Hi Mia, I enjoyed looking at your poster! I was wondering what your methodology was for assigning the forward and backward rate determining steps? I thought the rate determining steps would factor in the net energy change, but it seems like you may have a different method? Katherine Hi Katherine, Great question. We did have a slightly different method due to the cyclical nature of catalysts. We used Step 7 as an anchoring point since it was approximately half way through one cycle. We then found the highest energy step that occurred before step 7. That was our rate determining step for the backwards direction since it was the step with the highest energy barrier preventing the reaction from going backwards. We similarly identified the highest energy step that occurred after Step 7. That was our rate determining step for the forwards direction since it was the step with the highest energy barrier preventing the reaction from going forwards. Hi Mia, This is great work! I was wondering if there is a qualitative explanation for why asymmetric bulky groups kinetically disfavor the backwards reaction. Thanks for sharing your work. Hi Dr. Kuwata, The explanation is most likely sterics. In this specific catalytic productive cycle, bulky groups help to prevent the various alternative options (ex. alkylidene reacting with internal alkene) that could occur during different steps along the cycle (increase selectivity), but too much sterics prevents makes it challenging for the cycle to occur. My hypothesis is the sterics help to prevent the wrong reactant from entering close enough to react, but certain pockets are needed so the right reactants can come in at the right moments in the cycle - hence asymmetry. Hi Mia! This is super cool! I have two questions: Do you know why asymmetry in the catalyst leads to higher selectivity, or is that just a nifty observation? Also, can the unwanted internal alkane products further react with the catalyst to produce terminal alkenes? Glancing at the structures, it looks feasible, so I was curious as to why this might not be the case. Hi Sean, Appreciate the questions! Hi Mia, I enjoyed reading through your poster! I'm curious why you chose the basis sets that you did for the geometry optimization step. I'm familiar with B3LYP/6-31G(d), but LANL2DZ is new to me. What does it do well? Why only use it for Ruthenium? Caleb B. Hi Caleb, We used the LANL2DZ for Ruthenium since Ruthenium is a much heavier metal atom than H,C, N or Cl. Quantum methods are harder to apply to elements further down the periodic table since the number of electrons increase. Ruthenium has a lot more core electrons that do not play a significant role in chemical behavior. LANL2DZ uses an Effective Core Potential (ECP) which replaces core electrons with a "pseudo-potential" instead and then the basis set DZ allows for quantum methods to be done on the remaining electrons. Hi Mia, I enjoyed reading you poster. I had one question, how did you choose those specific ligands? Were they ones found to be most effective in literature? Alex L. Hi Alex, This is a great question! First we wanted to do a general comparison of NHC vs. CAAC ligands to just compare the selectivity of the two main groups of Ruthenium catalysts. Then, we picked other ligands based on experimental results from previous literature. Interesting work, Mia! Thanks for sharing. I am curious whether you tried to examine any other symmetric ligands to see whether the observation that asymmetrical ligands are more selective holds true. It might be interesting to see if replacing the symmetrical Mes groups with symmetrical but bulkier diisopropylarenes would produce similiar results to SIMes. Hi Mia, very impressive work! I am afraid to ask, because you have so many structures (even the short list of selected structures highlighted in your Conclusions includes 12 structures), but were any dispersion corrected functionals considered to see if dispersion might change any energetic barriers that are significantly influenced by steric bulk? I see that you mentioned the DFT methods were well validated so I suspect you may have already tried this. It looks like you are almost done. Is there anything else you would like to try in the future? Interesting work, Mia! Thanks for sharing. I am curious whether you tried to examine any other symmetric ligands to see whether the observation that asymmetrical ligands are more selective holds true. It might be interesting to see if replacing the symmetrical Mes groups with symmetrical but bulkier diisopropylarenes would produce similiar results to SIMes. Hi Dr. Stoffregen, We did not try any other symmetric ligands other than just SIMes. That's a trend that has been observed from experimental results in literature, but we did not computationally test any other symmetric ligands. I like your idea of symmetrical bulkier groups and that's something we will definitely consider doing in the future. Mia Hi Mia, very impressive work! I am afraid to ask, because you have so many structures (even the short list of selected structures highlighted in your Conclusions includes 12 structures), but were any dispersion corrected functionals considered to see if dispersion might change any energetic barriers that are significantly influenced by steric bulk? I see that you mentioned the DFT methods were well validated so I suspect you may have already tried this. It looks like you are almost done. Is there anything else you would like to try in the future? Hi Dr. Morales, Appreciate the questions! I don't believe that any dispersion corrected functionals were considered in our current DFT methods. Our methods were chosen based on previous computational analyses with ethenolysis catalysts from literature , so I suspect dispersion was probably considered at one point, but if not that is definitely something we should consider especially since the catalysts often involve aromatic components. In terms of moving forward, I would like to continue to computationally model more ligands from literature. The ones so far that we have modeled, with the exception of SIMes, have all had pretty high experimental selectivity, so I'd like to try a compound with a lot lower experimental selectivity and see if anything interesting is revealed in the productive pathway, and if the trend of asymmetrical bulky groups holds. MiaComputational study of the selectivity of ruthenium catalysts in ethenolysis.
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#11 · February 22, 2023, 8:58 pm
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#12 · February 22, 2023, 9:07 pm
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#13 · February 22, 2023, 9:14 pm
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