Highly active copolymerization of ethylene with 10‐undecen‐1‐ol using phenoxy‐based zirconium/methylaluminoxane catalysts

Activated with methylaluminoxane (MAO), phenoxy‐based zirconium complexes bis[(3‐^tBu‐C₆H₃‐2‐O)‐CH?NC₆H₅]ZrCl₂, bis[(3,5‐di‐^tBu‐C₆H₂‐2‐O)‐PhC?NC₆H₅] ZrCl₂, and bis[(3,5‐di‐^tBu‐C₆H₂‐2‐O)‐PhC?N(2‐F‐C₆H₄)]ZrCl₂ for the first time have been used for the copolymerization of ethylene with 10‐undecen‐1‐ol. In comparison with the conventional metallocene, the phenoxy‐based zirconium complexes exhibit much higher catalytic activities [>10⁷ g of polymer (mol of catalyst)^?1 h^?1]. The incorporation of 10‐undecen‐1‐ol into the copolymers and the properties of the copolymers are strongly affected by the catalyst structure. Among the three catalysts, complex c is the most favorable for preparing higher molecular weight functionalized polyethylene containing a higher content of hydroxyl groups. Studies on the polymerization conditions indicate that the incorporated commoner content in the copolymers mainly depends on the comonomer concentration in the feed. The catalytic activity is slightly affected by the Al_(MAO)/Zr molar ratio but decreases greatly with an increase in the polymerization temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5944–5952, 2005     

Living regioselective copolymerization of ethylene with nonconjugated bicyclic dienes using (salicylaldiminato)(β‐enaminoketonato) titanium catalysts

A series of heteroligated (salicylaldiminato)(β‐enaminoketonato)titanium complexes [3‐^tBu‐2‐OC₆H₃CH?N(C₆F₅)] [PhN?C(CF₃)CHCRO]TiCl₂ [ 3a : R = Ph, 3b : R = C₆H₄Cl(p), 3c : R = C₆H₄OMe(p), 3d : R = C₆H₄Me(p), 3e : R = C₆H₄Me(o)] were synthesized and characterized. Molecular structures of 3b and 3c were further confirmed by X‐ray crystallographic analyses. In the presence of modified methylaluminoxane as a cocatalyst, these unsymmetric catalysts displayed favorable ability to incorporate 5‐vinyl‐2‐norbornene (VNB) and 5‐ethylidene‐2‐norbornene (ENB) into the polymer chains, affording high‐molecular weight copolymers with high‐comonomer incorporations and alternating sequence under the mild conditions. The comonomer concentration in the polymerization medium had a profound influence on the molecular weight distribution of the resultant copolymer. At initial comonomer concentration of higher than 0.4 mol/L, the titanium complexes with electron‐donating groups in the β‐enaminoketonato moiety mediated room‐temperature living ethylene/VNB or ENB copolymerizations. Polymerization results coupled with density functional theory calculations suggested that the highly controlled living copolymerization is probably a consequence of the difficulty in chain transfer of VNB (or ENB)‐last‐inserted species and some characteristics of living ethylene polymerization under limited conditions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Insight into Oxide‐Bridged Heterobimetallic Al/Zr Olefin Polymerization Catalysts

Reaction of (TBBP)AlMe ? THF with [Cp*₂Zr(Me)OH] gave [(TBBP)Al(THF)?O?Zr(Me)Cp*₂] (TBBP=3,3’,5,5’‐tetra‐tBu‐2,2'‐biphenolato). Reaction of [DIPPnacnacAl(Me)?O?Zr(Me)Cp₂] with [PhMe₂NH]⁺[B(C₆F₅)₄]^? gave a cationic Al/Zr complex that could be structurally characterized as its THF adduct [(DIPPnacnac)Al(Me)?O?Zr(THF)Cp₂]⁺[B(C₆F₅)₄]^? (DIPPnacnac=HC[(Me)C=N(2,6‐iPr₂?C₆H₃)]₂). The first complex polymerizes ethene in the presence of an alkylaluminum scavenger but in the absence of methylalumoxane (MAO). The adduct cation is inactive under these conditions. Theoretical calculations show very high energy barriers (ΔG=40–47 kcal mol^?1) for ethene insertion with a bridged AlOZr catalyst. This is due to an unfavorable six‐membered‐ring transition state, in which the methyl group bridges the metal and ethene with an obtuse metal‐Me‐C angle that prevents synchronized bond‐breaking and making. A more‐likely pathway is dissociation of the Al‐O‐Zr complex into an aluminate and the active polymerization catalyst [Cp*₂ZrMe]⁺.     

Phosphine (oxide)‐(thio) phenolate palladium complexes: Synthesis,characterization and (co)polymerization of norbornene

A series of palladium complexes ( 2a–2g ) ( 2a : [6‐^tBu‐2‐PPh₂‐C₆H₃O]PdMe(Py); 2b : [6‐C₆F₅–2‐PPh₂‐C₆H₃O]PdMe(Py); 2c : [6‐^tBu‐2‐PPh^tBu‐C₆H₃O]PdMe(Py); 2d : [2‐PPh^tBu‐C₆H₄O] PdMe(Py); 2e : [6‐SiMe₃–2‐PPh₂‐C₆H₃O]PdMe(Py); 2f : [2‐^tBu‐6‐(Ph₂P=O)‐C₆H₃O]PdMe(Py); 2g : [6‐SiMe₃–2‐(Ph₂P=O)‐C₆H₃S]PdMe(Py)) bearing phosphine (oxide)‐(thio) phenolate ligand have been efficiently synthesized and characterized. The solid‐state structures of complexes 2d , 2f and 2g have been further confirmed by single‐crystal X‐ray diffraction, which revealed a square‐planar geometry of palladium center. In the presence of B(C₆F₅)₃, these complexes can be used as catalysts to polymerize norbornene (NB) with relatively high yields, producing vinyl‐addition polymers. Interestingly, 2a /B(C₆F₅)₃ system catalyzed the polymerization of NB in living polymerization manner at high temperature (polydispersity index 1.07, M_n up to 1.5 × 10⁴). The co‐polymerization of NB and polar monomers was also studied using catalysts 2a and 2f . All the obtained co‐polymers could dissolve in common solvent.     

Synthesis and polymerization behavior of novel C 1 and C s titanium ansa‐cyclopentadienyl‐amido catalysts for ethylene and propylene polymerization

Four titanium ansa‐cyclopentadienyl‐amido complexes of the general formula [C₅H₃RMe₂SiN(2,6‐Me₂C₆H₃)]TiX₂(R = H,Me,Bz,^tBu;X = NMe₂ or Cl) have been synthesized. The complexes polymerize both ethylene and propylene in the presence of methylaluminoxane or Ph₃CB(C₆F₅)₄–triisobutylaluminum and were most active at lower temperatures. In general, the smaller the substituent on the cyclopentadienyl group, the more active the catalyst. The catalysts were found to be poorly stereoselective for the polymerization of polypropylene, with the tertiary‐butyl substituted catalyst giving a polymer with the greatest [mmmm] (14.2%). The structure of [C₅H₄Me₂SiN(2,6‐Me₂C₆H₃)] Ti(NMe₂)₂ was determined by X‐ray diffraction. The complex crystallizes in the monoclinic system space group P2₁/n, with a = 16.437(2), b = 8.652(3), c = 16.494(4),β = 117.54(2) and Z = 4. Copyright © 2002 John Wiley & Sons, Ltd.     

Efficient ethylene/norbornene copolymerization by half‐titanocenes containing imidazolin‐2‐iminato ligands and MAO catalyst systems

Ethylene copolymerizations with norbornene (NBE) using half‐titanocenes containing imidazolin‐2‐iminato ligands, Cp′TiCl₂[1,3‐R₂(CHN)₂C?N] [Cp′ = Cp ( 1 ), ^tBuC₅H₄ ( 2 ); R = ^tBu ( a ), 2,6‐ⁱPr₂C₆H₃ ( b )], have been explored in the presence of methylaluminoxane (MAO) cocatalyst. Complex 1a exhibited remarkable catalytic activity with better NBE incorporation, affording high‐molecular‐weight copolymers with uniform molecular weight distributions, whereas the tert‐BuC₅H₄ analog ( 2a ) showed low activity, and the resultant polymer prepared by the Cp‐2,6‐diisopropylphenyl analog ( 1b ) possessed broad molecular weight distribution. The microstructure analysis of the poly(ethylene‐co‐NBE)s prepared by 1a suggests the formation of random copolymers including two and three NBE repeating units. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2575–2580     

Synthesis of novel zirconium complexes bearing mono‐Cp and tridentate Schiff base [ONO] ligands and their catalytic activities for olefin polymerization

A series of novel zirconium complexes {R²Cp[2‐R¹‐6‐(2‐CH₃OC₆H₄N?CH)C₆H₃O]ZrCl₂ ( 1 , R¹ = H, R² = H, 2 : R¹ = CH₃, R² = H; 3 , R¹ = ^tBu, R² = H; 4 , R¹ = H, R² = CH₃; 5 , R¹ = H, R² = n‐Bu)} bearing mono‐Cp and tridentate Schiff base [ONO] ligands are prepared by the reaction of corresponding lithium salt of Schiff base ligands with R²CpZrCl₃·DME. All complexes were well characterized by ¹H NMR, MS, IR and elemental analysis. The molecular structure of complex 1 was further confirmed by X‐ray diffraction study, where the bond angle of Cl? Zr? Cl is extremely wide [151.71(3)°]. A nine‐membered zirconoxacycle complex Cp(O? 2? C₆H₄N?CHC₆H₄‐2? O)ZrCl₂ ( 6 ) can be obtained by an intramolecular elimination of CH₃Cl from complex 1 or by the reaction of CpZrCl₃·DME with dilithium salt of ligand. When activated by excess methylaluminoxane (MAO), complexes 1–6 exhibit high catalytic activities for ethylene polymerization. The influence of polymerization temperature on the activities of ethylene polymerization is investigated, and these complexes show high thermal stability. Complex 6 is also active for the copolymerization of ethylene and 1‐hexene with low 1‐hexene incorporation ability (1.10%). Copyright © 2006 John Wiley & Sons, Ltd.     

Cation‐Mediated Conversion of the State of Charge in Uranium Arene Inverted‐Sandwich Complexes

Two new arene inverted‐sandwich complexes of uranium supported by siloxide ancillary ligands [K{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 3 ) and [K₂{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 4 ) were synthesized by the reduction of the parent arene‐bridged complex [{U(OSi(OtBu)₃)₃}₂(μ‐η⁶:η⁶‐C₇H₈)] ( 2 ) with stoichiometric amounts of KC₈ yielding a rare family of inverted‐sandwich complexes in three states of charge. The structural data and computational studies of the electronic structure are in agreement with the presence of high‐valent uranium centers bridged by a reduced tetra‐anionic toluene with the best formulation being U^V–(arene^4?)–U^V, KU^IV–(arene^4?)–U^V, and K₂U^IV–(arene^4?)–U^IV for complexes 2 , 3 , and 4 respectively. The potassium cations in complexes 3 and 4 are coordinated to the siloxide ligands both in the solid state and in solution. The addition of KOTf (OTf=triflate) to the neutral compound 2 promotes its disproportionation to yield complexes 3 and 4 (depending on the stoichiometry) and the U^IV mononuclear complex [U(OSi(OtBu)₃)₃(OTf)(thf)₂] ( 5 ). This unprecedented reactivity demonstrates the key role of potassium for the stability of these complexes.     

Quasi‐living copolymerization of ethylene with 1‐hexene by heteroligated (salicylaldiminato β‐enaminoketonato) titanium complexes

A series of heteroligated (salicylaldiminato)(β‐enaminoketonato)titanium complexes [3‐Bu^t‐2‐OC₆H₃CH = N(C₆F₅)] [PhN = C(R₁)CHC(R₂)O]TiCl₂ [ 3a : R₁ = CF₃, R₂ = ^tBu; 3b : R₁ = Me, R₂ = CF₃; 3c : R₁ = CF₃, R₂ = Ph; 3d : R₁ = CF₃, R₂ = C₆H₄Ph(p ); 3e : R₁ = CF₃, R₂ = C₆H₄Ph(o ); 3f : R = CF₃, R₂ = C₆H₄Cl(p ); 3g : R₁ = CF₃; R₂ = C₆H₃Cl₂(2,5); 3h : R₁ = CF₃, R₂ = C₆H₄Me(p )] were investigated as catalysts for ethylene (co)polymerization. In the presence of modified methylaluminoxane as a cocatalyst, these complexes showed activities about 50%–1000% and 10%–100% higher than their corresponding bis(β‐enaminoketonato) titanium complexes for ethylene homo‐ and ethylene/1‐hexene copolymerization, respectively. They produced high or moderate molecular weight copolymers with 1‐hexene incorporations about 10%–200% higher than their homoligated counterpart pentafluorinated FI‐Ti complex. Among them, complex 3b displayed the highest activity [2.06 × 10⁶ g/mol_Ti?h], affording copolymers with the highest 1‐hexene incorporations of 34.8 mol% under mild conditions. Moreover, catalyst 3h with electron‐donating group not only exhibited much higher 1‐hexene incorporations (9.0 mol% vs. 3.2 mol%) than pentafluorinated FI‐Ti complex but also generated copolymers with similar narrow molecular weight distributions (M _w/M _n = 1.20–1.26). When the 1‐hexene concentration in the feed was about 2.0 mol/L and the hexene incorporation of resultant polymer was about 9.0 mol%, a quasi‐living copolymerization behavior could be achieved. ¹H and ¹³C NMR spectroscopic analysis of their resulting copolymers demonstrated the possible copolymerization mechanism, which was related with the chain initiation, monomer insertion style, chain transfer and termination during the polymerization process. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 2787–2797     

Highly Active,Thermally Stable,Ethylene‐Polymerisation Pre‐Catalysts Based on Niobium/Tantalum?Imine Systems

The reactions of MCl₅ or MOCl₃ with imidazole‐based pro‐ligand L¹H, 3,5‐tBu₂‐2‐OH‐C₆H₂‐(4,5‐Ph₂‐1H‐)imidazole, or oxazole‐based ligand L²H, 3,5‐tBu₂‐2‐OH‐C₆H₂(1H‐phenanthro[9,10‐d])oxazole, following work‐up, afforded octahedral complexes [MX(L^{1, 2})], where MX=NbCl₄ (L¹, 1 a ; L², 2 a ), [NbOCl₂(NCMe)] (L¹, 1 b ; L², 2 b ), TaCl₄ (L¹, 1 c ; L², 2 c ), or [TaOCl₂(NCMe)] (L¹, 1 d ). The treatment of α‐diimine ligand L³, (2,6‐iPr₂C₆H₃N?CH)₂, with [MCl₄(thf)₂] (M=Nb, Ta) afforded [MCl₄(L³)] (M=Nb, 3 a ; Ta, 3 b ). The reaction of [MCl₃(dme)] (dme=1,2‐dimethoxyethane; M=Nb, Ta) with bis(imino)pyridine ligand L⁴, 2,6‐[2,6‐iPr₂C₆H₃N?(Me)C]₂C₅H₃N, afforded known complexes of the type [MCl₃(L⁴)] (M=Nb, 4 a ; Ta, 4 b ), whereas the reaction of 2‐acetyl‐6‐iminopyridine ligand L⁵, 2‐[2,6‐iPr₂C₆H₃N?(Me)C]‐6‐Ac‐C₅H₃N, with the niobium precursor afforded the coupled product [({2‐Ac‐6‐(2,6‐iPr₂C₆H₃N?(Me)C)C₅H₃N}NbOCl₂)₂] ( 5 ). The reaction of MCl₅ with Schiff‐base pro‐ligands L⁶H–L¹⁰H, 3,5‐(R¹)₂‐2‐OH‐C₆H₂CH?N(2‐OR²‐C₆H₄), (L⁶H: R¹=tBu, R²=Ph; L⁷H: R¹=tBu, R²=Me; L⁸H: R¹=Cl, R²=Ph; L⁹H: R¹=Cl, R²=Me; L¹⁰H: R¹=Cl, R²=CF₃) afforded [MCl₄(L^6–10)] complexes (M=Nb, 6 a – 10 a ; M=Ta, 6 b – 9 b ). In the case of compound 8 b , the corresponding zwitterion was also synthesised, namely [Ta^?Cl₅(L⁸H)⁺] ? MeCN ( 8 c ). Unexpectedly, the reaction of L⁷H with TaCl₅ at reflux in toluene led to the removal of the methyl group and the formation of trichloride 7 c [TaCl₃(L^7‐Me)]; conducting the reaction at room temperature led to the formation of the expected methoxy compound ( 7 b ). Upon activation with methylaluminoxane (MAO), these complexes displayed poor activities for the homogeneous polymerisation of ethylene. However, the use of chloroalkylaluminium reagents, such as dimethylaluminium chloride (DMAC) and methylaluminium dichloride (MADC), as co‐catalysts in the presence of the reactivator ethyl trichloroacetate (ETA) generated thermally stable catalysts with, in the case of niobium, catalytic activities that were two orders of magnitude higher than those previously observed. The effects of steric hindrance and electronic configuration on the polymerisation activity of these tantalum and niobium pre‐catalysts were investigated. Spectroscopic studies (¹H NMR, ¹³C NMR and ¹H? ¹H and ¹H? ¹³C correlations) on the reactions of compounds 4 a / 4 b with either MAO(50) or AlMe₃/[CPh₃]⁺[B(C₆F₅)₄]^? were consistent with the formation of a diamagnetic cation of the form [L⁴AlMe₂]⁺ (MAO(50) is the product of the vacuum distillation of commercial MAO at +50 °C and contains only 1 mol % of Al in the form of free AlMe₃). In the presence of MAO, this cationic aluminium complex was not capable of initiating the ROMP (ring opening metathesis polymerisation) of norbornene, whereas the 4 a / 4 b systems with MAO(50) were active. A parallel pressure reactor (PPR)‐based homogeneous polymerisation screening by using pre‐catalysts 1 b , 1 c , 2 a , 3 a and 6 a , in combination with MAO, revealed only moderate‐to‐good activities for the homo‐polymerisation of ethylene and the co‐polymerisation of ethylene/1‐hexene. The molecular structures are reported for complexes 1 a – 1 c , 2 b , 5 , 6 a , 6 b, 7 a, 8 a and 8 c .     

Propylene polymerization with nickel–diimine complexes containing pseudohalides

DADNiX₂ nickel–diimine complexes [DAD = 2,6‐iPr₂? C₆H₃? N?C(Me)? C(Me)?N? 2,6‐iPr₂? C₆H₃] containing nonchelating pseudohalide ligands [X = isothiocyanate (NCS) for complex 1 and isoselenocyanate (NCSe) for complex 2 ] were synthesized, and the propylene polymerization with these complexes and also with the Br ligand (X = Br for complex 3 ) activated by methylaluminoxane (MAO) were investigated (systems 1 , 2 , and 3 /MAO). The polypropylenes obtained with systems 1 , 2 , and 3 were amorphous polymers and had high molecular weights and narrow molecular weight distributions. Catalyst system 1 showed a relatively high activity even at a low Al/Ni ratio and reached the maximum activity at the molar ratio of Al/Ni = 500, unlike system 3 . Increases in the reaction temperature and propylene pressure favored an increase in the catalytic activity. The spectra of polypropylenes looked like those of propylene–ethylene copolymers containing syndiotactic propylene and ethylene sequences. At the same temperature and pressure, system 2 presented the highest number of propylene sequences, and system 3 presented the lowest. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 458–466, 2006     

Synthesis,Structure, and Reactivity of a Gold Carbenoid Complex That Lacks Heteroatom Stabilization

Hydride abstraction from the neutral gold cycloheptatrienyl complex [( P )Au(η¹‐C₇H₇)] ( P =P(tBu)₂(o‐biphenyl)) with triphenylcarbenium tetrafluoroborate at ?80 °C led to the isolation of the cationic gold cycloheptatrienylidene complex [( P )Au(η¹‐C₇H₆)]⁺ BF₄^? in 52 % yield, which was characterized in solution and by single‐crystal X‐ray diffraction. This cycloheptatrienylidene complex represents the first example of a gold carbenoid complex that lacks conjugated heteroatom stabilization of the electron‐deficient C1 carbon atom. The cycloheptatrienylidene ligand of this complex is reactive; it can be reduced by mild hydride donors, and converted to tropone in the presence of pyridine N‐oxide.     

Synthesis of norbornene/divinylbenzene copolymers catalyzed by anilinonaphthoquinone-ligated nickel complexes and their applications for the synthesis of graft polymers

The copolymerization of norbornene (NB) and divinylbenzene (DVB) was carried out using anilinonaphthoquinone-ligated nickel complexes of the type [Ni(C₁₀H₅O₂NAr)(Ph)(PPh₃)] ( 1a : Ar = C₆H₃-2,6- ⁱPr; 1b : Ar = C₆H₂-2,4,6-Me; 1c: Ar = C₆H₅) with modified methylaluminoxane (MMAO) as a cocatalyst. The DVB content was varied (5–25 mol%) and the resulting copolymers exhibited number-average molecular weights (M_n) of 40,000–69,000 g/mol with polydispersities (PDI = 1.5–1.8). The styryl group of the NB/DVB copolymer was used for grafting poly(methyl methacrylate) by reverse atom transfer radical polymerization using azobisisobutyronitrile in the presence of copper chloride and bipyridine.     

Synthesis and Characterization of m‐Terphenyl (1,3‐Diphenylbenzene) Compounds Containing Trifluoromethyl Groups

The bis(silyl)triazene compound 2,6‐(Me₃Si)₂‐4‐Me‐1‐(N?N? NC₄H₈)C₆H₂ ( 4 ) was synthesized by double lithiation/silylation of 2,6‐Br₂‐4‐Me‐1‐(N?N? NC₄H₈)C₆H₂ ( 1 ). Furthermore, 2,6‐bis[3,5‐(CF₃)₂‐C₆H₃]‐4‐Me‐C₆H₂‐1‐(N?N? NC₄H₈)C₆H₂ derivative 6 can be easily synthesized by a C,C‐bond formation reaction of 1 with the corresponding aryl‐Grignard reagent, i.e., 3,5‐bis[(trifluoromethyl)phenyl]magnesium bromide. Reactions of compound 4 with KI and 6 with I₂ afforded in good yields novel phenyl derivatives, 2,6‐(Me₃Si)₂‐4‐MeC₆H₂? I and 2,6‐bis[3,5‐(CF₃)₂? C₆H₃]‐4‐MeC₆H₂? I ( 5 and 7 , resp.). On the other hand, the analogous m‐terphenyl 1,3‐diphenylbenzene compound 2,6‐bis[3,5‐(CF₃)₂? C₆H₃]C₆H₃? I ( 8 ) could be obtained in moderate yield from the reaction of (2,6‐dichlorophenyl)lithium and 2 equiv. of aryl‐Grignard reagent, followed by the reaction with I₂. Different attempts to introduce the ^tBu (Me₃C) or neophyl (PhC(Me)₂CH₂) substituents in the central ring were unsuccessful. All the compounds were fully characterized by elemental analysis, melting point, IR and NMR spectroscopy. The structure of compound 6 was corroborated by single‐crystal X‐ray diffraction measurements.     

Ethylene polymerization and copolymerization with 10‐undecen‐1‐ol using the catalyst system DADNi(NCS)2/MAO

The catalyst DADNi(NCS)₂ (DAD = (ArN?C(Me)? C(Me)?ArN); Ar = 2,6‐C₆H₃), activated by methylaluminoxane, was tested in ethylene polymerization at temperatures above 25 °C and variable Al/Ni ratio. The system was shown to be active even at 80 °C and when supported on silica. However, catalyst activity decreased. The catalyst system was also tested in ethylene and 10‐undecen‐1‐ol copolymerization at different ethylene pressures. The best activities were obtained at low polar monomer concentration (0.017 mol/L), using triisopropylaluminum (Al‐i‐Pr₃) to protect the polar monomer. The incorporation of the comonomer increased with the increase of polar monomer concentration. According to ¹³C NMR analyses, all the resulting polyethylenes were highly branched and the polar monomer incorporation decreased as ethylene pressure increased. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5199–5208, 2007     

Olefin polymerization and copolymerization by complexes bearing [ONNO]‐Type salan ligands: Effect of ligand structure and metal type (titanium,zirconium, and vanadium)

A series of novel titanium(IV) complexes bearing tetradentate [ONNO] salan type ligands: [Ti{2,2′‐(OC₆H₃‐5‐t‐Bu)₂‐NHRNH}Cl₂] (Lig¹TiCl₂: R = C₂H₄; Lig²TiCl₂: R = C₄H₈; Lig³TiCl₂: R = C₆H₁₂) and [Ti{2,2′‐(OC₆H₂‐3,5‐di‐t‐Bu)₂‐NHC₆H₁₂NH}Cl₂] (Lig⁴TiCl₂) were synthesized and used in the (co)polymerization of olefins. Vanadium and zirconium complexes: [ M{2,2′‐(OC₆H₃‐3,5‐di‐t‐Bu)₂‐NHC₆H₁₂NH}Cl₂] (Lig⁴VCl₂: M = V; Lig⁴ZrCl₂: M = Zr) were also synthesized for comparative investigations. All the complexes turned out active in 1‐octene polymerization after activation by MAO and/or Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄]. The catalytic performance of titanium complexes was strictly dependent on their structures and it improves for the increasing length of the aliphatic linkage between nitrogen atoms (Lig¹TiCl₂ << Lig²TiCl₂ < Lig³TiCl₂) and declines after adding additional tert‐Bu group on the aromatic rings (Lig³TiCl₂ < Lig⁴TiCl₂). The activity of all titanium complexes in ethylene polymerization was moderate and the properties of polyethylene was dependent on the ligand structure, cocatalyst type, and reaction conditions. The Et₂AlCl‐activated complexes gave polymers with lover molecular weights and bimodal distribution, whereas ultra‐high molecular weight PE (up to 3588 kg mol^?1) and narrow MWD was formed for MAO as a cocatalyst. Vanadium complex yielded PE with the highest productivity (1925.3 kg mol_v^?1), with high molecular weight (1986 kg mol^?1) and with very narrow molecular weight distribution (1.5). Copolymerization tests showed that titanium complexes yielded ethylene/1‐octene copolymers, whereas vanadium catalysts produced product mixtures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2111–2123     

Facile synthesis of zwitterionic organoaluminum complexes containing formally dianionic homoscorpionate ligands

A series of zwitterionic aluminum complexes of the type AlX[(2‐O‐3,5‐tBu₂C₆H₂)₃PZ] (AlX [O₃PZ]; X = Cl, Me, Et, and iBu; Z = H, Me) containing C₃‐symmetric, formally dianionic, facially tridentate ligands [O₃PZ]^2? were prepared and structurally characterized. Although serendipitous, these complexes can be readily synthesized by partial protonolysis of AlX₃ with equal molar (2‐HO‐3,5‐tBu₂C₆H₂)₃P (H₃[O₃P]) or [(2‐HO‐3,5‐tBu₂C₆H₂)₃p.m.e](OTf) ({H₃[O₃PMe]}OTf) in THF at 25°C or elevated temperatures. Alcoholysis of AlMe[O₃PMe] ( 2 ) with an excess amount of MeOH in refluxing toluene generates AlOMe[O₃PMe] ( 10 ). Salt metathesis of AlCl[O₃PMe] ( 6 ) with nBuM (M = Li, MgCl) and NaOR (R = tBu, Ph) in ethereal solutions affords AlnBu[O₃PMe] ( 9 ) and AlOR[O₃PMe] (R = tBu ( 11 ), Ph ( 12 )), respectively. Reactivity of 10 , 11 , and 12 with respect to catalytic ring‐opening polymerization of ε‐caprolactone is assessed.     

Investigations of the Nature of ZnII−SiII Bonds

A series of zinc(II) silylenes was prepared by using the silylene {PhC(NtBu)₂}(C₅Me₅)Si. Whereas reaction of the silylene with ZnX₂ (X=Cl, I) gave the halide‐bridged dimers [{PhC(NtBu)₂}(C₅Me₅)SiZnX(μ‐X)]₂, with ZnR₂ (R=Ph, Et, C₆F₅) as reagent the monomers [{PhC(NtBu)₂}(C₅Me₅)SiZnR₂] were obtained. The stability of the complexes and the Zn?Si bond lengths clearly depend on the substitution pattern of the zinc atom. Electron‐withdrawing groups stabilize these adducts, whereas electron‐donating groups destabilize them. This could be rationalized by quantum chemical calculations. Two different bonding modes in these molecules were identified, which are responsible for the differences in reactivity: 1) strong polar Zn?Si single bonds with short Zn?Si distances, Zn?Si force constants close to that of a classical single bond, and strong binding energy (ca. 2.39 Å, 1.33 mdyn Å^?1, and 200 kJ mol^?1), which suggest an ion pair consisting of a silyl cation with a Zn?Si single bond; 2) relatively weak donor–acceptor Zn?Si bonds with long Zn?Si distances, low Zn?Si force constants, and weak binding energy (ca. 2.49 Å, 0.89 mdyn Å^?1, and 115 kJ mol^?1), which can be interpreted as a silylene–zinc adduct.     

Synthesis and Structural Characterization of Some Novel Trialkylsilyl‐substituted Lithium Benzyl Complexes [Li(tmeda)][CHRSiMe2R′] (R = Ph, 3,5‐Me2C6H3; R′ = Me,tBu, Ph)

The reactions of PhCH₂SiMe₃ ( 1 ), PhCH₂SiMe₂^tBu ( 2 ), PhCH₂SiMe₂Ph ( 3 ), 3,5‐Me₂C₆H₃CH₂SiMe₃ ( 4 ), and 3,5‐Me₂C₆H₃CH₂SiMe₂^tBu ( 5 ) with ⁿBuLi in tetramethylethylenediamine (tmeda) afford the corresponding lithium complexes [Li(tmeda)][CHRSiMe₂R′] (R, R′ = Ph, Me ( 6 ), Ph, ^tBu ( 7 ), Ph, Ph ( 8 ), 3,5‐Me₂C₆H₃, Me ( 9 ), and 3,5‐Me₂C₆H₃, ^tBu ( 10 )), respectively. The new compounds 5 , 7 , 8 , 9 and 10 have been characterized by ¹H and ¹³C NMR spectroscopy, compounds 7 , 8 and 9 also by X‐ray structure analysis.     

Synthesis of 2‐(N‐arylimino)pyrrolide nickel complexes and polymerization of methyl methacrylate

The synthesis, characterization and methyl methacrylate polymerization behaviors of 2‐(N‐arylimino)pyrrolide nickel complexes are described. The nickel complex [NN]₂Ni ( 1 , [NN] = [2‐C(H)NAr‐5‐tBu‐C₄H₂N]^?, Ar = 2,6‐iPr₂C₆H₃) was prepared in good yield by the reaction of [NN]Li with trans‐[Ni(Cl)(Ph)(PPh₃)₂] in THF. Reaction of [NN]Li with NiBr₂(DME) yielded the nickel bromide [NN]Ni(Br)[NNH] ( 2 ). Complexes 1 and 2 were characterized by ¹H NMR and IR spectroscopy and elemental analysis, and by X‐ray single crystal analysis. Both complexes, upon activation with methylaluminoxane, are highly active for the polymerization of methyl methacrylate to give high molecular weight polymethylmethacrylate with narrow molecular distributions. Copyright © 2009 John Wiley & Sons, Ltd.