chem 522 chapter 01 introduction. transition metal organometallic chemistry organic versus inorganic...
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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