Late-metal catalysts for ethylene homo- and copolymerization.

B. Anionic Ligands 302 IX. Group 9 Catalysts 302 X. Group 10 Catalysts 303 A. Neutral Ligands 303 1. R-Diimine and Related Ligands 303 2. Other Neutral Nitrogen-Based Ligands 304 3. Chelating Phosphorus-Based Ligands 304 B. Monoanionic Ligands 305 1. [PO] Chelates 305 2. [NO] Chelates 306 3. Other Monoanionic Ligands 306 4. Carbon-Based Ligands 306 XI. Group 11 Catalysts 307 XII. Group 12 Catalysts 307 XIII. Group 13 Catalysts 307 XIV. Summary and Outlook 308 XV. Glossary 308 XVI. References 308

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Advances in non-metallocene olefin polymerization catalysis.

One of the most exciting developments in the areas of catalysis, organometallic chemistry, and polymer science in recent years has been the intense exploration and commercialization of new polymerization technologies based on single-site and metallocene coordination olefin polymerization catalysts.1 The vast number of specifically designed/synthesized transition metal complexes (catalyst precursors) and main-group organometallic compounds (cocatalysts) allows unprecedented control over polymer microstructure, the generation of new polymer architectures, and the development of new polymerization reactions. Commercialization of new generations of single-site and metallocene catalyst-based technologies has provided the multibillion pound per year polyolefins industry with the ability to deliver a wide range of new and innovative olefin-based polymers having improved properties.2-4 The intense industrial activity in the field and the challenges to our basic understanding that have come to light have in turn 1391 Chem. Rev. 2000, 100, 1391−1434

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Cocatalysts for Metal-Catalyzed Olefin Polymerization: Activators, Activation Processes, and Structure−Activity Relationships

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Selectivity in propene polymerization with metallocene catalysts.

Using 1H and 13C NMR spectroscopy, the interaction between Cp2ZrMe2 and MAO in toluene solution was investigated in a wide range of Al/Zr ratios (10–4 000). Several intermediates (I–IV) were detected in the reaction. The structures of these intermediates were elucidated from detailed analysis of 13C-1H NMR data. Intermediate I is a weak complex of Cp2ZrMe2 with MAO. Intermediate II is the complex contact ion-pair [Cp2ZrMe(μ-Me)Cp2ZrMe]+[Me-MAO]– with symmetric binuclear cationic part. Species III a and III b are the heterodinuclear complex [Cp2Zr(μ-Me)2AlMe2]+[Me-MAO]– contact ion-pairs and the similar separated ion-pairs. Species IV are represented by the unsymmetrically Me-bridged complex Cp2(Me)Zr+ Me–-Al ≡ (MAO). Reaction equilibria involving intermediates I–IV were studied with varying Al/Zr ratio, MAO concentration and Al2Me6 content. With increasing Al/Zr ratio, complexes I, II, and free Cp2ZrMe2 gradually disappear and at high Al/Zr ratios at conditions, close to the usual polymerization conditions, only species III and IV were detected. At high Al/Zr ratios the molar ratio IV/III appears to be 1–4 depending on the Al2Me6 content, whereas at low Al/Zr (10–40) it is much greater and III is present only in very small amounts. These observations are rationalized assuming a gradual decrease of the average dissociation tendency of IV as the diverse Lewis acidic sites of MAO become occupied. A possible scheme of Cp2ZrMe2 interaction with MAO is suggested. Data on the interaction between Cp2ZrCl2 and MAO are given for comparison.

Mechanism of dimethylzirconocene activation with methylaluminoxane: NMR monitoring of intermediates at high Al/Zr ratios

The concept of the basic role of the transition metal-carbon bond in the catalytic polymerization of olefins was formulated in the early stages of the study of Ziegler-Natta catalysts (see Ref. 1). In this connection, attempts to use the individual organometallic transition metal compounds as catalysts for olefin polymerization have been made regularly when such compounds were synthesized[2–10]. Polymerization of ethylene in the presence of organometallic compounds containing [sbnd]CH3[2, 3], [sbnd]C6H5[7], [sbnd]CH2C6H5[5, 6], [sbnd]C3H5[4, 10], [sbnd]CH2-C(CH3)3[10], and [sbnd]CH2-Si(CH3)3[10] as organic ligands have been reported. In some cases such compounds were considered to be “models of the active centers.” However, considering the experimental results from this point of view led to a discrepancy with the following observations:

Supported Organometallic Catalysts for Olefin Polymerization

1 H and 2 H NMR spectroscopic monitoring of ferrous species formed via interaction of 2,6-bis[1-2,6-dimethylphenylimino)ethyl]pyridineiron (II) chloride (1) with AlMe 3 , MAO, AlMe 3 /B(C 6 F 5 ) 3 and AlMe 3 /CPh 3 (C 6 F 5 ) 4 is reported. At interaction of 1 with MAO in toluene solution, the new stable heterodinuclear neutral complexes with proposed structures LFe(II)(Cl)(u-Me) 2 AlMe 2 and LFe(II)(Me)(u-Me) 2 AlMe 2 are formed (L is initial tridentate ligand). Complex LFe(II)(Cl)(u-Me) 2 AlMe 2 predominates at low Al/Fe ratios (less than 50), while LFe(II)(Me)(U-Me) 2 AlMe 2 at high Al/Fe ratios (more than 500). Complex assigned to LFe(II)(Me)(u-Me) 2 AlMe 2 can be prepared via interaction of 1 with AlMe 3 . Activation of LFe(II)(Me)(u-Me) 2 AlMe 2 by B(C 6 F 5 ) 3 and CPh 3 B(C 6 F 5 ) 4 gives rise to formation of new complexes with proposed structures [LFe(u-Me) 2 AlMe 2 ] + [MeB(C 6 F 5 ) 3 ] - and [LFe(u-Me) 2 AlMe 2 ] + [B(C 6 F 5 ) 4 ] - . Unexpectedly, the activity at ethylene polymerization was even higher for 1/AlMe 3 than for 1/MAO catalytic system. The co-catalytic activity of MAO towards 1 dramatically decreased with the diminishing of AlMe 3 content in the composition of MAO. Activity of the catalyst 1/AlMe 3 and the molecular structure of polyethylene produced do not change noticeably at the addition of B(C 6 F 5 ) 3 to 1/AlMe 3 . These data allow to suggest, that active species of 1/AlMe 3 and 1/MAO systems are neutral methylated ferrous complexes but not cationic intermediates. Probably, complex LFe(II)(Me) 2 AlMe 2 is the closest precursor of these active species.

Polymerization of Ethylene Catalyzed by Iron Complex Bearing 2,6‐Bis(imine)pyridyl Ligand: 1H and 2H NMR Monitoring of Ferrous Species Formed via Catalyst Activation with AlMe3, MAO, AlMe3/B(C6F5)3 and AlMe3/CPh3(C6F5)4

Vladimir A. Zakharov

Papers

Mechanism of dimethylzirconocene activation with methylaluminoxane: NMR monitoring of intermediates at high Al/Zr ratios

Supported Organometallic Catalysts for Olefin Polymerization

Polymerization of Ethylene Catalyzed by Iron Complex Bearing 2,6‐Bis(imine)pyridyl Ligand: 1H and 2H NMR Monitoring of Ferrous Species Formed via Catalyst Activation with AlMe3, MAO, AlMe3/B(C6F5)3 and AlMe3/CPh3(C6F5)4

Active Intermediates of Ethylene Polymerization over 2,6-Bis(imino)pyridyl Iron Complex Activated with Aluminum Trialkyls and Methylaluminoxane

Formation of zirconium hydrides in supported organozirconium catalysts and their role in ethylene polymerization