Chemistry Reference
In-Depth Information
C4
C3
C12 C11
C10
C7
C5
C6
C2
C9
C8
C1
P1
Au1
N1 C1A C2A
P Au
N C Me
t
-Bu
t
-Bu
2b
1.25
Figure 1.10
A gold(I) biphenylphosphine complex. Reprinted with permission from Herrero-G omez, E.; Nieto-
Oberhuber, C.
et al. Angew. Chem., Int. Ed.
2006
,
45
, 5455.
c
2006 Wiley-VCH Verlag GmbH & Co. KGaA.
Bidentate phosphines have been used for many years (Figure 1.11). They provide the complex with greater
stability because, for complete ligand dissociation, two metal-phosphine bonds must be broken, rather than
one. Simple bidentate ligands consist of two diphenylphosphino units linked by an alkyl chain or group
(
1.26
-
1.30
). More complex ligands use more elaborate linkers. Bis(diphenylphosphino)ferrocene, with a
ferrocenyl linker, has proved to be a useful ligand. Most other linkers are based upon aromatic motifs. BINAP
1.33
, most often employed as a chiral ligand for asymmetric catalysis, has sometimes been used. Xantphos
1.34
and DPEphos
1.35
form a special subset of bidentate ligands. In square planar complexes, such as
complexes with palladium(II), due to the geometrical demands of the linker, the two phosphines are capable
of being
trans
.
21
The other bidentate ligands tend to be
cis
.
PPh
2
PMe
2
Ph
2
P
PPh
2
Ph
2
P
Me
2
P
1.27
dppe
(diphos)
1.26
dppm
1.28
dmpe
PPh
2
Ph
2
P
PPh
2
Ph
2
P
1.29
dppp
1.30
dppb
PPh
2
PPh
2
Fe
PPh
2
PPh
2
1.31
dppbz
1.32
dppf
Ph
2
P
PPh
2
Ph
2
P
PPh
2
PPh
2
PPh
2
O
O
1.34
Xantphos
1.35
DPEphos
1.33
BINAP
Figure 1.11
Bidentate phosphines.
