Phase Transfer Activation of Fluorous Analogs of Grubbs' Second-Generation Catalyst: Ring-Opening Metathesis Polymerization

Grubbs' second-generation alkene metathesis catalyst and the fluorous analog (H(2)IMes)((R(f8)(CH(2))(2))(3)P)-(Cl)(2)Ru(=CHPh) (1; H(2)IMes/R(f8) = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene/(CF(2))(7)CF(3)) catalyze ring-opening metathesis polymerizations of norbornene at essentially identical rates (CDCl(3), RT). However, dramatic accelerations can be observed with 1 in the presence of the fluorous solvent perfluoro(methylcyclohexane) (PFMC). The fluorous phosphine (R(f8)(CH(2))(2))(3)P must first dissociate from 1 to generate the 14-valence-electron intermediate that begins the catalytic cycle and should be scavenged by the PFMC phase (PFMC/toluene partition coefficient >99.7:<0.3). This would allow alkenes to more effectively compete for active catalyst. However, faster rates are seen only when 1 (partition coefficient 39.6:60.4) is added as a PFMC solution or a PFMC/CDCl(3) biphase mixture, as opposed to CDCl(3) solution, and possible additional contributing factors are analyzed. Analogous effects are observed with a 7-oxanorbornene-based N-butylsuccinimide. The molecular weights, polydispersities, glass transition temperatures, and cis/trans C=C linkage ratios of the polynorbornene produced under monophasic and biphasic conditions are compared and are usually similar.