Ethylene polymerization catalyzed by substituted pyrazole nickel complexes

(Pyrazole)nickel dibromide complexes, (3,5-Me₂pz)₂NiBr₂ (1), (3-Mepz)₄NiBr₂ (2), (pz)₄NiBr₂ (3) and (3,5-^tBu₂pz)₂NiBr₂ (4), were prepared by the reaction of the appropriate pyrazole with (DME)NiBr₂. Solid-state structures of these complexes show a direct relation between the steric bulk of the pyrazole ligand and structure, with more bulky ligands forming four-coordinate complexes (1 and 4) whereas the less bulky ligands formed six-coordinate complexes (2 and 3). Activation of selected complexes (1 and 3) with methylaluminoxane (MAO) produced species that catalyzed the polymerization of ethylene to form high density polyethylene.     

Ethylene polymerization with imine and phosphine nickel complexes containing isothiocyanate

Three isothiocyanate complexes of nickel(II) containing diimine [ArN?C(Me)? C(Me)?NAr]Ni‐ (NCS)₂ (1), iminophosphine [Ph₂PC₆H₄CH?NAr]Ni(NCS)₂ (2), or diphosphine (dppe)Ni(NCS)₂ (3), [Ar = 2, 6‐ⁱPr‐C₆H₃; dppe = 1, 2‐bis(diphenylphosphine)ethane] were synthesized and examined for ethylene polymerization activated by methylaluminoxane (MAO). Their behavior was compared with those of the corresponding halide analogues [ArN?C(Me)? C(Me)?NAr]NiBr₂ (4), [Ph₂PC₆H₄CH?NAr]NiBr₂ (5), and (dppe)NiCl₂ (6). The diimines showed the highest polymerization activity. Replacement of the halide for the NCS pseudo halide affected the activity and decreased the molecular weight of the polymer formed. The highest molecular weights were obtained with the diimine complexes. Highly branched polyethylenes were obtained with the bulkier complexes 1 and 4. Replacement of the halide for NCS in the diimine complexes also caused an increase in the branching content, whereas the opposite occurs for the iminophosphine complexes. The different activities and behavior of the catalyst systems with halide versus NCS in the polymerization of ethylene and the characteristics of the final products suggest a modification in the active species caused by the non‐chelating ligand. Polymer molecular weight and branching content is dependent on the MAO/Ni molar ratio and on the working temperature. Copyright © 2004 John Wiley & Sons, Ltd.     

Ethylene polymerization promoted by dinuclear titanium p-tert-butylthiacalix[4]arene complexes

The dinuclear titanium p-tert-butylthiacalix[4]arene complexes 1 and 2 after activation with methylaluminoxane have been tested as homogeneous catalysts for the polymerization of ethylene. The results show that the catalytic activity of 1, although still poor, is higher than those of the related mononuclear titanium complexes bearing calix[4]arene as ligand. The molecular weight of the polyethylene produced are high (M_W up to 1.4 × 10⁶ Dalton) with broad molecular weight distribution. The polyethylenes have high melting point (133-142 °C) indicating a linear polymer microstructure which was confirmed by ¹³C NMR analysis.     

Ethylene polymerization using immobilized fluorine-containing bis-salicylidenimine-titanium complexes

Russian Chemical Bulletin - A fluorine-containing bis-salicylidenimine-titanium(iv) complex TiCl2{η2-1-[C(H)=NC6F4]-2-O-Ph(But)2}2 has been synthesized and immobilized on silica gel, polysorb,...     

Ring opening polymerization of lactide promoted by alcoholyzed heteroscorpionate aluminum complexes

The alcoholysis of the heteroscorpionate methyl aluminum complex (bpzmp)AlMe₂ ( 1 ) (bpzmp = 2,4‐di‐tert‐butyl‐6‐(bis‐(3,5‐dimethylpyrazol‐1‐yl)methyl)phenoxo), promoted both by phenol and isopropanol, has been investigated. The reaction of 1 with phenol afforded the dimeric mono(phenoxo) derivative 2 , whereas the alcoholysis of 1 with the less acidic isopropanol involved the coordinated heteroscorpionate ligand and led to the tetrahedral complex 3 in which the aluminum atom is surrounded by one κ²‐N,O^? coordinated bpzmp ligand and one η¹‐O^? coordinated ppzmp ligand (ppzmp = 2,4‐di‐tert‐butyl‐6‐(i‐propoxy‐(3,5‐dimethylpyrazol‐1‐yl)methyl)phenoxo). Complexes 1 – 3 have been tested in the ring opening polymerization (ROP) of L ‐lactide. The dimeric mono(phenoxo) derivative 2 was inactive in the ROP of L ‐lactide. Quite surprisingly, complex 3 was found to be active in ROP of L ‐ and rac‐lactide, showing a good molar‐mass control. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3632–3639, 2010     

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     

Ethylene polymerization by chromium complexes with phosphorous‐bridged bisphenoxy ligand

Chromium catalysts combined with phosphorous‐bridged bisphenoxy ligands were found to be highly active for ethylene polymerization. The most efficient catalyst precursor among them, generated by combining bis[3‐tert‐butyl‐5‐methyl‐2‐hydroxyphenyl](phenyl)phosphine hydrochloride ( 1a ) and CrCl₃(THF)₃, was characterized. X‐ray analysis of (3‐tert‐butyl‐5‐methyl‐2‐phenoxy)(3‐tert‐butyl‐5‐methyl‐ 2‐hydroxyphenyl)(phenyl)phosphine bis(tetrahydrofuran)chromium dichloride ( 6 ), obtained by the reaction of 1a and CrCl₃(THF)₃ in the presence of NaH, revealed a unique structure in which one phenol moiety of the bisphenol did not coordinate to the chromium center. Complex 6 showed higher activities than those observed in the in situ catalyst system. Polyethylene of various molecular weights was obtained with differing activators. The highest activity (113.5 kg mmol (cat)^?1 h^?1) was observed when TIBA/TB was used as a cocatalyst. A medium molecular weight polymer with narrow molecular weight distribution (M_w = 128,700, M_w/M_n = 1.8) was obtained using a 6 ‐TIBA/B(C₆F₅)₃ system. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3668–3676, 2007     

Ethylene polymerization on titanium phenoxyimine complexes with different structures

The kinetics of ethylene polymerization in the presence of catalytic systems based on methylaluminoxane-activated titanium bis(phenoxyimine) complexes with different structures has been investigated in the temperature range 30–70°C. The structures of the complexes have different substituents at the imine nitrogen atom and in the phenoxy group in the ligand, which affect the activity of the system and the molecular weight of polyethylene resulting from polymerization over at least 1 h. The polymerization kinetics is most sensitive to the structure of the substituent at the imine nitrogen atom and to bulky substituents in the ortho position of the phenoxy group. The results obtained are explained. An attempt is made to classify the influence of the substituents in the ligands. Process conditions ensuring living polymerization have been found. The physicochemical properties and structural features of the polyethylenes obtained have been determined.     

Epoxidation of an alkene promoted by various nickel(II) multiaza macrocyclic complexes

The epoxidation of trans-β-methylstyrene promoted by various Ni(II) complexes of macrocyclic ligands (cyclam and 1–5) using PhIO as a terminal oxidant has been investigated. In terms of the rate of epoxide formation, the complexes of monocyclic ligands (cyclam, 1 and 2) are better catalysts than those of polycyclic ligands (3–5) and the cyclam complex without pendant arms is better catalyst than those (1 and 2) with pendant arms. However, a series of the complexes show remarkably similar reactivity in the transfer of oxygen from active high-valent intermediate to the alkene and they provide nearly the same final yield in certain reaction conditions. Therefore, the yield of epoxide produced in a given period depends mainly on the rate of reaction of the complex with PhIO, which is greatly affected by the ligand structure. In order to become a better catalyst, the complex should have low Ni(II)/Ni(III) oxidation potential and the macrocyclic ligand should exert less steric hindrance around the Ni(II) center to allow easy axial approach of the oxidant.     

Generation effects on the microstructure and product distribution in ethylene polymerization promoted by dendritic nickel catalysts

Carbosilane dendrimers Gn-[(ONNMe2)NiBr2]m, containing up to sixteen terminal pyridylimine nickel complexes, have been studied as catalysts for polymerization of ethylene; the microstructure and the oligomer/polymer distribution are significantly affected by the generation of the dendritic precursor.     

Styrene polymerization with nickel complexes/methylaluminoxane catalytic system

Polymerization of styrene using β‐diketiminate nickel (II) bromide complexes CH{C(R)NAr}₂NiBr (R = CH₃, Ar = 2,6‐ⁱPr₂C₆H₃, 1 ; R = CH₃, Ar = 2,6‐Me₂C₆H₃, 2 ; R = CF₃, Ar = 2,6‐ⁱPr₂C₆H₃, 3 ; R = CF₃, Ar = 2,6‐Me₂C₆H₃, 4 ) in the presence of methylaluminoxane was studied. Compound 3 is the most active styrene polymerization catalyst of all the nickel complexes tested. The activity of these catalysts increases with increases in steric bulk of the substituents on the aryl rings. The electronic nature of the ligand backbone also affects the activity. Weight‐average molecular weight of the prepared polystyrene ranges from 21 000 to 72 000, with polydispersity indexes of 1.95–2.78. The microstructure of the obtained products is atactic polystyrenes from NMR analyses. Copyright © 2008 John Wiley & Sons, Ltd.     

Ethylene polymerization using catalysts based on binuclear phenoxyimine titanium halide complexes

Nine new binuclear titanium halide complexes were obtained on the basis of first synthesized tetradentate bis-phenoxyimine ligand precursors with different bridge linkages, including sterically hindered ones, between imine groups. Their binuclear character is confirmed by molecular weights, measured using vapor phase osmometry, MALDI–ToF and diffusion coefficients as determined by NMR–DOSY method. Catalytic activities of catalytic systems on the basis of the binuclear bis-salicylaldimine titanium complexes in ethylene polymerization were investigated. The studied catalytic systems appeared to be rather highly active, (10–70 kg(PE)/[mmol(Ti)·MPa·h]) and considerably more thermostable as compared to mononuclear analogs and made it possible to obtain polyethylenes of high and superhigh molecular weights. The effects of the bridge linkage between imine nitrogens and o-, p-substituents in the phenoxy-group were established.     

Bimetallic nickel complexes of macrocyclic tetraiminodiphenols and their ethylene polymerization

Schiff’s base condensation of 2,6-diformyl-4-R-phenol and affords 34-membered macrocyclic tetraiminodiphenol compounds, (R = H and R′ = iPr, 1; R = Me and R′ = iPr, 2; R = F and R′ = iPr, 3; R = Me and R′ = Et, 4; R = F and R′ = Et, 5) in good yields (47-62%), from which dinuclear nickel complexes, (R = H and R′ =  iPr, 6; R = Me and R′ = iPr, 7; R = F and R′ = iPr, 8) are prepared. Molecular structures of 2, dipotassium salt of 1, and 7 were confirmed by X-ray crystallography. Addition of B(C₆F₅)₃ to a toluene solution of 6-8 gives insoluble precipitates which show good activity for ethylene polymerization.     

Styrene polymerization using nickel(II) complexes as catalysts

Styrene polymerization is investigated with neutral and cationic Ni(II) complexes, i.e. Ni(bipy)Me₂, 1, Ni(bipy)Br₂, 2, Ni(phen)Br₂, 3, or Ni(Me₂phen)Br₂, 4, Ni(acac)₂, 5, (bipy = 2,2′-bipyridine, phen = phenanthroline, Me₂phen = 2,9-dimethyl-1,10-phenanthroline, acac = acetylacetonate), activated by [NHMe₂Ph][B(C₆F₅)₄] or B(C₆F₅)₃ as cocatalysts, in the presence of AlMe₃. The influence on the polystyrene features and the reaction kinetics of the nickel complex and boron activator, the Al/Ni or B/Ni molar ratios as well as the monomer concentration are studied. Catalytic systems derived from 2, 3 or 5 and [NHMe₂Ph][B(C₆F₅)₄] at a Ni:B:Al ratio of 1:1:5 are the most efficient at room temperature.     

[N,N]-二齿镍配合物催化烯烃聚合

烯烃聚合催化剂的设计是烯烃配位聚合领域的一个核心科学问题,通过设计合成精确结构的催化剂可以有效地调控催化聚合性能以及聚合产物的结构.后过渡金属催化剂由于其易调变性、对聚合产物支化结构的可控性及对极性单体的容忍性,在烯烃聚合领域引起了广泛的关注.本文介绍了近年来本课题组在[N,N]-二齿镍烯烃聚合催化剂设计方面的研究进展,包括四元环的中性脒基镍催化剂、五元环的-二亚胺镍催化剂、2-胺基吡啶和-胺基亚胺系列镍催化剂,以及六元环的-二亚胺和苯胺基亚胺镍催化剂在烯烃聚合的应用.通过优化后过渡金属镍催化剂结构,可成功实施烯烃活性聚合.     

Synthesis of anilinonaphthoquinone-based nickel complexes and their application for olefin polymerization

A series of anilinonaphthoquinone-based nickel complexes, Ni(C₁₀H₅O₂NAr)(Ph)(PPh₃) (Ar = C₆H₃-2,6-Me (1c); Ar = C₆H₂-2,4,6-Me (2c); Ar = C₆H₃-2,6-Et (3c)), were synthesized and the structures of 1c-3c were confirmed by single crystal X-ray analyses. The anilinonaphthoquinone-ligated nickel complexes activated with B(C₆F₅)₃ showed high activities for ethylene polymerization at 40 °C under atmospheric pressure of ethylene and gave polyethylene with long chain branches and short chain branches. The activity of these systems was decreased by lowering polymerization temperature accompanied by increase in molecular weight. The number of the chain branches was also decreased with lowering polymerization temperature and increasing the bulkiness of the ligand.     

An electroanalytical investigation of the olefin isomerization reaction promoted by electrogenerated cationic nickel(I) complexes

Summary Evidence for the ability of the electrogenerated cationic nickel(I) complex [Ni(PPh₃)₄]⁺ to promote the isomerization of allylbenzene is reported. However, the corresponding triethylphosphitenickel(I) complex displays no catalytic activity, apparently due to the poor leavinggroup character exhibited by the phosphite. The involvement of a -allylnickel hydride in the isomerization reaction is inferred from a comparison of the results obtained with those for the same reaction promoted by nickel hydride.     

Living syndiospecific polymerization of propylene promoted by C1‐symmetric titanium complexes activated by dried MAO

A series of C₁‐symmetric titanium complexes with both salicylaldiminato and β‐enaminoketonato as the ligands have been synthesized and investigated as the catalysts for propylene polymerization. In the presence of dried methylaluminoxane (dMAO), the complex with bulky substituent tert‐butyl ortho to alkyl oxygen can promote living polymerization of propylene with improved catalytic activity at ambient temperature, producing high molecular weight syndiotactic polypropylenes (rrrr 90.2%) with narrow molecular weight distributions (M_w/M_n = 1.07–1.22), via a propagation of 1,2‐insertion of monomer and chain‐end control of stereoselectivity. The propagation of polymer chain is completely different from that mediated by FI catalysts (the titanium complexes with phenoxy‐imine chelate ligands) which favor 2,1‐insertion of monomer. The interaction between a fluorine and a β‐hydrogen of a growing polymer chain, negligible chain transfer to monomer and dMAO without any free AlMe₃ were responsible for the achievement of living propylene polymerization. The substituent ortho to alkyl oxygen determined the stereo structure of the resultant polypropylene. In the case of less steric congested complexes with two nonequivalent coordination positions, the growing polymer chain might swing back to the favorite coordination position (site‐epimerization), forming m dyads regioirregular units. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Vinyl polymerization of norbornene by mono‐ and trinuclear nickel complexes with indanimine ligands

A series of new indanimine ligands [ArN?CC₂H₃(CH₃)C₆H₂(R)OH] (Ar = Ph, R = Me ( 1 ), R = H ( 2 ), and R = Cl ( 3 ); Ar = 2,6‐i‐Pr₂C₆H₃, R = Me ( 4 ), R = H ( 5 ), and R = Cl ( 6 )) were synthesized and characterized. Reaction of indanimines with Ni(OAc)₂·4H₂O results in the formation of the trinuclear hexa(indaniminato)tri (nickel(II)) complexes Ni₃[ArN = CC₂H₃(CH₃)C₆H₂(R)O]₆ (Ar = Ph, R = Me ( 7 ), R = H ( 8 ), and R = Cl ( 9 )) and the mononuclear bis(indaniminato)nickel (II) complexes Ni[ArN?CC₂H₃(CH₃)C₆H₂(R)O]₂ (Ar = 2,6‐i‐Pr₂C₆H₃, R = Me ( 10 ), R = H ( 11 ), and R = Cl ( 12 )). All nickel complexes were characterized by their IR, NMR spectra, and elemental analyses. In addition, X‐ray structure analyses were performed for complexes 7 , 10 , 11 , and 12 . After being activated with methylaluminoxane (MAO), these nickel(II) complexes can polymerize norbornene to produce addition‐type polynorbornene (PNB) with high molecular weight M_v (10⁶ g mol^?1), highly catalytic activities up to 2.18 × 10⁷ gPNB mol^?1 Ni h^?1. Catalytic activities and the molecular weight of PNB have been investigated for various reaction conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 489–500, 2008