Isospecific Oligo-/Polymerization of Styrene with Soluble Cationic Nickel Complexes. The Influence of Phosphorus(III) Ligands

Abstract

The influence of several phosphorus(III) ligands upon the activity and the stereoregulation ability of the soluble organometallic complex [Ni(η3-(2-methylallyl))(η4-COD)]PF6 (COD = 1,5-cyclooctadiene), 1, is studied. There is a general increase of the catalytic activity which can be associated with the P(III) ligand's lability. A detailed analysis of the mass distribution and microstructure is carried out by GPC and 1H and 13C NMR of the solvent-fractionated polymers. In the majority of cases, regioregular low molecular weight polymers with the structure PhCHCH2[CH(Ph)CH2] n CH(Ph)CH3 are obtained. The addition of bulky phosphines, such as P(o-Tol)3 (o-Tol = o-tolyl) and PCy3 (Cy = cyclohexyl), affords highly isotactic oligomers (≈90%). For the latter, the regioselectivity of the chain growth is broken during the insertion of the last monomer, which results in the formation of a tail-to-tail end group, CH2C(C6H5)CH(C6H5)CH2−. The superimposed effects of η3-coordination of the chain end and the large stereochemical influence of these ligands seem to be the reason for the observed isospecifity.

Synthesis, Structure, and Polymerization Activity of Cyclopentadienylnickel(II) N‐Heterocyclic Carbene Complexes: Selective Cross‐Metathesis in Metal Coordination Spheres

“…The 13 C NMR spectra indicated that the obtained polymers were isotactic-rich atactic. [22] The MALDI-TOF mass spectra of the polymer produced with complex 2 featured peaks corresponding to the molecular formula [(C 8 H 8 ) n Ag]…”

“…These observations are in agreement with a cationic mechanism for styrene polymerization, [2,23] although a coordination/insertion mechanism involving an Ni-H species cannot be ruled out. [22,24] Selected complexes were also tested in the polymerization of phenylacetylene in the presence of an excess of MAO (Table 2). Moderate activities (TONs up to 600) were obtained under conditions similar to those for styrene.…”

Styrene polymerization catalyzed by nickel complexes bearing hydroxyindanone-iminate ligands

“…13 C NMR spectra of polymers were carried out on a Bruker AC 500 spectrometer instrument at room temperature in CDCl 3 solution using TMS as internal standard. Oligomer analyses were performed by GC/MS on a Hewlett Packard GC6890/MS5973 equipment.…”

“…According to the result reported by Ziegler et al [35] , there is a residual hydroxyindanone-iminate ligand on the active species which may influence catalytic performance by electronic and steric effects (Scheme 1). The analyses on the 13 C NMR spectra of polystyrene end-groups can help further to elucidate the polymerization mechanism (Figure 2) [11][12][13][24][25][26]34] .…”

“…Neutral η 3 -allylnickel complexes alone or activated by electron-poor additives produce nonstereospecific polystyrene [9,10] . Cationic η 3 -allylnickel complexes alone or modified by phosphine and phsophite ligands afford low molecular weight polystyrene without any addition of Lewis acids as cocatalysts [11][12][13][14] . Cationic nickel complexes containing indenyl and phosphine ligands can also catalyze styrene polymerization, and the molecular weight of polymer ranged from low to high with variation on the structure of catalyst [15][16][17] .…”