An iminophosphine dendrimeric ligand and its evaluation in the Heck reaction

DAB-dendr-(NH2)32 has been modified to produce two novel dendrimeric P,N-ligands, DAB-dendr-[1,2-(NCHC6H4PPh2)]32 and DAB-dendr-[1,2-(NHCH2C6H4PPh2)]32. These were both found to activate electron rich aryl bromides in the Heck reaction. The reactions seem to proceed better in a novel solvent system consisting of an equimolar mixture of a tertiary amine with acetic acid. A marked dependence of the conversion on the [equivalents of dendrimeric ligand]/[Pd] ratio has been observed with conversion decreasing as the ratio of dendrimer equivalents to Pd increases. This phenomenon is attributed to interactions of the arms bearing the metal with neighboring ones within the dendrimer.