The chapter on organometallic chemistry is the only chapter of Anslyn and Dougherty so far that I’ve found disappointing. Perhaps because it’s the subject I’ve known the least about, and needed the greatest help. However, It leaves out a lot of basic explanations (if such exist). For more detailed whining see https://luysii.wordpress.com/2011/11/17/disappointed-with-anslyns-chapter-12-on-organometallics-and-a-request-for-help/ although there is plenty in this post.
p. 707 — I’ve never understood why the 4s energy level is lower than the 3d, or the 5s than the 4d etc. etc. Any explanations out there?
p. 707 In the CH3Mn(CO)5 compound CH3 is said to give 7 electrons, when in fact it is giving 1.
p. 709 — Can more than 1 dz2-like orbital be formed? Interesting that it can be formed along any axis.
p. 710 – “All metals have characteristic oxidation states” . . . . ” We do not discuss in length, the origin of these oxidation states.” Well, why not? What is physical organic chemistry for? This makes their discussion of organotransition chemistry seem like medical school — we don’t know why it is the way it is just suck it up and memorize. The ability to explain things from a few fairly simple principles is one of the reasons I love organic chemistry (along with its great diversity of molecules). It would be great to know why and how Fe likes to sit inside a porphyrin ring in hemoglobin and why it binds oxygen and carbon monoxide. Apparently this book has no intention of telling you.
p. 711 “These subtle deviations from standard geometries (trigonal bipyramid, octahedral, tetrahedral, square planar, square pyramidal) are not dominant factors influencing reactivity” Why aren’t they? Altering carbon carbon geometry certainaly alters reactivity. The book is silent. It seems to me this is something a physical organic chemistry textbook should tell you.
p. 712 — Why an orbital should be raised in energy if it lies along the bond to a ligand to a metal is unclear and actually counter intuitive — in carbon chemistry, good orbital overlap lowers the energy of the molecule. I looked crystal field theory up in Crabtree — ligands are considered as having negative charge, and this would raise the energy of a filled d orbital — but what if the orbital is empty?
p. 714 — Stabilized cyclobutadiene — wow ! When did this happen. Are the CC bonds of the cyclobutadiene inthe Fe(CO)3 complex all the same length?
p. 715 — Any ideas as to why Mg, Zn, Zr, Sn, B, Al, Li are the elements involved in transmetallation? Interestingly only Zn, and Zr are actually transition metals. Seems like its back to med school — see above.
p. 715 — The definition of metathesis “the pair wise interchange of two ends of two bonds” is nearly incomprehensible as is the example. The later discussion of metathesis is too brief to be helpful.
p. 719 — A diagram with d orbitals in it at last. Everything so far (and up to p. 745) is just lines between metal and ligand. Not terribly informative.
p. 721 — A great example of a reaction impossible in ‘classic’ organic chemistry (I think), oxidative insertion of a metal, resulting in its insertion in a sp2 hybridized carbon – halogen bond. Impressivo.
p. 723 — The Hartwig catalyst for C-H activation looks like a dog’s breakfast of components. It’s an ugly asymmetric Rube Goldberg sort of molecule. How in the world did they ever find it?
p. 735 and previous — The number of essentially new transformations permitted by organometallics is incredible — and is probably equal to the number of named reactions in the field when I left it in ’62. I wonder what percentage of synthetic steps in the latest and greatest syntheses involve metallo-organics. The 7 reactions on p. 735 are particularly impressive.
p. 735 – Why is the metal an electron sink? Easy to see if it is in a positive oxidation state, but if neutral, the electronegativity of all (italics) the transition metals are at least .5 units LESS than carbon (at 2.5)
p. 738 — Wikipedia says that the Monsanto acetic acid synthesis was developed by BASF in 1960. Interesting, that it wasn’t being mentioned in grad school back then.
p. 742 — Interesting that 4/6 of the Palladium coupling reactions have Japanese names attached to them — Suzuki, Sonagashira, Negishi and Kumata — any idea why? Is there a Japanese grandfather organometallic chemist giving rise to them? From looking at their diversity, it’s obvious that these reactions have transformed organic synthesis, but now is not the time to get into them.
Why Palladium and not some other transition metal? Is there something about its electronic structure and atomic radius? Anslyn is silent. Were others tried? Would others work as well? If not, why not?
Clayden et. al. spent a lot of time on enolate anions and their use in synthesis in the first edition of their book (2001). The new edition will be out next year (personal communication). It will be interesting to see if more attention is paid to organometallics in synthesis, and in general, in that book. However (p.744) enolate anions are used in allylic alkylation. Looks like a whole new world to explore.
p. 744 –> The parts on olefin metathesis were too dense, and I’ll have to delve into this at a later date.
I’m going to try to finish Anslyn by year’s end, so I’ll get back to this organometallic chemisty later. I’m disappointed that the chapter didn’t give me a better theoretical background on why organometallic reactions occur.
I did get two books out of a local college library — “Molecular Chemistry of the Transition Elements” by Mathey and Sevin and “Organotransition Metal Chemistry” by A. F. Hill. The Hartwig book is signed out to one of the profs. Any thoughts on any of them?
Happy Thanksgiving to all ! ! !
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