Control of the Molecular Weight of Polyethene in Syntheses with Bis(ylide)nickel Catalysts

Abstract

We recently reported on highly active Ni-catalyst systems for ethene polymerization. These were generated from bis(cyclooctadiene)nickel(o), Ni(cod),, a carbonylstabilized and a non-stabilized ylide, Ph3PCRiC(0)R2 and R2PCR4RS, respectively.[" In the catalytically active, square-planar nickel complex, the non-stabilized ylide is structuraAy intact C-coordinated, whereas the stabilized ylide is PO-coordinated due to rearrangement. The activity of the catalyst can be optimized by variation of the intact ylide ligand; but modification of the substituent R2 in the carbonyl-stabilized ylide ligand also increases the catalytic activity in the Ni(cod),/Ph3PCHC(O)R2/Me,PCH, system : On going from the formylmethylene(tripheny1)phosphorane l a via the acetyl derivative l b to the benzoylmethylene(tripheny1)phosphorane l c (R2 = H, Me, Ph) the turnover number increases to ca. 0.5 x lo5 moles ethene per mole of nickel.['I Characterization of the polymers showed that the average chain length of the ethene polymerizates also increases with increasing catalyst activity. The intrinsic viscosities in tetralin at 140°C do not, however, exceed 0.2 dL/g, which corresponds to molecular weights M of about 5 x lo3 g/ mole.[*I We have therefore tried to noticeably increase the range of molecular weights accessible with this Ni-catalyst system by further variation of the carbonyl-stabilized ylide ligand.With the three ligands 2a-2c, we have indeed been able to obtain novel, very active bis(y1ide)nickel polymerization catalysts, which afford access to polyethene (PE) in practically all molecular weight ranges from PE waxes and hard waxes through high molecular weight high-density polyethene (HDPE) to ultrahigh molecular weight polyethene (UHMW-PE) with M > lo6 g/mole (Table I). 2a 2 b 2c

Catalytic polymerization of ethylene in toluene using a Pd-organometallic catalyst

“…Ostoja-Starzewski [24,25] and Klabunde et al [26] modifying the ligand structure of the neutral Ni(II)-P,O based catalysts were able to obtain very high molecular weights (M w = 10 6 g/mol) and high productivities in hexane (TOF = 30,446 × 10 −5 h −1 Pa −1 ); where TOF is the turnover frequency defined as TOF = mols ethylene-reacted mols CATused · time(h) · pressure(Pa) (1) In addition, the catalysts were active in polar organic media (acetone, DMF and alcohols) [25]. Johnson et al [27] developed a class of catalyst based on cationic metal (Ni, Pd) complexes of neutral multidentate ligands with nitrogen donor atoms substitutes with bulky groups.…”

Copolymerization of ethene with norbornene using palladium(II) α-diimine catalysts: Influence of feed composition, polymerization temperature, and ligand structure on copolymer properties and microstructure

“…In this process, square planar Ni complexes with anionic P o O chelate ligands were applied. Although these catalysts were later tuned to give high molar mass products [14][15][16][17], a breakthrough was achieved with the discovery by Brookhart et al [18][19][20] that cationic Ni and Pd complexes with bulky aryl-substituted a-diimine ligands are very efficient catalysts for the polymerization of ethene and a-olefins. 1 These catalysts are less sensitive to polar impurities and functional groups [26][27][28] and even allow the suspension polymerization of ethene in aqueous media [29][30][31][32][33].…”

Alkyl(amino)- and Alkyl(chloro)phosphanyl-Substituted Cyclopentadienyl Complexes of Titanium and Zirconium

“…The reaction affords oligomeric products which are difficult to analyse, (1)ϪC (11) 103.3(2), C(01)ϪP (1)ϪC (11) 108.0(2), C (19)ϪC (11)ϪP(1) 112.7(3), C(13)ϪC(12)ϪC(11) 110.9 (5) probably stemming from the very reactive phosphafulvenes generated in situ by β-''HCl'' elimination. [42] Thus, the elimination of HCl takes place faster than a nucleophilic substitution reaction (Scheme 4).…”