Stereoselective Ring Expansion Metathesis Polymerization with Cationic Molybdenum Alkylidyne N‑Heterocyclic Carbene Complexes

Molybdenum alkylidyne N-heterocyclic carbene (NHC) complexes of the type [Mo­(C-p-C6H4Y)­(OC­(R)­(CF3)2)2 (L)­(NHC)]­[B­(ArF)4] (Y = OMe, NO2; R = CH3, CF3; L = none, pivalonitrile, tetrahydrofuran; NHC = 1,3-dimesitylimidazol-2-ylidene (IMes), 1,3-dimesityl-3,4-dihydroimidazol-2-ylidene (IMesH2), 1...

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Published in:Journal of the American Chemical Society 2024-03, Vol.146 (12), p.8435-8446
Main Authors: Probst, Patrick, Groos, Jonas, Wang, Dongren, Beck, Alexander, Gugeler, Katrin, Kästner, Johannes, Frey, Wolfgang, Buchmeiser, Michael R.
Format: Article
Language:English
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Summary:Molybdenum alkylidyne N-heterocyclic carbene (NHC) complexes of the type [Mo­(C-p-C6H4Y)­(OC­(R)­(CF3)2)2 (L)­(NHC)]­[B­(ArF)4] (Y = OMe, NO2; R = CH3, CF3; L = none, pivalonitrile, tetrahydrofuran; NHC = 1,3-dimesitylimidazol-2-ylidene (IMes), 1,3-dimesityl-3,4-dihydroimidazol-2-ylidene (IMesH2), 1,3-dimesityl-3,4-dichloroimidazol-2-ylidene (IMesCl2), 1,3-diisopropylimidazol-2-ylidene (IiPr); B­(ArF)4 – = tetrakis­(3,5-bis­(trifluoromethyl)­phen-1-yl)­borate) were used in the ring expansion metathesis polymerization (REMP) of cyclic olefins. With cis-cyclooctene (cCOE) cyclic, low molecular weight oligomers were obtained at low monomer concentrations and the cyclic nature of the polymer was confirmed by MALDI-TOF measurements. High-molecular weight cyclic poly­(cCOE) became available at high monomer concentrations. Also, post-REMP allowed for converting low-molecular-weight cyclic poly­(cCOE) into high-molecular-weight cyclic poly­(cCOE). Tailored catalysts together with suitable additives offered access to the stereoselective REMP of functional norbornenes providing functional cis-isotactic (cis-it), cis-syndiotactic (cis-st) and trans-it poly­(norbornene)­s with up to 99% stereoselectivity. Mechanistic details supported by density functional theory (DFT) calculations are outlined.
ISSN:0002-7863
1520-5126
DOI:10.1021/jacs.3c14457