Palladium Pincer Complexes with Reduced Bond Angle Strain:  Efficient Catalysts for the Heck Reaction

Abstract

Palladium pincer complexes composed of six-membered fused metallacycles have been synthesized directly from 1,3-bis(2-pyridyloxy)benzene. The pincer complexes show remarkably high turnover numbers and frequencies in the Heck reaction.

Synthesis and structural characterization of enantiopure exo and endo six-membered oxazoline-derived palladacycles

“…By now, palladacycles of different sizes have been reported, including six-membered cycles [2]. The most common six-membered palladacycles belong to the CN type and are derivatives of the following N-containing compounds: amidines (A) [3], 2-substituted pyridines (B [4][5][6][7][8][9][10][11][12], C [13,14] and D [15]), amines (E [16][17][18], F [16] and G [19]), azo compounds (H, X = N) [20], azines (I [21]), imines [H (X = CH) [22], I [23][24][25][26][27][28][29][30], J [31,32] and K [33][34][35]) and oxazolines (L [36], M [37], N [38] and O [39], Chart 1). CP [40] and CS [19,41] palladacycles of this size have also been obtained.…”

Chiral Pt(II)/Pd(II) pincer complexes that show C–H⋯Cl hydrogen bonding: Synthesis and applications to catalytic asymmetric aldol and silylcyanation reactions

“…Moreover, this situation results in kinetically rather than thermodynamically controlled reaction pathways, and consequently, (ortho,para)-doubly metalated products rather than (ortho,ortho)-biscyclometallated species result [11]. Accordingly, we studied on the possibility of performing direct cyclometalation of NCN pincer ligands by screening appropriate metal sources and recently communicated our successful result in the synthesis of metal pincer complexes of achiral NCN ligands [12]. We also realized that chiral metal pincer complexes based on pyridine-based NCN ligands are rare, and thus initiated the synthesis of such metal pincer complexes for their potential applications to catalytic asymmetric reactions.…”

“…As a part of our continuing efforts on the synthesis, structural study and catalytic activity of pincer complexes [12], we report here the Pt(II)/Pd(II) complexes derived from the chiral pyridine based NCN pincer ligand. After completion of this work, we have found that the same but enantiomeric chloro-Pt(II)/Pd(II) complexes have been coincidentally pursued by other research group and their X-ray single crystal structures have been reported very recently [20].…”

Organonickel(II) complexes with anionic tridentate 1, 3-bis(azolylmethyl)phenyl ligands. synthesis, structural characterization and catalytic behavior

“…16 The ligand 2-bromo-1,3-bis(indazol-2-ylmethyl)benzene (2), in its turn, was obtained by reaction of 2-bromo-1,3-bis(bromomethyl)benzene with 1H-indazole in refluxing toluene in the presence of Et 3 N. Interestingly, the reaction with 1H-indazole gives the isomer with the indazolyl groups bonded to the carbon spacer through the N2 atom because the electron pair located at this nitrogen becomes more reactive than the corresponding one to N1 (Scheme 1). Index ranges Moreover, an X-ray diffraction study was undertaken in order to obtain a complete characterization.…”

“…(3,5-dimethylpyrazol-1-ylmethyl)benzene (1) This compound was prepared by modification of a reported method. 16 In a Schlenk tube provided with a reflux condenser, 3,5-dimethylpyrazole (1.970 g, 20.5 mmol), KOH (2.314 g, 41.2 mmol), tetrabutylammonium bromide (TBAB, 0.212 g, 0.63 mmol) and water (1 mL) were stirred at room temperature for 25 min. 2-Bromo-1,3-bis(bromomethyl)benzene (3.291 g, 9.6 mmol) and toluene (25 mL) were then added and the mixture refluxed for 72 h. The resulting mixture was washed with water and the organic layer separated and dried with magnesium sulphate.…”