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Oxidative addition and CO insertion reaction. 201450720 지 슬기. contents. Oxidative addition Mechanisms of oxidative addition Type of oxidative addition. CO insertion reaction. Two type of insertion reaction. Mechanisms of CO insertion . Oxidative addition reaction. Oxidative addition

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Presentation Transcript
contents
contents
  • Oxidative addition
    • Mechanisms of oxidative addition
    • Type of oxidative addition.
  • CO insertion reaction.
    • Two type of insertion reaction.
    • Mechanisms of CO insertion.
oxidative addition reaction
Oxidative addition reaction
  • Oxidative addition
    • Reverse reaction of reductive elimination.
    • A process that increases both the oxidation state and coordination number of a metal centre.
    • often a step in catalytic cycles, in conjunction with its reverse reaction, reductive elimination.

X

LnM + X-Y

LnM

oxidative addition

reductive elimination

Y

three center cis addition concerted pathway
Three center Cis-addition (Concerted pathway)

a

b

16e-

18e-

a : formation of σ complex

b : metal electrons are formally transferred to the σ* orbital of A-B

three center cis addition concerted pathway1
Three center Cis-addition (Concerted pathway)
  • example

d8IrCl(CO)(PPh3)2

d8IrCl(H2)(CO)(PPh3)2

s n 2 mechanism non concerted
SN2 Mechanism(non-concerted)
  • In the SN2 pathway, adopted for polarized A-B substrates such as alkyl halides, the metal electron pair of LnM directly attacks the A-B σ* orbital by an in-line attack at the least electronegative atom formally to give LnM2+ , A- and B- fragments.
s n 2 mechanism non concerted1
SN2 Mechanism(non-concerted)
  • Often found in the addition of methyl, allyl, acyl, and benzyl halides.
ionic mechanism
Ionic mechanism
  • Hydrogen halides(e.g. HCl, HBr, HI) are often largely dissociated in solution, and the anion and proton tend to add to metal complexes in separate steps.

H+ +Cl-

HCl

insertion reactions
Insertion Reactions
  • An insertion reaction is a chemical reaction where one chemical entity (a molecule or molecular fragment) interposes itself into an existing bond of typically a second chemical entity.
insertion reactions1
Insertion Reactions
  • There are two main types of insertion.
    • 1,1 insertion in which the metal and the X ligand end up bound to the same(1,1) atom
    • 1,2 insertion in which the metal and the X ligand end up bound to adjacent (1,2) atoms of an L-type ligand.
co insertion reactions
CO Insertion Reactions
  • Perhaps the most well-studied insertion reaction is carbonyl insertion, which involves the reaction of CO with an alkyl complex to give an acyl product.
  • H3C-Mn(CO)5 + CO CH3C-Mn(CO)5

O

co insertion reactions1
CO Insertion Reactions
  • Mechanism 1 : CO Insertion
  • direct insertion of CO into metal-carbon bond.
  • Mechanism 2 : CO Migration
  • migration of CO to give intramolecular CO insertion. This would alsogive a 5-coordinate intermediate with a vacant site available for an incoming CO.
  • Mechanism 3 : Alkyl Migration
  • the alkyl group would migrate, rather than the CO, and attach itself to a CO cis to the alkyl. This would also give a 5-coordinate intermediate with a vacant site available for an incoming CO.
co insertion reactions2
CO Insertion Reactions
  • Experimental evidence
  • Reaction of CH2Mn(CO)5 with 13CO gives a product with the labeled CO in carbonyl ligands only ; none is found in the acyl position.
  • the reverse reaction
  • The reverse reaction, when carried out with 13C in a carbonyl ligandcis to the acyl group, gives a product that has a 2:1 ratio of cis to trans product.

O

CH3C-Mn(CO)5 H3C-Mn(CO)5 + CO

reference
Reference
  • 이공학을 위한 무기화학 강의 p715~724
  • Wikipedia, google
  • Inorganic chemistry – third Edition, Gary L. Miessler ∙ Donald A. Tarr