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

Aqueous polymerization of styrene in biphasic media (styrene/water) has been achieved by water-soluble robust mononuclear hydride complexes [(η 6 -C 6 Me 6 )Ru II (bpy)H] n (X) {[ 1 ] n (X), where X = SO 4 ( n = 2) or CF 3 SO 3 ( n = 1), bpy = 2,2‘-bipyridine}. The hydride complex [ 1 ] 2 (SO 4 ) was synthesized from the reaction of an aqua complex [(η 6 -C 6 Me 6 )Ru II (bpy)(H 2 O)](SO 4 ) { 2 (SO 4 )} with a water-soluble hydrogen donor HCOONa in H 2 O in a pH range of 4−12 at 70−100 °C. The structures of [ 1 ] 2 (SO 4 ) and 1 (CF 3 SO 3 ) were determined by X-ray analysis, 1 H and 2 H NMR, IR, and electrospray ionization mass spectrometry (ESI-MS). X-ray analysis has revealed that complex 1 (CF 3 SO 3 ) adopts a distorted octahedral geometry with the Ru atom coordinated by one η 6 -C 6 Me 6 ligand, one bidentate bpy ligand, and one terminal hydrido ligand that occupies a bond position. Complex [ 1 ] 2 (SO 4 ) reacts with excess amounts of styrene in biphasic media to provide polystyrene in a 62% isolated yield for 8 h. The polydispersity ( M w / M n ) 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 [(C 6 Me 6 )Ru(bpy){(C 2 H 3 )(C 6 H 5 )} n H] + ( n = 1−4) were directly observed by ESI-MS.