5 research outputs found
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 iridiumÂ(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)Âelectrochemical,
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 iridiumÂ(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)Âelectrochemical,
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
The Power of Ferrocene, Mesoionic Carbenes, and Gold: Redox-Switchable Catalysis
Catalysis with goldÂ(I)
complexes is a useful route for synthesizing
a variety of important heterocycles. Often, silverÂ(I) additives are
necessary to increase the Lewis acidity at the goldÂ(I) center and
to make them catalytically active. We present here a concept in redox-switchable
goldÂ(I) catalysis that is based on the use of redox-active mesoionic
carbenes, and of electron transfer steps for increasing the Lewis
acidity at the goldÂ(I) center. A goldÂ(I) complex with a mesoionic
carbene containing a ferrocenyl backbone is presented. Investigations
on the corresponding iridiumÂ(I)–CO complex show that the donor
properties of such carbenes can be tuned via electron transfer steps
to make these seemingly electron rich mesoionic carbenes relatively
electron poor. A combined crystallographic, electrochemical, UV–vis–near-IR/IR
spectroelectrochemical investigation together with DFT calculations
is used to decipher the geometric and the electronic structures of
these complexes in their various redox states. The goldÂ(I) mesoionic
carbene complexes can be used as redox-switchable catalysts, and we
have used this concept for the synthesis of important heterocycles:
oxazoline, furan and phenol. Our approach shows that a simple electron
transfer step, without the need of any silver additives, can be used
as a trigger in gold catalysis. This report is thus the first instance
where redox-switchable (as opposed to only redox-induced) catalysis
has been observed with goldÂ(I) complexes
Multiple Bistability in Quinonoid-Bridged Diiron(II) Complexes: Influence of Bridge Symmetry on Bistable Properties
Quinonoid bridges
are well-suited for generating dinuclear assemblies that might display
various bistable properties. In this contribution we present two diironÂ(II)
complexes where the ironÂ(II) centers are either bridged by the doubly
deprotonated form of a symmetrically substituted quinonoid bridge,
2,5-bisÂ[4-(isopropyl)Âanilino]-1,4-benzoquinone (<b>H</b><sub><b>2</b></sub><b>L2′</b>) with a [O,N,O,N] donor
set, or with the doubly deprotonated form of an unsymmetrically substituted
quinonoid bridge, 2-[4-(isopropyl)Âanilino]-5-hydroxy-1,4-benzoquinone
(<b>H</b><sub><b>2</b></sub><b>L5′</b>) with
a [O,O,O,N] donor set. Both complexes display temperature-induced
spin crossover (SCO). The nature of the SCO is strongly dependent
on the bridging ligand, with only the complex with the [O,O,O,N] donor
set displaying a prominent hysteresis loop of about 55 K. Importantly,
only the latter complex also shows a pronounced light-induced spin
state change. Furthermore, both complexes can be oxidized to the mixed-valent
ironÂ(II)–ironÂ(III) form, and the nature of the bridge determines
the Robin and Day classification of these forms. Both complexes have
been probed by a battery of electrochemical, spectroscopic, and magnetic
methods, and this combined approach is used to shed light on the electronic
structures of the complexes and on bistability. The results presented
here thus show the potential of using the relatively new class of
unsymmetrically substituted bridging quinonoid ligands for generating
intriguing bistable properties and for performing site-specific magnetic
switching
Control of Complex Formation through Peripheral Substituents in Click-Tripodal Ligands: Structural Diversity in Homo- and Heterodinuclear Cobalt-Azido Complexes
The azide anion is widely used as
a ligand in coordination chemistry. Despite its ubiquitous presence,
controlled synthesis of azido complexes remains a challenging task.
Making use of click-derived tripodal ligands, we present here various
coordination motifs of the azido ligands, the formation of which appears
to be controlled by the peripheral substituents on the tripodal ligands
with otherwise identical structure of the coordination moieties. Thus,
the flexible benzyl substituents on the tripodal ligand TBTA led to
the formation of the first example of an unsupported and solely ÎĽ<sub>1,1</sub>-azido-bridged dicobaltÂ(II) complex. The more rigid
phenyl substituents on the TPTA ligand deliver an unsupported and
solely ÎĽ<sub>1,3</sub>-azido-bridged dicobaltÂ(II) complex.
Bulky diisoÂpropylÂphenyl substituents on the TDTA ligand
deliver a doubly ÎĽ<sub>1,1</sub>-azido-bridged dicobaltÂ(II)
complex. Intriguingly, the mononuclear copperÂ(II) complex [CuÂ(TBTA)ÂN<sub>3</sub>]<sup>+</sup> is an excellent synthon for generating mixed
dinuclear complexes of the form [(TBTA)ÂCoÂ(ÎĽ<sub>1,1</sub>-N<sub>3</sub>)ÂCuÂ(TBTA)]<sup>3+</sup> or [(TBTA)ÂCuÂ(ÎĽ<sub>1,1</sub>-N<sub>3</sub>)ÂCuÂ(TPTA)]<sup>3+</sup>, both
of which contain a single unsupported ÎĽ<sub>1,1</sub>-N<sub>3</sub> as a bridge. To the best of our knowledge, these are also
the first examples of mixed dinuclear complexes with a ÎĽ<sub>1,1</sub>-N<sub>3</sub> monoazido bridge. All complexes were crystallographically
characterized, and selected examples were probed via magnetometry
and high-field EPR spectroscopy to elucidate the electronic structures
of these complexes and the nature of magnetic coupling in the various
azido-bridged complexes. These results thus prove the power of click-tripodal
ligands in generating hitherto unknown chemical structures and properties