Nickel Complexes with Functional Zwitterionic N,O-Benzoquinonemonoimine-Type Ligands: Syntheses, Structures, and Catalytic Oligomerization of Ethylene

Abstract

The zwitterionic N,N‘-dialkyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium derivatives [C6H2(NHCH2CH2X)2(O)2] (X = NMe2, 9; X = NHEt, 10; X = OMe, 11), previously prepared from 4,6-diaminoresorcinol by a transamination reaction, and 12 (X = N(CH2CH2)2O) behave as tridentate ligands when reacted with [Ni(acac)2] to form the corresponding octahedral Ni(II) 2:1 complexes (13−16), respectively. In contrast, ligand 9 reacted | with NiCl2·6H2O in a tandemlike manner to afford the stabilized Ni(II) zwitterionic organometalate 1:1 complex (17). The bonding parameters | of complexes 13·H2O·CH2Cl2 and 17, determined by X-ray diffraction, and the conformation of the ligands around the nickel center as well as the supramolecular arrangements are discussed and compared with those of their previously reported Zn(II) analogues. Complexes 13−17 were tested in catalytic ethylene oligomerization with MAO and AlEtCl2 as cocatalysts. Complex 17 yielded the highest turnover frequencies, with values up to 20 300 and 48 200...