Photochemical displacement of co-ordinated ethene from [Rh(η5-C5H5)(PPh3)(C 2H4)]

Article abstract of DOI:10.1039/a803048k

The rhodium (triphenylphosphine)(ethene) complex [Rh(η⁵-C₅H₅)(PPh₃)(C ₂H₄)], was synthesized by reaction of [{Rh(C₂H₄)₂Cl}₂] with triphenylphosphine and thallium cyclopentadienide. Like in [Rh(η⁵-C₅H₅)(PMe₃)(C ₂H₄)], the co-ordinated ethene ligand may be displaced photochemically. Photoreaction of [Rh(η⁵-C₅H₅)(PPh₃)(C ₂H₄)] with SiR₃H (R = Prⁱ or Et) and hexafluorobenzene yielded [Rh(η⁵-C₅H₅)(PPh₃)(SiR ₃)H] and [Rh(η⁵-C₅H₅)(PPh₃)-(η ²-C₆F₆)], respectively. Oxidative addition of the C-H bonds of partially fluorinated arenes, C₆F₅H and 1,3-C₆F₂H₄, was demonstrated by NMR spectroscopy to result in formation of [Rh(η⁵-C₅H₅)(PPh₃)(R)H] (R = C₆F₅ or 2,6-C₆F₂H₃). Oxidative addition of benzene may be detected following photolysis in benzene-thf mixtures at 233 K, but the product decomposes on warming. The molecular structure of [Rh(η⁵-C₅H₅)(PPh₃)(SiPr ⁱ₃)H] has been determined crystallographically. The disorder of the isopropyl groups was modelled with two orientations of the SiPrⁱ₃ with equal occupancies. The Rh-Si bond length is 2.386(2) A, the first example of measurement of such a distance at cyclopentadienyl rhodium(III).

Full text of DOI:10.1039/a803048k

View Article Online / Journal Homepage / Table of Contents for this issue
Photochemical displacement of co-ordinated ethene from
[Rh(ç5-C5H5)(PPh3)(C2H4)]
Stephen N. Heaton,a Martin G. Partridge,a Robin N. Perutz,*,†,a Simon J. Parsonsb and
Frank Zimmermanna
a Department of Chemistry, University of York, York, UK YO10 5DD
b Department of Chemistry, University of Edinburgh, Edinburgh, UK EH9 3JJ
The rhodium (triphenylphosphine)(ethene) complex [Rh(η5-C5H5)(PPh3)(C2H4)], was synthesized by reaction of
[{Rh(C2H4)2Cl}2] with triphenylphosphine and thallium cyclopentadienide. Like in [Rh(η5-C5H5)(PMe3)(C2H4)],
the co-ordinated ethene ligand may be displaced photochemically. Photoreaction of [Rh(η5-C5H5)(PPh3)(C2H4)]
with SiR3H (R = Pri or Et) and hexafluorobenzene yielded [Rh(η5-C5H5)(PPh3)(SiR3)H] and [Rh(η5-C5H5)(PPh3)-
(η2-C6F6)], respectively. Oxidative addition of the C᎐H bonds of partially fluorinated arenes, C6F5H and 1,3-
C6F2H4, was demonstrated by NMR spectroscopy to result in formation of [Rh(η5-C5H5)(PPh3)(R)H] (R = C6F5
or 2,6-C6F2H3). Oxidative addition of benzene may be detected following photolysis in benzene–thf mixtures at
233 K, but the product decomposes on warming. The molecular structure of [Rh(η5-C5H5)(PPh3)(SiPri3)H] has
been determined crystallographically. The disorder of the isopropyl groups was modelled with two orientations of
the SiPri3 with equal occupancies. The Rh᎐Si bond length is 2.386(2) Å, the first example of measurement of such
a distance at cyclopentadienyl rhodium().
Photochemical displacement of co-ordinated ethene from the
trimethylphosphine complex, [Rh(η5-C5H5)(PMe3)(C2H4)], has
proved to be a valuable method of achieving oxidative addition
of carbon–hydrogen bonds, and of co-ordinating unusual
ligands such as hexafluorobenzene at the metal.1–5 In parallel
studies of the C5Me5 analogues, two additional entry routes to
the [Rh(η5-C5Me5)(PMe3)] intermediate have been employed,
photolysis of the dihydride complex and thermal displacement
of benzene from the phenyl hydride complex.2–6 The need to
generate the 16-electron intermediate in order to effect oxid-
ative addition, i.e. the need for a dissociative mechanism, is
emphasised by studies involving matrix isolation7–10 laser flash
photolysis,11–15 and quantum yield measurements16,17 on these
complexes and related carbonyl systems such as [Rh(η5-C5H5)-
(CO)2] and [Rh(η5-C5H5)(CO)(C2H4)]. Electron-releasing
ligands such as PMe3 and C5Me5 are not essential for C᎐H and
Si᎐H bond activation, as is evident from the reactivity of the
carbonyl complexes, but they certainly influence the stability of
the products {compare [Rh(η5-C5H5)(CO)(alkyl)H] and [Rh(η5-
C5Me5)(PMe3)(alkyl)H]}.6,11 The comparisons between the
Rh(η5-C5H5) and Rh(η5-C5Me5) systems show that the electron-
releasing abilities of the ligands influence the position of equi-
librium between RhI(η2-arene) and RhIII(aryl)H species in those
cases where such equilibria can be observed [e.g. arene = C6H4-
(CF3)2-1,4 or naphthalene].2,4
spectrum was later supplemented by a
103Rh᎐1H two-
dimensional spectrum.20b Complex 1 was also observed as a
product of photolysing [Rh(η5-C5H5)(C2H4)2] in the presence
of PPh3.21 We synthesized 1 by reaction of [{Rh(C2H4)2Cl}2]
with 2 equivalents of PPh3, and subsequent reaction with Tl-
(η5-C5H5), a similar procedure to that used for [Rh(η5-C5H5)-
(PMe3)(C2H4)].15 The complex exhibits the expected doublet
in the 31P-{1H} NMR spectrum. The value of JRhP of 209 Hz
provides a marker for rhodium() complexes of this type.
Photochemical reactions with trialkylsilanes, SiR3H (R ؍ Pri or
Et)
Irradiation of complex 1 in triisopropylsilane at 283 K gener-
ates a single stable product identified as [Rh(η5-C5H5)(PPh3)-
(SiPri3)H] 2 on the basis of the spectra described below. The 1H
NMR spectrum in the high field region shows a hydride reson-
ance as a doublet of doublets at δ Ϫ13.60 (JPH = 29.9, JRhH
=
28.2 Hz). In the low field region there are resonances for the η5-
C5H5 ligand at δ 5.10, the PPh3 ligand at δ 7.76–7.70 and two
resonances at δ 1.14 (pseudo t) and 0.85 (septet) which are
assigned to the CH3 and CH groups of the isopropyl group
respectively.‡ The 31P-{1H} NMR spectrum shows a doublet at
δ 56.8 (JRhP = 185 Hz). The photochemical synthesis of the
PMe3 analogue of 2 from [Rh(η5-C5H5)(PMe3)(η2-C6F6)] has
been described previously.3
In this study we report that the triphenylphosphine complex
[Rh(η5-C5H5)(PPh3)(C2H4)] 1 can be employed as a precursor
for Si᎐H bond activation and for co-ordination of hexafluoro-
benzene. We also present NMR evidence for C᎐H bond acti-
vation of partially fluorinated arenes. These results may also be
compared with studies of related triphenylphosphine com-
plexes, especially[Ir(η5-C5H5)(PPh3)(C2H4)]and[Rh(η5-C5Me5)-
(PPh3)H2].18,19
Irradiation of complex 1 in triethylsilane at 283 K proceeds
similarly to generate [Rh(η5-C5H5)(PPh3)(SiEt3)H] 3 as the sole
product (see Experimental section for NMR data). The 1H
NMR spectrum shows a triplet at δ 1.07 for the CH3 groups and
multiplets at δ 0.68 and 0.56 for the CH2 protons. On heating in
C6D6 the multiplets at δ 0.68 and 0.56 first coalesced (Tc = 316
K) and then sharpened to form one poorly resolved quartet at
341 K. This behaviour was reversed on cooling and did not
affect the other resonances in the spectrum. The coalescence
temperature and low-temperature limiting NMR data yield, via
Results
Synthesis of [Rh(ç5-C5H5)(PPh3)(C2H4)] 1
The synthesis of complex 1 from [Rh(MeCOCHCOMe)-
(C2H4)2] has been reported previously.20a The original NMR
‡ The pseudo-triplet splitting of the methyl resonances arises from
an overlapping pair of doublets. Complex 2 is chiral at rhodium and
the methyl groups are prochiral and therefore inequivalent {compare
[Rh(η5-C5Me5)Cl(CO)(SbPri3)]}.22
† E-Mail: rnp1@york.ac.uk
J. Chem. Soc., Dalton Trans., 1998, Pages 2515–2520
2515

View Article Online
Fig. 2 Diagram showing the disorder in the isopropyl groups of
complex 2, looking down the Si᎐Rh vector. One set of bonds of the
isopropyl group is shown in black, the other set as open lines
Fig. 1 An ORTEP23 diagram (30% ellipsoids) of [Rh(η5-C5H5)-
(PPh3)(SiPri3)H] 2. Only one of two disordered sets of isopropyl groups
is shown for simplicity and only the hydridic hydrogen is shown
Table 1 Selected bond lengths (Å) and angles (Њ) for [Rh(η5-C5H5)-
(PPh3)(SiPri3)H] 2
equation (1), an estimate of the free energy of activation for the
∆G‡ = ϪRTc ln πh∆νo/kBTc√2
(1)
Rh᎐C(1)
Rh᎐C(2)
Rh᎐C(3)
Rh᎐C(4)
Rh᎐C(5)
Rh᎐Si
Rh᎐P
Si᎐C(6Ј)
Si᎐C(9Ј)
2.278(9)
2.272(9)
2.270(10)
2.204(10)
2.280(10)
2.386(2)
2.231(2)
1.854(11)
1.927(12)
P᎐Rh᎐C(1)
P᎐Rh᎐C(2)
P᎐Rh᎐C(3)
P᎐Rh᎐C(4)
P᎐Rh᎐C(5)
P᎐Rh᎐Si
Si᎐Rh᎐C(1)
Si᎐Rh᎐C(2)
Si᎐Rh᎐C(3)
Si᎐Rh᎐C(4)
Si᎐Rh᎐C(5)
C(6Ј)᎐Si᎐Rh
C(9Ј)᎐Si᎐Rh
104.4(3)
100.8(3)
129.0(4)
160.0(3)
134.0(3)
102.08(8)
153.6(3)
137.3(4)
103.0(3)
95.9(3)
exchange process, ∆G‡ = 66 kJ molϪ1 (the symbols have their
standard meanings). The inequivalence of the two CH2 reson-
ances at room temperature may be attributed to restricted
rotation about the Si᎐C bonds in this congested molecule.
Crystal structure of [Rh(ç5-C5H5)(PPh3)(SiPri3)H] 2
Si᎐C(12Ј) 1.930(12)
Crystals of complex 2 were grown from toluene at 253 K and
investigated by X-ray diffraction. The resulting data confirm
the identity of 2 and provide useful data in spite of compli-
cations of disorder of the isopropyl groups. The structure (Fig.
1, Table 1) reveals a Rh᎐Si bond length of 2.386(2) Å and a
Rh᎐P bond length of 2.231(2) Å. The hydride was located in a
difference map, yielding a Rh᎐H bond length of 1.50(9) Å after
refinement. Two orientations of the SiPri3 group were refined
with equal occupancy. One orientation places the Si᎐C bonds in
an approximately staggered orientation with respect to Rh᎐P,
Rh᎐H and Rh᎐C5H5 bonds. The second orientation lies ca. 60Њ
with respect to the first and eclipses the bonds to rhodium
(Fig. 2).
Si᎐C(6)
Si᎐C(9)
Si᎐C(12)
P᎐C(15)
P᎐C(21)
P᎐C(27)
Rh᎐H
1.940(12)
1.933(12)
1.885(12)
1.842(8)
1.847(7)
1.833(8)
1.50(9)
120.6(3)
116.5(4)
113.3(5)
C(12Ј)᎐Si᎐Rh 105.6(5)
C(6)᎐Si᎐Rh
C(9)᎐Si᎐Rh
112.1(5)
117.7(5)
C(12)᎐Si᎐Rh 111.4(5)
Ϫ173.9 with integrations in the ratio 1:1:1 enabling the com-
plex to be identified as [Rh(η5-C5H5)(PPh3)(η2-C6F6)] 4 by
comparison with the PMe3 analogue.3
With partially fluorinated arenes. Complex 1 was irradiated in
pentafluorobenzene at ca. 273 K in an ampoule. The solution
was pumped to dryness and redissolved in [2H8]toluene for
Although the Rh(η5-C5R5)(SiRЈ3) functionality has been
investigated extensively,11,16,17,24,25a the only crystal structure
reported is for the rhodium() complex [Rh(η5-C5Me5)-
(SiEt3)2H2].25a This neutron structure gives a Rh᎐Si bond length
of 2.379(2) Å and a mean Rh᎐H distance of 1.581(3) Å. The
crystal structure of an octahedral rhodium() metallacyclic
complex, [Rh(PMe3)3(SiMe2CH2CH2SiMe2)H], gives a mean
Rh᎐Si distance of 2.386(2) Å.25b Further comparison can be
gained from the four-co-ordinate rhodium() complex
[Rh(PMe3)3(SiPh3)] with a Rh᎐Si distance of 2.317(1) Å.25c
1
NMR spectroscopy. The H NMR spectrum shows a hydride
resonance for the product with a doublet of doublets pattern
characteristic of coupling to rhodium and phosphorus. The 31P-
{1H} NMR spectrum shows a doublet resonance at δ 57.8 with
JRhP = 155 Hz which is indicative of a rhodium() complex.
The 19F NMR spectrum contains three signals at δ Ϫ104.1,
Ϫ164.6 and Ϫ165.8 with integrations in the ratio 2:1:2. The
product is readily assigned as the C᎐H activation product
[Rh(η5-C5H5)(PPh3)(C6F5)H] 5 and may be compared to its
PMe3 analogue.5 Attempts to isolate analytically pure material
did not prove successful.
Photochemical reaction of complex 1
With hexafluorobenzene. Irradiation of complex 1 in hexa-
fluorobenzene at 283 K yielded, on purification, a lemon-yellow
solid which was characterised by 31P and 19F NMR spec-
troscopy. The 31P-{1H} NMR spectrum shows a doublet of
triplets at δ 45.8 with JRhP = 203 and JFP = 54 Hz, which is
indicative of a rhodium() complex in which the 31P nucleus is
also coupled to two equivalent fluorine nuclei. The 19F NMR
spectrum contains three multiplets at δ Ϫ147.1, Ϫ158.2 and
Irradiation of complex 1 in 1,3-difluorobenzene was investi-
gated in a similar way. After photolysis, the high field region
1
of the H NMR spectrum contains a hydride resonance at δ
Ϫ11.51 which appears as a doublet of doublets, and in the low
field region there were resonances at δ 6.60 and 6.49. The 31P-
{1H} NMR spectrum shows a doublet resonance at δ 57.4
(JRhP = 159 Hz) indicative of a rhodium() complex. The 19F
NMR spectrum contains one signal at δ Ϫ76.15. The spectra
2516
J. Chem. Soc., Dalton Trans., 1998, Pages 2515–2520

View Article Online
Table 2 The NMR spectroscopic data [δ (J/Hz)] for products of
photolysis of [Rh(η5-C5H5)(PPh3)(C2H4)] in benzene–thf mixtures at
233 K
Rh
SiR3
Rh
Ph3P
H
Ph3P
F
F
F
Product A
Product B
F
F
2 R = Pri
3 R = Et
F
1H, hydride
Ϫ12.90 (dd, JPH = 41.9,
JRhH = 27.1)
5.11 (s)
Ϫ13.70 (ddd, JPH = 34.9,
JRhH = 27.9, JHH = 6.1)
5.21 (s)
4
hν
1H, C5H5
31P-{1H}
SiR3H
C6F6
hν
58 (d, JRhP = 166)
63 (d, JRhP = 165)
clearly identify the product as a single isomer of [Rh(η5-
C5H5)(PPh3)(C6F2H3)H] 6a. The equivalence of the fluorine
nuclei excludes the 2,4-C6F2H3 isomer from consideration. The
low field shift of the 19F resonance is characteristic of ortho sub-
stitution and a clear indicator that the 2,6-C6F2H3 isomer has
been generated (cf. the PMe3 analogue).5 The product was not
isolated.
The reaction of complex 1 with 1,3-difluorobenzene was
also investigated by photolysis of a [2H8]thf solution at 233 K.
Spectra were measured at the same temperature and in 10 K
steps up to room temperature. In addition to 6a, three further
rhodium() species were generated. One of them was also
formed in a control experiment with no fluoroarene (species B,
see below) and was converted at room temperature into 6a. The
remaining two species have very similar NMR parameters to
those of 6a and are tentatively assigned to [Rh(η5-C5H5)-
(PPh3)(2,4-C6F2H3)H] 6b and [Rh(η5-C5H5)(PPh3)(3,5-C6F2-
H3)H] 6c. Related behaviour was observed for the PMe3
analogue, but in that case the 2,4 and 3,5 isomers converted into
the thermodynamic 2,6 isomer below room temperature.5
Rh
Ph3P
1
F
F
hν
C6F5H
hν
Rh
Rh
H
H
Ph3P
Ph3P
F
F
F
F
F
F
F
6a
5
Scheme 1 Photochemical reactions of [Rh(η5-C5H5)(PPh3)(C2H4)] 1
[Rh(η5-C5H5)(PPh3)(C2H4)] 1 undergoes photochemical dis-
placement of ethene and yields products of Si᎐H activation and
C6F6 co-ordination (Scheme 1) similar to those obtained from
its PMe3 analogue.1,3,26 Carbon–hydrogen bond activation is
more limited, however. Partially fluorinated benzenes react to
form C᎐H activation products which may be observed at room
temperature: the C᎐F bonds probably enhance the strength of
the rhodium–carbon bonds (compare the PMe3 analogues).5
The product of reaction with benzene [Rh(η5-C5H5)(PPh3)-
(Ph)H] may be observed at low temperature, but decomposes on
warming to room temperature. It appears to be even less stable
than its η5-C5Me5 analogue which has been reported previ-
ously.19 The latter, [Rh(η5-C5Me5)(PPh3)(Ph)H], undergoes
reductive elimination of benzene ca. 1100 times faster than
[Rh(η5-C5Me5)(PMe3)(Ph)H] at 296 K.19 Complex 1 shows no
signs of undergoing photoinduced cyclometallation. The lack
of cyclometallation is in keeping with the properties of [Ir-
(η5-C5H5)(PPh3)(C2H4)]18 and of [Rh(η5-C5Me5)(PPh3)H2],19 but
contrasts with [Ir(η5-C5Me5)(PPh3)H2].28 The destabilisation of
[Rh(η5-C5H5)(PPh3)(Ph)H] compared with its PMe3 analogue
contrasts with the stability of the RhI(η2-C6F6) complexes both
with PPh3 and PMe3 coligands. Complex 4 joins the growing
number of complexes of η2-C6F6.1,3,29,30
With benzene. Irradiation of complex 1 in benzene at 283 K
caused considerable precipitation but generated no products
stable enough for NMR observation in C6D6 solution. In order
to observe labile products, samples of 1 dissolved in mixtures of
deuteriated and undeuteriated benzene and thf (1:1 benzene–
thf by volume) were irradiated at 233 K in NMR tubes and
NMR spectra were acquired in situ at the same temperature.
1
Hydride resonances were invariably observed in the H NMR
spectrum, providing evidence that the photoreactions are com-
plicated by H/D exchange, as has been observed with the irid-
ium analogue of 1.18 Two species were observed on irradiation
of 1 in a fully deuteriated benzene–thf mixture. Species A has
one cyclopentadienyl resonance and a hydride resonance in the
1H NMR spectrum and a doublet characteristic of RhIII in the
31P NMR spectrum (Table 2). Species B has similar character-
istics, but an extra doublet splitting in the hydride resonance.
On photolysis of 1 in [2H8]thf alone at 233 K, species B is
retained but A is eliminated. All the photoproducts disappear
on warming to 300 K. Species A is tentatively assigned as
the product of C᎐H activation of benzene, [Rh(η5-C5H5)-
(PPh3)(Ph)H]. Species B has not been identified conclusively,
but cyclometallation at triphenylphosphine can be excluded
since that would result in a large high field shift of the 31P NMR
resonance.
Conclusion
Photolysis of [Rh(η5-C5H5)(PPh3)(C2H4)] provides an effective
method of forming Si᎐H activation products, or of substituting
C2H4 by hexafluorobenzene, but only C᎐H bond activation
products from fluoroaromatics are sufficiently stable for room
temperature observation. The determination of the Rh᎐Si
bond length of [Rh(η5-C5H5)(PPh3)(SiPri3)H] is the first for a
cyclopentadienyl rhodium() complex, but the difference in
bond length compared to that of [Rh(η5-C5Me5)(SiEt3)2H2] is
barely significant.25a
Discussion
Irradiation of [Rh(η5-C5H5)(PMe3)(C2H4)] in solution provides
a convenient source of the unsaturated fragment [Rh(η5-
C5H5)(PMe3)], which reacts by oxidative addition with the C᎐H
bonds of aromatic hydrocarbons and the Si᎐H bonds of
trialkylsilanes.2–5,26 With naphthalene and with hexafluoro-
benzene, η2 co-ordination is observed.1,2,4 In contrast, the solu-
tion photochemistry of [Ir(η5-C5H5)(PR3)(C2H4)], both for
R = Me and Ph, is dominated by intramolecular C᎐H acti-
vation of co-ordinated ethene.18,27 Activation of benzene is not
observed at iridium when R = Me and represents only about
12% of the products when R = Ph. The current work shows that
Experimental
All operations were performed under a nitrogen or argon
atmosphere, either on a high-vacuum line using modified
Schlenk techniques or in a glove-box. Benzene was distilled
from a dark purple solution of benzophenone ketyl. [2H6]-
Benzene, [2H8]toluene and [2H8]thf were all distilled from dark
purple solutions of benzophenone ketyl and stored in ampoules
J. Chem. Soc., Dalton Trans., 1998, Pages 2515–2520
2517

View Article Online
with Teflon seals. The complex [{Rh(C2H4)2Cl}2] was syn-
thesized by the literature procedure.31 Pentafluorobenzene, 1,3-
difluorobenzene and hexafluorobenzene from Aldrich were
dried over molecular sieves. Triethylsilane and triisopropyl-
silane from Flurochem Ltd. were used without further purifi-
cation. All NMR spectra were recorded on Bruker MSL300 or
AMX500 spectrometers in tubes fitted with Young’s polytetra-
was dissolved in Et2O and again all volatiles were removed to
give complex 3 as a yellow oil isolated in 68% yield, based on
rhodium. NMR (C6D6, 296 K): 1H, δ 7.70–6.90 (m, 15 H,
PPh3), 5.10 (s, C5H5), 1.07 (t, JHH = 7.7, 9 H, CH2CH3), 0.68 (m,
JHH = 7.7, 3 H, CH2CH3), 0.56 (m, JHH = 7.7, 3 H, CH2CH3)
and Ϫ13.49 (t, JPH = JRhH = 29.1 Hz, 1 H, RhH); 31P-{1H}, δ
59.6 (d, JRhP = 188, PPh3); 29Si, δ 36.1 (dd, JPSi = 28.1, JRhSi
=
fluoroethylene (ptfe) stopcocks. All H and 13C chemical shifts
12.7 Hz); 13C-{1H}, δ 134.9 [d, JPC = 12, P(C6H5)3, ortho], 130.2
[s, P(C6H5)3, para], 128.5 [d, JPC = 10, P(C6H5)3, meta], 90.1
(t, JPC = JRhC = 3 Hz, C5H5), 13.4 (s, CH2CH3) and 10.7 (s,
CH2CH3). Electron-impact mass spectrum: m/z 518 (Mϩ, 1),
487 (Mϩ Ϫ 31, 1), 458 (Mϩ Ϫ 60, 1) and 430 [Rh(C5H5)-
(PPh3)ϩ, 100%].
1
are reported in ppm (δ) relative to tetramethylsilane and refer-
enced using the chemical shifts of residual protio solvent reson-
ances (benzene, δ 7.13; toluene, δ 2.1; thf, δ 3.7). The 19F
NMR spectra were referenced to external CFCl3, 31P NMR
spectra to external H3PO4. Solutions were irradiated in Pyrex
ampoules fitted with ptfe taps with an Applied Photophysics
250 W high pressure mercury arc or with an ILC 300 W xenon
arc fitted with a mirror reflecting 250–400 nm. Mass spectra
were measured with a VG Autospec instrument.
The NMR spectra of complex 3 were monitored as a func-
tion of temperature using the following method. An NMR tube
was charged with 3 (25 mg, 45.8 µmol), C6D6 (0.5 mL) and
C6D5CD3 (0.1 mL) (used as chemical shift calibrant). The tube
was placed in the probe of an NMR spectrometer and 1H NMR
spectra were acquired at temperatures in the range 296–341 K.
To achieve thermal equilibrium the solution was maintained
at the desired temperature for at least 10 min prior to each
acquisition.
Syntheses
[Rh(ç5-C5H5)(PPh3)(C2H4)] 1. An ampoule was charged with
[{Rh(C2H4)2Cl}2] (1.38 g, 3.56 mmol) and thf (30 mL). To this
solution was added PPh3 (1.89 g, 7.20 mmol) and the resulting
mixture stirred at ambient temperature for 2 h. The salt
Tl(C5H5) (2.38 g, 8.83 mmol) was added to the mixture and
stirring continued for 2 h. All volatiles were distilled from the
reaction vessel, the residue was dissolved in toluene and the
solution was filtered. The filtrate was eluted through an alu-
mina column with further toluene. All volatiles were removed to
give complex 1 as an orange crystalline solid in 69.7% yield,
based on rhodium. NMR (C6D6, 296 K): 1H, δ 7.63–6.75 (m, 15
H, PPh3), 5.06 (s, 5 H, C5H5), 2.83 (m, 2 H, C2H4) and 1.31 (m,
2 H, C2H4); 31P-{1H}, δ 58.9 (d, JRhP = 209 Hz, PPh3); 13C-{1H},
δ 133.8 [d, JPC = 11, P(C6H5)3, ortho], 129.8 [d, JPC = 2, P(C6H5)3,
[Rh(ç5-C5H5)(PPh3)(ç2-C6F6)] 4. An ampoule was charged
with complex 1 (60 mg, 0.13 mmol) and neat C6F6 (2 mL). The
contents were degassed and then warmed to 35 ЊC in order to
dissolve 1 completely. This solution was irradiated for 6 h at
283 K. All volatiles were removed in vacuo to give a dark brown
oily residue, which was dissolved in toluene and loaded onto an
alumina column. The column was first eluted with neat toluene
to remove unchanged starting material. Subsequent elution with
toluene–thf (90:10 v/v) afforded a bright yellow eluent from
which all volatiles were removed to give a lemon yellow solid.
Recrystallisation from the minimum volume of toluene and
hexane (2 mL) at Ϫ20 ЊC yielded yellow needle crystals of 4 in
29% yield, based on rhodium. NMR ([2H8]toluene, 296 K):
1H, δ 7.72–6.92 (m, 15 H, PPh3) and 4.39 (t, JPH = 0.5 Hz, 5 H,
C5H5); 31P-{1H}, δ 45.8 (dt, JRhP = 203.1, JFP = 54.4 Hz, PPh3);
19F, Ϫ147.14 (m, 2 F, F2), Ϫ158.20 (m, 2 F, F1) and Ϫ173.86 (m,
2 F, F3); F1 represents fluorine atoms bound to the co-ordinated
carbon atoms, F2 and F3 are labelled sequentially; 13C-{1H}
(C6D6), δ 135.9 [d, JPC = 9.7, P(C6H5)3, ortho], 131.2 [d,
JPC = 2.4, P(C6H5)3, para], 128.9 [d, JPC = 7.3, P(C6H5)3, meta],
90.6 (dd, JPC/JRhC = 4.5, 3.1 Hz, C5H5] (Found: C, 56.71; H,
3.34. Calc. for C29H20F6PRh: C, 56.49; H, 3.25%). Electron-
impact mass spectrum: m/z 597 (Mϩ Ϫ 19, 1), 429 (Mϩ Ϫ 186,
15) and 168 [Rh(C5H5)ϩ, 100%].
para], 127.3 [d, JPC = 10, P(C6H5)3, meta], 86.7 (dd, JPC
≈
JRhC = 3, C5H5) and 26.6 (dd, JRhC = 15, JPC = 2 Hz, C2H4)
(Found: C, 65.09; H, 5.26. Calc. for C25H24PRh: C, 65.52; H,
5.24%).
[Rh(ç5-C5H5)(PPh3)(SiPri3)H] 2. A degassed solution of
complex 1 (43 mg, 93.9 µmol) in neat SiPri3H (3 mL) was irradi-
ated for 4 h at 283 K. All volatiles were removed under vacuum
to give a clear yellow oil (1H NMR spectroscopy was used to
confirm that the oil contained no starting material). The oil
was dissolved in neat toluene and eluted through an alumina
column. Toluene was distilled from the eluent in vacuo to give
a clear yellow oil, which was dissolved in Et2O and again all
volatiles were removed giving a yellow solid. Complex 2 was
isolated as a dark yellow crystalline solid in 60% yield, based on
1
rhodium. NMR ([2H8]toluene, 296 K): H, δ 7.76–7.00 (m, 15
Spectroscopic investigations of photoreactions
H, PPh3), 5.10 (t, JRhH = JPH = 0.5, 5 H, C5H5), 1.14 [t, JHH
=
With pentafluorobenzene and 1,2-difluorobenzene. In a typical
experiment an ampoule was charged with complex 1 (ca. 30 mg,
66 µmol) and fluoroarene (2 mL). The resulting solution was
thoroughly degassed and irradiated for 8 h at ca. 273 K. The
solution darkened and some precipitation occurred. The
volatiles were removed in vacuo and [2H8]toluene was added to
the residue. The suspension was transferred to an NMR tube
through a filter. Spectroscopic data for [Rh(η5-C5H5)(PPh3)-
7.3, 18 H, CH(CH3)2], 0.85 [septet, JHH = 7.3, 3 H, CH(CH3)2]
and Ϫ13.60 (dd, JPH = 29.9, JRhH = 28.2 Hz, 1 H, RhH); 31P-
{1H}, δ 56.8 (d, JRhP = 185 Hz, PPh3); 29Si, δ 47.4 (dd, JPSi
=
31.6, JRhSi = 9.8 Hz); 13C-{1H}, δ 134.1 [d, JPC = 11, P(C6H5)3,
ortho], 129.1 [d, JPC = 2, P(C6H5)3, para], 127.0 [d, JPC = 9,
P(C6H5)3, meta], 89.2 (t, JPC = JRhC = 3 Hz, C5H5), 21.0 [s,
CH(CH3)2], 20.4 [s, CH(CH3)2] and 18.8 [s, CH(CH3)2] (Found:
C, 65.30; H, 7.76. Calc. for C32H42PRhSi: C, 65.3; H, 7.14%).
Electron-impact mass spectrum: m/z 545 (Mϩ Ϫ 43, 3), 501
(Mϩ Ϫ 87, 1), 458 (Mϩ Ϫ 130, 1) and 430 [Rh(C5H5)(PPh3)ϩ,
100%].
1
(C6F5)H] 5. NMR ([2H8]toluene, 296 K), H, δ 7.40–6.90 (m,
15 H, PPh3), 5.04 (t, JRhH = JPH = 0.8, 5 H, C5H5) and Ϫ11.50
(dd, JPH = 43.9, JRhH = 21.6 Hz, RhH); 31P-{1H}, δ 57.8 (d,
JRhP = 154.9 Hz, PPh3); 19F, δ Ϫ104.10 (d, JFF = 30.5, 2 F, Fortho),
Ϫ164.59 (t, JFF = 21, 1 F, Fpara) and Ϫ165.80 (t, JFF = 23 Hz,
2 F, Fmeta); 13C-{1H}, δ 133.2 [d, JPC = 11, P(C6H5)3, ortho], 129.6
[s, P(C6H5)3, para], 127.5 [d, JPC = 11, P(C6H5)3, meta] and 88.2
(t, JPC = JRhC = 3 Hz, C5H5]; electron-impact mass spectrum m/z
598 (Mϩ, 0.4), 458 (Mϩ Ϫ 140, 1), 430 (Mϩ Ϫ 168, 56) and 168
[Rh(C5H5)ϩ, 100%].
[Rh(ç5-C5H5)(PPh3)(SiEt3)H] 3. A degassed solution of
[Rh(η5-C5H5)(PPh3)(C2H4)] 1 (37 mg, 80.8 µmol) in neat SiEt3H
(2 mL) was irradiated for 5 h at 283 K. All volatiles were
removed under vacuum to give a clear yellow oil (1H NMR
spectroscopy was used to confirm that the oil contained no
starting material). The oil was dissolved in neat toluene and
eluted dropwise through an alumina column. Toluene was dis-
tilled from the eluent in vacuo to give a clear yellow oil, which
Spectroscopic data for [Rh(η5-C5H5)(PPh3)(2,6-C6F2H3)H]
6a: NMR ([2H8]toluene, 296 K), 1H, δ 7.50–6.90 (m, 15 H,
2518
J. Chem. Soc., Dalton Trans., 1998, Pages 2515–2520

View Article Online
based on ψ-scans was rather unsatisfactory, leading to no sig-
nificant improvement in data-fitting parameters compared with
a refinement performed against uncorrected data. A correction
was therefore applied using the program DIFABS,32 but even
here the range of transmission factors (0.233–0.695) was larger
than anticipated from the size of the crystal and µ. It is most
likely that, in addition to correcting for absorption, DIFABS
has compensated for systematic errors in the intensity meas-
urements which arise from the factors described above. While
the geometry of this molecule has been determined with little
cause for doubt, little credence should be given to the displace-
ment parameters. The structure was solved by Patterson
methods (DIRDIF)33 and completed by iterative cycles of
least-squares refinement and Fourier-difference syntheses
(SHELXL 97).34 Hydrogen atoms (with the exception of the
hydride) were placed in idealised positions and subsequently
allowed to ride on their parent atoms. The hydride was located
in a difference map. During refinement, the direction of the
Rh᎐H vector was fixed, but the distance allowed to refine. The
SiPri3 group is disordered by a ca. 60Њ rotation about the Rh᎐Si
bond. The two orientations were refined with equal occupancies
of 50% and restrained to be geometrically similar with local
threefold symmetry in chemically equivalent bond lengths and
angles (but not torsions). All non-H atoms were modelled with
anisotropic displacement parameters; for neighbouring partial
weight atoms the parameters were restrained to have equal Uij
components.
Table 3 Crystallographic parameters for complex 2
Empirical formula
M
C32H42PRhSi
588.63
Crystal system
Space group
Monoclinic
P21/c
Z
a/Å
b/Å
c/Å
4
10.596(4)
16.730(6)
17.049(6)
105.76(3)
2908.4(17)
1.344
β/Њ
U/Å3
Dc/g cmϪ3
µ(Mo-Kα)/mmϪ1
T/K
0.702
220(2)
No. reflections measured
No. independent reflections
Data/restraints/parameters
Reflection to parameter ratio
Residuals [F > 4σ(F)]
Residuals (all data, F2)
6694
5111 (Rint = 0.1697)
5111/249/398
12.84
R1 = 0.0677 (3134 data)
wR2 = 0.1849
PPh3), 6.60 (m, 1 H, Hpara), 6.49 (t, J = 7.4, 2 H, Hmeta), 5.13 (s,
5 H, C5H5) and Ϫ11.51 (dd, JPH = 40.4, JRhH = 20.9 Hz, 1 H,
RhH); 31P-{1H}, δ 57.4 (d, JRhP = 158.9 Hz, PPh3); 19F, Ϫ76.15
(s, 2 F, Fortho); 13C-{1H}, δ 168.2 (ddt, JFC = 228, 18, JPC
=
JRhC = 2, C6F2H3, CF), 133.5 [d, JPC = 11.4, P(C6H5)3, ortho],
129.3 [s, P(C6H5)3, para], 127.4 [d, JPC = 10, P(C6H5)3, meta], 123
(t, JFC = 10, C6F2H3, CH, para), 108.7 (dd, JFC = 35, 3, C6F2H3,
CH, meta) and 88.6 (t, JPC = JRhC = 3 Hz, C5H5).
CCDC reference number 186/1032.
See http://www.rsc.org/suppdata/dt/1998/2515/ for crystallo-
graphic files in .cif format.
Low temperature irradiation of complex 1 in [2H8]thf in the
presence of an excess 1,3-C6F2H4 was performed as for the reac-
tion with benzene (see below). Spectroscopic data for [Rh-
(η5-C5H5)(PPh3)(2,4-C6F2H3)H] 6b and [Rh(η5-C5H5)(PPh3)-
(3,5-C6F2H3)H] 6c. We cannot distinguish which resonance
Acknowledgements
We are grateful to EPSRC for support. We appreciated helpful
discussions with Dr. S. B. Duckett and Dr. T. Braun.
belongs to 6b and which to 6c. NMR ([2H8]thf, 296 K): H,
1
δ Ϫ11.62 (JPH = 36, JRhH = 27) and Ϫ11.76 (JPH = 41, JRhH = 22
References
Hz); 31P-{1H}, δ 56.4 (JRhP = 162) and 54.9 (JRhP = 158 Hz).
1 S. T. Belt, S. B. Duckett, M. Helliwell and R. N. Perutz, J. Chem.
Soc., Chem. Commun., 1989, 928.
2 S. T. Belt, L. Dong, S. B. Duckett, W. D. Jones, M. G. Partridge and
R. N. Perutz, J. Chem. Soc., Chem. Commun., 1991, 266.
3 S. T. Belt, M. Helliwell, W. D. Jones, M. G. Partridge and R. N.
Perutz, J. Am. Chem. Soc., 1993, 115, 1429.
4 R. M. Chin, L. Dong, S. B. Duckett, M. G. Partridge, W. D. Jones
and R. N. Perutz, J. Am. Chem. Soc., 1993, 115, 7685.
5 A. D. Selmeczy, W. D. Jones, M. G. Partridge and R. N. Perutz,
Organometallics, 1994, 13, 522.
With benzene. (a) Room temperature experiments. An
ampoule was charged with complex 1 (30 mg, 66 µmol) and
benzene (2 mL). The resulting solution was thoroughly degassed
and irradiated for 15 h at 283 K. All volatiles were removed
under vacuum and the resulting dark brown residue was dis-
solved in C6D6. This solution was filtered prior to loading into
an NMR tube.
(b) Low temperature irradiation of complex 1 in thf and/or
benzene. A range of experiments were performed in which
complex 1 was irradiated in either neat [2H8]thf, or mixtures of
C6D6–thf, C6D6–[2H8]thf and C6H6–[2H8]thf. In a typical experi-
ment an NMR tube was charged with 1 (37 mg, 81 µmol), C6D6
(0.3 mL) and [2H8]thf (0.3 mL). This solution was thoroughly
degassed and the tube was suspended in a thermally insulated
Pyrex tube through which flowed a stream of cold nitrogen
vapour. The solution was cooled to 233 K and irradiated with a
xenon arc at <400 nm for 5 h. The tube was then placed in the
precooled probe of an NMR spectrometer (233 K) and multi-
nuclear NMR spectra were acquired (see Table 2).
6 W. D. Jones and F. J. Feher, Acc. Chem. Res., 1989, 22, 91.
7 M. G. Partridge, A. McCamley and R. N. Perutz, J. Chem. Soc.,
Dalton Trans., 1994, 3519.
8 P. E. Bloyce, A. J. Rest and I. Whitwell, J. Chem. Soc., Dalton Trans.,
1990, 813.
9 A. J. Rest, I. Whitwell, W. A. G. Graham, J. K. Hoyano and A. D.
McMaster, J. Chem. Soc., Dalton Trans., 1987, 1181.
10 D. M. Haddleton, A. McCamley and R. N. Perutz, J. Am. Chem.
Soc., 1988, 110, 1810.
11 S. T. Belt, F. W. Grevels, W. E. Klotzbücher, A. McCamley and
R. N. Perutz, J. Am. Chem. Soc., 1989, 111, 8373.
12 E. P. Wasserman, C. B. Moore and R. G. Bergman, Science, 1992,
255, 315.
13 B. H. Weiller, E. P. Wasserman, R. G. Bergman, C. B. Moore and
G. C. Pimentel, J. Am. Chem. Soc., 1989, 111, 8288.
14 R. H. Schultz, A. A. Bengali, M. J. Tauber, B. H. Weiller, E. P.
Wasserman, K. R. Kyle, C. B. Moore and R. G. Bergman, J. Am.
Chem. Soc., 1994, 116, 7369.
15 A. A. Bengali, R. H. Schultz, C. B. Moore and R. G. Bergman,
J. Am. Chem. Soc., 1994, 116, 9585.
16 D. P. Drolet and A. J. Lees, J. Am. Chem. Soc., 1990, 112, 5878;
1992, 114, 4186.
17 A. A. Purwoko and A. J. Lees, J. Organomet. Chem., 1995, 504,
107.
Crystallography
Data were collected on a Stoe Stadi-4-diffractometer equipped
with an Oxford Cryosystems low-temperature device. Crystal-
lographic parameters are listed in Table 3. The diffraction pro-
files were characterised by rather uneven backgrounds, tailing
off slowly towards low angle. In addition, one reflection out of
22 located in a random search had non-integral Miller indices
relative to the remainder, suggesting a small amount of multi-
plicity in the sample. Other crystals in the sample showed simi-
lar features. Possibly for these reasons, an absorption correction
18 T. W. Bell, S. A. Brough, M. G. Partridge, R. N. Perutz and A. D.
Rooney, Organometallics, 1993, 12, 2933.
19 W. D. Jones and V. L. Kuykendall, Inorg. Chem., 1991, 30, 2615.
J. Chem. Soc., Dalton Trans., 1998, Pages 2515–2520
2519

View Article Online
20 (a) A. J. Oliver and W. A. G. Graham, Inorg. Chem., 1971, 10, 1165;
(b) R. Benn, H. Brenneke and A. Rufinska, J. Organomet. Chem.,
1987, 320, 115.
21 S. T. Belt, S. B. Duckett, D. M. Haddleton and R. N. Perutz,
Organometallics, 1989, 8, 748.
22 T. Braun, M. Laubender, O. Gevert and H. Werner, Chem.
Ber./Recueil, 1997, 130, 559.
23 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National
Laboratory, Oak Ridge, TN, 1976.
26 S. T. Belt, D.Phil. Thesis, University of York, 1988; S. N. Heaton,
D.Phil. Thesis, University of York, 1995.
27 T. W. Bell, D. M. Haddleton, A. McCamley, M. G. Partridge, R. N.
Perutz and H. Willner, J. Am. Chem. Soc., 1990, 112, 9212.
28 R. G. Bergman and A. H. Janowicz, J. Am. Chem. Soc., 1982, 104,
352.
29 C. L. Higgitt, A. H. Klahn, M. H. Moore, B. Oelckers, M. G.
Partridge and R. N. Perutz, J. Chem. Soc., Dalton Trans., 1997,
1269.
24 A. J. Oliver and W. A. G. Graham, Inorg. Chem., 1971, 10, 1; D. M.
Haddleton and R. N. Perutz, J. Chem. Soc., Chem. Commun., 1985,
1372; S. B. Duckett, D. M. Haddleton, S. A. Jackson, R. N. Perutz,
M. Poliakoff and R. K. Upmacis, Organometallics, 1988, 7, 1526;
S. B. Duckett and R. N. Perutz, J. Chem. Soc., Chem. Commun.,
1991, 28; P. O. Bentz, R. Ruiz, B. E. Mann, C. M. Spencer and P. M.
Maitlis, J. Chem. Soc., Chem. Commun., 1985, 1374; J. Ruiz, P. O.
Bentz, B. E. Mann, C. M. Spencer, B. F. Taylor and P. M. Maitlis,
J. Chem. Soc., Dalton Trans., 1987, 2709.
30 I. Bach, K.-R. Pörschke, R. Goddard, C. Kopiske, C. Krüger,
A. Rufinska and K. Seevogel, Organometallics, 1996, 15, 4959.
31 R. Cramer, Inorg. Synth., 1974, 14, 15.
32 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158.
33 P. T. Beurskens, G. Beurskens, W. P. Bosman, R. de Gelder,
S. García-Granda, R. O. Gould, R. Israël and J. M. M. Smits,
DIRDIF 96, Crystallography Laboratory, University of Nijmegen,
1996.
34 G. M. Sheldrick, SHELXL 97, University of Göttingen, 1997.
25 (a) M. J. Fernandez, P. M. Bailey, P. O. Bentz, J. S. Ricci, T. F.
Koetzle and P. M. Maitlis, J. Am. Chem. Soc., 1984, 106, 5458;
(b) K. Osakada, K. Hataya, Y. Nakamura, M. Tanaka and
T. Yamamoto, J. Chem. Soc., Chem. Commun., 1993, 577; (c) D. L.
Thorn and R. L. Harlow, Inorg. Chem., 1990, 29, 2017.
Received 23rd April 1998; Paper 8/03048K
2520
J. Chem. Soc., Dalton Trans., 1998, Pages 2515–2520