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Relevant academic research and scientific papers

Synthesis of N-heterocyclic carbene-Pd(II)-5-phenyloxazole complexes and initial studies of their catalytic activity toward the Buchwald-Hartwig amination of aryl chlorides

Three new N-heterocyclic carbene (NHC)-Pd(II) complexes using 5-phenyloxazole as the ancillary ligand have been obtained in moderate to good yields by a one-pot reaction of the corresponding imidazolium salts, palladium chloride and 5-phenyloxazole under mild conditions. Initial studies showed that one of the complexes is an efficient catalyst for the Buchwald-Hartwig amination of aryl chlorides with various secondary and primary amines under the varied catalyst loading of 0.01-0.05 mol%, thus it will enrich the chemistry of NHCs and give an alternative catalyst for the coupling of challenging while cost-low aryl chlorides.

Cu-Catalyzed C-N Coupling with Sterically Hindered Partners

Copper, an earth-abundant metal, has reemerged as a viable alternative to the versatile Pd-catalyzed C-N coupling. Coupling sterically hindered reaction partners, however, remains challenging. Herein, we disclose the discovery and development of a pyrrole-ol ligand to facilitate the coupling of ortho-substituted aryl iodides with sterically hindered amines. The ligand was discovered through a library screening approach and highlights the value of mining heteroatom-rich pharmaceutical libraries for useful ligand motifs. Further evaluation revealed that this ligand is uniquely effective in these challenging transformations. The reaction enables the coupling of sterically hindered primary and secondary amines, anilines, and amides with broad functional group tolerance.

Sterically Hindered Amination of Aryl Chlorides Catalyzed by a New Carbazolyl-Derived P,N-Ligand-Composed Palladium Complex

A family of 2-(9 H -carbazol-9-yl)phenyl-based phosphine ligands were synthesized and their efficacy in promoting the steric hindered Buchwald-Hartwig amination was evaluated. In the presence of Pd(OAc) 2 (0.03-1.0 molpercent) associated with t

Facile Buchwald-Hartwig coupling of sterically encumbered substrates effected by PNP ligands

The diphosphinoamine ligands [(Ph2P)2N(Ar); 1 (Ar = C6H5), 2 (Ar = 2,6-iPr2C6H3)] were effectively utilized in Buchwald-Hartwig coupling of a range of sterically demanding substr

N-Heterocyclic carbene-palladacyclic complexes: synthesis, characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01 mol%).

Pd-PEPPSI-IPentAn Promoted Deactivated Amination of Aryl Chlorides with Amines under Aerobic Conditions

We report herein a highly efficient Pd-catalyzed amination by "bulky-yet-flexible" Pd-PEPPSI-IPentAn complexes. The relationship between the N-heterocyclic carbenes (NHCs) structure and catalytic properties was discussed. Sterically hindered (hetero)aryl chlorides and a variety of aliphatic and aromatic amines can be applied in this cross-coupling, which smoothly proceeded to provide desired products. The operationally simple protocol highlights the rapid access to CAr-N bond formation under mild conditions without the exclusion of air and moisture.

[Pd(IPr*R)(acac)Cl]: Efficient bulky Pd-NHC catalyst for Buchwald-Hartwig C-N cross-coupling reaction

A series of bulky palladium catalysts based on N-heterocyclic carbene, (Pd(NHC)(acac)Cl: NHC = IPr*me = N,N′-bis(2,6-bis(di-p-tolylmethyl)-4-methylphenyl)-imidazol-2 -ylidene, Pd(IPr*me)(acac)Cl; NHC = IPr*ipr = N,N′-bis(2,6-bis(di-4-isopropylphenyl)-4-methylphenyl)-imidazol-2 -ylidene, Pd(IPr*ipr)(acac)Cl; and NHC = IPr*tBu = N,N′-bis(2,6-bis(di-4-(tert-butyl)phenyl)- 4-methylphenyl)- imidazol-2-ylidene, Pd(IPr*tBu)(acac)Cl; acac = acetylacetonate), have been designed and synthesized. These three new catalysts showed much better catalytic activity in the Buchwald?Hartwig arylamination coupling reaction as compare to the earlier congener (IPr*)Pd(acac)Cl (IPr* = N,N′-bis(2,6-diphenylmethyl)-4-methylphenylimidazol-2-ylidene). The highly active PdII precatalyst [Pd(IPr*me)(acac)Cl] has been fully explored by using a wide range of substrates with different electronic and steric demands of coupling partners, for which up to 99% isolated yields were obtained. Remarkably, the moderate isolated yield was obtained for the challenging coupling of the amine bearing very bulky groups.

Mechanistic Study of the Role of Substrate Steric Effects and Aniline Inhibition on the Bis(trineopentylphosphine)palladium(0)-Catalyzed Arylation of Aniline Derivatives

The mechanism of the bis(trineopentylphosphine)palladium(0) (Pd(PNp3)2)-catalyzed coupling of aryl halides and aniline derivatives was studied in an effort to understand the role of substrate steric effects on the reaction. Prior studies had shown that the rate of Pd/PNp3-catalyzed coupling of aryl bromides and aniline derivatives was largely unaffected by substrate steric demand. The oxidative addition of aryl bromides to Pd(PNp3)2 is found to follow first-order kinetics with a rate that is independent of both ligand and aryl halide concentration. Thus, the rate limiting step for oxidative addition of aryl bromides is irreversible ligand dissociation. In the case of aryl chlorides, the oxidative addition rate has a first-order dependence on [ArCl] and an inverse dependence on [PNp3], indicating a mechanism involving reversible dissociation of the ligand followed by rate limiting oxidative addition. This difference in aryl halide effect was also found for the catalytic coupling reaction. Aryl bromide steric demand does not affect the coupling rate with hindered anilines, whereas the coupling rate of aryl chlorides is negatively affected by substrate steric demand. These results suggest that oxidative addition is rate limiting in the catalytic reaction for aryl chlorides but that oxidative addition is not rate limiting for aryl bromides. Aniline was found to give coupling rates significantly slower than those of 2,6-diisopropylaniline for both aryl bromides and chlorides. Aniline promotes the decomposition of the [(PNp3)Pd(Ar)(μ-X)]2 catalytic intermediate to a catalytically inactive palladacycle ([(κ2-P,C-Np2PCH2C(Me2)CH2)Pd(μ-X)]2) through C-H activation of a neopentyl group and elimination of arene. These studies show that the ability of the Pd/PNp3 catalyst system to tolerate steric demand in aryl bromides stems from the fact that the rate limiting step of the catalytic cycle is independent of the concentration and steric demand of aryl bromides. A catalyst deactivation pathway involving ligand metalation was identified that is promoted by unhindered aniline derivatives.

N-heterocyclic carbene-palladium complex, and preparation method and application thereof

The invention discloses an N-heterocyclic carbene-palladium complex, and a preparation method and application thereof. The N-heterocyclic carbene-palladium complex disclosed by the invention is shown in Formula (I), wherein L1 is a quinoline ligand or isoquinoline ligand, and N in the L1 is connected with Pd; L2 is an N-heterocyclic carbene ligand, and carbene carbon in the L2 is connected with the Pd; and X1 and X2 are respectively independently an anionic ligand. The N-heterocyclic carbene-palladium complex disclosed by the invention can efficiently catalyze carbon-carbon or carbon-heteroatom coupling reaction using aryl halide as a substrate. The formula is shown in the specification.

Synthesis and characterization of N-heterocyclic carbene-palladium(II) chlorides-1-methylindazole and -1-methylpyrazole complexes and their catalytic activity toward C-N coupling of aryl chlorides

A series of N-heterocyclic carbene-palladium(ii) chlorides-1-methylindazole and -1-methylpyrazole complexes was successfully synthesized and fully characterized by X-ray single crystal diffraction. In addition, initial investigations of their catalytic activity showed that they were efficient catalysts in the C-N coupling of primary and secondary amines with aryl chlorides at low catalyst loadings.