pH-Responsive Ruthenium-Based Olefin Metathesis Catalysts: Controlled Ring-Opening Metathesis Polymerization in Alcoholic and Aqueous Media upon Acid Addition

The new hexacoordinate catalysts (PCy3)(DMAP)2Cl2RuCH(p-C6H4)CH2NMe2 (7) and (PCy3)(DMAP)2Cl2RuCH(p-C6H4)N(CH3)2 (8) have been synthesized via exchange of a PCy3 ligand for two DMAP ligands from their (PCy3)2Ru precursors 4 and 5 in a one-step reaction in high yield. The catalysts promoted controlled ROMP of two cationic exo-7-oxanorbornene derivatives under homogeneous conditions in various acidic protic media, including acidic aqueous media. Very low polydispersities were accomplished in TFE/0.1 M HClaq. (1:1 v/v) with PDIs as low as 1.05.