Chemistry Reference
In-Depth Information
lyst preparation is therefore of great importance. Dry THF is normally used for catalyst
preparation. A considerable number of protocols have been devised.
(A) Dissolution of [Ir(COD)Cl]
2
and ligand
L
* in 1:2 molar ratio in THF. A complex
[Ir(COD)
L
* Cl] (
K1
) is formed by breaking up chloro bridges (Scheme 8B.77).
The application of this procedure is limited to aminations with aliphatic amines
[288,307]. It has been most successfully used in conjunction with ligand
L60
[290] .
(B) Procedure A with additional LiCl (1 equiv). This procedure gave good results
for alkylations in combination with
L60
[299,308]; it was less successful with
L59
as ligand [287c,309] .
(C) Addition of base (TBD [307] , DABCO [310] ,
n
- propylamine [310] , DBU [311c] )
to a 1:2 mixture of [Ir(COD)Cl]
2
and
L
* to effect C -H activation at a CH3 group
(Scheme 8B.77 ) [289] . C -H activation is much faster for
L60
than
L59
[312] .
This explains why procedure B is successful with ligand
L60
but not
L59
. Likely,
even weak bases such as malonate anion are able to effect C-H activation in
the case of ligand
L60
.
(D) This procedure was developed for alkylations in conjunction with ligand
L59
[313]. TBD is added to a solution of [Ir(COD)Cl]
2
,
L *
and tetrahydrothiophene
(THT) in THF at rt. After 2 h, the allylic carbonate and CuI are added.
(E) Tsuji ' s variant (salt - free conditions) [30] : The catalyst is prepared according to
C, and the conjugate acid HNu of a nucleophile Nu
−
is used as pronucleophile
[311,312]. An alkoxide is generated upon use of an allylic carbonate. This is a
strong base, which deprotonates the pronucleophile HNu.
8B.7.1.5.2. Catalytic Cycle and Absolute Confi guration of the Substitution Products
The
complexes
K3
are coordinatively saturated. Dissociation of
L
appears necessary to gen-
erate the reactive species
K4
(Scheme 8B.78 ). Marcovi
and Hartwig found that the
product complex
K6
is the resting state of the reaction of cinnamyl methyl carbonate
with aniline (ligand
L59
) [314]. Remarkably, the allyl complex
K5
was not found. The
authors propose, on the basis of the reaction kinetics, that the formation of
K5
is
ć
aS
L
base
O
Ir
[Ir(COD)
L*
Cl]
L
P
O
K1
N
Me
S
Ar
Ar
K3
N
N
N
N
N
H
N
N
TBD
DABCO
DBU
Scheme 8B.77.
Preparation of (phosphoramidite)Ir complexes
K3
by C- H activation.
