Kinetic and Thermodynamic Investigations of CO 2 Insertion Reactions into Ru–Me and Ru–H Bonds – An Experimental and Computational Study

The rates of CO 2 insertion into trans ‐Ru(dmpe) 2 (Me)H [ 1 , dmpe = 1,2‐bis(dimethylphosphino)ethane] and trans ‐Ru(dmpe) 2 (Me) 2 ( 2 ) derivatives were monitored by in situ infrared and 1 H NMR spectroscopy. The reactions are first order in both CO 2 and metal complex concentrations, and CO 2 insertion into the Ru–H bond of 1 occurs instantaneously at 0 °C. The reverse process, decarboxylation, was observed to occur readily at ambient temperature as revealed by 13 CO 2 exchange with subsequent CO 2 insertion into the Ru–Me bond at higher temperatures. No further CO 2 insertion into the Ru–H bond of the resulting acetate complex was observed. The activation barrier for CO 2 insertion into the first Ru–Me bond of 2 was determined to have Δ H ‡ and Δ S ‡ values of 12.7 ± 0.6 kcal mol –1 and –31.9 ± 2.0 e.u., respectively, which are indicative of a highly ordered transition state. The rate of CO 2 insertion into the second Ru–Me bond was two orders of magnitude slower at ambient temperature and resulted in the formation of trans ‐Ru(dmpe) 2 (O 2 CMe) 2 . In general, the insertion of CO 2 into the Ru–H or Ru–Me bonds of trans ‐Ru(dmpe) 2 (X)R (R = H or Me) was disvavored in the presence of poorly electron‐donating X ligands. For example, the insertion of CO 2 into the Ru–H bond of trans ‐Ru(dmpe) 2 (Cl)H was not observed even under forcing conditions. Computational results were in excellent agreement with these observations and predict a significant enhancement in CO 2 activity and resultant complex stability if dmpe is replaced with tetramethylethylenediamine (tmeda).