1. Chemistry 125: Lecture 52 February 16, 2011 Transition Metal Catalysis: Hydrogenation & Polymerization Additions by Radicals & Electrophilic Carbon; Isoprenoids; Tuning Polymer Properties This For copyright notice see final page of this file

2. Other “Simultaneous” Reagents Cl 2 C: (Carbene) R 2 BH (Hydroboration) CH 2 I 2 Zn/Cu (Carbenoid) O 3 (Ozonolysis) H-metal (Catalytic Hydrogenation) R-metal (Metathesis, Polymerization) RC (Epoxidation) OOHOOH O OsO 4 or MnO 4 - (Dihydroxylation)

3. OsO 4 and Permanganate Os analogue of cyclic acetal H-O-H OsO 4 is poisonous and expen$ive! Use as a 1% catalyst by adding oxidant. H 2 O 2 (1936) “NMO” (1976 - Upjohn) Chiral Amine Ligand e.g. J&F Sec. 10.5c p. 443 Osmate Ester H H C C H3CH3C CH 3 H H C C H3CH3C OO O O Os O O OO O HH Sharpless Asymmetric Dihydroxylation (1988) SAD C C K+K+ O-O- O Mn OO 97% ee C C OO O-O- O Mn O HH H2OH2O K+K+ 85% yield KMnO 4 MeOH / H 2 O NaOH, 20°C all syn (S,S) + (R,R) syn addition to trans 2-butene

4. H  * LUMO  HOMO orthogonal Catalytic Hydrogenation HOMO/LUMO : Concerted H  * LUMO  HOMO CC H CC H H CCCC  * LUMO  HOMO (“works” with metal catalysts!) HOMO-HOMO repulsive empty Pd e.g. J&F Sections Sec 4.9A, 168ff., 10.2a (410-413), 10.10 (452)

5. Orbital Variety from Metals

6. Pd HOMO (4d ) Ethylene LUMO (   ) HOMO (  ) HOMO-4 Ethylene-Pd Complex …(4d) 10 (5s) 0 (5p) 0 13%   40% 4d xy 47%  C-H x 2 -y 2 z2z2 xy xzyz

7. 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% 

8. Sigma Bond Analogue “Oxidative” Addition (crummy PM3 calculation) H-H + Pd 10 5 0 kcal/mole H 2 dissociates on bulk Pd surface, then hydrides move. (entropy help) bonding H 2 to Pd splitting H 2

9. kcal/mole

10. H Catalytic Hydrogenation  “ oxidative addition”  “ oxidative addition” Pd CC C C HH H H “ reductive elimination” Pd H CC H H C C H Pd addition concerted (syn) Pd H C C H H C C Experts discuss the extent of bonding in this “  -complex” H atoms replace Pd frontside  syn hydrogenation product

11. Catalytic Hydrogenation Stereochemistry syn addition e.g. J&F pp. 412

12. Stereochemistry No yields specified! No literature reference! A general elementary text e.g. Loudon, Sec. 7.9 E p. 313

13. pp. 20-22 of H. O. House Modern Synthetic Chemistry (1972) (a graduate-level text)

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

15. Suppose there is an allylic H in the alkene: can lead to allylic rearrangement H Catalytic Hydrogenation Pd H H C C H C C H H C C H C C CHCH H H C C CHCH C C alkene isomerized symmetric C C C H H H

16. 10 1 2 3 45 6 7 8 9 1 2 3 45 6 7 8 9 ?? VIIVIII

17. Alkene Metathesis metallacyclobutane CC Grubbs Catalyst Ru C C C C C C C C C C C C C Nobel Prize 2005 a metal alkylidene complex

18. Tall Prof. F. Ziegler (not Prof. Karl Ziegler) with Prof. R. Grubbs Tourists Ziegler Grubbs Host Prof. S.-I. Murahashi

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

20. 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 = 800-250,000 Ziegler-Natta Polymerization 45 x 10 6 tons (2007) -(CH 2 -CH) n - CH 3 n up to 10 5 isotactic Heterogeneous Catalyst hard to study mechanism R RR Et 3 Al+ TiCl 4

21. Stereochemistry: Tacticity All head-to-tail, but stereorandom (atactic) All head-to-tail, and stereoregular (isotactic) All head-to-tail, and stereoregular (syndiotactic) How do you know which is which? NMR (coming soon) How do you control what you make?

22. R 2 B-H C=C-CH 3 R’ R C-C-CH 3 Stereochemistry: Tacticity All head-to-tail, but stereorandom (atactic) All head-to-tail, and stereoregular (isotactic) All head-to-tail, and stereoregular (syndiotactic) axis Homogeneous “Kaminsky” catalysts activated by MAO (“methyaluminoxane”) homotopic faces mirror enantiotopic faces achiral faces C=C-CH 3 R’ C-C-CH 3 R R C=C-CH 3 R’ C-C-CH 3 + Alkenes approach from alternate faces

23. Radical Polymerization (e.g. J&F Sec 11.5 pp.487-489) R H Occasional butyl side-chains inhibit close packing.

24. ClCCl 3 RCl Controlling Polymer Chain Length CCl 4 is a “Chain-Transfer Agent” shortens polymer molecules without terminating chain reaction Properties like viscosity and melting point depend on chain length. etc. Cl k transfer /k polymerization ~ 0.01 for styrene polymerization        When other termination is negligible, molecular length ~ k p [styrene] / k t [CCl 4 ] “dispersity”

25. Alkene/Diene Oligomerization and Polymerization Using Carbon Electrophiles R+R+ (S N 1) R-LR-L ** (S N 2) (“oligo”, a few)

26. CH 3 H2CH2CC R + Electrophile in Formation of 2,2,4-Trimethylpentane, “Isooctane” CH 3 CH H2CH2CC CCH 2 CH 3 HC H 2 SO 4 + CH 3 C + C + CH 2 C H + (defined as “100 octane”) inter molecular hydride shift (Bartlett, 1944) chain poly(isobutylene) “butyl rubber” air-tight + CH 3 CH 2 C CH 3 C CH 2 C etc. CH 3 H2CH2CC H C +

27. e.g. J&F Sec. 12.13 pp. 554-562 R-L and R + Electrophiles in ** Terpene/Steroid Biogenesis

28. End of Lecture 52 February 16, 2011 Copyright © J. M. McBride 2011. 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