Chemistry Reference
In-Depth Information
O
1. 2 EtMgBr
2.
n
-PrC
ZrCp
2
≡
C
n
-Pr
CuCl.2LiCl
Cp
2
ZrCl
2
n
-Pr
n
-Pr
5.227
5.238
O
ZrCp
2
n
-Pr
1.
n
-Bu
4
NCl
2. PhCHO
3. H
+
n
-Pr
xs NBS
5.239
O
O
OH
Br
Ph
Br
Br
n
-Pr
n
-Pr
n
-Pr
n
-Pr
5
2
5
2
1
Scheme 5.68
of an allyl complex
5.245
. Complexes of this type are nucleophilic and further reactions are possible. The
allyl complex can be trapped with aldehydes, as well as other electrophiles.
81
The insertion of alkenes and alkynes with the alkyne complex generates metallocyclopentenes and met-
allocycopentadienes
5.247
(Scheme 5.70). The metal-carbon bonds in these complexes are quite polar and
may be cleaved by a variety of electrophiles, including acids, halogens and molecular oxygen. Addition of
reagents such as sulfur and phosphorus chlorides yields various unusual and interesting heterocycles.
An alternative route to alkyne complexes avoids the intermediacy of the metallocenes and allows formation
of complexes of unstable alkynes, such as benzyne and cyclohexyne. Treatment of Cp
2
ZrMeCl with an
aryl or vinyl lithium gives the expected aryl (or vinyl) complex
5.250
(Scheme 5.71).
82
Mild heating then
2
-alkyne complex
5.251
, which can also be drawn as its
metallacyclopropane resonance structure
5.252
. These complexes become sufficiently stable to be isolated if
an additional ligand, such as trimethylphosphine, is added, giving the adduct
5.253
. Analysis of the structures
causes loss of methane and formation of the
Cl
Cl
H
H
H
Li
Zr
ZrCp
2
ZrCp
2
Cp
Cp
H
H
H
5.242
5.243
5.244
OH
H
H
1. RCHO, BF
3
.OEt
2
2. NaHCO
3
1
3
R
η
→ η
ZrCp
2
Me
H
H
5
2
5
5
.
2
6
Scheme 5.69
