Influence of a diimine ligand and an activator on the processes taking place in Brookhart-type nickel catalytic systems

Ni(I) Intermediates Formed upon Activation of a Ni(II) α-Diimine Ethylene Polymerization Precatalyst with AlR3 (R = Me, Et, and iBu), AlR2Cl (R = Me, Et), and MMAO: A Comparative Study

“…Brookhart with co-workers disclosed the key role of cationic Ni­(II)-alkyl complexes ([LNi II -R] + , L = N , N -α-diimine ligand, R = alkyl) as the active species of the nickel α-diimine-based catalyst systems of ethylene polymerization. , More recently, the importance of neutral heterobinuclear complexes of monovalent nickel ([LNi I (μ-R) 2 AlMe 2 ], L = N , N -α-diimine ligand, R = Me or Br) as the resting state of α-diimine Ni­(II) polymerization catalysts was recognized. − ,− However, until now, there have been no systematic studies of the effect of various activators on the nature of Ni­(I) species formed upon the activation of the Ni­(II) α-diimine precatalyst and their role in polymerization. Herein, we present the results of our electron paramagnetic resonance (EPR) and 1 H NMR studies of Ni­(I) species formed upon the activation of [LNi II Br 2 ] ( 1 ) (L = 1,2-bis­[(2,6-diisopropylphenyl)­imino]­acenaphthene, Figure ) with various cocatalysts: aluminum trialkyls (AlMe 3 , AlEt 3 , and Al i Bu 3 ), methylalumoxane, modified with Al i Bu 3 (MMAO), and dialkylaluminum chlorides (AlMe 2 Cl and AlEt 2 Cl).…”

Nature of Heterobinuclear Ni(I) Complexes Formed upon the Activation of the α-Diimine Complex LNiIIBr2 with AlMe3 and MMAO

“…Along with designing new catalysts, the nature of Ni species conducting the polymerization remains the subject of extensive research. In addition to the direct observation of cationic divalent nickel­(II)–alkyl complexes ([LNi II -R] + ; L = N , N -α-diimine ligand, R = alkyl)putative active sites of ethylene polymerizationboth in the model (Brookhart) and real (Talsi) catalyst systems, a number of publications emerged discussing the possible roles of monovalent Ni species in ethylene polymerization. − …”

α-Diimine Ni-Catalyzed Ethylene Polymerizations: On the Role of Nickel(I) Intermediates

“…The key role of Ni(II)-alkyl complexes as active sites of ethylene polymerization was disclosed by Brookhart and co-workers almost 20 years ago [21], and has been extensively corroborated in further studies [22][23][24]. However, although Ni(I) species have been found to be ubiquitous in such systems, their nature and role have remained unclear until recently [25][26][27][28][29][30][31][32]. In the present perspective, we survey the existing experimental data, related to the structure of the monovalent nickel species formed in Ni(II) α-diimine-based catalyst systems, and discuss their possible roles in the ethylene polymerization process.…”

“…Despite the generally recognized role of Ni(II)-alkyl complexes as the active sites of ethylene polymerization, the nature and role of Ni(I) complexes in polymerization continues to be a subject of extensive studies [25][26][27][28][29][30][31][32]37,38]. Because of the lower tolerance (compared with Ni(II) counterparts) of Ni(I) α-diimine complexes to trace amounts of moisture and oxygen, the number of examples of their successful isolation and characterization has been limited [31,32,[39][40][41][42][43].…”