23 research outputs found
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<sup>III</sup> complex from the 1,3,5-substituted
benzene derived tris-triazolium salt. The dinuclear Ir<sup>III</sup> 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<sup>III</sup> 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