Aqueous Polymerization of Styrene Promoted by Water-Soluble Robust Ruthenium Hydride Complexes

Abstract

Aqueous polymerization of styrene in biphasic media (styrene/water) has been achieved by water-soluble robust mononuclear hydride complexes [(η6-C6Me6)RuII(bpy)H]n(X) {[1]n(X), where X = SO4 (n = 2) or CF3SO3 (n = 1), bpy = 2,2'-bipyridine}. The hydride complex [1]2(SO4) was synthesized from the reaction of an aqua complex [(η6-C6Me6)RuII(bpy)(H2O)](SO4) {2(SO4)} with a water-soluble hydrogen donor HCOONa in H2O in a pH range of 4−12 at 70−100 °C. The structures of [1]2(SO4) and 1(CF3SO3) were determined by X-ray analysis, 1H and 2H NMR, IR, and electrospray ionization mass spectrometry (ESI-MS). X-ray analysis has revealed that complex 1(CF3SO3) adopts a distorted octahedral geometry with the Ru atom coordinated by one η6-C6Me6 ligand, one bidentate bpy ligand, and one terminal hydrido ligand that occupies a bond position. Complex [1]2(SO4) reacts with excess amounts of styrene in biphasic media to provide polystyrene in a 62% isolated yield for 8 h. The polydispersity (Mw/Mn) of the obtained polystyrene is 1.8. The isolated yield of polystyrene shows a maximum around pH 8. The pH-dependence is similar to the pH-dependent formation of 1. Growing polymer intermediates [(C6Me6)Ru(bpy){(C2H3)(C6H5)}nH]+ (n = 1−4) were directly observed by ESI-MS.