Conformational analysis of olefin-carbene ruthenium metathesis catalysts

We settle a long-standing disagreement ofDFT with experiment (both solution and gas phase) for the phosphine dissociation process in Grubbs metathesis catalysis. Our findings with the M06 functional provide further support to gas-phase experimental work, concluding that for the ring-closing metathesis of norbornene, the resting state is the alkylidene-olefin complex and the rate-determining step is the loss ofnorbornene as a ligand and generation of the 14-electron activated species. Comparing to recent solution NMR data on olefin-carbene Ru complexes relevant to olefin metathesis, we find that the M06 density functional leads to accurate predictions for the stability of conformers, 0.5 kcal/mol better than is found by B3LYP. Using this methodology, we suggest that Piers and co-workers observed the cis-dichloro "down" isomer exclusively following the ring opening of acenaphthalene.