A series of new binuclear neutral κ2-N,O-chelated Ni(II) complexes [(H2C)n{[(2,6-R2-4-yl-C6H2)-N═C(H)-(3,5-I2-2-O-C6H2)-κ2-N,O]Ni(CH3)(pyridine)}2] (R = iPr, 3,5-(CF3)2C6H3; n = 0, 1) are reported. The complexes are single-component catalyst precursors for ethylene polymerization. Catalyst activities exceed those of mononuclear analogues studied substantially. With 3.4 × 105 TO h−1, high molecular weight polymer is obtained (Mw 9.2 × 105 g mol−1; Mn 2.8 × 105 g mol−1). Semicrystalline polyethylene with a low degree of branching is formed (2 to 12 branches/1000 carbon atoms; prepared at 30 to 70 °C polymerization temperature), with Tm 112 to 136 °C. Polymerization in aqueous emulsion affords polyethylene dispersions.

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A series of (kappa(2)-N,O)-salicylaldiminato Ni(II)-methyl pyridine complexes 7-pyr and 8-pyr derived from 3,5-diiodosalicyaldehyde (3a) and 3-(9-anthryl)salicylaldehyde (3b), and terphenylamines 2,6-(3,5-R-4-R'-C6H2)(2)C6H3-NH2 (4a, R = CF3, R' = H; 4b, R = Bu-t, R' = H; 4c, R = Bu-t, R' = OH; 4d, R = Me, R' = H; 4e, R = Me, R' = MeO; 4f, R = MeO, R' = H; 4g, R = MeO, R' = MeO), was prepared by reaction of the respective salicylaldimine (5a-BOBO-f, 6a-g) with [(tmeda)Ni(CH3)(2)] (tmeda = N,N,N',N'-tetramethylethylenediamine) or [(pyridine)(2)Ni(CH3)(2)]. Complexes 7-pyr and 8-pyr are highly active single component catalysts for the polymerization of ethylene, producing a wide range of different polyethylene microstructures. While comparable complexes derived from 3a, 3b, 5-nitrosalicylaldehyde, 3-tert-butylsalicylaldehyde, 3,5-[3,5-(CF3)(2)C6H3](2)-salicylaldehyde, and 2,6-[3,5-(CF3)(2)C6H3](2)C6H3-NH2 afford polyethylenes with similar degrees of branching, variation of the terphenyl moieties in complexes 7-pyr and 8-pyr allows access to a wide range of polyethylene microstructures under identical reaction conditions. The X-ray diffraction analyses of complexes 7b-pyr and 8f-pyr are reported.

Ethylene/norbornene and ethylene/1-butene copolymerization with nickel(II) salicylaldiminato complexes [{kappa(2)-N, O-6-C(H)dN(2,6-R2C6H3)-2,4-R'2C6H2O}NiMe(pyridine)] (1a, R) 3,5-Me2C6H3, R' = I; 1b, R, R') 3,5-(F3C)(2)C6H3; 1c, R = 3,5-(F3C)(2)C6H3, R' = I; 2, R = Pr-i, R' = I) were studied in toluene as a reaction medium and in emulsion, the latter affording polymer dispersions. High molecular weight copolymers (M-n > 10(4) g mol(-1)) are formed. Incorporation of ethylene is much preferred over butene incorporation, X-Bu/x(Bu) similar to 0.05 under typical reaction conditions, by comparison incorporation of the strained olefin norbornene is higher, X-NB/x(NB) similar to 0.25 (X = comonomer mole fraction in polymer; x = comonomer mole fraction in reaction mixture). Dispersions contained copolymers with up to 6 mol % comonomer (12wt% for 1-butene; 20 wt% for norbornene). Incorporation of a few mol % of norbornene strongly decreases polymer crystallinity, which enhances the film forming properties of dispersions. Microstructure analysis by C-13 NMR shows that butene is incorporated in a 1,2-, 1,3- and 1,4-fashion. Whether 1,2- or 1,3- incorporation is predominant depends on the catalyst ( nature of R).

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTAqueous Dispersions of Polypropylene and Poly(1-butene) with Variable Microstructures Formed with Neutral Nickel(II) ComplexesPeter Wehrmann and Stefan MeckingView Author Information Universität Konstanz, Fachbereich Chemie, Universitätsstrasse 10, D-78457 Konstanz, Germany Cite this: Macromolecules 2006, 39, 18, 5963–5964Publication Date (Web):August 4, 2006Publication History Received29 June 2006Revised17 July 2006Published online4 August 2006Published inissue 1 September 2006https://pubs.acs.org/doi/10.1021/ma061462lhttps://doi.org/10.1021/ma061462lrapid-communicationACS PublicationsCopyright © 2006 American Chemical SocietyRequest reuse permissionsArticle Views574Altmetric-Citations40LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Catalysts,Colloids,Hydrocarbons,Microstructures,Polymers Get e-Alerts

The preparation of aqueous dispersions of very small particles (size < 30 nm) of various polymers (polyethylenes, stereoregular 1,2-polybutadiene, and polyalkenamers) by catalytic polymerization with a water-soluble catalyst, or with microemulsions of lipophilic catalysts is reviewed.

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTControlled, Copper-Catalyzed Functionalization of PolyolefinsM. Mar Díaz-Requejo, Peter Wehrmann, Mark D. Leatherman, Swiatoslaw Trofimenko, Stefan Mecking, Maurice Brookhart, and Pedro J. PérezView Author Information Laboratorio de Catálisis Homogénea, Departamento de Química y Ciencia de los Materiales, Unidad Asociada al CSIC, Campus de El Carmen s/n, Universidad de Huelva, 21007-Huelva, Spain; Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716; Department of Chemistry, University of North Carolina, Chapel Hill, CB3290, Chapel Hill, North Carolina 27599; and Universität Konstanz, Fachbereich Chemie, 78457 Konstanz, Germany Cite this: Macromolecules 2005, 38, 12, 4966–4969Publication Date (Web):May 18, 2005Publication History Received25 March 2005Revised29 April 2005Published online18 May 2005Published inissue 1 June 2005https://pubs.acs.org/doi/10.1021/ma050626fhttps://doi.org/10.1021/ma050626frapid-communicationACS PublicationsCopyright © 2005 American Chemical SocietyRequest reuse permissionsArticle Views1786Altmetric-Citations56LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Catalysts,Functionalization,Materials,Organic compounds,Polymers Get e-Alerts

Very small polymer particles of 10-30 nm size with various microstructures (polyethylene, syndiotactic 1,2-polybutadiene, poly(cycloolefins)) are prepared by catalytic polymerization with aqueous catalyst microemulsion.

friendliness. 1 By contrast to polymerization in solution or in the bulk, in emulsion polymerization a large portion of polymer can be generated in a given volume of reaction mixture without a strong increase in viscosity. The nontoxicity and nonflammability of water are also advantageous. To date, emulsion polymerization is industrially carried out by free radical processes exclusively. This limits the range of accessible polymer microstructures, and correspondingly the attainable materials properties. Therefore, the preparation of polymer latexes by catalytic polymerization of simple olefinic monomers is receiving increasing interest. 2 The synthesis of dispersions from olefins directly obtained from cracking of hydrocarbon feedstocks, without the need for further energy and raw material consuming conversion to other monomers is desirable. To obtain polymer latexes in catalytic emulsion polymerization, water-soluble complexes can be used, in analogy to traditional freeradical polymerization or as an alternative concept aqueous miniemulsions of a solution of a lipophilic catalyst precursor in a small amount of hydrocarbon can be utilized. The latter approach enables the use of the generally more common lipophilic catalysts and in addition somewhat water-sensitive catalysts can also be employed. Attractive and challenging issues are catalysts enabling high polymerization activities, a design of simple and industrially applicable catalytic systems and the control of latex particle size and structure.

More than 70 million tons of polyethylene and polypropylene are produced annually. The majority is prepared by catalytic polymerization employing Ziegler or Phillips catalysts based on early transition metals. More recently, olefin polymerization by complexes of late transition metals has also received increasing attention. A major motivation is their higher tolerance towards polar reagents due to a reduced oxophilicity by comparison to early transition-metal catalysts. Thus, ethylene and 1-olefins can be copolymerized with acrylates in a random fashion, and ethylene homoand copolymerizations can be carried out in aqueous emulsion to afford polymer latexes (i.e., aqueous dispersions of polymer particles of about 50–1000 nm size). The discovery by Brookhart and co-workers of the unique catalytic properties of cationic nickel and palladium diimine catalysts in olefin polymerization has given a strong impulse to the field. As a result, polymerization with neutral Ni complexes has received renewed interest, as these catalysts are expected to be more functional-group tolerant than their cationic Ni counterparts. However, catalyst activity and stability over time and the capability to form polymers with higher molecular weights at the same time are critical issues, particularly if the effort for catalyst synthesis is also considered. By analogy with the influence of bulky alkyl or aryl groups in cationic diimine complexes, in neutral Ni kN,O salicylaldiminato complexes bulky isopropyl groups on theN-aryl moiety retard chain transfer, which is supported by computational studies by Ziegler and co-workers. Introduction of electron-withdrawing substituents in the ortho or para position of the O donor in neutral nickel(ii) complexes has been reported to increase catalytic activities substantially, again in accordance with theoretical calculations. Most specifically for this class of catalysts, Grubbs and co-workers have shown that bulky groups in the C3 position of the Ocoordinating phenolate moiety of salicylaldimine ligands substantially increase polymerization activity. While these ligands afford highly active catalysts, their syntheses require multistep procedures with very low yields. Our particular interest in the design of novel Ni salicylaldiminato complexes stems from the recent finding that the known isopropyl-substituted complexes enable the synthesis of latexes of high-molecular-weight polyethylene, which are, to date, inaccessible by other techniques. Such polyolefin latexes can provide environmentally friendly and economically attractive coatings, which, for example, can be stable towards UV light and hydrolysis at the same time in contrast to current commodity coatings. In view of applications, a very active catalyst based on conveniently accessible ligands, and that is suited to polymerization in emulsion to higher-molecular-weight polyethylene is a prerequisite. Such a system is equally attractive for fundamental studies of catalytic polymerization in emulsion, in which well-defined catalyst precursors are also desirable. Our investigations subject to this report were initiated by the reasoning that an aryl substituent with strongly electron-withdrawing groups could provide steric bulk and electron withdrawing properties at the same time. Suzuki coupling provided a convenient synthetic method for the introduction of electron-withdrawing substituted aryl groups in the C2 and C6 position of the aniline aryl ring (Scheme 1). A series of salicylaldimine ligands with systematically varied electronic properties, 1a–e, resulted from the condensation of the corresponding substituted anilines with 3,5-diiodo-salicylaldehyde. The C NMR resonances of the compounds were fully assigned by H–H COSY, heteronuclear H-C 2D NMR and H–C 2D longrange-coupling NMR spectroscopy. The chemical shifts of the carbon atom para to the imine function in 1a–e (atom labeled p in Scheme 1) are d= 126.90, 126.96, 126.55, 126.48, and 126.56 ppm, respectively, and for the imine carbon atom, C= N, d= 168.42, 168.05, 166.99, 166.23, and 166.26 ppm were observed. Although the differences in chemical shifts are moderate, this trend follows the electron withdrawing/donating character of the R group and indicates that the electronic character of the substituents R in 1 indeed affects the electronic properties of the neighboring aryl ring and the imine function. Reaction of 1a–e in diethylether with [(tmeda)Ni(CH3)2] [12] (tmeda=N,N,N’,N’-tetramethylethylenediamine) in the presence of excess pyridine afforded the neutral methylnickel(ii) complexes 2a–e in high yield (Scheme 1). The molecular structure of 2a and 2c was determined by single-crystal X-ray crystallography (Figure 1). 14] To our knowledge, these are the first examples of structurally characterized neutral methylnickel complexes, which are precursors to very active olefin polymerization catalysts. Such methyl complexes are of particular interest, in comparison to the more frequent phenyl complexes [*] Dr. M. A. Zuideveld, Dipl. Chem. P. Wehrmann, Priv.-Doz. Dr. S. Mecking Institut f$r Makromolekulare Chemie und Freiburger Materialforschungszentrum der Albert-Ludwigs-Universit*t Freiburg Stefan-Meier-Strasse 31, 79104 Freiburg (Germany) Fax: (+49)761-203-6319 E-mail: stefan.mecking@makro.uni-freiburg.de