Highly active methyl methacrylate polymerization catalysts obtained from bis(3,5‐dinitro‐salicylaldiminate)nickel(II) complexes and methylaluminoxane

The homopolymerization of methyl methacrylate was investigated with bis(salicylaldiminate)nickel(II) complexes, such as bis[3,5‐dinitro‐N(2,6‐diisopropylphenyl)salicylaldiminate]nickel(II) ( IIIa ) and bis[3,5‐dinitro‐N(phenyl)salicylaldiminate]nickel(II) ( IIIb ), and with methylaluminoxane (MAO) as an activator. In particular, the effect of the Al/Ni molar ratio on the catalytic activity and on the properties of the resulting poly(methyl methacrylate) (PMMA) was checked. The maximum activity was ascertained when an Al/Ni molar ratio equal to about 100 was used. However, the productivity of the catalytic systems was rather low. When the IIIa /MAO catalytic system was prepared under an ethylene atmosphere, an extremely high activity was observed, a productivity value of up to around 150,000 g of PMMA/(mol of Ni × h) being obtained, the highest ever found with nickel‐based catalysts. No appreciable presence of ethylene counits in the polymeric products was also ascertained. When the IIIb /MAO system was used, similar results were found, and high molecular weight PMMAs were obtained, despite the absence of bulky isopropyl substituents in positions ortho and ortho′ to the N‐aryl moiety of the salicylaldiminate ligand. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2117–2124, 2003     

Ethylene polymerization by bis(salicylaldiminate)nickel(II)/aluminoxane catalysts

The homopolymerization of ethylene by using different catalytic systems based on dinitro‐substituted bis(salicylaldiminate)nickel(II) precursors such as bis[3,5‐dinitro‐N(2,6‐diisopropylphenyl)]nickel(II) and bis[3,5‐dinitro‐N(phenyl)]nickel(II) in combination with organoaluminum compounds was investigated. In particular, the catalytic performances were studied as a function of the main reaction parameters, such as temperature, pressure, Al/Ni molar ratio, and duration. Methylaluminoxane resulted in the best co‐catalyst. Activities up to 200 kg polyethylene/(mol Ni × h) to give a linear high‐molecular‐weight polymer were achieved. The influence of the bulkiness of the substituents on the N‐aryl group of the aldimine ligand was also checked; it resulted in a determinant for catalytic activity rather than for polymer characteristics. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2534–2542, 2004     

Highly active and easily accessible catalysts for vinyl polymerization of norbornene obtained by oxidative addition of salicylaldimine ligands to bis(1,5‐cyclooctadiene)nickel(0) and methylaluminoxane

Highly active, cheap, and easy to synthesize catalytic systems, obtained in situ by the oxidative addition of salicylaldimine ligands to bis(1,5‐cyclooctadiene)nickel(0) and activated by methylaluminoxane (MAO), are now reported for the vinyl polymerization of norbornene. Their activity resulted mainly influenced by the nature of the substituents present both on the phenolate moiety and on the N‐aryl ring as well as the content of free trimethylaluminum (TMA) present in the commercial MAO. In particular, the maximum activity, up to about 78,000 kg polynorbornene/mol Ni × h, was ascertained when 3,5‐dinitro‐N‐(2,6‐diisopropylphenyl)salicylaldimine ligand was adopted in conjunction with Ni(cod)₂ and TMA‐depleted MAO. This remarkable performance, to the best of our knowledge, the highest never reported working in toluene instead of chlorinated aromatics, was reached adopting this more sustainable reaction medium. The influence of the main reaction parameters such as reaction time, temperature, monomer/Ni, and Al/Ni molar ratios on the catalytic performances and polymer characteristics was studied as well. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Homopolymerization of Methyl Methacrylate by Novel Ziegler‐Natta‐Type Catalysts Based on Bis(chelate)‐nickel(II) Complexes and Methylaluminoxane

Novel catalytic systems based on bis‐(chelate)nickel(II) precursors, such as bis(α‐nitroacetophenonate)nickel(II) [Ni(naph)₂] and bis(2,6‐diisopropylbenzenesalicylaldiminate)nickel(II) [Ni(dipbs)₂], and methylaluminoxane (MAO) as the cocatalyst were employed for the polymerization of methyl methacrylate (MMA). Reaction parameters were examined. Under proper conditions, the Ni(dipbs)₂/MAO system allowed to obtain poly(MMA) with a very high productivity (TOF up to 70 000 h^–1) and a remarkable syndiospecificity degree (rr > 80%) at room temperature without addition of an ancillary Lewis base.     

Homo‐ and copolymerization of methyl methacrylate with ethylene by novel Ziegler‐Natta‐Type nickel catalysts based on N,O‐nitro‐substituted chelate ligands

New Nickel (II) catalytic systems based on N,O chelate ligands, activated by methylaluminoxane, have been checked in the homopolymerization of methyl methacrylate (MMA) and its copolymerization with ethylene. In particular, the bis(8‐hydroxy‐5‐nitro‐quinolate)nickel(II)/methylaluminoxane system as well as the catalysts obtained by oxidative addition of either 8‐hydroxy‐5‐nitro‐quinoline or 8‐hydroxy‐5,7‐dinitro‐quinoline or 4‐nitro‐2‐(p‐nitrobenzylideneamino)‐phenol to Ni(cod)₂, subsequently activated by methylaluminoxane, have been employed. The influence of the reaction parameters on the catalytic activity and the characteristics of the resulting polymers has been investigated. All the obtained poly(methyl methacrylate) samples display a largely prevailing syndiotacticity degree, high molecular weights and a rather large polydispersity. The catalytic systems obtained through the oxidative procedure are able also to give copolymers of MMA with ethylene producing highly linear polyethylenes containing a low amount (1.5–2 mol %) of MMA counits, thus affording materials with improved surface properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 620–633, 2006     

Bis(β‐ketoamino)copper(II)/methylaluminoxane systems for homo‐ and copolymerizations of methyl acrylate and 1‐hexene

Two bis(β‐ketoamino)copper [ArNC(CH₃)CHC(CH₃)O]₂Cu ( 1 , Ar = 2,6‐dimethylphenyl; 2 , Ar = 2,6‐diisopropylphenyl) complexes were synthesized and characterized. Homo‐ and copolymerizations of methyl acrylate (MA) and 1‐hexene with bis(β‐ketoamino)copper(II) complexes activated with methylaluminoxane (MAO) were investigated in detail. MA was polymerized in high conversion (>72%) to produce the syndio‐rich atactic poly(methyl acrylate), but 1‐hexene was not polymerized with copper complexes/MAO. Copolymerizations of MA and 1‐hexene with 1 , 2 /MAO produced acrylate‐enriched copolymers (MA > 80%) with isolated hexenes in the backbone. The calculation of reactivity ratios showed that r(MA) is 8.47 and r(hexene) is near to 0 determined by a Fineman‐Ross method. The polymerization mechanism was discussed, and an insertion‐triggered radical mechanism was also proposed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1113–1121, 2010     

Synthesis and characterization of a series of 2‐aminopyridine nickel(II) complexes and their catalytic properties toward ethylene polymerization

A series of 2‐aminopyridine Ni(II) complexes bearing different substituent groups {(2‐PyCH₂NAr)NiBr, Ar = 2,4,6‐trimethylphenyl ( 3a) , 2,6‐dichlorophenyl ( 3b ), 2,6‐dimethylphenyl ( 3c) , 2,6‐diisopropylphenyl ( 3d ), 2,6‐difluorophenyl ( 3e ); (2‐PyCH₂NHAr)₂NiBr₂, Ar = 2,6‐diisopropylphenyl ( 4a )} have been synthesized and investigated as precatalysts for ethylene polymerization in the presence of methylaluminoxane (MAO). High molecular weight branched polymers as well as short‐chain oligomers were simultaneously produced with these complexes. Enhancing the steric bulk of the ortho‐aryl‐substituents of the catalyst resulted in higher ratio of solid polymer to oligomer and higher molecular weight of the polymer. With ortho‐haloid‐substitution, the catalysts afforded a product with low polymer/oligomer ratio ( 3b ) and even only oligomers ( 3e ) in which C₁₄H₂₈ had the maximum content. Compared with complex 3d containing ionic ligand, complex 4a containing neutral ligand exhibited obviously low catalytic activity for ethylene polymerization. The molecular weight, molecular weight distribution, and microstructure of the resulted polymer were characterized by gel permeation chromatography and ¹³C NMR spectrogram. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1618–1628, 2008     

Molecular structure determination of Ni(II) diimine complex and DMA analysis of Ni(II) diimine‐based polyethenes

Dynamic mechanical thermoanalysis showed that polyethene, prepared under suitable polymerization conditions with the Brookhart‐type catalyst dibromo‐N,N′‐1,2‐acenaphthylenediylidenebis[2,6‐bis(1‐methylethyl)benzeneamine]Ni(II)/methylaluminoxane (MAO), behaved like an elastomer, even though no comonomer was added. A structural characterization showed that the polymers contained methyl to hexyl branches and some longer branches. The effect of the polymerization conditions on branching was investigated through variations in the pressure and temperature of the polymerization. Depending on the degree and type of branching, polyethene was either quite amorphous or highly crystalline with a high melting temperature. The solid‐state structure of the catalyst dibromo‐N,N′‐1,2‐acenaphthylenediylidenebis[2,6‐bis(1‐methylethyl)benzeneamine]Ni(II) consisted of two centrosymmetrically related monomeric moieties, where Ni atoms were bridged by two bromide ligands. The Ni atom was five‐coordinated, with a square pyramidal coordination polyhedron. The sixth coordination site of the octahedral geometry was effectively blocked by the isopropyl groups of the 2,6‐C₆H₃(i‐Pr) substituents of the diimine ligand. In solution in the presence of MAO, the longer bridging Ni? Br bonds broke, and the complex dissociated to a monomeric species. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1426–1434, 2001     

Novel titanium complexes bearing two chelating phenoxy‐imine ligands and their catalytic performance for ethylene polymerization

Three substituted salicylaldimine ligands ( 1a, 2a, 3a ) and their titanium complexes bis[N‐(5‐nitrosalicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 1 ), bis[N‐(5‐chlorosalicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 2 ) and bis[N‐(5‐bromosalicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 3 ) were synthesized and characterized by mass spectra, ¹H NMR and elemental analyses, as well as complex 1 by X‐ray structure analysis. In the presence of methylaluminoxane (MAO), 1, 2 and 3 are efficient catalysts for ethylene polymerization in toluene. Under the conditions of T = 60 °C, p = 0.2 MPa, and n(MAO)/n(cat) = 1500, the activities of 1–3 reached 4.55–8.80 × 10⁶ g of PE (mol of Ti h bar)^?1, which is much higher than that of the unsubstituted complex bis[N‐(salicylidene)‐2,6‐diisopropylanilinato]titanium(IV)dichloride ( 4 ). The viscosity‐average molecular weight of polyethylene ranged from 24.8 × 10⁴ to 44.9 × 10⁴ g/mol for 1–3 and the molecular weight distribution M_w/M_n from 1.85 to 2.34. The effects of reaction conditions on the polymerization were examined in detail. The increase in ethylene pressure and rise in polymerization temperature are favorable for 1–3 /MAO to rise the catalytic activity and the molecular weight of polyethylene. Copyright © 2007 John Wiley & Sons, Ltd.     

Cu(0)/2,6‐bis(imino)pyridines catalyzed single‐electron transfer‐living radical polymerization of methyl methacrylate initiated with poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)

A series of 2,6‐bis(imino)pyridines, as common ligands for late transition metal catalyst in ethylene coordination polymerization, were successfully employed in single‐electron transfer‐living radical polymerization (SET‐LRP) of methyl methacrylate (MMA) by using poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) (P(VDF‐co‐CTFE)) as macroinitiator with low concentration of copper catalyst under relative mild‐reaction conditions. Well‐controlled polymerization features were observed under varied reaction conditions including reaction temperature, catalyst concentration, as well as monomer amount in feed. The typical side reactions including the chain‐transfer reaction and dehydrochlorination reaction happened on P(VDF‐co‐CTFE) in atom‐transfer radical polymerization process were avoided in current system. The relationship between the catalytic activity and the chemical structure of 2,6‐bis(imino)pyridine ligands was investigated by comparing both the electrochemical properties of Cu(II)/2,6‐bis(imino)pyridine and the kinetic results of SET‐LRP of MMA catalyzed with different ligands. The substitute groups onto N‐binding sites with proper steric bulk and electron donating are desirable for both high‐propagation reaction rate and C? Cl bonds activation capability on P(VDF‐co‐CTFE). The catalytic activity of Cu(0)/2,6‐bis(imino)pyridines is comparable with Cu(0)/2,2′‐bipyridine under the consistent reaction conditions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4378–4388     

Homo‐ and copolymerization of ethylene and norbornene with bis(β‐diketiminato) titanium complexes activated with methylaluminoxane

Homo‐ and copolymerization of ethylene and norbornene were investigated with bis(β‐diketiminato) titanium complexes [ArNC(CR₃)CHC(CR₃)NAr]₂TiCl₂ (R = F, Ar = 2,6‐diisopropylphenyl 2a; R = F, Ar = 2,6‐dimethylphenyl 2b ; R = H, Ar = 2,6‐diisopropylphenyl 2c ; R = H, Ar = 2,6‐dimethylphenyl 2d) in the presence of methylaluminoxane (MAO). The influence of steric and electric effects of complexes on catalytic activity was evaluated. With MAO as cocatalyst, complexes 2a–d are moderately active catalysts for ethylene polymerization producing high‐molecular weight polyethylenes bearing linear structures, but low active catalysts for norbornene polymerization. Moreover, 2a – d are also active ethylene–norbornene (E–N) copolymerization catalysts. The incorporation of norbornene in the E–N copolymer could be controlled by varying the charged norbornene. ¹³C NMR analyses showed the microstructures of the E–N copolymers were predominantly alternated and isolated norbornene units in copolymer, dyad, and triad sequences of norbornene were detected in the E–N copolymers with high incorporated content of norbornene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 93–101, 2008     

Vinyl polymerization of norbornene by bis(nitro‐substituted‐salicylaldiminate)nickel(II)/methylaluminoxane catalysts

The polymerization of norbornene has been investigated in the presence of different bis(salicylaldiminate)nickel(II) precursors activated by methylaluminoxane. These systems are highly active in affording nonstereoregular vinyl‐type polynorbornenes (PNBs) with high molecular weights. The productivity of the catalytic systems is strongly enhanced (up to 35,000 kg of PNB/mol of Ni × h) when electron‐withdrawing nitro groups are introduced on the phenol moiety. On the contrary, the presence of bulky alkyl groups on the N‐aryl moiety of the ligand does not substantially affect the activity or characteristics of the resulting PNBs. The catalytic performances are also markedly influenced by the reaction parameters, such as the nature of the solvent, the reaction time, and the monomer/Ni and Al/Ni molar ratios. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1514–1521, 2006     

Block copolymer micelles as nanoreactors for single‐site polymerization catalysts

New micelle‐like organic supports for single site catalysts based on the self‐assembly of polystyrene‐b‐poly(4‐vinylbenzoic acid) block copolymers have been designed. These block copolymers were synthesized by sequential atom transfer radical polymerization (ATRP) of styrene and methyl 4‐vinylbenzoate, followed by hydrolysis. As evidenced by dynamic light scattering, self‐assembly in toluene that is a selective solvent of polystyrene, induced the formation of micelle‐like nanoparticles composed of a poly(4‐vinylbenzoic acid) core and a polystyrene corona. Further addition of trimethylaluminium (TMA) afforded in situ MAO‐like species by diffusion of TMA into the core of the micelles and its subsequent reaction with the benzoic acid groups. Such reactive micelles then served as nanoreactors, MAO‐like species being efficient activators of 2,6‐bis[1‐{(2,6‐diisopropylphenyl)imino}ethyl]pyridinyl iron toward ethylene polymerization. These new micelle‐like organic supports enabled the production of polyethylene beads with a spherical morphology and a high bulk density through homogeneous‐like catalysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 197–209, 2009     

New soluble functional polymers by free‐radical copolymerization of methacrylates and bipyridine ruthenium complexes

The luminescent complex [4‐(3‐hydroxypropyl)‐4′‐methyl‐2,2′‐bipyridine]‐bis(2,2′‐bipyridine)‐ruthenium(II)‐bis(hexafluoroantimonate) and its methacrylate derivative were successfully synthesized and fully characterized by two‐dimensional ¹H and ¹³C{¹H} NMR techniques [correlation spectroscopy (COSY) and heteronuclear multiple‐quantum coherence experiment (HMQC)], as well as matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry. The respective labeled methyl methacrylate‐ruthenium(polypyridyl) copolymers were obtained by free‐radical copolymerization with methyl methacrylate and were characterized utilizing NMR, IR, and UV–visible spectroscopy and gel permeation chromatography. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3954–3964, 2003     

Effect of the co‐catalyst on the polymerization of ethylene and styrene by nickel‐diimine complexes

The attempt to copolymerize ethylene and styrene using η³‐methallyl‐nickel‐diimine {[η³‐2‐MeC₃H₄]Ni[1,4‐bis(2,6‐diisopropylphenyl)C₂H₂N₂][PF₆]} ( 1 ) associated with MAO or TMA produces polystyrene, polyethylene and polyethylene with styrene end groups. Characteristics of the formed polymer depend on the reaction conditions. The presence of styrene in the medium reduces the polymerization productivity and the molecular weight of polyethylene. Incorporation of styrene into polyethylene is favored by a 1 /ethylene/MAO pre‐contact time and depends on the amount of styrene. Maximum incorporation was 4.4 wt.‐%. If styrene is introduced after the pre‐contact time, a bimodal product distribution is observed, suggesting the occurrence of two different catalytic species. If the co‐catalyst is changed from MAO to TMA, no copolymer is formed but the presence of styrene leads to higher amounts of branched polyethylene.     

Solvent dependence of the solid‐state structures of salicylaldiminate magnesium amide complexes

There are challenges in using magnesium coordination complexes as reagents owing to their tendency to adopt varying aggregation states in solution and thus impacting the reactivity of the complexes. Many magnesium complexes are prone to ligand redistribution via Schlenk equilibrium due to the ionic character within the metal–ligand interactions. The role of the supporting ligand is often crucial for providing stability to the heteroleptic complex. Strategies to minimize ligand redistribution in alkaline earth metal complexes could include using a supporting ligand with tunable sterics and electronics to influence the degree of association to the metal atom. Magnesium bis(hexamethyldisilazide) was reacted with salicylaldimines [¹L = N‐(2,6‐diisopropylphenyl)salicylaldimine and ²L = 3,5‐di‐tert‐butyl‐N‐(2,6‐diisopropylphenyl)salicylaldimine] in either nondonor (toluene) or donor solvents [tetrahydrofuran (THF) or pyridine]. The structures of the magnesium complexes were studied in the solid state via X‐ray diffraction. In the nondonor solvent, i.e. toluene, the heteroleptic complex bis{μ‐2‐[(2,6‐diisopropylphenyl)iminomethyl]phenolato}‐κ³N,O:O;κ³O:N,O‐bis[(hexamethyldisilazido‐κN)magnesium(II)], [Mg₂(C₁₉H₂₂NO)₂(C₆H₁₈NSi₂)₂] or [¹LMgN(SiMe₃)₂]₂, (1), was favored, while in the donor solvent, i.e. pyridine (pyr), the formation of the homoleptic complex {2,4‐di‐tert‐butyl‐6‐[(2,6‐diisopropylphenyl)iminomethyl]phenolato‐κ²N,O}bis(pyridine‐κN)magnesium(II) toluene monosolvate, [Mg(C₂₇H₃₈NO)₂(C₅H₅N)₂]·C₅H₅N or [{²L₂Mg₂(pyr)₂}·pyr], (2), predominated. Heteroleptic complex (1) was crystallized from toluene, while homoleptic complexes (2) and the previously reported [¹L₂Mg·THF] [Quinque et al. (2011). Eur. J. Inorg. Chem. pp. 3321–3326] were crystallized from pyridine and THF, respectively. These studies support solvent‐dependent ligand redistribution in solution. In‐situ¹H NMR experiments were carried out to further probe the solution behavior of these systems.     

Moderately branched ultra‐high molecular weight polyethylene by using N,N′‐nickel catalysts adorned with sterically hindered dibenzocycloheptyl groups

Five examples of unsymmetrical 1,2‐bis (arylimino) acenaphthene ( L1 – L5 ), each containing one N‐2,4‐bis (dibenzocycloheptyl)‐6‐methylphenyl group and one sterically and electronically variable N‐aryl group, have been used to prepare the N,N′‐nickel (II) halide complexes, [1‐[2,4‐{(C₁₅H₁₃}₂–6‐MeC₆H₂N]‐2‐(ArN)C₂C₁₀H₆]NiX₂ (X = Br: Ar = 2,6‐Me₂C₆H₃ Ni1 , 2,6‐Et₂C₆H₃ Ni2 , 2,6‐i‐Pr₂C₆H₃ Ni3 , 2,4,6‐Me₃C₆H₂ Ni4 , 2,6‐Et₂–4‐MeC₆H₂ Ni5 ) and (X = Cl: Ar = 2,6‐Me₂C₆H₃ Ni6 , 2,6‐Et₂C₆H₃ Ni7 , 2,6‐i‐Pr₂C₆H₃ Ni8 , 2,4,6‐Me₃C₆H₂ Ni9 , 2,6‐Et₂–4‐MeC₆H₂ Ni10 ), in high yield. The molecular structures Ni3 and Ni7 highlight the extensive steric protection imparted by the ortho‐dibenzocycloheptyl group and the distorted tetrahedral geometry conferred to the nickel center. On activation with either Et₂AlCl or MAO, Ni1 – Ni10 exhibited very high activities for ethylene polymerization with the least bulky Ni1 the most active (up to 1.06  ×  10⁷ g PE mol^?1(Ni) h^?1 with MAO). Notably, these sterically bulky catalysts have a propensity towards generating very high molecular weight polyethylene with moderate levels of branching and narrow dispersities with the most hindered Ni3 and Ni8 affording ultra‐high molecular weight material (up to 1.5  ×  10⁶ g mol^?1). Indeed, both the activity and molecular weights of the resulting polyethylene are among the highest to be reported for this class of unsymmetrical 1,2‐bis (imino)acenaphthene‐nickel catalyst.     

Chiral nickel(II) and palladium(II) catalysts bearing strong electron‐withdrawing fluorine groups: synthesis,characterization and their application in catalytic polymerization for ethylene and styrene

A series of new chiral and achiral nickel(II) and palladium(II) complexes, {bis[N,N′‐(2,6‐diethyl‐4‐naphthylphenyl)imino]‐1,2‐dimethylethane}dibromonickel 3a , {bis[N,N′‐(4‐fluoro‐2‐methyl‐6‐sec‐phenethylphenyl)imino]‐1,2‐dimethylethane}dibromonickel rac‐(RS)‐ 3b , {bis[N,N′‐(4‐fluoro‐6‐sec‐phenethylphenyl)imino]‐1,2‐dimethylethane}dibromonickel rac‐(RR/SS)‐ 3c and {bis[N,N′‐(4‐fluoro‐6‐sec‐phenethylphenyl)imino]‐1,2‐dimethylethane}dichloropalladium rac‐(RR/SS)‐ 3d were successfully synthesized and characterized. The molecular structures of representative ligand rac‐(RS)‐ 2b , nickel complex 3a , rac‐(RR/SS)‐ 3c and palladium complex rac‐(RR/SS)‐ 3d were determined by X‐ray crystallography. The structures of complexes 3a and rac‐(RR/SS)‐ 3c have pseudo‐tetrahedral geometry about the nickel center, showing C₂ molecular symmetry. However, the structure of palladium complex rac‐(RR/SS)‐ 3d has pseudo‐square planar geometry about the palladium center, showing C₂ molecular symmetry. Complex 3e {bis[N,N′‐(2,6‐dimethylphenyl)imino]‐1,2‐dimethylethane}dibromonickel was also synthesized for comparison. Nickel complex rac‐(RS)‐ 3b bearing strong electron‐withdrawing fluorine group in the para‐aryl position and a chiral sec‐phenethyl group in the ortho‐aryl position of the ligand (one methyl group in the ortho‐aryl position) displays the highest catalytic activity for ethylene and styrene polymerization, and produced highly branched polyethylene and syndiotactic‐rich polystyrene. However, palladium complex rac‐(RR/SS)‐ 3d shows low catalytic activity for ethylene and styrene polymerization due to the poor leaving group, Cl, attached to palladium and the unfavorable molecular structure. Copyright © 2014 John Wiley & Sons, Ltd.     

Crystal structure and DFT analyses of a pentacoordinated PCP pincer nickel(II) complex

The reaction of NiCl₂ with 1,3‐bis[(diphenylphosphanyl)methyl]hexahydropyrimidine in the presence of 2,6‐dimethylphenyl isocyanide and KPF₆ afforded a new pentacoordinated PCP pincer Ni^II complex, namely {1,3‐bis[(diphenylphosphanyl)methyl]hexahydropyrimidin‐2‐yl‐κN²}(2,6‐dimethylphenyl isocyanide‐κC)nickel(II) hexafluoridophosphate 0.70‐hydrate, [Ni(C₉H₉N)(C₃₀H₃₀ClN₂P₂)]PF₆·0.7H₂O or [NiCl{C(NCH₂PPh₂)₂(CH₂)₃‐κ³P,C,P′}(Xylyl‐NC)]PF₆·0.7H₂O, in very good yield. Its X‐ray structure showed a distorted square‐pyramidal geometry and the compound does not undergo dissociation in solution, as shown by variable‐temperature NMR and UV–Vis studies. Density functional theory (DFT) calculations provided an insight into the bonding; the nickel dsp²‐hybridized orbitals form the basal plane and the nearly pure p orbital forms the axial bond. This is consistent with the NBO (natural bond orbital) analysis of analogous nickel(II) complexes.     

Combination of nickel and titanium complexes containing nitrogen ligands as catalyst for polyethylene reactor blending

Ethylene was polymerized using a combination of Ni(diimine)Cl₂ ( 1 ) (diimine = 1,4‐bis(2,6‐diisopropylphenyl)‐acenaphthenediimine) and {Tp^Ms*}TiCl₃ ( 2 ) (Tp^Ms* = hydridobis(3‐mesitylpyrazol‐1‐yl)(5‐mesitylpyrazol‐1‐yl)) compounds in the presence of methylaluminoxane (MAO) at 30°C. The productivity reaches a maximum at X_Ni = 0.75 (1 400 kg of PE/mol[M]· h), and the produced polyethylene (PE) showed maximal melt flow index (0.13 g/10 min) and minimal intrinsic viscosity (2.24 dL/g) compared to polyethylenes obtained with different values of nickel loading fractions (X_Ni). Productivity, intrinsic viscosity data, as well as melt flow index measurements markedly depend upon the content of the late transition metal, thus suggesting a synergic effect between nickel and titanium catalysts.