Palladacyclic complexes bearing CNN-type ligands as catalysts in the Heck reaction

Abstract

Preparations of novel unsymmetrical, tridentate nitrogen ligand precursors, PhN=C(CMe2)(NPh)C=N(CH2)2NMe2(1) and PhN=C(CMe2)(NPh)C=N(CH2)Py (2), are described. Treatment of 1 with 1 molar equiv. (COD)PdCl2 in the presence of NEt3 or with 1 molar equiv. Pd(OAc)2 affords orthometallated palladium(II) complexes, [PhN=C(CMe2)(N-eta1-Ph)C=N(CH2)2NMe2]PdX (X=Cl (3); X=OAc (4)), respectively. Compound can be yielded via the reaction of with an excess of LiCl in methanol. Treatment of with 1 molar equiv. of (COD)PdCl2, Pd(OAc)2 or Pd(TFA)2 affords orthometallated palladium(II) complexes, [PhN=C(CMe2)(N-eta1-Ph)C=NCH2Py]PdX (X=Cl (5); X=OAc (6); X=TFA (7)), respectively. The crystal and molecular structures are reported for compounds 2, 3, 5 and 6. The application of these novel palladacyclic complexes to the Heck reaction with aryl halide substrates was examined.

Synthesis, Characterization, and Catalytic Applications of Palladacyclic Complexes Bearing C,N,S‐Donor Ligands

“…of Pd(OAc) 2 at room temperature yields complexes 4 and 5, respectively, as pale brown solids. Similar to the results reported previously, [31] an additional tertiary carbon was found in the phenyl ring region of the 13 C{ 1 H} NMR spectrum that indicates the presence of a metallated carbon atom, which was created during the reactions. Crystals of 4 suitable for structural determination were obtained from a CH 2 Cl 2 /hexane solu-Scheme 1.…”

“…2,2-Dimethyl-N,NЈ-diphenyl-malonamide and 2,2-dimethyl-N,NЈ-diphenylpropanediimidoyl dichloride were prepared by a method reported in the literature. [31] PhN=C The procedure for the preparation of 3 was similar to that used for 2. A white solid was obtained.…”

“…The N-Pd-C metallated bite angle [93.47(12)°] involving the imino nitrogen and metallated carbon atoms is similar to those [93.20(104)°, 93.77(8)°, and 94.51(10)°] found in our previous work. [31] The N-Pd-S bite angle [84.62(8)°] involving the imino nitrogen atom and the pendant group is in the range [84.46(10)-85.1(1)°] found for C,N,S-donor complexes with two carbon spacer atoms between the nitrogen and sulfur atoms. [32][33][34] [31,[39][40][41] The reaction of 4 and 5 with an excess of lithium chloride, in methanol at room temperature, yielded complexes 6 and 7, respectively, as yellow solids.…”

“…of NEt 3 using a similar procedure to that reported in the literature. [31] The new ligand precursors 2 and 3 were synthesized from 1 via a nucleophilic substitution reaction with the corresponding thiol [R = C(CH 3 ) 3 for 2; R = Ph for 3]. [20] Compounds 1, 2, and 3 were characterized by NMR spectroscopy and elemental analysis, which indicated that they are four-membered ring diimine compounds with the different functionalities.…”

“…[20][21][22][23][24][25][26][27][28][29][30] Their success in catalyzing cross-coupling reactions encouraged us to study the catalytic performance exhibited by palladacycles with pendant thioether functionalities. Following our previous work on four-membered ring diimino palladacycles, [31] we report here the synthesis and characterization of novel mononuclear palladacycles incorporating unsymmetrical C,N,S-donor ligands. Their catalytic activities toward the Suzuki and Heck reactions were investigated.…”