Talk:Noyori asymmetric hydrogenation

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Proposed BINAP-Ru scheme[edit]

The newly proposed BINAP-Ru scheme (1:1 replacement of existing one) was deemed to large and with errors. Size can be remedied like below. I have checked both versions and can find no immediate errors. I am used to clockwise cycles?. V8rik (talk) 21:02, 3 July 2014 (UTC)

BINAP-Ru catalytic pathway
BINAP-Ru catalytic pathway stereoselectivity
These issues come to the mind of an organometallic chemist:
  • 1) As is normal for Ru, this catalyst hydrogenates without change in oxidation state, but this scheme invokes Ru(I) as the products of steps C and D.
  • 2) it would probably be more instructive to show stepwise transfer of hydride in the enantioselecting step, followed by separate hydrogenolysis of the Ru-alkoxide to regenerate the starting hydrido chloride. The scheme invokes coupled protonation and hydride transfer.
  • 3) In the current scheme, catalyst regeneration is achieved by addition of H dot. Often sign of a problem.

Picky things that might bother experts:

  • H2 generates the pro-catalyst by hydrogenolysis of a Ru-Cl bond. H2 then is consumed catalytically. The double arrow from H2 is confusing because it implies that both reaction channels consume H2 comparably, but they don’t of course. Double arrows, except in the case of resonance structures, confuse to non-experts and are distracting to experts.
  • typically ketone hydrogenation (vs transfer hydrogenation) proceeds via h2-ketone, not O-bonded ketones as invoked here. Otherwise the hydride can’t reach the carbon.

Most generally:

  • A mechanistic review doi:10.1016/j.ccr.2004.04.007 is more circumspect about the mechanism than the scheme above. So to me, the above scheme verges on original research or conjecture, intriguing nonetheless.
  • My guess (only that) is that the Ru(BINAP)HCl(solv)2 and BINAPRuX2(diamine) systems have been eclipsed by the cymeneRu(TsDPEN) system. The latter, like the diamine catalyst, operates by transfer hydrogenation. The Ru-TsDPEN system probably merits mention.--Smokefoot (talk) 02:34, 8 July 2014 (UTC)
Thank you for your comments. The original mechanism suffers from many of the same problems, then, yes? I don't have access to the article (getting it through interlibrary loan, soon), what changes can we make to the mechanism to make both the original and the redesign mechanistically accurate? I did wonder about the distance and hydride reaching the carbon, but assumed the original mechanism to be accurate.Azmanam (talk) 13:37, 8 July 2014 (UTC)
Well, I dont think that the mechanism needs the BINAP shown since it does not change throughout the cycle: the resulting Ru-H catalyzed hydrogenation, the resulting image would be more compact. I agree that the eta-2 ketone is not typically shown. The bigger issue is that this is one of three (that I know of) major catalyst types invented by the Nagoya group. --Smokefoot (talk) 13:55, 8 July 2014 (UTC)

"Scheme 3 presents our proposed mechanism for the asymmetric reaction of b-keto esters.[10c] The hydrogenation probably proceeds via a RuII monohydride 2 formed by the heterolysis of a hydrogen molecule by the ruthenium dichloride 1. The Ru hydride 2 interacts reversibly with the keto ester to form the chelating complex 3. Protonation of the keto oxygen changes the geometry of 3 from the s to the p complex and, at the same time, increases the electrophilicity of the carbonyl carbon, facilitating intramolecular hydride transfer.[ 25, 26] The resulting Ru ± hydroxy ester complex 4 readily releases the chiral product by the action of solvent molecules. The cationic ruthenium species 5 reacts with hydrogen to revert back to 2, completing the catalytic cycle" V8rik (talk) 11:44, 19 July 2014 (UTC)

Thanks for sticking with this issue and thanks for the citation to the Noyori and Ohkuma (N&O) review. Great diligence. The main problem, as indicated in my opening remarks above, is oxidation states. Oxidation state is a big deal to the organometallic folks, but you can see from their review that the focus is on products not mech, that is the reason that a more organometallic review for those interested in details. Even N&O are careful oxidation states as indicated by charge on the proposed intermediates. N&O follow various presentation aspects that might be useful style guides, like not drawing huge ligands in each step, avoiding double arrows. But those aspects are a matter of taste. Cheers, --Smokefoot (talk) 15:48, 19 July 2014 (UTC)