Synthesis and characterization of novel five-membered palladacycles

3-(2-Chloroquinolin-3-yl)-1,5-bis(3,4,5-trimethoxy-phenyl)-pentane-2,4-dione derivatives 3a-b were conveniently synthesized in excellent yields (82% each) by tandem Knoevenagel condensation reactions of 2-chloro-3-carbaldehyde-quinoline 1a-b with 3,4,5-trimethoxy acetophenone, followed by a base catalyzed Michael addition, such as DBU (1,8-diazabicyclo[5,4,0]undec-7-ene) with or without solvent. The reactions of 3a-b with Pd(dba)(2) in the presence of PPh3 (1:2) in degassed acetone provided the dinuclear palladium complexes {Pd(C,N-2-C9H4N-CH-[-CH2CO(3,4,5-(OMe-)(3)-C6H2-](2)-3-R-6)Cl(PPh3)}(2) [(R=H (4a), R=OMe (4b)] in moderate yields (38% and 43%), which in turn reacted with an excess of isonitrile XyNC (Xy = 2,6-Me2C6H3) to give the corresponding palladacycles 5a-b in moderate yields (45% and 43%). The palladacycles Sa-b were also obtained in similar yields (32% and 33%) via a one-pot oxidative addition reaction of 3a-b with isonitrile XyNC:Pd(dba)(2) (4:1). The products were characterized by satisfactory elemental analysis and spectral studies (IR, H-1, and P-31 NMR). The crystal structure of 5a was determined by X-ray crystallography diffraction studies. (C) 2009 Published by Elsevier Ltd.