3 research outputs found
Ruthenium Azocarboxamide Half-Sandwich Complexes: Influence of the Coordination Mode on the Electronic Structure and Activity in Base-Free Transfer Hydrogenation Catalysis
Azocarboxamides were
used as chelating ligands in ruthenium half-sandwich
complexes. The synthesis and characterization of two new complexes
with an unprecedented coordination motif are presented together with
an in-depth investigation of two recently published complexes. Three
different coordination modes of the ligands were realized, as evident
by NMR spectroscopy and single-crystal X-ray diffraction. The use
of base during the synthesis leads to a coordination of a deprotonated
ligand, while the introduction of additional donor atoms results in
a noncoordinated amide group. The first systematic experimental (cyclic
voltammetry and UV–vis–NIR and EPR spectroelectrochemistry)
and theoretical (DFT) investigation of the electronic structure of
metal complexes bearing this redox-active ligand class is presented,
revealing redox processes with ligand contribution. The absorption
spectra and electrochemistry are mainly determined by the protonation
state of the ligand. While complexes <b>2Â[PF</b><sub><b>6</b></sub><b>]</b>, <b>3Â[PF</b><sub><b>6</b></sub><b>]</b>, and <b>4Â[PF</b><sub><b>6</b></sub><b>]</b> with neutral azocarboxamides show similar electronic spectra and
cyclovoltammograms, the incorporation of a deprotonated monoanionic
ligand in complex <b>1</b> leads to significant changes of these
properties. In contrast, the catalytic activity in the base-free transfer
hydrogenation reaction is mainly dependent on the coordination of
the amide group, with only minor effects of the protonation state.
While complexes <b>3Â[PF</b><sub><b>6</b></sub><b>]</b> and <b>4Â[PF</b><sub><b>6</b></sub><b>]</b>, with
an uncoordinated amide group, are inactive without the addition of
base, complexes <b>1</b> and <b>2Â[PF</b><sub><b>6</b></sub><b>]</b>, with a metal-bound amide group, show activity
under base-free conditions. The impact of the position of the amide
group together with the detection of metal hydride species in <sup>1</sup>H NMR spectroscopy suggests the operation of metal–ligand
bifunctional catalysis to take place when no base is added
Ruthenium Azocarboxamide Half-Sandwich Complexes: Influence of the Coordination Mode on the Electronic Structure and Activity in Base-Free Transfer Hydrogenation Catalysis
Azocarboxamides were
used as chelating ligands in ruthenium half-sandwich
complexes. The synthesis and characterization of two new complexes
with an unprecedented coordination motif are presented together with
an in-depth investigation of two recently published complexes. Three
different coordination modes of the ligands were realized, as evident
by NMR spectroscopy and single-crystal X-ray diffraction. The use
of base during the synthesis leads to a coordination of a deprotonated
ligand, while the introduction of additional donor atoms results in
a noncoordinated amide group. The first systematic experimental (cyclic
voltammetry and UV–vis–NIR and EPR spectroelectrochemistry)
and theoretical (DFT) investigation of the electronic structure of
metal complexes bearing this redox-active ligand class is presented,
revealing redox processes with ligand contribution. The absorption
spectra and electrochemistry are mainly determined by the protonation
state of the ligand. While complexes <b>2Â[PF</b><sub><b>6</b></sub><b>]</b>, <b>3Â[PF</b><sub><b>6</b></sub><b>]</b>, and <b>4Â[PF</b><sub><b>6</b></sub><b>]</b> with neutral azocarboxamides show similar electronic spectra and
cyclovoltammograms, the incorporation of a deprotonated monoanionic
ligand in complex <b>1</b> leads to significant changes of these
properties. In contrast, the catalytic activity in the base-free transfer
hydrogenation reaction is mainly dependent on the coordination of
the amide group, with only minor effects of the protonation state.
While complexes <b>3Â[PF</b><sub><b>6</b></sub><b>]</b> and <b>4Â[PF</b><sub><b>6</b></sub><b>]</b>, with
an uncoordinated amide group, are inactive without the addition of
base, complexes <b>1</b> and <b>2Â[PF</b><sub><b>6</b></sub><b>]</b>, with a metal-bound amide group, show activity
under base-free conditions. The impact of the position of the amide
group together with the detection of metal hydride species in <sup>1</sup>H NMR spectroscopy suggests the operation of metal–ligand
bifunctional catalysis to take place when no base is added
Ruthenium Azocarboxamide Half-Sandwich Complexes: Influence of the Coordination Mode on the Electronic Structure and Activity in Base-Free Transfer Hydrogenation Catalysis
Azocarboxamides were
used as chelating ligands in ruthenium half-sandwich
complexes. The synthesis and characterization of two new complexes
with an unprecedented coordination motif are presented together with
an in-depth investigation of two recently published complexes. Three
different coordination modes of the ligands were realized, as evident
by NMR spectroscopy and single-crystal X-ray diffraction. The use
of base during the synthesis leads to a coordination of a deprotonated
ligand, while the introduction of additional donor atoms results in
a noncoordinated amide group. The first systematic experimental (cyclic
voltammetry and UV–vis–NIR and EPR spectroelectrochemistry)
and theoretical (DFT) investigation of the electronic structure of
metal complexes bearing this redox-active ligand class is presented,
revealing redox processes with ligand contribution. The absorption
spectra and electrochemistry are mainly determined by the protonation
state of the ligand. While complexes <b>2Â[PF</b><sub><b>6</b></sub><b>]</b>, <b>3Â[PF</b><sub><b>6</b></sub><b>]</b>, and <b>4Â[PF</b><sub><b>6</b></sub><b>]</b> with neutral azocarboxamides show similar electronic spectra and
cyclovoltammograms, the incorporation of a deprotonated monoanionic
ligand in complex <b>1</b> leads to significant changes of these
properties. In contrast, the catalytic activity in the base-free transfer
hydrogenation reaction is mainly dependent on the coordination of
the amide group, with only minor effects of the protonation state.
While complexes <b>3Â[PF</b><sub><b>6</b></sub><b>]</b> and <b>4Â[PF</b><sub><b>6</b></sub><b>]</b>, with
an uncoordinated amide group, are inactive without the addition of
base, complexes <b>1</b> and <b>2Â[PF</b><sub><b>6</b></sub><b>]</b>, with a metal-bound amide group, show activity
under base-free conditions. The impact of the position of the amide
group together with the detection of metal hydride species in <sup>1</sup>H NMR spectroscopy suggests the operation of metal–ligand
bifunctional catalysis to take place when no base is added