Palladium(II)–N-heterocyclic carbene complexes derived from proline: synthesis and characterization

N-Heterocyclic Carbene–Rhodium(I) Complexes Derived from Proline for the 1,4-Conjugate Addition of Arylboronic Acids to Enones in Neat Water

“…First, the imidazolium salts 1a and 1b were prepared as previously reported [60]. Then, NHC-Rh(I) complexes 2a and 2b were synthesized by treatment of 1a and 1b with [Rh(cod)Cl] 2 in the presence of KO t Bu in refluxing THF, respectively [61,62].…”

“…But, by contrast, only very few examples among NHC-Rh(I) complexes catalyzed 1,4-conjugate addition of arylboronic acids to a,b-unsaturated carbonyl compounds, have been reported in the literature [57][58][59]. In recent years we addressed our attention to the development of proline-based NHC-metal complexes and some NHC-Pd(II) complexes derived from proline have been successfully synthesized [60]. These results prompted us to further develop other NHC-metal complexes derived from proline.…”

Crystal structure of (1-((1-benzylpyrrolidin-2-yl-κN)methyl)-3-isopropyl-1H-imidazol-2(3H)-ylidene–κC)dibromidopalladium(II), C18H25Br2N3Pd

“…The title compound was prepared according to a reported method [1]. Single crystals suitable for X-ray di raction were obtained by crystallization in a mixture of dichloromethane and ethyl acetate.…”

Imidazole‐coordinated monodentate NHC–Pd(II) complex derived from proline and its application to the coupling reaction of arylboronic acids with carboxylic acid anhydrides in water at room temperature

“…Based on our previously reported results, [3] the reaction of imidazolium salt 4 (1.0 mmol) with Pd(OAc) 2 (0.5 mmol) was carried out in refluxing tetrahydrofuran (THF) for 18 h. To our pleasure, a new NHC-Pd(II) complex 5 was obtained as the sole product in 82% yield after careful silica-gel chromatography (Scheme 3). The structure of complex 5 was fully determined by X-ray single crystal diffraction ( Fig.…”

“…That is, when an electron-rich group such as benzyl group was attached to the N-atom, both the N-atom and NHC were coordinated to the Pd(II) center, while when an electron-poor group such as Ts group was attached, a dimeric mono-coordinated NHC-Pd(II) was obtained exclusively (Scheme 1). [3] Encouraged by this development, we then turned our attention to the synthesis of NHC-palladium complexes derived from other substituted prolines. Herein, we wish to report the elimination of an alkyl group from the corresponding precursor (imidazolium salt) and the preparation of imidazole-coordinated monodentate NHC-Pd(II) complex derived from N-phenyl substituted proline and its catalytic activity towards the coupling reaction of arylboronic acids with carboxylic acid anhydrides in water at room temperature.…”