1. Chemistry 125: Lecture 51 February 15, 2010 More Addition to Alkenes: Organometallic Reagents and Catalysts This For copyright notice see final page of this file

2. Mechanism for Acid-Catalyzed Hydrolysis of Acetal RO CH 2 + H HOH : : RO CH 2 + HROH RO-CH 2 + HO RO CH 2 + H First remove RO, and replace it by HO. HO RO CH 2 Now remove second RO, then H (from HO) + H : HO RO CH 2 + H RO=CH 2 + cation unusually stable; thus easily formed ROH H-O-CH 2 + O=CH 2 ROH RO CH 2 O H H  : Overall Transformation: H 2 O + Acetal Carbonyl + 2 ROH H+H+ (pp. 785-787) (hemiacetal) ? ? SN1SN1 E1

3. HOHO O=CH 2 CH 2 HO-O O H H O-O O H2CH2C O H H H H H 2 C=O Ozonide is a Double Acetal So Double Hydrolysis and hydrogen peroxide Gives Two Carbonyl Compounds which oxidizes aldehydes to carboxylic acids!

4. Sec. 10.5b pp. 440-441 Add a reducing agent like (CH 3 ) 2 S (or Zn) to destroy HOOH and save RCH=O. Or go with the flow and add more HOOH to obtain a good yield of RCOOH.

5. 3-membered ring with O-O bond is even worse. What Happens to HOOH + RCHO? O C H R O OH - O C H R O - O C H R O - HOH - O CR O R B R R O OH - Cf. Problem: Try drawing an analogous acid-catalyzed mechanism in which HOOH attacks the protonated carbonyl, then H + is lost from one O of the HOOH fragment in the product and added to the other before rearrangement. OH OH - is a bad leaving group from C, but O-O bond is very weak. Hydride Shift

6. “Nucleophilic” Addition to C=O

7. The nucleophilic addition of methyl lithium to carbonyl groups* is formally quite different from these additions of electrophiles to alkenes, but the following transition state analysis reveals a marked mechanistic similarity. * which will be discussed in more detail later.

8. Transition State Motion Li-CH 3 O=CH 2 Li CH 3 O CH 2

9. Transition State Orbital Mixing Li-CH 3 O=CH 2 HOMOLUMO+2  * LUMO  HOMO

10. Orbital Variety from Metals

11. overlaps with alkene  *overlaps with alkene  LUMOHOMO OsO 4 / Permanganate Sec. 10.5c p. 443 Os or Mn - Os analogue of cyclic acetal H2OH2O Diol + O 2 Os=O OsO 4 is poisonous and expen$ive! Use as a 1% catalyst by adding oxidant. H 2 O 2 (1936) “NMO” (1976) Chiral Amine Ligand Sharpless (1988) R R R R

12. H  * LUMO  HOMO orthogonal Sections 10.2a (410-413), 10.10 (452) Catalytic Hydrogenation HOMO/LUMO : Concerted H  * LUMO  HOMO CC H CC H H CCCC  * LUMO  HOMO (“works” with Pt/C Catalyst! Sec 4.9A, 168ff ) HOMO-HOMO repulsive empty Pd

13. HOMO (4d) Ethylene LUMO (   ) HOMO (  ) HOMO-4 Ethylene-Pd Complex …(4d) 10 (5s) 0 (5p) 0 13%   40% 4d xy 47%  C-H

14. HOMO (  ) Pd HOMO (4d) Ethylene UMO ( 5s ) UMO ( 5p ) (4d) 10 (5s) 0 (5p) 0 HOMO Ethylene-Pd Complex + 6% 5s 5% 5p 15% 4d z 2 67% 

15. Sigma Bond Analogue “Oxidative” Insertion (crummy PM3 calculation) H-H + Pd 10 5 0 kcal/mole H 2 dissociates on bulk Pd surface (and moves and dissolves) (entropy help)

17. H Catalytic Hydrogenation  “ oxidative insertion”  “ oxidative insertion” Pd CC C C HH H H “ reductive elimination” Pd H CC H C C H C C H H C C H Pd addition concerted; H replaces Pd twice  syn addition

18. Catalytic Hydrogenation Stereochemistry syn addition (p. 412)

19. Stereochemistry (Loudon, Sec. 7.9 E p. 313 ) No yields specified! No literature reference!

20. pp. 20-22 of H. O. House Modern Synthetic Chemistry (1972)

21. J. Chem. Soc., 1354 (1948) H 2 / Pt R’ = Ac

22. H Catalytic Hydrogenation Pd H H C C H C C H H C C H C C C C H HH H C C C H H C C C H H C C C H CC alkene isomerized

23. 10 1 2 3 45 6 7 8 9 1 2 3 45 6 7 8 9 ?? VIIVIII

24. Alkene Metathesis   CC Grubbs Catalyst Ru C C C C C C C C C C C C C Nobel Prize 2005

25. Tall Fred Ziegler (not Karl Ziegler) with Robt. Grubbs Tourists Ziegler Grubbs Host

26. ROMP Ring-Opening Metathesis Polymerization Ru C C C n n metathesis metatheses

27. Catalytic Hydrogenation Ti R CC R C C R C C H Pd H C C H C C H C C H H C C H 25 x 10 6 tons (2004) -(CH 2 -CH 2 ) n - n = 800-8000 Ziegler-Natta Polymerization 45 x 10 6 tons (2007) -(CH 2 -CH) n - CH 3 n up to 10 5 isotactic All head-to-tail, but stereorandom (atactic)All head-to-tail, and stereoregular (isotactic)

28. End of Lecture 51 Feb. 15, 2010 Copyright © J. M. McBride 2010. Some rights reserved. Except for cited third-party materials, and those used by visiting speakers, all content is licensed under a Creative Commons License (Attribution-NonCommercial-ShareAlike 3.0).Creative Commons License (Attribution-NonCommercial-ShareAlike 3.0) Use of this content constitutes your acceptance of the noted license and the terms and conditions of use. Materials from Wikimedia Commons are denoted by the symbol. Third party materials may be subject to additional intellectual property notices, information, or restrictions. The following attribution may be used when reusing material that is not identified as third-party content: J. M. McBride, Chem 125. License: Creative Commons BY-NC-SA 3.0