1. Inorganic Chemistry Year 3

2. Transition Metal Catalysis

3. Eighteen Electron Rule 1. Get the number of the group that the metal is in (this will be the number of d electrons) 2. Add to this the charge 1. Negative chargeMore electronsAdd to the count 2. Positive chargeLess electronsRemove from the count 3. Add the number of donating ligands to the count A stable complex has a total count of 18 Revision

4. Eighteen Electron Rule - Test Revision Rh(PPh 3 ) 3 Cl HCo(CO) 4 [RhI 2 (CO) 2 ] - Ni(η 3 -C 3 H 5 ) 2 Fe(CO) 4 (PPh 3 ) 16 18 16 18

5. 16 Electron Square Planar Complexes Complexes with d 8 configuration Fe Ru Os Have a strong preference for square planar 16 electron arrangements Why? - Ligands provide 8 electrons, and the metal provides 8 electrons - d x2-y2 raised in energy above d z2 - Back – bonding becomes less efficient Revision

6. Oxidation State 1. Start at zero 2. Ignore all formally neutral ligands (ie CO, PPh 3 ) 3. Add 1 for anionic ligand 4. Positive change, electron removed, add 1 5. Negative charge, electron added, subtract 1 6. Give your result in roman numerals Revision

7. Oxidation State - Test Revision Rh(PPh 3 ) 3 Cl HCo(CO) 4 [RhI 2 (CO) 2 ] - Ni(η 3 -C 3 H 5 ) 2 Fe(CO) 4 (PPh 3 ) (I) (II) (0)

8. Catalytic Cycles Reaction Steps L n L’MLnMLnM L n M(S) B A Product - L’ + L’ + S - S

9. Catalytic Cycles L n L’M - L’ + L’ + S - S L n M(S) A B LnMLnM Substrate Product Reaction Steps

10. Constructing Catalytic Cycles  Reasonable 18 electron counts and coordination numbers  Types of reactions  Ligand association  Ligand dissociation  Migration  Elimination  Oxidative Addition  Reductive Elimination  Metallacycle formation  Transmetallation Reaction Steps

11. Ligand Association / Dissociation  18 electron complexes electronically saturated  Most are co- ordination saturated  Therefore exchange of ligands require initial dissociation  The rate of this reaction can be slow Reaction Steps

12. Oxidative Addition / Reductive Elimination  Complementary process  Requires two accessible oxidation states of 2 units apart  Change of co-ordination number is also 2 Reaction Steps

13. Oxidative Addition Types of A – B H-H X-X C-C H-X C-X M-X Favoured by:  Low oxidation number  Electron donating ligands  Anionic complexes  Vacant sites Square planar complexes are ideal for oxidative addition Reaction Steps

14. Oxidative Addition Ortho Metallation  Low valent systems can attack the C-H bonds of an already bound ligand Reaction Steps

15. Reductive Elimination  The reverse of oxidative addition  Takes place in a cis sense  Favoured by the opposite factors:  High oxidation state  Crowded co-ordination sphere  Electron withdrawing ligands Reaction Steps

16. Migration Alkyl / Hydride Insertion Reaction Ligand Y migrates which enlarges ligand X Can often be seen as a nucleophilic attack of Y on X Migrating Ligand Y can be alkyl or halide X Ligands can be a wide range, CO, CNR, CR 2, C=C, O 2, SO 2 Reaction Steps

17. Hydride Migration Regiochemistry at Alkene Reaction Steps

18. β - elimination Reverse of hydride migration to an alkene Coordination number increases during intermediate Needs a vacant site M-C-C-H group must be syn coplanar Must have a beta-hydrogen for beta-elimination to take place Reaction Steps

19. α - elimination Alpha-elimination is the reverse of hydride migration to an alkylidene (Carbene) Usually not seen if beta-elimination is possible due to the less favourable transition state Reaction Steps

20. Reaction Steps - Test What reaction steps are required for the conversion… Mn(CO) 5 Me + CO  Mn(CO) 5 (COMe) Reaction Steps

21. Reaction Steps - Test Draw a balanced scheme showing beta-hydride elimation from [Cp 2 Ti(n-Pr)] + Reaction Steps

22. Reaction Steps - Test Complex of the type Pt(PR 3 ) 4 can form PtCl 2 (PR 3 ) 2 when reacted with HCl: suggest an explanation for this result, including a reaction scheme naming the elementary reactions involved and showing the byproducts. Reaction Steps

23. Addition to Alkene Hydrogenation Catalysed by: Wilkinson’s Catalysis RhCl(PPh 3 ) 3

24. Hydrogenation - Test Addition to Alkene Treatment of the ionic rhodium complex [Rh(COD) 2 ][BF 4 ] (COD = cyclo-octa-1,4-diene) with bis(diphenylphosphino)ethane (‘dppe’) in n-butanol leads to the formation of a highly- effective system for the hydrogenation of alkenes (a)Draw a catalytic cycle for the conversion of ethene and hydrogen to ethane with this system

25. Hydrogenation - Test Addition to Alkene Treatment of the ionic rhodium complex [Rh(COD) 2 ][BF 4 ] (COD = cyclo-octa-1,4-diene) with bis(diphenylphosphino)ethane (‘dppe’) in n-butanol leads to the formation of a highly- effective system for the hydrogenation of alkenes (a)Draw a catalytic cycle for the conversion of ethene and hydrogen to ethane with this system

26. Hydrogenation - Test Addition to Alkene Treatment of the ionic rhodium complex [Rh(COD) 2 ][BF 4 ] (COD = cyclo-octa-1,4-diene) with bis(diphenylphosphino)ethane (‘dppe’) in n-butanol leads to the formation of a highly- effective system for the hydrogenation of alkenes (b) Give electrons counts for each of the intermediates. 1234512345 NA 12 14 16 14

27. Hydrogenation - Test Addition to Alkene Treatment of the ionic rhodium complex [Rh(COD) 2 ][BF 4 ] (COD = cyclo-octa-1,4-diene) with bis(diphenylphosphino)ethane (‘dppe’) in n-butanol leads to the formation of a highly- effective system for the hydrogenation of alkenes (c) State the oxidation state of the metal centre in each of the intermediates 1234512345 NA 12 14 16 14 NA (I) (III)

28. Hydrogenation - Test Addition to Alkene Treatment of the ionic rhodium complex [Rh(COD) 2 ][BF 4 ] (COD = cyclo-octa-1,4-diene) with bis(diphenylphosphino)ethane (‘dppe’) in n-butanol leads to the formation of a highly- effective system for the hydrogenation of alkenes (d) Name each of the reaction steps in the catalytic cycle. ABCDEABCDE Dis/Associaton Ligand Exchange Oxidative Addition Alkene Binding Hydride Migration Reductive Elimination

29. Phosphine Ligands  The phosphine ligand is one of the best ligands for hydrogenation  Good two electron donor with steric tuning of coordination sphere and metal accessibility by changing the phosphine substituents (pi-acidity and tolman cone angle)  Fast turnover needs  Bulky group favours dissociation  Good donors favour oxidative addition Addition to Alkene

30. Chiral Hydrogenation  The hydrogenation of an unsymmetrical alkene like this will result in stereoisomers due to a chiral compound  If you need a specific isomer you need to use a chiral catalyst, and to do this you need chiral ligands.  Chiral phosphines are the best due to the above reasons Addition to Alkene BINAP-(R)

31. Transfer Hydrogenation Addition to Alkene You do not need to use pure hydrogen and an alkene. A secondary alcohol and an imine works just as good. Remember nitrogen has lone pair to coordionate Arene Hydrogenation Has cis stereospecificity. Only one face of an aromatic is hydrogenated

32. Addition to Alkene Hydrosilation Catalysed by: A range of well-defined complex: Fe, Mn, Co, Ru, Rh, Ir, Pd and Pt examples. Related to hydrogenation but with SiR 3 as a ‘super-proton’ First developed by H 2 PtCl 6 Strong tendency to form linear products

33. Addition to Alkene Hydrocyanation

34. Addition to Alkene Hydroformylation oxo-reaction Catalysed by: HCo(CO) 4 / HRh(PPh 3 ) 2 (CO) Cobalt: Harsh Conditions. Moderate selectivity, competitive hydrogenation Rhodium: Mild conditions. Excess phosphine needed for high selectivity Addition of a hydrogen atom and a formyl (CHO) group to an alkene

35. Addition to Alkene Addition to Alkene - Test Suggest a plausible mechanism for the reaction and catalysed by Wilkinsons catalyst

36. Addition to Alkene Addition to Alkene - Test Suggest a plausible mechanism for the reaction and catalysed by Wilkinsons catalyst

37. Carbonylation HydroformylationAdding CO + H 2 to a substrate CarbonylationAdding just a CO to a substrate The most important carbonylation reaction is the conversion of methanol to acetic acid R-OH + CO  R-COOH Acetate Derivatives Acetic AcidH 3 CCOOH AcetaldehydeH 3 CCHO Methyl AcetateH 3 CCOOMe Vinyl AcetateH 3 CCOOCH=H 2 Acetic acid is manufactured on large scale!

38. Carbonylation Carbonylation Catalysts Cobalt-basedReppe/BASF Rhodium-basedMonsanto [RhI 2 CO 2 ] - Iridium-basedBP Cativa Better than rhodium at forming alkyl bond Rate-limiting step is methyl migration Kinetics more complicated than Monsanto process Reaction ‘promoted’ by species such as [Ru(CO) 3 I 2 ] 2 Mechanism likely to involve neutral and anionic species and competing processes

39. Carbonylation The Monsanto Process Rhodium-based

40. Carbonylation Polyketone formation Catalyst: [PdL 2 (OR)] +

41. Coupling Grignard Reagents  Grignard reagents couple with aryl halides Catalyst: Ni(acac) 2 / (dppe)NiCl 2 / FeCl 3 / CoCl 2 / CrCl 2 Coupling Reactions

42. Organometallic Coupling  Negishi coupling Catalyst: (Ph 3 P) 4 Ni / (Ph 3 P) 2 PdCl 2 | Coupling an aryl halide with an organozinc (RZnX)  Stille coupling Catalyst: Pd(dba) 3 | Coupling an aryl halide with an organotin reagent (RSnR’ 3 )  Make sure you have no beta-hydrogens  Alkyl < benzyl ~ allyl < aryl < alkenyl < alkynyl (reactivity from transfer from tin)  Me 3 Sn best choice for control but t Bu 3 Sn much safer  Bulky phosphine ligands and highly basic additives (CsF) facilitates cross coupling of aryl chlorides Coupling Reactions

43. Organometallic Coupling Coupling Reactions

44. Organometallic Coupling Mechanism Coupling Reactions Catalyst: Can be Pd(0) or Pd(II) pre-catalyst

45. Mizoroki-Heck reaction Mechanism Coupling Reactions Catalyst: Can be Pd(0) or Pd(II) pre-catalyst | Note number of ligands can change PdL n

46. Coupling Reactions - Test A palladium-catalysed coupling may be carried out using either a Suzuki or a Stille protocol. What are the advantages of each approach? Coupling Reactions Stille Organotin complexes Reaction is facile (low temp, fast), but starting materials are still stable in air so practically east Suzuki Organoboron complexes Low toxicity of starting material and byproducts Some boronic acids commercially availiable

47. Carbenes  Carbene is defined as a neutral divalent carbon. Free carbenes can be formed. Looking at metal-carbine complexes Fischer Carbenes  Metal in low oxidation state  Heteroatom substituents on carbene cation Schrock Carbenes  Metal in high oxidation state  Substituents on carbene carbon usually carbon or hydrogen  Carbene may be called an alkylidene Nucleophilic Carbenes  Ideally carbine ligands introduced like phosphines using free carbine  Wanzlick proposed stabilisation using heteroatom substiuents Carbenes ` ` ``

48. Metal-Carbene Bonding Carbenes Free carbenes may be either in triplet (sp) or singlet (sp 2 ) state Bonding to metals is best described by invoking singlet carbenes As with phosphines, this allows bonding from carbene to metal (lone pair in sp 2 orbital) and back-bonding (to empty p orbital) Back bonding is significant in fisher and schrock carbenes but not with nucleophilic carbenes For electron counting all carbenes donate two electrons For oxidation state: Fisher / Shrock carbenes (alylidenes) are dianionic (-2) Nucleophillic carbenes are neutral (phosphines)

49. Carbenes / Coupling - Test Why might the complex below be a better catalyst for both of these coupling routes than the more ‘traditional’ palladium-phosphine systems [Ar = 2,6-(i-Pr) 2 C 6 H 3 ]? Carbenes N-Heterocyclic carbene ligand will bind tightly to metal preventing formation of Pd metal, pyridine ligand is labile so rapidly forms free site

50. Metathesis Alkene Methesis – Very small free energy differences Equilibria must be driven (for example loss of gas) Schrock’s Catalysts Highly active React with hindered alkenes Control reactivity by altering alkoxide groups Poor functional group tolerance Grubb’s Catalysts 3 different types Undergo the following mechanism Metathesis

51. Metathesis Mechanism The Chauvin Mechanism Metathesis

52. Metathesis in synthesis Metathesis

53. Metathesis / Carbene - Test Metathesis Treating EtOCH=CH 2 with RuCl 2 (PCy 3 ) 2 (CHPh) (Grubbs’ I) does not lead to catalytic turn- over but gives a stable metal complex and one equivalent of a styrene (PhCH=CH 2 ) as a byproduct. Predict the structure of this product and explain why the reaction is stoichiometric.

54. Alkene Polymerisation Ziegler Catalyst TiCl 4 Activated by AlEt 3 Mild Conditions Controlled process: Yields HIGH DENSITY linear polymer TACTICITY ISOTATIC SYNDIOTATIC ATATIC

55. Cossee-Arlman Mechanism Alkene Polymerisatioin

56. Metallocene Mechanism Alkene Polymerisatioin

57. MAO Methylaluminoxane Alkene Polymerisation Hydrolysis of AlMe 3 gives MAO [-Al(Me)-O-]n

58. Co-Catalysts and Activators Alkene Polymerisation Triphenylcarbenum (trityl) salts [Ph 3 C] + powerful alkyl abstractor

59. Ligand Symmetry and Tacticity Alkene Polymerisation

60. Alkene Polymerisation Catalysts Alkene Polymerisation Essential Features: Electron Deficiency Vacant coordination site adjacent to the growing polymer chain Steric protection at the metal centre to prevent beta-hydride elimination Cations and Anions

61. Alkene Polymerisation - Test Alkene Polymerisation Show how MAO activates metal halide complexes containing bidentate ligands to act as polymerisation catalysts: use the general formula (L-L)MX 2 to represent the pre-catalyst What other role does MAO play in the reaction? What is the mechanism for polymerisation of alkenes by the activated catalyst?

62. PAST EXAM PAPER MODEL ANSWERS Alkene Polymerisation

63. Transfer Hydrogenation Hydroformylation Alkene Metathesis Alkene Polymerisation