EPR Spectroscopy of catalytic systems based on nickel complexes of 1,4-diaza-1,3-butadiene (α-diimine) ligands in hydrogenation and polymerization reactions

Abstract

Articles you may be interested inAdsorption and ring-opening of lactide on the chiral metal surface Pt(321) S studied by density functional theory J. Chem. Phys. 142, 044703 (2015); 10.1063/1.4906151Role of the reaction intermediates in determining PHIP (parahydrogen induced polarization) effect in the hydrogenation of acetylene dicarboxylic acid with the complex [Rh (dppb)]+ (dppb: 1,4bis(diphenylphosphino)butane)EPR spectroscopy is used to study catalytic hydration and polymerization reaction systems based on a-diimine complexes of Ni(0) and Ni(II) with the general formula NiBr 2 (DAD-R) (R ¼ -C 3 H 7 or -CH 3 ) or Ni(DAD-CH 3 ) 2 (DAD(-C 3 H 7 ) ¼ 1,4-bis(2,6-diiso-propylphenyl)-2,3-(dimethyl-1,4diazabuta-1,3-diene, DAD(-CH 3 ) ¼ 1,4-bis(2,6-dimethylphenyl)-2,3-dimethyl-1,4-diazabuta-1,3diene)), in combination with Lewis acids (AlEt 3 , AlEt 2 Cl, AlEtCl 2 , B(F 5 C 6 ) 3 , BF 3 ÁOEt 2 ). Ni(I) complexes of the form (DAD-R)NiX 2 AlX 0 y (C 2 H 5 ) 3-y composition (an aluminum atom can be replaced by a boron atom) were identified, where R ¼ -CH 3 or -C 3 H 7 , X ¼ Br, and X 0 ¼ Cl or -C 2 H 5 and a-diimine anion radicals are included in derivatives of aluminum or boron. Oxidation reactions of the Ni(DAD-CH 3 ) 2 complex with aluminum alkyl halides and boron derivatives with formation of paramagnetic nickel complexes are observed. It is found that there is no direct relationship between the polymerization activity of ethylene or hydration of the alkenes and the concentration of paramagnetic particles. V C 2015 AIP Publishing LLC.

Unified Electrochemical Synthetic Strategy for [2 + 2 + 2] Cyclotrimerizations: Construction of 1,3,5- and 1,2,4-Trisubstituted Benzenes from Ni(I)-Mediated Reduction of Alkynes

“…Interestingly, under the 1,3,5-selective conditions, wherein no external Ni is added to the reaction mixture, both Ni­(I) and Ni­(II) species were observed within 10 min of the reaction, which suggested that Ni­(II) is leached from the Ni anode and reduced at the RVC cathode (Figure B, red line). The EPR signals of Ni­(I) and Ni (II) are consistent with the EPR signal of Ni­(I) in a literature report and with the EPR signal observed experimentally for Ni­(ClO 4 ) 2 ·6H 2 O or Ni (II) (Figure B, blue line), respectively.…”

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].…”