Novel Ir-complexes Ligated By Neutral/Ionic Phosphines: Syntheses, Characterization And Catalysis For Hydroformylation

For the high value of the derivative of aldehydes, hydroformylation of olefins is one of the most important processes in homogeneous catalysis with the advantage of 100% atom economy. Although rhodium complexes along with phosphines are the most efficient catalysts for this process, the high cost of Rh-complexs and the disadvantages of phosphines in terms of instability in air and sensitivity to water inspire the search for the alternative transition-metal catalytic systems. Iridium (+1) with economic advantages and rhodium (+1) possess the same valent-electron structure and then the corresponding complexes usually have the similar geometry configurations. Hence, in this thesis, we make the effort to develop the iridium catalytic system for homogeneous hydroformylation as the alternative to Rh-P catalytic systems.It is believed that the electronic and steric effects of the phosphine could dramatically influence the catalytic performance of the transition metals for hydroformylation. So, firstly, three kinds of ionic phosphine ligands were prepared in which the positive charge in imidazolium was adjacent to the phosphine fragment. It was found that the involved positive charges in imidazoliums exhibited the strong electron-withdrawing effect on the neighbored phosphine fragments, rendering ionic ligands more π-acceptor ability. The magnitudes of Jse-p in the 77Se isotopomer of the phosphine-selenides in 31P NMR spectra and the CO vibrational frequency of iridium complexes observed by FT-IR spectra also confirmed the increased π-acceptor ability of the ionic phosphines. Secondly, the novel iridium complexes ligated by the developed phosphines were successfully synthesized and fully charactered. The molecular structures of these obtained iridium complexes showed that as for the Ir-center in+1 valent state, the Ir-complexes possessed the typical square-planar geometry which were ligated by a PCP (phosphine-carboanion-phosphine) pincer or monodentate phosphine ligand. As for the Ir-center in+2 valent state, the unique Ir-complexe in trigonal bipyramid geometry was ligated by a PCC (phosphine-carboanion-carbene) pincer. Finally, the inherent catalytic performance of these Ir-complexes and the effect of the involved phosphines were investigated for hydroformylation of 1-octene. It indicated that the changed coordination ability because of the introduction of the positive charges in imidazoliums could result in the different catalytic performance for hydroformylation. With the similar structure and the same Ir+ center, the iridium complexes ligated by the phosphines with relatively stronger a-donor ability exhibited better catalytic performance in comparison to the ionic ones with less a-donor ability. The latter preferred to the hydrogenation of alkene.