Water-Soluable Ruthenium Alkylidene Complexes: Synthesis and Applications to Olefin Metathesis in Protic Solvents

Citation

Lynn, David Michael (1999) Water-Soluable Ruthenium Alkylidene Complexes: Synthesis and Applications to Olefin Metathesis in Protic Solvents. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/7910-ds67. https://resolver.caltech.edu/CaltechTHESIS:08212024-214619136

Abstract

This thesis describes the application of well-defined ruthenium alkylidene complexes to olefin metathesis in protic solvents. Chapter 2 describes the application of (Cy₃P)₂Cl₂Ru=CHPh to the living ring-opening metathesis polymerization (ROMP) of functionalized monomers in aqueous emulsions. In these systems, monomers were dispersed in water using a cationic surfactant, and polymerization was initiated by injection of a catalyst solution. These polymerizations were shown to take place in the absence of chain transfer and chain termination reactions, passing all experimental criteria for living systems.

Chapter 4 describes the synthesis, characterization, and application of ruthenium alkylidenes of the type (Cy₂RP)₂Cl₂Ru=CHPh bearing charged phosphine ligands. These complexes were completely soluble and stable in protic, high-dielectric solvents such as methanol and water. Interestingly, the alkylidene protons in these new complexes were found to exchange with deuterons when they were dissolved in perdeuterated protic solvents (as described in Chapter 5).

Chapter 6 describes the application of these new water-soluble alkylidenes to ROMP in aqueous solution. The propagating alkylidenes in these reactions were found to decompose on the time scale of the polymerizations. In the presence of a Bronsted acid, however, polymerization was rapid and quantitative. The effect of the acid in these systems was twofold-in addition to eliminating hydroxide ions, catalyst activities were enhanced by protonation of phosphine ligands. These activated alkylidenes were used to initiate living polymerizations in aqueous solution. Both chain termination and chain transfer reactions were demonstrated to be absent on the time scale of the polymerizations, and this living polymerization protocol was used to synthesize water­ soluble block copolymers.

Chapter 7 describes the application of water-soluble alkylidenes to the ring-closing metathesis (RCM) of diene substrates in water and methanol. These alkylidenes could not be used to cyclize α,ω-dienes due to the instability of the catalytically-active methylidene complexes in these reactions. Substrates containing an internal olefin, however, were readily cyclized. The activities of these alkylidene complexes were found to correlate with predicted activities based on analyses of the steric and electronic character of the phosphine ligands in these complexes (as described in Chapter 3).

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