86 research outputs found
CCDC 169020: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures
CCDC 169022: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures
CCDC 169021: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures
Insight into the Efficiency of Cinnamyl-Supported Precatalysts for the Suzuki–Miyaura Reaction: Observation of Pd(I) Dimers with Bridging Allyl Ligands During Catalysis
Despite widespread
use of complexes of the type Pd(L)(η<sup>3</sup>-allyl)Cl as
precatalysts for cross-coupling, the chemistry
of related Pd<sup>I</sup> dimers of the form (μ-allyl)(μ-Cl)Pd<sub>2</sub>(L)<sub>2</sub> has been underexplored. Here, the relationship
between the monomeric and the dimeric compounds is investigated using
both experiment and theory. We report an efficient synthesis of the
Pd<sup>I</sup> dimers (μ-allyl)(μ-Cl)Pd<sub>2</sub>(IPr)<sub>2</sub> (allyl = allyl, crotyl, cinnamyl; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene)
through activation of Pd(IPr)(η<sup>3</sup>-allyl)Cl type monomers
under mildly basic reaction conditions. The catalytic performance
of the Pd<sup>II</sup> monomers and their Pd<sup>I</sup> μ-allyl
dimer congeners for the Suzuki–Miyaura reaction is compared.
We propose that the (μ-allyl)(μ-Cl)Pd<sub>2</sub>(IPr)<sub>2</sub>-type dimers are activated for catalysis through disproportionation
to Pd(IPr)(η<sup>3</sup>-allyl)Cl and monoligated IPr–Pd<sup>0</sup>. The microscopic reverse comproportionation reaction of monomers
of the type Pd(IPr)(η<sup>3</sup>-allyl)Cl with IPr–Pd<sup>0</sup> to form Pd<sup>I</sup> dimers is also studied. It is demonstrated
that this is a facile process, and Pd<sup>I</sup> dimers are directly
observed during catalysis in reactions using Pd<sup>II</sup> precatalysts.
In these catalytic reactions, Pd<sup>I</sup> μ-allyl dimer formation
is a deleterious process which removes the IPr–Pd<sup>0</sup> active species from the reaction mixture. However, increased sterics
at the 1-position of the allyl ligand in the Pd(IPr)(η<sup>3</sup>-crotyl)Cl and Pd(IPr)(η<sup>3</sup>-cinnamyl)Cl precatalysts
results in a larger kinetic barrier to comproportionation, which allows
more of the active IPr–Pd<sup>0</sup> catalyst to enter the
catalytic cycle when these substituted precatalysts are used. Furthermore,
we have developed reaction conditions for the Suzuki-Miyaura reaction
using Pd(IPr)(η<sup>3</sup>-cinnamyl)Cl which are compatible
with mild bases
Insight into the Efficiency of Cinnamyl-Supported Precatalysts for the Suzuki–Miyaura Reaction: Observation of Pd(I) Dimers with Bridging Allyl Ligands During Catalysis
Despite widespread
use of complexes of the type Pd(L)(η<sup>3</sup>-allyl)Cl as
precatalysts for cross-coupling, the chemistry
of related Pd<sup>I</sup> dimers of the form (μ-allyl)(μ-Cl)Pd<sub>2</sub>(L)<sub>2</sub> has been underexplored. Here, the relationship
between the monomeric and the dimeric compounds is investigated using
both experiment and theory. We report an efficient synthesis of the
Pd<sup>I</sup> dimers (μ-allyl)(μ-Cl)Pd<sub>2</sub>(IPr)<sub>2</sub> (allyl = allyl, crotyl, cinnamyl; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene)
through activation of Pd(IPr)(η<sup>3</sup>-allyl)Cl type monomers
under mildly basic reaction conditions. The catalytic performance
of the Pd<sup>II</sup> monomers and their Pd<sup>I</sup> μ-allyl
dimer congeners for the Suzuki–Miyaura reaction is compared.
We propose that the (μ-allyl)(μ-Cl)Pd<sub>2</sub>(IPr)<sub>2</sub>-type dimers are activated for catalysis through disproportionation
to Pd(IPr)(η<sup>3</sup>-allyl)Cl and monoligated IPr–Pd<sup>0</sup>. The microscopic reverse comproportionation reaction of monomers
of the type Pd(IPr)(η<sup>3</sup>-allyl)Cl with IPr–Pd<sup>0</sup> to form Pd<sup>I</sup> dimers is also studied. It is demonstrated
that this is a facile process, and Pd<sup>I</sup> dimers are directly
observed during catalysis in reactions using Pd<sup>II</sup> precatalysts.
In these catalytic reactions, Pd<sup>I</sup> μ-allyl dimer formation
is a deleterious process which removes the IPr–Pd<sup>0</sup> active species from the reaction mixture. However, increased sterics
at the 1-position of the allyl ligand in the Pd(IPr)(η<sup>3</sup>-crotyl)Cl and Pd(IPr)(η<sup>3</sup>-cinnamyl)Cl precatalysts
results in a larger kinetic barrier to comproportionation, which allows
more of the active IPr–Pd<sup>0</sup> catalyst to enter the
catalytic cycle when these substituted precatalysts are used. Furthermore,
we have developed reaction conditions for the Suzuki-Miyaura reaction
using Pd(IPr)(η<sup>3</sup>-cinnamyl)Cl which are compatible
with mild bases
Effect of 2‑Substituents on Allyl-Supported Precatalysts for the Suzuki–Miyaura Reaction: Relating Catalytic Efficiency to the Stability of Palladium(I) Bridging Allyl Dimers
One of the most commonly used classes
of precatalysts for cross-coupling are Pd(II) complexes of the type
(η<sup>3</sup>-allyl)Pd(L)Cl. Here, we report the first full
investigation of how the steric and electronic properties of the 2-substituent
affect the catalytic properties of precatalysts of the type (η<sup>3</sup>-allyl)Pd(L)Cl. Specifically, we have prepared and studied
a series of well-defined 2-substituted precatalysts of the type (η<sup>3</sup>-2-R-allyl)Pd(IPr)Cl (R = H, Ph, Me, <sup>t</sup>Bu, OMe,
CN), as well as their related Pd(I) (μ-2-R-allyl)(μ-Cl)Pd<sub>2</sub>(IPr)<sub>2</sub> dimers. The catalytic performance of the
Pd(II) monomers and their Pd(I) μ-allyl dimer congeners is compared
for the Suzuki–Miyaura reaction. When Pd(II) monomers are used
as precatalysts, we observe the formation of the Pd(I) μ-allyl
dimers during catalysis. In fact, we find that the catalytic efficiency
of (η<sup>3</sup>-2-R-allyl)Pd(IPr)Cl precatalysts correlates
inversely with the thermodynamic stability of the related Pd(I) μ-allyl
dimers. Therefore, we have examined the structural and electronic
properties of the Pd(I) μ-allyl dimers in detail and probed
the mechanism of the (μ-2-R-allyl)(μ-Cl)Pd<sub>2</sub>(IPr)<sub>2</sub> dimer/(η<sup>3</sup>-2-R-allyl)Pd(IPr)Cl
monomer interconversion both experimentally and computationally. Overall,
this study shows that the formation of Pd(I) μ-allyl dimers
can play a crucial role in determining the catalytic efficiency of
precatalysts of the type (η<sup>3</sup>-allyl)Pd(IPr)Cl
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