Nickel salicylaldimine complexes

Polymerizations with nickel salicylaldimine complexes 87-101 were performed in a 1 L steel autoclave at 40 bar and 30 °C. The nickel complexes (0.09 mmol) were activated with equimolar amounts of Ni(COD)2 in toluene solutions for 30 min after which the autoclave was pressurized with ethene. The reaction was terminated after 1.5 h by venting the ethene and the formed polymer powder was isolated. Details are summarized in Tab. 3.9. For comparison, complex 134, a nickel salicylaldimine complex with a 2,6-(diisopropyl)phenyl imine substituent, was screened under the same conditions. 

Effects of Different Metal Salicylaldimine Chelates. Varying the central metal profoundly affected catalytic and inhibitory properties. There were only small quantitative variations, however, between N-phenyl- and V-butylsalicylaldimines having the same central metal atom. The only other salicylaldimines where catalyst-inhibitor conversion could be demonstrated were those of copper (II). With copper (II) both the catalytic and the inhibitory effects are much less pronounced than for cobalt (II). Surprisingly nickel (II) complexes behaved like conventional catalysts for hydrocarbon autoxidation—i.e., the rate is proportional to... 

Five-coordination is now quite common in nickel(II) complexes and many polydentate ligands such as polyamines, salicylaldimines, polyarsines and polyphosphines have been designed with the purpose of favouring this stereochemistry.7,8 However, five-coordinate complexes with monodentate ligands ([Ni(CN)s]3 and [Ni(OAsMe)s]2+) are also known. 

An extensive series of jS-ketoimine complexes of type b with nickel (II) (31) and cobalt(II) (32) have recently been studied. Nickel(II) complexes, where R = H, have been found to be 100% planar up to 80°C. in chloroform solution. Similar nickel (II) complexes, where R = CH3, are <5% tetrahedral at room temperature, whereas the corresponding cobalt(II) complexes are totally tetrahedral (32). Holm (32) proposed that the most important conclusion from these results is that ligands which stabilize a measurable amount of tetrahedral nickel(II) induce 100% tetrahedral cobalt(II), and ligands which stabilize a measurable amount of planar cobalt(II) induce 100% planar nickel(II). In the nickel(II) complexes, when R is sec-alkyl, the complexes are 100% tetrahedral, whereas with n-alkyl groups the planar form dominates. This behavior is similar to the salicylaldimines. In all these complexes there is little doubt that there is much 7T bonding between the metal ion and the ligand system. 

These interconversions are quite rapid and have been studied by laser T-jump" and ultrasonic relaxation. Kinetic studies suggest that several nickel(II)-salicylaldimine complexes favor ligand substitution through the square-planar isomer. 

The mechanism of ethylene oligomerization by SHOP and related catalysts, such as phosphinophenolate complexes, has been the subject of intense investigation (see COMC (1982), Chapter 52, references cited by Heinicke et al. and Pietsch et air It is generally agreed that the actual catalytic species are nickel hydride complexes, generated by ethylene insertion into the Ni-aryl bond of the precursor followed by /3-H elimination reaction (Scheme 50). Styrene or styrene derivatives can be detected in the reaction medium as a product of this activation process. In the case of the salicylaldiminate and anilinotropolone catalysts, styrene elimination is not required,... 

The coordination process may either stabilize or destabilize aromatic Schiff bases. If nickel (II) salts are added to ammoniacal solutions of salicylaldehyde, the precipitate obtained is the inner complex salt of nickel (II) and salicylaldimine (61). If beryllium chloride is added to the Schiff base derived from 2-hydroxy-l-naphthaldehyde and ethylamine, however, the Schiff base is decomposed and the inner complex of beryllium (II) and 2-hydroxy-1-naphthaldehyde is obtained (59). Here the strength of the coordinate bonds formed with the metal seems to determine which complex will be formed. 

Recently, Grubbs and co-workers reported the use of neutral salicylaldimine nickel complexes (e.g., complex III) for ethylene polymerizations.A phosphine scavenger (e.g., Ni(COD)2) is used as an activa-... 

A few copper and nickel complexes based on A-alkyl[5-(4-decyloxybenzoyloxy]salicylaldimine (alkoxybenzoate group meta to the ring position of the imine carbon) were also prepared and their mesomorphism compared to that of their isomers (213). Except for the A-methyl derivatives which exhibited enantiotropic phases over large temperature ranges (M = Cu Cr 188 SmC 243 N 267 I, M = Ni Cr 240 SmC 267 N 281 I), the mesomorphism was in general suppressed. The range of the nematic phase diminished drastically for the A-ethyl derivative (M = Cu Cr 164 N 170 I) the phase was suppressed or monotropic for longer alkylamine chains. 

Heteronuclear complexes based on ferrocene-containing salicylaldimines have also been reported to be mesomorphic (224). The first investigation was carried out on the copper complexes, and for chain lengths equal to 10 and 12, the trinuclear complexes exhibited a narrow-temperature-range nematic phase. This study was later extended to other metal ions ((224) Ni, Pd, V=0, Fe—Cl, =12), and for all of them, except the nickel derivative which decomposed before clearing, a nematic phase was found (Table 73). Important reductions in... 

The neutral salicylaldimine nickel complexes described hy Grubbs and coworkers (195,196) show unprecedented fimctional group tolerance and are capable of incorporating substituted norbornenes, carbon monoxide, and a-co fimctional olefins into polyolefins with well-defined compositional distributions (eq. 7) (196). Furthermore, ethylene can be homopoljnnerized with these catalysts in the presence of various functional additives including acetone, water, ethyl alcohol, and triethyl amine. In the presence of 1500 equivalents of H2O, polyethylene was produced at a rate of 5.4 x 10 g PE/mol Ni/h. 

Supported complexes of palladium and nickel on chitosan are reported in this overview of work by our group. Palladium catalysts are immobilized using a pyridylimine fimctionalized chitosan, and are active in C-C bond-forming reactions. Nickel (II) is immobilized either directly or via a salicylaldimine ligand. Diese materials are active in the Baeyer-Villiger lactonisation. 

Other -substituted salicylaldimines have been used as complexing ligands. All copper, nickel and vanadium complexes studied, 49, show N and/or SmC phases depending on the chain length [109], and characterized by X-ray diffraction studies [110]. 

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