Titanacalixarenes in homogeneous catalysis: Synthesis, conformation and catalytic activity in ethylene polymerisation

Variously substituted titanacalixarenes were synthesised and tested for their performance as catalysts in ethylene polymerisation: p-tert-butylcalix[4] arene was derivatised to afford distal diether p-tert-butylcalix[4]arenes L1-L4, distal dihydroxy-depleted L5, proximal dihydroxy-depleted L6, proximal diether p-tert-butylcalix[4]arene L7, proximal intra-bridged disiloxane L8 and proximal monoether L9. (Dichlorotitana)-p-tert-butylcalix[4]arenes 1-8 and (monochlorotitana)-p-tertbutylcalix[4]arene 9 have been successfully synthesised by reacting L1-L4 with TiCl₄·2THF or L5-L9 with TiCl ₄. The structural conformation of complexes 1-9 in solution were determined by ¹H NMR, ¹³C NMR, NOESY and COSY spectroscopic studies. Compounds 2, 3 and 4 have been structurally characterised by single-crystal X-ray diffraction. Upon activation with methylaluminoxane, compounds 1-8 revealed low to moderate activities for the production of high-density polyethylene (HDPE) to ultra-high-molecular-weight polyethylene (UHMWPE). 6/MAO gave the best activity at 770 kg_PE(molTi) ^-1h^-1.