The reaction of TlTp′ (Tp′ ) HB(3-mesitylpyrazolyl) 3 -(Tp Ms ), HB(3-mesitylpyrazolyl) 2 (5mesitylpyrazolyl) -(Tp Ms* )) with NiCl 2 ‚6H 2 O affords Tp Ms NiCl (1) and Tp Ms* NiCl (2) in good yield. The compound 2 undergoes an isomerization process to form [{Tp Ms** }NiCl] 2 (3) (Tp Ms** ) HB(5-mesitylpyrazolyl) 2 (3-mesitylpyrazolyl) -) in 68% yield. Treatment of the tris(pyrazolyl)borate nickel compounds 1 and 2 with alkylaluminum cocatalysts such as methylalumoxane (MAO) and trimethylaluminum (TMA) in toluene generates active catalysts for ethylene oligomerization. The compound 1 shows turnover frequencies in the range of (2.2-43.1) × 10 3 h -1 . Oligomerization reaction conditions can be adjusted that lead to selectivities as high as 81% for butene-1.

The polymerization of ethylene in the presence of 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediiminenickel(II) dichloride (1) and methylaluminoxane (MAO) gives hyperbranched polyethylene (HBPE) in appropriate reaction conditions. The system 1/MAO is active in solvents like toluene or hexane at temperatures as high as 80 °C and ethylene pressures ranging from 1 to 15 atm. The polyethylenes obtained show high molecular weights (up to 467 kg · mol−1) and more than 218 branches per 1 000 backbone carbon atoms, qualifying these materials as hyperbranched. Dynamic‐mechanical thermal analysis (DMTA) of these materials shows high β‐transitions, directly related to the branch content of these polyethylenes. DMTA analysis of polyethylenes obtained with 1/MAO at 0, 30, and 50 °C (corresponding to entries 1, 2 and 3).magnified imageDMTA analysis of polyethylenes obtained with 1/MAO at 0, 30, and 50 °C (corresponding to entries 1, 2 and 3).

No abstract