Towards the synthesis of perfluoroalkylated derivatives of Xantphos

Article abstract of DOI:10.1016/j.tet.2004.02.070

An analogue of Xantphos incorporating four perfluoroalkyl groups has been prepared and successfully used as a ligand in the rhodium-catalysed hydroformylation of 1-octene in toluene. A number of perfluoroalkylated xanthene backbones have also been synthesised, but their conversion into preferentially perfluorocarbon solvent soluble Xantphos-type ligands, suitable for catalysis in fluorocarbon solvents, has not been successful.

Full text of DOI:10.1016/j.tet.2004.02.070

Tetrahedron 60 (2004) 4079–4085
Towards the synthesis of perfluoroalkylated derivatives
of Xantphos
Dave J. Adams,a David J. Cole-Hamilton,b Duncan A. J. Harding,a Eric G. Hope,a
Peter Pogorzelecb and Alison M. Stuarta
,
*
aDepartment of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, UK
bCatalyst Evaluation and Optimisation Service, School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK
Received 18 December 2003; revised 30 January 2004; accepted 25 February 2004
Abstract—An analogue of Xantphos incorporating four perfluoroalkyl groups has been prepared and successfully used as a ligand in the
rhodium-catalysed hydroformylation of 1-octene in toluene. A number of perfluoroalkylated xanthene backbones have also been synthesised,
but their conversion into preferentially perfluorocarbon solvent soluble Xantphos-type ligands, suitable for catalysis in fluorocarbon solvents,
has not been successful.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
The fluorous biphasic approach has been shown to be a
useful tool for the efficient separation of catalyst from
products in the rhodium-catalysed hydroformylation of long
chain alkenes,1 amongst other catalytic reactions.2 We have
recently shown that P(C6H4-4-C6F13)3 can be used in the
rhodium-catalysed hydroformylation of 1-octene in the
fluorous phase resulting in good selectivity to the required
linear aldehyde with minimal rhodium leaching (0.05%)
into the non-fluorous product phase on phase separation post
reaction.3 With a view to increasing the selectivity further,
we investigated the perfluoroalkyl derivatives of analogues
of established bidentate phosphines and phosphites that
have been shown to offer excellent selectivity in this
process.4 Surprisingly, although a large number of per-
fluoroalkyl derivatised monodentate phosphorus(III)
ligands, prepared by a variety of routes,4 have been
described in the literature, the number of perfluoroalkyl
derivatised bidentate phosphorus(III) ligands is still rela-
tively small with only those incorporating the ethyl
backbone being perfluorocarbon soluble.5 Xantphos has
been shown to be a remarkable ligand for the rhodium-
catalysed hydroformylation of long chain alkenes, giving
exceptionally high selectivity to the industrially useful
linear aldehyde (linear/branched ratio¼50:1).6 Here, we
report our investigations directed towards the synthesis of
perfluoroalkylated derivatives of Xantphos.
The approach followed in this work draws upon precedents
set in earlier Xantphos-6 and fluorous-based3 hydroformyl-
ation studies. The catalytic data available for Xantphos
clearly shows that the bite angle of the bisphosphine is
critical for the high selectivities achieved in the hydro-
formylation of long chain alkenes.6 Therefore, in order to
minimise the steric effects of the perfluoroalkyl groups,
linear perfluoroalkyl groups directly attached to the
aromatic rings in the para positions on the pendant arms
(R1 in Fig. 1) or the meta positions (for ease of synthesis) on
the backbone (R2) are likely to be the most successful.
Indeed, water-soluble versions of Xantphos have incorpo-
rated sulfonate or dialkylamino groups in these positions.7
Furthermore, although a wide range of perfluoroalkyl
groups have been incorporated into phosphines, many
include a so-called spacer group to ameliorate their
electron-withdrawing effect. However, in the hydro-
formylation of alkenes, electron-withdrawing groups are
known to lead to catalysts which give greater rates of
reaction and higher ratios of linear/branched aldehydes in
the final hydroformylation product mixtures than those with
Keywords: Fluorine; Fluorinated ligands; Phosphines; Homogeneous
catalysis; Hydroformylation.
*
Corresponding author. Tel.: þ44-116-252-2108; fax: þ44-116-252-3789;
Figure 1. Xantphos skeleton, showing the sites where fluorinated side
chains may be readily attached (R1 and R2).
e-mail address: egh1@le.ac.uk; djc@st-and.ac.uk2
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.02.070

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D. J. Adams et al. / Tetrahedron 60 (2004) 4079–4085
greater electron density.3 We, therefore, decided to focus
solely on ligands with linear perfluoroalkyl groups directly
attached to the aromatic rings thereby maximising the
electronic advantages of these fluorinated substituents.
High fluorous phase solubility is required for the successful
application of a ligand in a fluorous phase reaction. Previous
work has suggested that 60% fluorine (w/w) is generally
required for preferential solubility in a perfluorocarbon
solvent over an organic solvent.11 Although a single
perfluoroalkyl group per aromatic ring is capable of
generating a compound that is preferentially soluble, 1 has
only 4 tails for 6 aromatic rings. With only 53.4% fluorine
content it is, therefore, unsurprising that the perfluoroalkyl-
ated Xantphos (1) has a low solubility in perfluoro-1,3-
dimethylcyclohexane (PP3). Partition coefficient determi-
nations in a PP3/toluene biphase were complicated further
by the low solubility of (1) in both phases. This low
solubility has been previously noted for other high
molecular weight fluorinated compounds. To increase the
partition coefficient, the number of perfluoroalkyl groups on
the molecule would need to be increased, which could be
achieved by increasing the number of tails on the pendant
arms. 3,5-Bis-substitution has been used in other ligand
systems, but this has a dramatic influence on their steric
properties, which would seriously compromise the high
selectivity of Xantphos-based hydroformylation catalysts.
Alternatively, using a silicon spacer unit, up to three
tails per phenyl ring could be introduced. However, as
illustrated by van Koten et al.12 with a molecular weight
in excess of 4500 Da, the absolute solubility of such a ligand
in any solvent would be so low as to obviate its use in
catalysis.
Figure 2. Bis(4-tridecafluoro-n-hexylphenyl) ethoxy phosphinite.
Although quenching the dilithiate of 9,9-dimethylxanthene
with Ph2PCl gives reproducibly high yields of Xantphos, the
8
analogous reaction with ClP(C6H4-4-C6F13)2 in diethyl
ether resulted in the isolation of only trace amounts of the
desired perfluoroalkylated Xantphos. Instead, bis(4-trideca-
fluoro-n-hexylphenyl) ethoxy phosphinite was isolated,
Figure 2. Decomposition of ethereal solvents by organo-
lithiates is a well-known process, giving, in the case of
diethyl ether, lithium ethoxide and ethene.9 Here, therefore,
the isolated phosphinite results from the reaction between
chlorophosphine and lithium ethoxide. We have detected,
by 31P NMR spectroscopy, an analogous reaction during the
synthesis of Xantphos itself although, in this case,
ethoxydiphenyl phosphinite is only formed in trace
amounts. This difference in reactivity between the two
chlorophosphines is undoubtedly due to the presence of the
highly electron-withdrawing perfluoroalkyl groups in
ClP(C6H4-4-C6F13)2. A 17% yield of the perfluoroalkylated
Xantphos (1) could be achieved by carrying out the reaction
in hexane, but the low solubility of the chlorophosphine in
this solvent required its addition as a refluxing suspension.
By adding the chlorophosphine in THF to the lithiate in
hexane, a similar yield could be obtained, which could be
increased to 26% by refluxing the solution for 30 min prior
to the addition of the chlorophosphine, Scheme 1.
Therefore, to increase the percentage fluorine further,
derivatising the xanthene backbone at position R2 (Fig. 1)
is likely to be the only viable approach. Perfluoroalkyl
groups can be incorporated at position R2 most simply by
converting bis(4-bromophenyl)ether to bis(4-tridecafluoro-
n-hexylphenyl)ether (2) by a copper mediated coupling
reaction with C6F13I which affords the desired product in a
77% yield. Similarly, 2,7-dibromo-9,9-dimethylxanthene
(prepared by direct bromination of 9,9-dimethylxanthene)
was converted to 2,7-bis(tridecafluoro-n-hexyl)-9,9-
dimethylxanthene (3) in a 79% yield, Scheme 2.
The yield was improved further by following an alternative
method. 4,5-Bis[bis(diethylamino)phosphine]-9,9,-dimethyl-
xanthene, prepared via the method of van Leeuwen et al.10
was converted to 4,5-bis(dichlorophosphino)-9,9-dimethyl-
xanthene by reaction with dry HCl in ether. Reaction of
this chlorophosphine with the aryl lithiate derived from
4-(tridecafluoro-n-hexyl)bromobenzene gave the perfluoro-
alkylated Xantphos (1) in a 56% yield, Scheme 1.
Direct lithiation of (2) or (3) at room temperature
(CAUTION! Lithiations of aromatic rings substituted with
perfluoroalkyl groups have been reported to lead to
explosion)13 followed by quenching with ClPPh2 in ether
Scheme 1.

D. J. Adams et al. / Tetrahedron 60 (2004) 4079–4085
4081
Scheme 2.
led to an inseparable mixture of phosphines being formed.
The desired bisphosphine could be detected by 31P NMR
spectroscopy in each case, but could only be isolated in the
case of (2). Even then, the bisphosphine could only be
isolated with a purity of 90%. In each case, in addition to
lithiating ortho to the oxygen, as occurs with 9,9-di-
methylxanthene, lithiation ortho to the perfluoroalkyl group
also occurs as evidenced by the strong P–F coupling in the
31P NMR spectra of the quenched product.8 It is apparent
that the strongly electron-withdrawing perfluoroalkyl
groups are having a profound effect on the regioselectivity
of the lithiation. The most obvious way to solve this
problem is to introduce a spacer between the perfluoroalkyl
chain and the aromatic ring and there are numerous suitable
groups now available.12,14 We introduced an alkyl spacer
group by conversion of 2,7-dibromo-9,9-dimethylxanthene
to 9,9-dimethylxanthene-2,7-dicarbaldehyde (4), followed
by a Wittig reaction with [Ph3PCH2CH2C6F13]þI2 follow-
ing the known methodology.15 After hydrogenation with
Pd/C in DCM, 2,7-bis(1H,1H,2H,2H,3H,3H-perfluorono-
nanyl)-9,9-dimethylxanthene (6) could be isolated in an
overall yield of 12% from the dibromoxanthene, Scheme 3.
Unfortunately, repeated attempts at lithiating 6, followed
by quenching with Ph2PCl, failed to yield any of the
desired product. Despite a strong colour change upon the
addition of n-BuLi, the starting xanthene was recovered
unchanged after reaction, along with a small amount of a
product, the 19F NMR spectrum of which suggested
attack at or near the perfluoroalkyl groups had
occurred. This infers that, rather than deprotonating the
aromatic ring, lithiation of the alkyl spacer group had
occurred.
2.1. Catalysis
The effect of the perfluoroalkyl groups on the donor ability
of the phosphorus atoms has been probed previously by
1
examination of the change in JPPt of the cis-[PtCl-2-L]
(L¼bidentate or two monodentate phosphines).5b As can be
seen from Table 1, perfluoroalkylated Xantphos (1) shows a
similar trend to (C6H4-4-C6F13)2PCH2CH2P(C6H4-4-
1
C6F13)2 with a decrease in the magnitude of JPPt as
expected following the introduction of strongly electron-
withdrawing groups.
Scheme 3.

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D. J. Adams et al. / Tetrahedron 60 (2004) 4079–4085
Table 1. Pt–P coupling constants for platinum complexes containing
bidentate ditertiary phosphines
3. Conclusion
This work has shown the difficulties in attempting to
generate a perfluorocarbon soluble analogue of a known
bisphosphine, although a number of new perfluoroalkylated
intermediates have been prepared and fully characterised.
A derivative of Xantphos has been prepared incorporating
four perfluoroalkyl groups. Unfortunately, this is not
sufficient to render the bisphosphine preferentially soluble
in a perfluorocarbon solvent and attempts at further
derivatising this compound have failed. However, the
derivatised Xantphos is still an effective ligand for the
rhodium catalysed hydroformylation of 1-octene in toluene,
offering good selectivity to the desired linear aldehydes
but the fluorous groups appear to effect the amount of
isomerisation.
Complex
1JPtP (Hz)
cis-[PtCl2(dppe)]a
3594
3568
3694
3662
cis-[PtCl2{(CH2P(C6H4-4-C6F13)2}2]a
[PtCl2(Xantphos)]b
[PtCl2(1)]b
a
CD3COCD3, data from Ref. 5b.
CDCl3.
b
Although 1 does not have sufficiently high perfluorocarbon
solubility for use in a fluorous biphasic reaction, it can be
successfully used as a ligand in the rhodium catalysed
hydroformylation of 1-octene in toluene. We rationalised
that the fluoroalkyl groups should have a beneficial effect in
this reaction, since electron-withdrawing groups have been
shown by others to increase rates of reaction and selectivity
in such reactions.16 Hydroformylation of 1-octene was
carried out at 80 8C and 20 bar of 1:1 CO/H2 using
2.2 equiv. of 1 with respect to rhodium. The results are
shown in Table 2 and compared to the same reaction carried
out with Xantphos. As with Xantphos, the selectivity for
the required linear aldehyde is relatively high (linear
aldehyde/branched aldehyde¼22.9:1 compared to 4.7:1
for P(4-C6F13C6H4)3). However, the isomerisation is greater
when 1 is used compared with Xantphos. These findings
mirror those found elsewhere for derivatives of thixantphos,
where isomerisation to the 2-octene increased as phosphine
basicity decreased.16c This has been attributed to an
increased tendency of the branched alkyl rhodium species
to form 2-octene instead of the branched aldehyde. A
possible alternative explanation is that the poorer donor
ability and larger size of 1 compared with Xantphos may
reduce its coordinating power and leave some rhodium
uncoordinated to the phosphine. This type of complex is a
known alkene isomerisation catalyst, but is poorly selective
and rather sluggish in hydroformylation reactions under
these conditions. Support for this suggestion comes from the
observation that lower loadings of ligand (1:Rh¼1.7) give
much lower linear/branched ratios and significant amounts
of aldehydes derived from isomerised alkenes. The
rhodium–Xantphos complexes are essentially inactive for
the hydroformylation of internal alkenes. This last experi-
ment was carried out in perfluoromethylcyclohexane. This
is unlikely to be a medium effect, since our previous work
has shown that triphenylphosphine is more selective when
the reaction is carried out in a perfluorocarbon solvent as
compared to toluene.3b At the end of the reaction, both
organic and fluorous phases were yellow in colour,
confirming that 1 is insufficiently fluorinated to immobilise
the catalyst completely within the fluorous phase.
4. Experimental
4.1. General Remarks
1H, 19F and 31P NMR spectroscopies were carried out on a
Bruker ARX250 spectrometer at 250.13, 235.34 and
101.26 MHz or a Bruker DPX300 spectrometer at 300.14,
282.41 and 121.50 MHz respectively and were referenced to
external SiMe4 (1H), external CFCl3 (19F) and to external
H3PO4 (31P) using the high frequency positive convention.
Due to the complicated spectra arising from the extensive
coupling to the fluorine atoms, all 13C NMR are quoted
without the values for the perfluoroalkyl groups (105–
120 ppm). Abbreviations for NMR spectral multiplicities
are as follows: s¼singlet, d¼doublet etc., m¼multiplet.
Elemental analyses were performed by the Elemental
Analysis Service at the University of North London. Mass
spectra were recorded on a Kratos Concept 1H mass
spectrometer. cis-[PtCl2(MeCN)2]17 and 4-(tridecafluoro-n-
hexyl)bromobenzene18 were prepared by the literature
routes. 4,5-Bis(diethylaminophosphino)-9,9-dimethyl-
xanthene was prepared via the method of Goertz et al.11
[Ph3PCH2CH2C6F13]þI2 was prepared via the method of
Rocaboy et al.15
4.1.1. 4,5-Bis(dichlorophosphino)-9,9-dimethylxanthene.
4,5-Bis(diethylaminophosphino)-9,9-dimethylxanthene
(0.98 g, 1.76 mmol) was dissolved in ether (30 mL).
Concentrated HCl was bubbled through the solution for
15 min. The solution was then flushed with nitrogen for 2 h,
filtered through celite and the solvent removed in vacuo
to give a white solid (0.54 g, 75%). Anal. calcd for
C15H12OP2Cl4: C, 43.90; H, 2.93. Found: C, 44.02; H,
Table 2. Products from the hydroformylation of 1-octene catalysed by rhodium complexes of Xantphos based ligands in toluene at 80 8C and 20 bar CO/H2 (1:1)
Ligand
Ligand/Rh
1-Nonanal (%)
2-Methyloctanal (%)
% Isomera
l:bb
k (s21 c
)
Xantphos
1
2.2
2.2
1.7
82.1
81.0
65.6
1.9
3.5
17.7
3.4
11.5
15.5
43.5
22.9
3.7
1.2£1024
1.2£1024
5.0£1024
1d
a
Percentage isomerisation to 2-octene.
Linear over branched ratio.
b
c
d
First order rate constant calculated from gas up take plots at constant pressure.
In perfluoromethylcyclohexane.

D. J. Adams et al. / Tetrahedron 60 (2004) 4079–4085
4083
1
2.92. m/z (EI): 412 (MHþ). H NMR (C6D6) 7.80 (2H, dd,
was quenched with water, the organic layer removed, dried
with sodium sulfate and the solvent removed in vacuo. The
resulting semi-solid was passed down a short silica column
to give a yellow solid (87% pure by NMR, 0.36 g, 31%). m/z
3JHH¼7.6 Hz, JHH¼1.8 Hz, H3), 6.96 (2H, dd, JHH
¼
4
3
4
3
7.6 Hz, JHH¼1.8 Hz, H1), 6.79 (2H, t, JHH¼7.6 Hz, H2)
1.07 (6H, s, CH3). 31P{1H} NMR (C6D6) 158.9 (s). 13C
NMR (C6D6) 150.8 (t, JPC¼13.5 Hz), 130.7, 130.4, 129.2,
128.3, 123.4, 34.4, 31.4.
1
(FAB): 1175 (MHþ). H NMR (CDCl3) 7.25 (2H, s, H5),
3
7.17 (8H, m, ArH), 7.05 (2H, d, JHH¼9.0 Hz, H2), 6.91
3
4
(12H, m, ArH), 6.29 (2H, dd, JHH¼9.4 Hz, JHH¼3.5 Hz,
4
4.1.2. 4,5-Bis-(bis(4-tridecafluoro-n-hexyl-phenyl)phos-
phino)-9,9-dimethylxanthene (1). 4-(Tridecafluoro-n-hex-
yl)bromobenzene (1.44 g, 3.03 mmol) was dissolved in
diethyl ether (20 mL) under nitrogen and cooled to 278 8C.
n-BuLi (1.9 mL of a 1.6 M solution in hexane, 3.04 mmol)
was added over 1 h and the solution stirred for 4 h at
278 8C. 4,5-Bis(dichlorophosphino)-9,9-dimethylxanthene
(0.31 g, 0.76 mmol) in diethyl ether (20 mL) was then added
dropwise and the solution allowed to warm to room
temperature overnight. Water was then added (30 mL), the
organic solution separated and dried. The solvent was
removed in vacuo to give a yellow solid. This was washed
with perfluoro-1,3-dimethylcyclohexane (3£10 mL) to give
a white solid (0.372 g, 27%). By repeatedly cooling the
perfluoro-1,3-dimethylcyclohexane solution to 240 8C, a
further 0.294 g of 4,6-bis-{bis(4-tridecafluoro-n-hexyl-
phenyl}phosphino)-9,9-dimethylxanthene was collected
(21%). m/z (FAB) 1851 (MHþ). Anal. calcd for
C63H28OP2F52: C, 40.86; H, 1.51. Found: C, 40.76; H,
1.54. 1H NMR (C6D6) 7.51–7.21 (18H, m, ArH), 6.97 (2H,
H3). 19F{1H} NMR (CDCl3) 281.39 (6F, t, JFF¼8.5 Hz,
CF3), 2110.52 (4F, t, 4JFF¼14.1 Hz, a-CF2), 2121.82 (4F,
m, CF2), 2122.54 (4F, m, CF2), 2123.60 (4F, m, CF2),
2126.69 (4F, m, CF2). 31P{1H} NMR (CDCl3) 215.5 (s).
4.1.5. 2,7-Dibromo-9,9-dimethylxanthene. Bromine
(0.51 mL, 10.0 mmol) in glacial acetic acid (1 mL) was
added slowly to a stirred solution of 9,9-dimethylxanthene
(0.843 g, 4.00 mmol) in acetic anhydride (10 mL) at 0 8C.
The solution was then allowed to warm to room temperature
and stirred for 2 h. The solution was then poured onto an
excess of ice-cold water and the precipitate collected by
filtration. The white solid was washed with sodium bisulfate
(10% aqueous solution) and water and dried in vacuo
(1.33 g, 90%). Anal. calcd for C15H12OBr2: C, 48.95; H,
3.29. Found: C, 49.03; H, 3.19. Mp 113–115 8C. m/z (FAB):
1
4
368 ([M]þ). H NMR (CDCl3) 7.59 (2H, d, JHH¼2.3 Hz,
3
4
H1), 7.40 (2H, dd, JHH¼8.7 Hz, JHH¼2.3 Hz, H3), 7.03
(2H, d, JHH¼8.7 Hz, H4), 1.70 (6H, s, CH3). 13C NMR
3
(CDCl3) 149.6, 132.0, 130.9, 129.4, 118.7, 116.1, 34.9,
32.6.
3
3
4
t, JHH¼7.6 Hz, H2), 6.76 (2H, dd, JHH¼7.6 Hz, JHH
¼
1.6 Hz, H3), 1.62 (6H, s, CH3). 19F{1H} NMR (C6D6)
281.45 (12F, t, 4JFF¼10.6 Hz, CF3), 2110.63 (8F, t, 4JFF¼
14.6 Hz, a-CF2), 2121.78 (16F, m, CF2), 2123.14 (8F, m,
CF2), 2126.41 (8F, m, CF2). 31P{1H} NMR (C6D6) 218.2.
4.1.6. 2,7-Bis(tridecafluoro-n-hexyl)-9,9-dimethyl-
xanthene (3). Tridecafluoro-n-hexyl iodide (4.82 g,
10.8 mmol), 2,7-dibromo-9,9-dimethylxanthene (1.00 g,
2.7 mmol), 2,20-bipyridine (0.12 g, 0.8 mmol) and copper
bronze (1.37 g, 21.6 mmol) were heated to 100 8C in DMSO
(40 mL) and fluorobenzene (40 mL) for 4 days. The cooled
solution was poured onto a mixture of diethyl ether
(100 mL) and water (100 mL), filtered and the organic
layer washed three times with water. After drying, the
solvent was removed in vacuo and the resulting yellow solid
triturated with methanol, giving a white solid, which was
recovered by filtration (1.80 g, 79%). Anal. calcd for
C27H12OF26: C, 38.30; H. 1.42. Found: C, 38.29; H, 1.42.
4.1.3. 4,40-Bis(tridecafluoro-n-hexyl)phenyl ether (2).
Perfluoro-n-hexyl iodide (55.31 g, 124.0 mmol) was added
to a stirred solution of para-dibromodiphenyl ether (10.03 g,
30.6 mmol), copper bronze (15.75 g, 247.8 mmol) and
2,20-bipyridine (1.34 g, 9.0 mmol) in DMSO (200 mL) and
fluorobenzene (120 mL) under nitrogen at 100 8C. The
solution was stirred for 3 days, cooled and poured on to an
diethyl ether (300 mL)/water (300 mL) mixture and filtered.
The organic layer was separated and washed three times
with water, dried and the solvent removed in vacuo. The
resulting yellow oil crystallised on standing and was washed
with methanol to give a white powder (19.00 g, 77%). Mp
59–61 8C. Anal. calcd for C24H8OF26 C, 35.73; H, 0.99.
1
Mp 84–85 8C. m/z (FAB): 846 (Mþ). H NMR (CDCl3)
3
4
7.55 (2H, bs, H1), 7.38 (2H, dd, JHH¼8.5 Hz, JHH
¼
3
1.6 Hz, H3), 7.11 (2H, d, JHH¼8.5 Hz, H4), 1.60 (6H, s,
CH3); 19F{1H} NMR (CDCl3) 281.32 (6F, t, 4JFF¼10.6 Hz,
CF3), 2110.58 (4F, t, 4JFF¼14.6 Hz, CF2), 2121.89 (4F, m,
CF2), 2122.38 (4F, m, CF2), 2123.26 (4F, m, CF2),
2126.60 (4F, m, CF2). 13C NMR (CDCl3) 152.8, 130.4,
127.0, 125.9, 125.0, 124.6, 124.2, 117.4, 34.6, 32.9.
Found: C, 35.80; H, 0.96. m/z (FAB): 806 (Mþ). H NMR
1
3
(CDCl3) 7.59 (4H, d, JHH¼8.7 Hz, H3), 7.15 (4H, d,
3JHH¼8.7 Hz, H2); 19F{1H} NMR (CDCl3) 281.29 (6F, t,
4JFF¼9.3 Hz, CF3), 2110.52 (4F, t, JFF¼14.6 Hz, CF2),
4
2121.89 (4F, m, CF2), 2122.27 (4F, m, CF2), 2123.25 (4F,
m, CF2), 2126.59 (4F, m, CF2).
4.1.7. 9,9-Dimethylxanthene-2,7-dicarbaldehyde (4).
2,7-Dibromo-9,9-dimethylxanthene (1.40 g, 3.80 mmol)
was dissolved in diethyl ether (100 mL) and cooled to
278 8C. n-BuLi (5.10 mL of a 1.6 M solution in hexane,
8.16 mmol) was added over 30 min and the solution allowed
to warm to room temperature over 90 min. After stirring for
4 h at room temperature, the solution was cooled to 278 8C
and N,N-dimethylformamide (3.00 mL, 38.79 mmol) added.
The solution was allowed to warm to room temperature
overnight to give a yellow solution with a white precipitate.
This was hydrolysed (100 mL), the organic layer separated,
dried with sodium sulfate and the solvent removed in vacuo.
4.1.4. Bis[(2-diphen0ylphosphino-4-tridecafluoro-n-hexyl)-
phenyl]ether. 4,4 -Bis(tridecafluorohexyl)phenyl ether
(0.81 g, 1.0 mmol) was dissolved in diethyl ether (30 mL).
TMEDA (0.24 g, 2.1 mmol) was added, followed by n-BuLi
(1.25 mL of a 1.6 M solution in hexane, 2.0 mmol) dropwise
(CAUTION! Lithiations of aromatic rings substituted with
perfluoroalkyl groups have been reported to lead to
explosions[13]). The resulting red solution was stirred for
3 h and then quenched with chlorodiphenyl phosphine
(0.44 g, 2.0 mmol). After stirring overnight, the solution

4084
D. J. Adams et al. / Tetrahedron 60 (2004) 4079–4085
The yellow solid was recrystallised from ethanol to give a
yellow solid (0.57 g, 56%). Mp 109–110 8C. m/z (FAB):
267 (MHþ). HRMS (FAB) 267.1022. Calcd for C17H14O3
(FAB): 2081 (M2Cl). 1H NMR (CDCl3) 7.66 (2H, d,
3JHH¼7.1 Hz, H3), 7.49 (8H, m), 7.29 (12H, m), 1.49 (6H, s,
CH3). 19F{1H} NMR (CDCl3) 281.38 (12F, t, 4JFF¼8.5 Hz,
CF3), 2112.50 (4F, m, CF2), 2112.68 (4F, m, CF2),
2122.11 (8F, m, CF2), 2122.99 (8F, m, CF2), 2123.49 (8F,
m, CF2), 2126.85 (8F, m, CF2). 31P{1H} NMR (CDCl3) 7.5
1
267.1021. H NMR (CDCl3) 9.88 (2H, s, CHO), 7.93 (2H,
4
3
4
d, JHH¼1.8 Hz, H1), 7.70 (2H, dd, JHH¼8.3 Hz, JHH
¼
3
1.8 Hz, H3), 7.14 (2H, d, JHH¼8.3 Hz, H4), 1.65 (6H, s,
CH3). 13C NMR (CDCl3) 191.1, 154.6, 133.2, 130.8, 128.9,
117.9, 34.6, 31.4.
1
(s, JPtP¼3674 Hz).
4.1.11. [{Xantphos}PtCl2]. Prepared as above from
Xantphos (0.139 g, 0.24 mmol) and cis-[PtCl2(MeCN)2]
(0.083 g, 0.24 mmol) giving the product as a white powder
(0.183 g, 90%). Anal. calcd for C39H32OP2Cl2Pt: C, 55.45;
H, 3.79. Found: C, 55.39; H, 3.61. m/z (FAB): 844 (Mþ). 1H
4.1.8. 2,7-Bis(1H,2H,3H,3H-perfluoronon-1-enyl)-9,9-
dimethylxanthene (5). 9,9-Dimethylxanthene-2,7-dicar-
baldehyde (3.30 g, 12.41 mmol), [Ph3PCH2CH2C6F13]þI2
(20.13 g, 27.35 mmol) and potassium carbonate (4.46 g,
32.09 mmol) were heated to 110 8C for 3 days in dioxane
(90 mL) and water (3 mL). After cooling, the solvent was
removed in vacuo, the solid redissolved in dichloromethane
(100 mL) and washed well with water. After drying with
magnesium sulphate, the solvent was removed in vacuo and
passed through a silica plug with hexane. The solvent was
removed in vacuo to give a white glass (2.57 g, 22%). b.p.
202 8C at 0.05 mm Hg. Anal. calcd for C33H20OF26: C,
42.77; H, 2.16. Found: C, 42.81; H, 2.17. m/z (FAB): 925
(M2H). 1H NMR (CDCl3) 7.23 (2H, m, H1), 6.99 (4H, m,
3
NMR (CDCl3) 7.80 (2H, d, JHH¼7.3 Hz, H3), 7.70–7.10
(24H, m), 2.04 (6H, s, CH3). 31P{1H} NMR (CDCl3) 5.90 (s,
1JPtP¼3694 Hz).
4.2. Catalysis
An autoclave, fitted with a substrate injector containing
1-octene (1.0 mL, 6.37 mmol), a mechanical stirrer, a gas
delivery system, an injection port and a thermocouple was
flushed with CO/H2 (1:1) to remove air. Degassed toluene
(4.0 mL) containing dicarbonyl(2,4-pentanedionato)-
rhodium(I) ([Rh(acac)(CO)2], 0.01 mmol) and ligand (2 or
Xantphos) (0.022 mmol) was added through the injection
port against a stream of CO/H2 using a syringe. The
autoclave was pressurised with CO/H2 (1:1) to 20 bar and
the pressure released. This flushing procedure was repeated
twice more. It was repressurised to 16 bar, the stirrer was
started (600 rpm) and the autoclave was heated to 80 8C for
45 min. The 1-octene was then added to the autoclave by
forcing it in through the substrate injector using a CO/H2
pressure of 20 bar. The data recorder was started and the
temperature, pressure in the autoclave and pressure in a
ballast vessel, from which gas was fed into the autoclave
through a mass flow controller to keep the pressure within
the autoclave constant at 20 bar, were monitored and
recorded every 5 s. After gas uptake had become very slow
(5–8 h), the stirrer was stopped and the autoclave was
allowed to cool. The gases were vented and the mixture was
syringed into a sample vial for analysis by GC. Kinetic data
were obtained from an analysis of the pressure drop in the
ballast vessel. A similar reaction was carried out but using 2
(0.017 mmol) in perfluoromethylcyclohexane (4.0 mL). The
resulting product consisted of two phases, both of them
yellow. GC analysis was carried out on the upper phase.
3
H2, H3), 6.75 (2H, d, JHH¼11.4 Hz, CHAr), 5.63 (2H, dt,
3
3
3JHH¼11.4 Hz, JHH¼7.3 Hz, CHCH2), 3.02 (td, JHF
¼
18.4 Hz, JHH¼7.3 Hz, CH2), 1.55 (6H, s, CH3); 19F{1H}
3
NMR (CDCl3) 281.27 (6F, t, 4JFF¼8.5 Hz, CF3), 2113.54
4
(4F, t, JFF¼14.2 Hz, a-CF2), 2122.37 (4F, m, CF2),
2122.39 (4F, m, CF2), 2123.68 (4F, m, CF2), 2126.66
(4F, m, CF2). 13C NMR (CDCl3) 150.0, 135.7, 131.3, 130.2,
2
128.8, 126.8, 119.5, 118.0, 34.3, 32.6, 30.9 (t, JCF
22.2 Hz).
¼
4.1.9. 2,7-Bis(1H,1H,2H,2H,3H,3H-perfluorononanyl)-
9,9-dimethylxanthene (6). 2,7-Bis(1H,2H,3H,3H-perfluor-
onon-1-enyl)-9,9-dimethylxanthene (2.50 g, 2.70 mmol)
was dissolved in dichloromethane (75 mL) and palladium
on charcoal (0.25 g) added. The mixture was stirred
overnight under an atmosphere of hydrogen and then
filtered through a celite plug. The solvent was removed to
give a white solid (2.49 g, 99%). Mp 101–102 8C. Anal.
calcd for C33H24OF26: C, 42.58; H, 2.58. Found: C, 42.63;
1
H, 2.51. m/z (FAB): 929 (M2H). H NMR (CDCl3) 7.11
3
(2H, m, H1), 6.90 (4H, m, H2, H3), 2.61 (2H, t, JHH
7.1 Hz, CH2), 1.88 (4H, m, CH2CH2), 1.54 (6H, s, CH3).
¼
19F{1H} NMR (CDCl3) 281.40 (6F, t, 4JFF¼10.0 Hz, CF3),
4
2114.57 (4F, t, JFF¼13.9 Hz, a-CF2), 2122.41 (4F, m,
CF2), 2122.38 (4F, m, CF2), 2124.02 (4F, m, CF2),
2126.65 (4F, m, CF2). 13C NMR (CDCl3) 148.1, 134.1,
2
129.0, 128.1, 126.3, 115.5, 33.6, 33.1, 31.2, 29.2 (t, JCF
22.3 Hz), 21.1.
¼
Acknowledgements
We thank the Royal Society (EGH, AMS) and the EPSRC
(DJA) for financial support.
4.1.10. [{4,5-Bis-(bis(4-tridecafluoro-n-hexyl-phenyl)-
phosphino)-9,9-dimethylxanthene}PtCl2]. A slurry of
cis-[PtCl2(MeCN)2] (0.009 g, 0.027 mmol) and 4,5-bis-
(bis(4-tridecafluoro-n-hexyl-phenyl)phosphino)-9,9-dimethyl-
xanthene (0.050 g, 0.027 mmol) in dichloromethane
(20 mL) was heated to reflux for 15 h in a sealed tube
under nitrogen to give a clear solution. After cooling, the
solvent was removed in vacuo and the resulting solid was
washed well with petroleum ether and dried in vacuo to give
a white solid (0.024 g, 42%). Anal. calcd for C63H28OP2-
Cl2F52Pt: C, 35.74; H, 1.32. Found: C, 35.69; H, 1.26. m/z
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