Cooperativity in Highly Active Ethylene Dimerization by Dinuclear Nickel Complexes Bearing a Bifunctional PN Ligand

Abstract

In order to examine the possibility to promote cooperative effects on catalytic activity and selectivity in ethylene dimerization through ligand design, the bisphosphino-iminato ligands syn- L and anti- L were prepared to support the dinuclear nickel complexes syn -Ni 2 and anti- Ni 2 . The Ni centers are successfully locked in relatively close proximity in syn- Ni 2 (6.433(5) Å) but are much farther apart in anti- Ni 2 because of the rigid anthracene skeleton. The mononuclear complex [NiBr2(C14H9-NCH-C6H4-2-PPh2)] (Ni 1 ) was also prepared for control experiments. In the presence of EtAlCl2, syn -Ni 2 showed a remarkably high activity for ethylene dimerization (>90%) (up to 9.10 × 106 g (mol of Ni)−1 h–1), which is approximately 1.5- and 3.3-fold higher, respectively, than those of anti- Ni 2 or of mononuclear Ni 1 . The redox properties of dinuclear complexes were studied by cyclic voltammetry (CV) and their comparison with those of the mononuclear complex indicates the possible existence of cooperativity between the two metal centers in the dinuclear structures. Although a detailed mechanism has not been elucidated, cooperative effects favor the isomerization of 1-butene, and dinuclear syn- Ni 2 and anti- Ni 2 exhibited higher selectivity for 2-butene in comparison to mononuclear Ni 1 under otherwise identical reaction conditions.

Chromium complexes supported by NNO-tridentate ligands: an unprecedented activity with the requirement of a small amount of MAO

“…The conden-sation reaction was catalyzed by p-TsOH in methanol at room temperature to give the desired NNO-tridentate ligands LH1-LH6 in high yields (77-95%). 58,59 All the organic ligands were characterized by 1 H and 13 C NMR (Fig. S1-S12 †), and elemental analysis.…”

Synthesis of L2Ni(ORF)2 (RF = C(CF3)3) Complexes and Their Reactivity in Ethylene Oligomerization

“…Up to now, the limited selectivity observed with nickel-based catalysts is mainly rationalized through a Cossee–Arlman mechanism with the active species featuring a Ni–H or Ni–C bond. , Nonetheless, only few nickel catalysts have been reported to be highly selective in ethylene dimerization to butenes/1-butene. − In these cases, the precise mechanism has not been studied, yet, in general, catalysts that follow a metallacyclic mechanism are known to be much more selective toward a unique 1-alkene. − Moreover, it has been shown that nickel was able, with activated alkenes such as tetrafluoroethylene (TFE), norbornadiene, or dimethylcyclopropene, to achieve an oxidative coupling to reach metallacyclic complexes (Scheme , top). − In addition, Grubbs showed that butenes can be obtained from a mixture of (Cy 3 P) 2 NiCl 2 and 1,4-dilithiobutane, through the proposed decomposition of the nickellacyclopentane . Binger reported one year after that an isolated nickellacycle yielded 1-butene upon heating at 165 °C (Scheme , bottom) …”

Optical Study of Solvatochromic Isocyanoaminoanthracene Dyes and 1,5-Diaminoanthracene

“…Among them, hydrogen bonding represents an appropriate tool [10][11][12], as it is evidenced by biological systems in which the combination of π-stacking and hydrogen bonds determines the macrostructure of proteins or nucleic acids, just to mention well-known examples. One of the most important members of diamino PAHs is 1,5-diaminoanthracene, which is used to construct organic semiconductors [13], dinuclear nickel complexes for highly active ethylene dimerization [14], self-assembled small-molecule-based hole-transporting material for inverted perovskite solar cells [15], photoactivated healable vitrimeric copolymers [16], amorphous porous organic polymers for highly efficient iodine capture [17], bimetallic aluminum complexes for ring-opening polymerization of lactide [18], Luminescent Supramolecular Lanthanide Complexes [19], Squaraine dyes [20] and others. Despite its widespread application, the literature on the optical properties of 1,5-diaminoanthracene is very limited.…”