Metal carbonyls may be mononuclear or polynuclear

1. Metal carbonyls may be mononuclear or polynuclear

2. Characterization of metal carbonyls IR spectroscopy (C-O bond stretching modes)

3. Effect of charge u(free CO) 2143 cm-1 Lower frequency, weaker CO bond Effect of other ligands Increasing elec donating ability of phosphines PF3 weakest donor (strongest acceptor) PMe3 strongest donor (weaker acceptor)

4. The number of active bands as determined by group theory

5. Typical reactions of metal carbonyls Ligand substitution: Always dissociative for 18-e complexes, may be associative for <18-e complexes Migratory insertion:

6. Metal complexes of phosphines PR3 as a ligand Generally strong s donors, may be π-acceptor strong trans effect Electronic and steric properties may be controlled Huge number of phosphines available

7. Metal complexes of phosphines Basicity: PCy3 > PEt3 > PMe3 > PPh3 > P(OMe)3 > P(OPh)3 > PCl3 > PF3 Can be measured by IR using trans-M(CO)(PR3) complexes Steric properties: Rigid structures create chiral complexes apex angle of a cone that encompasses the van der Waals radii of the outermost atoms of the ligand

8. Typical reactions of metal-phosphine complexes Ligand substitution: presence of bulky ligands (large cone angles) can lead to more rapid ligand dissociation Very important in catalysis Mechanism depends on electron count

9. Metal hydride and metal-dihydrogen complexes Terminal hydride (X ligand) Bridging hydride (m-H ligand, 2e-3c) Coordinated dihydrogen (h2-H2 ligand) Hydride ligand is a strong s donor and the smallest ligand available H2 as ligand involves -donation and π-back donation

10. Synthesis of metal hydride complexes Characterize these kinds of reactions.

11. Characterization of metal hydride complexes 1H NMR spectroscopy High field chemical shifts (d 0 to -25 ppm usual, up to -70 ppm possible) Coupling to metal nuclei (101Rh, 183W, 195Pt) J(M-H) = 35-1370 Hz Coupling between inequivalent hydrides J(H-H) = 1-10 Hz Coupling to 31P of phosphines J(H-P) = 10-40 Hz cis; 90-150 Hz trans IR spectroscopy n(M-H) = 1500-2000 cm-1 (terminal); 800-1600 cm-1 bridging n(M-H)/n(M-D) = √2 Weak bands, not very reliable

12. Some typical reactions of metal hydride complexes Transfer of H- Transfer of H+ A strong acid !! Insertion A key step in catalytic hydrogenation and related reactions

13. Bridging metal hydrides Anti-bonding Non-bonding 4-e ligand 2-e ligand bonding

14. Metal dihydrogen complexes Characterized by NMR (T1 measurements) Very polarized d+, d- back-donation to s* orbitals of H2 the result is a weakening and lengthening of the H-H bond in comparison with free H2 If back-donation is strong, then the H-H bond is broken (oxidative addition)

15. Metal-olefin complexes 2 extreme structures sp3 sp2 Zeise’s salt π-bonded only metallacyclopropane Net effect weakens and lengthens the C-C bond in the C2H4 ligand (IR, X-ray)

16. Effects of coordination on the C=C bond C=C bond is weakened (activated) by coordination

17. Characterization of metal-olefin complexes IR n(C=C) ~ 1500 cm-1 (w) NMR 1H and 13C, d < free ligand X-rays C=C and M-C bond lengths indicate strength of bond

18. Reactions of metal-olefin complexes

19. Metal alkyl, carbene and carbyne complexes

20. Metal-alkyl complexes Main group metal-alkyls known since old times (Et2Zn, Frankland 1857; R-Mg-X, Grignard, 1903)) Transition-metal alkyls mainly from the 1960’s onward Ti(CH3)6 W(CH3)6 PtH(CCH)L2 Cp(CO)2Fe(CH2CH3)6 [Cr(H2O)5(CH2CH3)6]2+ Why were they so elusive? Kinetically unstable (although thermodynamically stable)

21. Reactions of transition-metal alkyls Blocking kinetically favorable pathways allows isolation of stable alkyls

22. Metal-carbene complexes L ligand Late metals Low oxidation states Electrophilic X2 ligand Early metals High oxidation states Nucleophilic

23. Fischer-carbenes

24. Schrock-carbenes Synthesis Typical reactions Compare to Wittig + olefin metathesis (we will speak more about that)

25. Grubbs carbenes Excellent catalysts for olefin metathesis

26. Metal cyclopentadienyl complexes Metallocenes (“sandwich compounds”) Bent metallocenes “2- or 3-legged piano stools”

27. Homogeneous catalysis: an important application of organometallic compounds Catalysis in a homogeneous liquid phase Very important fundamentally Many synthetic and industrial applications

28. Fundamental reaction of organo-transition metal complexes

29. Combining elementary reactions

30. Completing catalytic cycles Olefin hydrogenation (reductive elimination)

31. Completing catalytic cycles Olefin isomerization b-H elimination no net reaction b-H elimination resulting in C=C bond migration

32. Completing catalytic cycles Olefin isomerization

33. Completing catalytic cycles Olefin hydrogenation

34. Wilkinson’s hydrogenation catalyst RhCl(PPh3)3 Very active at 25ºC and 1 atm H2 Very selective for C=C bonds in presence of other unsaturations Widely used in organic synthesis Prof. G. Wilkinson won the Nobel Prize in 1973

35. Other hydrogenation catalysts [Rh(H)2(PR3)2(solv)2]+ With a large variety of phosphines including chiral ones for enantioselective hydrogenation RuII/(chiral diphosphine)/diamine Extremely efficient catalysts for the enantioselective hydrogenation of C=C and C=O bonds Profs. Noyori, Sharpless and Knowles won the Nobel Prize in 2001

36. Olefin hydroformylation Cat: HCo(CO)4; HCo(CO)3(PnBu3) HRh(CO)(PPh3)3; HRh(CO)(TPPTS)3 • 6 million Ton /year of products worldwide • Aldehydes are important intermediates towards plastifiers, detergents

37. reductive elimination CO insertion Olefin hydrogenation (reductive elimination) What else could happen if CO is present? R behaves as H did

38. Olefin hydroformylation

39. Catalysts for polyolefin synthesis • Polyolefins are the most important products of organometallic catalysis • (> 60 million Tons per year) • Polyethylene (low, medium, high, ultrahigh density) used in packaging, • containers, toys, house ware items, wire insulators, bags, pipes. • Polypropylene (food and beverage containers, medical tubing, bumpers, • foot ware, thermal insulation, mats)

40. Catalytic synthesis of polyolefin

41. Catalytic synthesis of polyolefin High density polyethylene (HDPE) is linear, d 0.96 “Ziegler catalysts”: TiCl3,4 + AlR3 Vacant site Coordinated alkyl Electrophilic metal center Insoluble (heterogeneous) catalyst

42. Catalytic synthesis of polyolefin Isotactic polypropylene is crystalline “Natta catalysts”: TiCl3 + AlR3 Vacant site Coordinated alkyl Electrophilic metal center Insoluble (heterogeneous) catalyst, crystal structure determines tacticity

43. Catalytic synthesis of polyolefin “Kaminsky catalysts” Vacant site Coordinated alkyl Electrophilic metal center Soluble (homogeneous) catalyst, structural rigidity determines tacticity

44. Polymerization mechanism

45. Schrock catalyst Grubbs catalyst Olefin metathesis The Nobel Prize 2005 (Chauvin, Schrock, Grubbs)

47. The metathesis mechanism (Chauvin, 1971)