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

Abstract

Grubbs’ second-generation alkene metathesis catalyst and the fluorous analog (H2IMes)((Rf8(CH2)2)3P)(Cl)2Ru(CHPh) (1; H2IMes/Rf8 = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene/(CF2)7CF3) catalyze ring-opening metathesis polymerizations of norbornene at essentially identical rates (CDCl3, RT). However, dramatic accelerations can be observed with 1 in the presence of the fluorous solvent perfluoro(methylcyclohexane) (PFMC). The fluorous phosphine (Rf8(CH2)2)3P 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/CDCl3 biphase mixture, as opposed to CDCl3 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.

Synthesis of Polypentenamer and Poly(Vinyl Alcohol) with a Phase‐Separable Polyisobutylene‐Supported Second‐Generation Hoveyda–Grubbs Catalyst

“…[16][17][18] However, even after a single chromatography step the residual ruthenium in the final product in some cases is still too high 2-2400 ppm. Some of the most commonly employed strategies to obtain supported metathesis catalysts consist of immobilizing the ruthenium alkylidene complex on to insoluble polymers, [19][20][21][22] soluble polymers, [23][24][25][26] inorganic supports, 27-29 perfluorinated 30,31 and ionic-liquid tags. [32][33][34][35] ( Figure 1).…”

Fluorous Organometallic Chemistry

“…1). Displacement of pyridine from the Grubbs-Hoveyda catalyst with fluorous trialkyl phosphines (1) generates new ring-opening metathesis polymerisation catalysts that offer dramatic rate accelerations in a two-phase organic-fluorous system where "phase transfer activation" following phosphine dissociation is envisaged [76][77][78]. Cleavage of the chloride bridges in [( p-cymene)RuCl 2 ] 2 with a perfluoroalkyl-tagged pyridine generates the anticipated mononuclear complexes (2) in high yield [79].…”

An Analogue of Grubbs Third‐Generation Catalyst with Fluorophilic Pyridine Ligands: Fluorous/Organic Phase‐Transfer Activation of Ring‐Closing Alkene Metathesis

“…[1][2][3][4] This protocol is designedt oe nhance the effectivenesso fm etal-basedc atalystp recursors in which al igand (L) must initially dissociate to generate the active species (Scheme 1, top). [1][2][3][4] This protocol is designedt oe nhance the effectivenesso fm etal-basedc atalystp recursors in which al igand (L) must initially dissociate to generate the active species (Scheme 1, top).…”

“…Accordingly,t here are literature reports of various additives that can accelerate rates of alkene metatheses with Grubbs first-and second-generation catalysts, [7] for whichr eversiblei nitial phosphine dissociationh as been established. [1][2][3][4] The idea is that when catalysis is subsequently effected under liquid/liquid (Scheme 1, middle) [1][2][3] or liquid/solid [4] biphasic conditions, the dissociated ligand will phaset ransfer to the second phase. However,a dditives can also introduce deactivation pathways involving the ruthenium fragment.…”

“…In efforts to date,w eh ave prepareda nalogues of Grubbs second-generation catalysts with fluorophilic phosphine li-gands, [1,3] as exemplifiedb y1,a nd hydrophilic ligands, as exemplifiedb y2 (Scheme 1, bottom). [2] Both 1 and 2 gave marked rate enhancementsi nr eactions conducted under organic/fluorous or organic/aqueousc onditions, as opposed to reactions conducted under organic monophasic conditions.…”