Room temperature polymerization of norbornene with a hydride-bridged dinuclear ruthenium complex system

A two-component system, [Ru( p -cymene)Cl 2 ] 2 ( C1 )/BH 3 •NMe 3 , allows for the catalytic ring-opening metathesis polymerization (ROMP) of norbornene at 60 °C. A hydride-bridged complex isolated from the two-component system, [RuCl( p -cymene)] 2 (μ-H)(μ-Cl) ( C2 ), is also active in the ROMP reaction, albeit at a reduced rate. Abstraction of one chloride ligand from C2 , by the reaction with 1 equiv of either AgPF 6 or AgSbF 6 , leads to the generation of either [{Ru( p -cymene)} 2 (μ-H)(μ-Cl) 2 ]PF 6 ( C3 ) or [{Ru( p -cymene)} 2 (μ-H)(μ-Cl) 2 ]SbF 6 ( C4 ) and further reduction of ROMP activity. Importantly, a reaction of C2 with 2 equiv each of AgSbF 6 and BH 3 •NMe 3 provides the ability to achieve room temperature ROMP of norbornene. Various hydride-bridged dinuclear ruthenium complexes have been observed in the room temperature system based on 1 H NMR analysis. An independent synthesis of a complex mixture containing [{Ru( p -cymene)} 2 (μ-H) 3 ]PF 6 ( C5 ) and a single-component complex [{Ru(η 6 -C 6 Me 6 )} 2 (μ-H) 3 ]PF 6 ( C6 ) rules out the catalytic capacity of this tri-μ-hydrido species. A di-μ-hydrido complex, [{Ru( p -cymene)} 2 (μ-H) 2 (μ-Cl)]PF 6 ( C7 ), is therefore postulated to act as the ROMP reaction center at room temperature.