Synthesis, molecular structure and catalytic activity of chiral benzamidinate nickel complexes

Two new nickel complexes containing the chiral benzamidinate ligation: [PhC(N-SiMe3)(N′-myrtanyl)]2Ni(py)2(3) and {[PhC(NH)(N′-myrtanyl)]2Ni}2 (6) have been synthesized and characterized. The solid-state molecular structures of these complexes have been determined by low-temperature X-ray diffraction analysis. Complex 3 was obtained via two different procedures. In complex 3, the metal adopts a nearly ideal octahedral environment, whereas in complex 6 the two divalent nickel metals are coordinated in a square-planar geometry, forming a dimer. Complex 3 activated with MAO has been found to oligomerize propylene producing a mixture of dimers, trimers and tetramers with a turnover frequency of 5200 h−1, whereas complex 6 being activated with MAO oligomerizes ethylene to a mixture of dimers and trimers with a high turnover frequency of 15,400 h−1. In addition, when activated with MAO both complexes showed a good activity for the vinyl-type polymerization of norbornene.

The chiral myrtanyl β-diketiminate lithium salt [{(SiMe3)NC(Ph)N(myrtanyl)] [Li-TMEDA] reacts with Ni(acac)2(TMEDA) in toluene forming the dimeric complex [{(SiMe3)NC(Ph)N(myrtanyl)]2Ni, which upon the solvatation with pyridine produces the octahedral complex 3. When the same reaction is carried out in a mixture of pyridine-toluene, complex 6 is obtained in which all the TMS groups have been cleaved. Both complexes activated by MAO (MAO = methylalumoxane) have been studied for the oligomerization of α-olefins towards the production of dimers and trimers, with high turnover frequencies.Figure optionsDownload as PowerPoint slide