Samantha D. Drouin

Ligand manipulation and design for ruthenium metathesis and tandem metathesis-hydrogenation catalysis

Results of investigations into tandem ring-opening metathesis polymerization (ROMP)-hydrogenation are reviewed, in which hydrogen and 3-chloro-3-methyl-1-butyne provide simple chemical toggles to switch between metathesis and hydrogenation chemistry, enabling multiple tandem catalysis in chlorocarbon solvent. In the presence of methanol, hydrogenation of metathesis polymers can be carried out under 1 atm H 2 . Issues of ligand design are examined in developing new Ru-diphosphine catalysts with improved selectivity, and an important decomposition pathway is identified for RuCl 2 (PP)(CHR) systems (PP = chelating diphosphine).

An Attractive Route to Olefin Metathesis Catalysts: Facile Synthesis of a Ruthenium Alkylidene Complex Containing Labile Phosphane Donors

Reaction of RuHCl(PPh3)34 with 3-chloro-3-methyl-1-butyne effects transformation into RuCl2(PPh3)2(CHCHCMe2) 1c. Starting 4 is available commercially, or via quantitative reaction of RuCl2(PPh3)3 with one equivalent of alkali phenoxides or isopropoxides in refluxing benzene-2-propanol. Phosphane exchange between 1c and PCy3 or 1,3-(CH2PCy2)2C6H4 is rapid at RT, affording RuCl2(PCy3)2(CHCHCMe2) 1b or the novel alkylidene complex RuCl2[1,3-(CH2PCy2)2C6H4](CHCHCMe2) 7. Much slower exchange occurred on use of RuCl2(PCy3)2(CHPh) (1a) as precursor. Complex 1c is stable indefinitely (months) in the solid state at RT under N2, but dimerizes slowly in solution to give RuCl(PPh3)2(μ-Cl)3Ru(PPh3)2(CHCHCMe2) 6a. 2,7-Dimethyl-octa-2,4,6-triene, the formal product of carbene coupling, is observed by 1H NMR. Dimerization does not compete with phosphane exchange. A side-product arising from use of excess 3-chloro-3-methyl-1-butyne in the synthesis of 1c was identified as Ru(IV) carbyne complex RuCl3(PPh3)2(≡CCHCMe2) 5, the structure of which was confirmed by X-ray crystallography.