Olefin oligomerization by main group Ga(3+) and Zn(2+) single site catalysts on SiO(2)

In heterogeneous catalysis, olefin oligomerization is typically performed on immobilized transition metal ions, such as Ni(2+) and Cr(3+). Here we report that silica-supported, single site catalysts containing immobilized, main group Zn(2+) and Ga(3+) ion sites catalyze ethylene and propylene oligomerization to an equilibrium distribution of linear olefins with rates similar to that of Ni(2+). The molecular weight distribution of products formed on Zn(2+) is similar to Ni(2+), while Ga(3+) forms higher molecular weight olefins. In situ spectroscopic and computational studies suggest that oligomerization unexpectedly occurs by the Cossee-Arlman mechanism via metal hydride and metal alkyl intermediates formed during olefin insertion and β-hydride elimination elementary steps. Initiation of the catalytic cycle is proposed to occur by heterolytic C-H dissociation of ethylene, which occurs at about 250 °C where oligomerization is catalytically relevant. This work illuminates new chemistry for main group metal catalysts with potential for development of new oligomerization processes.