Synthesis, Structure, and Reactivity of Cationic Ruthenium(II) Carbene Complexes with Bulky Chelating Bisphosphines:  Design of Highly Active Ring Opening Metathesis Polymerization (ROMP) Catalysts

Complexes of the type [{( t- Bu) 2 P(CH 2 ) n P( t- Bu) 2 -κ 2 P }XRu CHR] 2 (Y) 2 have been prepared and characterized in solution as well as in the solid state. Parameters governing the ring opening metathesis polymerization (ROMP) activity of these highly active ruthenium catalysts in solution have been assessed. Especially, chloro-bridged dinuclear dicationic ruthenium carbenes with a bis(di- tert -butylphosphino)methane ligand and weakly coordinating or noncoordinating anions display extremely high ROMP activity. Comparison of the solution-phase reactivity reported here with high throughput screening results from gas-phase experiments provide further mechanistic insight into the metathesis reaction with these compounds.