The “Nickel Effect”

Abstract

Whereas the reaction of ethylene and triethylaluminum under pressure at 100°C yields trialkylaluminum compounds having long alkyl chains, the presence of small amounts of nickel salts induces the formation of butene. The discovery of this "nickel effect" represents the starting point for the development of the Ziegler catalysts. Comparatively little was formerly known about the nature and the mode of action of the catalytically active nickel species. A basis for the elucidation of the effect was provided by studies on the reduction of nickel compounds by organoaluminum compounds, on the occurrence and existence of nickel hydrides, and on interactions between nickel(0) and Lewis acids as well as organic compounds of main group metals. The most significant result of these studies is the recognition that multicenter bonding systems involving trialkylaluminum compounds and nickel atoms are involved. These react further with complex bonded ethylene in what is probably a concerted manner.

Neutral and Cationic Methylaluminium Complexes of 2‐Anilinotropone Ligands: Synthesis, Characterization, and Reactivity toward Ethylene

“…[7] In addition, alkylaluminium complexes have long been known to catalyse olefin oligomerizations, [8] and are the preferred cocatalysts in various important industrial processes catalysed by transition metals, such as the ZieglerϪNatta olefin polymerisation, [9] the Wilke alkene dimerization [10] and the Ziegler nickel effect. [11] The disclosure by Coles and Jordan in 1997 that certain cationic methylaluminium amidinate compounds promote ethylene polymerisation, although with low activity, [12] has encouraged a growing interest in exploring the reactivity of various aluminium compounds. Dialkylaluminium compounds bearing monoanionic chelating ligands, such as the N,N bidentate aminotroponiminate, [13] the tridentate N,N,N pyridylaminoamide [14] or the tridentate O,N,N and O,N,O pendant arm Schiff-base ligands [15] showed, after activation with the ionising agents traditionally used in homogeneous ZieglerϪNatta catalysis {i.e.…”

Nanoscopic Pt Colloids in the “Embryonic State”

“…Alternatively, the single metal atoms may be stabilized by complexation with ligands such as olefins and phosphanes, a process that is the basis of a rich organotransition metal chemistry. [2] On repeating an old experiment for the formation of Ni colloids, published by Karl Ziegler in the context of the famous ™nickel effect∫ [3,4] as early as 1954, we recently developed a novel, straightforward, general pathway to mono-and bimetallic nanoparticulates by the ™reductive stabilization∫ of colloidal transition metals using trialkylaluminum compounds, which act both as reducing agents and as colloid stabilizers. [5] We now report that in the case of Pt we have been able to establish the mechanism of the colloid formation by a combination of NMR, ASAXS (anomalous small-angle X-ray scattering), XAS (X-ray absorption spectroscopy), DFT (density functional theory) computations, and electron microscopy.…”

Metal‐Catalyzed Hydroalumination Reactions

“…In spite of the modest asymmetric induction it was concluded that at least one of the chiral ligands is coordinated to the nickel in the catalytically active species. An alternative interpretation was given by Wilke and coworkers [29]. They could show that (methylsalicylidene)dimethylaluminum forms a stable adduct with nickel(0) complexes.…”

“…Eisch and Foxton suggested that nickel hydride species like R-Ni-H or R 2 Al-Ni-H play a key role in the catalytic reaction [26]. Based on extensive investigations into the chemistry of well-defined nickel(0) complexes, Wilke and coworkers suggested that the catalytically active species contains nickel in an oxidation state of 0 [29,30]. Furthermore, they could show that nickel(II) salts are rapidly reduced to elemental nickel or nickel(0) complexes by aluminum alkyls, thereby disproving the mechanistic proposal by Pino.…”

“…Nickel catalysts promote the hydroalumination of alkenes using trialkylalanes R 3 Al and dialkylalanes such as i Bu 2 AlH as the aluminum hydride sources [9,29,30,33]. However, exhaustive studies of the range of substrates capable of hydroalumination with these reagents has not been carried out.…”