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Issue 114, 2016
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Alpha and beta diimine cobalt complexes in isoprene polymerization: a comparative study

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Abstract

Two cobalt complexes, the α-diimine complex 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene-cobalt(II) dibromide (A) and the β-diimine complex 2,4-bis[(2,6-diisopropylphenyl)imino]pentane-cobalt(II) dibromide (B) were synthesized and fully characterized by elemental analysis, electrospray MS and single crystal X-ray diffraction. These complexes were then assessed as pre-catalysts of the polymerization of isoprene in chlorobenzene using diethylaluminiumchloride (DEAC) as co-catalyst at 35 °C. While the aryl substituents were identical in each case, the β-diimine complex B was over 100-fold more active (Rp = 1.17 × 10−3 M s−1) than α-diimine complex A (Rp = 1.07 × 10−5 M s−1). A produced polyisoprene with molecular weight (Mn = 2.1 × 105 g mol−1) double that achieved with B. The polymers produced by both A and B were predominantly cis-1,4 enchained (80%) with 3,4 regioerrors (20%). For B, this 1,4 : 3,4 selectivity ratio was not influenced by aluminium alkyl reagent (ethylaluminiumsesquichloride (EASC), or DEAC) whereas for A, where EASC co-catalyst was used, a 1,4-trans-rich (61%) polyisoprene was obtained. Moreover, increasing Al mole ratio decreased the activity for B but increased it for A.

Graphical abstract: Alpha and beta diimine cobalt complexes in isoprene polymerization: a comparative study

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Publication details

The article was received on 19 Sep 2016, accepted on 30 Nov 2016 and first published on 01 Dec 2016


Article type: Paper
DOI: 10.1039/C6RA23308B
Citation: RSC Adv., 2016,6, 113803-113814
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    Alpha and beta diimine cobalt complexes in isoprene polymerization: a comparative study

    M. N. Alnajrani, S. A. Alshmimri and O. A. Alsager, RSC Adv., 2016, 6, 113803
    DOI: 10.1039/C6RA23308B

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