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Catalysts 2017, 7(12), 381; doi:10.3390/catal7120381

Novel Allyl Cobalt Phosphine Complexes: Synthesis, Characterization and Behavior in the Polymerization of Allene and 1,3-Dienes

1
CNR, Istituto per lo Studio delle Macromolecole (ISMAC), via A. Corti 12, I-20133 Milano, Italy
2
CNR, Istituto di Scienze e Tecnologie Molecolari (ISTM), Università degli Studi di Milano, via C. Golgi 19, I-20133 Milano, Italy
*
Author to whom correspondence should be addressed.
Received: 16 November 2017 / Revised: 1 December 2017 / Accepted: 1 December 2017 / Published: 7 December 2017
(This article belongs to the Special Issue Catalysts for the Controlled Polymerization of Conjugated Dienes)
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Abstract

Novel allyl cobalt complexes, i.e., (η3-C4H7)(η4-C4H6)Co(PCyPh2) (1), (η3-C4H7)(η4-C4H6)Co(PMePh2) (2) and (η3-C5H9)(η4-C5H8)Co(PMePh2) (3), were synthesized by reacting CoCl2(PRPh2)2 (R = methyl, cyclohexyl) with 1,3-butadiene or isoprene in presence of metallic zinc. The complexes were fully characterized by Nuclear Magnetic Resonance (NMR) spectroscopy (1H and 2D experiments); in case of 1, single crystals, suitable for X-ray analysis, were obtained and the molecular structure was determined. The allyl cobalt phosphine complexes alone gave highly crystalline 1,2 polymers from 1,2-propadiene, but they did not polymerize 1,3-dienes. Nevertheless, in the presence of a stoichiometric amount of methylaluminoxane (MAO), they were able to polymerize 1,3-butadiene and substituted 1,3-butadienes such as isoprene, (E)-1,3-pentadiene, (E)-1,3-hexadiene, and (E)-3-methyl-1,3-pentadiene. Specifically, 1/MAO gave predominantly syndiotactic 1,2 polymers from 1,3-butadiene and terminally substituted 1,3-butadienes (e.g., 1,3-pentadiene and 1,3-hexadiene), but it was practically not active in the polymerization of internally substituted 1,3-butadienes (e.g., isoprene and 3-methyl-1,3-pentadiene); 2/MAO and 3/MAO exhibited instead an opposite behavior, giving predominantly isotactic 1,2 polymers from 3-methyl-1,3-pentadiene, and showing very low activity in the polymerization of 1,3-butadiene, 1,3-pentadiene and 1,3-hexadiene. The results obtained are interesting from the mechanistic point of view, and some hypotheses to explain this particular behavior were formulated. View Full-Text
Keywords: allyl cobalt phosphine complexes; X-ray structure; NMR characterization; 1,3-butadiene; polymerization of conjugated dienes; 1,2-polyallene allyl cobalt phosphine complexes; X-ray structure; NMR characterization; 1,3-butadiene; polymerization of conjugated dienes; 1,2-polyallene
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MDPI and ACS Style

Ricci, G.; Boccia, A.C.; Leone, G.; Forni, A. Novel Allyl Cobalt Phosphine Complexes: Synthesis, Characterization and Behavior in the Polymerization of Allene and 1,3-Dienes. Catalysts 2017, 7, 381.

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