Auf der Suche nach einer neuen Generation von Katalysatoren zur Olefinpolymerisation: „Leben” jenseits der Metallocene

Investigations on the Ethylene Polymerization with Bisarylimine Pyridine Iron (BIP) Catalysts

The kinetics and terminations of ethylene polymerization, mediated by five bisarylimine pyridine (BIP) iron dichloride precatalysts, and activated by large amounts of methyl aluminoxane (MAO) was studied. Narrow distributed paraffins from initially formed aluminum polymeryls and broader distributed 1-polyolefins and (bimodal) mixtures, thereof, were obtained after acidic workup. The main pathway of olefin formation is beta-hydrogen transfer to ethylene. The rate of polymerization in the initial phase is inversely proportional to the co-catalyst concentration for all pre-catalysts; a first-order dependence was found on ethylene and catalyst concentrations. The inhibition by aluminum alkyls is released to some extent in a second phase, which arises after the original methyl groups are transformed into n-alkyl entities and the aluminum polymeryls partly precipitate in the toluene medium. The catalysis is interpretable in a mechanism, wherein, the relative rate of chain shuttling, beta-hydrogen transfer and insertion of ethylene are determining the outcome. Beta-hydrogen transfer enables catalyst mobility, which leads to a (degenerate) chain growth of already precipitated aluminum alkyls. Stronger Lewis acidic centers of the single site catalysts, and those with smaller ligands, are more prone to yield 1-olefins and to undergo a faster reversible alkyl exchange between aluminum and iron.

Silica-Grafted Tris(neopentyl)aluminum: A Monomeric Aluminum Solid Co-catalyst for Efficient Nickel-Catalyzed Ethene Dimerization

A silica-supported monomeric alkylaluminum co-catalyst was prepared via surface organometallic chemistry by contacting tris(neopentyl)aluminum and partially dehydroxylated silica. This system, fully characterized by solid-state ²⁷ Al NMR spectroscopy augmented by computational studies, efficiently activates (ⁿ Bu₃ P)₂ NiCl₂ towards dimerization of ethene, demonstrating comparable activity to previously reported dimeric diethylaluminum chloride supported on silica. Three types of aluminum surface species have been identified: monografted tetracoordinated Al species as well as two types of bisgrafted Al species-tetra- and pentacoordinated. Of them, only the monografted Al species is proposed to be able to activate the (ⁿ Bu₃ P)₂ NiCl₂ complex and generate the active cationic species.

Strong Preference of the Redox-Neutral Mechanism over the Redox Mechanism for the TiIV Catalysis Involved in the Carboamination of Alkyne with Alkene and Diazene

Titanium catalysis generally prefers redox-neutral mechanisms. Yet it has been reported that titanium could promote bond formations in a way similar to reductive elimination. Accordingly, redox catalytic cycles involving Ti^IV /Ti^II cycling have been considered. By studying, as an example, the carboamination of alkynes with alkenes and azobenzene catalyzed by the [Ti^IV ]=NPh imido complex, we performed DFT computations to gain an understanding of how the "abnormal" catalysis takes place, thereby allowing us to clarify whether the catalysis really follows Ti^IV /Ti^II redox mechanisms. The reaction first forms an azatitanacyclohexene by alkyne addition to the [Ti^IV ]=NPh bond, followed by alkene insertion. The azatitanacyclohexene can either undergo C^α -C^γ coupling, to afford bicyclo[3.1.0]imine, or β-H elimination, to yield a [Ti^IV ]-H hydride, which then undergoes C^α =C^β or C^γ =C^δ insertion to give an α,β- or β,γ-unsaturated imine, respectively. Both the geometric and electronic structures indicate that the catalytic cycles proceed through redox-neutral mechanisms. The alternative redox mechanisms (e.g., by N-H or C-H reductive elimination) are substantially less favorable. We concluded that electronically, the Ti^IV catalysis intrinsically favors the redox-neutral mechanism, because a redox pathway would involve Ti^II structures either in the triplet ground state or in the high-lying open-shell singlet state, but the involvement of triplet Ti^II structures is spin-forbidden and that of singlet Ti^II structures is energetically disadvantageous.

Two Discrete RuCp* (Cp*=Pentamethylcyclopentadienyl) Binding Modes of N-Confused Porphyrins: Peripheral π Complex and Sitting Atop Ruthenocenophane Complex by Skeletal Transformation

Complexation of a RuCp* cation with N-confused tetraarylporphyrins (NCPs) forms directly bound ruthenium(II) pentamethylcyclopentadienyl (Cp*) π-complex on a specific meso-aryl group (e.g., phenyl) neighboring peripheral imino nitrogen of NCPs in high yields. In contrast, in the case of NCPs bearing bulky meso-substituents (e.g., 3,5-di-tert-butylphenyl), new ruthenocenophane-like complex embedded on an N-confused calix[4]phyrin was formed through multiple C-H bond activation of methyl groups of Cp* ligand. The mechanistic insight into the formation of the ruthenocenophane was derived from DFT calculations.

Mechanistic details of ethylene polymerization reaction using methallyl nickel(ii) catalysts

We present a mechanistic study of the ligand functionalization of bulky boron co-activators on neutral methallyl Ni(ii) catalysts for polyethylene production. This provides a blueprint for the development and design of catalysts with a high degree of tunability in a more efficient way.

Zirconium complexes based on an ethylene linked amidinate–amido ligand: synthesis, characterization and ethylene polymerization

Monomer/dimer zirconium complexes 4–6 were synthesized by changing the molar ratio of ZrCl4 : ligand. The catalytic behaviors of these zirconium complexes were investigated in the presence of MAO as a cocatalys.

Group IV compounds bearing a novel tridentate N-donor ligand: synthesis, structures and ethylene polymerization

In this paper, treatment of [PhN(CH₂)₃NC(Ph)NSiMe₃]₂Li₄·2Et₂O with group IV metal chlorides yields corresponding compounds 3–5. The catalytic behaviors of 3–5 were investigated in the presence of MAO as co-catalyst for ethylene polymerization.

Post-metallocenes in the industrial production of polyolefins

Research on "post-metallocene" polymerization catalysis ranges methodologically from fundamental mechanistic studies of polymerization reactions over catalyst design to material properties of the polyolefins prepared. A common goal of these studies is the creation of practically useful new polyolefin materials or polymerization processes. This Review gives a comprehensive overview of post-metallocene polymerization catalysts that have been put into practice. The decisive properties for this success of a given catalyst structure are delineated.

Tunable fluorophores based on 2-(N-arylimino)pyrrolyl chelates of diphenylboron: synthesis, structure, photophysical characterization, and application in OLEDs

Reactions of 2-(N-arylimino)pyrroles (HNC4H3C(H)=N-Ar) with triphenylboron (BPh3) in boiling toluene afford the respective highly emissive N,N'-boron chelate complexes, [BPh2 {κ(2)N,N'-NC4H3C(H)=N-Ar}] (Ar=C6H5 (12), 2,6-Me2-C6H3 (13), 2,6-iPr2-C6H3 (14), 4-OMe-C6H4 (15), 3,4-Me2-C6 H3 (16), 4-F-C6H4 (17), 4-NO2-C6H4 (18), 4-CN-C6H4 (19), 3,4,5-F3-C6H2 (20), and C6F5 (21)) in moderate to high yields. The photophysical properties of these new boron complexes largely depend on the substituents present on the aryl rings of their N-arylimino moieties. The complexes bearing electron-withdrawing aniline substituents 17-20 show more intense (e.g., ϕf =0.71 for Ar=4-CN-C6H4 (19) in THF), higher-energy (blue) fluorescent emission compared to those bearing electron-donating substituents, for which the emission is redshifted at the expense of lower quantum yields (ϕf=0.13 and 0.14 for Ar=4-OMe-C6H4 (15) and 3,4-Me2-C6H3 (16), respectively, in THF). The presence of substituents bulkier than a hydrogen atom at the 2,6-positions of the aryl groups strongly restricts rotation of this moiety towards coplanarity with the iminopyrrolyl ligand framework, inducing a shift in the emission to the violet region (λmax =410-465 nm) and a significant decrease in quantum yield (ϕf=0.005, 0.023, and 0.20 for Ar=2,6-Me2-C6H3 (13), 2,6-iPr2-C6H3 (14), and C6F5 (21), respectively, in THF), even when electron-withdrawing groups are also present. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have indicated that the excited singlet state has a planar aryliminopyrrolyl ligand, except when prevented by steric hindrance (ortho substituents). Calculated absorption maxima reproduce the experimental values, but the error is higher for the emission wavelengths. Organic light-emitting diodes (OLEDs) have been fabricated with the new boron complexes, with luminances of the order of 3000 cd m(-2) being achieved for a green-emitting device.

Access to Ultra-High-Molecular Weight Poly(ethylene) and Activity Boost in the Presence of Cyclopentene With Group 4 Bis-Amido Complexes

Zr^IV complexes of the type [Me₂ Si{(NR)(6-{2-(diethylboryl)phenyl}pyridyl-2-yl-N)}ZrCl₂ ⋅thf] (R=tBu (4), adamantyl (7 a); thf=tetrahydrofuran), [Me₂ Si{(NAd)(6-{2-(diphenylboryl)phenyl}pyridyl-2-yl-N)}ZrCl₂ ] (Ad=adamantyl (7 b)), the nonbridged half-titanocene complexes of the type [(N-{6-(2-diethylborylphenyl)pyrid-2-yl}-NR)Cp'TiCl₂ ] (R=Me, Cp'=C₅ H₅ (12), Cp'=C₅ Me₅ (13)), and the titanium(IV)-based metallocene-type complex [bis{N-(6-{2-(diethylboryl)phenyl}pyrid-2-yl)NMe}TiCl₂ ] (14) have been synthesized. The structures of complexes 7 b, 12, and 13 were determined by single-crystal X-ray diffraction analysis. In solution, complex 4 slowly rearranges to [Me₂ Si{(N-tBu)(6-{2-(diethylboryl)phenyl}pyridyl-2-yl-N)}₂ Zr] (4 a), the structure of which was unambiguously confirmed by single-crystal X-ray crystallography. Similarly, reaction of HfCl₄ with Me₂ Si({RNLi}{6-[2-(diethylboryl)phenyl]pyridyl-2-ylNLi}) yielded the corresponding Hf^IV complexes [Me₂ Si{(NR)(6-{2-(diethylboryl)phenyl}pyridyl-2-ylN)}₂ Hf] (R=tBu (8) and Ad (9)). Upon activation of these complexes with methylalumoxane (MAO), complexes 4, 7 a, 7 b, and 12-14 showed activities up to 750 kg of polyethylene (PE)/mol_cat.  bar h in the homopolymerization of ethylene (E), producing mainly linear PE (high-density PE, HDPE) with molecular weights in the range of 1 800 000<M_n <4×10⁶  g mol^-1 . In the copolymerization of E with cyclopentene (CPE), the polymerization activities of complexes 4, 7 a, and 7 b can be enhanced by a factor of 140 up to 7500 kg PE/mol_cat.  bar h, which produced PE-co-poly(CPE) containing 3.5 mol % of CPE. This dramatic increase in polymerization activity for E in the presence of CPE can be attributed to an involvement of CPE in the polymerization process rather than to solvent polarity.

Synthesis and structures of (R)-cyclopentadienyl-binaphthoxy titanium(IV) complexes and catalytic properties for olefin polymerization

Two new chiral pre-ligands, (R)-3,3'-bis(tetramethylcyclopentadienyl)-2,2'-bismethoxy-1,1'-bisnaphthalene (1) and (R)-3-tetramethylcyclopentadienyl-2,2'-bismethoxy-1,1'-bisnaphthalene (2), were synthesized by reaction of (R)-3,3'-dilithium-2,2'-bismethoxy-1,1'-bisnaphthalene with 2,3,4,5-tetramethyl-2-cyclopentenone at room temperature. Treatment of the pre-ligands 1 and 2 with butyllithium and Me(3)SiCl first, and subsequently with TiCl(4) (2 and 1 equiv for 1 and 2, respectively) afforded a binuclear complex (R)-3,3'-bis[(tetramethylcyclopentadienyl)trichlorotitanium]-2,2'-bismethoxy-1,1'-bisnaphthalene (3) and a mononuclear complex (R)-3-(tetramethylcyclopentadienyl)trichlorotitanium-2,2'-bismethoxy-1,1'-bisnaphthalene (4) in moderate yields. Complexes 3 and 4 were further converted into constrained geometry complexes (R)-1,1'-bis{2,2'-naphthoxy-3,3'-bis[(tetramethylcyclopentadienyl)dibromotitanium]} (5) and (R)-1-(2-naphthoxy)-1'-(2'-naphthol)-3-(tetramethylcyclopentadienyl)dibromotitanium (6) by treatment with BBr(3). The pre-ligands 1 and 2 were characterized by (1)H and (13)C NMR and high resolution mass spectroscopy (HRMS), and the new titanium complexes 3-6 were characterized by (1)H and (13)C NMR and elemental analyses. Molecular structures of 4, 5, and 6 were determined by single-crystal X-ray diffraction analysis. Complexes 4, 5, and 6 all have a pseudo-octahedral coordination environment and adopt a three-legged piano stool geometry around the titanium atom in their solid state structures. When activated with Al(i)Bu(3) and Ph(3)CB(C(6)F(5))(4), the chiral complexes 5 and 6 show moderate catalytic activities for propylene, 1-hexene, and 5-ethylidene-2-norbornene (ENB) polymerization and ethylene/1-hexene copolymerization. The polymers produced by the chiral 5/(i)Bu(3)Al/Ph(3)CB(C(6)F(5))(4) catalyst system from the 1-hexene, and ENB polymerization and ethylene/1-hexene copolymerization with high comonomer contents exhibit optical activity.

Group 4 dimethylsilylenebisamido complexes bearing the 6-[2-(diethylboryl)phenyl]pyrid-2-yl motif: synthesis and use in tandem ring-opening metathesis/vinyl-insertion copolymerization of cyclic olefins with ethylene

Two novel Zr(IV)- and Hf(IV)-based bisamido complexes bearing the 6-[2-(diethylboryl)phenyl]pyrid-2-yl motif, that is, [ZrCl(2){Me(2)Si(DbppN)(2)}(thf)] (9) and [HfCl(2){Me(2)Si(DbppN)(2)}(thf)(2)] (10) (DbppN=6-[2-(diethylboryl)phenyl]pyridine-2-amido) have been prepared. Their reactivities have been compared with that of a model precatalyst that does not bear the aminoborane motif. Upon activation with methylalumoxane, precatalysts 9 and 10 are active in the homopolymerization of ethylene (E) yielding high-density polyethylene (HDPE). In the copolymerization of E with cyclopentene (CPE), for example by the action of 9, the presence of CPE resulted in a dramatic increase in the polymerization activity of E, while CPE incorporation remained close to or at zero. In the vinyl-insertion copolymerization of norborn-2-ene (NBE) with E by the action of 9, statistical cyclic olefin copolymers of these two monomers were obtained. At higher NBE concentrations, however, 9 gave rise to reversible ring-opening metathesis (ROMP)/vinyl-insertion polymerization (VIP) of NBE with E, resulting in the formation of multi-block copolymers of the general formula poly(NBE)(ROMP)-co-poly(NBE)(VIP)-co-poly(E). This particular feature of precatalyst 9, that is, the ability to induce a reversible α-H elimination/α-H addition reaction, is attributed to the unique role of the 6-[2-(diethylboryl)phenyl]pyrid-2-yl ligand. Accordingly, a model precatalyst lacking this ligand does not have the ability to induce α-H elimination/α-H addition reactions. The different (11)B NMR shifts of various diethylborylphenylpyrid-2-ylamines and -amides permit a ranking of the strengths of the B-N bonds in these compounds. This strength of the B-N bond is correlated with the propensity of 9/MAO to produce poly(NBE)(ROMP)-co-poly(NBE)(VIP)-co-poly(E) at different temperatures.

Synthesis of [3]ferrocenophane-bridged Cp-amido zirconium complexes and ansa-zirconocene complexes and their use in catalytic polymerisation reactions

Starting from 1,1'-diacetylferrocene the ortho-amino,α-dimethylamino[3]ferrocenophane system 3 was prepared. This was converted to the o-imino,α-Cp-derivative 6. Subsequent treatment with e.g. an excess of methyllithium followed by ZrCl(2)(NMe(2))(2)(thf)(2) and Me(2)SiCl(2) eventually gave the [3]ferrocenophane based Cp-amido zirconium complex 11b. In a similar way the [3]ferrocenophane derived fluorenyl-Cp ansa-zirconocene dichloride complex 20 was obtained. The 20-methylalumoxane (MAO) system is an active homogeneous Ziegler-Natta catalyst for ethylene polymerization. The 11b-MAO system reacts efficiently with an ethene-1-octene mixture to yield a mixture of linear polyethylene plus the ethene-1-octene copolymer. The compounds 5, 8, 10b, 11b, 13, 14, and 20 were characterized by X-ray diffraction.