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Latent and Air‐Stable Pre‐Catalysts for the Polymerization of Dicyclopentadiene: From Penta‐ to Hexacoordination in Molybdenum Imido Alkylidene N‐Heterocyclic Carbene Complexes
Author(s) -
Elser Iris,
Kordes Benjamin R.,
Frey Wolfgang,
Herz Katharina,
Schowner Roman,
Stöhr Laura,
Altmann Hagen J.,
Buchmeiser Michael R.
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201801862
Subject(s) - dicyclopentadiene , chemistry , carbene , polymerization , molybdenum , romp , polymer chemistry , medicinal chemistry , metathesis , steric effects , chelation , catalysis , organic chemistry , polymer
The pentacoordinated, 16‐valence electron (VE) Mo imido alkylidene N‐heterocyclic carbene (NHC) complexes I1 – I5 and the hexacoordinated 18‐VE Mo imido alkylidene NHC complexes 1 – 4 , 8 , 10 and 12 containing a chelating ligand have been prepared and used as thermally latent catalysts in the ring‐opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD). Both 10 and 12 are the first Mo imido alkylidene complexes with a chelating alkylidene featuring a carboxylate group. Complexes I1 – I3 and I5 as well as 1 – 4 proved to be fully thermally latent in the presence of DCPD. With the changes in both the electronic and steric situation at the imido ligand provided by these pre‐catalysts, different temperatures of the onset of polymerization ( T onset =65–140 °C) and for the exothermic maximum of the curing curve ( T exo,max =98–183 °C) of DCPD were achieved. Also, the degree of crosslinking was successfully varied as indicated by swelling experiments in toluene, which revealed degrees of swelling between 0 and 50 %. While the introduction of a chelating alkylidene increases T onset , the introduction of more electron‐donating anionic ligands ( tert‐ butoxide, phenoxide) resulted in a drastic reduction in T onset , underlining the high flexibility of these systems. The hexacoordinated high‐oxidation state molybdenum imido alkylidene NHC complexes 2 , 3 and 4 were stable under air for at least twelve hours in the solid state.