Structure and dynamics of the η2-hexafluorobenzene complexes [Re(η5-C5H4R)(CO)2(η 2-C6F6)] (R = H or Me) and [Rh(η5-C5Me5)(PMe3)(η 2-C6F6)]

Article abstract of DOI:10.1039/a608135e

Photolysis of [Re(η⁵-C₅H₄R)(CO)₃] (R = H or Me) in hexafluorobenzene yielded [Re(η⁵-C₅H₄R)(CO)₂(η ²-C₆F₆)] containing the η²-co-ordinated arene. The complex containing η²-C₅H₅ has been characterised crystallographically. It forms monoclinic crystals in space group P2₁ln with Z = 4, a = 7.926(2), b = 12.179(4), c = 13.675(4) A and β = 102.91(2)°. The structure reveals the expected features of distortion of the C₆F₆ unit from planarity at the co-ordinated C-C bond; The rhenium lies 2.059(7) A from the mid-point of the co-ordinated C-C bond of C₆F₆. The IR and low-temperature ¹⁹F NMR spectra reveal the presence of two rotamers, which are interconverted by rotation about the metal-C₆F₆ bond with ΔG^? = 36.7 kJ mol^-1 at 184 K. At higher temperatures a second intramolecular rearrangement causes broadening of the ¹⁹F 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 (η⁵-C₅H₄Me) complex is extremely similar. The crystal structure of [Rh(η⁵-C₅Me₅)(PMe₃)(η ²-C₆F₆)], 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) A 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) A from the mid-point of the co-ordinated C-C bond of the C₆F₆ unit. The shortening of the M-C₆F₆ bond is associated with the stereochemical rigidity of this complex. The C-F bonds of the co-ordinated carbons atoms are 0.049(7) A longer than the remaining C-F bonds. Comparison of structural features of three η²-C₆F₆ complexes revealed ,that the distortions of the C₆F₆ unit are almost constant, indicating a hard potential-energy surface. The analogy to co-ordinated C₂F₄ is reinforced by the similarity in co-ordination geometry. The electron-withdrawing character of η²-C₆F₆ is confirmed by the v(CO) frequencies of [Re(η⁵-C₅H₅)(CO)₂(η ²-C₆F₆)] which lie at the high limit for complexes of the type [Re(η⁵-C₅H₅)(CO)₂L].

Full text of DOI:10.1039/a608135e

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2
Structure and dynamics of the ç -hexafluorobenzene complexes
5
2
[
[
Re(ç -C H R)(CO) (ç -C F )] (R = H or Me) and
5
4
2
6
6
5
2
Rh(ç -C Me )(PMe )(ç -C F )]
5
5
3
6
6
a
b
a
b
Catherine L. Higgitt, A. Hugo Klahn, Madeleine H. Moore, Beatriz Oelckers,
a
,a
Martin G. Partridge and Robin N. Perutz*
a
Department of Chemistry, University of York, York YO1 5DD, UK
Department of Chemistry, Universidad Catolica de Valparaiso, Casilla 4059 Valparaiso, Chile
b
5
5
2
Photolysis of [Re(η -C H R)(CO) ] (R = H or Me) in hexafluorobenzene yielded [Re(η -C H R)(CO) (η -C F )]
5
4
3
5
4
2
6
6
2
5
containing the η -co-ordinated arene. The complex containing η -C H has been characterised
5
5
crystallographically. It forms monoclinic crystals in space group P2 /n with Z = 4, a = 7.926(2), b = 12.179(4),
1
c = 13.675(4) Å and β = 102.91(2)Њ. The structure reveals the expected features of distortion of the C F unit from
6
6
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
1
9
bond of C F . The IR and low-temperature F NMR spectra reveal the presence of two rotamers, which are
6
6
‡
Ϫ1
interconverted by rotation about the metal–C F bond with ∆G = 36.7 kJ mol at 184 K. At higher temperatures
a second intramolecular rearrangement causes broadening of the F resonances. This fluxional process has been
6
6
1
9
identified as a [1, 2]-shift of the site of rhenium co-ordination by linewidth and exchange spectroscopy
‡
Ϫ1
‡
Ϫ1
Ϫ1
5
measurements: ∆H = 57.6 ± 0.5 kJ mol , ∆S = Ϫ7 ± 2 J K mol . The dynamic behaviour of the (η -
5
2
C H Me) complex is extremely similar. The crystal structure of [Rh(η -C Me )(PMe )(η -C F )], synthesised
5
4
5
5
3
6
6
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)Њ. 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 F unit. The shortening of the M᎐C F bond is associated with the stereochemical rigidity of this complex. The
6
6
6
6
C᎐F bonds of the co-ordinated carbons atoms are 0.049(7) Å longer than the remaining C᎐F bonds. Comparison
2
of structural features of three η -C F complexes revealed that the distortions of the C F unit are almost
6
6
6
6
constant, indicating a hard potential-energy surface. The analogy to co-ordinated C F is reinforced by the
2
4
2
similarity in co-ordination geometry. The electron-withdrawing character of η -C F is confirmed by the ν˜ (CO)
6
6
5
2
5
frequencies of [Re(η -C H )(CO) (η -C F )] which lie at the high limit for complexes of the type [Re(η -
5
5
2
6
6
C H )(CO) L].
5
5
2
Although co-ordination of arenes through all six carbon atoms
many multinuclear complexes are known with bridging and
capping arenes. Arenes which act as bridging ligands in multi-
nuclear complexes serve as models for intermediate steps in
arene-exchange reactions and for adsorbates on metal
6
(η ) remains the norm, the last few years have seen progress in
stabilising structures in which the arene is co-ordinated through
2
4
two or four carbon atoms (η and η ). Properties of such co-
1
9–22
ordinated arenes are altered substantially from those of the free
surfaces.
Many of these systems are highly fluxional and
2
22,23
arene. Complexes with η -co-ordinated arenes play an import-
have been investigated by one- and two-dimensional NMR.
We have shown that hexafluorobenzene is particularly effect-
1
ant role in facilitating activation of arene C᎐H bonds.
2
2
4
The first examples of η -arene complexes were reported in
the 1960s and the first example of an η -complex with a fused
polycyclic arene was reported in 1977. Prior to the studies by
Harman and Taube of [Os(NH ) (η -arene)] only a handful
ive as a ligand for η - and η -co-ordination at electron-rich
5 2
2
2
metal centres. We have characterised [Rh(η -C R )(PMe )(η -
5 5 3
24 5 2 25 5
3
C F )], [Ir(η -C R )(C H )(η -C F )], [Ir(η -C H )(PMe )-
6 6 5 5 2 4 6 6 5 5 3
2 24 5 4 25
4
–7
2
2ϩ
(η -C F )]
and [Ir(η -C R )(η -C F )]
(R = H or Me).
6 4
3
5
6
6
5
5
6
6
2
of η -arene complexes were known. Examination of the reac-
Timms and co-workers have shown that η -C F and η -C F
6 6 6 6
tions of fused polycyclic aromatics has revealed the origin of
complexes may be generated by metal vapour synthesis and
6 6
2
the tendency to form η -complexes and provided examples of
have characterised a series of complexes [W(η -C F ) ], [M(η -
6 6 2
6
2
3,8–10
η -arene and aryl hydride complexes in equilibrium.
C F )(η -arene)] (M = Mo or W; arene = C H , C H F -1,3,5 or
6
6
6
6
6
3
3
6
4
26 4 6
The hapticity shift from η to η may play a key role in substi-
C H Me -1,3,5) and [M(η -C F )(η -arene)] (M = Ru or Os;
6
3
3
6
6
27
tution reactions of arenes and be important in transition-metal
arene = C H Me -1,3,5, C H Me -1,3 or C H ).
6
3
3
6
4
2
6
6
4
catalysed hydrogenation of arenes but examples of η -arene
A number of alternative types of reactions of hexafluoro-
benzene at transition-metal centres have been documented.
Hexafluorobenzene may act as a one-electron oxidising agent
1
1
12
complexes are limited. Geiger and co-workers have recently
Ϫ
examined arene co-ordination in formally 19 e Ru and Rh
sandwich complexes and η to η hapticity changes of arenes
induced by electron transfer. Co-ordination of C H in the η -
6
4
6
28
as with [Cr(η -C H ) ], or may undergo oxidative addition.
6 6 2
4
The direct product of oxidative addition is expected to be of
6
6
5
mode has been reported in a series of neutral and charged com-
the type M(C F )F and is observed on irradiation of [Rh(η -
6
5
2
4
2Ϫ
4
Ϫ 11,13,14
24
plexes: [Cr(η -C H )(CO) ]
,
[Mn(η -C H )(CO) ] ,
C Me )(PMe )(η -C F )] or on thermal reaction of [PtH(db-
5 5 3 6 6
t t 29
6
6
3
6
6
3
4
ϩ 15
5
4
16
[
Ir{MeC(CH PPh ) }(η -C H )] ,
and [Rh(η -C H )(η -C H )].
[Ir(η -C H )(η -C H )]
pm)(CH CMe )] (dbpm = Bu PCH PBu ) with C F . How-
2
2
3
4
6
6
17
5
5
6
6
2
3
2
2
2
6
6
5
ever, metal dihydrides react with the elimination of HF yielding
5
5
6
6
24,30
The scope of the co-ordination modes of C H6 and other
M(C F )H complexes.
Elimination of HF also provides the
5
6
6
5
arenes has become apparent. Initially, arene co-ordination was
driving force for the reaction of [Re(η -C Me )(CO) ] with C F
5 5 3 6 6
6 31
1
8
observed principally for mononuclear complexes but now
to form [Re(η -C Me CH )Re(CO) (C F )]. Homogeneous
5 4 2 2 6 5
J. Chem. Soc., Dalton Trans., 1997, Pages 1269–1280
1269

View Article Online
3
5
5
Fig. 1 An ORTEP diagram (50% thermal ellipsoids) of [Re(η -
2
C H )(CO) (η -C F )]
5
5
2
6
6
catalytic conversion of C6F6 to C F H has recently been
33
6
5
3
2
achieved with a rhodium complex. Kiplinger and Richmond
report selective room-temperature hydrogenolysis of aromatic
C᎐F bonds using a low-valent zirconocene species. The reac-
tions of C F with a variety of transition-metal complexes have
5
2
Fig. 2 Infrared spectra of [Re(η -C H )(CO) (η -C F )] (a) in hexane
5
5
2
6
6
solution at 298 K, (b) in argon matrix at 12 K
6
6
3
4
been reviewed recently.
The molecular structures of [Rh(η -C H )(PMe )(η -C F )]
form the second plane, bent at 44.4(2)Њ to the first, and lying
adjacent to the carbonyl groups. The angle between the C6F4
and the C H planes is 31.3(3)Њ. The Re atom lies at 2.059(7) Å
from the mid-point of C(1)᎐C(6) [labelled D(2)] and 1.947 Å
from the centroid of the C H ring [labelled D(1)]. The
5
2
24
5
5
3
6
6
5
2
25
and [Ir(η -C H )(C H )(η -C F )] both show that the two
5
5
2
4
6
6
5
5
fluorine atoms bonded to the co-ordinated carbon atoms are no
longer co-planar with the remaining C6F moiety. The C᎐C
4
5
5
bonds of the C F unit are distorted so that the ligand contains
6
6
D(1)᎐Re᎐D(2) angle is 129.7Њ. Further details of the structure
will be examined in the discussion.
a co-ordinated C᎐C bond and unco-ordinated diene unit. The
2
M(η -C F ) complexes characterised so far have proved to be
6
6
5
stereochemically rigid on the NMR timescale. However, [Ir(η -
5
2
Infrared studies of [Re(ç -C H R)(CO) (ç -C F )] (R = H or Me)
5
4
2
6
6
2
C R )(C H )(η -C F )] (R = H or Me) is present as two isomers,
5
5
2
4
6
6
5
2
The IR spectrum of [Re(η -C H )(CO) (η -C F )] [Fig. 2(a)]
assigned as the species related by rotation of C F about the
5
5
2
6
6
6
6
2
5
recorded in hexane at room temperature shows two pairs of
Ir᎐C6F6 bond. The rate of interconversion of the isomers is
Ϫ1 Ϫ1
bands at 2030 and 1970 cm and at 2022 and 1957 cm , which
are assigned to two isomeric forms of the product. The isomers
slow compared to the NMR relaxation time.
5
In this paper, we report the syntheses of [Re(η -
5
2
are present in the approximate ratio of 1.3:1. Similarly, [Re(η -
C H Me)(CO) (η -C F )] shows bands at 2026, 2019, 1966 and
954 cm in the same solvent. It proved impossible to discover
the effect of altering the solvent on the isomer ratio for [Re-
C H R)(CO) (η -C F )] (R = H or Me) and the crystal structure
5
4
2
6
6
2
5
of the η -C H complex. We show that these molecules are
5
4
2
6
6
5
5
Ϫ1
1
stereochemically non-rigid, undergoing two types of intra-
molecular rearrangement. We also report the crystal structure
5
2
5
2
(η -C H R)(CO) (η -C F )] as the IR bands were very broad
5 4 2 6 6
5
of [Rh(η -C Me )(PMe )(η -C F )], which proves to be free of
5
5
3
6
6
5
in more polar solvents. Instead, IR spectra of [Re(η -
the disorder which reduced the value of the structure of the η -
2
2
4
2
C H )(CO) (η -C F )] were recorded in hexane at a series of
temperatures down to 213 K. At 213 K the ratio had altered to
:1. The IR spectrum was also investigated in an argon matrix.
The vapour of a sample at 323 K was condensed with argon
onto a window at 20 K, which was then cooled to 12 K. The
spectrum of [Re(η -C H )(CO) (η -C F )] again shows four
bands at 2037, 2026, 1976 and 1964 cm although each is split
into multiple components by matrix effects [Fig. 2(b)]. Thus in
an Ar matrix there are still two isomeric forms present in a
similar ratio to that seen at room temperature in solution. This
ratio is likely to reflect the ratio of isomers present in the vapour
prior to deposition.
C H analogue. Comparison of three structures containing η -
5
5
2
6
6
5
5
co-ordinated C F rings shows very little variation in geometric
6
6
1
parameters. Finally, we assess the electronic characteristics of
hexafluorobenzene as a ligand.
5
2
5
5
2
6
6
Results
Ϫ1
5
2
Syntheses of [Re(ç -C H R)(CO) (ç -C F )] (R = H or Me)
5
4
2
6
6
5
The irradiation of [Re(η -C H )(CO) ] in C F (λ > 315 nm
5
5
3
6
6
5
for 15 h) generates a single product identified as [Re(η -
2
5
C H )(CO) (η -C F )]. The complex [Re(η -C H Me)(CO) -
5
2
5
2
6
6
5
4
2
(
η -C F )] is prepared via a similar route.
5
6
6
On the basis of the IR data alone we deduce that [Re(η -
C H )(CO) (η -C F )] exists as the two rotamers [shown in
equation (1)] as seen for [Ir(η -C R )(C H )(η -C F )]. The
2
5
5
2
6
6
5
2
Crystal and molecular structure of [Re(ç -C H )(CO) (ç -C F )]
5
2
25
5
5
2
6
6
5 5 2 4 6 6
5
2
The crystal structure of [Re(η -C H )(CO) (η -C F )] shows the
5
5
2
6
6
2
same features that have proved characteristic of other η -
2
4,25
hexafluorobenzene complexes (Fig. 1, Table 1).
The hexa-
fluorobenzene ligand is folded at the co-ordinated C᎐C bond,
C(1)᎐C(6). The atoms of the C6F4 unit, C(1)–C(6) and F(2)–
F(5) are almost coplanar (r.m.s. deviation 0.020 Å) and tipped
towards the C H5 ring. The atoms C(1), C(6), F(1) and F(6)
5
1
270
J. Chem. Soc., Dalton Trans., 1997, Pages 1269–1280

View Article Online
5
2
Table 1 Bond lengths (Å) and angles (Њ) for [Re(η -C H )(CO) (η -
5
5
2
C F )] with estimated standard deviations (e.s.d.s) in the least signifi-
6
6
cant figure(s) in parentheses
Re᎐C(8)
Re᎐C(7)
Re᎐C(1)
Re᎐C(6)
Re᎐C(10)
Re᎐C(9)
Re᎐C(11)
Re᎐C(12)
Re᎐C(13)
F(1)᎐C(1)
F(2)᎐C(2)
F(3)᎐C(3)
F(4)᎐C(4)
F(5)᎐C(5)
F(6)᎐C(6)
1.908(9)
1.914(9)
2.165(7)
2.205(7)
2.256(7)
2.267(7)
2.289(7)
2.307(7)
2.307(8)
1.395(9)
1.332(10)
1.332(11)
1.341(10)
1.337(10)
1.383(10)
O(1)᎐C(7)
O(2)᎐C(8)
C(1)᎐C(2)
C(1)᎐C(6)
C(2)᎐C(3)
C(3)᎐C(4)
C(4)᎐C(5)
C(5)᎐C(6)
C(9)᎐C(13)
C(9)᎐C(10)
C(10)᎐C(11)
C(11)᎐C(12)
C(12)᎐C(13)
1.155(11)
1.150(11)
1.418(11)
1.476(12)
1.337(12)
1.430(13)
1.313(13)
1.442(13)
1.383(13)
1.431(14)
1.415(14)
1.383(12)
1.424(14)
5
2
Fig. 3 Fluorine-19 NMR spectra of [Re(η -C H )(CO) (η -C F )] in
5
5
2
6
6
2
[
H ]thf in the temperature range 320–260 K
8
C(8)᎐Re᎐C(7)
C(8)᎐Re᎐C(1)
C(7)᎐Re᎐C(1)
C(8)᎐Re᎐C(6)
C(7)᎐Re᎐C(6)
C(1)᎐Re᎐C(6)
C(8)᎐Re᎐C(10)
C(7)᎐Re᎐C(10)
C(1)᎐Re᎐C(10)
C(6)᎐Re᎐C(10)
C(8)᎐Re᎐C(9)
C(7)᎐Re᎐C(9)
C(1)᎐Re᎐C(9)
C(6)᎐Re᎐C(9)
C(10)᎐Re᎐C(9)
C(8)᎐Re᎐C(11)
C(7)᎐Re᎐C(11)
C(1)᎐Re᎐C(11)
C(6)᎐Re᎐C(11)
C(10)᎐Re᎐C(11)
C(9)᎐Re᎐C(11)
C(8)᎐Re᎐C(12)
C(7)᎐Re᎐C(12)
C(1)᎐Re᎐C(12)
C(6)᎐Re᎐C(12)
C(10)᎐Re᎐C(12)
C(9)᎐Re᎐C(12)
C(11)᎐Re᎐C(12)
C(8)᎐Re᎐C(13)
C(7)᎐Re᎐C(13)
C(1)᎐Re᎐C(13)
C(6)᎐Re᎐C(13)
C(10)᎐Re᎐C(13)
C(9)᎐Re᎐C(13)
C(11)᎐Re᎐C(13)
C(12)᎐Re᎐C(13)
F(1)᎐C(1)᎐C(2)
F(1)᎐C(1)᎐C(6)
C(2)᎐C(1)᎐C(6)
86.5(4)
87.3(3)
113.9(3)
95.3(3)
75.9(3)
39.5(3)
102.7(3)
97.0(3)
148.2(3)
160.3(3)
138.5(3)
89.8(3)
131.1(3)
123.8(3)
36.9(4)
92.9(3)
131.8(4)
114.2(3)
151.6(3)
36.3(4)
60.1(4)
116.2(4)
149.5(3)
88.5(3)
118.7(3)
59.9(3)
59.7(3)
35.0(3)
151.0(3)
116.8(3)
97.4(3)
106.5(3)
59.9(3)
35.2(3)
59.1(3)
36.0(3)
111.5(7)
114.9(7)
116.2(7)
F(1)᎐C(1)᎐Re
C(2)᎐C(1)᎐Re
C(6)᎐C(1)᎐Re
F(2)᎐C(2)᎐C(3)
F(2)᎐C(2)᎐C(1)
C(3)᎐C(2)᎐C(1)
F(3)᎐C(3)᎐C(2)
F(3)᎐C(3)᎐C(4)
C(2)᎐C(3)᎐C(4)
C(5)᎐C(4)᎐F(4)
C(5)᎐C(4)᎐C(3)
F(4)᎐C(4)᎐C(3)
C(4)᎐C(5)᎐F(5)
C(4)᎐C(5)᎐C(6)
F(5)᎐C(5)᎐C(6)
F(6)᎐C(6)᎐C(5)
F(6)᎐C(6)᎐C(1)
C(5)᎐C(6)᎐C(1)
F(6)᎐C(6)᎐Re
C(5)᎐C(6)᎐Re
C(1)᎐C(6)᎐Re
O(1)᎐C(7)᎐Re
O(2)᎐C(8)᎐Re
C(13)᎐C(9)᎐C(10) 108.1(8)
C(13)᎐C(9)᎐Re
C(10)᎐C(9)᎐Re
C(11)᎐C(10)᎐C(9) 106.7(9)
C(11)᎐C(10)᎐Re
C(9)᎐C(10)᎐Re
C(12)᎐C(11)᎐C(10) 109.0(8)
C(12)᎐C(11)᎐Re
C(10)᎐C(11)᎐Re
C(11)᎐C(12)᎐C(13) 107.7(8)
C(11)᎐C(12)᎐Re
C(13)᎐C(12)᎐Re
118.9(5)
118.4(6)
71.7(4)
120.2(8)
117.4(8)
122.4(8)
122.7(8)
116.5(8)
120.8(9)
121.2(9)
121.0(8)
117.8(9)
121.8(9)
120.9(8)
117.2(9)
111.4(7)
115.5(7)
118.6(8)
115.2(5)
121.4(6)
68.8(4)
5
2
Fig. 4 Fluorine-19 NMR spectrum of [Re(η -C H )(CO) (η -C F )] in
5
5
2
6
6
177.6(8)
174.1(7)
2
[
H ]thf at 254.5 K. Top observed and bottom simulated spectrum
8
74.0(5)
71.1(4)
73.1(5)
72.0(4)
73.2(4)
70.6(4)
71.8(4)
72.0(4)
C(9)᎐C(13)᎐C(12) 108.4(8)
C(9)᎐C(13)᎐Re
C(12)᎐C(13)᎐Re
70.8(5)
72.0(4)
–ꢀ– –
enthalpy change, |∆H |, for the interconversion of the
5
2
Ϫ1
Fig. 5 Fluorine-19 NMR spectrum of [Re(η -C
5
H
5
)(CO)
(η -C F )] in
2 6 6
rotamers is ca. 1.5 kJ mol and the free energy change,
2
–
ꢀ– –
[ H ]thf at 178.5 K showing splitting of the δ Ϫ151 resonance (inset)
Ϫ1
8
|
∆G 300| ≈ 0.7 kJ mol .
1
9
parison with a F NMR spectrum at 253 K recorded at 84.57
MHz shows that the fine structure of the resonance at δ Ϫ151.5
arises from J coupling of a single isomer rather than two iso-
mers (the major splitting is 28 Hz at both field strengths).
Nevertheless, on further cooling to 173 K, each resonance of
1
9
5
Variable-temperature F NMR studies of [Re(ç -C H R)(CO) -
5
4
2
2
(
ç -C F )] (R = H or Me)
6
6
1
9
5
2
The F NMR (470 MHz) spectrum of [Re(η -C H )(CO) (η -
C F )] in [ H ]thf shows three broad resonances at 301.5 K
figures in parentheses are the full widths at half maximum,
5
5
2
2
6
6
8
5
2
(
the 470 MHz spectrum of [Re(η -C H )(CO) (η -C F )] starts
5 5 2 6 6
f.w.h.m.): δ Ϫ144.2 (189), Ϫ151.5 (106) and Ϫ171.7 (94 Hz). On
warming from 301.5 to 322 K the three resonances broaden
further. The resonance at δ Ϫ144 broadens at approximately
twice the rate of the other two resonances.
On cooling, the spectrum sharpens and at 280 K fine struc-
ture starts to appear in each resonance (Fig. 3). At 254.5 K
there is optimum resolution of the fine structure (Fig. 4). Com-
to broaden again. The resonance at δ Ϫ151.5 broadens faster
than the other two, reaching a f.w.h.m. of 76 Hz at 186 K
(compared to 63 Hz for the δ Ϫ144 resonance and 58 Hz for the
δ Ϫ171 resonance). At 186 K the coalescence point for the δ
Ϫ151.5 resonance is reached and below this temperature this
resonance splits into two signals at δ Ϫ150.90 and Ϫ150.85
(Fig. 5).
J. Chem. Soc., Dalton Trans., 1997, Pages 1269–1280
1271

View Article Online
In all the samples there are traces of free C F {ratio of
6
6
5
2
19
19
[
Re(η -C H )(CO) (η -C F )]:C F ≈ 25:1}. The linewidth of
Table 2 Fluorine-19 chemical shifts and F– F coupling constants
5
5
2
6
6
6
6
5
2
2
the C6F6 resonance at δ Ϫ162.9 (f.w.h.m. = 2–3 Hz) does not
obtained by simulation for [Re(η -C
5
H
5
)(CO) (η -C F )] in [ H ]thf
2 6 6 8
alter over the temperature range explored.
1
9
5
2
δ
J/Hz
J/Hz
J/Hz
The F NMR spectrum of [Re(η -C H Me)(CO) (η -C F )]
5
4
2
6
6
2
5
2
δA = Ϫ151.5
δM = Ϫ144.4
δX = Ϫ171.3
JAM = 36.5
JAM Ј = Ϫ11.0
JAX = 4.0
JAXЈ = 0.9
JM X = 13.8
JM XЈ = 3.0
JAAЈ = 25.6
JM M Ј = 18.1
JXXЈ = 13.7
in [ H ]thf is similar to that of [Re(η -C H )(CO) (η -C F )]. At
8
5
5
2
6
6
3
(
9
02.5 K three broad resonances are detected: δ Ϫ144.2
f.w.h.m. = 193), Ϫ152.2 (f.w.h.m. = 103) and Ϫ172.0 (f.w.h.m. =
3 Hz). Again, the resonances sharpen on cooling, reaching an
optimum at 257 K, before broadening on cooling further.
Again, the spectrum at 257 K seems to indicate the presence of
the frequencies of F , F and F . Similar results were obtained
a
m
x
5
2
one isomeric species. For [Re(η -C H Me)(CO) (η -C F )] the
5
2
2
5
4
2
6
6
for [Re(η -C H Me)(CO) (η -C F )] in [ H ]thf at 237.0 and
5 4 2 6 6 8
coalescence point for the δ Ϫ152 resonance is reached at 184 K
and below this temperature the resonance splits again into two
at δ Ϫ150.55 and Ϫ150.60.
2
43.5 K (τ = 50, 100 and 150 ms).
m
5
2
Analysis of the dynamics of [Re(ç -C H R)(CO) (ç -C F )]
5
4
2
6
6
(
R = H or Me)
At 300 K three broad singlets are seen in the F NMR spec-
1
9
19
5
2
F᎐ F EXSY studies of [Re(ç -C H R)(CO) (ç -C F )] (R = H
5
4
2
6
6
1
9
or Me)
5
2
trum of [Re(η -C H )(CO) (η -C F )]. The sharp resonances
of free C F and the lack of cross-peaks to C F in the EXSY
5
5
2
6
6
3
6–38
Exchange spectroscopy (EXSY)
investigating slow exchange processes and determining the rates
of exchange. At about 240 K the longitudinal relaxation times,
T , of the three pairs of F nuclei of [Re(η -C H )(CO) (η -
C F )] are approximately equal (T ≈ 500–600 ms measured by
inversion-recovery sequence). Thus [Re(η -C H )(CO) (η -
is a suitable method for
6
6
6
6
spectra both indicate that there is no intermolecular exchange.
On cooling, fine structure starts to appear for each resonance,
reaching optimum resolution at 254.5 K. The symmetrical pat-
terns which also appear in spectra run on a lower field instru-
ment indicate that the fine structure results from F–F coupling.
1
9
5
2
1
5
5
2
6
6
1
5
2
5
5
2
C F )] is amenable to study by EXSY at these temperatures
6
6
Simulation of the second-order effects in this [AMX] spin sys-
2
using a simplified approach to data analysis (see below). The
tem yields the couplings listed in Table 2 which must corres-
pond to the averaged spectrum for the two rotamers identified
from the IR.
The EXSY spectra indicate that the three pairs of fluorine
nuclei undergo intramolecular chemical exchange. The inten-
sities of the EXSY cross-peaks are consistent with the whizzing
process shown below in which the point of attachment of the
metal to the C F ring undergoes a [1,2]-shift. As expected the
relative intensity of the Fa to Fx cross-peak increases as the
mixing time and temperature are increased (probably due to
multiple [1,2] hops). Further evidence for this [1,2]-shift comes
from the observation that the δ Ϫ144 resonance broadens at
twice the rate of the other two resonances in the 300–322 K
region. In Scheme 1, only one of the two A nuclei changes
chemical shift at each step, only one of the X nuclei changes but
both of the M nuclei change chemical shift. This effect adds an
independent method of assigning the δ Ϫ144 resonance to Fm.
If a [1,3]-shift occurred as the dominant process, all the reson-
1
9
19
5
2
F᎐ F EXSY spectra of [Re(η -C H )(CO) (η -C F )] in
5
5
2
6
6
2
[
H ]thf were recorded at 236.5 and 243.5 K with mixing times,
8
τm, of 50, 100, 150 and 500 ms (470.4 MHz). Pure two-
dimensional absorption lineshapes were recorded through the
use of suitable phase cycling. The EXSY spectra show intense
cross-peaks linking sites F to Fm and Fm to F and a less intense
cross-peak linking sites Fa to Fx (approximately 80 times less
intense at the lowest temperature with the shortest mixing
time). No cross-peaks are seen to the free C F resonance. Fig. 6
a
x
6
6
6
6
shows one-dimensional sections from the EXSY spectrum at
3
9
ances should broaden at the same rate.
Since the spectra at 250 K are consistent with the presence of
a single species, they are in the high-temperature limit of the
Re᎐C6F6 rotation, but in the slow exchange region for ring-
whizzing throughout the temperature range 250–320 K. Analy-
sis of the bandwidths of the three fluorine resonances between
2
98.5 and 318.5 K was carried out to determine the rate and the
activation parameters for this ‘ring-whizzing’ process. This tem-
perature region was chosen as fine structure arising from F–F
coupling makes a very small contribution to the linewidth. The
5
2
spectra for [Re(η -C H Me)(CO) (η -C F )] over the temper-
5
4
2
6
6
ature range 297.5–325.0 K can be analysed in a similar way. The
rate constant for exchange was determined from equation (2)
Fig. 6 One-dimensional sections at the frequencies of (a) F (δ Ϫ171.3),
x
₁
₁
kwhizz = π(w Ϫ w )
(2)
1
9
19
₂
0₂
(
b) F (δ Ϫ151.5) and (c) F (δ Ϫ144.4) from the F– F EXSY spec-
a m
5 2 2
trum of [Re(η -C H )(CO) (η -C F )] in [ H ]thf at 243.5 K (τ = 50
ms) (note the absence of F F cross-peaks)
5
5
2
6
6
8
m
where kwhizz = rate constant of dynamic process at temperature
T (averaged over the three resonances); w = f.w.h.m. (Hz) of the
resonance at the temperature T [take w as equal to 0.5 f.w.h.m.
Hz) for the δ Ϫ144 resonance]; w0 = natural f.w.h.m. (Hz) of
the resonance before exchange broadening sets in {best fit
a
x
₁
₂

₁
₂
(
₁
₂
5
2
achieved when set to 5.0 Hz for [Re(η -C H )(CO) (η -C F )]
and 10.0 Hz for [Re(η -C H Me)(CO) (η -C F )]}. Fig. 7(a)
5
2
5
2
6
6
5
5
4
2
6
6
shows the rate constant for ring-whizzing, kwhizz, versus tem-
5
2
perature, T, for [Re(η -C H R)(CO) (η -C F )] (R = H or Me)
5
4
2
6
6
2
in [ H ]thf (Table 3).
8
1
272
J. Chem. Soc., Dalton Trans., 1997, Pages 1269–1280

View Article Online
Scheme 1
Values of the rate constant for ring-whizzing, kwhizz, at lower
temperatures were determined by analysis of the EXSY spectra.
Cross-peaks in the spectra arise from chemical exchange.
Appropriate phase cycling was used to suppress unwanted sig-
nals arising from coherent phenomena such as relayed magnet-
isation and single- and multiple-quantum coherence transfer
,
37,38
processes.†
If cross-relaxation effects are neglected, the rela-
tionship between the cross-peak intensities, I , and the first-
ij
order rate constant for chemical exchange from site i to site j,
kij, may be written as shown in equation (3) (adapted from
ϪRτ
m
I (τ ) = (e
) M Њ
(3)
ij
m
ij
j
Fig. 7 (a) Rate constant for ring whizzing, kwhizz, versus temperature, T,
5
2
for [Re(η -C H R)(CO) (η -C F )] (R = H ᭺ or Me ᭡). (b) Eyring plot:
3
8,40–42
5
4
2
6
6
Macura and Ernst)
where M Њ = equilibrium magnetis-
5
2
j
ln(kwhizz/T) versus 1/T for [Re(η -C H )(CO) (η -C F )]
5 5 2 6 6
ation of the nuclei in site j (intensity of the on-diagonal peak in
site j when τ = 0); R = relaxation matrix which comprises con-
m
tributions from cross relaxation, spin–lattice relaxation and
chemical exchange. The matrix has off-diagonal elements
R = Ϫk .
Table 3 Rate constants for ring-whizzing, k
, at given temperatures
2
whizz
5
2
for [Re(η -C H R)(CO) (η -C F )] (R = H or Me) in [ H ]thf
5
4
2
6
6
8
ji
ij
The values of M Њ were determined with τm of 1 ms. For this
j
R = H
T/K
R = Me
T/K
system, M Њ is equal for each site j. By including M Њ values in
j
j
Ϫ1
Ϫ1
kwhizz/s
the calculation, values for the spin–lattice relaxation rate for the
k
whizz/s
4
0
nucleus in the jth site can be determined in addition to kij.
236.5
243.5
0.380
1.01
230
267
283
332
432
545
657
806
237.0
243.5
297.5
301.5
302.5
305.0
307.5
311.0
313.5
316.0
319.5
0.370
0.980
182
For general multiple-site exchange equation (3) cannot be
solved analytically. However, if sufficiently short mixing times
are used, approximate solutions can be found by invoking the
initial rate approximation given in equation (4). If τm is
2
3
3
98.5
00.5
01.5
256
277
324
403
526
645
828
988
304.0
06.5
310.0
3
ϪRτ
m
e
≈ 1 ϩ Rτm
(4)
3
3
12.5
15.5
increased, it is necessary to include higher terms of the expan-
ϪRτ
m
318.5
1010
sion of e
to take account of multiple [1,2] hop processes.
5
3
3
22.0
25.0
1230
1480
The rate constant for the [1,2]-shift process for [Re(η -
2
C H )(CO) (η -C F )] was calculated using the initial rate
5
5
2
6
6
Ϫ1
approximation to be 0.38 ± 0.03 s at 236.5 K and 1.01 ± 0.03
Ϫ1
5
s
at 243.5 K. For a direct [1,3]-shift the rate was calculated to
be some 600 times slower at 243.5 K. For [Re(η -C H Me)-
5
4
2
(
CO) (η -C F )] the EXSY spectra yielded rate constants for
2 6 6
Ϫ1
the [1,2]-shift process of 0.37 ± 0.05 s at 237.0 K and 0.98 ±
.06 s at 243.5 K. The rate of the [1,3]-shift process was again
†
In coupled spin systems, zero-quantum coherence and longitudinal
Ϫ1
0
scalar or dipolar order can also give rise to cross-peaks (referred to as ‘J
3
7,38
cross-peaks’) that cannot be removed by phase cycling.
Longi-
much slower.‡
tudinal scalar or dipolar order effects can be minimised by careful cali-
bration of π/2 pulses. The ‘J cross-peak’ contributions to cross-peak
intensities are shown to be negligible by the low intensity of the cross-
peak linking the J–J coupled sites F to F . The amplitudes of ‘J cross-
peaks’ show a sinusoidal (dampened) dependence on τm while the
amplitudes of exchange cross-peaks rapidly increase (due to exchange)
and then slowly decay away (due to spin-lattice relaxation) as τm
increases. The value of the rate constant for the [1,2]-shift process was
found to be invariant (within experimental error) with mixing time over
the region investigated. This observation gives further support to the
assumption that the contribution to cross-peak intensities from ‘J cross-
peaks’ is negligible.
Combination of the high-temperature rate constant data
determined from linewidth analysis with the low-temperature
data from the EXSY experiments allows the activation param-
eters for the ‘ring-whizzing’ process to be calculated. The
Eyring plot of ln[kwhizz/T] versus 1/T [Fig. 7(b)] yields the acti-
vation parameters in Table 4. Rate data at intermediate temper-
atures are difficult to determine because of the complicating
a
x
Ϫ1
‡ At ca. 240 K, the exchange rate of ca. 0.8 s is slightly slower than
Ϫ1
Ϫ1
the inverse relaxation time, T1 ≈ 2 s
.
J. Chem. Soc., Dalton Trans., 1997, Pages 1269–1280
1273

View Article Online
5
2
Table 4 Activation parameters for ring-whizzing and propeller rotation in [Re(η -C H R)(CO) (η -C F )] (R = H or Me)
5
4
2
6
6
Ring whizzing
Propeller rotation
‡
Ϫ1
‡
Ϫ1
Ϫ1
‡
Ϫ1
‡
Ϫ1
‡
a
Ϫ1
R
∆H / kJ mol
∆S / J K mol
∆G 300/ kJ mol
∆G
/ kJ mol
∆G
/ kJ mol
186
186
H
Me
57.6 ± 0.5
57.4 ± 0.7
Ϫ7.0 ± 1.8
Ϫ8.3 ± 2.4
59.7 ± 0.7
59.9 ± 1.0
58.9 ± 0.6b
58.9 ± 0.8
36.7b
38.1
a
Ϫ1
b
‡
There is no statistical error for this quantity. We assume error bars of ±2 kJ mol . ∆G is reported at 184 K for R = Me.
5
Table
5
Bond2 lengths (Å) and angles (Њ) for [Rh(η -
C Me )(PMe )(η -C F )] with e.s.d.s in the least significant figure(s) in
5
5
3
6
6
parentheses
Rh᎐C(6)
Rh᎐C(1)
Rh᎐C(13)
Rh᎐C(11)
Rh᎐C(12)
Rh᎐C(10)
Rh᎐C(14)
Rh᎐P
P᎐C(9)
P᎐C(8)
P᎐C(7)
F(1)᎐C(1)
F(2)᎐C(2)
F(3)᎐C(3)
F(4)᎐C(4)
F(5)᎐C(5)
F(6)᎐C(6)
2.050(5)
2.059(5)
2.255(5)
2.260(4)
2.278(4)
2.285(5)
2.288(5)
2.299(2)
1.821(5)
1.820(5)
1.821(6)
1.403(5)
1.351(6)
1.354(7)
1.353(7)
1.353(6)
1.401(5)
C(1)᎐C(2)
C(1)᎐C(6)
C(2)᎐C(3)
C(3)᎐C(4)
C(4)᎐C(5)
C(5)᎐C(6)
C(10)᎐C(14)
C(10)᎐C(11)
C(10)᎐C(15)
C(11)᎐C(12)
C(11)᎐C(16)
C(12)᎐C(13)
C(12)᎐C(17)
C(13)᎐C(14)
C(13)᎐C(18)
C(14)᎐C(19)
1.460(7)
1.459(7)
1.317(8)
1.426(9)
1.329(8)
1.437(7)
1.385(7)
1.454(7)
1.513(7)
1.415(7)
1.503(7)
1.423(7)
1.492(7)
1.420(7)
1.506(7)
1.526(7)
3
5
5
Fig. 8 An ORTEP diagram (50% ellipsoids) of [Rh(η -C Me )-
5
5
2
C(6)᎐Rh᎐C(1)
C(6)᎐Rh᎐C(13)
C(1)᎐Rh᎐C(13)
C(6)᎐Rh᎐C(11)
C(1)᎐Rh᎐C(11)
C(13)᎐Rh᎐C(11)
C(6)᎐Rh᎐C(12)
C(1)᎐Rh᎐C(12)
C(13)᎐Rh᎐C(12)
C(11)᎐Rh᎐C(12)
C(6)᎐Rh᎐C(10)
C(1)᎐Rh᎐C(10)
C(13)᎐Rh᎐C(10)
C(11)᎐Rh᎐C(10)
C(12)᎐Rh᎐C(10)
C(6)᎐Rh᎐C(14)
C(1)᎐Rh᎐C(14)
C(13)᎐Rh᎐C(14)
C(11)᎐Rh᎐C(14)
C(12)᎐Rh᎐C(14)
C(10)᎐Rh᎐C(14)
C(6)᎐Rh᎐P
C(1)᎐Rh᎐P
C(13)᎐Rh᎐P
C(11)᎐Rh᎐P
C(12)᎐Rh᎐P
C(10)᎐Rh᎐P
C(14)᎐Rh᎐P
C(9)᎐P᎐C(8)
C(9)᎐P᎐C(7)
C(8)᎐P᎐C(7)
C(9)᎐P᎐Rh
C(8)᎐P᎐Rh
C(7)᎐P᎐Rh
41.6(2)
108.2(2)
105.7(2)
168.0(2)
142.4(2)
60.8(2)
137.0(2)
111.2(2)
36.6(2)
C(2)᎐C(3)᎐C(4)
F(3)᎐C(3)᎐C(4)
C(5)᎐C(4)᎐F(4)
C(5)᎐C(4)᎐C(3)
F(4)᎐C(4)᎐C(3)
C(4)᎐C(5)᎐F(5)
C(4)᎐C(5)᎐C(6)
F(5)᎐C(5)᎐C(6)
F(6)᎐C(6)᎐C(5)
F(6)᎐C(6)᎐C(1)
C(5)᎐C(6)᎐C(1)
F(6)᎐C(6)᎐Rh
C(5)᎐C(6)᎐Rh
C(1)᎐C(6)᎐Rh
C(14)᎐C(10)᎐C(11) 107.7(4)
C(14)᎐C(10)᎐C(15) 125.2(5)
C(11)᎐C(10)᎐C(15) 126.4(5)
C(14)᎐C(10)᎐Rh
C(11)᎐C(10)᎐Rh
C(15)᎐C(10)᎐Rh
C(12)᎐C(11)᎐C(10) 107.7(4)
C(12)᎐C(11)᎐C(16) 124.8(5)
C(10)᎐C(11)᎐C(16) 126.1(5)
C(12)᎐C(11)᎐Rh
C(10)᎐C(11)᎐Rh
C(16)᎐C(11)᎐Rh
C(11)᎐C(12)᎐C(13) 107.4(4)
C(11)᎐C(12)᎐C(17) 126.7(5)
C(13)᎐C(12)᎐C(17) 125.9(5)
C(11)᎐C(12)᎐Rh
C(13)᎐C(12)᎐Rh
C(17)᎐C(12)᎐Rh
120.8(6)
117.1(6)
121.6(7)
120.7(6)
117.5(6)
120.5(6)
122.4(6)
117.1(5)
109.3(4)
115.9(4)
117.1(5)
120.0(3)
120.2(4)
69.5(3)
(
PMe )(η -C F )]
3 6 6
factor of the second-order F–F coupling effects and because of
the unsuitability of EXSY for faster exchange processes.
1
9
5
The broadening of the F resonances for [Re(η -C H )-
5
5
2
5
2
(
CO) (η -C F )] and [Re(η -C H Me)(CO) (η -C F )] noted on
2 6 6 5 4 2 6 6
cooling below 250 K is consistent with the onset of coalescence
36.3(2)
2
due to the internal rotation of the η -co-ordinated C F . The
134.7(2)
165.3(2)
60.3(2)
37.3(2)
61.0(2)
108.0(2)
130.6(2)
36.4(2)
60.5(2)
60.6(2)
6
6
5
two resonances seen around δ Ϫ151 in the spectra of [Re(η -
C H )(CO) (η -C F )] at 178.5 K and of [Re(η -C H Me)-
2
5
5
5
2
6
6
5
4
2
(
CO) (η -C F )] at 173 K correspond to the resonances for the
2 6 6
2
fluorines attached to the η -co-ordinated carbons for the two
1
9
rotamers. The remaining F resonances must have smaller
chemical shift differences for the rotamers as expected for nuclei
distant from the point of co-ordination.
72.5(3)
70.4(3)
129.5(4)
5
2
2
For [Re(η -C H )(CO) (η -C F )] in [ H ]thf the coalescence
5
5
2
6
6
8
35.2(2)
95.6(2)
91.6(2)
point is reached at 186 K for the δ Ϫ151 resonance. Using the
separation between the resonances around δ Ϫ151 measured at
1
78.5 K as the separation at slow exchange, the rate constant for
156.24(13)
95.53(13)
121.91(14)
103.10(14)
135.85(14)
99.2(3)
102.7(3)
101.5(3)
116.7(2)
123.2(2)
110.7(2)
110.0(4)
116.3(4)
117.1(5)
118.9(3)
120.5(4)
68.9(3)
72.5(3)
72.3(3)
131.2(4)
Ϫ1
interconversion of the rotamers at 186 K, k , is 53.1 s and the
free energy of activation, ∆G 186, is 36.7 kJ mol . For com-
parison, ∆G 1 for the ‘ring-whizzing’ process at 186 K is calcu-
lated to be 58.9 ± 0.6 kJ mol
rot
‡
Ϫ1
‡
86
Ϫ1
.
5
2
2
For [Re(η -C H Me)(CO) (η -C F )] in [ H ]thf the coales-
5
4
2
6
6
8
71.1(3)
70.8(3)
125.7(3)
cence point is reached at the slightly lower temperature of 184
K for the δ Ϫ152 resonance. The rate constant at 184 K, krot, is
Ϫ1
‡
C(14)᎐C(13)᎐C(12) 108.4(4)
C(14)᎐C(13)᎐C(18) 124.7(5)
C(12)᎐C(13)᎐C(18) 125.4(5)
C(14)᎐C(13)᎐Rh
C(12)᎐C(13)᎐Rh
C(18)᎐C(13)᎐Rh
C(10)᎐C(14)᎐C(13) 108.8(4)
C(10)᎐C(14)᎐C(19) 125.6(5)
C(13)᎐C(14)᎐C(19) 125.4(5)
C(10)᎐C(14)᎐Rh
C(13)᎐C(14)᎐Rh
C(19)᎐C(14)᎐Rh
5
9.3 s and the free energy of activation, ∆G 184, is 38.1 kJ
Ϫ
1
‡
mol . For comparison, ∆G 1 for the ‘ring-whizzing’ process
84
Ϫ1
F(1)᎐C(1)᎐C(2)
F(1)᎐C(1)᎐C(6)
C(2)᎐C(1)᎐C(6)
F(1)᎐C(1)᎐Rh
C(2)᎐C(1)᎐Rh
C(6)᎐C(1)᎐Rh
C(3)᎐C(2)᎐F(2)
C(3)᎐C(2)᎐C(1)
F(2)᎐C(2)᎐C(1)
C(2)᎐C(3)᎐F(3)
at 184 K is calculated to be 58.9 ± 0.8 kJ mol
.
73.1(3)
72.6(3)
131.6(4)
5
2
Crystal and molecular structure of [Rh(ç -C Me )(PMe )(ç -
5
5
3
C F )]
6
6
5
The complex [RhH(η -C Me )(PMe )(C H )] has been shown
5
5
3
6
5
121.5(6)
121.9(6)
116.6(6)
122.0(7)
5
24
to be a good thermal source of [Rh(η -C Me )(PMe )].
Accordingly, a sample of [RhH(η -C Me )(PMe )(C H )] was
heated in C F (80 C for 27 h) resulting in elimination of ben-
zene and the formation of [Rh(η -C Me )(PMe )(η -C F )].
72.3(3)
70.5(3)
127.0(4)
5
5
3
5
5
5
3
6
5
o
6
6
5
2
5
5
3
6
6
1
274
J. Chem. Soc., Dalton Trans., 1997, Pages 1269–1280

View Article Online
The complex has already been fully characterised by multi-
2
4
nuclear NMR and IR spectroscopy. Unlike the Re case, this
complex is stereochemically rigid and exhibits one isomer over
the wide temperature range explored. Small orange crystals
were grown from diethyl ether solution at room temperature
5
and X-ray crystallography confirmed their identity as [Rh(η -
2
C Me )(PMe )(η -C F )].
5
5
3
6
6
5
2
The crystal structure of [Rh(η -C Me )(PMe )(η -C F )]
5
5
3
6
6
proved free of the disorder problems which limited the reliabil-
ity of the structure of the C H analogue. This is the first struc-
5
5
2
ture of an η -C F complex of a second-row metal which is free
6
6
of disorder and provides more accurate geometric data than the
structures of the Re and Ir complexes. The basic characteristics
of the co-ordination geometry resemble those for the other
complexes (Fig. 8, Table 5). The co-ordinated C᎐C bond is
extended to 1.459(7) Å relative to free C F [1.394(7) Å]. The
unco-ordinated C᎐C bonds form a diene pattern [1.449(7) Å for
mean of C(1)᎐C(2) and C(6)᎐C(5), 1.323(8) Å for mean of
C(2)᎐C(3) and C(4)᎐C(5) and 1.426(9) Å for C(3)᎐C(4)]. The
C᎐F bonds for C(1) and C(6) average 1.402(5) Å compared to
6
6
2
Fig. 9 Principalstructuralfeaturesof [M](η -C F )complexes:mean of
6 6
5 5 5
data from [M] = Re(η -C H )(CO) , Rh(η -C Me )(PMe ) and Ir(η -
C H )(C H ). The figures in brackets represent the range of values of
bond lengths or angles measured for the three complexes. In the
exceptional case of free C F the figure represents the e.s.d. for the bond
5
5
2
5
5
3
5
5
2
4
6
6
1
.353(6) Å for the remainder, an extension of 0.049 Å or
length
approximately 10 e.s.d.s. The Rh atom lies 1.920(5) Å from the
midpoint of C(1)᎐C(6) [labelled D(2)]. The distance from the
Rh to the centroid of C Me [D(1)] is 1.926(5) Å and the
5
5
D(1)᎐Rh᎐D(2) angle is 140.1Њ. There is a short contact between
F(6) and one of the PMe carbon atoms, C(8), of 2.805 Å
3
1
accounting for the significant coupling JF H observed in the H
NMR spectrum.
Discussion
5
The photoreaction of [Re(η -C Me )(CO) ] with C F yields
the HF elimination product [Re(η -C Me CH )(CO) (C F )].
In contrast, [Re(η -C H )(CO) ] and [Re(η -C H Me)(CO) ]
react to form simple η -C F complexes.
5
5
3
6
6
6
31
5
4
2
2
6
5
5
5
5
2
5
3
5
4
3
6
6
Comparison of crystal structures
The structural parameters of the four [M](η -C F ) com-
2
6
6
plexes investigated crystallographically are shown in Table 6.
The principal features are shown diagrammatically in Fig. 9 as
mean bond angles and distances, with the figures in parentheses
showing the range for three of the complexes, rather than the
5
e.s.d.s. The data for [M] = Rh(η -C H )(PMe ) may be taken to
5
5
3
be less accurate than the remainder because of disorder in the
PMe group, and are omitted from Fig. 9. The co-ordinated
3
C᎐C bond averages 1.47 Å and varies in length by ±0.01 Å.
The geometry of the unco-ordinated diene unit varies even less.
The angle between the C6F4 plane and the C(1)C(6)F(1)F(6)
plane averages 45.9Њ and varies by ±1.3Њ. The angle between the
C F plane and the MC(1)C(6) plane averages 114.3Њ and varies
6
4
by ±0.4Њ. Thus it can be seen that the C F ligand resembles a
6
6
2
co-ordinated alkene in geometry. The analogy may be pursued
by examining the distortion of the hexafluorobenzene by Ibers’
Fig. 10 Diagram of co-ordinated alkene M(η -C X ) defining the
2 4
angles of deformation following Ibers. (a) The angle α is defined as the
angle between the normals to the CX planes. The angle β is the angle
4
3
method for a co-ordinated alkene. The angles α, β, γ and δ
2
between one of these normals and the C᎐C vector. (b) The angle γ is the
torsional angle X᎐C᎐C᎐XЈ where X and XЈ are trans to one another.
The angle δ is the torsional angle M᎐C᎐C᎐X. As bending back of the
alkene increases, α increases from 0Њ, β decreases from 90Њ, γ decreases
from 180Њ and δ increases from 90Њ
(
Fig. 10) are close to those for the C F unit of C2F4 com-
2 4
44,45 46
plexes.
Pörschke et al.2 have recently determined the crystal
2
structure of another η -C F complex, [Ni(dbpe)(η -C F )-
6
6
6
6
t
t
(dbpe Bu PCH CH PBu )]. The structural features of the
2 2 2 2
2
Table 6 Structural parameters for [M](η -C F )
6
6
Mean of
C(1)᎐C(2) and
C(6)᎐C(5)/Å
Mean of
C(2)᎐C(3) and
C(4)᎐C(5)/Å
Angle between
planes C F and
C(1)C(6)F(1)F(6)/Њ
Angle between
planes C F and
MC(1)C(6)/Њ
6
4
6
4
[
M]
C(1)᎐C(6)/Å
C(3)᎐C(4)/Å
Rh(C Me )(PMe )
1.459(7)
1.476(12)
1.47(2)
1.449(7)
1.430(12)
1.425(20)
1.473(8)
1.323(8)
1.325(12)
1.335(20)
1.331(8)
1.426(9)
1.430(13)
1.43(2)
46.4(2)
44.4(2)
47.0
114.3(3)
113.8(3)
114.6
5
5
3
Re(C H )(CO)
2
5
5
2
5
Ir(C H )(C H )
5
5
2
4
2
4
Rh(C H )(PMe )
1.397(12)
1.354(12)
43.8
108.6
5
5
3
J. Chem. Soc., Dalton Trans., 1997, Pages 1269–1280
1275

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2
2
Table 7 Distortions of the hexafluorobenzene moiety in [M](η -C F ) and [M](η -C F ) analysed by Ibers’ method
6
6
2
4
2
[
M](η -C F )
D(2)᎐M
α/Њ
β/Њ
|γ|/Њ
|δ|/Њ
6
6
Rh(C Me )(PMe )
1.920(5)
2.059(7)
1.941(2)
78.1(6)
76.2(8)
76.7
51.0
51.9
51.8
132.9, 131.3
130.8, 138.0
132.5
114.4, 112.8
108.7, 114.1
113.5
5
5
3
Re(C H )(CO)
5
5
2
2
5
Ir(C H )(C H )
5
5
2
4
2
[
M](η -C F )
2 4
4
4
Rh(C H )(C H )
1.898(5)
1.925(6)
1.929(5)
74.3
73.9
73.7
52.8
53.0
53.1
131.4
131.0
131.0
114.3
114.5
114.5
5
5
2
4
4
5
Ru(C Me )(acac)
5
5
4
5
[
(C Me )Ru(C F )Cl]
5 5 2 4 2
*
D(2) is defined as the centre of the co-ordinated C᎐C bond of C F or C F .
6 6 2 4
Table 8 Ligand effect constants, experimental and calculated ν
˜
(CO)
frequencies for [Re(C H )(CO) L]
5
5
2
Ϫ1
ν˜ /cm
Ligand effect
constant, εL
a
L
Experimental
Calculated
b
f
PMe3c
Ϫ38.7
1937, 1872
1978, 1911
1943, 1881
1974, 1920
2031, 1940
2030, 1970
2022, 1957
1950, 1876
1974, 1906
1954, 1881
1976, 1908
2024, 1930
—
f
f
f
f
C H4
4.0
Ϫ31.7
6.0
37.3
98.9
2
b
PPh3
N2
d
CO
2
e
η -C F (i)
6
6
2
e
η -C F (ii)
82.0
—
6
6
a
b
c
All IR data in hexane, except PPh in cyclohexane. Ref. 52. Ref. 53.
3
d
e
f
2
Ref. 54. (i) and (ii) denote the two rotamers. Ref. 51.
co-ordinated C6F6 resemble those of the four [M](η -C F )
6
6
complexes investigated previously, with a co-ordinated C᎐C
bond of 1.486(6) Å, an angle between the C F plane and the
Table 9 Infrared stretching frequences, ν˜ (CO), of [ReX (CO) (C H )]
2 2 5 5
6
4
C(1)C(6)F(1)F(6) plane of 44Њ and an angle between the C6F4
plane and the MC(1)C(6) plane of 114Њ.
complexes
Ϫ1
Complex
ν˜
/cm
Although there is minimal difference between the geometries
of the C F ligand in the three disorder-free structures reported
a
c
cis-[ReCl (CO) (C H )]
2061, 1988
2040, 1977d
2022, 1954
2
2
5
5
6
6
a
d
cis-[ReI (CO) (C H )]
here, there is a notable difference in the distance between ligand
2
2
5
5
b
5
trans-[ReH
2
(CO)
2
(C
5
H
)]
5
and metal [M᎐D(2)]. The Re᎐D(2) distance in [Re(η -
2
a
b
c
d
C H )(CO) (η -C F )] is 0.12 Å longer than the Ir᎐D(2) dis-
Ref. 55. Ref. 56. In CHCl3. In alkane.
5
5
2
6
6
5
2
25
tance in [Ir(η -C H )(C H )(η -C F )]. This extension may
5
5
2
4
6
6
well contribute to the lower barrier to ring rotation and ring
whizzing in the rhenium complex by reducing steric effects.
Theoretical work has been reported on the preferred orient-
5
ation of alkenes co-ordinated to the fragments M(η -C H )L
(
5
5
2
5
47–50
isolobal to ML ) and M(η -C H )L (isolobal to ML ).
5 5 5 4
In each case, conformation (b) is preferred, as observed in the
4
7–50
crystal structures of the complexes reported here.
as contrasted with the extreme of minimal π back donation
2
2
(right). Thus the electron-withdrawing character of η -C F is
6
6
Ligand effect of ç -C F
6
6
indicated both by the IR data and by the similarity of the struc-
tures of complexes with co-ordinated C F and C F .
The ν˜ (CO) frequencies of [Re(η -C H )(CO) L] provide a
continuous scale of electron density at the metal, which is not
accessible for the compounds without carbonyl ligands. On the
other hand, the Rh–P coupling constants of Rh(η -
C R )(PMe ) complexes have proved characteristic of the oxi-
dation state of the metal, with values close to 150 Hz for many
rhodium() complexes and 200 Hz for rhodium() complexes.
This parameter points unequivocally to an Rh formulation for
5
1
In 1979, Timney proposed a method for predicting ν˜ (CO)
2
4
6
6
5
values for mononuclear transition-metal carbonyls. Using
energy factoring, the stretching force constants, kCO, were
evaluated using the relationship (5) where k is the stretching
5 5 2
d
5
θ
kCO = k ϩ
εL
(5)
d
͚
5
5
3
L
1
force constant for an isolated M(CO) unit with the appropriate
number of d electrons and εL are ‘ligand effect constants’,
which quantify the effect of adding a ligand, L, at an angle θ to
the M(CO) unit. Thus, the ν
θ
I
5
2
24
[Rh(η -C R )(PMe )(η -C F )] (R = H or Me).
5 5 3 6 6
5
˜
(CO) values for a series of [Re(η -
C H )(CO) L] complexes can be used to determine a ‘ligand
5
5
2
Fluxional behaviour
effect constant’ for C F and to assess the electronic character-
6
6
5
2
istics of C F as a ligand (Table 8). The ν
˜
(CO) frequencies of
For [Re(η -C H R)(CO) (η -C F )] (R = Me or H) the rapid
6
6
5
4
2
6
6
5
2
[
[
Re(η -C H )(CO) (η -C F )] are higher than those of any other
ring-rotation process that interconverts the two rotamers is
analogous to the propeller rotation observed in many alkene
5
5
2
6
6
I
5
Re (η -C H )(CO) L] complex. The values for one of the
5
5
2
III
5
47
rotamers are close to those for [Re (H) (η -C H )(CO) ] (Table
9
complexes. High barriers to propeller rotation are generally
2
5
5
2
2
). If the bonding in η -co-ordinated C F is viewed in terms of
found in complexes with electronegative substituents on the
6
6
4
7,49,57
45
the Dewar–Chatt model for alkene bonding
the system
alkene. Since such complexes show metallacyclopropane
can be considered as approaching the metallacyclopropane
extreme (left) where the alkene acts as a strong acceptor ligand,
structures, it is easy to suppose that a metallacyclopropane
structure will lead to a high barrier for rotation. An example is
4
5
1
276
J. Chem. Soc., Dalton Trans., 1997, Pages 1269–1280

View Article Online
5
2
5
2
Table 10 Crystallographic parameters for [Re(η -C H )(CO) (η -C F )] and [Rh(η -C Me )(PMe )(η -C F )]
5
5
2
6
6
5
5
3
6
6
5
2
5
2
[
Re(η -C H )(CO) (η -C F )]
[Rh(η -C Me )(PMe )(η -C F )]
5 5 3 6 6
5
5
2
6
6
Empirical formula
C H F O Re
C H F PRh
19 24 6
1
3
5
6
2
M
493.37
500.26
Colour, dimensions/mm
Pink, 0.40 × 0.25 × 0.10
7.926(2)
Orange, 0.30 × 0.10 × 0.10
8.694(9)
16.818(9)
14.642(6)
106.69(6)
2051(3)
1.620
a/Å
b/Å
c/Å
β/Њ
12.179(4)
13.675(4)
102.91(2)
1286.6(6)
2.547
3
U/Å
Ϫ3
D /g cm
c
F(000)
µ(Mo-Kα)/cm
912
95.22
1008
9.64
Ϫ1
hkl Index ranges
θ Range/Њ
0–9, 0–14, Ϫ16 to 15
2.27–25
0–9, 0–20, Ϫ17 to 16
2.73–25
No. reflections measured, unique
No. of variables
2273, 2272 (Rint = 0)
200
4019, 3618 (Rint = 0.040)
253
Reflection/parameter ratio
Residuals [I > 2σ(I)]
Residuals (all data)
11.4
14.3
R1 = 0.0258, wR2 = 0.0851
R1 = 0.0380, wR2 = 0.0971
0.770
R1 = 0.0349, wR2 = 0.0725
R1 = 0.0731, wR2 = 0.0859
0.995
2
Goodness of fit on F
a, b In weighting scheme, w
Largest difference peak, hole/e Å
0.10, 0
0.718, Ϫ0.685
0.0348, 1.1158
0.339, Ϫ0.438
Ϫ3
Details in common: monoclinic, space group P2 /n, Z = 4, Rigaku AFC6S diffractometer, Mo-Kα radiation (λ = 0.710 69 Å), T = 293(2) K,
1
2
Ϫ1
2
2
2
2
2
refined by full-matrix least squares on F . w = σ (F ) ϩ (aP) ϩ bP where P = (F ϩ 2F )/3.
o
o
c
8
5
2
d [Rh(η -C H )(C F )(C H )] where rapid rotation of the C H
C H )(CO) (η -C F )] will serve to reduce steric effects and
5 5 2 6 6
5
5
2
4
2
4
2
4
ligand is observed, while rotation of the co-ordinated C F is
keep the barrier low.
Until the recent paper of Pörschke et al., the ring-whizzing
2
4
4
4
45
46
not detectable up to 100 ЊC. Curnow et al. have recently
‡
Ϫ1
5
2
reported that facile propeller rotation (∆G = 55 ± 2 kJ mol
)
process noted for [Re(η -C H R)(CO) (η -C F )] (R = Me or
5
4
2
6
6
6
5
2
is also observed in the d metallacyclopropane complex [Ru(η -
C Me )(acac)(η -C F )] (acac = acetylacetonate). The two types
H) had not been observed in η -C F complexes. In his
6 6
2
investigation of the rearrangement of metals on π-systems,
5
5
2
4
3
9
n
of complex under study here have very similar co-ordination
geometries for C F , but quite different barriers to rotation. For
Mann states that in all η -C H (n < m) ring systems (with
m m
6
the exception of η -C H ), whizzing proceeds by a [1,2]-shift
6
6
8
8
5
2
[
3
Re(η -C H R)(CO) (η -C F )] (R = H or Me) the barrier is ca.
7 kJ mol , for [Rh(η -C Me )(PMe )(η -C F )] the barrier to
as observed here. Mann related the variations in barriers to
5
4
Ϫ1
2
6
6
5
2
39,62 2
the Woodward–Hoffmann rules.
All η -C F complexes
6 6
5
5
3
6
6
rotation is too high to measure.
have proved stereochemically rigid except for the rhenium com-
1
0
Ϫ
2
From theoretical studies, it is proposed that low
rotation barriers should be found in complexes where the
plexes reported here and the d 16 e [Ni(dbpe)(η -C F )]
6 6
46
which shows equivalent fluorine nuclei down to 193 K.
6
Ϫ
4
alkene is bound to a d ML5 fragment or an isolobal ana-
Pörschke et al. propose an 18 e η -C F complex as an
6 6
Ϫ
4
9,58
6
logue.
In d ML fragments there are two filled, orthogonal
intermediate in the ring-whizzing. The related 16 e nickel(0)
5
2
and degenerate metal d orbitals available for π back bonding to
complexes [Ni{η -C (CF ) }L ] [L = C H , L = P(OR) or
6
3
6
2
2
8
12
3
6
3
the alkene, so the back bonding interaction is cylindrically
PR3], are also fluxional at low temperature, but a barrier of
ca. 45 kJ mol was reported for the platinum analogue,
[Pt{η -C (CF ) }(PEt ) ]. Although NMR spectra of η -C H
4
9
5
5
Ϫ1
symmetric.
Since the Re(η -C H R)(CO) and Ru(η -
5
4
2
6
2
63
2
C Me )(acac) fragments are isolobal with d ML5 fragments,
5
5
6
3
6
3
2
6
6
5
the low rotation barriers observed both for [Re(η -C H R)-
complexes are commonly reported to show averaging of
the benzene resonances, we have found no quantitative
5
4
2
5
(
(
CO) (η -C F )] (R = H or Me) and [Ru(η -C Me )(acac)-
2
6
6
5
5
2 45,50,58
4–7,64
η -C F )] can be explained.
Another example of an ana-
investigations.
2
4
6
5
ϩ
1a
logue of d ML with a low barrier is [Fe(η -C H )(CO) (C H )]
∆G = 32.6 kJ mol ).
Curnow et al. state clearly that there should be no correl-
In 1984, Jones and Feher proposed a mechanism for the
5
5
5
2
2
4
‡
Ϫ1 59
5
(
isomerisation of [RhH(η -C Me )(PMe )(C D )] involving the
5
5
3
6
5
4
5
2
intermediacy of an η -arene species. The isomerisation was
ation between acceptor properties of an alkene and the barrier
to propeller rotation. They note that differences in the barrier
arise from variations in the symmetries and energies of the fron-
tier orbitals presented by the metal fragment to the alkene, dif-
ferences in orbital overlap along the rotation path and other
attractive or repulsive interactions in the transition state.
found to proceed stepwise around the ring, indicating that
ring-whizzing in the η -arene intermediate is slow compared to
2
oxidative addition. This contrasts with the rapid ring-whizzing
5
2
detected for [Re(η -C H R)(CO) (η -C F )] (R = Me or H).
5
4
2
6
6
5
ϩ
Studies of [Ru(η -C H )(L )(alkene)] (L = PPh3, L = 1,4-
5
5
2
2
Conclusion
diisopropyl-1,4-diazabuta-1,3-diene or 1,4-di-p-tolyl-1,4-diaza-
buta-1,3-diene) complexes have confirmed that the barrier to
rotation of the alkene does not correlate with the strength of
5
(1) The photochemical reactions of [Re(η -C H R)(CO) ] with
5
4
3
5
2
C6F6 yield [Re(η -C H R)(CO) (η -C F )] (R = H or Me). (2)
The IR spectra of these complexes reveal the presence of two
rotamers. (3) The variable-temperature F NMR spectra dem-
5
4
2
6
6
6
0
the metal–alkene interaction in the ground state. In contrast,
6
1
19
quantum calculations predict that the barrier to rotation in
Pt(PH ) (C H )] will be higher when the alkene is constrained
[
onstrate that interconversion of the rotamers is very rapid
3
2
2
4
‡
Ϫ1
to be highly pyramidalised than in the unconstrained case. Such
pyramidalisation is associated with stronger bonding. In the
absence of electronic effects, the rotation barrier must arise
from some unfavourable steric interaction in the transition
(∆G ≈ 37 kJ mol at 186 K). The complexes also undergo
fast ring-whizzing via intramolecular [1,2]-shift processes
‡
Ϫ1
‡
Ϫ1
Ϫ1
with ∆H ≈ 57 kJ mol and ∆S ≈ Ϫ8 J K mol . (4) The
5
2
crystal structure of [Re(η -C H )(CO) (η -C F )] reveals distor-
5
5
2
6
6
5
state. The long Re᎐C6F6 distance [Re᎐D(2)] in [Re(η -
tion of the C F moiety to form a co-ordinated alkene and an
6 6
J. Chem. Soc., Dalton Trans., 1997, Pages 1269–1280
1277

View Article Online
unco-ordinated diene unit. The same features are observed in
Matrix isolation
5
2
the structure of [Rh(η -C Me )(PMe )(η -C F )]. The metal–
67
5
5
3
6
6
The matrix isolation equipment has been described previously.
Samples were deposited onto a CsI window cooled by an Air
Products CS202 closed-cycle Displex refrigerator to 20 K. The
carbon (C F ) bonds of the rhenium complex are considerably
6
6
longer than those of the rhodium complex. (5) The geometry of
2
the C F ligand in three M(η -C F ) complexes is shown to vary
5
2
6
6
6
6
compound [Re(η -C H )(CO) (η -C F )] was sublimed from a
5
5
2
6
6
minimally pointing to high force constants for alteration of this
structure. It is close to the metallacyclopropane limit. (6) The
right-angled glass tube (at 323 K) at the same time as matrix gas
BOC Research Grade argon, 99.999%) was deposited through
(
5
2
CO stretching frequencies of [Re(η -C H R)(CO) (η -C F )]
Ϫ1
5
4
2
6
6
a separate inlet. Typical deposition rates were 2 mmol h for
Ar. The samples were cooled to 12 K before recording IR spec-
tra, 1 cm resolution, 128 scans coaveraged.
are indicative of electron density at the metal closer to that in
rhenium()than in rhenium()complexes.However,thefluxional
behaviour of the rhenium complexes and the values of J(Rh᎐P)
in the rhodium complexes support a metal–alkene formulation
Ϫ1
2
Crystallographic methods
for η -C F complexes. (7) The low barrier to rotation about the
6
6
5
2
metal–C6F bond is associated with the electronic structure
6
Crystals of [Re(η -C H )(CO) (η -C F )] suitable for X-ray dif-
5 5 2 6 6
5
6
of the Re(η -C H )(CO) unit, isolobal with d ML , and the
5
5
2
5
fraction were obtained by recrystallisation from hexane at 253
5
2
longer metal–ligand bonds of the rhenium complex compared
K. Small orange crystals of [Rh(η -C Me )(PMe )(η -C F )]
5
5
3
6
6
8
to the d analogues.
suitable for X-ray diffraction were grown from diethyl ether
solution at room temperature. The crystallographic parameters
for the two complexes are summarised in Table 10. In each case
a single crystal was mounted on a glass fibre in epoxy cement.
Data were collected on a Rigaku AFC6S diffractometer.
Data reduction, application of Lorentz, polarisation and
Experimental
General methods
All syntheses and manipulations were performed under argon
using standard Schlenk and high vacuum techniques, or in a
glove box. Dirhenium decacarbonyl (98%) was purchased from
Aldrich and used without further purification. All solvents for
general use were dried by refluxing over sodium–benzophenone
and distilled under argon. Hexafluorobenzene (99.9%) from
Aldrich was condensed onto molecular sieves (grade 4 Å) under
vacuum prior to use. Deuteriated solvents were obtained from
Goss and dried over potassium and vacuum distilled before use.
The solutions, prepared in small Pyrex ampoules fitted with
PTFE taps, were degassed with three freeze–pump–thaw cycles
and then back-filled with argon before irradiation with either
an Applied Photophysics 250 W high-pressure mercury arc with
a water filter to remove excess heat or a Rayonet RPR-100
photochemical reactor. Reaction mixtures requiring irradiation
through a thin film were placed in a Pyrex sleeve reactor (path-
2
θ-dependent absorption corrections were applied with the
68
TEXSAN system.
with full-matrix least-squares refinement carried out using the
TEXSAN software package. The hydrogen atoms were
included at calculated sites and refined with a ‘riding’ model.
Final refinement was carried out using SHELXL 93.
Atomic coordinates, thermal parameters, and bond lengths
and angles have been deposited at the Cambridge Crystallo-
graphic Data Centre (CCDC). See Instructions for Authors,
J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the
CCDC for this material should quote the full literature citation
and the reference number 186/441.
The structure was solved by direct methods
6
8
6
9
Syntheses
5
2
24
5
The syntheses of [Rh(η -C Me )(PMe )(η -C F )] and [Re(η -
C H )(CO) ] have been reported previously. The compound
5
5
3
6
6
7
0
3
length 2 mm, volume 15 cm ) with Schlenk connections. The
5
5
3
5
[
Re(η -C H Me)(CO) ] was prepared using an analogous pro-
5 4 3
70b 5
sleeve reactor fitted over the Pyrex immersion-well of an
Applied Photophysics reactor (RB125) with an immersible 125
W medium-pressure mercury lamp. All NMR tubes (Wilmad
cedure to that of Casey et al.
for [Re(η -C H )(CO) ]:
5 5 3
[
Re(CO) Br] and sodium methylcyclopentadienyl (5% excess)
5
5
were refluxed in benzene for 4 h, [Re(η -C H Me)(CO) ] was
isolated by extraction with hexane followed by column chroma-
tography over alumina to remove traces of [Re (CO) ] (63%
5
28-PP) were either fitted with Young’s taps to allow sealing
5
4
3
under an argon atmosphere, or were flame sealed under
vacuum.
2
10
yield).
Spectroscopic methods
5
2
5
[
Re(ç -C H )(CO) (ç -C F )]. The compound [Re(η -
5 5 2 6 6
Infrared spectra were recorded on a Mattson Unicam Research
Series FTIR spectrometer, linked to a PC with ‘WINFIRST’
C H )(CO) ] (90–100 mg) was dissolved in hexafluorobenzene
5 5 3
3
(≈8 cm ) in a sleeve reactor. The sleeve reactor was fitted over
the immersion-well of an Applied Photophysics reactor and the
mixture photolysed for 8 h. The excess hexafluorobenzene was
removed under vacuum and the oily brown residue was succes-
software. The sample chamber was purged with dry, CO -free
2
air. Low-temperature IR measurements were carried out using a
vacuum-tight liquid cell with CaF2 windows (cooled with dry
ice–acetone slush) supplied by Graseby Specac. Most one- and
all two-dimensional NMR spectra were recorded on a Bruker
AMX500 spectrometer. Additionally some spectra were
recorded using a Bruker MSL300 and a JEOL FX 90Q. Proton
NMR chemical shifts were referenced to residual protiated
3
sively extracted with 7 cm portions of hexane. The IR spec-
trum in hexane solution showed absorptions at 2030 and 1940
Ϫ1
5
cm for [Re(η -C H )(CO) ] and 2030, 2022, 1970 and 1957
5
5
3
Ϫ1
5
2
cm for [Re(η -C H )(CO) (η -C F )] in the ratio ≈5:1. The
5
5
2
6
6
solution was reduced in volume, at room temperature, to ≈10
2
13
1
3
solvent: [ H ]thf (δ 1.80), C-{ H} NMR chemical shifts were
cm . The resulting precipitate was separated from the solution
8
2
19
5
referenced to solvent peaks: [ H ]thf (δ 26.7), F NMR spectra
{which contained unreacted [Re(η -C H )(CO) ]}, washed
8
5
5
3
3
are referenced to external CFCl at δ 0.0 or to internal C F at δ
twice with ≈2 cm of cold hexane and dried under vacuum to
5 2
3
6
6
3
1
1
Ϫ162.9 and P-{ H} NMR chemical shifts were referenced to
external H PO (85%) at δ 0.0. The temperatures for variable-
yield [Re(η -C H )(CO) (η -C F )]. The product was recrystal-
5 5 2 6 6
lised twice from hexane–diethyl ether (16:1) at Ϫ20 ЊC to give a
pale pink solid in low yield (ca. 10%) (Found: C, 31.55; H, 1.05.
3
4
temperature NMR spectroscopy were calibrated using a sample
6
5
2
of 100% methanol in a capillary inside the NMR tubes. The
Calc. for C H F O Re: C, 31.60; H, 1.00%). NMR ([ H ]thf,
1
3
5
6
2
8
1
9
5
2
1
13
1
F NMR spectrum of [Re(η -C H )(CO) (η -C F )] belongs to
300 K): H, δ 5.53 (s, C H ); C-{ H}, δ 92.2 (s, C H ), 197.5
5
5
2
6
6
5
5
5
5
6
6
an [AMX] spin system which was simulated using the WIN-
(CO); at 260 K the CO resonance appears as a multiplet
66
2
DAISY 2.1 (Bruker-Franzen Analytik GmbH) and gNMR ver-
sion 3.6 (Cherwell Scientific) packages. Mass spectra were
recorded on a VG Autospec.
([AAЈXXЈ] system; |JF C ϩ JF CЈ| ≈ 16 Hz) and three new reson-
ances can be seen at δ 83.4 (d, 254, C F ), 132.1 (d, 256, C F ),
6
6
6
6
151.2 (d, 262 Hz, C F ). Electron impact mass spectrum: m/z
6
6
1
278
J. Chem. Soc., Dalton Trans., 1997, Pages 1269–1280

View Article Online
ϩ
ϩ
5
ϩ
4
94 [M] , 438 [M Ϫ 2CO] , 419 [Re(η -C H )(C F )] , 308
13 V. S. Leong and N. J. Cooper, J. Am. Chem. Soc., 1988, 110, 2644;
5
5
6
5
ϩ
ϩ
5
ϩ
J. A. Corella II and N. J. Cooper, J. Am. Chem. Soc., 1990, 112,
2832; R. L. Thompson, S. J. Geib and N. J. Cooper, J. Am. Chem.
Soc., 1991, 113, 8961.
[
[
M Ϫ C F ] , 280 [M Ϫ CO Ϫ C F ] , 252 [Re(η -C H )] , 186
6
6
6
6
5
5
ϩ
C F ] .
6
6
1
4 V. S. Leong and N. J. Cooper, Organometallics, 1988, 7, 2058.
5
2
5
[
Re(ç -C H Me)(CO) (ç -C F )]. The compound [Re(η -
15 C. Bianchini, K. G. Caulton, C. Chardon, O. Eisenstein,
K. Folting, J. J. Johnson, A. Meli, M. Peruzzini, D. J. Rauscher,
W. E. Streib and F. Vizza, J. Am. Chem. Soc., 1991, 113, 5127;
C. Bianchini, K. G. Caulton, K. Folting, A. Meli, M. Peruzzini,
A. Polo and F. Vizza, J. Am. Chem. Soc., 1992, 114, 7290;
C. Bianchini, P. Frediani, M. Graziani, J. Kaspar, A. Meli,
M. Peruzzini and F. Vizza, Organometallics, 1993, 12, 2886;
C. Bianchini, M. Graziani, J. Kaspar, A. Meli and F. Vizza,
Organometallics, 1994, 13, 1165; C. Bianchini, K. G. Caulton,
C. Chardon, M. L. Doublet, O. Eisenstein, S. A. Jackson, T. J.
Johnson, A. Meli, M. Peruzzini, W. E. Streib, A. Vacca and F. Vizza,
Organometallics, 1994, 13, 2010.
5
4
2
6
6
C H Me)(CO) ] (125–175 mg) was dissolved in hexafluoroben-
5
4
3
3
zene (≈10 cm ) and degassed with three freeze–pump–thaw
cycles. The mixture was irradiated for 8 h (λ = 300 nm) at room
temperature using a Rayonet RPR-100 photochemical reactor
in Pyrex tubes (≈1 cm external diameter). The solutions turned
light brown and some brown solid formed. The solvent was
removed under vacuum and the oily brown residue was succes-
sively extracted with 7 cm portions of hexane. The resulting
yellow solution was reduced in volume to ≈10 cm at room
temperature. The resulting white precipitate was separated from
3
3
1
6 J. Müller, P. E. Gaede and K. Qiao, J. Organomet. Chem., 1994, 480,
5
the
solution
{which
contains
unreacted
[Re(η -
213.
3
C H Me)(CO) ]}, washed twice with ≈2 cm of cold hexane and
dried under vacuum to yield [Re(η -C H Me)(CO) (η -C F )].
The product was recrystallised from hexane–diethyl ether
16:1) at Ϫ20 ЊC. Yield = 15% (Found: C, 32.65; H, 1.4. Calc.
for C H F O Re: C, 33.15; H, 1.4%). NMR ([ H ]thf, 300 K):
H, δ 2.36 (s, C H Me), 5.36 and 5.55 (dd, C H Me, [AX] sys-
tem); C-{ H} δ 14.87 (s, C H Me), 83.6 (d, 245 Hz, C F ),
0.93 and 92.87 (MeCC H ), 111.51 (MeCC H ), 132.2 (d, 262
Hz, C F ), 151.2 (br, C F ), 198.46 (CO); at 260 K the CO
17 J. Müller, P. E. Gaede and K. Qiao, Angew. Chem., Int. Ed. Engl.,
1993, 32, 1697; J. Müller, C. Hirsch, K. Qiao and K. Ha, Z. Anorg.
Allg. Chem., 1996, 622, 1441.
5
4
3
5
2
5
4
2
6
6
1
8 E. L. Muetterties, J. R. Bleeke and E. J. Wucherer, Chem. Rev., 1982,
2, 499.
(
8
2
1
4
7
6
2
8
19 D. Braga, P. J. Dyson, F. Grepioni and B. F. G. Johnson, Chem. Rev.,
1994, 94, 1585.
20 B. F. G. Johnson, P. J. Dyson and C. M. Martin, J. Chem. Soc.,
Dalton Trans., 1996, 2395.
1
5
4
5
4
2
1
3
1
5
4
6
6
9
4 4 4 4
2
2
2
1 E. Maslowsky, jun., J. Chem. Educ., 1993, 70, 980.
6
6
6
6
2 H. Wadepohl, Angew. Chem., Int. Ed. Engl., 1992, 31, 247.
3 M. A. Gallop, B. F. G. Johnson, J. Keeler, J. Lewis, S. J. Heyes and
C. M. Dobson, J. Am. Chem. Soc., 1992, 114, 2510.
resonance appears as
JF C ϩ JF CЈ| ≈ 15.2 Hz). Chemical ionization mass spectrum:
m/z 508 [M] , 489 [M Ϫ F] , 429 [Re(CO) (C F )] , 322
a
multiplet ([AAЈXXЈ] system;
6
6
|
ϩ
ϩ
ϩ
2
6
6
24 S. T. Belt, M. Helliwell, W. D. Jones, M. G. Partridge and R. N.
ϩ
ϩ
[
M Ϫ C F ] , 186 [C F ] .
Perutz, J. Am. Chem. Soc., 1993, 115, 1429.
6
6
6
6
2
5 T. W. Bell, M. Helliwell, M. G. Partridge and R. N. Perutz, Organo-
metallics, 1992, 11, 1911.
Acknowledgements
26 J. J. Barker, A. G. Orpen, A. J. Seeley and P. L. Timms, J. Chem.
Soc., Dalton Trans., 1993, 3097.
We would like to acknowledge the support of the EPSRC and
the assistance and advice of Dr. S. B. Duckett, Dr. S. J. Heyes,
A. Kraus, F. R. Manby, Professor B. E. Mann, Dr. B. A.
Messerle, Dr. P. D. Morran and G. Wilson. A. H. K. thanks
Universidad Catolica de Valparaiso and FONDECYT-Chile
for financial support (grants DGIP 125.776-96 and 1960383
respectively). B. O. acknowledges Fundacion Andes for a
Doctoral fellowship.
2
7 A. Martín, A. G. Orpen, A. J. Seeley and P. L. Timms, J. Chem. Soc.,
Dalton Trans., 1994, 2251.
28 C. Aspley, C. L. Higgitt, C. Long and R. N. Perutz, unpublished
work.
2
3
9 P. Hofmann and G. Unfried, Chem. Ber., 1992, 125, 659.
0 M. K. Whittlesey, R. N. Perutz and M. H. Moore, Chem. Commun.,
1
996, 787.
3
1 A. H. Klahn, M. H. Moore and R. N. Perutz, J. Chem. Soc., Chem.
Commun., 1992, 1699.
3
2 M. Aizenberg and D. Milstein, Science, 1994, 265, 359; M. Aizen-
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3 J. L. Kiplinger and T. G. Richmond, Chem. Commun., 1996, 1115.
4 J. L. Kiplinger, T. G. Richmond and C. E. Osterberg, Chem. Rev.,
1994, 94, 373.
3
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