New tantalum ligand-free catalyst system for highly selective trimerization of ethylene affording 1-hexene: new evidence of a metallacycle mechanism.

Mild and salt-free reduction of MCl(5) (M = Nb, Ta) has been achieved by using 3,6-bis(trimethylsilyl)-1,4-hexadiene derivatives as reducing reagents. The salt-contact-free low-valent TaCl(3) exhibits high catalytic activity for the trimerization of ethylene to 1-hexene (>1000 TOF) with excellent selectivity (>98%). This salt-free tantalum system enables us to observe new evidence for a metallacycle mechanism.