Cyclopentadienyl-Complexes-
Sandwich-compounds-
Structures-
CO
Ni Fe Ti
Ru CO
Mo Mo
Ni Ni O O O O
O O
Mn
OC O
CO CO O
• Accidental-discovery!-
• Two-groups-in-1951-
– (a)-Miller-and--
– (b)-Pauson-and-Kealy-
• ProperDes-don’t-match-
the-properDes-of-the-
expected-cpd-nor-the-
properDes-of-the-
structure-proposed-by-
Pauson-and-co..-
Proposed-structures-of-Wilkinson-/-
Woodward-and-Fischer-
-
DiamagneDsm-
Chemical-behaviour-
Xray-analysis-
Fe Fe
Sandwich-Structure- Double-cone-
• -Fischer-and-Wilkinson-
enter-a-“historic-race”-
to-make-the-Periodic-
Table-of-metallocenes!- M
• -It-ends-in-a-Nobel-
Prize-in-1973-for-
both!!-
• Cp-is-[C5H5]X---
• Pentamethyl-cyclopentadienyl-group-is-also-popular--[C5Me5]X---=---Cp*-
• It-is-essenDally-an-anionic-group-R!-but-has-the-ability-to-coordinate-
mulDple-(5)-C-atoms-to-the-metal.--
– Allyl-had-3-C-atoms-
– Cp-has-5-C-atoms-
A-line-in-the-centre-implies-
All-5-C-atoms-are-bonded!-
PreparaDon-of-metallocenes --
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-
CH2
-
CH
Aromatic anion
-
Aromatic anion
-
CH
+
CH2
+ H
Any base will do! Et 3N works very well
TransmetallaDon-
• TlCp-is-easily-made-and-can-be-
stored.-So-it-is-considered-a-
convenient-source-of-
cyclopentadienyl-complexes!-
• Tl-is-toxic-and-so-should-be-handled-
with-care!--
• CpMgBr-and-CpLi-can-be-used-as-well.-
• CpLi-can-be-made-from-CpH-and-Li-
sand.-
Direct-ReacDon-
• Ferrocene-can-be-made-from-FeCl3-and-
Fe-powder-with-Et3N-and-CpH-under-
reflux-condiDons.-
• The-amine-removes-the-HCl-that-is-
generated!-
• Fe-reduces-the-Fe(III)-to-Fe(II)-
• Alt:--Fe-and-Et3N.HCl-at-a-higher-temp.-
• Always,-CpH-is-freshly-prepared-from-
cracking-C10H10-(CpH)2--
Bonding-
z-
Dxy,-dx2Xy2,--
y-
x-
4py- 3dyz-
3dxz-
4px-
4pz- 3dz2-
Energy-Levels-
Cyclopentadienyl-MO-
z-
y-
x-
Mix-and-Match-
z-
y-
x-
px- dxz-
pz- dz2-
Remember-there-are-two-Cp-rings!-
px- dxz-
s- pz- dz2-
MO-Energy-diagram-of-Ferrocene-
4p-
e2g-
e2u- dyz,((dxz( 4s-
dz2-
dx2!y2,((dxy(
3d-
e1g-
e1u- e1u-
-
e1g-
a1g- a2u-
a2u- -
a1g-
Electron-Count!-Iron-is-the-best!-
4p-
e2g-
e2u- dyz,((dxz( 4s-
dz2-
dX2XY2,--dXY-
3d-
e1g-
e1u- e1u-
-
e1g-
a1g- a2u-
a2u- -
a1g-
ProperDes!-
(Metallocene( Color( upe( Exper.( Expected( Interplanar(
B.M( B.M( distance(
(pm)(
VCp2- Purple- 3- 3.84- 3.87-
CrCp2- Red- 2- 3.2- 2.83- 361-
-
MnCp2- Amber- 5- 5.81- 5.92-
-
FeCp2- Orange- 0- 0.00- 0- 332-
-
CoCp2- Black-- 1- 1.76- 1.73- 340-
-
NiCp2- green- 2- 2.86- 2.83- 360-
Ti Cr Fe Ni Zn
Ferrocene:---Most-stable,-300+-oC-
Sublimes-and--is-used-for-making-carbon-nanotubes!-
Bond-distance-is-shortest-for-Fe-(18-electron-system)-
MagneDc-properDes-are-predictable!!-
-
[Co(Cp)2]+------should-be-a-very-stable-system!-It-is--
-
[Mn(Cp)2]X----is-not-as-stable-as-it-should-be-because,-CpX-is-lost!-
Look-at-the-MO-diagram.--
• Bonding-mode-should-depend-on-
the-electron-count!--
CO
Many-of-the-M2+-
structures-are-
Cu Be slipped-from-the-
centre-
• But-most-structures-are-fluxional.--
-
Importantly,-the-Cp-is-a-ligand-which-can-adjust-the-electron-donaDon-
By-sliding-the-metal--along-the-line-shown-by-the-arrow-
4-C-are-interacDng-
Very-rare!-
CH3 H
H3C CH3 H M
H3C CH3 M H
H
H H
Allyl-like-coordinaDon-
M-
• Ferrocenes-can-be-oxidized-and-protonated.-
• Fe(Cp)2--is-oxidized-with-AgBF4-to-produce-a-[Fe(Cp)2]+--
species.--It-leaves-behind-silver-metal-
• H+-can-be-added-to-ferrocene-to-give-[Fe(Cp)2]H+--
AromaDcity-
• Acetyl-chloride-/-AlCl3----
O
O
M CH3
H3C M
Cl
AromaDcity-
• LithiaDon-
Li Li
M
Li metal
M + M
Li H
TMEDA
(C5H5)2Ti-The-“mysteryXcene”-
1956-Wilkinson-group-reports-formaDon-of-
bright-green-paramagneDc-solid.-It-transforms-to-
a-brown-solid-spontaneously!-
Much-later,-Wam,-Baye-and-Drummond-
said-that-Dtanocene-was-diamagneDc-and-
had-a-molecular-weight-of-346!-Twice-
what-is-expected-for-(C5H5)2Ti-
14-years-aoer-Wilkinson,-in-1970,-
a-strong-band-at-1230-cmX1-is-
idenDfied-as-a-TiXH-bond-in-the-
Dtanocene.-Britzinger-and-Bercaw-
suggest-the-structure:-
-((C5H5)XC5H4)TiH)2---
20-years-later,1976:--
LT-NMR-spectrum-of-the-compound-confirms-the-
presence-of-TiXH-bond-
Finally--in-1992,-the-crystal-structure-of-
Dtanocene-is-confirmed.-It-is-not-what-
Wilkinson-proposed,-it-was-a-dimer-with-
a-TiXH-bridge.-
XXray-structure-of-Dtanocene-
Arene Sandwich Complexes
Hein (1919) mixed ArMgX and Metal CrCl3 to make Cr(Ar)3 and accidentally
made a compound that analyzed for Cr(ArH)2
M
M is a chromium
group metal
More rational approach
Fischer Hafner (1955) synthesis
• Mix Al (powder) + 3 CrCl3 + 6ArH
• Forms 2 [(ArH)2Cr ]+ + AlCl4-
• What is obtained is the Cr(+1) complex !!
• Used AlCl3 and Al as catalysts! Later used Na2S2O8 as
a reductant to generate the Cr(0) species in good yield
Limitations of F-H synthesis
• Does not work with all metals
V Cr Fe Co Ni
Mo Tc Ru Rh Pd
W Re Os Ir Pt
Limits on the aromatic rings
• Ar-X where X = any group with a lone pair
of electrons
• The lone pair complexes with AlCl3 and
stops the reaction.
Cyclotrimerization of alkynes
• Me-C≡C-Me is trimerized with some metals in a
template synthesis to give an arene:
Reduction and substitution
– MCln(THF)6-n + nLiC10H8
– This METHOD WORKS for Cr, Mo, and V
Surprise! Surprise!
ZrCl4(THF)2 + 4LiC10H8
Metal atom ligand vapor co-
condensation
• Works even when the electron count is
bad Cr, Ti, Zr, Hf, Nb, Y, Gd,
• Eg. Ti(g) + 2 C6H6
Schematic Representation of
Metal Vapor Synthesis
Ligand
high High Vacuum
+ -
current
Liquid N2
coling
Metal atom ligand vapor co-condensation CC
• Coordinating arenes: Chlorobenzene, dimethylamino
benzene
Metal atom ligand vapor co-
condensation
• Works even with sterically inaccessible phenyl groups:
Biphenyl, tri-tbutylbenzene
Metal prefers aromatic centers!
Bonding and Structure
MO treatment
z
x
Bonding
z
Dxy, dx2-y2,
y
x
4py 3dyz
Metal along the z axis!
3dxz
4px
4pz 3dz2
Frost’s Energy level diagram
three
nodes
two
nodes
one
node
Zero
node
Benzene MO
z
x
z
Mix and Match
y
px dxz
pz dz2
y
Top view of MO’s (down z axis)
three
nodes
x
two
nodal
planes
one
nodal
plane
Zero nodes
except for plane
of benzene ring
Remember there are two arene rings!
px dxz
s pz dz2
Mix and Match
z
px dxz
pz dz2
MO Interaction diagram of bis-benzene
chromium (Eclipsed Geometry)
b2g
b1u
4p
e2g
e2u dyz, dxz 4s
dz2
dx2-y2, dxy
3d
e1g
e1u e1u
e1g
a1g a2u
a2u
a1g
Electron Count!
Chromium is the Best!
b2g
b1u
4p
e2g
e2u dyz, dxz 4s
dz2
dX2-Y2, dXY
3d
e1g
e1u e1u
e1g
a1g a2u
a2u
a1g
• Cr bears a +Ve charge of 0.7 e • Bond energy of bis benzene
• Benzene bears -0.35 e chromium is 170 kJ mol-1
• Attributed to Cr transferring
electrons through δ bonding • Ferrocene has a value of
260 kJ mol-1
• Look at some
structures of these
molecules!
DBENCR ENEZOM
• Structures of a few
arene complexes!
SIGJAT
Properties!
Metallocene Color upe Exper. Expected Interplanar
B.M B.M distance (pm)
(C6H6)2Ti red 0 0 0
(C6H6)2V Dark 1 1.68 1.73
Red
(C6H6)2Cr brown 0 0 0 322
(C6Me6)2Fe 2 3.08 2.83
(C6Me6)2Co Black 1 1.86 1.73
(C6Me6)2Ni 2 3.00 2.83
Reactions of arene complexes
Is the aromaticity retained?
Ligand exchange
η4 complexes
- 2 electrons Ru
+
++
H3C CH3
η6 and η6
H3C Ru CH3
H3C CH3
H3C CH3
H3C CH3
H3C CH3
NaBH4 / THF
2H- units are added
η4 and η6 H H
H
H
H3C Ru CH3
η4 and η6
H3C CH3
H3C CH3
η4 complexes
Neutral complexes can be made by
reducing the Ru2+ cation which is a
18 electron complex with Na/ NH3
X-ray reveals complete bond
Localization and bending, NMR
shows a dynamic structure!
Ru
Hetero-Sandwiches
Electron Counting
• CpMC6H6 what would be M ?
– 6 electrons from the arene
– 5 from the Cp (neutral method)
– M has to give 7 electrons! M=Mn
• CBDMC6H6 What should be M
– 4 from Cyclobutadiene CBD
– 6 from Arene
– 8 from metal! M= Fe
Cyclopropenyl rings
Cyclobutadiene sandwich!
Cycloheptatrienyl
Beyond 7 it is difficult for d group metal ions
but lanthanides and actinides like U can
form complexes!
[C8H8 ]2- + UCl4 U
Summary
• 18 electron rule holds good!
• Possible to have some reactions of the
benzene ring
• One can make hetereo sandwiches!
Sandwich)Complexes)
Half,)Bent,)Open)and)Mul:)
Journal(of(the(Chemical(Society((Resumed),"1956"p."1969 "
doi:10.1039/JR9560001969 )
The"Possible"Existence"of"TransiAonBmetal"
Complexes"of"cyclo(Butadiene.(
((((((By))
H.)C.)LONGUETCHIGGINS)and)L.)E.)ORGEL.)
• “The)possibility)that)the)unstable)cyclobutadiene)
molecule)can)be)stabilised))by)combina:on)with)a"
suitable"transiAonBmetal"ion"is"invesAgated"by"
use"of)molecularCorbital)theory.”))
• “complexes)of)the)type)MnX2(C4H4,),)where)M)is)
nickel,)palladium,)or)pla:num)and)X)is)a)univalent)
ligand,)may)be)stable,”))
• “Ni(CN)2(C4H4))is)an)intermediate)in)the)Reppe)
synthesis)of)cyclooctatetraene.”)
Synthesis)of)4)membered)rings)…)
Ph Ph
Ph
CH3 Ph
Sn
CH
+ NiBr2
Ph
3
Ph Ph
Ph NiBr2
2
Cl
Cl + Fe2(CO)9
Fe + FeCl2
OC CO
CO
Crystal)structure)of)a)CBD)complex)
P.D.Harvey,)W.P.Schaefer,)H.B.Gray,)D.F.R.Gilson,)I.S.Butler,)Inorg.Chem.)(1988),)27,)57)
Synthe:c)routes)
Reac:vity)
Aroma:c)Behavior!)
Other)half)sandwich)complexes)
CpTO!)
The)organic)metal)oxide!)
Methyltrioxorhenium)
Arene)half)sandwiches)
Templated)synthesis)of)Piano)stool)
CH3
complexes)
AlR 3 + + CrCl3
+ CO
CH3
H3C
CH3
H3C CH3
H3C CH3
Cr
CO
OC CO
η7)complexes)are)possible!)
Ethyl cyclohexane H
Mo(CO)6 + C7H8
Mo
OC CO CO
[Ph3C+][BF4]-
-
BF4
Mo
OC CO
OC
C3H3)half)sandwiches)
η2)arene)complexes)
1.51 angstroms
1.33
1.36 1.48
Pt PPh3
Ph 3P
Mixed)Sandwiches)to)half)sandwiches!)
Bent)Metallocenes)
Bent):tanocenes)
Catalysis,)fluxional)behaviour)
Open)Sandwiches)
• Acyclic)version)of)cpC)is)C5H7C))
(η5CPentadienyl)Ctris(trimethylphosphine)Ciron)tetrafluoroborate)
GEVDOA)from)CSDS)
Synthesis)of)Open)Metallocene)
Structure)of)Open)Metallocene)
Ruthenium)analog)of)the)open)metallocene)
Ruthenium)vs.)Iron)
What)is)the)difference?)
)
Trimethylenemethane)
Structure)of)TMMCFe(CO)3)
(η4CTrimethylenemethane)CtricarbonylCiron)
• Note)Inverted) REHZEK)from)CSDS)
umbrella)structure)
• Staggered)
orienta:on)of)tmm!)
Exo:c)Sandwiches)
• Hetero)atom)containing)
“bread”)
– CCH))is)converted)to)N)
– CCH)is)replaced)by)P)
– CHC)is)replaced)by)S!)
• Thiophene)
CC)with)pyridine!)
P5)Sandwich!)
(η5CEthyltetramethylCcyclopentadienyl)C(h5Ccyclopentaphosphorus)Ciron)
)
GEVRUU)from)CSDS)
Mul:metal)Sandwich)
Mul:decker)Sandwiches)
• What)is)the)use)of)
making)sandwich)
complexes?) +
Ni
• Observed)in)the)mass)
Ni
spectrometer)and)later)
synthesized.)
Inverse)Sandwich)
COT)as)an)inverse)sandwich)synthon)
YUHRUO)from)CSDS)
Inverse)and)Exo:c!)
( µ2C(η10CCyclopentaphosphorus))Cbis(η5CpentamethylCcyclopentadienyl)CdiCchromium)
DOMYAF)from)CSDS)
Summary)
• The)sky)is)the)limit!)
• 18)electron)rule)is)a)great)guiding)principle)
• The)complexes)are)useful)as)catalysts)as)the)
“bread”)is)flexible)and)can)change)hap:city!)
Reac%vity*Changes*of*
Coordinated*Ligands*
Modified*Ligand*Reac%vity*
General*features*of*M:olefin*bonding.*
* • **1.*Nucleophilic*addi%on*
• Removal*of*electron*density* enhanced**/*Electrophilic*reac%ons*
from*olefin*π*by*metal.* suppressed*
*
• Popula%on*of*the*π *orbital*
of*the*olefin/polyene*by* • **2.*Photochemical*type*of*
reac%vity.*
metal*'d'*electrons.*
**
Oxida%on*of*Dienes*with*Pd*
Pd(0)***+**O2***+*HOAC***::::!*****Pd(OAC)2***+*H2O*
*
Involves*a*nucleophilic*aRack*on*the*coordinated*olefin!!*
Oxida%on*of*alkenes*at*the*allylic*
posi%on*
Allylic*complex*is*a*“chem”eleon*
CpFe(CO)2CH2:CH=CH2*
Fe*allyl*complexes*behaved*as*allyl*anion*
*
Ni(0)*/*Pd(0)*based*coupling*is*almost*like*allyl*radical*coupling*
*
Ru(IV)*allyl*complexes*behaved*as*if*they*were*allyl*ca%ons*
Modified*Ligand*Reac%vity*
General*features*of*M:olefin*bonding.*
•
*
Unavailability*for*usual*reac%ons* 3.*Protec%on*from*hydrogena%on*
common*for*double*bonds.** *****************or*
Enhanced*reac%vity*of*other*D.B.*
• Loss*of*conjuga%on*in*a*polyene.*
4.#Alternate#reac,ons#due#to#1,2,3.**
Protec%on*of*an*alkyne!*
Different*Reac%vity*for*the*arene*
Increased
Acidity H
H
Nucleophilic. X X
Substitution
X Increased Hydrolysis
Cr
Steric hindrance
The*source*of*anchimeric*assistance*
b2g*
b1u*
4p*
e2g*
e2u* dyz,##dxz# 4s*
dz2*
dX2:Y2,**dXY*
3d*
e1g*
e1u* e1u*
*
e1g*
a1g* a2u*
a2u* *
a1g*
Reduced*Nucleophilic*ARack!*
Dilithio*and*
Monolithio*
Cpds*are**
formed*
• Cr*bears*a*+Ve*charge*of*0.7*e*
• Benzene*bears*:0.35*e*
• ARributed*to*Cr*transferring*
electrons*through*δ*bonding*
Enhancing*nucleophilic*aRack*
Metal*effect*
Half*Sandwich*complexes*
Ligand*effect*
M
C
C O M
C
O
O
Nucleophilic*subs%tu%on*
Nucleophilic*subs%tu%on*
Oxida%on*
iodine/*CAN*
Two*step*addi%on*elimina%on*
Mar%n*Semmelhack*
Nucleophilic*subs%tu%on*
H
H R- R
_
Cr Cr
I2
X-ray crystallography of
the intermediate carried out!
-CH CN
2
Different*Reac%vity*for*the*arene*
Increased
Acidity H
H
Nucleophilic. X X
Substitution
X Increased Hydrolysis
Cr
Steric hindrance
Reduced*aroma%city*
Electrophilicity*reac%vity*index**
*
Davies*Mingos*and*Green*
• Nucleophilic*aRack*occurs*preferen%ally*at*even*
coordinated*polyenes*
• Nucleophilic*addi%on*to*open*coordinated*polyenes*
is*prefered*over*closed*polyene*ligands*
• In*the*case*of*even*polyenes,*nucleophilic*aRack*
always*occurs*at*the*terminal*carbon*atom.*
DMG*rules*
Even*and*odd*polyenes*are*present.*Rule*1*says*that*the*even**polyene*
will*be*aRacked*by*the*nucleophile.*Rule*2*says*it*will*be*the*open*polyene.*
Davies*Mingos*and*Green*
• For*odd*polyenyls,*aRack*at*the*terminal*
carbon*atom*occurs*only*if*the*metal*is*a*
rela%vely*strong*electron*withdrawing*
fragment*
DMG*rules*
Only*odd*polyenes*are*present.*Rule*3*says*that*the*odd*open*polyene*
will*be*aRacked*by*the*nucleophile.*Rule*4*says*it*will*be*at*the*center*posi%on.*
DMG*rules*
Odd*polyenes*are*present.*Open*is*to*be*aRacked*but*it*is*aRacked**
on*the*terminal**
Altered*Reac%vity*of*coordinated*
ligands*
Ph
(CO5)M x =c
H
x = S,Se
M = G,W
H Ph
C X
+
X H Ph
endo / exo
7 :1
H Ph M(CO)5
C
+ X
X
H Ph
M(CO)5 M = Cr 1:6.
= W 1:7
How does the reactivity change ?
a. Change in selectivity.
b. Rate of reaction decreases.
How can we be sure it is the metal ?
Asymmetric*Catalysis*
Summary*
• Altered*reac%vity:*primarily*enhanced*and*
directed*nucleophilic*aRacks!*
• Metal*oxida%on*state*makes*a*difference*
• Ligands*like*CO*enhance*reac%vity*
• Protec%on*of*triple*/*double*bonds*
• Reduc%on*of*aroma%city*/*conjuga%on*
• Steric*effects*that*introduce*“facial”*selec%vity**
