金属有机化学第五章

rate =
-d[MeMn(CO)5] dt
k1k2[L][MeMn(CO)5] k2[L]
k1[MeMn(CO)5]
First order reaction
ii. If k-1 is large relative to k2[L], then the equation becomes:
rate =
C MAB
1,1 insertion
C +L
MA
elimination
-L
B
L C
MA
B
C
C
A 1,2 insertion M
A +L
B elimination M B
-L
LC
A MB
General Features: • There is no change in the formal oxidation state of the metal unless AB is an alkylidene or alkylidyne. • The groups undergoing migratory insertion must be cis to one another. In complexes where the cis coordination sites are blocked by strongly coordinated ligands, insertion or elimination processes are not possible. • An open coordination site is created during migratory insertion. Therefore, for the reverse reaction--elimination--to occur, an open coordination site must be generated by ligand dissociation.
saturation in the ligand concentration dependence.
rate =
-d[MeMn(CO)5] dt
k1k2[L][MeMn(CO)5] k-1 + k2[L]
kobs[MeMn(CO)5]
kobs =
k1k2[L] k-1 + k2[L]
Under pseudo-first order conditions ([L] >>
Chapter 5 Migratory Insertion and Elimination
第五章 迁移插入和消除
The third fundamental transformation involved in organometallic transformations (ligand substitution and oxidative addition /reductive elimination being the others we've discussed) is migratory insertion/elimination.
• In cases where C is a chiral carbon center, the reaction usually occurs with retention of configuration. • Cases where C migrates to AB followed by coordination of L in place of C, and where AB migrates to C followed by coordination of L in place of AB are both known.
1,1-Migratory Insertion: Insertion of CO:
Most of the early mechanistic work has been carried out on iron and manganese alkyls. A. Kinetics and Mechanism:
[MeMn(CO)5], a plot of 1/kobs vs. 1/[L] will have slope = k-1/k1k2 and y intercept = 1/k1.
B. Stereochemistry at the Metal:
For the migratory insertion of CO into a Mn-Me bond, two limiting mechanisms could be envisioned. Methyl migration to a bound CO (A), or CO migration to the Mn-Me bond (B).
CH3
OC OC
Mn
CO k1 CO k-1
OC OC
Mn
CO CH3
CO
CO O
L
L OC

CO
Mn k2 OC
CH3
CO O
rate =
-d[MeMn(CO)5] dt
k1k2[L][MeMn(CO)5] k-1 + k2[L]
i. If k-1 is very small relative to k2[L], then the rate expression is simplified to:
-d[MeMn(CO)5]
k1k2[L][MeMn(CO)5]
dt k1k2[L][MeMn(CO)5]
k-1
k-1 + k2[L]
Second order reaction
iii. If k-1 and k2[L], have similar magnitudes, then a complex rate expression is observed that displays
CH3
OC
CO
Mn
OC
CO
CO
A
CH3
OC
CO
Mn
OC
CO
CO
B
Calderazzo looked at the migratory insertion of
CH3Mn(CO)5 labeled with 13CO cis to the methyl substituent. There are 4 possible stereochemical