Synthesis Of N-heterocyclic Carbene Palladium Complex And Their Catalytic Applications In Suzuki Cross-coupling Reaction

In this thesis, two new CCN pincer-type palladium (Ⅱ) complexes containing N-heterocyclic carbene groups and one cyclic dimeric palladium (Ⅱ) complexe have been synthesized. All the new compounds were fully characterized. The catalytic activities of the palladium complexes in the Suzuki cross-coupling reaction of aryl chlorine with arylboronic acids were studied. The main results are as follows:1. The new compounds 4a-d were prepared from commercially available m-phthalaldehyde in six steps (Scheme 1). The Aldehyde groups on the two sides of the central aryl were selectively reduced, brominated, and then nucleophilicly substituted by diethylamine,3,5-dimethyl pyrazole, and N-substituented imidazoles respectively, Utilizing the silver carbene transfer method,5a-c were obtained from the corresponding Ag(Ⅰ) complexes (Scheme 2-3). All the new compounds were characterized by elemental analysis, IR,1H NMR,13C NMR and MS-ESI spectra. The molecular structures of 5a and 5c were further confirmed by single-crystal X-ray analysis. 2. The effectiveness of palladium complexes 5 were tested in Suzuki cross-coupling reaction of aryl chlorides with arylboronic acid (Scheme 4). The optimized reaction conditions were K3PO4·3H2O as the base in ethanol at 78℃for 12 h. Compound 5a was found to be the most active catalyst. With a loading of 1 mol% of 5a, the coupling of various aromatic chlorides with arylboronic acid were carried out efficiently to afford the cross-coupling products. In most cases, good yields can be achieved (up to 99%). The sterically hindered or electron rich aryl bromides also can react smoothly with phenylboronic acid.