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Has anyone done the preparation and IR identification of Mo(CO)4(PR3)2 isomers (cis vs. trans)? The complexes give me pretty much everything I want (relatively short syntheses and distinct differences in the number of IR peaks that students can analyze via group theory), but I'm not thrilled with the potential hazards of the starting reagents (Mo(CO)6 and piperidine). I've also seen conflicting reports on whether or not the syntheses need to be performed under N2. (One prep says yes, another mentions nothing about refluxing under N2.) Should I go for it, or stay far far away?
I haven't done those labs, but I have done my fair share of reactions with Mo(CO)6. I think as long as you keep things in a hood you should be fine. I expect you would be doing this on a relatively small scale. You might also consider using Mo(CO)4(MeCN)2 of Mo(CO)4(EtCN)2 as starting materials. I have included preps but have never done them before.
I would think that even if you stick with the piperidine starting material you are going to want to do this under N2. It seems UCLA has some nice info on this lab.
http://www.chem.ucla.edu/~bacher/CHEM174/hints/Mo%28CO%294L2.html
http://www.chem.ucla.edu/~bacher/CHEM174/Lectures/Chem+174%96Lecture4c…
Good Day Amanda,
I have used Mo(CO)6 in the preparation of piano stool complexes with undergraduate students. The complex is prepared under nitrogen in a hood. A major difficulty associated with using Mo(CO)6 is sublimation where the solid ends up bound to the condensor when using high boiling point solvents. A trick is to use the condensor with no water, thus allowing the solvent to wash down the solid, otherwise you have poor yields.
Good Luck.
Sincerely,
Cliff
Hi Amanda,
I've made some (bpy)Mo(CO)4 species and they were air-stable. I made them by refluxing under N2 just to be safe, but I don't think it mattered too much and once they were isolated as solids they were fine. In solution I have seen them react/decompose over time (over the course of hours in CDCl3 in an NMR tube). I think they are light/heat sensitive in solution. I would recommend storing any solids in the freezer just to be safe once you make them if you need to store for another lab period. In my experience Mo(CO)6 is fine to work with, except for the sublimation issue that Cliff mentioned. If you reflux Mo(CO)6 in MeCN, you can make the Mo(CO)3(MeCN)3 species which is apparently very reactive/unstable but useful for making LMo(CO)3 compounds. In contrast, the Mo(CO)3(py)3 species that can be made in refluxing pyridine is very stable, so the stability depends on the ligands you are using.
Kyle
Another option with the reflux clogging problem is add a little bit of hexanes to the solution. That does a good job of keeping the solid from depositing in the condensor.
Hi Amanda,
We do that lab here (I just did the Mo(pip)2(CO)4 synth part with my students) and it goes fine. Reflux in heptane under air for 2-3 hours and you get a decent yeild. I threw their samples under vac to dry for next time, when they will be doing the phosphine work.
Shoot me an email (kgrice1@depaul.edu) and we can chat if you are still interested in this. If you found an alternative lab, I would love to hear it too.
Kyle
Kyle,
We ran the lab this year with good success earlier in the semester. I think it will be one to keep.
Amanda
Hi Amanda,
Glad to hear it went well!
Kyle