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• 244187-81-3 1,3-bis-(2,6-diisopropylphenyl)-imidazol-2-ylidene 

Relevant academic research and scientific papers

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 PdI 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 PdII monomers and their PdI 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 PdI dimers is also studied. It is demonstrated that this is a facile process, and PdI dimers are directly observed during catalysis in reactions using PdII precatalysts. In these catalytic reactions, PdI 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.

Synthesis and reactivity of alkylpalladium N-heterocyclic carbene complexes

The transamination of alkylpalladium halide N-heterocyclic carbene complexes has enabled the isolation of products that reveal interesting insights into the factors which might be barriers to the development of a palladium-catalysed alkyl-amination reaction. The Royal Society of Chemistry.

Alkylpalladium n-heterocyclic carbene complexes: Synthesis, reactivity, and catalytic properties

The dimers [trans-[(neopentyl)Pd(μ-Cl)(rBu)]2, 2, and (cis-[(neopentyl)Pd(μ-Cl)(IPr)]2,3 (ItBu = 1,3-bis-tert-butylimidazol-2-ylidene, IPr = l,3-bis-2,6-diidopropylimidazol-2- ylidene), have been synthesized from [Pd(neopentyl)(Cl)(l,5-COD)], and their reactivity toward a variety of nucleophiles has been evaluated. In particular, this study revealed that 2 can be readily cleaved by primary and secondary amines, affording stable transamination products, which are surprisingly resistant to deprotonation. Dimer 3 was subsequently used as a catalyst in a series of Buchwald-Hartwig animation reactions of aryl chlorides.

Palladium(0) NHC complexes: A new avenue to highly efficient phosphorescence

We report the first examples of highly luminescent di-coordinated Pd(0) complexes. Five complexes of the form [Pd(L)(L′)] were synthesized, where L = IPr, SIPr or IPr? NHC ligands and L′ = PCy3, or IPr and SIPr NHC ligands. The photophysical properties of these complexes were determined in degassed toluene solution and in the solid state and contrasted to the poorly luminescent reference complex [Pd(IPr)(PPh3)]. Organic light-emitting diodes were successfully fabricated but attained external quantum efficiencies of between 0.3 and 0.7%.

Synthesis, characterization, and reactivity of N-heterocyclic carbene palladium(II) hydroxide dimers

Palladium hydroxide dimers were prepared by reactions of CsOH with monomeric [Pd(NHC)(η3-allyl)Cl] starting materials. The dimers represent species proposed as intermediates in important cross-coupling reactions. These complexes were tested for their catalytic activity in Suzuki-Miyaura coupling and Buchwald-Hartwig aryl amination. The hydroxide complexes were susceptible to hydrogenolysis on exposure to H2 gas. Following H2O elimination and β-hydride elimination of an additional cinnamyl ligand, a Pd(0) species is formed which can react with other available ligands.

Palladium(I)-bridging allyl dimers for the catalytic functionalization of CO2

In general, the chemistry of both η1-allyl and η3-allyl Pd complexes is extremely well understood; η1-allyls are nucleophilic and react with electrophiles, whereas η3-allyls are electrophilic and react with nucleophiles. In contrast, relatively little is known about the chemistry of metal complexes with bridging allyl ligands. In this work, we describe a more efficient synthetic methodology for the preparation of PdI-bridging allyl dimers and report the first studies of their stoichiometric reactivity. Furthermore, we show that these compounds can activate CO2 and that an N-heterocyclic carbene-supported dimer is one of the most active and stable catalysts reported to date for the carboxylation of allylstannanes and allylboranes with CO 2.

Facile oxidative addition of organic halides to heteroleptic and homoleptic Pd0-N-heterocyclic carbene complexes

Novel heteroleptic Pd0 complexes with an N-heterocyclic carbene (NHC) ligand [(Me3P)Pd(NHC)] (NHC = IPr, 1; SIPr, 2) were obtained from [Pd(CH2=CHPh)(PMe3)2] and an equivalent of NHC [NHC = 1,3-bis(2,