Synthesis and characterization of novel five-membered palladacycles

Abstract

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 PPh 3 (1:2) in degassed acetone provided the dinuclear palladium complexes {Pd( C, N-2-C 9H 4N–CH–[–CH 2CO(3,4,5-(OMe-) 3–C 6H 2-] 2–3-R-6)Cl(PPh 3)} 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-Me 2C 6H 3) to give the corresponding palladacycles 5a– b in moderate yields (45% and 43%). The palladacycles 5a– 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, 1H, and 31P NMR). The crystal structure of 5a was determined by X-ray crystallography diffraction studies.