Organometalic

• Delta bonding

  • Overlap of 4 d orbitals
  • +, -, +, ‐
  • 2 nodal planes including the bond axis
• Eta bonding (hapticity)


  Unsaturated ligands can bind through more than one C atom

  • n is used in superscript for no. carbons
  • If n = 1, don't write it

  
• Mu bonding- C-M bonds- 3-centre-2-electron bond


  • n = no. of metal centres
  • If n = 1, it is not bridging
  • If n = 2 don't write it

  
• Pi bonding


  The interaction of 𝛑 and 𝛑* orbtials
• Ligand and formal removal of charge

  
• Oxidation state = charge on M - sum of ligand charges
• No. d electrons = metal group no. - oxidation state
• Electron Deficient Complexes

  There are insufficient electrons to fill valence orbitals

  A 3-way bond between 2 metal centres and a C atom

  All atoms are sp3 hybridised

  If sp3 lobes are all +ve phase - bonding MO (constructive overlap)

  If one sp3 is -ve phase - antibonding MO (desructive)

  
• Halide bridging


  
  

  • Has one 𝛔 bond to M
  • Has one coordinate bond to a second M
  • Tend to show in pairs
• Coordinative Unsaturation


  
  

  Compounds that have less than 18 electrons

  May be a tendency to add more ligands (reactive)

  There must be one or more vacant orbitals available
• Coordinative Saturation


  Complexes with an 18-electron count

  Will most likely to lose a ligand
• Pauling Electroneutrality Principle


  Neutral molecules, or those with a ±1/2 charge are more likely to form, than highly charged species

  • The greater the charge/polarisation, the greater the tendency to react
• The Isolobal Analogy


  Their frontier orbitals (HOMO/LUMO) have a similar:

  • Number of electrons
  • Symmetry properties
  • Aprox. energy
  • Shape (in space)

  Shown by a reversible arrow above a unfilled circle

  If a molecule's fragments are isolobal, then the molecule is said to be isolobal

  
• ML6 MO diagram


  s,p,d orbtials of M are combines - sp3d2 hybrid

  
• Isolobal fragments


  Energies of the frontier electrons are similar - fufills isolobal criteria

  
• Kinetic stability of complexes


  Organometalics with vacant d-shell may decompose by 𝛃 hydride/reductive elimination (low energy)
• Thermodynamic stability of complexes


  Organometalics with full d shell may decompose by homolysis (high energy)
• Preventing decomposition


  • Use ligands stable to 𝛃 hydride elimination
  • Form a bridgehead alkyl, as the bridgehead alkene is unfavourable
  • Form an aryne from arenes
  • Can use bulky ligands
  • Can saturate the coordination sphere (use multidentate ligands)
  • Pauling Electroneutrality Principle (less charged = less reactove)
  • Make 18-electron count compounds
• Electron count


  16 electron count including M electrons - Square planar

  O.S. = complex charge - formal ligand charge

  d electrons = group no. - O.S.
• Salt elimination


  Metal halide + group 1 alkyl = M alkyl + insoluble ionic salt 
• Lattice enthalpy

  Is proportional to the first part of the Kapulstinski's equation:

  Modulus of charges × no. ions/ionic radii

  Smaller radii, larger charges and no. ions = larger lattice enthalpy
• Protonolysis


  Metal alkyl + acid = M salt + alkyl
• Oxidative addition

  Installs 2 ligands onto M

  Requires

  • Non-bonding electron density on M
  • A vacant coordination site
  • M must have accessible O.S. separated by 2 units
• Reductive elimination

  Opposite of oxidative addition

  Both ligands involved must be cis to each other
• Oxidative coupling

  Common in d2 complexes

  Alkene ligands are bonded via their 𝛑 system

  M becomes part of a cycloalkane - metallocycle
• Reductive cleavage

  Opposite of oxidative coupling

  Exists in equilibrium
• 𝛂 hydride elimination

  The transfer of a H on the 𝛂 position on a ligand, to M (a type of O.A.)

  Forms H-M=L

  Cannot occur in d0 or d1 complexes
• 𝛂 hydride abstraction

  Occurs in d0 and d1 complexes

  An 𝛂 H is transfered to an adjacent ligand from M
• 𝛃 hydride elimination

  Most common way of decomposition

  The transfer of H from the 𝛃 C on a ligand to M

  Square transition state

  Forms C double bond C and a M hydride
• 𝛔 bond metathesis

  a double decomposition

  A-B + C-D = A-C + B-D works with 𝛑
• Metal 𝛔 alkyl reactivity

  Insertion of CO/CO2/alkene between M and C

  Cleavage of M-C by electrophilic attack/cleavage or hydrogenolysis

  Reductive elimination
• Metal hydride synthesis

  • 𝛃-hydride elimination
  • Hydrogenolysis if a metal-alkyl
  • Oxidative addition to an electron rich metal
• Migratory insertion

  An easy way to form C-C and C-N bonds

  Reactions look like ‘insertion’ has occurred - usually migration that occurs

  1,1-migratory insertion

  Is inserted one atom away from the metal

  1,2-migratory insertion

  Is inserted two atom away from the metal