Alpha and beta diimine cobalt complexes in isoprene polymerization: a comparative study. Issue 114 (5th December 2016)

• Record Type: Journal Article
• Authors: Alnajrani, Mohammed N.; Alshmimri, Sultan A.; Alsager, Omar A.
• Is Part Of: RSC advances. Volume 6:Issue 114(2016)
• Page Start: 113803
• Page End: 113814
• Publication Date: 2016-12-05
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c6ra23308b
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : Isoprene was polymerized by diimine cobalt catalyst in the presence of DEAC to produce cis -1, 4 and 3, 4 polyisoprene. 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 complexB was over 100-fold more active ( R p = 1.17 × 10 −3 M s −1 ) than α-diimine complexA ( R p = 1.07 × 10 −5 M s −1 ).A produced polyisoprene with molecular weight ( M n = 2.1 × 10 5 g mol −1 ) double that achieved withB . The polymers produced by bothA andB were predominantly cis -1, 4 enchained (80%) with 3, 4 regioerrors (20%). ForB, this 1, 4 : 3, 4 selectivity ratio was not influenced by aluminium alkyl reagent (ethylaluminiumsesquichloride (EASC), or DEAC) whereas forA, where EASC co-catalyst was used, a 1, 4- trans -rich (61%) polyisoprene was obtained. Moreover, increasing Al mole ratio decreased the activity forB but increased it forA .