Site-Isolation Effects in a Dendritic Nickel Catalyst for the Oligomerization of Ethylene

Abstract

Dendrimers, specifically suited to construct site-isolated groups due to their well-defined hyperbranched structure, have been used as a ligand design element for the construction of nickel catalysts for ethylene oligomerization. The dendritic P,O ligand indeed suppresses the formation of inactive bis(P,O)Ni complexes in toluene, as is evident from NMR studies, and, as a consequence, outperforms the parent ligand in catalysis in this solvent. The dendritic effect observed in methanol is more subtle because both the dendritic ligand 1 and the parent 2 form bis(P,O)nickel complexes in solution according to NMR spectroscopy. Unlike the parent complex 8, the dendritic bis(P,O)Ni complex 7 derived from dendrimer ligand 1 is able to dissociate to a mono-ligated species under catalytic conditions, that is, 40 bar ethylene and 80 degrees C, which can enter the catalytic cycle. Indeed, dendritic ligand 1 gives much more active nickel catalysts for the oligomerization in methanol than does 2.

Increased Efficacies of an Individual Catalytic Site in Clustered Multivalent Dendritic Catalysts

“…Specifically, the dendrimer peripheries fully substituted with ligand-metal complex have been studied in several occasions previously, ever since the first report of Reetz and co-workers a decade ago. [4a] Various types of dendrimers have been utilized, that include, (i) poly(propylene imine) dendrimers; [4,5,8,14] (ii) poly(amidoamine) dendrimers; [10,20] (iii) poly(aryl ether) dendrimers; [9,12,13] (iv) carbosilane dendrimers; [3,16,17] phosphorus-containing dendrimers [6] and (iv) poly(propyl ether imine) dendrimers. [19] In the later case, concerning the use of poly(propyl ether imine) dendrimers, reported previously by us, the ligand constitution was (bis-diphenylphosphinopropyl)amine ligand attached to the dendrimer backbone.…”

Bimetallic nickel complexes of trimethyl phenyl linked salicylaldimine ligands: Synthesis, structure and their ethylene polymerization behaviors

“…Since Grubbs et al [3] pioneered that the neutral salicylaldiminato nickel complexes could be used as catalysts for ethylene/(functionalized norbornene) co-polymerizations and ethylene homo-polymerizations even in the presence of polar compounds without any cocatalysts, various neutral nickel catalysts have been prepared [3][4][5][6][7][8]. And ethylene polymerizations even in water phase have been successfully achieved with the neutral nickel catalysts to produce polyethylene latex [9].…”

Advances in the Elegance of Chemistry in Designing Dendrimers

“…van Leeuwen and co-workers have successfully constructed two second generation carbosilane-based dendrons which contain bidentate P,O-ligands that form complexes with nickel for important industrial reactions ( Figure 7). [41] Unfunctionalized parent (P,O)Ni compound forms bis(P,O)Ni complexes that causes deactivation of the catalytic complex. In comparison, the presence of the dendritic framework around this complex prevented the formation of the undesirable bis(P,O)Ni complexes in toluene, and thus enhanced the productivity of the parent complex.…”