mesoionic carbenes are reported. Halide complexes of the type (MIC)CuI (with MIC = 1,4-(2,6-diisopropyl)-phenyl-3-methyl-1,2,3-triazol-5-ylidene (for 1b), 1-benzyl-3-methyl-4-phenyl-1,2,3-triazol-5-ylidene (for 1c)) and cationic complexes of the general formula [Cu(MIC)2]X (with MIC =1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene, X = CuI2− (for 2á), 1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene, X = BF4− (for 2a), 1,4-(2,6-diisopropyl)phenyl-3-methyl-1,2,3-triazol-5-ylidene, X = BF4− (for 2b), 1-benzyl-3-methyl-4-phenyl-1,2,3-triazol-5-ylidene, X = BF4− (for 2c)) have been prepared from CuI or [Cu(CH3CN)4](BF4) and the corresponding ligands, respectively. All complexes were characterized by elemental analysis and standard spectroscopic methods. Complexes 2á and 1b were studied by single-crystal X-ray diffraction analysis. Structural analysis revealed 2á to adopt a cationic form as [Cu(MIC)2](CuI2) and comparison of the NMR spectra of 2á and 2a confirmed this conformation in solution. In contrast, after crystallization complex 1b was found to adopt the desired neutral form. All complexes were tested for the reduction of cyclohexanone under hydrosilylation condition at elevated temperatures. These complexes were found to be efficient catalysts for this reaction. 2c was also found to catalyze this reaction at room temperature. Mechanistic studies have been carried out as well

Di- and Trinuclear Iridium(III) Complexes with Poly-Mesoionic Carbenes Synthesized through Selective Base-Dependent Metalation

Mutidentate carbene ligands based on a rigid aromatic platform are valuable synthons for generating carbene complexes with higher nuclearity. We present here the selective, base-dependent synthesis of a dinuclear or a trinuclear Ir^III complex from the 1,3,5-substituted benzene derived tris-triazolium salt. The dinuclear Ir^III complex features an unreacted triazolium unit which enables us to compare the metric parameters between the bonded 1,2,3-triazol-5-ylidene to their parent triazolium salt present in the same molecule. Single crystal X-ray diffraction studies confirm the di- and trinuclear nature of the complexes and establish their configuration and conformation. Both the di- and trinuclear Ir^III complexes have been used for catalytic transfer hydrogenation, and these complexes are potent precatalysts delivering good to excellent yields for the reduction of benzaldehyde, acetophenone, benzophenone, and cyclohexanone. Furthermore, they show a preference for reducing nitrobenzene to either azoxybenzene or azobenzene. Mercury poisoning tests conclusively prove the homogeneous nature of the reported catalysis. The lack of orthometalation in these complexes and the possible effect thereof on catalysis are discussed

Redox Activity and Bond Activation in Iridium–Diamidobenzene Complexes: A Combined Structural, (Spectro)electrochemical, and DFT Investigation

Noninnocent ligands are special because of their ability to act as electron reservoirs and tune reactivity at a metal center “on-demand”. In the following we present two iridium­(III) complexes with a diamidobenzene ligand: one that is coordinatively unsaturated and a second one that is a coordinatively saturated, regular 18 valence electron complex. We show the electrochemical interconversion between the two complexes and propose a mechanism for the same. Both the complexes have been isolated in pure forms and characterized by spectroscopic, (spectro)­electrochemical, and crystallographic techniques. Additionally, results from DFT calculations are presented to decipher the bonding situation within the two complexes and to investigate the bond activation pathway leading to the interconversion of one form into another. In this work we make use of the increasingly popular concept of using redox steps at noninnocent ligands to tune bond activation and chemical reactivity at the metal center

Redox Activity and Bond Activation in Iridium–Diamidobenzene Complexes: A Combined Structural, (Spectro)electrochemical, and DFT Investigation

Noninnocent ligands are special because of their ability to act as electron reservoirs and tune reactivity at a metal center “on-demand”. In the following we present two iridium­(III) complexes with a diamidobenzene ligand: one that is coordinatively unsaturated and a second one that is a coordinatively saturated, regular 18 valence electron complex. We show the electrochemical interconversion between the two complexes and propose a mechanism for the same. Both the complexes have been isolated in pure forms and characterized by spectroscopic, (spectro)­electrochemical, and crystallographic techniques. Additionally, results from DFT calculations are presented to decipher the bonding situation within the two complexes and to investigate the bond activation pathway leading to the interconversion of one form into another. In this work we make use of the increasingly popular concept of using redox steps at noninnocent ligands to tune bond activation and chemical reactivity at the metal center