Group 4 5 6 7 8 9 10

3d row Ti V Cr Mn Fe Co Ni

4d row Zr Nb Mo Tc Ru Rh Pd5d row Hf Ta W Re Os Ir Pt

Neutral stable compounds

0 ML7 ML6 ML5 ML4

I MXL6 MXL5 MXL3 (16e)II MX2L6 MX2L5 MX2L4 MX2L2 (16e)III MX3L4 (16e) MX3L4 MX3L3

IV MX4L4 (16e) MX4L3 (16e) MX4L3 MX4L2

V MX5L2 (16e)

Each X will increase the oxidation number of metal by +1.

Each L and X will supply 2 electrons to the electron count.

Group 4 5 6 7 8 9 10

3d row Ti V Cr Mn Fe Co Ni

4d row Zr Nb Mo Tc Ru Rh Pd5d row Hf Ta W Re Os Ir Pt

Stable monocationic compounds

0IIIIIIIVV

Group 4 5 6 7 8 9 10

3d row Ti V Cr Mn Fe Co Ni

4d row Zr Nb Mo Tc Ru Rh Pd5d row Hf Ta W Re Os Ir Pt

Stable monocationic compounds

0 [M(NO)L6]+ [M(NO)L5]

+ [M(NO)L4]+ ML4

I [ML6]+ (16e) [ML6]

+ [ML4]+

(16e)

II [MXL7]+ [MXL6]

+ [MXL5]+ MX2L2 (16e)

III [MX2L5]+

(16e) [MX2L5]+ [MX2L4]

+

IV [MX3L5,6]+ [MX3L4]

+ (16e) [MX3L4]+ MX4L2

V [MX4L3]+

(16e)

Now looking at compounds having a charge of +1 to obey 18 e rule.

NO+ is isoelectronic to CO

X increases O N by 1

Elec count: 4 (M) +2 (NO) +12 (L6) = 18

Elec Count: 4 (M) + 4 (L2) + 10 (L5)

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 !)

Organometallic Chemistry1.2 Fundamental Reactions

Reaction (FOS) (CN) (NVE)

Association-Dissociation of Lewis acids 0 ±1 0

Association-Dissociation of Lewis bases 0 ±1 ±2

Oxidative addition-Reductive elimination ±2 ±2 ±2

Insertion-deinsertion 0 0 0

Fundamental reaction of organo-transition metal complexes

FOS: Formal Oxidation State;

CN: Coordination Number

NVE: Number of valence electrons

(FOS) = 0; (CN) = ± 1; (NVE) = 0

Lewis acids are electron acceptors, e.g. BF3, AlX3, ZnX2

W:H

H+ BF3 W

H

HBF3

This shows that a metal complex may act as a Lewis base

The resulting bonds are weak and these complexes are called adducts

Association-Dissociation of Lewis acids

(FOS) = 0; (CN) = ± 1; (NVE) = ±2

Association-Dissociation of Lewis bases

A Lewis base is a neutral, 2e ligand “L” (CO, PR3, H2O, NH3, C2H4,…)in this case the metal is the Lewis acid

HCo(CO)4 HCo(CO)3 + CO

Crucial step in many ligand exchange reactionsFor 18-e complexes, only dissociation is possible

For <18-e complexes both dissociation and association are possiblebut the more unsaturated a complex is, the less it will tend to dissociate a ligand

(FOS) = ±2; (CN) = ± 2; (NVE) = ±2

Oxidative addition-reductive elimination

Very important in activation of hydrogen

Cl PPh3

COIrI

Ph3P+ H2

Cl PPh3

HIrIII

Ph3P

H

COVaska’s compound

Mn+ +M(n+2)+

X YX-Y

Oxidative addition-reductive elimination

Cl PPh3

COIrI

Ph3P+ H2

Cl PPh3

HIrIII

Ph3P

H

COVaska’s compound

H

H

M

Concerted reaction

via

Cl PPh3

COIrI

Ph3P+ CH3I

Cl PPh3

COIrIII

Ph3P

CH3

Cl PPh3

COIrIII

Ph3P

CH3

I

+

I-

SN2 displacement

cis addition

trans addition

Also radical mechanisms possible

Ir: Group 9

H becomes H-

CH3+ has become CH3

-

Oxidative addition-reductive elimination

Mn+ +M(n+2)+

X YX-Y

Not always reversible

Mn+ +M(n+2)+

X RR-X

Mn+ +M(n+2)+

H RR-H

(FOS) = 0; (CN) = 0; (NVE) = 0

Insertion-deinsertion

M-X + L M-L-X

(CO)5Mn-CH3 + CO (CO)5Mn-C-CH3

O

Very important in catalytic C-C bond forming reactions(polymerization, hydroformylation)

Also known as migratory insertion for mechanistic reasons

Mn: Group 7

Migratory Insertion

MnOC

OC CO

CO

CH3

CO

+ COMn

OC

OC C

CO

CO

CO

O

CH3

Mn

OC

OC C

CO

CO

O

CH3

k1 k2

+ CO

Also promoted by including bulky ligands in initial complex

Insertion-deinsertionThe special case of 1,2-addition/-H elimination

LnM H

R2C CR'2

LnM

R2C

CR'2

H

A key step in catalytic isomerization & hydrogenation of alkenesor in decomposition of metal-alkyls

Also an initiation step in polymerization

Attack on coordinated ligands

M L

Nu-

E+

Favored for electron-poor complexes(cationic, e-withdrawing ligands)

Favored for electron-rich complexes(anionic, low O.S., good donor ligands)

Very important in catalytic applications and organic synthesis

Some examples of attack on coordinated ligands

Nucleophilic addition Electrophilic addition

Nucleophilic abstraction Electrophilic abstraction

PtCl

Cl py pyPt

Cl

Cl py

N+

-

FeCp

OCOC OH

OH-

FeCp

OCOC OH2

+

FeCp

OCOC

-H2O

Ta

Cp

Cp

CH3

CH3

+ Me3PCH2 Ta

Cp

Cp

CH2

CH3

+ Me4P+

O

Fe(CO)3

O

Fe(CO)3

Et

+

Et3O+

Part 2. Some physical and chemical properties of important classesof coordination and organometallic compounds

Brooklyn CollegeChem 76/76.1/710G Advanced Inorganic Chemistry

(Spring 2009)

Suggested reading:Miessler/Tarr Chapters

13 and 14

Unit 6Organometallic

Chemistry

Metal Carbonyl Complexes

M-CO

CO is an inert molecule that becomes activated by complexation to metals

CO as a ligand donor, π-acceptorstrong trans effectsmall steric effect

Frontier orbitals

Larger homo lobe on C

“C-like MO’s”

6CO ligands x 2 e each

12 bonding e“ligand character”

“18 electrons”

non bonding

anti bonding

“metal character”

Mo(CO)6

Metal carbonyls may be mononuclear or polynuclear

Synthesis ofmetal carbonyls

Characterization of metal carbonyls

IR spectroscopy M-C-O (C-O bond stretching modes)

Effect of charge

Effect of other ligands

PF3 weakest donor (strongest acceptor) PMe3 strongest donor (weaker acceptor)

Lower frequency, weaker CO bond(free CO) 2143 cm-1

The number of active bandsas determined by group theory

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 170-290 ppm (diagnostic signals)

Very long T1

(use relaxation agents like Cr(acac)3 and/or enriched samples)

Typical reactions of metal carbonyls

Ligand substitution:

Cr(CO)6 + CH3CN Cr(CO)5(CH3CN) + CO

Always dissociative for 18-e complexes, may be associative for <18-e complexes

OC CO

COMn

OC

CH3

CO

OC CO

COMn

C

CO

H3C

OOC CO

COMn

C

CO

CO

H3C

OCO

Migratory insertion:

Metal complexes of phosphines

PR3 as a ligandGenerally strong donors, may be π-acceptor

strong trans effectElectronic and steric properties may be controlled

Huge number of phosphines available

M-PR3

Metal complexes of phosphines

M-PR3

Basicity: PCy3 > PEt3 > PMe3 > PPh3 > P(OMe)3 > P(OPh)3

> PCl3 > PF3

Can be measured by IR using trans-M(CO)(PR3) complexesSteric properties:

P

R1

R2

R3

M

The cone angleRigid structures create chiral complexes

R2P

PR2

M

apex angle of a cone that encompassesthe van der Waals radii of the outermost

atoms of the ligand

Tolman’s electronic and steric parameters of phosphines

Typical reactions of metal-phosphine complexes

Ligand substitution:

HCo(CO)4 + PBu3 HCo(CO)3(PBu3) + CO

HRh(CO)(PPh3)3 + C 2H4 HRh(CO)(PPh3)2(C2H4) + PPh3

Very important in catalysisMechanism depends on electron count

presence of bulky ligands (large cone angles)

can lead to more rapid ligand dissociation

Metal hydride and metal-dihydrogen complexes

Terminal hydride (X ligand)

Bridging hydride (-H ligand, 2e-3c)

Coordinated dihydrogen (2-H2 ligand)

Hydride ligand is a strong donor and the smallest ligand availableH2 as ligand involves -donation and π-back donation

M H

HMM

MH

H

Synthesis of metal hydride complexes

IrCl(CO)(PPh3)2 + H2 Ir(H)2Cl(CO)(PPh3)2

RuCl2(PPh3)3 + H 2Et3N

RuHCl(PPh3)3 + Et 3N.HCl

Co2(CO)8 + H 2 2 HCo(CO)4

[Fe(CO)4]2- + H+ [HFe(CO)4]-

Cp2ZrCl2 + NaBH4 Cp2ZrHCl

Characterization of metal hydride complexes

1H NMR spectroscopy

High field chemical shifts ( 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

(M-H) = 1500-2000 cm-1 (terminal); 800-1600 cm-1 bridging(M-H)/(M-D) = √2Weak bands, not very reliable

Some typical reactions of metal hydride complexes

Transfer of H-

Cp2Zr(H)2 + 2CH2O Cp2Zr(OCH3)2

Transfer of H+

HCo(CO)4 H+ + [Co (CO)4]- A strong acid !!

Insertion

IrH(CO)(PPh3)3 + (C 2H4) Ir(CH2CH3)(CO)(PPh3)3

A key step in catalytic hydrogenation and related reactions

Bridging metal hydrides

2-e ligand 4-e ligand

bonding

Non-bonding

Anti-bonding

Metal dihydrogen complexes

H H

M

H

H

M

PiPr3

W

PiPr3

OC

COOC

H

H

If back-donation is strong, then the H-H bond is broken (oxidative addition)

Very polarized+, -

Characterized by NMR (T1 measurements)

back-donation to * orbitals of H2

the result is a weakening and lengthening of the H-H bond in comparison with free H2

Metal-olefin complexes

2 extreme structures

metallacyclopropane π-bonded only

sp3

sp2

Zeise’s salt

Net effect weakens and lengthens the C-C bond in the C2H4 ligand (IR, X-ray)

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

Characterization of metal-olefin complexes

NMR 1H and 13C, < free ligand

X-rays C=C and M-C bond lengths indicate strength of bond

IR (C=C) ~ 1500 cm-1 (w)

[PtCl4]2- + C2H4 [PtCl3(C2H4)]- + Cl-

Synthesis of metal-olefin complexes

RhCl3.3H2O + C2H4 + EtOH [(C2H4)2Rh(-Cl)2]2

Reactions of metal-olefin complexes

Metal alkyl, carbene and carbyne 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(CCH)L2

Cp(CO)2Fe(CH2CH3)6 [Cr(H2O)5(CH2CH3)6]2+

Why were they so elusive?

Kinetically unstable (although thermodynamically stable)

Metal-alkyl complexes

Reactions of transition-metal alkyls

LnM

R

XLnM + R-X

LnM R LnM+ + R-H+ H+

Blocking kinetically favorable pathways allows isolation of stable alkyls

Metal-carbene complexes

C

R

R: C

R

R

..

sp2 sp2

pzpz

singlet carbene triplet carbene

C

R

R:M

:C

R

RM

..

..

d

d d

d

Fischer carbene Schrock carbene

M C

R

OR

M C

R

R

M C

R

OR-+

L ligandLate metalsLow oxidation statesElectrophilic

X2 ligandEarly metalsHigh oxidation statesNucleophilic

Fischer-carbenes

Schrock-carbenes

Synthesis

Np3Ta

Cl

Cl

2LiNpNp3Ta

t-Bu

t-Bu

H

-NpHNp3Ta

t-Bu

Typical reactions

Np3Ta

t-Bu

X Y

O

Np3Ta O

X

Y

H

t-Bu+

+

+ olefin metathesis (we will speak more about that)

Grubbs carbenes

Excellent catalysts for olefin metathesis

Metal cyclopentadienyl complexes

M

M

M

L L

M

LL L

Metallocenes(“sandwich compounds”)

Bent metallocenes

“2- or 3-leggedpiano stools”

Homogeneous catalysis:an important application of organometallic compounds

Catalysis in a homogeneous liquid phase

Very important fundamentally

Many synthetic and industrial applications

M H

M CO

M H

M PR3

M Cp

M

• 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

Comparison of heterogeneous and homogeneous catalysts

Difficulties in separation and catalyst regeneration have prevented a wider use of homogeneous catalysts in industry

Reaction (FOS) (CN) (NVE)

Association-Dissociation of Lewis acids 0 ±1 0

Association-Dissociation of Lewis bases 0 ±1 ±2

Oxidative addition-Reductive elimination ±2 ±2 ±2

Insertion-deinsertion 0 0 0

Fundamental reaction of organo-transition metal complexes

Combining elementary reactions

MLn + H2 MLn

H H

(oxidative addition)

MLn

H H

+MLx

H H-L(ligand exchange)

MLx

H H

MLn

H C C H(insertion)

Completing catalytic cycles

H H

H C C

H3C H CH3

H

CH3

H H

CH3

H3CMLx

MLn

MLx

H HH C C H

MLx MLn

-H eliminationno net reaction

-H elimination resulting in C=C bond migration

Olefin isomerization

Completing catalytic cycles

Olefin isomerization

H H

H C C

H3C H CH3

H

CH3

H H

CH3

H3CMLx

MLn

MLx

H H

MLx

MLx

H2

Completing catalytic cycles

(reductive elimination)

Olefin hydrogenation

MLx

H H

MLn

H C C H(insertion)

MLn

H C C H

MLn + C C

H H

H H

H C CH H

H

MLx

MLn

MLx

H H

MLx

H2H2C CH2

H

HH3C CH3

Completing catalytic cycles

Olefin hydrogenation

Wilkinson’s hydrogenation catalyst

RhCl(PPh3)3

Very active at 25ºC and 1 atm H2

Very selective for C=C bondsin presence of other unsaturations

Widely used in organic synthesis

AcO

AcOH

H

H2 RhCl(Ph3)3

Prof. G. Wilkinson won the Nobel Prize in 1973

The mechanism of olefin hydrogenation by Wilkinson’s catalyst

Other hydrogenation catalysts

[Rh(H)2(PR3)2(solv)2]+ With a large variety of phosphinesincluding chiral ones for enantioselective hydrogenation

RuII/(chiral diphosphine)/diamine

Extremely efficient catalysts for the enantioselective hydrogenationof C=C and C=O bonds

Profs. Noyori, Sharpless and Knowles won the Nobel Prize in 2001

Olefin hydroformylation

R

+ H2 + COcat

R

O

H

R

O

+

n-isomer i-isomer

Cat: HCo(CO)4; HCo(CO)3(PnBu3) HRh(CO)(PPh3)3; HRh(CO)(TPPTS)3

6 million Ton /year of products worldwideAldehydes are important intermediates towards plastifiers, detergents

(reductive elimination)

Olefin hydrogenation

MLx

H H

MLn

H C C H(insertion)

MLn

H C C H

MLn + C C

H H

What else could happen if CO is present?

MLn

H C C H

OCCO MLn

H C C

C

O

HMLn +

H

C C

C

O

HCO insertion reductive elimination

Olefin hydroformylation

H H

H C C

H H

H

MLx

MLn

MLx

H H

MLx

H2H2C CH2

H

H

H3CH2C

H C C

O CH3

HMLn

H

CHO

CO

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)

Catalytic synthesis of polyolefin

H2C CH2

H2C CH

CH3

isotactic

syndiotactic

atactic

Monomers

Polymerizationcatalysts

Polymers

Catalytic synthesis of polyolefin

H2C CH2

High density polyethylene (HDPE) is linear, d 0.96

“Ziegler catalysts”: TiCl3,4 + AlR3

Ti Cl + R3Al TiR

+

Electrophilic metal center

Vacant site

Coordinated alkyl

Insoluble (heterogeneous) catalyst

Catalytic synthesis of polyolefin

Isotactic polypropylene is crystalline

“Natta catalysts”: TiCl3 + AlR3

Ti Cl + R3Al TiR

+

Electrophilic metal center

Vacant site

Coordinated alkyl

Insoluble (heterogeneous) catalyst, crystal structure determines tacticity

H2C CH

CH3

Catalytic synthesis of polyolefin

“Kaminsky catalysts”

Electrophilic metal center

Vacant site

Coordinated alkyl

Soluble (homogeneous) catalyst, structural rigidity determines tacticity

H2C CH

CH3

+ MAO ZrR

+

XZr

R

+

X

Polymerization mechanism

M X + "R-Al" MR

initiation

MR

+ MR

M

R'

propagation

M

R' -HM H + P

+H2M H + P

+HXM X + P

termination

The catalytic synthesis of acetaldehyde(Wacker process, oxidation of ethylene)

C2H4 + PdCl2 CH3CHO + Pd(0) + 2 HCl

Pd(0) + 2CuCl2PdCl2 + 2CuCl

2CuCl + 2HCl + 1/2O2 2CuCl2 + H2O

C2H4 + 1/2O2 CH3CHO

The catalytic synthesis of acetaldehyde(Wacker process, oxidation of ethylene)

C2H4 + PdCl2 CH3CHO + Pd(0) + 2 HCl

2Cu2+

2Cu+

H+/O2

H2O

PdII

PdII

OH2

H+

HO

PdII

H2CCH2

OH

PdIIHH

OH

H

H

Pd(0)CH3CHO

Nucleophilic attack

Olefin metathesisThe Nobel Prize 2005 (Chauvin,

Schrock, Grubbs)

RCH=CHR + R'CH=CHR' 2RCH=CHR'

N NRR

Ru

PCy3

PhCl

Cl N

Mo

H

CMe2Ph

O-C(CF3)2CH3H3C(F2C)2CO

Grubbs catalyst Schrock catalyst

(CH2)n

ring-closing (RCM)

ring-opening (ROM)

(CH2)n +

ADMET

n

n

ROMP

The metathesis mechanism (Chauvin, 1971)

Concepts and skil ls Unit 6 Chem 76/76.1/710G (Advanced Inorgan ic Chemistry)

Chapters 13-14. Organometallic chemistry and catalysis.

Main concepts Main skills Ligand classification and the 18-electron rule Oxidat ion states, coordination numbers Bonding of CO, alkenes, H2, carbenes to transition metals

To be ab le to identify L, X, LX, LnXm ligands and their electron count To be ab le to determine the number of valence electrons for a complex and to associate those values with stable, reactive and unstable complexes

Phospine ligands, electronic and steric par ameters Genera l features of metal complexes of hydride, phosphine, alkyl, alkene, carbene and cyclopentadienyl ligands. Fundamental react ions in organometallic chemistry: Lewis acid and Le wis base association dissociation, oxidative addition/reductive elimination, insert ion/deinsertion ( -H elimination). Attack on coordinated ligands. Reaction mechanisms Elements of homogeneous catal ysis: hydrogenation, hydroformylation, metathesis, polymerization, oxid ation

To qualitatively describe the bonding of metals to: ¹ -acid ligands (CO, alkenes, H2), carbenes To predict reactivity of metal complexes on the basis of fundamental reactions covered (ligand exchange, oxidative addition-reduc tive elimination, insert ion-deinsertion, attack on coordinated liigands) To explain stability/instability of metal alkyls (kinetic vs. thermodynamic stability) To select appr opriate characterization methods for various types of metal complexes To describe some important homogeneous catalysts and some general mechanisms of the catalytic reactions studied