Monolith‐ and Silica‐Supported Carboxylate‐Based Grubbs–Herrmann‐Type Metathesis Catalysts

Abstract

The synthesis of silica-and monolithsupported Grubbs±Herrmann-type catalysts is described. Two polymerizable, carboxylate-containing ligands, exo, exo-7-oxanorborn-2-ene-5,6-dicarboxylic anhydride and 7-oxanorborn-2-ene-5-carboxylic acid were surface-immobilized onto silica-and ring-opening metathesis (ROMP-) derived monolithic supports using ™grafting-from∫ techniques. The ™1 st generation Grubbs catalyst∫, RuCl 2 ( CHPh)(PCy 3 ) 2 , was used for these purposes. In addition, a poly(norborn-2-eneb-exo, exo-norborn-2-ene-5,6-dicarboxylic anhydride) -coated silica 60 was prepared. The polymer supported anhydride and carboxylate groups were converted into the corresponding mono-and disilver salts, respectively, and reacted with the Grubbs±Herrmann catalyst RuCl 2 ( CHPh)(IMesH 2 )(PCy 3 ) [IMesH 2 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene]. Heterogenization was accomplished by exchange of one chlorine ligand with the polymeric, immobilized silver carboxylates to yield monolithsupported catalysts 4, 5, and 6 as well as silicasupported systems 7, 8 and 9. The actual composition of these heterogenized catalysts was proven by the synthesis of a homogeneous analogue, RuCl[7-oxanorbornan-2-(COOAg)-3-COO]( CHPh)(IMesH 2 )(PCy 3 ) (3). All homogeneous and heterogeneous catalysts were used in ring-closing metathesis (RCM) of diethyl diallylmalonate, 1,7-octadiene, diallyldiphenylsilane, methyl trans-3-pentenoate, diallyl ether, N,N-diallyltrifluoracetamide and t-butyl N,N-diallylcarbamate allowing turnover numbers (TON×s) close to 1000. In a flow-through set-up, an auxiliary effect of pendant silver carboxylates was observed with catalyst 5, where the silver moiety functions as a (reversible) phosphine scavenger that both accelerates initiation and stabilizes the catalyst by preventing phosphine elution. Detailed catalytic studies were carried out with the monolith-supported systems 4 and 6 in order to investigate the effects of temperature and chain-transfer agents (CTA×s) such as cis-1,4-diacetoxybut-2-ene. In all RCM experiments Ruleaching was low, resulting in a Ru-content of the RCM products 3.5 mg/g (3.5 ppm).

Strategies to Immobilize Well‐Defined Olefin Metathesis Catalysts: Supported Homogeneous Catalysis vs. Surface Organometallic Chemistry

“…[45] A Grubbs II catalyst can also be supported on monoliths (10c) or silica (10d). [46] Immobilized Grubbs-Hoveyda or Grubbs-Hoveyda-Grela catalysts can also be prepared on monoliths based on PS-DVB polymers (10e-g). [45,[47][48][49] These catalysts display good performances in RCM.…”

Evidências da formação de monocamada de óxido de alumínio sobre sílica, através de reações de enxerto

“…As sílicas também têm sido usadas na sua forma modificada. Nesse caso, a modificação química da superfície pode ser feita com outros óxidos inorgânicos 3-5 , ou então, com grupos orgânicos quelantes que podem imobilizar um catalisador metálico na forma de um complexo 6,7 . Uma das formas de se modificar a superfície de sílicas com outros óxidos inorgânicos é através do uso de reações de enxerto.…”

Catalysts Immobilized on Organic Polymeric Monolithic Supports: From Molecular Heterogeneous Catalysis to Biocatalysis

“…[6,107,108] Conversion of the grafted anhydrides to silver carboxylates allowed the attachment of second generation Grubbs catalysts through halogen exchange ( Figure 7). [6,39,107,108] RCM reactions with these supports showed high DEDAM turnover numbers around 1000 and low ruthenium contamination (< 3 ppm), with catalyst loadings of approximately 3.5 mg Ru g…”

“…[93,106,107] However, Buchmeiser et al proved that deleterious scrambling could be avoided by using a bidentate carboxylate ligand. [39,106] Grafting of anhydride functional monomers, namely, 7-oxanorborn-2-enedicarboxylic anhydride, was achieved on a classic ROMP-based monolithic support. [6,107,108] Conversion of the grafted anhydrides to silver carboxylates allowed the attachment of second generation Grubbs catalysts through halogen exchange ( Figure 7).…”