CHEM 433 Reaction

Dissociative Substitutions

-analogous to SN1

-A two step mechanism that proceeds via a rate limiting M-X bond cleavage, leading to a
short-lived reactive intermediate, that can either back react with X or with Y to
give product—usually irreversibly

-first order

rate = d[L5 MY]/dt =
(k1 k2[L5 MX][Y])/(k-1 [X] + k2 [Y])
If k 2[Y] >> k-1[X], then rate = k1[L5 MX]

Associative Substitutions

-analogous to SN2
-A two step mechanism that proceeds via a rate limiting M-Y bond forming step, leading
to a short-lived reactive intermediate with an expanded coordination number, that can
either back react by loss of Y or lose X to give product—usually irreversibly.

-second order

rate = d[L3 MY]/dt =
(k1k2 [L 3MX][Y])/(k-1 + k2)

Intercahgen Mechanism

Generally, the intermediates formed in the previous mechanisms are not observable and
may even be transition states. In the interchange mechanism, a more concerted process
in which M-X bond breakage occurs simultaneously with M-Y bond formation takes place

Mechanisms are classified as Id or Ia depending on the relative degrees of M-X
bond breakage vs M-Y bond formation in the transition state:
Id à M-X bond breakage is more complete than M-Y formation
Ia à M-Y bond formation is more complete than M-X bond breakage

Concerted Mechanism (Non-polar) of oxidative addition

concerted Mechanism (Polar) of oxidative addition

Reductive Elimination—Mechanism.

has to be cis to each other

Insertion reactions (1,1)

d[P]/dt = k 1k 2 [L'][SM]
/(k -1 + k 2 [L'])

Olefin Insertion and Beta-Hydride Elimination

Olefin Hydrogenation Hydride Path

Olefin Hydrogenation Olefin Path

Hydrosilation by dn Catalysts

Hydroformylation

hydroformylation vs hydrogenation