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 mol of C2H4/((mol of Ni) h), in the presence of 400 equiv of MAO and 10 equiv of AlEtCl2, respectively. Selectivities for ethylene dimers were slightly higher when using MAO: 94% (14 in the presence of 100 equiv of MAO) and 90% (14 in the presence of 6 equiv of AlEtCl2). The selectivities for 1-butene within the C4 fraction were much higher when using MAO as cocatalyst, with values up to 68% (15 in the presence of 100 equiv of MAO). The fact that 17, which contains only one tridentate ligand per nickel center, leads to higher activities than 13−16 underlines the importance of the metal center accessibility in the catalytic process.

Reactions of Amines with Zwitterionic Quinoneimines: Synthesis of New Anionic and Zwitterionic Quinonoids

“…In particular, benzoquinonemonoimines have been found to display unique properties in various areas such as color, [34] organic, [35,36] supramolecular, [37] coordination, and organometallic chemistry [37][38][39][40][41][42][43][44] and homogeneous catalysis. [39,43,45] The first member of a new family of 12π-electron quinone-based zwitterions (1, R = tBu) was reported in 2002. [36] Its original preparation involved the reaction of 1,2,4,5-tetraaminobenzene with tBuC(O)Cl in wet acetonitrile, which led to an aromatic diamidodiester derivative, 3340 amine.…”

Nickel Complexes Bearing 2‐(Benzimidazol‐2‐yl)‐1,10‐phenanthrolines: Synthesis, Characterization and Their Catalytic Behavior Toward Ethylene Oligomerization

“…In addition to the P ∧ O chelating nickel complexes used in the SHOP process, [2,6] there are numerous nickel catalysts being investigated with bidentate ligands, such as N ∧ O, [7,8] P ∧ N, [9,10] and N ∧ N, [3,[11][12][13] and tridentate ligands, such as N ∧ N ∧ O, [14] N ∧ P ∧ N, [15] P ∧ N ∧ P, [16] P ∧ N ∧ N, [13d,16] and N ∧ N ∧ N, [17,18] as well as organometallic compounds. [15a] Considering N ∧ N ∧ N tridentate nickel complexes as catalysts for ethylene oligomerization, several models with high activities have been developed in our group by using 2-imino-1,10-phenanthrolines (A), [18b] 2-(2-benzimidazole)-6-iminopyridine (B) ligands, [19] and 6-imino-2-quinoxalinylpyridines.…”

2‐Arylimino‐9‐phenyl‐1,10‐phenanthrolinyl‐iron, ‐cobalt and ‐nickel Complexes: Synthesis, Characterization and Ethylene Oligomerization Behavior

“…[3][4][5] This was stimulated by the pioneering work by Brookhart's group, [6] who discovered that cationic α-diiminonickel complexes are effective catalysts for ethylene oligomerization and polymerization. Since this initial investigation of tetracoordinate nickel complexes, more attention has been paid recently to pentacoordinate complexes of nickel incorporating tridentate ligands such as N ∧ N ∧ O, [7] N ∧ P ∧ N, [8] P ∧ N ∧ N, [9] P ∧ N ∧ P, [9a] and N ∧ N ∧ N, [10][11][12][13][14][15] as well as their iron and cobalt analogues. The discovery of highly active iron-and cobalt-based olefin polymerization catalysts was made possible by the design of bis(imino)pyridines as tridentate ligands by the Brookhart and Gibson groups, [16] who carried out detailed investigations of metal complexes bearing bis(imino)pyridine ligands by modifying the substituents on the aryl ring linked to the imino group and checking their influence on ment with MAO or MMAO, while the cobalt complexes show higher activities than their iron analogues and lead to the formation of C 6 and C 8 oligomers.…”