ausblenden:
Schlagwörter:
heterogeneous catalysis; high throughput screening; metathesis; molybdenum; polymers; ruthenium
Zusammenfassung:
Two metathesis catalysts, RuCl2(PCy3)(NHC)(CHPh) (1) [NHC=1-(2,4,5-trimethylphenyl)-3-(6-hydroxyhexyl)-imidazol-2-ylidene] and Mo(N-2,6-i-Pr2-C6H3)(CHCMe2Ph)(BIPHEN) (2) [BIPHEN=(R)-3,3′-di-t-butyl-5,5′,6,6′-tetramethyl-2,2′-biphenolate) have been immobilized on polymeric, monolithic discs using a “grafting from” protocol. Monolithic discs were prepared via ring-opening metathesis polymerization (ROMP) from norborn-2-ene (NBE), tris(norborn-5-ene-2-ylmethyleneoxy)methylsilane [(NBE-CH2O)3-SiCH3], 2-propanol, toluene and RuCl2(PCy3)2(CHPh). Catalyst loadings of 0.55 and 0.7 wt %, respectively, were obtained. Monolithic disc-immobilized 1 was used in various metathesis-based reactions including ring-closing metathesis (RCM), ring-opening cross metathesis and enyne metathesis. Using 0.23–0.59 mol % of supported 1, turnover numbers (TONs) up to 330 were achieved. Monolithic disc-immobilized 2 was used in various enantioselective RCM and desymmetrization reactions. Using 9–13 mol % of supported catalyst, excellent yields up to 100% and high enantiomeric excess (ee≤88%) were observed. In both cases, metal leaching was low (≤3 and ≤2%, respectively). In addition, 1 catalyzed the cyclopolymerization of diethyl dipropargylmalonate (DEDPM) to yield poly(ene)s consisting of 5-membered rings, i.e., cyclopent-1-ene-1-vinylene units. The polymerization proceeded via non-stoichiometric initiation yielding polymers with unimodal molecular weight distribution. Using a catalyst to monomer ratio of 1 : 170, molecular weights of Mw=16,400 and Mn=11,700 g/mol, PDI=1.40 were obtained.
