Monolithic disk-supported metathesis catalysts for use in combinatorial chemistry

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-Pr-2-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 I 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 less than or equal to 88%) were observed. In both cases, metal leaching was low ( less than or equal to 3 and less than or equal to 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 M, = 16,400 and Mn = 11,700 g/mol, PDI = 1.40 were obtained.