Cyclopentadiene-TM, Ferrocene complex .pdf

Organometallic chemistry- Ferrocene
Synthesi Structure and reaction

1. Metal-Cyclopentadienecomplexes
1

2. •η
5-Cyclopentadienylor“Cp”isoneofthemostcommonligands
encountered inorganotransition-metalchemistry
•Complexesofthisligandareknownforalltransitionandmostf-
block metals
•Thegroupisaprincipalmemberoftheclassofplanararomatic
ligandssuch asbenzene
2

3. •Itplayedmajorroleinthedevelopmentoforganometallicchemistry
•Althoughthepot.derivativeofcyclopentadienideanionwasdescribedas
earlyas1901byThiele,yetanexcitingphaseinmetalcyclopentadienyl
chemistrybeganinearly1950’swiththediscoveryof ‘ferrocene’
•Ferrocenehave a novel ‘sandwich’ structure with all the carbons of both
the Cpringswithinbondingdistanceof themetalatom
3

4. •largenumberofTM-Cp complexes known
•Fact:Cpligandboundfirmlytothemetalatomandmostinertto
nucleophilic andelectrophilicattack
(η
5-C5H5)2M complexesformedbythereactionbetweentheCpanionand
suitablederivativesof theTMsare--->metallocenes
4

5. Ex:(η
5-C5H5)2Fe
Ferrocene
(η
5-C5H5)2Ni
Nickelocene
(η
5-C5H5)2Co
Cobaltocene
Ferroceneisthemostimportantmetallocene
Highlystableanddecomposesabove500°C,onlyairstablemetallocene
Ferrocenewasdiscoveredaccidentallybytwo independent groups (1 group: TJ
Kealyand P.L. Pausonin1951, other group: S.A.Miller, J.A.Tebboth and
J.F.Tremaine, 1952) *
TwoscientistsnamelyGWilkinson& Woodward and E.O.Fischer independently
deduce structurelater in1954.JointNobelprizein1973
5

6. •Theyproposedthatitisadoubleconestructurewiththebaseofthecone
representedbytwocyclopentadieneligandandmetalbeingatthecenter.
•Diamagnetic,18valenceelectron(2Cpringscompletenoblegas
configuration of iron)
6

7. Classification of η
5-Cp-TMderivatives
•Onthe basisofreactivity:
1)Covalentandoxidativelyaswellasthermodynamicallystable
(Ex: Ferrocene,Ruthenocene)
2)Covalentand highlyreactive
(Ex:Titanocene,Molybdenocene)
3)Ionic
(Ex:Manganocene,Lanthanocene)
7

8. •Onthebasisofstructure:
a)Symmetrical “sandwich” type derivatives , M(Cp)2METALLOCENES
with mutuallyparallelCprings
Ex: Fe(η
5-C5H5)2,Co(η
5-C5H5)2,Mn(η
5-C5H5)2
ParallelCpringseithereclipsedorstaggeredintheirorientationwitheach
other.
EclipsedinV(Cp)2,Cr(Cp)2andRu(Cp)2 inCo(Cp)2and
Fe(Cp)2
8

9. b)Bentmetallocenederivatives,(Cp)2MLx,inwhichtermxofunidentate
ligandsL(H
-,R,CO,etc) variesbetween1and3.
Here2Cpringsnotparallel,anglebetweenthenormalstoeachring,180°
Ex:Cp2Mo(CO),(Mo(II),d
4),Cp2FeH
+,(Fe(IV)d
4)Cp2Zr(Cl)H(Zr(IV)d
0)
c)Half-sandwich compounds,CpMLyin which number y of unidentate
ligands Lvariesfromonetofour
9

10. Ex:Mn(CO)2(PPh3)(η
5-C5H5),Co(CO)2(PPh3)(η
5-C5H5)
CpMLyareoftenreferredtoas“two-,three-,or four-leggedpiano
stools,”withtheCpbeingregardedasthe“seat”andtheotherligandsas
the “legs.”
Themetallocenes,MCp2arealsoimportantinthehistoricaldevelopment
of organometallicchemistry,
Buttheirchemistryissomewhatlessrichthanthatofthepianostools:
10

11. •fewerligandscanbindtothemetalloceneswithoutoversteppingthe
18e
-limit.
•Theirmostimportantapplicationisalkenepolymerization.
•ThesandwichstructureoftheorangecrystallineCp2Fewasdeducedby
WilkinsonandWoodwardandbyFischer in1954.
•Oneofthemostsignificantdiscoveriesduringtheearlydevelopmentof
organotransitionmetalchemistryandhelpedtolaunchitasan
independent fieldinitsownright.
11

12. •Formation of di-andpoly-nuclear
derivatives withsimilaror different
metalatomsinthesamemoleculeleads
to further structural diversification
•Cp can act as mono-hapto,tri-hapto
and penta-haptoligand
12

13. •The η
1structure is found where the coligands are sufficiently firmly
bound sothattheCpcannotrearrangetoη
5
•Trihapto-Cpgroupsareratherrare,theCpfoldssotheuncomplexed
C=Cgroupcanbendawayfromthemetal.
13

14. •There are cases in which 18e
-piano
stool complexes have been found to
undergosubstitutionbyan
associative mechanism,anditis
therefore assumed thatthe Cp can
slip inthetransition state.
14

15. •Rearrangement of an η
5Cp to a
stable η
1structureon the addition
ofaligand isalso known:
•In this casetwo other possible
rearrangements that might have
relieved the electron count on the
metal:
bendingoftheNOor
methylmigrationto CO.
•It is likelythat one of these
two processes may be
important in the initialattack
of the phosphine, but that slip
ofthe Cpgives thestable
product shown.
21

16. •η
1-CpgroupstendtoshowbothlongandshortC−Cdistances,as
appropriate for anuncomplexeddiene.
•The η
5form has essentially equal C=C distances, and the substituents
bend veryslightlytowardthemetal.
•Indiamagneticcomplexes, groups usuallyshow a resonancein the
1HNMRspectrumat3.5–5.5δ,asappropriateforanaromaticgroup.
16

17. •ThisaromaticitywasoneofthefirstpropertiesoftheCpgrouptoattract
the attentionof
•RobertWoodward,thecelebratedorganicchemist,whoshowedthat
ferrocene, likebenzene,undergoes
•η
1-Cpgroupscanshowamorecomplex
1HNMRpattern:
•The αhydrogen appearsat about3.5δ and
at5–7δ.
17

18. Preparation
FirstmetallocenediscoveredaccidentlybyT.JKealyandP.L.Pausonin
1951
theyweretryingtosynthesize by the dimerization of Cp.
CpMgBrin(Et)2OwithFeCl3
18

19. •Insteadoffulvalene,endedupwithorangecrystalscontaining
with remarkablestability
•Theinitialstepgenerallyinvolvedinthepreparationofcyclopentadienyl
derivatives of TMs is the reaction of
compound withanionicspecies suchas
or some other suitable
(M=Li,Na,K,Mg,Tl)
19

20. •Cyclopentadienylchemistrystartedin1901,whenThieleuseditinthe
preparation of pot.cyclopentadienide
H
H
H
H
2
150
o
C
300
o
C
Dicyclopentadiene Cyclopentadiene
K+C5H6 55K
+CH
-+1/2H
2
PhH
C
5H
6+EtMgBr
Et
2O/PhH
C
5H
5MgBr+C
2H
6
20

21. OtherPreparationmethods
1.Reactionofcyclopentadienewithmetal
M+C5H6
K+C5H6
-
MC5H5
-+1/2H2
(M=Li,Na,K)
K
+C5H5+1/2H2(Thielein1901)
M+2C5H6 (C5H5)2M+H2(Miller,Tebboth,Tremaine in
(M=Mg,Fe) 1952)
562CH+Fe (CH)Fe+H
552 2
500
oC
300
oC
Al,Mooxide
THF
THF
C
5H
6+Tl
2SO
4
KOH
Tl
+
CH
-
55+
CH
26
21

22. 2. Starting fromsodiumcyclopentadienide
22

23. MCl+2NaCH
2 55 552(CH)M
M=V, Cr, Mn, Fe, Co
Solvent=THF,DME, Liq.NH3
Solvent
23

24. 3.treatmentofCpwithmetalhalidesinthepresenceofexcessstrongbase
24

25. •Forunderstandingnatureofbondinginmetallocenesbytakingexample
offerrocene,
pictureforcyclopentadienide•firsthaveto
ligand(s)
•Then which have the correct symmetryand
energiestooverlapwiththeligandgrouporbitalsfor effectivebonding
25

26. •Cyclopentadienideanion-delocalizedstructure(i.e.,non-localized
multiplebonds)
•Alltheten(5Cand5H)atomsarecoplanar,withthesamecarbon-carbon
bondlength(1.39A),intermediatebetweenthoseofethene(1.34A)and
ethane(1.54A)andissimilartothatinbenzene
26

27. StructureandBonding
•Each C-atom of the cyclic planar
C5H5group issp
2hybridised
•Each carbon has a singly filled
2pzatomic orbitalperpendicular
to themolecularplane
•TheseAOstakepartinlinear
combinationproducingfiveπ
MOs(3BMOsand2ABMOs)
27

28. 28

29. •Themostimportantoverlapsareψ1withthemetaldz
2
•ψ2and ψ3withthe dxzand dyzorbitals
•ψ4andψ5with d
x
2
-y
2
and d
xybut not interact very
stronglywithmetalorbitals,
29

30. •TheCpgroupisthereforenot aparticularlygoodπacceptor.
fromthemetaltothe
•ThisfactandtheanionicchargeonCpsuggests:
Cpcomplexesare ,
The presence of the Cp
otherligandspresent.
If weputtwoCpgroupsandonemetaltogether,weobtaintheMO
diagramfor ametallocene
30

31. •The d-orbitalsplittingpatternforan
octahedralcrystalfield,highlightedina
box
•Have tolookatthe symmetryof pairsof
Cp orbitalsandseehowtheywillinteract
with themetalorbitals.
31

32. •Indevelopingtheligandgrouporbitalsforapair ofC5H5rings,
MOsof thesameenergyandsamenumberof nodespairup;for
example,thezero-nodeorbitalof oneringpairupwiththezero-node
orbital of theother.
Molecular orbitalspairupinsuchawaythatthenodalplanesare
coincident.
Furthermore,ineachpairingtherearetwopossibleorientationsofthe
ring molecular orbitals:
32

33. inwhichlobesoflikesignarepointedtowardeachother,and
oneinwhichlobesofoppositesignarepointedtowardeach
other.
•Forexample,thezero-nodeorbitalsoftheC
5H
5ringsmaybe
pairedin the following two ways:
33

34. •Bondinginteraction
(Gerade set)
Anti-bondinginteraction
(Ungerade set)
Orbital lobes of
opposite sign pointed
towardeachother
Orbitallobesoflike
signpointedtoward
eachother
34

35. •Eightothergrouporbitals
arisingfromthe C5H5ligands are
35

36. •II
Interactionofψ1MO’softwoCpunitstogivegroup orbitals
36

37. •As anexample,takethecombinationof
the ψ1’sofbothrings,which hasthe
symmetry labela1g, itcaninteractwith
thedz
2
orbital onthe metal,
•Takingtheoppositecombinationof ψ1’s
(labeled asa2u),theinteractionnow takes
place withpz.
37

38. •i.e.,ifbothringshavethe+velobesoftheirlowestenergyorbitalsonthe
sidesnearertothemetal,thensanddz
2
orbitals would have the correct
symmetry
•If oneof theringshasthe+velobesneartothemetalandfor theother
ring, the -ve lobe is nearer to the metal, the pzorbital has the correct
symmetry
38

39. •Interactions, between the dyz
orbital of metal andits
appropriate group orbital i.e; one
ofthe 1-node grouporbitals
39

40. Thecompleteenergyleveldiagram forthemolecularorbitalsofferrocene
40

41. •Themolecularorbitalresultingfromthedyzbondinginteraction,labeled
1intheMOdiagram,containsapair ofelectrons.
•Its counterpart,2,is
•Theorbitalsofferrocenethatareofmost are those having the
greatest ; these arealso theHOMO and LUMO
•TheseorbitalsarehighlightedintheboxinFigure
41

42. character,are•Twoof theseorbitals, havinglargely
and are
•One,havinglargelycharacter,isessentially andisalso
•Two,havingprimarilyandcharacter,
•Therelativeenergiesoftheseorbitalsandtheird-orbital-group-orbital
interactions areshownas:
42

43. 43

44. *
44

45. •A perusal of the MO diagram for ferrocene indicates that ligand group
orbitals canbecategorisedinthreesets:
a filled pair ofa1ganda2usymmetry
ahigher energyfilledsetof e1gande1usymmetry
andevenahigher energyunfilledsetof e2gande2usymmetry
The metal dxzand dyzorbitals (e1gsymmetry) interact more effectively
withthecyclopentadienylligandgrouporbitalsthanthemetals(a1g);px,
py(e1u);andpz(a2u)orbitals.
45

46. •Thesebondsprovidemostofthestabilizationthatholdstheferrocene
molecule together
•Thee2gligandorbitalsinteractwiththemetal3dx
2
-y
2
and3dxyorbitals
producing slightly BMOswhich comprise mostly of metal orbitals.
•BasedontheMOdiagramof ferrocene,where9MOs(a
1g
b
to a
1g
nb
)
of thelowest energyareoccupiedbye-sisthemoststable
metallocene
46

47. •Theoverallbondinginferrocenecanbesummarizedas:
•The occupied orbitals of the η
5-C5H5ligands are stabilized by their
interactions withiron.
•Especiallythestabilizationinenergyof0-nodeand1-nodegroup
orbitalsthathavebondinginteractionswiththemetal,formingmolecular
orbitals thatareprimarilyligandinnature
•(thesearetheorbitalslabeled,fromlowesttohighestenergy,a
1g, a
2u ,
e
1gsetand e
1uset).
47

48. •Theorbitalsnexthighestinenergy(i.e., e
2gset, a
1g
nb
and e*
1gset) are
largelyderivedfromirondorbitals;theyarepopulatedby6electrons
fromiron(II),ad
6metalion.
•Thesemolecularorbitalsalsohavesomeligandcharacter,withthe
exceptionof themolecular orbitalderivedfromdz
2
.
•Themolecularorbitalderivedfromhasalmost
,
becauseitscone-shapednodalsurfacepointsalmostdirectlytowardthe
lobesofthematchinggrouporbital,makingoverlapslightandgiving
48

49. anessentially orbital localized onthe iron.
•Themolecularorbitaldescriptionof fitsthe rule.
•Inthecaseofferrocene,allthebonding(both ligandand metal
characterorbitals)and nonbonding(dz
2
)orbitalsareexactlyfilled
49

50. •Metallocenesfromgroups9(Co,d
7)and10(Ni,d
8)haveoneor two
in
(20e)are
orbitals; thisis whyCoCp2(19e) and NiCp2
and muchmore reactivethanferrocene.
•Theextraelectronshaveimportantchemicalandphysicalconsequences:
themetal-liganddistanceincreases,andΔHformetal-liganddissociation
decreases.
•CobaltoceneandNickelocenereadilylosee
-
sinABMOtoattain18e
configuration.
50

51. •Manyofthechemicalreactionsof thelatterarecharacterizedbya
tendency toyield18-electronproducts.
•Cobaltocenealsohasan18ecationicform,Cp2Co
+.
•Cobalticiniumreactswithhydridetogiveaneutral,18-electron
sandwichcompoundinwhichonecyclopentadienylligandhasbeen
modified intoη
4-C5H6,
51

52. Although isoelectronic with [Fe(Cp)
2], [Co(Cp)
2]
+
(18e-)
shows more oxidative stability
=> In [Co(Cp)
2]
+
, Co is in Co(III), while in ferrocene Fe is
in Fe(II)
52

53. Chromoceneand andvanadocenehavefewerthan 18e and are also
paramagnetic,astheelectronoccupationdiagrampredicts.
•d
5ions have no crystal field stabilization in their high-spin form,
thereforehigh-spinMnCp2(5unpairede
-s)isveryreactiveandstrongly
ionic incharacter.EC: (e
2g
b
)
2
(a
1g
nb
)
1
(e
1g
*
)
2
•Thehigher-fieldligandC5Me5,(pentamethyl cyclopentadienyl)onthe
otherhand,givesalow-spin manganocenewhichisstable(1unpaired
e
-)EC: (e
2g
b
)
4
(a
1g
nb
)
1
(e
1g
*
)
0
53

54. Thedorbitaloccupationpatternsforsomefirst-rowmetallocenes.
54
e
2g
b
(d
x
2
-y
2
, d
xy)
a
1g
nb
(d
z
2
)
e
1g
*
(d
xz, d
yz)

55. [Mn(Cp)
2] is high spin while [Re(Cp)
2] is a low spin
complex
Re heavier congener of Mn
Hence higher crystal field splitting power
55

56. 56

57. and metalloceneswhichdonotsatisfythe18eruleare
and difficulttoisolate
•Thesesubstancesshowapronouncedtendencytoformadditional
covalent bonds: Cp rings tilted back from their parallel positions
•This changes the MO energy diagram.
•Tilting of Cp-rings allows the a
1g
nb
and e
2g
b
(degenerate) orbitals
to create threenew MOs through their appropriate mixing.
57

58. •These three MOs can accommodate 6 electrons.
•In this event, the lower 6 MOs (i.e. upto e
1u
b
) remain more or less
unpurturbed.
•These 6 MOs accommodate 12 electrons and 3 new MOs can
accommodate 6 electrons to give the 18e configuration
•Ex: [(η
5
-Cp)
2Re-H], [(η
5
-Cp)
2Mo(H)
2], [(η
5
-Cp)
2Ti(CO)
2], [(η
5
-
Cp)
2Ta(H)
3]
•For ex, Cp2Re(17e) and Cp2Re
+(16e) are unstable, Cp2ReH is very
stable
58

59. Inferrocene,ironatomissandwichedbetween two parallel and planar
cyclopentadienyl rings
Twoconformations:staggered(D5dsymmetry)andeclipsed(D5h)
Properties
59

60. Both the forms are in transition
Energybarrier torotationisverylow(≤5kJ/mol)
Structural featuresofferrocenebelow 169Kare:
C-C distance 139+/-6pm
Fe-Cdistance203+/-2pm
All the C’sareat equidistant fromFe
60

61. PROPERTIES
Ferrocene: Orangecolouredcrystallinecompound MP:173C
Diamagnetic
Thermally stable,decomposeabove500℃Stable toair and H2O
Unattacked by boilingNaOH andHCl
Can be oxidisedto blueferrociniumion
Reversible
61

62. •Metallocenes of other 3d-
transition metals also intensly
coloured
62

63. •Cyclopentadienyl derivatives of
TMs available invarious
ox.states
Ex: [CpMo(CO)3]
-
, CpMn(CO)3,
Fe(Cp)2, [Co(Cp)2]
+,TiCl2(Cp)2,
NbBr3(Cp)2
•with central metals in
0,1,2,3,4 & 5 ox.states
respectively
•Metallocenes from the 3d
transition series -generally
paramagnetic
•Exception: Fe(η
5-C
5H
5)
2,
[Co(η
5-C
5H
5)
2]
+andTi(η
2-
Cp)
2
63

64. Cprings are aromaticin nature
NotypicalreactionsofDiene,i.e.,Diels-Alderreaction
Cpringsofferrocenereadilyundergoelectrophilicsubstitutionreaction
characteristic of aromaticcompound
Ferrocenesbehaviourasanelectronricharomaticcompound,itsfacile
metallationandunusualabilitytostabilisecarbocationsatitsbenzyliclike
positionarepropertieswhichpavethewaytopreparefunctionalised
substituted ferrocene
64

65. Theeaseofelectrophilicsubstitution,scopeofhavingplanarchiralityand
redoxactiveironatomfacilitatedthedevelopmentofferrocenechemistry
indiversedirections
Majorinterestinferrocenechemistryiscenteredarounddevelopingchiral
chelatingligandswithplanarandlateralchiralityandtheiruseasprochiral
ligandinasymmetriccatalysis
UseofFerrocenophanesasprecursorsforferrocenebasedpolymer-another
application
65

66. Ferroceneisaromaticandtheorganicchemistryisimportantsinceinsome
cases itsreactivityissuperior toarenes
Generally the electrophile interacts first with e2gor a1g*electron pair of the
metalatomthentheelectrophileistransferredto the Cp ring followed by
deprotonation
66

67. Theacylationofmetalloceneshasbeeninvestigatedmoreextensivelythan
any other substitutionreaction.
The Friedel-Crafts reaction between ferrocene and acetyl chloride or Ac2O
inthepresenceofanhyd.AlCl3orphosphoricacidisagoodexample.
Whenequimolaramountsofthesereactantsareemployed,
monoacetylferroceneisformedalmostexclusively
67

68. •Whenanexcessofacetylchlorideandaluminumchlorideisemployed,a
mixtureoftwoisomericdiacetylferrocenesisproduced1,l'-
diacetylferroceneand1,2-diacetylferroceneina60:1ratio
•Theproductscanbeseparatedbycarefulchromatographyonactivated
alumina.
•Notenearlyallmetallocenesarehighlycoloredandcanbe
advantageously separatedbycolumnchromatography.
68

69. •Themajorproductistheheteroannulardisubstitutedderivative,1,l'-
diacetylferrocene.Verysmallamountofahomoannularisomer,1,2-
diacetylferrocene,isalsoobtained.
•Thefirstacetylgroupappearstodeactivatethesubstitutedringtoward
further electrophilicsubstitution,andthesecondacetylgroup
preferentially enterstheoppositering.
69

70. Fromthe sitereactivities, acylation is
enhancedin thesubstituted ring
compared to theunsubstituted ring, as
mightbe expectedbythe presence of
an electron-releasing alkyl group.
Substitution at the 3-position is
favored overthe 2-position.
70

71. In contrast to alkylferrocenes, the 2-
position isfavored over the 3-
position.
This isthe resultofenhanced
resonance stabilizationofthe
transition stateinsubstitution
involving electrophilicattackat the
2-position.
Acetylation of phenylferrocene also
produces threesimilar
acetylphenylferrocenes
(VI,VII,VIII;R= C6H5)(as wellas
a verysmall amountof an isomer in
which thephenyl groupis
acetylated), thesitereactivities are
quite different
71

72. Acylationatthe3-positionwas
evenmorepronouncedinthecase
of 1,1’-diisopropylferrocene,
suggesting that stericfactors play an
important rolein determiningthe
mechanismof homoannular
acylation of alkylferrocenes.
•Another interesting series of
reactions involving acylation
concerns bridging or cyclization
ofω-ferrocenylcarboxylicacids.
72

73. •β-Ferrocenylpropionicacid(IX,n=2),whentreatedwitheither
polyphosphoric acid or trifluoroacetic anhydride or PCl3yields the
bridgedketone1,1’-ketotrimethyleneferrocene(X) .
•Ferrocenylbutyricorvalericacids(IX,n=3,4)producehomoannular
cyclized products(XI,n=3,4).
73

74. 74

75. •Acetylferroceneisaprecursorformakingahostof chiralderivatives
•WidelyusedderivativesarealkynylferroceneandN,N-dimethyl-1-
ferrocenylethylamine.
•Ugisamineopenedupdiversesyntheticroutesforintroducingboth
planar andcentralchiralityonferrocenederivatives
75

76. Ru(η
5
-C
5H
5)
2 Ru(η
5
-C
5H
4COMe)(η
5
-C
5H
5)
Os(η
5
-C
5H
5)
2 Os(η
5
-C
5H
4COR)(η
5
-C
5H
5)
76
MeCOCl/AlCl
3
RCOCl/AlCl
3

77. Ferroceneisreadilyalkylatedbyalkylhalides,alcohols,orolefinsto
produce alkylatedderivatives.
Theexceedinglygreatreactivityofferroceneundertheseconditionsresults
intheformationofmixturesofmono-,di-,tri-,andpoly-alkylatedproducts,
andtheyieldof anyonealkylationproductisusuallylow.
Theintroductionofanalkylgroupintotheferrocenenucleusfacilitates
subsequentalkylation inthesamering.
77

78. 78

79. Alkylferrocenescanserveasusefulsyntheticintermediates,sinceithas
recentlybeenshownthattheyareconvenientlyoxidizedbyactivated
manganesedioxide tocarbonylcompounds
Methylferrocene,for example,canbeconvertedto
ferrocenecarboxaldehydewithoutapparentlyoxidizingtheironatom.
79

80. HauserandLindsayfirstshowedthatferrocene
undergoesaMannich-type reactionwith
formaldehydeanddimethylamine to form
dimethylaminomethylferrocene(XXIX)
This amine is readily converted to a
methiodide.
Thisquaternarysalt isanimportant synthetic
intermediateinferrocenechemistry.
80

81. •Reduction of the methiodide of XXIX with
sodiumamalgam,forexample,produces
methylferroceneinhighyield
•Treatmentwithsolutionsof potassium cyanide
-ferrocenylacetonitrile
•KOH-ferrocenylcarbinol
•BenzenedoesnotundergoMannich reaction
•Ferrocene resembles more reactive Thiophene
and Phenol thanBenzene
81

82. •Reaction with potassiumamide in
liquid ammoniaresults ina
Stevens rearrangement to give β-
dimethylaminoethylferrocene.
82

83. Anotherveryimportantsubstitutionreactionofferroceneisitsabilitytoundergo
metalationwithorganolithiumandorganosodiumcompounds.
Metalationwithn-butyllithiuminethylether,firstreportedbyNesmeyanovandco-
workersandindependentlybyBenkeser,Goggin,andSchroll,leadstoratherlowyields
of ferrocenyllithium(XXXVI, ;M=Li)and1,l'-ferrocenylenedilithium (XXXVII,M=
Li).
83

84. Lithiatedferrocenesareusefulprecursorsfornewferrocenederivatives
Itwassubsequentlyshownthat the use of the mixedsolvent ethyl ether-
tetrahydrofuran1:1leadstogreatlyimprovedyieldsoflithioferrocenes,andthis
procedure hasbeenextensivelyusedinfurthersyntheticapplications
Puremonolithiatedferroceneformedexclusivelybut inpooryieldwhenthereactionis
carried outinEt2Oat lowT
Lithioderivativessensitivetooxidationandhydrolysis
84

85. Similarreactionsofferrocenewithphenylsodiumorn-amylsodiumleadto
thecorrespondingsodiatedproducts(XXXVI,XXXVII,M=Na)
Thestericcourseofbothmetalationreactionshasbeenstudied,andithas
beenprovedthatdimetalationoccursinoppositecyclopentadienylrings.
Bothruthenoceneandosmocenehavebeenmetalatedwithn-butyllithium.
It has been shown that under comparable conditions ruthenocene is
metalated to a greater extent than is ferrocene.
85

86. •Carbonationandsubsequenthydrolysisofeitherlithiatedorsodiated
metallocenesleadtothecorrespondingcarboxylicacids.
86
Fe(η
5
-C
5H
5)(η
5
-C
5H
4 CO
2H)
Fe(η
5
-C
5H
5)
2 + LiBu
Fe(η
5
-C
5H
5)(η
5
-C
5H
4 Li)
CO
2/H
2O

87. •Ferrocenecarboxylicacidandferrocene-l,l’-dicarboxylicacidarereadily
producedinthismannerandcanbeconvenientlyseparatedbyextraction
oftheformerwithethyletherorbenzene.
•Metalatedferroceneshaveservedasveryvaluableintermediatesforthe
synthesisofanumberofotherderivatives.
87

88. 88

89. HNO3isanoxidising agent
Metallocene sensitive tooxidation
No directnitration
Indirectnitrationwith N2O4
Nitroferrocene can be reduced to
amine derivative
89

90. Carbonation andsubsequent hydrolysis
ofeither lithiatedor sodiated
metallocenes leadtothe corresponding
carboxylic acids. Ferrocenecarboxylic
acid and ferrocene-l,l’-dicarboxylic acid
are readilyproduced inthis manner and
can beconveniently separatedby
extraction of theformer with ethylether
orbenzene.
90

91. Ferrocenereacts readilywith mercuric
acetatetoformmercuratedderivatives.
Ferrocenecould bemercurated under
relatively mild conditions in eitherethyl
ether -alcohol or benzene-alcohol
solution
The acetoxymercuri-ferrocenesformedin
this mannerare usually treatedwithan
alcoholicsolution of an alkalimetal halide.
Theresultingproducts,
chloromercuriferrocene (XXXII) and
1,l'-di (ch1oromercuri)ferrocene
(XXXI I I), can be conveniently
separated byextraction withn-butyl
alcohol.
91

92. Ferrocene, similar to other highly
reactive aromaticsystems, readily
formylated by N-methylformanilide
in the presenceofphosphorus
oxychloride
Only the monosubstituted product,
ferrocenecarboxyaldehyde(XX),is
92

93. produced even when a large excess
offormylatingagent isused.
Ferrocenecarboxaldehyde, like
benzaldehyde, is readily reduced to
the corresponding carbinoland
undergoes the Cannizzaro reaction
withalcoholic potassiumhydroxide
solution.
•While ferrocenecarboxaldehyde
apparently does notundergoa
self-benzoin condensation it will
condense with benzaldehyde to
forma mixedbenzoin.
93

94. PlanarChirality
Planarchiralityisuniqueformetallocenesandhalfsandwichcompounds
Itisobtainedby the lossof a plane of symmetryinthemetallocene molecule.
thus,mirrorimagesofferrocenehavingtwodifferentsubstituentsonthesameCpring
arenotsuperimposable.
Oneofthe advantagesof planarchiralityisthatit doesnotundergoracemisation
94
Cahn-Ingold-Prelogrulesforassigning
planar chirality in Ferrocene molecule
is shown here

95. Centralchirality
Central chiralityalsoknown aslateral
chirality isthesecondtypeof chirality
found inferrocene andsimilar
compounds.
It isbasically duetoa chiralcarbon
centre directlyattachedto theCpring.
Ex:Ugi’samine,[(R)-N,N-dimethyl-1-
ferrocenylethylamine]
95

96. M(Cp)2
Fe
Ru
Ti
96

97. (Cp)2MLx
M H
L
M
L
M
L
L
L
Bentmetallocene
97

98. CpMLy
Mn
CO
CO
PPh
3
Co
CO CO
Half-sandwichCyclopentadienylderivatives
98