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)­(η³-allyl)Cl as precatalysts for cross-coupling, the chemistry of related Pd^I dimers of the form (μ-allyl)­(μ-Cl)­Pd₂(L)₂ 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^I dimers (μ-allyl)­(μ-Cl)­Pd₂(IPr)₂ (allyl = allyl, crotyl, cinnamyl; IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene) through activation of Pd­(IPr)­(η³-allyl)Cl type monomers under mildly basic reaction conditions. The catalytic performance of the Pd^II monomers and their Pd^I μ-allyl dimer congeners for the Suzuki–Miyaura reaction is compared. We propose that the (μ-allyl)­(μ-Cl)­Pd₂(IPr)₂-type dimers are activated for catalysis through disproportionation to Pd­(IPr)­(η³-allyl)Cl and monoligated IPr–Pd⁰. The microscopic reverse comproportionation reaction of monomers of the type Pd­(IPr)­(η³-allyl)Cl with IPr–Pd⁰ to form Pd^I dimers is also studied. It is demonstrated that this is a facile process, and Pd^I dimers are directly observed during catalysis in reactions using Pd^II precatalysts. In these catalytic reactions, Pd^I μ-allyl dimer formation is a deleterious process which removes the IPr–Pd⁰ active species from the reaction mixture. However, increased sterics at the 1-position of the allyl ligand in the Pd­(IPr)­(η³-crotyl)Cl and Pd­(IPr)­(η³-cinnamyl)Cl precatalysts results in a larger kinetic barrier to comproportionation, which allows more of the active IPr–Pd⁰ 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)­(η³-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)­(η³-allyl)Cl as precatalysts for cross-coupling, the chemistry of related Pd^I dimers of the form (μ-allyl)­(μ-Cl)­Pd₂(L)₂ 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^I dimers (μ-allyl)­(μ-Cl)­Pd₂(IPr)₂ (allyl = allyl, crotyl, cinnamyl; IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene) through activation of Pd­(IPr)­(η³-allyl)Cl type monomers under mildly basic reaction conditions. The catalytic performance of the Pd^II monomers and their Pd^I μ-allyl dimer congeners for the Suzuki–Miyaura reaction is compared. We propose that the (μ-allyl)­(μ-Cl)­Pd₂(IPr)₂-type dimers are activated for catalysis through disproportionation to Pd­(IPr)­(η³-allyl)Cl and monoligated IPr–Pd⁰. The microscopic reverse comproportionation reaction of monomers of the type Pd­(IPr)­(η³-allyl)Cl with IPr–Pd⁰ to form Pd^I dimers is also studied. It is demonstrated that this is a facile process, and Pd^I dimers are directly observed during catalysis in reactions using Pd^II precatalysts. In these catalytic reactions, Pd^I μ-allyl dimer formation is a deleterious process which removes the IPr–Pd⁰ active species from the reaction mixture. However, increased sterics at the 1-position of the allyl ligand in the Pd­(IPr)­(η³-crotyl)Cl and Pd­(IPr)­(η³-cinnamyl)Cl precatalysts results in a larger kinetic barrier to comproportionation, which allows more of the active IPr–Pd⁰ 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)­(η³-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 (η³-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 (η³-allyl)­Pd­(L)­Cl. Specifically, we have prepared and studied a series of well-defined 2-substituted precatalysts of the type (η³-2-R-allyl)­Pd­(IPr)Cl (R = H, Ph, Me, ^tBu, OMe, CN), as well as their related Pd­(I) (μ-2-R-allyl)­(μ-Cl)­Pd₂(IPr)₂ 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 (η³-2-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)­Pd₂(IPr)₂ dimer/(η³-2-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 (η³-allyl)­Pd­(IPr)­Cl