Preparation And Characterization Of Cyclopalladated Arylimine Self-assembly Films And Their Application In Catalyzing Sonogashira Coupling Reaction

In this paper, a series of new cyclopalladated monomers were synthesized and characterized by 1H NMR, 13 C NMR, 31 P NMR, IR and MS. Their self-assembly films on hydrophobic substrate were prepared by hydrogen initiation and were characterized by water contact angle, AFM, XPS and Raman spectra. Sonogashira cross-coupling reaction as a templet model catalyzed by catalyst 4a containing different alkane chains self-assembled films in heterogeneous system were systematic studied. Moreover, the catalytic mechanism of Sonogashira reaction in heterogeneous system was proposed preliminarily.1. A series of amphiphilic cyclopalladated arylimine monomers(4a-c)(Scheme 1) were prepared and characterized by 1H NMR, 13 C NMR,31 P NMR, IR and MS. The crystal structures of 4b-c were determined by X-ray single-crystal diffraction.2. A series of cyclopalladated arylimine monomers(4a-c) self-assembly films were prepared by H-surface initiation on hydrophobic substrate and used for catalyzing the Sonogashira reaction in heterogeneous system(Scheme 2).3. Sonogashira cross-coupling reaction catalyzed by catalyst 4a-c self-assembled films were investigated. The results showed as follow: 1) These self-assembly films have a highly active(TON up to105) which was better than that observed in homogeneous. Among of them, the self-assembly film of 4a could be reused seven times. 2) Effect of length of chain on its catalytic properties were also systematic investigated, in which the V(H2O)/V(Et OH) ratio was significantly increase with increasing of chain length due to the extended and ordered chains in the each system which made the substrates contact with active center. However, the increased alkane chains would make penetration of substrates difficult for contacting with active center resulting in burying of a reaction center under the surface, which also affected their recycle ability.4. Research on the mechanism of Sonogashira reaction showed that the reaction was indeed heterogeneous, which occurred in the surface of the substrate. In this approach, it could be rationalized that Pd(II) species should be reduced to the Pd(0) catalyst as an active species(Scheme 3).