Structure and dynamics of the η2-hexafluorobenzene complexes [Re(η5-C5H4R)(CO) 2(η2-C6F6)] (R = H or Me) and [Rh(η5-C5Me5)(PMe3)( η2-C6F6)]
Abstract
Photolysis of
[Re(η
5
-C
5
H
4
R)(CO)
3
]
(R = H or Me) in hexafluorobenzene yielded
[Re(η
5
-C
5
H
4
R)(CO)
2
(
η
2
-C
6
F
6
)] containing the
η
2
-co-ordinated arene. The complex containing
η
5
-C
5
H
5
has been characterised
crystallographically. It forms monoclinic crystals in space group
P2
1
/n with Z = 4,
a = 7.926(2),
b = 12.179(4),
c = 13.675(4) Å and
β = 102.91(2)°. The structure reveals the
expected features of distortion of the C
6
F
6
unit
from planarity at the co-ordinated C–C bond. The rhenium lies
2.059(7) Å from the mid-point of the co-ordinated
C–C bond of C
6
F
6
. The IR and
low-temperature
19
F NMR spectra reveal the presence of two
rotamers, which are interconverted by rotation about the
metal–C
6
F
6
bond with
ΔG
‡
= 36.7 kJ
mol
-1
at 184 K. At higher temperatures a second
intramolecular rearrangement causes broadening of the
19
F
resonances. This fluxional process has been identified as a [1, 2]-shift
of the site of rhenium co-ordination by linewidth and exchange
spectroscopy measurements:
ΔH
‡
= 57.6
± 0.5 kJ mol
-1
,
ΔS
‡
= -7
± 2 J K
-1
mol
-1
.
The dynamic behaviour of the
(η
5
-C
5
H
4
Me) complex is extremely
similar. The crystal structure of
[Rh(η
5
-C
5
Me
5
)(PMe
3
)(
η
2
-C
6
F
6
)], synthesised previously,
has been determined for comparison. It crystallises in the same space
group with a = 8.694(9),
b = 16.818(9),
c = 14.642(6) Å and
β = 106.69(6)°. The structural features of this
rhodium complex are very similar to the rhenium complex, but the metal
lies 1.920(5) Å from the mid-point of the co-ordinated
C–C bond of the C
6
F
6
unit. The shortening
of the M–C
6
F
6
bond is associated with the
stereochemical rigidity of this complex. The C–F bonds of the
co-ordinated carbons atoms are 0.049(7) Å longer than the
remaining C–F bonds. Comparison of structural features of three
η
2
-C
6
F
6
complexes revealed that the
distortions of the C
6
F
6
unit are almost constant,
indicating a hard potential-energy surface. The analogy to co-ordinated
C
2
F
4
is reinforced by the similarity in
co-ordination geometry. The electron-withdrawing character of
η
2
-C
6
F
6
is confirmed by the
![[small nu, Greek, tilde]](https://www.rsc.org/images/entities/char_e0e1.gif)
(CO) frequencies of
[Re(η
5
-C
5
H
5
)(CO)
2
(η
2
-C
6
F
6
)] which lie at the high limit
for complexes of the type
[Re(η
5
-C
5
H
5
)(CO)
2
L].
‡
= 36.7 kJ
mol
-1
at 184 K. At higher temperatures a second
intramolecular rearrangement causes broadening of the
19
F
resonances. This fluxional process has been identified as a [1, 2]-shift
of the site of rhenium co-ordination by linewidth and exchange
spectroscopy measurements:
ΔH
‡
= 57.6
± 0.5 kJ mol
-1
,
ΔS
‡
= -7
± 2 J K
-1
mol
-1
.
The dynamic behaviour of the
(η
5
-C
5
H
4
Me) complex is extremely
similar. The crystal structure of
[Rh(η
5
-C
5
Me
5
)(PMe
3
)(
η
2
-C
6
F
6
)], synthesised previously,
has been determined for comparison. It crystallises in the same space
group with a = 8.694(9),
b = 16.818(9),
c = 14.642(6) Å and
β = 106.69(6)°. The structural features of this
rhodium complex are very similar to the rhenium complex, but the metal
lies 1.920(5) Å from the mid-point of the co-ordinated
C–C bond of the C
6
F
6
unit. The shortening
of the M–C
6
F
6
bond is associated with the
stereochemical rigidity of this complex. The C–F bonds of the
co-ordinated carbons atoms are 0.049(7) Å longer than the
remaining C–F bonds. Comparison of structural features of three
η
2
-C
6
F
6
complexes revealed that the
distortions of the C
6
F
6
unit are almost constant,
indicating a hard potential-energy surface. The analogy to co-ordinated
C
2
F
4
is reinforced by the similarity in
co-ordination geometry. The electron-withdrawing character of
η
2
-C
6
F
6
is confirmed by the
(CO) frequencies of
[Re(η
5
-C
5
H
5
)(CO)
2
(η
2
-C
6
F
6
)] which lie at the high limit
for complexes of the type
[Re(η
5
-C
5
H
5
)(CO)
2
L].
Please wait while we load your content...
