Boron- and silicon-bridged bis(diphenylphosphino)-type ligands for chromium-catalyzed ethylene oligomerization

PNP-type ligands showed very good property in the catalytic systems of PNP/Cr(III)/methylaluminoxane (MAO) for ethylene selective tetramerization toward 1-octene. In this research, two PNP analogues bis(diphenylphosphino)phenylborane and bis(diphenylphosphino)dimethylsilane have been synthesized and characterized. In combination with CrCl3(THF)3 as active center and MAO as cocatalyst, these ligands produced a new catalytic systems for ethylene oligomerization to linear α-olefins with catalytic activities of up to 3.07 × 106 g mol−1 (cat) h−1. Herein, we report the effects of the reaction temperature, ethylene pressure, and the molar ratio of Al/Cr on the catalyst activities and product selectivities.