Synthesis and characterization of amide-functionalized N-heterocyclic carbene–Pd complexes

Kamisue, Ryo; Sakaguchi, Satoshi

doi:10.1016/j.jorganchem.2011.02.009

Cited by 22 publications

(5 citation statements)

References 34 publications

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“…Chelating NHC-based ligands, functionalized with anionic donors (e.g., amide, alkoxide, and phenoxide) are useful, as they allow for the synthesis of NHC complexes of metals in high oxidation states. − Of particular interest in our research is the combination of NHCs with deprotonated amide (amidate or amido) donors. Ligands of this type and their metal complexes have been the subject of a number of studies. − In particular, Ghosh and co-workers have investigated both the potential catalytic and biomedical application of such ligands with a variety of metals. − These researchers have described a series of dianionic amidate functionalized NHC ligands designed to form highly stable Ni(II) complexes (e.g., iii ) as potential immunotolerance agents. , …”

Section: Introductionmentioning

confidence: 99%

Nickel(II) and Palladium(II) Complexes with Chelating N-Heterocyclic Carbene Amidate Ligands: Interplay between Normal and Abnormal Coordination Modes

et al. 2013

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A series of six Ni(II) and Pd(II) complexes of two bidentate and two tetradentate N-heterocyclic carbene (NHC)/amidate ligands have been prepared. The complexes are uncharged, with square-planar coordination geometries, and the ligands are bound via the NHC groups and the deprotonated amide nitrogen atoms. Pd(II) complexes were prepared for the bidentate ligands, and in each case, two chelating bidentate ligands were bound to the metal center, yielding cis/trans geometric isomeric forms. The Pd(II) complexes of the tetradentate ligands were obtained as a series of constitutional isomeric forms that were separable by fractional crystallization. The constitutional isomers differed in the coordination mode of the NHC groups, which were bound as either “normal” (nNHC) or “abnormal” (aNHC) carbenes. Density functional theory (DFT) studies show that the energies of the isomeric forms increase in the order nNHC/nNHC < nNHC/aNHC < aNHC/aNHC and suggest that the “abnormal” NHC coordination mode occurs in kinetic rather than thermodynamic reaction products. The Ni(II) complexes of the tetradentate ligand showed only “normal” NHC coordination, suggesting that the mechanism by which aNHC binding occurs is metal dependent. The Ni(II) and Pd(II) complexes with nNHC donors displayed distorted-square-planar coordination geometries and axial chirality.

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Section: Introductionmentioning

confidence: 99%

Nickel(II) and Palladium(II) Complexes with Chelating N-Heterocyclic Carbene Amidate Ligands: Interplay between Normal and Abnormal Coordination Modes

et al. 2013

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“…Kamisue and Sakaguchi,10 who observed amide‐functionalized NHC Pd complexes in the form of [(mono‐NHC)(PPh 3 ) 2 PdCl] + Cl – , suggested that these rare cationic metal centers are most probably stabilized by the strong donating capability of the NHC and phosphane. In our case, the cationic mono‐NHC Pd center is also stable in the presence of the weakly σ‐donating acetonitrile.…”

Section: Resultsmentioning

confidence: 99%

“…With respect to a remotely possible coordination of the N‐donor atom of the heterocyclic structure, the weakness of the Pd–N stretching features in the IR and Raman spectra makes it difficult to determine the Pd–N stretching frequency in the low‐frequency region, as this overlaps with the bands for the Pd–Cl stretching mode (350–300 cm –1 ), the in‐plane skeletal deformational modes (250–100 cm –1 ) of a square‐planar structure, and the out‐of‐plane skeletal deformation of heterocycles and aromatic rings (230–160 cm –1 ). It is noteworthy that only a few cationic Pd II complexes with one NHC ligand are reported in the literature 10,15. Most of these either contain a chelating NHC ligand with a P‐, N‐, or S‐donor functionality11b,12,16 or a monodentate NHC and other ligands such as phosphane and allyl.…”

Section: Resultsmentioning

confidence: 99%

Synthesis and Characterization of a Cationic Phthalimido‐Functionalized N‐Heterocyclic Carbene Complex of Palladium(II) and Its Catalytic Activity

et al. 2014

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“…Previously, we have shown the synthesis of the NHC-Pd, NHC-Ag, and NHC-Ir complexes by employing the hydroxy-amide functionalized azolium salt 1 as NHC precursor. , However, it was difficult to obtain a NHC-Cu complex from the hydroxy-amide functionalized azolium salt. Attempt to prepare a NHC-Cu species by allowing 1 to react with Cu 2 O or with CuCl in the presence of t BuOK failed due to the formation of an unidentified product .…”

Section: Resultsmentioning

confidence: 99%

“…This combination generates a strongly coordinating polydentate ligand that can lock stereodirecting functional groups in a fixed conformation. Thus, Pd-catalyzed intermolecular Heck-type couplings as well as Ir-catalyzed hydrosilane reduction of ketones with high enantioselectivities (over 90% ee) have been developed. In addition, the functionalized azolium salt 1 was tested in the Cu-catalyzed asymmetric conjugate addition of dialkylzincs to cyclic enones .…”

Section: Introductionmentioning

confidence: 99%

Hydroxy-amide Functionalized Azolium Salts for Cu-Catalyzed Asymmetric Conjugate Addition: Stereocontrol Based on Ligand Structure and Copper Precatalyst

et al. 2012

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A series of hydroxy-amide functionalized azolium salts have been designed and synthesized for Cu-catalyzed asymmetric conjugate addition reaction. The (CH(2))(2)-bridged hydroxy-amide functionalized azolium ligand precursors 2, in addition to the previously reported CH(2)-bridged azolium salts 1, have been prepared from readily available enantiopure β-amino alcohols. The combination of a Cu species with 1 or 2 efficiently promoted the 1,4-addition reaction of cyclic enones with dialkylzincs. For example, the reaction of 2-cyclohepten-1-one (17) with Bu(2)Zn in the presence of catalytic amounts of Cu(OTf)(2) and 1 gave (S)-3-butylcycloheptanone (20) in 99% yield and 96% ee. On the other hand, when the reaction was carried out under the influence of Cu(OTf)(2) combined with 2, (R)-20 in preference to (S)-20 was obtained in 98% yield and 80% ee. In this manner, the enantioselecvity was switched by controlling the structure of chiral ligand. Additionally, the reversal of enantioselectivity was also achieved by changing the Cu precatalyst from Cu(OTf)(2) to Cu(acac)(2) with the same ligand. The combination of Cu(acac)(2) with CH(2)-bridged azolium salt 1 in the reaction of 17 with Bu(2)Zn led to formation of (R)-20 as a major product in 55% yield and 80% ee. This result was in contrast to the Cu(OTf)(2)/1 catalytic system, where the 1,4-adduct with opposite configuration was obtained. Moreover, use of the Cu(acac)(2)/2 catalytic system produced (S)-20, while (R)-20 was formed by the Cu(OTf)(2)/2 catalytic system. Thus, it was found that either varying the linker of the chiral ligands or changing the counterion of Cu species between a OTf and acac ligand initially on the metal led to dual enantioselective control in the 1,4-addition reaction.

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Synthesis and characterization of amide-functionalized N-heterocyclic carbene–Pd complexes

Cited by 22 publications

References 34 publications

Nickel(II) and Palladium(II) Complexes with Chelating N-Heterocyclic Carbene Amidate Ligands: Interplay between Normal and Abnormal Coordination Modes

Nickel(II) and Palladium(II) Complexes with Chelating N-Heterocyclic Carbene Amidate Ligands: Interplay between Normal and Abnormal Coordination Modes

Synthesis and Characterization of a Cationic Phthalimido‐Functionalized N‐Heterocyclic Carbene Complex of Palladium(II) and Its Catalytic Activity

Hydroxy-amide Functionalized Azolium Salts for Cu-Catalyzed Asymmetric Conjugate Addition: Stereocontrol Based on Ligand Structure and Copper Precatalyst

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