Tag Archives: Metathesis

You gotta love this structure

Science vol. 352 pp. 1555 – 1559 has a structure you have to love. It is a molecular knot containing a mere 30 pyridines and 10 benzenes all tied together in a knot which looks like a five pointed star. The tying was done by metathesis of benzenes with CH2 CH2 CH = CH2 dangling from them. To think of what needed to be tied to what was extremely clever.

Surprisingly with all this going on the knot coordinates just a single halogen atom. This shows why you must build a model of a complicated organic compound to see what it really looks like, something I learned with adamantane years ago — you can draw all the chairs you want, making it look rather spiky, but the damn thing is actually spherical. Well, no model was built, but the structure was determined using Xray crystallography (figure 3) Anyone playing with tinkertoys back in the day (or Legos now) and loving it will have a natural affinity for organic chemistry

The New Clayden pp. 1003 – 1028

p. 1004 — The nitrosoureas are known carcinogens.  They form DNA adducts (not sure exactly what they are) and are used experimentally to produce random mutations.  Could they be forming carbenes in vivo?

Also, how do you make N-Methyl N-nitroso urea?  N-methyl, N-nitroso toluene sulfonic acid?  

p. 1007 — I assume you make tosyl azide from tosyl chloride plus sodium azide

p. 1007 Rh2(OAc)4 — presumably the structure will be given in the next chapter. 

p. 1014 “Spin flipping, which can occur only through collision with another molecule (solvent usually) is relatively slow on the time scale of molecular rotations . . . “  Well how slow?  These numbers are known.  Why not give them.  Also why does a collision have to be involved for spin flipping to occur?  I think this question has been answered before.  Sorry about asking it again. How about another link to it. 

p. 1016 Interesting bunch of natural products containing cyclopropanes.  How does Nature actually manage their synthesis? 

p. 1018 — How do you make N2-CO2Et?  Possibly using the tosyl hydrazone?

p. 1023 — Metathesis at last.  When I type it, I have to stop myself from typing an awful word I’ve had to type (and utter) for years — Metastasis. 

p. 1024 — In the mechanism shown — why doesn’t the ‘carbene’ attached to Rh leave the Ru and form a cyclopropane with the other olefin? 

Also, all stereochemistry has vanished ! ! !

The catalyst goes from having 5 bonds to various things, to 6 with the bonds shown coming off the ruthenium atom like quills from a porcupine.  Surely the disposition of the bonds in space must be known?  Doesn’t it matter?   Ditto for the metathesis catalysts on 1025.  This is the way things were drawn (if they were drawn at all), in my orgo book of 54 years ago — English and Cassidy.

Hopefully the chapter on organometallics will be more enlightening about what is going on in metathesis reactions.  The discussion in this chapter takes me back to med school — this is what happens — remember it — never mind why.  At least in med school it was because no one knew why.  Here, perhaps they do but they aren’t telling.