Lecture Subset TM Complexes
Ligands and Bonding and Electron Counting in Organo-Transition Metal
Compounds
Stable electronic configurations: MO Energy Level Diagrams Reviewed
Electron count preference
Electron count and Oxidation States
Stable electronic configurations: MO Energy Level Diagrams Reviewed
Electron count preference
Electron count and Oxidation States
Ligands
• Carbon Monoxide
• Phosphines
• Cyclopentadienide and arenes
• Hydrides and dihydrogen
, Classification of Ligands: II
The L, X, Z approach
Malcolm Green : The CBC Method for Covalent Bond Classification used
extensively in organometallic chemistry.
L ligands are derived from charge-neutral precursors: NH3, amines,
N-heterocycles such as pyridine, PR3, CO, alkenes etc.
X ligands are derived from anionic precursors: halides, hydroxide, alkoxide
alkyls—species that are one-electron neutral ligands, but two electron
donors as anionic ligands. EDTA4- is classified as an L2X4 ligand,
features four anions and two neutral donor sites. C5H5 is classified an
L2X ligand.
Z ligands are RARE. They accept two electrons from the metal center.
They donate none. The “ligand” is a Lewis Acid that accepts electrons
rather than the Lewis Bases of the X and L ligands that donate electrons.
,Electron Counts
Electron counting and the 18-electron “Rule” (Guide
is better. It is the “octet” rule for transition
metals—but not as rigorously obeyed.)
2 Approaches => Same answer:
Ionic (method A on next slide):
# of electrons on Metal its oxidation state +
# of electrons from donated pairs (X- is 2; L is 2)
Neutral:
# of electrons on Metal in ox. State of 0 +
# of electrons from ligands (X is 1; L is 2)
, Table listings of no. of electrons
Donated by ligands.
Advantage of Method A
(the “ionic” method)
Oxidation state of metal
Automatically obtained)
Illustration from page 57
Spessard Copyright
Organometallic Chemistry
© 2010 by Oxford University Press, Inc.
Ligands and Bonding and Electron Counting in Organo-Transition Metal
Compounds
Stable electronic configurations: MO Energy Level Diagrams Reviewed
Electron count preference
Electron count and Oxidation States
Stable electronic configurations: MO Energy Level Diagrams Reviewed
Electron count preference
Electron count and Oxidation States
Ligands
• Carbon Monoxide
• Phosphines
• Cyclopentadienide and arenes
• Hydrides and dihydrogen
, Classification of Ligands: II
The L, X, Z approach
Malcolm Green : The CBC Method for Covalent Bond Classification used
extensively in organometallic chemistry.
L ligands are derived from charge-neutral precursors: NH3, amines,
N-heterocycles such as pyridine, PR3, CO, alkenes etc.
X ligands are derived from anionic precursors: halides, hydroxide, alkoxide
alkyls—species that are one-electron neutral ligands, but two electron
donors as anionic ligands. EDTA4- is classified as an L2X4 ligand,
features four anions and two neutral donor sites. C5H5 is classified an
L2X ligand.
Z ligands are RARE. They accept two electrons from the metal center.
They donate none. The “ligand” is a Lewis Acid that accepts electrons
rather than the Lewis Bases of the X and L ligands that donate electrons.
,Electron Counts
Electron counting and the 18-electron “Rule” (Guide
is better. It is the “octet” rule for transition
metals—but not as rigorously obeyed.)
2 Approaches => Same answer:
Ionic (method A on next slide):
# of electrons on Metal its oxidation state +
# of electrons from donated pairs (X- is 2; L is 2)
Neutral:
# of electrons on Metal in ox. State of 0 +
# of electrons from ligands (X is 1; L is 2)
, Table listings of no. of electrons
Donated by ligands.
Advantage of Method A
(the “ionic” method)
Oxidation state of metal
Automatically obtained)
Illustration from page 57
Spessard Copyright
Organometallic Chemistry
© 2010 by Oxford University Press, Inc.
