[Rh(cycloolefin)(acac)] complexes as catalysts of polymerization of aryl- and alkylacetylenes: Influence of cycloolefin ligand and reaction conditions

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• 作者：Olga Trhl¨ªkov¨¢ ; Ji?¨ª Zedn¨ªk ; Hynek Balcar ; Ji?¨ª Brus ; Jan Sedl¨¢?ek
• 关键词：Catalysis ; Conjugated polymers ; Rhodium complexes ; Kinetics ; Polyacetylenes
• 刊名：Journal of Molecular Catalysis A: Chemical
• 出版年：2013
• 出版时间：1 November, 2013
• 年：2013
• 卷：378
• 期：Complete
• 页码：57-66
• 全文大小：1244 K

文摘

Complexes [Rh(nbd)(acac)], [Rh(cod)(acac)] and [Rh(cot)(acac)] (nbd = norborna-2,5-diene, cod = cycloocta-1,5-diene, cot = cyclooctatetraene) were investigated as catalysts of polymerization of monosubstituted acetylenes into stereoregular cis-transoid poly(monosubstituted acetylene)s. All complexes (without cocatalyst) are highly active in phenylacetylene (PhA) polymerization in both coordinating (THF) and non-coordinating (CH₂Cl₂) solvents. [Rh(cot)(acac)] prepared in situ by ligand substitution in [Rh(ethylene)₂(acac)] with cot is efficient in PhA polymerization even in systems with a high cot content. Selection of solvent and cycloolefin ligand of the catalyst allows the control over poly(phenylacetylene) molecular weight (M_w = 3 ¡Á 10⁴ to 4 ¡Á 10⁵). [Rh(nbd)(acac)] exhibit (moderate) activity also in polymerization of alkylacetylenes (alkyl = n-butyl, tert-butyl, 4-chlorobutyl, cyclopropyl, yields up to 28 % , M_w up to 7.3 ¡Á 10⁴) and in copolymerization of alkylacetylenes with arylacetylenes. In situ ¹H NMR monitoring of polymerization systems revealed monomer-assisted transformation of [Rh(cycloolefin)(acac)] complexes into precursors of polymerization centres consisting in proton transfer from the monomer to acac ligand of the catalyst under release of acetylacetone. [Rh(cycloolefin)(acac)] catalysts thus differ from the widely used [Rh(nbd)Cl]₂ catalyst which is transformed into active centres precursors only in reaction with cocatalyst or a molecule of coordinating solvent and which is efficient only in presence of a proper cocatalyst and/or coordinating solvent.