1. Each X will increase the oxidation number of metal by +1.
Each L and X will supply 2 electrons to the electron count.

3. Now looking at compounds having a charge of +1 to obey 18 e rule.
Elec count: 4 (M) +2 (NO) +12 (L6) = 18
NO+ is isoelectronic to CO
X increases O N by 1
Elec Count: 4 (M) + 4 (L2) + 10 (L5)

4. Actors and spectators
Actor ligands are those that dissociate or undergo a chemical transformation
(where the chemistry takes place!)
Spectator ligands remain unchanged during chemical transformations
They provide solubility, stability, electronic and steric influence
(where ligand design is !)

5. Organometallic Chemistry 1.2 Fundamental Reactions

6. Fundamental reaction of organo-transition metal complexes
D(FOS)
D(CN)
D(NVE)
Association-Dissociation of Lewis acids ±1
Association-Dissociation of Lewis bases ±2
Oxidative addition-Reductive elimination
Insertion-deinsertion
FOS: Formal Oxidation State;
CN: Coordination Number
NVE: Number of valence electrons

7. Association-Dissociation of Lewis acids
D(FOS) = 0; D(CN) = ± 1; D(NVE) = 0
Lewis acids are electron acceptors, e.g. BF3, AlX3, ZnX2
This shows that a metal complex may act as a Lewis base
The resulting bonds are weak and these complexes are called adducts

8. Association-Dissociation of Lewis bases
D(FOS) = 0; D(CN) = ± 1; D(NVE) = ±2
A Lewis base is a neutral, 2e ligand “L” (CO, PR3, H2O, NH3, C2H4,…)
in this case the metal is the Lewis acid
Crucial step in many ligand exchange reactions
For 18-e complexes, only dissociation is possible
For <18-e complexes both dissociation and association are possible
but the more unsaturated a complex is, the less it will tend to dissociate a ligand

9. D(FOS) = ±2; D(CN) = ± 2; D(NVE) = ±2
Oxidative addition-reductive elimination
D(FOS) = ±2; D(CN) = ± 2; D(NVE) = ±2
Vaska’s compound
Very important in activation of hydrogen

10. Oxidative addition-reductive elimination
H becomes H-
Concerted reaction
Vaska’s compound
via
Ir: Group 9
cis addition
CH3+ has become CH3-
SN2 displacement
trans addition
Also radical mechanisms possible

11. Oxidative addition-reductive elimination
Not always reversible

12. Insertion-deinsertion
D(FOS) = 0; D(CN) = 0; D(NVE) = 0
Mn: Group 7
Very important in catalytic C-C bond forming reactions
(polymerization, hydroformylation)
Also known as migratory insertion for mechanistic reasons

13. Migratory Insertion
Also promoted by including bulky ligands in initial complex

14. Insertion-deinsertion The special case of 1,2-addition/-H elimination
A key step in catalytic isomerization & hydrogenation of alkenes
or in decomposition of metal-alkyls
Also an initiation step in polymerization

15. Attack on coordinated ligands
Very important in catalytic applications and organic synthesis

16. Some examples of attack on coordinated ligands
Nucleophilic addition
Electrophilic addition
Nucleophilic abstraction
Electrophilic abstraction

17. Organometallic Chemistry
Brooklyn College
Chem 76/76.1/710G Advanced Inorganic Chemistry (Spring 2009)
Unit 6
Organometallic Chemistry
Part 2. Some physical and chemical properties of important classes
of coordination and organometallic compounds
Suggested reading:
Miessler/Tarr Chapters 13 and 14

18. Metal Carbonyl Complexes
CO as a ligand
s donor, π-acceptor
strong trans effect
small steric effect
CO is an inert molecule that becomes activated by complexation to metals

19. “C-like MO’s”
Frontier orbitals
Larger homo lobe on C

20. Mo(CO)6 anti bonding “metal character” non bonding “18 electrons”
6CO ligands x 2s e each
12 s bonding e
“ligand character”

21. Metal carbonyls may be mononuclear or polynuclear

22. Synthesis of
metal carbonyls

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

24. Effect of other ligands
Effect of charge
u(free CO) cm-1
Lower frequency, weaker CO bond
Effect of other ligands
PF3 weakest donor (strongest acceptor)
PMe3 strongest donor (weaker acceptor)

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

26. 13C NMR spectroscopy
13C is a S = 1/2 nucleus of natural abundance 1.108%
1.6% as sensitive as 1H only
For metal carbonyl complexes d ppm (diagnostic signals)
Very long T1
(use relaxation agents like Cr(acac)3 and/or enriched samples)

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

28. 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

29. 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

30. Tolman’s electronic and steric parameters of phosphines

31. 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

32. 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

33. Synthesis of metal hydride complexes

34. 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) = Hz
Coupling between inequivalent hydrides J(H-H) = 1-10 Hz
Coupling to 31P of phosphines J(H-P) = Hz cis; Hz trans
IR spectroscopy
n(M-H) = cm-1 (terminal); cm-1 bridging
n(M-H)/n(M-D) = √2
Weak bands, not very reliable

35. 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

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

37. 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)

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

39. Effects of coordination on the C=C bond
Compound
C-C (Å)
M-C (Å)
C2H4
1.337(2)
C2(CN)4
1.34(2)
C2F4
1.31(2)
K[PtCl3(C2H4)]
1.354(2)
2.139(10)
Pt(PPh3)2(C2H4)
1.43(1)
2.11(1)
Pt(PPh3)2(C2(CN)4)
1.49(5)
2.11(3)
Pt(PPh3)2(C2Cl4)
1.62(3)
2.04(3)
Fe(CO)4(C2H4)
1.46(6)
CpRh(PMe3)(C2H4)
1.408(16)
2.093(10)
C=C bond is weakened (activated) by coordination

40. Characterization of metal-olefin complexesIR
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

41. Synthesis of metal-olefin complexes
[PtCl4] C2H4  [PtCl3(C2H4)]- + Cl-
RhCl3.3H2O + C2H4 + EtOH  [(C2H4)2Rh(m-Cl)2]2

42. Reactions of metal-olefin complexes

43. Metal alkyl, carbene and carbyne complexes

44. 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
W(CH3)6
Ti(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)

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

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

47. Fischer-carbenes

48. Schrock-carbenes Synthesis Typical reactions
+ olefin metathesis (we will speak more about that)

49. Grubbs carbenes
Excellent catalysts for olefin metathesis

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

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

52. Comparison of heterogeneous and homogeneous catalysts
Usually distinct solid phase
Readily separated
Readily regenerated and recycled
Rates not usually as fast as homogeneous
May be difussion limited
Quite selective to poisons
Lower selectivity
Long service life
Often high-energy process
Poor mechanistic understnding
Same phase as reaction medium
Often difficult to separate
Expensive/difficult to recycle
Often very high rates
Not diffusion controlled
Usually robust to poisons
High selectivity
Short service life
Often takes place under mild conditions
Often mechanism well understood
Difficulties in separation and catalyst regeneration have
prevented a wider use of homogeneous catalysts in industry

53. Fundamental reaction of organo-transition metal complexes
D(FOS)
D(CN)
D(NVE)
Association-Dissociation of Lewis acids ±1
Association-Dissociation of Lewis bases ±2
Oxidative addition-Reductive elimination
Insertion-deinsertion

54. Combining elementary reactions

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

56. Completing catalytic cycles
Olefin isomerization

57. (reductive elimination)
Completing catalytic cycles
Olefin hydrogenation
(reductive elimination)

58. Completing catalytic cycles
Olefin hydrogenation

59. 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

60. The mechanism of olefin hydrogenation by Wilkinson’s catalyst

61. 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

62. 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

63. What else could happen if CO is present?
Olefin hydrogenation
(reductive elimination)
What else could happen if CO is present?
CO insertion
reductive elimination

64. Olefin hydroformylation

65. 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)

66. Catalytic synthesis of polyolefin

67. 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

68. 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

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

70. Polymerization mechanism

71. The catalytic synthesis of acetaldehyde
(Wacker process, oxidation of ethylene)
Pd(0) + 2CuCl2
PdCl 2
+ 2Cu Cl
2Cu Cl
+ 2HCl + 1/2O 2
Cl2 + H O

72. The catalytic synthesis of acetaldehyde
(Wacker process, oxidation of ethylene) C 2 H 4
+ PdCl CH 3
CHO + Pd(0) HCl
Nucleophilic attack

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

75. The metathesis mechanism (Chauvin, 1971)