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

•The mechanism of initiation of polymerization with [Rh(cycloolefin)(acac)] is proposed.•The extent of initiation is influenced by solvent, cycloolefin ligand of catalyst.•Solvent and cycloolefin ligand of catalyst allows the control over the polymers MW.•Polymerization activity was achieved also in alkylacetylenes polymerization.•New polymerization catalysts can be prepared by in situ ligand exchange of [Rh(ethylene)2(acac)].

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 (Mw = 3 × 104 to 4 × 105). [Rh(nbd)(acac)] exhibit (moderate) activity also in polymerization of alkylacetylenes (alkyl = n-butyl, tert-butyl, 4-chlorobutyl, cyclopropyl, yields up to 28%, Mw up to 7.3 × 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.

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