CHEM 522Chapter 01

Introduction

Transition Metal Organometallic Chemistry

• Organic versus inorganic chemistry

• Transition metals– Oxidation state– d orbitals

• Ligands (L)

• Coordination compounds or complexes (MLn)

Werner Complexes

• Lewis acids and bases• Common types

– Octahedral ML6

– Tetrahedral ML4

– Square planar ML4

– Trigonal bipyramid ML5

– Square pyramid ML5

• Stereochemistry– cis, trans isomers– optical isomers

Bridging

• When the ligand have more than one site for binding it could make a bridge

• 3c-2e bond

M M

Cl

Cl

M M

H

H

Chelate Effect

• Chelating ligand can bind through more than one donor atom

• Example ethylene diamine

• Chelating ligands are favored from entropy point of view

M(NH3)6n+ + 3en M(en)3

n+ + 6NH3

The Trans Effect

• Trans influence:

certain ligands make ligands trans to it more labile.

• For platinum complexes the order is:

OH- < NH3 < Cl- < CN- , CO < PR3 < H-

Hard and Soft Bases

• Hard base small and high charge

• Soft base large and low charge

• Soft-soft and hard-hard interaction is prefer over hard-soft interaction

Effect of ligands on d-orbitals

Octahedral Complex and d-Orbital Energies

Crystal Field Theory

Energy Effects in Octahedral Complexes

Crystal Field Theory

∆o versus P

• Hund’s rule

• pairing energy considerations

• ∆ > P low spin

• ∆ < P high spin

Magnetic Properties of CoordinationCompounds and Crystal Field Theory.

Magnetic moment

• Magnetic moment μs

μs = √n(n+2)Where n = number of unpaired electrons

n μs

1 1.732 2.833 3.874 4.905 5.92

Colors of Transition-Metal Complexes

• Transition-metal complexes can be red, purple, blue, green, yellow, orange, etc.

• Most other compounds are colorless (or, white).

• Why are transition-metal complexes special?

Absorption of Light

• If a compound is colored, it must absorb visible light.

• To absorb visible light a compound must have an empty (or partially filled) electronic energy level that is just a little higher in energy than another filled (or partially filled) level.

• The d orbitals in transition-metal ions often meet this test.

t2g1eg

0 –> t2g0eg

1

•

Spectrochemical Series

• Ligands can be arranged into a spectrochemical series according to the magnitude of splitting of the d-orbitals

• Large splitting is associated with strong field ligands

• Small splitting is associated with weak field ligands

• CN-1>en>NH3>H2O>F->SCN-> Cl-> Br-> I-

Crystal field splitting

Weak and Strong Field Ligands

Tetrahedral Crystal Field

Tetrahedral Splitting Pattern of d-Orbitals

• ∆O>∆T thus no strong field vs. weak field cases

Square Planar Crystal Field

Pi Bond Donor

MCl

Pi Bond Acceptor

Interaction with л-donor ligands

Interaction with л-acceptor ligands

л-donor ligands л-acceptor ligands

                                                                                                                                                                                

MO diagram of M(CO)6

Types of Ligands

• Simple sigma (σ)donor

M-Cl M-NH3

• M can also bond to C=C л bond and H-H σ bond

• This is known as hapticity (η)

• η2 H2CCH2

• η2 H2

M-H2 Bond (η2)

M

H

H

M

H

H

Interaction with Double Bond (η2)

MC

C

M

C

C

Interaction with Double Bond

R2P PR2

(η5) (η1)

Fe(CO)nM

Type of Ligands

• σ bonding electron pair donors (always consider 2-e are donated by ligand so ligand will be NH3, H-, R3C-,

• σ bonding, strong л-acceptor CO, CN-, PR3,

• σ bonding л-donor Cl-, F-,

• л-bonding electron pair donor л-acceptor C2H4, O2,

Common Ligands

• Table 1.10• CO, CN-

• Cp

• PR3

• bipy• dpe• acac

R2P PR2

CH

H3C CH3

C C

O O