Intramolecular dehydrofluorinative coupling of the asymmetric diphosphine Ph2PCH2CH2PPh(C5F4N-4) and pentamethylcyclopentadienyl ligands in a rhodium complex

Article abstract of DOI:10.1021/om020874p

The tetrafluoropyridyl-substituted diphosphine Ph₂PCH₂CH₂PPh(C₅F₄N-4) (1) has been prepared in three steps from dppe. Comparison of the spectroscopic properties between trans-[RhCl(CO){PPh₂(C₅F₄N-4)}₂] and analogous complexes of other fluorinated triaryl phosphines reveals the lower basicity of tetrafluoropyridylphosphines relative to pentafluorophenylphosphines. The reaction between [Cp*RhCl(μ-Cl)]₂ and 1 in the presence of [BF₄^-] yielded racemic diastereoisomers of [Cp*RhCl(1)][BF₄]. In the S_RhR_P and R_RhS_P pair of enantiomers the Cp* and tetrafluoropyridyl groups have a cis disposition about the Rh-P bond, and in the S_RhS_P and R_RhR_P pair the groups are trans. In situ NMR experiments reveal that the cis pair, in which the Cp* and tetrafluoropyridyl groups are close, underwent rapid dehydrofluorinative C-C coupling to give the respective enantiomers of [{η⁵,κP,κP-C₅Me₄CH₂- 2-C₅F₃N-4-PPhCH₂CH₂ PPh₂}RhCl][BF₄] (6·[BF₄]). The trans pair did not undergo coupling, but isomerized to the cis pair on heating in ethanol. The reaction between [Cp*RhCl(μ-Cl)]₂ and 1 in refluxing benzene afforded 6·[BF]₄ in 64% yield after anion metathesis. The structures of OPPh₂-(C₅F₄N-4), the cis isomer of [Cp*RhCl(1)][BF₄], and one enantiomer of 6·[BF₄], which crystallizes as a conglomerate, have been determined by single-crystal X-ray diffraction.

Full text of DOI:10.1021/om020874p

1802
Organometallics 2003, 22, 1802-1810
Articles
In tr a m olecu la r Deh yd r oflu or in a tive Cou p lin g of th e
Asym m etr ic Dip h osp h in e P h 2P CH2CH2P P h (C5F 4N-4) a n d
P en ta m eth ylcyclop en ta d ien yl Liga n d s in a
Rh od iu m Com p lex
Ronan M. Bellabarba, Mark Nieuwenhuyzen, and Graham C. Saunders*
School of Chemistry, Queen’s University Belfast, David Keir Building, Belfast BT9 5AG, U.K.
Received October 22, 2002
The tetrafluoropyridyl-substituted diphosphine Ph2PCH2CH2PPh(C5F4N-4) (1) has been
prepared in three steps from dppe. Comparison of the spectroscopic properties between trans-
[RhCl(CO){PPh2(C5F4N-4)}2] and analogous complexes of other fluorinated triaryl phosphines
reveals the lower basicity of tetrafluoropyridylphosphines relative to pentafluorophenylphos-
phines. The reaction between [Cp*RhCl(µ-Cl)]2 and 1 in the presence of [BF4-] yielded racemic
diastereoisomers of [Cp*RhCl(1)][BF4]. In the SRhRP and RRhSP pair of enantiomers the Cp*
and tetrafluoropyridyl groups have a cis disposition about the Rh-P bond, and in the SRhSP
and RRhRP pair the groups are trans. In situ NMR experiments reveal that the cis pair, in
which the Cp* and tetrafluoropyridyl groups are close, underwent rapid dehydrofluorinative
C-C coupling to give the respective enantiomers of [{η5,κP,κP-C5Me4CH2-2-C5F3N-4-PPhCH2-
CH2PPh2}RhCl][BF4] (6‚[BF4]). The trans pair did not undergo coupling, but isomerized to
the cis pair on heating in ethanol. The reaction between [Cp*RhCl(µ-Cl)]2 and 1 in refluxing
benzene afforded 6‚[BF4] in 64% yield after anion metathesis. The structures of OPPh2-
(C5F4N-4), the cis isomer of [Cp*RhCl(1)][BF4], and one enantiomer of 6‚[BF4], which
crystallizes as a conglomerate, have been determined by single-crystal X-ray diffraction.
Sch em e 1
In tr od u ction
We have been developing intramolecular dehydroflu-
orinative C-C coupling as a convenient route to com-
plexes of trifunctional hybrid η5,κP,κP-cyclopentadienyl-
diphosphine ligands.1-3 To date we have concentrated
on (C6F5)2PCH2CH2P(C6F5)2 (dfppe) as the diphosphine
ligand, which yields products containing cyclic trifunc-
tional ligands with two linkages between the cyclopen-
tadienyl and phosphine moieties (CpdPP ligands), such
as η5,κP,κP-C5Me3{CH2-2-C6F4P(C6F5)CH2}2-1,3 (Scheme
1). The products obtained from chelating diphosphine
ligands with only one bis(pentafluorophenyl)phosphine
moiety will contain ligands with a single linkage be-
tween the cyclopentadienyl and phosphine moieties
(Cp-PP ligands). A three-legged piano stool complex of
one of these ligands would contain a stereogenic metal
atom by virtue of the four different groups coordinated
to the metal. Chiral-at-metal piano stool complexes [(η5-
C5R5)MX(P2)]n+ (R ) H or Me, X ) one-electron donor
ligand, P2 ) diphosphine or related ligand) can serve
as stoichiometric reagents or precursors to Lewis acid
catalyts for stereoselective organic transformations.4-6
However, these complexes suffer from the disadvantage
that, under certain conditions, they undergo epimer-
ization at the metal, with the loss of chiral information
at the metal leading to a loss of stereoselectivity in
reactions.5-7 Coupling of the cyclopentadienyl and diphos-
phine ligands is expected to confer configurational
stability on a complex. Mechanisms for inversion at the
metal can be devised, but these are expected to involve
(4) (a) Davies, S. G. Organotransition Metal Chemistry: Applications
to Organic Synthesis; Pergamon Press: Oxford, 1982. (b) Carmona,
D.; Cativiela, C.; Garc´ıa-Correas, R.; Lahoz, F. J .; Lamata, M. P.; Lo´pez,
J . A.; Lo´pez-Ram de V´ıu, M. P.; Oro, L. A.; San J ose´, E.; Viguri, F. J .
Chem. Soc., Chem. Commun. 1996, 1247. (c) Bruin, M. E.; Ku¨ndig, E.
P. J . Chem. Soc., Chem. Commun. 1998, 2635. (d) Ku¨ndig, E. P.;
Saudan, C. M.; Bernadinelli, G. Angew. Chem., Int. Ed. 1999, 38, 1219.
(5) Consiglio, G.; Morandini, F. Chem. Rev. 1987, 87, 761.
(6) Carmona, D.; Lahoz, F. J .; Oro, L. A.; Lamata, M. P.; Viguri F.;
San J ose´, E. Organometallics 1996, 15, 2961.
* Corresponding author. E-mail: g.saunders@qub.ac.uk.
(1) Bellabarba, R. M.; Nieuwenhuyzen, M.; Saunders, G. C. J . Chem.
Soc., Dalton Trans. 2001, 512.
(2) Bellabarba, R. M.; Saunders; G. C. J . Fluor. Chem. 2001, 112,
139.
(3) Bellabarba, R. M.; Nieuwenhuyzen, M.; Saunders, G. C. Inorg.
Chim. Acta 2001, 323, 78.
(7) Standfest-Hauser, C.; Slugovc, C.; Mereiter, K.; Schmid, R.;
Kirchner, K.; Xiao, L.; Weissensteiner, W. J . Chem. Soc., Dalton Trans.
2001, 2989.
10.1021/om020874p CCC: $25.00 © 2003 American Chemical Society
Publication on Web 03/25/2003

Intramolecular Dehydrofluorinative Coupling
Organometallics, Vol. 22, No. 9, 2003 1803
Sch em e 2
Sch em e 3
involving R2P(C5F4N-4) nucleophilic attack will be at a
carbon meta to the nitrogen. The rate of nucleophilic
substitution of a meta fluorine of pentafluoropyridine
is ca. 10 times more rapid than that of a fluorine atom
of hexafluorobenzene.12 Furthermore, since the nitrogen
atom of pentafluoropyridine is virtually nonbasic,13 it
is likely that that of R2P(C5F4N-4) is similarly unreac-
tive. Thus, the tetrafluoropyridyl-substituted diphos-
phine Ph2PCH2CH2PPh(C5F4N-4) (1) was envisaged to
be ideal for our study because of the expected conven-
ience of preparation by the reaction between Ph2PCH2-
CH2PPhSiMe3 and pentafluoropyridine and the en-
hanced rate of nucleophilic substitution of an ortho
fluorine atom (meta to nitrogen) over dfppe.
Here we demonstrate the potential of intramolecular
dehydrofluorinative carbon-carbon coupling to generate
desirable configurationally stable, chiral-at-metal com-
plexes of Cp-PP ligands through the use of an asym-
metric diphosphine. The preparation of the tetrafluo-
ropyridyl-substituted diphosphine Ph2PCH2CH2PPh-
(C5F4N-4) and its coupling to an η5-pentamethylcyclo-
pentadienyl ligand to yield a racemic Cp-PP rhodium
complex are reported.
processes with high activation energies: dissociation of
both κ-ligating fragments of the chelating ligand, inver-
sion at the phosphorus atom and recoordination, or
dissociation of the cyclopentadienyl and phosphine,
inversion at the phosphorus atom, and recoordination.3
Although the asymmetric phosphine ligands (C6F5)2P-
L, where L is a ligating fragment, such as a thioether
or a non-fluorinated phosphine moiety, would yield
chiral-at-metal complexes, these would be formed as a
racemic mixture. One method of controlling the stereo-
chemistry at the metal center would be through the use
of an enantiopure (C6F5)RP-L ligand. Although initial
coordination of this ligand would result in diastereo-
isomers, intramolecular dehydrofluorinative C-C cou-
pling can give only one enantiomer of the product
(Scheme 2).8 If the L moiety is sufficiently labile, then
the diastereoisomers can isomerize readily and the
product may be formed in 100% yield; if the L group is
nonlabile, then a yield dependent on the ratio of
diastereoisomers would be expected. We are interested
in synthesizing diphosphines of the type R2PCH2CH2-
PRArF, where ArF is a suitable fluorinated aromatic
group, and coupling these to Cp* ligands in order to
generate configurationally stable, chiral-at-metal com-
plexes of Cp-PP ligands.
Recently it has been reported that trimethylsilylphos-
phines react with polyfluoroaromatic compounds, pro-
ducing phosphines bearing a polyfluoroaromatic sub-
stituent and trimethylsilyl fluoride.9,10 The driving force
for the reaction is the high enthalpy of Si-F bond
formation. The reaction is particularly successful for
pentafluoropyridine. Although our studies of dehydro-
fluorinative coupling have concentrated on pentafluo-
rophenylphosphines, tetrafluoropyridyl-substituted phos-
phines should be no less amenable to intramolecular
dehydrofluorinative CsC coupling, which is postulated
to occur by nucleophilic attack at an ortho carbon of the
pentafluorophenyl group.1,2,11 For the coupling reaction
Resu lts a n d Discu ssion
The three-step synthesis of diphosphine 1 is outlined
in Scheme 3. A dark green solution of sodium naphtha-
lide in THF was added to Ph2PCH2CH2PPh2 (dppe) and
the mixture left at room temperature until a dark red
solution containing Na[Ph2PCH2CH2PPh] and NaPh
had developed by P-C(Ph) bond cleavage.14 An excess
of Me3SiCl was added, causing the immediate disap-
pearance of the color as Ph2PCH2CH2PPhSiMe3, Ph-
SiMe3, and NaCl were formed. Treatment of pentaflu-
oropyridine with Ph2PCH2CH2PPhSiMe3 in benzene at
room temperature gave diphosphine 1, which was
purified by column chromatography and obtained as a
white solid in 50% yield. Unfortunately 1 was contami-
nated by a small amount of unreacted dppe (ca. 2%),
from which it could not be separated. The phosphine
Ph2P(C5F4N-4), 2,10 was also obtained, showing that
P-CH2 bond cleavage had also occurred in the reaction
between dppe and sodium naphthalide, yielding Ph2P-
then Ph2PSiMe3 on treatment with Me3SiCl. Charac-
(8) Bellabarba, R. M.; Nieuwenhuyzen, M.; G. C. Saunders, G. C.
Organometallics 2002, 21, 5726.
(9) Goryunov, L. I.; Grobe, J .; Shteingarts, V. D.; Krebs, B.; Linde-
mann, A.; Wu¨rthwein, E.-U.; Mu¨ck-Lichtenfeld, C. Chem. Eur. J . 2000,
6, 4612.
(10) Veits, Y. A.; Karlstedt, N. B.; Churchuryukin, A. V.; Beletskaya,
I. P. Russ. J . Org. Chem. 2000, 36, 750.
(12) (a) Chambers, R. D.; Close, D.; Williams, D. L. H. J . Chem. Soc.,
Perkin Trans. 2 1980, 778. (b) Chambers, R. D.; Martin, P. A.;
Waterhouse, J . S.; Williams, D. L. H.; Anderson, B. J . Fluor. Chem.
1982, 20, 507. (c) Brooke, G. M. J . Fluor. Chem. 1997, 86, 1.
(13) (a) Bell, S. L.; Chambers, R. D.; Musgrave, W. K. R.; Thorpe,
J . G. J . Fluor. Chem. 1971/2, 1, 51. (b) Chambers, R. D. Adv. Heterocycl.
Chem. 1981, 28, 1.
(11) Hughes, R. P.; Lindner, D. C.; Rheingold, A. L.; Yap, G. P. A.
Organometallics 1996, 15, 5678.
(14) Chou, T.-S.; Tsao, C.-H.; Hung, S. C. J . Organomet. Chem. 1986,
312, 53.

1804 Organometallics, Vol. 22, No. 9, 2003
Bellabarba et al.
terization of 1 was based on NMR spectroscopy and
mass spectrometry. The resonance of the PPh2 phos-
phorus atom occurs at δ -11.3, which is similar to that
of δ -12.5 for dppe.15 The resonance of the PPh(C5F4N-
4) phosphorus atom occurs at δ -20.3 and shows a
coupling to two fluorine atoms of 19 Hz. The value of δ
is similar to those of 2 (δ -18.9),10 PPh2(C6F5) (δ
-24.7),16 and PPh2(C6H3F2-2,6) (δ -27.7),17 but the P-F
coupling is roughly half that of these monophosphines
(30, 38, and 42.2 Hz, respectively). The three-bond P-P
coupling of 40 Hz is similar to that of 47.2 Hz found for
(C6H3F2-2,6)2PCH2CH2P(C6H3F2-2,6)2.18 Despite con-
tamination by dppe, 1 was found to be amenable to
further reaction.
The tetrafluoropyridyl group is more electron-with-
drawing than pentafluorophenyl,12 and so phosphines
bearing the former might be expected to be less basic
than those bearing the latter. To assess the electronic
effect of the tetrafluoropyridyl substituent on phos-
phines, we sought to compare the spectroscopic proper-
ties of the rhodium complexes trans-[RhCl(CO)(P)2],
where P ) 2, Ph2P(C6F5), and Ph2P(C6H3F2-2,6). The
value of the cone angle, θ, for Ph2P(C6H3F2-2,6)17 has
been shown to be almost identical to that of Ph2P(C6F5)
(158°),19 and the similarity of the respective P-C, PC-
C, and C-F distances and C-C(P)-C and PC-C-F
angles of [Cp*RhClL][BF4] for L ) 1 (vide infra), dfppe,20
and (C6H3F2-2,6)2PCH2CH2P(C6H3F2-2,6)218 suggests a
cone angle for 2 similar to that of Ph2P(C6F5) and Ph2P-
(C6H3F2-2,6). Thus, these phosphines exert similar steric
effects on the complex and differences between the
values of ν(CtO) can be ascribed to the differences in
the electronic properties of the phosphines. Complex 3
was prepared in 80% yield by treatment of [Rh(µ-Cl)-
(CO)2]2 with 2. The 31P{1H} NMR spectrum exhibits a
F igu r e 1. Structure of one of the independent molecules
of OPPh2(C6F5N-4) (4) (molecule A). Thermal ellipsoids are
at the 30% probability level. Hydrogen atoms are omitted
for clarity.
etry and NMR spectrometry. (Although 4 has been
prepared previously, only the 31P NMR data were
reported.10) In addition the structure of 4 was deter-
mined by single-crystal X-ray diffraction. There are two
molecules in the asymmetric unit; the structure of one
is shown in Figure 1. Crystal and refinement data are
given in Table 1, and selected bond distances and angles
of 4 are given in Table 2. The two molecules of 4 possess
identical bond distances and angles with the exception
of the PdO distances, which differ by at least 0.01 Å,
and the OdP-C5F4N and C(Ph)-P-C5F4N angles. The
mean PdO distance of 1.454(3) Å is significantly shorter
than that of 1.474 Å reported for OPPh2(C6F5) (no esd’s
are given for this structure)23 and that of 1.487(3) Å for
OPPh3.24 The molecule of 4 with the longer PdO bond
has a smaller OdP-C5F4N angle by ca. 3°. The C-P-
C(C5F4N) angles differ slightly, with a range of ca. 3°,
between the two molecules but are consistent with those
of 105.1(2)° and 106.8(2)° for SPMe2(C5F4N).9 The
P-C5F4N distance is the same as in SPMe2(C5F4N). The
P-C(Ph) distances and the C-C distances of the phenyl
rings are consistent with those of OPPh3 (1.795(5)-
1.804(5) and 1.341(9)-1.398(8) Å, respectively)24 and
OPPh2(C6F5) (means of 1.796 and 1.378 Å, respec-
tively).23 The two pairs of O-P-C(Ph) angles for each
molecule are identical and consistent with those of
OPPh3 (111.8(2)-113.3(2)°). The C(Ph)-P-C(Ph) angles
are consistent with the three identical C(Ph)-P-C(Ph)
angles of OPPh3 (106.4(2)°).24
1
doublet at δP 27.8 with a coupling, J RhP, of magnitude
110 Hz. These data are comparable with those of the
analogous complexes of Ph2P(C6F5) (δP 24.0, 1J RhP ) 133
Hz)21 and Ph2P(C6H3F2-2,6) (δP 18.7, 1J RhP ) 133 Hz).17
The IR spectrum of 3 exhibits ν(CtO) at 1993 cm-1
.
This is higher than those of the complexes of PPh2(C6F5)
(1982 cm-1 21 and PPh2(C6H3F2-2,6) (1967 cm-1 17
)
)
and
is consistent with the poorer donor ability of 2 compared
to these phosphines, which are poorer donors than
PPh3.22 The data suggest that, as expected, the PPh-
(C5F4N-4) functionality of diphosphine 1 is less basic
than the PPh2 functionality.
During this study we found that on exposure to air
for several weeks phosphine 2, a pale yellow oil,
deposited colorless crystals of OPPh2(C5F4N-4), 4.10
Phosphine oxide 4 was characterized by mass spectrom-
Treatment of [Cp*RhCl(µ-Cl)]2 with diphosphine 1 in
the presence of sodium tetrafluoroborate yielded a ca.
1:1 mixture of racemic diastereoisomers of [Cp*RhCl-
(1)][BF4], 5a , and 5b in ca. 50% yield (Scheme 4). In
the SRhRP and RRhSP pair of enantiomers the Cp* and
tetrafluoropyridyl groups have a cis disposition on the
Rh-P bond of the RhP2(CH2)2 ring (5a ), and in the
(15) Grim, S. O.; Briggs, W. L.; Barth, R. C.; Tolman, C. A.; J esson,
J . P. Inorg. Chem. 1974, 13, 1095.
(16) Nichols, D. I. J . Chem. Soc., Dalton Trans. 1969, 1471.
(17) Corcoran, C.; Fawcett, J .; Friedrichs, S.; Holloway, J . H.; Hope,
E. G.; Russell, D. R.; Saunders, G. C.; Stuart, A. M. J . Chem. Soc.,
Dalton Trans. 2000, 161.
S
RhSP and RRhRP pair the groups are trans (5b). Chelat-
(18) Fawcett, J .; Friedrichs, S.; Holloway, J . H.; Hope, E. G.; McKee,
V.; Nieuwenhuyzen, M.; Russell, D. R.; Saunders, G. C. J . Chem. Soc.,
Dalton Trans. 1998, 1477.
ing diphosphines are not expected to be labile and
interconversion of 5a and 5b is not expected to be rapid
at room temperature, which is confirmed by studies of
the reaction of the mixture with proton sponge (vide
infra); thus the ratio of 5a to 5b is a consequence of the
(19) Tolman, C. A. Chem. Rev. 1977, 77, 313.
(20) Atherton, M. J .; Fawcett, J .; Holloway, J . H.; Hope, E. G.;
Karac¸ar, A.; Saunders, G. C. J . Chem. Soc., Dalton Trans. 1996, 3215.
(21) Atherton, M. J .; Coleman, K. S.; Fawcett, J .; Holloway, J . H.;
Hope, E. G.; Karac¸ar, A.; Peck, L. A.; Saunders, G. C. J . Chem. Soc.,
Dalton Trans. 1995, 4029.
(22) Fernandez, A. L.; Wilson, M. R.; Prock, A.; Giering, W. P.
Organometallics 2001, 20, 3429.
(23) Naae, D. G.; Lin, T. W. J . Fluor. Chem. 1979, 13, 473.
(24) Thomas, J . A.; Harmor, T. A. Acta Crystallogr. Sect. C 1993,
49, 355.

Intramolecular Dehydrofluorinative Coupling
Organometallics, Vol. 22, No. 9, 2003 1805
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t for Com p ou n d s 4, 5b‚0.5CH2Cl2, a n d 6‚[BF 4]
4
5b‚0.5CH2Cl2
6‚[BF4] a
formula
fw
C
17H10F4NOP
C35.5H35BCl2F8NP2Rh
874.21
C35H33BClF7P2Rh
811.73
351.23
cryst dimens, mm
T, K
0.42 × 0.24 × 0.10
0.48 × 0.24 × 0.20
0.24 × 0.18 × 0.10
153(2)
153(2)
153(2)
cryst syst
space group
monoclinic
P2(1)/c
monoclinic
P2(1)/n
orthorhombic
P212121
unit cell dimens
a, Å
b, Å
c, Å
18.1475(15)
9.5981(8)
19.1255(15)
114.107(2)
3040.8(7)
8
8.6204(7)
23.2170(19)
18.0923(15)
102.1340(10)
3540.1(5)
4
9.7712(10)
14.9173(16)
22.791(3)
90
3321.9(6)
4
â, deg
U, Å3
Z
calc density, g cm-3
F(000)
1.534
1424
1.640
1764
1.623
1640
θ, deg
1.23-28.89
1.45-28.31
0.93-28.95
abs coeff, mm-1
total data
0.229
0.795
0.758
7179
8049
7914
unique data, Rint
final R indices [I > 2σ(I)]
3258, 0.0865
R1 ) 0.0517
wR2 ) 0.1230
R1 ) 0.1314
wR2 ) 0.1566
0.859
7065, 0.0559
R1 ) 0.0343
wR2 ) 0.0841
R1 ) 0.0401
wR2 ) 0.0866
1.047
4312, 0.1347
R1 ) 0.0588
wR2 ) 0.1221
R1 ) 0.1393
wR2 ) 0.1648
0.943
R indices (all data)
GoF on F2
largest diff peak and hole, e Å-3
0.482, -0.467
0.547, -0.830
0.802, -1.711
a
Flack parameter 0.03(5).
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 4
molecule A
molecule B
PdO
1.441(3)
1.467(2)
P-C(C5F4N)
1.832(3)
1.836(3)
P-C(Ph)
1.792(3), 1.798(3)
1.343(4), 1.343(4)
1.336(4), 1.340(4)
1.293(4), 1.312(5)
1.375(4)-1.394(4)
1.367(5)-1.389(5)
113.02(15)
112.19(15), 113.23(15) 112.67(15), 113.94(14)
105.40(15), 106.37(15) 104.06(15), 108.46(15)
106.01(15)
1.788(3), 1.798(3)
1.344(4), 1.346(4)
1.339(4), 1.341(4)
1.301(4), 1.303(4)
1.370(5)-1.393(4)
1.371(5)-1.397(4)
110.27(14)
C-F (ortho-P)
C-F (meta-P)
C-N
C-C(C5F4N)
C-C(Ph)
O-P-C(C5F4N)
O-P-C(Ph)
C-P-C(C5F4N)
C(Ph)-P-C(Ph)
106.96(15)
O-P-C-C(C5F4N) 45.9, -130.1
O-P-C-C(Ph)
-48.9, 128.3
-44.1, 136.2
-27.0, 149.6
51.0, -128.2
31.8, -147.4
F igu r e 2. Structure of the SRhSP enantiomer of the cation
of [Cp*RhCl{Ph2PCH2CH2PPh(C5F4N-4)}][BF4] (5b). Ther-
mal ellipsoids are at the 30% probability level. Hydrogen
atoms are omitted for clarity.
Sch em e 4
frequency of the cis isomer resonance is consistent with
the spectra of cis- and trans-[Cp*RhCl{κP,κS-(C6F5)Ph-
PC6H4SMe-2}][BF4].8 The two-bond P-P coupling differs
considerably between the two isomers. The value for 5a
(11 Hz) is less than half that of 5b (26 Hz). The 19F NMR
spectrum shows the expected four resonances, two at
ca. δ -88 and two at ca. δ -130 assigned to two pairs
of meta(P) and ortho(P) flourine atoms, respectively, in
addition to those resonances assigned to [BF4-].
Although an attempt to separate 5a and 5b by
fractional crystallization on the bulk scale was unsuc-
cessful, a crystal of 5b was isolated and the structure
of this isomer determined by single-crystal X-ray dif-
fraction. Both the SRhSP and RRhRP enantiomers were
present in the unit cell. The structure of the SRhSP
enantiomer is shown in Figure 2, crystal and refinement
data are given in Table 1, and selected bond distances
and angles are given in Table 3. The Cp†-Rh distance
is consistent with those of similar [Cp*RhCl(P2)]+
salts.6,18,20 The Rh-P distances of 5b are identical to
kinetics of the coordination of 1 to the [Cp*RhCl]+
fragment. The PPh2 phosphorus resonances of 5a and
5b occur at similar chemical shifts, δ 70.5 and 66.8,
respectively, and both exhibit coupling to rhodium of
ca. 130 Hz. The PPh(C5F4N-4) phosphorus resonances
are at lower frequency, with that of 5a (δ 58.2) lower
than that of 5b (δ 64.6). (The assignments of the
resonances of 5a and 5b are based on the reaction of
the mixture with proton sponge, vide infra.) The lower

1806 Organometallics, Vol. 22, No. 9, 2003
Bellabarba et al.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5b
5b and 6‚[BF4] in a ratio of ca. 1:2 and a small amount
of 5a , but also the presence of small amounts of
unidentified phosphorus- and fluorine-containing com-
pounds. The data confirm the hypothesis that isomer-
ization does occur in ethanol at elevated temperature,
but that this method does not produce pure 6‚[BF4]. The
formation of impurities has been noted in the thermoly-
sis of other [(η5-C5M4R)RhX(dfppe)]+ salts in ethanol.25,26
Cp†-Rh
1.867(2)
2.3165(6)
1.489(4)
1.834(2)
1.832(2)
1.833(2)
Rh-P(1)
2.3154(6)
2.4009(5)
1.524(3)
1.841(2)
1.820(2)
1.815(2)
Rh-P(2)
Rh-Cl
mean C-CH3
P(1)-C(11)
P(1)-C(11A)
P(2)-C(21A)
C(11)-C(12)
P(2)-C(12)
P(1)-C(11B)
P(2)-C(21B)
Cp†-Rh-Cl
120.9(1)
131.6(1)
Cp†-Rh-P(1)
P(1)-Rh-P(2)
131.4(1)
84.54(2)
86.952(19)
118.12(7)
Cp†-Rh-P(2)
P(1)-Rh-Cl
It has been noted that salts of [{η5,κP,κP-C5HMe2-3,4-
[CH2-2-C6F4P(C6F5)CH2]2-1,2}RhX]+ (X ) Br or Cl) are
precipitated from the reaction between [(η5-C5Me4H)-
RhX(µ-X)]2 and dfppe in refluxing benzene.25 Although
the precipitates are a mixture of halide and tetrafluo-
roborate salts, they are free of contamination by starting
materials and salts of the intermediate cations [(η5-
C5Me4H)RhCl(dfppe)]+ and [{η5,κP,κP-C5HMe3CH2-2-
C6F4P(C6F5)CH2CH2P(C6F5)2}RhX]+. Thus the reaction
between [Cp*RhCl(µ-Cl)]2 and 1 in refluxing benzene
was attempted in the expectation that 6‚Cl might be
obtained as a precipitate free from 5a and 5b. Heating
a slurry of [Cp*RhCl(µ-Cl)]2 and 1 in benzene under
reflux for 9 h yielded a yellow precipitate and an orange
solution, which were readily separated by filtration.
NMR spectroscopy revealed the precipitate to comprise
the cation [{η5,κP,κP-C5Me4CH2-2-C5F3N-4-PPhCH2-
CH2PPh2}-RhCl]+ as the only phosphorus- and hydrogen-
containing species. Presumably the product was present
predominantly as the chloride salt, 6‚Cl, but the 19F
NMR spectrum also shows the presence of small amounts
of tetrafluoroborate (<2%) and hexafluorosilicate (<5%),
which are formed by the reaction of the byproduct HF
with the borosilicate glass vessel.20 The salt 6‚Cl was
readily converted to 6‚[BF4] by anion metathesis with
NaBF4 in methanol, giving an overall isolated yield of
64%. The 31P{1H} NMR spectrum of 6‚[BF4] exhibits two
mutually coupled phosphorus resonances at δ 78.3 and
67.0 assigned to PPh(C5F3N)CH2C5Me4 and PPh2, re-
spectively. The higher frequencies relative to the re-
spective resonances of 5a are consistent with the
coupling of Cp* and phosphines in other complexes.3,8,20
Both resonances exhibit coupling to rhodium of ca. 130
Hz, which is consistent with those of 5a , as is the two-
bond P-P coupling of 16 Hz. As expected the 19F NMR
spectrum exhibits three multiplet resonances (δ -72.39,
-85.82, and -134.09) in addition to those of [BF4-]. The
1H NMR spectrum contains two mutually coupled
resonances at δ 3.98 and 3.24, the former of which is
also coupled to phosphorus, which are assigned to the
nonequivalent hydrogen atoms of the methylene bridge
between the cyclopentadienyl ring and the trifluoropy-
ridyl group. Three multiplet resonances at δ 3.47, 3.26,
and 2.97, integrating for one, one, and two hydrogen
atoms, respectively, are assigned to the ethylene back-
bone of the diphosphine moiety. The four methyl reso-
nances occur as three doublets at δ 1.91, 1.20, and 0.23
and a doublet of doublets at δ 1.66. The chloride salt of
6 gave similar NMR spectra with small shifts of δ and
changes in coupling constant. The differences in the
86.46(2) P(2)-Rh-Cl
Rh-P(1)-C(11)
Rh-P(1)-C(11B)
C(11)-P(1)-C(11B) 104.01(10) C(11A)-P(1)-C(11B) 101.88(10)
Rh-P(2)-C(12)
Rh-P(2)-C(21B)
C(12)-P(2)-C(21B) 101.83(10) C(21A)-P(2)-C(21B) 105.50(10)
106.53(7) Rh-P(1)-C(11A)
117.42(8) C(11)-P(1)-C(11A) 107.78(11)
109.65(7) Rh-P(2)-C(21A)
119.83(7) C(12)-P(2)-C(21A) 108.39(10)
110.87(7)
the shorter Rh-P distance of [Cp*RhCl{Ph2PCH2CH-
(Me)PPh2}]+ 6 and significantly shorter than those of
[Cp*RhCl(dfppe)]+ and [Cp*RhCl{(C6H3F2-2,6)2PCH2-
CH2P(C6H3F2-2,6)2}]+ (2.329(1)-2.362(1) Å).18,20 The
shorter distance in 5b is consistent with the lower steric
demand of 1 in comparison to diphosphines in which
fluorine atoms occupy all the ortho aryl positions.
However, it is noted that the Rh-Cl distance of 5b is
longer than those of other [Cp*RhCl(P2)]+ salts (2.385-
(1)-2.393(1) Å).6,18,20 The P-Rh-P angle is identical to
that of the non-fluorinated diphosphine cation [Cp*RhCl-
{Ph2PCH2CH(Me)PPh2}]+ and slightly larger than those
of the [Cp*RhCl(dfppe)]+ and [Cp*RhCl{(C6H3F2-2,6)2-
PCH2CH2P(C6H3F2-2,6)2}]+ (83.00(5)° and 84.05(8)°,
respectively).18,20 The Cp* ligand is distorted from C5
symmetry about the Cp†-Rh axis. The C(1)-C(2) and
C(3)-C(4) bonds (1.418(3) and 1.422(3) Å, respectively),
which are approximately trans to P(1) and P(2), respec-
tively, are significantly shorter than the three other
internal C-C ring bonds (1.443(3)-1.446(4) Å). Further,
the Rh-C(5) bond (2.184(2) Å), approximately trans to
chloride, is ca. 0.03 Å shorter than Rh-C(2) and Rh-
C(3) (2.225(2) and 2.231(2) Å, respectively), which are
themselves significantly shorter than Rh-C(1) and Rh-
C(4) (2.263(2) and 2.249(2) Å, respectively). The data
are suggestive of slight ring slippage from η5 to η2,η2,κC
coordination of Cp*.
In situ NMR studies of the reaction between proton
sponge and the mixture of 5a and 5b in CDCl3 at room
temperature revealed that 5a underwent rapid dehy-
drofluorinative C-C coupling to give [{η5,κP,κP-C5Me4-
CH2-2-C5F3N-4-PPhCH2CH2PPh2}RhCl][BF4], 6‚[BF4],
whereas, as expected, 5b, in which the tetrafluoropy-
ridyl group is distant to the pentamethylcyclopentadi-
enyl ligand, showed no reaction (Scheme 4). This result
was confirmed by a preparative scale reaction which
yielded a mixture of 5b and 6‚[BF4]. Attempts to
separate 6‚[BF4] from this mixture were unsuccessful.
Since the salt [Cp*RhCl{Ph2PCH2CH(Me)PPh2}][BF4]
has been reported to undergo epimerization on heating
in polar solvents,6 and [Cp*RhCl(dfppe)][BF4] is known
to undergo dehydrofluorinative coupling on thermolysis
in refluxing ethanol,20 we reasoned that when heated
in ethanol 5b in the mixture would isomerize to 5a ,
which would undergo dehydrofluorinative coupling to
give 6‚[BF4], thereby providing a method to produce the
product free of 5b. The mixture of 5b and 6‚[BF4] was
heated in ethanol for 13 h, after which time the 31P-
{1H} and 19F NMR spectrum indicated the presence of
(25) (a) Atherton, M. J .; Holloway, J . H.; Hope, E. G.; Saunders, G.
C. J . Organomet. Chem. 1998, 558, 209. (b) Nieuwenhuyzen, M.;
Saunders, G. C. J . Organomet. Chem. 2000, 595, 292.
(26) Atherton, M. J .; Fawcett, J .; Holloway, J . H.; Hope, E. G.;
Russell, D. R.; Saunders, G. C. J . Organomet. Chem. 1999, 582, 163.

Intramolecular Dehydrofluorinative Coupling
Organometallics, Vol. 22, No. 9, 2003 1807
CH2P(C6F5)2}RhCl][BF4] and consistent with those of
salts of [(CpdPP)RhX]+ (122.2(1)-126.3(1)°). The Cp†-
Rh-PPh2 angle is identical to the Cp†-Rh-P(C6F5)2 of
[{η5,κP,κP-C5Me4CH2-2-C6F4P(C6F5)CH2CH2P(C6F5)2}-
RhCl][BF4] and consistent with those of salts of
[Cp*RhCl(P2)]+ (130.98(5)-135.5(13)°). The Rh-Cl dis-
tance is considerably shorter than that of 5b and is
similar to that of [{η5,κP,κP-C5Me3[CH2-2-C6F4P(C6F5)-
CH2]-1,3}RhCl][BF4] (2.380(3) Å).27 The P-Rh-P angle
is ca. 2° larger than that of 5b and similar to those of
[(CpdPP)RhX]+ and [(Cp-PP)RhCl]+ salts (86.94(7)-
87.9(1)°).6,26,27 No distortion of the C5 ring from C5
symmetry about the Cp†-Rh axis is evident: with the
exception of Rh-C(4) (2.261(8) Å) the Rh-C distances
are the same within 3σ (2.198(8)-2.243(9) Å); likewise
all five internal ring C-C distances are the same
(1.420(12)-1.461(12) Å). Unfortunately the nature of the
crystals did not permit manual separation of the enan-
tiomers.
F igu r e 3. Structure of the SRhRP enantiomer of the cation
of [{η5,κP,κP-C5Me4[CH2-2-C5F3N-4-PPhCH2CH2PPh2}-
RhCl][BF4] (6‚[BF4]). Thermal ellipsoids are at the 30%
probability level. Hydrogen atoms are omitted for clarity.
The red benzene filtrate obtained from the reaction
between [Cp*RhCl(µ-Cl)]2 and 1 yielded a red solid on
evaporation of the solvent. The 31P{1H} NMR spectrum
exhibited at least six resonances in the range δ 50-80
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 6‚[BF 4]
Cp†-Rh
1.851(9)
2.312(2)
1.498(12)
1.518(13)
1.818(8)
1.819(8)
1.802(8)
Rh-P(1)
2.272(2)
2.368(2)
1.509(12)
1.558(11)
1.819(8)
1.821(8)
1.818(8)
with couplings to rhodium of 120-160 Hz. The pre-
Rh-P(2)
Rh-Cl
1
dominant of these are doublets at δ 79.5 (dm, J RhP
)
mean C-CH3
C(10)-C(12A)
P(1)-C(1A)
P(1)-C(11A)
P(2)-C(11B)
C(1)-C(10)
C(1A)-C(2A)
P(2)-C(2A)
P(1)-C(21A)
P(2)-C(21B)
1
2
147 Hz) and 66.3 (dd, J RhP ) 134 Hz, J PP ) 16 Hz),
which are assigned to 6‚Cl. Other doublets are consis-
tent with cations of formulation [Cp*RhCl(1)]+ (the
cations of 5a and 5b). The 19F NMR spectrum is
consistent with the presence of 6‚Cl and [Cp*RhCl(1)]+,
but also shows the presence of other fluorine-containing
compounds as well as [SiF62-] and [BF4-]. In addition
the 31P{1H} spectrum exhibits a broad resonance be-
tween δP 27 and 40, and the 19F NMR spectrum exhibits
resonances at δ -89.85 and -123.87. These data are
consistent with the neutral compound [(Cp*RhCl2)2-
{µ,κP,κP-Ph2PCH2CH2PPh(C5F4N-4)}] (vide infra).
Cp†-Rh-Cl
121.9(3) Cp†-Rh-P(1)
134.0(3) P(1)-Rh-P(2)
90.17(8) P(2)-Rh-Cl
126.0(3)
86.12(8)
84.85(8)
113.4(3)
Cp†-Rh-P(2)
P(1)-Rh-Cl
Rh-P(1)-C(1A)
Rh-P(1)-C(11B)
108.7(3) Rh-P(1)-C(11A)
118.5(3) C(1A)-P(1)-C(11A) 105.8(4)
C(1A)-P(1)-C(11B) 107.8(4) C(11A)-P(1)-C(11B) 101.9(4)
Rh-P(2)-C(2A)
Rh-P(2)-C(21B)
105.8(3) Rh-P(2)-C(21A)
120.0(3) C(2A)-P(2)-C(21A) 105.2(4)
115.7(3)
C(12)-P(2)-C(21B) 105.1(4) C(21A)-P(2)-C(21B) 103.7(4)
The reaction between [Cp*RhBr(µ-Br)]2 and dfppe in
benzene proceeded via the cation [Cp*RhBr(dfppe)]+,26
and it is presumed that the reaction between [Cp*RhCl-
(µ-Cl)]2 and 1 in benzene proceeds via the chloride salts
of the cations of 5a and 5b. From the synthesis of 5a
and 5b it might be expected that the cis and trans
isomers would be formed in ca. 1:1 ratio, although under
thermodynamic control the trans isomer might predomi-
nate because of the greater steric crowding in the cis
isomer. Assuming no isomerization of the cation of 5b
to that of 5a , the maximum yield of 6‚[BF4] would be
50%. The higher yield of 6‚[BF4] obtained strongly
suggests that epimerization of the chloride salt of 5b to
5a did occur. This is in contrast to the epimerization of
[Cp*RhCl{Ph2PCH2CH(Me)PPh2}][BF4], which has been
reported to occur only in polar solvents.6 However, it is
noted that the presence of chloride ions accelerated the
rate of epimerization. A number of mechanisms for the
isomerization can be proposed, involving either dissocia-
tion of one or both of the phosphine functionalities or
chloride dissociation/coordination or coordination/dis-
sociation.8 To confirm the intermediacy of the cation 5a
and the isomerization of the cation of 5b to that of 5a ,
and to attempt to elucidate the mechanism for this, an
NMR study of the reaction was undertaken.
NMR spectra between the two salts are not as great as
have been observed in CpdPP rhodium complex-
es.3,18,20,25
Salt 6‚[BF4] crystallized as a conglomerate from
acetone, and the structure of one enantiomer was
determined by single-crystal X-ray diffraction (Figure
3). Crystal and refinement data are given in Table 1,
and selected bond distances and angles are given in
Table 4. The Cp†-Rh distance is shorter than in 5b and
is consistent with that of 1.842(2) Å found for the only
other structurally characterized [(Cp-PP)RhX]+ salt,
[{η5,κP,κP-C5Me4CH2-2-C6F4P(C6F5)CH2CH2P(C6F5)2}-
RhCl][BF4].8 The Rh-PPh(C5F3NCH2C5Me4) distance is
identical to that of the Rh-P(C6F5)(C5F4CH2C5Me4)
distance of [{η5,κP,κP-C5Me4CH2-2-C6F4P(C6F5)CH2-
CH2P(C6F5)2}RhCl][BF4] and consistent with those of
double-linked [(CpdPP)RhX]+ salts (2.256(2)-2.283(3)
Å),26,27 The Rh-PPh2 distance is similar to the Rh-
P(C6F5)2 distance of [{η5,κP,κP-C5Me4CH2-2-C6F4P-
(C6F5)CH2CH2P(C6F5)2}RhCl][BF4] (2.3306(11) Å) and
consistent with those of [Cp*RhCl(P2)]+ salts (2.314(2)-
2.362(2) Å).6,18,20 The Cp†-Rh-PPh(C5F3NCH2C5Me4)
angle is identical to the Cp†-Rh-P(C6F5)(C5F4CH2C5-
Me4) angle of [{η5,κP,κP-C5Me4CH2-2-C6F4P(C6F5)CH2-
(27) Atherton, M. J .; Fawcett, J .; Holloway, J . H.; Hope, E. G.;
Karac¸ar, A.; Russell, D. R.; Saunders, G. C. J . Chem. Soc., Chem.
Commun. 1995, 191.
The H, 19F, and 31P{1H} NMR spectra of a mixture
[Cp*RhCl(µ-Cl)]2 and 1 in a 1:2 ratio were recorded in
1

1808 Organometallics, Vol. 22, No. 9, 2003
Bellabarba et al.
C6D6. At room temperature a red solution and a red
solid, presumably [Cp*RhCl(µ-Cl)]2, which is sparingly
soluble in benzene, were present. The 31P{1H} NMR
spectrum contains resonances at δ 44.9 (dd) and -6.76
(dt), with a mutual coupling of 46 Hz. The former
resonance also shows coupling to rhodium (1J RhP ) 144
Hz) and the latter to two fluorine atoms (3J PF ) 20 Hz).
There is also a broad resonance or collection of reso-
nances between δ 40 and 50. The 19F NMR spectrum
shows two sets of resonances with integrations in a 1:2
ratio: δ -90.70 and -124.18, both of which show slight
broadening, and multiplets at δ -92.18 and -133.00.
also show that the tetrafluoropyridyl-substituted phos-
phine group is readily displaced by the more strongly
donating non-fluorinated phosphine group, which is
consistent with the lack of observation of the isomer of
8 [Cp*RhCl2{κP-(C5F4N-4)PhPCH2CH2PPh2}]. Thus an
equilibrium between 7 and 8, dependent on the relative
proportions of [Cp*RhCl(µ-Cl)]2 and 1, is established
rapidly. This was confirmed by NMR spectra after
addition of more 1 to the mixture. The data also show
that neither phosphine group of 1 is labile on the NMR
time scale. The similarity of the NMR data with those
of the mixture in C6D6, allowing for the effects of solvent
on δ, strongly suggests that 7 and 8 are those present
in the benzene solution at room temperature (in a 1:2
ratio). Over time the spectra of the mixture in C6D6/
CDCl3 developed resonances consistent with the cations
of 5a and 5b in a ratio of ca. 1:1. The presence of these
cations in a mixture of benzene and chloroform but not
in benzene at room temperature is presumably a
consequence of the greater polarity of chloroform. Ad-
dition of an excess of [Cp*RhCl(µ-Cl)]2 to this mixture
immediately increased the amount of 7 relative to 8,
but had no effect on the amounts of cations of 5a and
5b, even over several hours. Heating this solution at
60 °C for 9.5 h had little effect on the proportions of the
cations of 5a and 5b relative to 7. These observations
show that neither phosphine group of 1 can be readily
displaced from the cations [Cp*RhCl(1)]+ up to 60 °C.
The spectra also revealed that a small amount of 6‚Cl
(<5%) had been formed under these conditions.
1
The H NMR spectrum exhibits resonances that can be
assigned to phenyl rings (δ 6.8-8.2) and the ethylene
backbone (δ 2.0-3.6) of coordinated 1 and three doublet
resonances at δ 1.11, 1.04, and 1.02 with couplings of
ca. 3 Hz and integrations in a ratio of ca. 1:4:1 assigned
to Cp* hydrogen atoms. Additionally a low-intensity
singlet at δ 1.35, assigned to [Cp*RhCl(µ-Cl)]2, is
present. No change in the appearance of the mixture
or the spectra was observed after 72 h at room temper-
ature. The species responsible for these resonances were
identified from the spectra of mixtures of varying ratios
of [Cp*RhCl(µ-Cl)]2 and 1 in C6D6/CDCl3 (3:7), in which
both reagents and all products are soluble. For a sample
1
containing <1 equiv of 1 the H NMR spectrum showed
the presence of [Cp*RhCl(µ-Cl)]2 (δ 1.73) and contained
two doublets at δ 1.50 and 1.42 with couplings, 4J PH, of
3.8 and 3.4 Hz, respectively, and integrations in a ratio
of 1:1. The 19F NMR contains two major resonances at
δ -89.48 and -123.56, accounting for >90% of the total
integration, and the 31P{1H} NMR spectrum exhibits a
broad resonance or collection of resonances between δ
30 and 40. On cooling to -20 °C, the 31P{1H} NMR
spectrum (recorded at 202.47 MHz) exhibits only two
doublets of doublet resonances at δ 38.0 and 34.9 with
An NMR tube containing a mixture of [Cp*RhCl(µ-
Cl)]2 and 1 in a ca. 1:2 ratio in C6D6 with a small amount
CDCl3 added in an attempt to keep the intermediates
and products in solution was heated at 70 °C, and at
2-3 h intervals the spectra were recorded (at 25 °C).
The occurrence of reaction was evident after 2.5 h from
the presence of resonances assigned to 6‚Cl in the 31P-
{1H} and 19F NMR spectra. After 13 h, the solution was
lighter in color and a small amount of yellow precipitate
was present. The spectra showed the presence of 7, 8,
the cations of 6 and 5b, and the anions [BF4-] and
[SiF62-]. The resonances of 8 decreased in intensity with
time until after 21.5 h they were no londer observed.
The resonances of 7 were observed throughout the
experiment. The reaction was continued for 45 h, at
which time no changes in the spectra were observed and
a significant amount of yellow precipitate was present.
The spectra of the product mixture, obtained by removal
of the solvent under reduced pressure, were recorded
in CDCl3, in which it was completely soluble, giving an
1
couplings to rhodium, J RhP, of 157 and 142 Hz, with a
mutual coupling of 20 Hz. These data are similar to
those of the compound [(Cp*RhCl2)2{µ,κP,κP-Ph2PCH2-
CH(Me)PPh2}] (at -50 °C and 121.4 MHz: δ 38.3, 1J RhP
1
3
) 145 Hz, δ 30.5, J RhP ) 143 Hz, J PP ) 18 Hz).6 It is
argued that the fluxionality of this compound arises
from hindered rotation about the Rh-PPh2CH(Me) bond
and rotation about the Rh-PPh2CH2 bond being slowed
at low temperature. Different resonances were observed
1
for [Cp*RhCl(µ-Cl)]2 and 1 in a 1:2 ratio. The H NMR
spectrum shows a doublet at δ 0.99 with a coupling,
4J PH, of 3.5 Hz, as well as resonances consistent with
the ethylene and phenyl groups of coordinated 1. The
19F spectrum exhibits two multiplet resonances at δ
-92.39 and -132.80. The 31P NMR spectrum exhibits
a doublet of doublets at δ 31.4 with a coupling to
1
orange-red solution. The 31P{1H} and H NMR spectra
indicated the presence of three major phosphorus- and
fluorine-containing species: the cations of 6 and 5b, in
a ratio of ca. 3:1, and 7. The lack of observation of
resonances of the cation of 5a does not preclude its
intermediacy, since the intramolecular dehydrofluori-
native coupling to give 6 may be too rapid for there to
be a sufficient concentration of 5a for observation by
NMR. In support of this, [Cp*RhCl(dfppe)]+ was not
observed in the reaction between [Cp*RhCl(µ-Cl)]2 and
dfppe in benzene, but [Cp*RhBr(dfppe)]+ was observed
in the reaction between [Cp*RhBr(µ-Br)]2 and dfppe, in
which the dehydrofluorinative coupling is much slower.26
Unfortunately the data are insufficient to aid the
1
rhodium, J RhP, of 140 Hz and a doublet of triplets at δ
-20.0 with a coupling to fluorine, 3J PF, of ca. 20 Hz with
a mutual coupling of 45 Hz. These data are comparable
to those of [Cp*RhCl2{κP-Ph2PCH2CH(Me)PPh2}] (δ
34.7, 1J RhP ) 141 Hz, δ -16.4, 3J PP ) 25 Hz).6 Addition
of [Cp*RhCl(µ-Cl)]2 to this mixture leads to the appear-
ance in the spectra of the resonances observed in the
spectra of the mixture containing <1 equiv of 1. These
data are consistent with [(Cp*RhCl2)2{µ,κP,κP-Ph2PCH2-
CH2PPh(C5F4N-4)}], 7, and [Cp*RhCl2{κP-Ph2PCH2-
CH2PPh(C5F4N-4)}], 8, formed from [Cp*RhCl(µ-Cl)]2
and 1 in a 1:1 ratio and 1:2 ratio, respectively. The data

Intramolecular Dehydrofluorinative Coupling
Organometallics, Vol. 22, No. 9, 2003 1809
7.39 (m, 13H, C6H5), 2.50 (m, 2H, CH2), 2.11 (m, 2H, CH2). 19
F
elucidation of the mechanism of the isomerization of the
cation of 5b to that of 5a .
(CDCl3): δ -91.87 (m, 2F, Fmeta-P), -132.96 (m, 2F, Fortho-P).
3
3
31P{1H} (CDCl3): δ -11.3 (d, J PP ) 40 Hz), -20.25 (dt, J PP
) 40 Hz, J PF ) 19 Hz). EIMS, m/z (rel int): 471 M+ (24), 393
3
Con clu sion s
[M - C6H5 - H]+ (47), 335 [M - 2C6H5 + F]+(21), 183 [H2-
PC5F4N]+ (77), 151 [C5F4N + H]+ (70). HRMS: calcd for
The asymmetric tetrafluoropyridyl-substituted diphos-
phine 1 can be conveniently prepared from dppe in
moderate yield. Comparison of ν(CtO) for the complexes
trans-[RhCl(CO)P2] between P ) PPh2(C5F4N-4) (2) and
P ) PPh2(C6F5) and PPh2(C6H3F2-2,6) indicates that the
effect of the tetrafluoropyridyl group is to decrease the
basicity of the phosphine. The tetrafluoropyridyl-
substituted phosphine moiety of 1 is less basic than
those of dppe. Diphosphine 1 can be linked to a Cp*
ligand in a cationic rhodium(III) complex by intramo-
lecular dehydrofluorinative carbon-carbon coupling to
give a cationic complex of a Cp-PP ligand, 6. The
reaction is best carried out by treating [Cp*RhCl(µ-Cl)]2
with 1 in refluxing benzene, since diastereoisomers,
which are not readily separated, are formed by the
reaction between [Cp*RhCl(µ-Cl)]2 and 1 in the presence
of [BF4-], and only one undergoes the coupling reaction
on treatment with proton sponge. Although racemic 1
leads to racemic 6, the reaction shows the potential of
this methodology to provide a convenient route to
nonracemic, configurationally stable, chiral-at-metal
complexes from nonracemic chelating phosphines.
C
25H19F4NP2, 471.09289; found M+, 471.09272.
P P h 2(C5F 4N-4) (2). Phosphine 2 was prepared as de-
scribed.10 1H (CDCl3): δ 7.43 (m, 10H, C6H5). 19F (CDCl3): δ
-91.46 (m, 2F, Fmeta-P), -131.40 (m, 2F, Fortho-P). 31P{1H}
3
(CDCl3): δ -18.9 (t, J PF ) 30 Hz). EIMS, m/z (rel int): 335
M+ (96), 183 [H2PC5F4N]+ (99). HRMS: calcd for C17H10F4NP,
335.04870; found M+, 335.04936.
tr a n s-[Rh Cl(CO){P P h 2(C5F 4N-4)}2] (3). A slurry of [Rh-
(µ-Cl)(CO)2]2 (0.036 g, 0.093 mmol) and 2 (0.139 g, 0.41 mmol)
in dichloromethane (20 cm3) was stirred for 3 h, after which
time the solvent was removed by rotary evaporation and the
resulting solid washed with hot hexane (50 cm3) to afford 3 as
a yellow solid. Yield: 0.127 g (82%). 1H (CDCl3): δ 6.8-7.9 (20H,
m, C6H5). 19F (CDCl3): δ -90.22 (m, 2F, Fmeta-P), -127.91 (m,
2F, Fortho-P). 31P{1H} (CDCl3): δ 27.8 (d, 1J RhP ) 110 Hz). Anal.
Calcd for C35H20ClF8N2OP2Rh: C, 50.23; H, 2.41; N, 3.35.
Found: C, 50.19; H, 2.44; N, 3.11. IR (KBr, cm-1): ν(CtO) 1993
(s).
OP P h 2(C5F 4N-4) (4). Crystals of 4 were deposited from 2
1
on exposure to air over several weeks. H (CDCl3): δ 7.72 (m,
4H), 7.64 (m, 2H), 7.55 (m, 4H). 19F (CDCl3): δ -88.84 (m, 2F,
F
meta-P), -131.00 (m, 2F, Fortho-P). 31P{1H} (CDCl3): δ 21.8 (s).8
HRMS: calcd for
351.04481.
C
17H10F4NOP, 351.04362; found M+,
[Cp *Rh Cl{P h 2P CH2CH2P P h (C5F 4N)}][BF 4] (5). A slurry
of [Cp*RhCl(µ-Cl)]2 (0.069 g, 0.11 mmol), 1 (0.101 g, 0.23
mmol), and NaBF4 (ca. 0.44 g, 4 mmol) in dichloromethane
(20 cm3) and methanol (40 cm3) was stirred for 1 h, after which
time the solvent was removed by rotary evaporation. The
product was extracted into dichloromethane (2 × 50 cm3), the
solution filtered, and the solvent removed from the filtrate by
rotary evaporation to yield the product, a mixture of 5a and
5b (ca. 1:1), as an orange solid. 0.086 g (47%) A sample for
analysis was obtained by recrystallization from dichlo-
romethane. The assignments of the NMR resonances were
made by studying the reaction of the mixture with proton
sponge. 5a : 1H (CDCl3): δ 7.3-7.7 (m, 13H), 7.03 (dd, J ) 11.5,
7.4 Hz, 2H), 3.15 (m, 1H, PCH2), 2.77 (m, 3H, PCH2), 1.47 (ddd,
Exp er im en ta l Section
Gen er a l Con sid er a tion s. [Cp*RhCl(µ-Cl)]2 and dppe (Al-
drich) were used as supplied. Pentafluoropyridine (Lancaster)
was stored over MgSO4. Me3SiCl (Aldrich) was purified by
distillation in vacuo and stored under dinitrogen over Na2CO3.
The preparations of 1 and 2 were performed under dinitrogen
using THF and benzene dried by distillation under dinitrogen
from potassium and storage over molecular sieves (4A). No
precautions to exclude air or moisture were taken for the other
preparations.
The 1H, 19F, and 31P NMR spectra were recorded using
Bruker DPX300 or DRX500 spectrometers. 1H NMR spectra
(300.01 or 500.13 MHz) were referenced internally using the
residual protio solvent resonance relative to SiMe4 (δ 0), 19F
(282.26 MHz) externally to CFCl3 (δ 0), and 31P (121.45 or
202.47 MHz) externally to 85% H3PO4 (δ 0). All chemical shifts
are quoted in δ (ppm), using the high-frequency positive
convention, and coupling constants in Hz. The IR spectrum
was recorded on a Perkin-Elmer RX I Fourier transform
spectrometer. EI and LSIMS mass spectra were recorded on
a VG Autospec X series mass spectrometer. Elemental analy-
ses were carried out by ASEP, The School of Chemistry,
Queen’s University Belfast.
4J PH ) 10.2 Hz, J Ph ) 3.4 Hz, J RhH ) 3.4 Hz, 15H, Me). 19F
(CDCl3): δ -88.07 (m, 2F, Fmeta-P), -129.46 (m, 2F, Fortho-P),
-154.18 (0.8F, s, [10BF4-]), -154.23 (3.2F, s, [11BF4-]). 31P{1H}
(CDCl3): δ 70.5 (dd, 1J RhP ) 126 Hz, 3J PP ) 11 Hz, PPh2), 58.2
4
3
1
(dm, J RhP ) 137 Hz, PPh(C5F4N)). 5b: 1H (CDCl3): δ 7.3-7.7
(m, 15H), 3.47 (m, 1H, PCH2), 3.15 (m, 1H, PCH2), 2.44 (m,
1H, PCH2), 2.26 (m, 1H, PCH2), 1.20 (m, 15H, Me). 19F
(CDCl3): δ -88.10 (br s, 2F, Fmeta-P), -129.86 (br s, 2F, Fortho-P),
-154.18 (0.8F, s, [10BF4-]), -154.23 (3.2F, s, [11BF4-]). 31P{1H}
(CDCl3): δ 66.8 (dd, 1J RhP ) 134 Hz, 2J PP ) 26 Hz, PPh2), 64.6
(ddm, 1J RhP ) 140 Hz, 3J PP ) 26 Hz, PPh(C5F4N)). LSIMS, m/z
(rel int): 744 M+ (54), 709 [M - Cl]+ (22). HRLSIMS: calcd
for C35H34ClF4NP2Rh, 744.08462; found M+, 744.08437. Anal.
Calcd for C35H34BClF8NP2Rh‚0.25CH2Cl2: C, 49.64; H, 4.08;
N, 1.64. Found: C, 49.64; H, 4.12; N, 1.37.
[{η5,KP ,KP -C5Me4[CH2-2-C5F 3N-4-P (C6F 5)CH2CH2P P h 2}-
Rh Cl][BF 4] (6‚[BF 4]). A slurry of [Cp*RhCl(µ-Cl)]2 (0.108 g,
0.17 mmol) and 1 (0.150 g, 0.34 mmol) in benzene (60 cm3)
was heated under dinitrogen for 9 h. The resulting yellow
precipitate of 6‚Cl was filtered off, washed with hexane (2 ×
20 cm3), and dried in vacuo. The solid was dissolved in
methanol (60 cm3), and NaBF4 (ca. 0.2 g) added. The mixture
was stirred for 3 h, then filtered. The solvent was removed
from the filtrate by rotary evaporation. The product was
extracted into dichloromethane (2 × 80 cm3), and the combined
extracts were dried over MgSO4. After filtration the solvent
was removed by rotary evaporation, yielding 6‚[BF4] as a
P h 2P CH2CH2P P h (C5F 4N) (1). Sodium naphthalide in THF
(150 cm3), prepared from naphthalene (1.64 g, 13.0 mmol), was
added to dppe (2.00 g, 5.0 mol) and the solution left at room
temperature for 72 h until a deep red solution had formed.
Me3SiCl (ca. 1.2 g, 13 mmol) was added, resulting in an
immediate loss of color. The volatiles were removed under
reduced pressure to give a pale yellow oil. Benzene (100 cm3)
was added and the extract filtered and added to pentafluoro-
pyridine (ca. 0.85 g, 5 mmol). The reaction mixture was left
at ambient temperature for 20 h, during which time the
solution darkened. The solvent was removed under reduced
pressure and the resulting oil chromatographed on deactivated
neutral alumina (6% H2O). Naphthalene was eluted with
hexane, phosphine 2 with dichloromethane/hexane (1:9), and
diphosphine 1 with dichloromethane/hexane (1:1). Recrystal-
lization from methanol/dichloromethane gave 1 as a white
1
solid. Yield: 1.19 g (51%). H (CDCl3): δ 7.52 (m, 2H, C6H5),

1810 Organometallics, Vol. 22, No. 9, 2003
Bellabarba et al.
yellow solid, which was dried in vacuo. Yield: 0.173 g (64%).
Lorentz and polarization corrections were applied. Empirical
absorption corrections were applied using SADABS.29 The
structures were solved using direct methods and refined with
the program package SHELXTL version 5,30 and the non-
hydrogen atoms were refined with anisotropic thermal pa-
rameters. Hydrogen atom positions were added, and idealized
positions and a riding model with fixed thermal parameters
(Uij ) 1.2Ueq for the atom to which they are bonded (1.5 for
CH3)) were used for subsequent refinements. The function
1H (CD2Cl2): δ 7.53 (m, 10H, C6H5), 7.37 (m, 1H, C6H5), 7.28
4
(m, 2H, C6H5), 6.64 (m, 2H, C6H5), 3.98 (dd, 1H, J PH ) 16.3
2
Hz, J HH ) 16.3 Hz, C5CHH’C5F3N), 3.47 (m, 1H, PCH2), 3.26
2
(m, 1H, PCH2), 3.24 (d, 1H, J HH ) 16.3 Hz, C5CHH’C5F3N),
4
2.97 (m, 2H, PCH2), 1.91 (d, 3H, J PH ) 5.4 Hz, Me), 1.66 (dd,
4
4
3H, J PH
≈
4J PH ≈ 5.2 Hz, Me), 1.20 (d, 3H, J PH ) 7.7 Hz,
Me), 0.23 (d, 3H, J PH ) 2.1 Hz, Me). 19F (CD2Cl2): δ -72.39
(m, 1F), -85.82 (m, 1F), -134.09 (m, 1F), -153.55 (0.8F, s,
[10BF4-]), -153.60 (3.2F, s, [11BF4-]). 31P{1H} (CD2Cl2): δ 78.3
(dm, J RhP ) 129 Hz, PPh(C5F3N)), 67.0 (dd, J RhP ) 130 Hz,
3J PP ) 16 Hz, PPh2). LSIMS, m/z (rel int): 724 M+ (100), 689
[M - Cl]+ (22). HRLSIMS: calcd for C35H33ClF3NP2Rh,
724.07839; found M+, 724.07686. Anal. Calcd for C35H33BClF7-
NP2Rh‚0.5CH2Cl2: C, 49.92; H, 4.01; N, 1.64. Found: C, 49.98;
H, 3.93; N, 1.42.
4
2
2
minimized was ∑[w(|Fo| - |Fc| )] with reflection weights w-1
1
1
2
2
2
) [σ2 |Fo| + (g1P)2 + (g2P)] where P ) [max |Fo| + 2|Fc| ]/3.
Additional material available from the Cambridge Crystal-
lographic Data Centre comprises relevant tables of atomic
coordinates, bond lengths and angles, and thermal parameters
(CCDC numbers: 4 194821, 5b 194822, 6‚[BF4] 194823)
X-r a y Cr ysta llogr a p h y. Crystals of 4 were deposited from
neat 2. Crystals of 5b and 6‚[BF4] were grown from dichlo-
romethane/ethanol and acetone, respectively. Crystal data are
listed in Table 1. Diffraction data were collected on a Bruker
SMART diffractometer using the SAINT-NT28 software with
graphite-monochromated Mo KR radiation. A crystal was
mounted on the diffractometer at low temperature, ca. 120 K.
Ack n ow led gm en t. We are grateful to Dr. G. Sand-
ford for valuable discussions, M. W. Masterson and A.
McGibbon for some preliminary synthetic studies, and
the EPSRC for support (to R.M.B.).
Su p p or tin g In for m a tion Ava ila ble: A listing of atomic
coordinates, anisotropic displacement parameters, bond dis-
tances, and bond angles for 4, 5b‚0.5CH2Cl2, and 6‚[BF4]. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(28) SAINT-NT; Bruker AXS Inc.: Madison, WI, 1998.
(29) Sheldrick, G. M. SADABS; University of Go¨ttingen: Germany
1996.
(30) Sheldrick, G. M. SHELXTL version 5; Bruker AXS Inc.:
Madison, WI, 1998.
OM020874P