7 research outputs found
Heteroditopic Chelating NHC Ligand-Supported Co<sup>III</sup> Complexes: Catalysts for the Reductive Functionalization of Carbon Dioxide under Ambient Conditions
Synthesis and characterization of heteroditopic chelating
NHC ligand-supported
air stable CoIII–NHC complexes (1a–d), featuring variable triazole N-substituents and thus, being
structurally tunable, are reported. These complexes were observed
to be very effective catalysts for the reductive functionalization
of CO2 with aromatic amines using hydrosilane under ambient
conditions (1 bar of CO2 pressure and room temperature)
to yield diverse N-formylated amines, and importantly, the catalytic
activity of the complexes was found to be reasonably tuned by the
triazole N-substituents, which is probably due to some electronic
modulations, supported by electrochemical analysis, rather than any
considerable steric alterations as indicated by the percent buried
volume calculation. Notably, the corresponding CoIII–NHC
complexes generated in situ were also found to be
equally effective. It is worth mentioning that this is the first report
on the effective N-formylation of less nucleophilic aromatic primary
amines by employing a homogeneous Co complex, to the best of our knowledge.
In addition, control experiments suggest that this protocol proceeds
via Co hydride and formoxysilane intermediate formation
Heteroditopic Chelating NHC Ligand-Supported Co<sup>III</sup> Complexes: Catalysts for the Reductive Functionalization of Carbon Dioxide under Ambient Conditions
Synthesis and characterization of heteroditopic chelating
NHC ligand-supported
air stable CoIII–NHC complexes (1a–d), featuring variable triazole N-substituents and thus, being
structurally tunable, are reported. These complexes were observed
to be very effective catalysts for the reductive functionalization
of CO2 with aromatic amines using hydrosilane under ambient
conditions (1 bar of CO2 pressure and room temperature)
to yield diverse N-formylated amines, and importantly, the catalytic
activity of the complexes was found to be reasonably tuned by the
triazole N-substituents, which is probably due to some electronic
modulations, supported by electrochemical analysis, rather than any
considerable steric alterations as indicated by the percent buried
volume calculation. Notably, the corresponding CoIII–NHC
complexes generated in situ were also found to be
equally effective. It is worth mentioning that this is the first report
on the effective N-formylation of less nucleophilic aromatic primary
amines by employing a homogeneous Co complex, to the best of our knowledge.
In addition, control experiments suggest that this protocol proceeds
via Co hydride and formoxysilane intermediate formation
Mixed Alkyl Hydrido Complexes of Zinc: Synthesis, Structure, and Reactivity
The (NNNN)-type macrocycle 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane
(Me<sub>3</sub>TACD, 1,4,7-Me<sub>3</sub>[12]aneN<sub>4</sub>) reacted
with 1 equiv of ZnEt<sub>2</sub> under ethane elimination to give
the mononuclear ethyl complex [(Me<sub>3</sub>TACD)ZnEt] (<b>1</b>). Upon treatment of (Me<sub>3</sub>TACD)H with 2 equiv of ZnEt<sub>2</sub>, the dinuclear complex [(Me<sub>3</sub>TACD)(ZnEt)(ZnEt<sub>2</sub>)] (<b>2</b>) was formed, which was converted with an
additional 1 equiv of (Me<sub>3</sub>TACD)H to <b>1</b>. Reaction
of <b>1</b> with PhSiH<sub>3</sub> led to the formation of a
tetranuclear ethyl hydrido complex [{(Me<sub>3</sub>TACD)ZnEt}<sub>2</sub>(ZnEtH)<sub>2</sub>] (<b>3</b>). Single-crystal X-ray
diffraction study revealed <b>3</b> to be a centrosymmetric
dimer featuring two [(Me<sub>3</sub>TACD)ZnEt] units coordinated to
a [Zn(μ-H)<sub>2</sub>Zn] core via amido nitrogen atoms of the
Me<sub>3</sub>TACD ligands. Substitution of the two [(Me<sub>3</sub>TACD)ZnEt] units in <b>3</b> by N-heterocyclic carbene IMes
[1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] gave [(IMes)ZnEtH]<sub>2</sub> (<b>4b</b>). The mixed alkyl hydrido complexes [(IMes)ZnRH]<sub>2</sub> (R = Me, <b>4a</b>; Et, <b>4b</b>) were alternatively
synthesized in quantitative yield by reacting [(IMes)ZnR<sub>2</sub>] (R = Me, Et) with [(IMes)ZnH<sub>2</sub>]<sub>2</sub> in 2:1 ratio.
Methyl complex <b>4a</b> reacted with CO<sub>2</sub> (<i>p</i>(CO<sub>2</sub>) = 0.5 bar) under facile insertion of CO<sub>2</sub> into Zn–H bonds to give dinuclear formate complex
[(IMes)ZnMe(O<sub>2</sub>CH)]<sub>2</sub> (<b>5a</b>). Treatment
of <b>4b</b> with CO<sub>2</sub> (<i>p</i>(CO<sub>2</sub>) = 0.5 bar) afforded a mixture of di- and trinuclear formate
complexes [(IMes)ZnEt(O<sub>2</sub>CH)]<sub>2</sub> (<b>5b</b>) and [(IMes)<sub>2</sub>Zn<sub>3</sub>Et<sub>3</sub>(O<sub>2</sub>CH)<sub>3</sub>] (<b>6</b>) under elimination of one IMes as
CO<sub>2</sub> adduct <b>IMes</b>·<b>CO</b><sub><b>2</b></sub>
Mixed Alkyl Hydrido Complexes of Zinc: Synthesis, Structure, and Reactivity
The (NNNN)-type macrocycle 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane
(Me<sub>3</sub>TACD, 1,4,7-Me<sub>3</sub>[12]aneN<sub>4</sub>) reacted
with 1 equiv of ZnEt<sub>2</sub> under ethane elimination to give
the mononuclear ethyl complex [(Me<sub>3</sub>TACD)ZnEt] (<b>1</b>). Upon treatment of (Me<sub>3</sub>TACD)H with 2 equiv of ZnEt<sub>2</sub>, the dinuclear complex [(Me<sub>3</sub>TACD)(ZnEt)(ZnEt<sub>2</sub>)] (<b>2</b>) was formed, which was converted with an
additional 1 equiv of (Me<sub>3</sub>TACD)H to <b>1</b>. Reaction
of <b>1</b> with PhSiH<sub>3</sub> led to the formation of a
tetranuclear ethyl hydrido complex [{(Me<sub>3</sub>TACD)ZnEt}<sub>2</sub>(ZnEtH)<sub>2</sub>] (<b>3</b>). Single-crystal X-ray
diffraction study revealed <b>3</b> to be a centrosymmetric
dimer featuring two [(Me<sub>3</sub>TACD)ZnEt] units coordinated to
a [Zn(μ-H)<sub>2</sub>Zn] core via amido nitrogen atoms of the
Me<sub>3</sub>TACD ligands. Substitution of the two [(Me<sub>3</sub>TACD)ZnEt] units in <b>3</b> by N-heterocyclic carbene IMes
[1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] gave [(IMes)ZnEtH]<sub>2</sub> (<b>4b</b>). The mixed alkyl hydrido complexes [(IMes)ZnRH]<sub>2</sub> (R = Me, <b>4a</b>; Et, <b>4b</b>) were alternatively
synthesized in quantitative yield by reacting [(IMes)ZnR<sub>2</sub>] (R = Me, Et) with [(IMes)ZnH<sub>2</sub>]<sub>2</sub> in 2:1 ratio.
Methyl complex <b>4a</b> reacted with CO<sub>2</sub> (<i>p</i>(CO<sub>2</sub>) = 0.5 bar) under facile insertion of CO<sub>2</sub> into Zn–H bonds to give dinuclear formate complex
[(IMes)ZnMe(O<sub>2</sub>CH)]<sub>2</sub> (<b>5a</b>). Treatment
of <b>4b</b> with CO<sub>2</sub> (<i>p</i>(CO<sub>2</sub>) = 0.5 bar) afforded a mixture of di- and trinuclear formate
complexes [(IMes)ZnEt(O<sub>2</sub>CH)]<sub>2</sub> (<b>5b</b>) and [(IMes)<sub>2</sub>Zn<sub>3</sub>Et<sub>3</sub>(O<sub>2</sub>CH)<sub>3</sub>] (<b>6</b>) under elimination of one IMes as
CO<sub>2</sub> adduct <b>IMes</b>·<b>CO</b><sub><b>2</b></sub>
Two Different, Metal-Dependent Coordination Modes of a Dicarbene Ligand
The
bisimidazolium salt H<sub>2</sub>-<b>1</b>(PF<sub>6</sub>)<sub>2</sub> featuring a bridging 1,4-phenylene group reacts with
0.5 equiv of [PdCl(allyl)]<sub>2</sub> in the presence of Cs<sub>2</sub>CO<sub>3</sub> to give the dinuclear complex [<b>2</b>](PF<sub>6</sub>)<sub>2</sub>, whereas the reaction of the same bisimidazolium
salt with 0.5 equiv of [Ir(Cl)<sub>2</sub>(Cp*)]<sub>2</sub> yields
the mononuclear orthometalated complex [<b>3</b>]PF<sub>6</sub> with one remaining imidazolium unit. The unreacted imidazolium group
in complex [<b>3</b>]PF<sub>6</sub>, however, can also be metalated
with Rh<sup>III</sup> to yield the doubly orthometalated heterobimetallic
complex [<b>4</b>]. In complex [<b>4</b>], each M<sup>III</sup> center (M = Ir<sup>III</sup> and Rh<sup>III</sup>) is coordinated
by one NHC unit and orthometalates the central aryl ring of the ligand
Facile Reversibility by Design: Tuning Small Molecule Capture and Activation by Single Component Frustrated Lewis Pairs
A series of single component FLPs
has been investigated for small
molecule capture, with the finding that through tuning of both the
thermodynamics of binding/activation and the degree of preorganization
(i.e., Δ<i>S</i><sup>⧧</sup>) reversibility
can be brought about at (or close to) room temperature. Thus, the
dimethylxanthene system {(C<sub>6</sub>H<sub>4</sub>)<sub>2</sub>(O)CMe<sub>2</sub>}(PMes<sub>2</sub>)(B(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>): (i) heterolytically cleaves dihydrogen to give an equilibrium
mixture of FLP and H<sub>2</sub> activation product in solution at
room temperature and (ii) reversibly captures nitrous oxide (uptake
at room temperature, 1 atm; release at 323 K)
Facile Reversibility by Design: Tuning Small Molecule Capture and Activation by Single Component Frustrated Lewis Pairs
A series of single component FLPs
has been investigated for small
molecule capture, with the finding that through tuning of both the
thermodynamics of binding/activation and the degree of preorganization
(i.e., Δ<i>S</i><sup>⧧</sup>) reversibility
can be brought about at (or close to) room temperature. Thus, the
dimethylxanthene system {(C<sub>6</sub>H<sub>4</sub>)<sub>2</sub>(O)CMe<sub>2</sub>}(PMes<sub>2</sub>)(B(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>): (i) heterolytically cleaves dihydrogen to give an equilibrium
mixture of FLP and H<sub>2</sub> activation product in solution at
room temperature and (ii) reversibly captures nitrous oxide (uptake
at room temperature, 1 atm; release at 323 K)