An Alternative Mechanistic Concept for Homogeneous Selective Ethylene Oligomerization of Chromium-Based Catalysts: Binuclear Metallacycles as a Reason for 1-Octene Selectivity?

An alternative concept for the selective catalytic formation of 1‐octene from ethylene via dimeric catalytic centers is proposed. The selectivity of the tetramerization systems depends on the capability of ligands to form binuclear complexes that subsequently build up and couple two separate metallacyclopentanes to form 1‐octene selectively. Comparison of existing catalytic processes, the ability of the bis(diarylphosphino)amine (PNP) ligand to bridge two metal centers, and the experimental background support the proposed binuclear mechanism for ethylene tetramerization. 2+2+2=6 and 2×4=8? This concept explains the differences of selectivity between ethylene tri‐ and tetramerization by the capability of the ligands to form binuclear complexes that subsequently build up two metallacyclopentanes in one moiety. These two C4 units are then coupled to form 1‐octene selectively (see scheme).