Dimerization of olefins with nickel-surface complexes in X-type zeolite or on silica

摘要: EPR spectroscopy shows that monomeric paramagnetic Ni(I) species, dispersed in X-type zeolite or on SiO2, can reversibly bind ligands (L) such as CO, C2H4 and C3H6 to lead various Ni(L)+n depending the pressure. Under low pressure (<40 torr), tetrahedral Ni(L)+ square planar Ni(L)+2 entities are obtained. At higher pressure, has a trigonal bipyramid structure forms Ni(L)+3 Ni(L)+4 complexes. This stereochemistry implies each case given number of surface O2−s acting ligand. The 17- 19-electron complexes easily undergo monosubstitution reactions their coordination sphere, while addition observed for 17-electron 298 K supported ions active selective ethylene propylene dimerization. After pretreatment at 973 K, silica-supported catalyst leads trimerization together with Via poisoning experiments, it is shown two olefin molecules bonded favours