Complexes of η5, κp-cyclopentadienyl-phosphine ligands by chelate-assisted dehydrofluorinative coupling; the coupling of bis{bis(pentafluorophenyl)phosphino}methane to η5- pentamethylcyclopentadienyl in a rhodium complex

Article abstract of DOI:10.1016/j.inoche.2006.01.019

The reaction between [{(η⁵-C₅Me ₅)RhCl(μ-Cl)}₂] and (C₆F₅) ₂PCH₂P(C₆F₅)₂ in refluxing benzene yields the singly linked complex [{(η

Full text of DOI:10.1016/j.inoche.2006.01.019

Inorganic Chemistry Communications 9 (2006) 407–409
www.elsevier.com/locate/inoche
Complexes of g5, jP-cyclopentadienyl-phosphine ligands by
chelate-assisted dehydrofluorinative coupling; the coupling
of bis{bis(pentafluorophenyl)phosphino}methane to
g5-pentamethylcyclopentadienyl in a rhodium complex
*
Andrew C. Marr, Mark Nieuwenhuyzen, Ciara L. Pollock, Graham C. Saunders
School of Chemistry and Chemical Engineering, Queen’s University Belfast, David Keir Building, Belfast BT9 5AG, UK
Received 6 January 2006; accepted 30 January 2006
Available online 15 March 2006
Abstract
The reaction between [{(g5-C5Me5)RhCl(l-Cl)}2] and (C6F5)2PCH2P(C6F5)2 in refluxing benzene yields the singly linked complex
[{(g5,jP-C5Me4CH2C6F4-2-P(C6F5)CH2P(C6F5)2)}RhCl2] in which only one phosphorus atom is coordinated to the rhodium.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Cyclopentadienyl ligands; Fluorinated ligands; Phosphine ligands; C–C coupling
Intramolecular dehydrofluorinative coupling of methyl-
substituted cyclopentadienyl and chelating polyfluoroaryl-
substituted phosphine ligands provides a convenient route
to rhodium and iridium complexes of trifunctional g5,jP,
jL-cyclopentadienyl-phosphine-donor (Cp–PL) ligands
(Scheme 1) [1–3]. The reactions are rapid and high-yielding,
and can be performed directly from [{(g5-C5Me5)MCl(l-
Cl)}2] (M = Rh or Ir) and a chelating phosphine (P2), via
the intermediate [(g5-C5Me5)MCl(jP,jP-P2)]+ [4], as for
the synthesis of [{(g5,jP,jP–C5Me4CH2C5F3N-2-PPhCH2-
CH2PPh2)}RhCl]+[2]. Access to ligands of this type had
previously been problematic, involving elaborate, multiple
step, low-yielding syntheses [5]. Rhodium and iridium com-
plexes of bidentate g5,jP-cyclopentadienyl-phosphine
(Cp–P) ligands can also be prepared using intramolecular
dehydrofluorinative coupling from monodentate polyflu-
oroaryl-substituted phosphine ligands, but the reaction
times are longer, the yields are lower and it has proved dif-
ficult to obtain the products pure [1,3].
The complexes of Cp–P ligands offer greater reaction
diversity than those of Cp–PL ligands, since they possess
one more latent coordination site. For example, [{(g5,jP–
C5Me4CH2CH2PEt2)}Rh(CO)] can undergo oxidative-
addition/reductive-elimination cycles enabling it to catalyse
methanol carbonylation [6], whereas [{(g5,jP,jP-C5Me4
CH2C5F3N-2-PPhCH2CH2PPh2)}RhCl]+ cannot and con-
sequently shows no catalytic activity for carbonylation
reactions. It is therefore, desirable to extend the conve-
nience of the synthesis of complexes of Cp–PL ligands to
those of Cp–P ligands.
Since a chelating PL ligand is necessary for rapid and
clean coupling, any method will rely on the conversion of
a Cp–PL ligand to a Cp–P ligand. One approach is to
develop a Cp–PL ligand in which the P–L linkage can be
cleaved and the L functionality removed. Alternatively, a
chelating PL ligand which couples to the cyclopentadienyl
ligand to give a Cp–PL ligand that disfavours coordination
of the L functionality can be used. If necessary the L func-
tionality can then be converted to a non-ligating function-
ality. One group of chelating PL ligands that may show this
ability are those which give small bite (P–M–L) angles. It
*
Corresponding author.
E-mail address: g.saunders@qub.ac.uk (G.C. Saunders).
1387-7003/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2006.01.019

408
A.C. Marr et al. / Inorganic Chemistry Communications 9 (2006) 407–409
+
+
- HF
M
M
X
X
L
F
L
F
P
P
R
R
Scheme 1.
has been established that coupling of the phosphine to
cyclopentadienyl reduces both the Cp–M–P angle and the
M–P bond length [1,2], and this geometric change may dis-
allow coordination of the L functionality.
Ethylene-bridged diphosphines favour chelation giving
bite angles of >80ꢁ [7]. In contrast, methylene-bridged
diphosphines, R2PCH2PR2, either chelate to give strained
four-membered rings with P–M–P bite angles of ca. 72ꢁ
[7] or bridge between two metals depending on the nature
of the substituent R. The strain of the four-membered ring
typically leads to the diphosphines bridging between met-
Rh
Cl(2)
P(2)
Cl(1)
P(1)
C(12)
t
als, but sterically demanding substituents, such as butyl
and cyclohexyl, lead to chelation being more favourable
[8]. The dehydrofluorinative coupling reaction requires at
least one aryl substituent bearing ortho fluorine atoms
and since fluorinated aryl groups are much more sterically
demanding than the non-fluorinated analogues [9], bis
{(pentafluorophenyl)phosphino}methane was considered
an ideal candidate for testing the hypothesis that a PL
ligand with a small bite angle will lead to a complex of
Cp–P ligands with an uncoordinated L functionality.
The reaction between [{(g5-C5Me5)RhCl(l-Cl)}2] and
two equivalents of (C6F5)2PCH2P(C6F5)2 in refluxing ben-
zene gave the singly linked neutral complex [{(g5,jP–
C5Me4CH2C6F4-2-P(C6F5)CH2P(C6F5)2)}RhCl2], 1, which
was isolated in 70% yield (Scheme 2) [10]. Complex 1 was
structurally characterized by single-crystal X-ray diffraction
(Fig. 1) [11]. The Rh–P distance and Cp –Rh–P angle are
consistent with those of rhodium complexes in which a
cyclopentadienyl ring is linked to a phosphine by a benzyl
or similar group [1,2,12] and the P–CH2–P angle is identical
within 3r to that of Ph2PCH2PPh2 (dppm) (106.2(3)ꢁ) [13].
The analytical and NMR spectroscopic data are consistent
with the formulation. The 1H NMR spectrum exhibits four
resonances in the range d 3.9–5.2 assigned to the non-equiv-
Fig. 1. Molecular structure of the S enantiomer of compound 1. Thermal
ellipsoids are at the 30% probability level. Hydrogen atoms are omitted for
clarity. Cp –Rh 1.804(6), Rh–P(1) 2.2624(10), Rh–Cl(1) 2.4085(16), Rh–
Cl(2) 2.3952(16), P(1)–C(12) 1.849(5), P(2)–C(12) 1.842(5) A, Cp –Rh–
P(1) 127.7(2), Cp –Rh–Cl(1) 123.8(2), Cp –Rh–Cl(2) 121.5(2), P(1)–
˚
C(12)–P(2) 106.9(3)ꢁ.
alent hydrogen atoms of the two methylene groups and four
resonances in the range d 1–2 assigned to four non-equiva-
lent methyl groups. Two mutually coupled resonances at d
43.1 and ꢀ66.6 are observed in the 31P{1H} NMR spec-
trum. The former shows coupling to rhodium and is
assigned to the coordinated phosphorus atom. The latter,
with a chemical shift consistent with non-coordinated
bis(pentafluorophenyl)-phosphines [1,14] and showing no
coupling to rhodium, is assigned to the non-coordinated
F
½ [(η5-C5Me5)RhCl(μ-Cl)]2
Δ, C6H6
F
+
Rh
Cl
- HF
P
Cl
(C6F5)2PCH2P(C6F5)2
F
C6F5
F
P
F5C6
C6F5
1
Scheme 2.

A.C. Marr et al. / Inorganic Chemistry Communications 9 (2006) 407–409
409
(b) A.E.C. McConnell, P. Pogorzelec, A.M.Z. Slawin, G.L. Williams,
P.I.P. Elliott, A. Haynes, A.C. Marr, D.J. Cole-Hamilton, J. Chem.
Soc., Dalton Trans. (2006) 91–107.
phosphorus atom. The magnitude of the two-bond phos-
phorus–phosphorus coupling (185 Hz) is significantly larger
than that of 28.1 Hz reported for [(g5-C5Me5)RhCl2(jP–
Ph2PCH2PPh2)] [15], but is consistent with larger couplings
occurring for more electronegative substituents [16]. The
19F NMR spectrum exhibits thirteen resonances integrating
for nineteen fluorine atoms. Four resonances are assigned
to the unique fluorine atoms of the tetrafluorophenyl link.
The three pentafluorophenyl groups are non-equivalent,
but rotation about the P–C bonds leads to the equivalence
of the respective ortho and meta fluorine atoms, giving a fur-
ther nine resonances, of which six integrate for two fluorine
atoms each.
[7] P. Dierkes, P.W.N.M. van Leeuwen, J. Chem. Soc., Dalton Trans.
(1999) 1519–1529.
[8] (a) R.J. Puddephat, Chem. Soc. Rev. 12 (1983) 99–127;
(b) F. Eisentra¨ger, A. Go¨thlich, I. Gruber, H. Heiss, C.A. Kiener, C.
Kruger, J.U. Notheis, F. Rominger, G. Scherhag, M. Schultz, B.F.
¨
Straub, M.A.O. Volland, P. Hofmann, New J. Chem. 27 (2003) 540–
550.
[9] (a) C.A. Tolman, Chem. Rev. 77 (1977) 313–348;
(b) D. White, N.J. Colville, Adv. Organomet. Chem. 36 (1994) 95–
158.
[10] A slurry of [{(g5-C5Me5)RhCl(l-Cl)}2] (0.141 g, 0.23 mmol) and
(C6F5)2PCH2P(C6F5)2 (0.312 g, 0.42 mmol) in benzene (100 cm3) was
heated at reflux for 95 h. After cooling, the solution was concentrated
to ca. 50 cm3 by rotary evaporation and hexane (50 cm3) added. The
resulting red-brown precipitate was filtered off, washed with hot
hexane (3 · 10 cm3) and dried in vacuo (0.285 g, 70%). Anal. Calcd
for C35H16Cl2F19P2Rh: C, 40.65; H, 1.55. Found: C, 41.37; H, 2.45%.
LSIMS: 997 (100) [M+ꢀCl], 961 (29) [M+ꢀ2Cl]. HRLSIMS:
C35H1365ClF19P2Rh requires 996.9167; found M+: 996.9173. 1H
NMR (300.01 MHz, (CD3)2CO, 25 ꢁC): d = 5.15 [1H, dd, 2J(PH)
Attempts to force g5,jP,jP coordination of the ligand
by treatment of 1 with sodium tetrafluoroborate or
sodium hexafluoroantimonate were unsuccessful. This
observation supports the hypothesis that it is the change
of geometry on coupling that prevents coordination of
both phosphorus atoms. Since dehydrofluorinative cou-
pling has previously been observed only for cations in
which a pentafluorophenyl group has been held close to
the pentamethylcyclopentadienyl ligand, it is likely that
the reaction proceeds via the cation [(g5-C5Me5)RhCl{jP,
jP–(C6F5)2PCH2P(C6F5)2}]+. We are currently undertak-
ing studies to confirm this.
2
2
14.3 Hz, J(HH0) 14.3 Hz, PCHH0P], 4.35 [1H, dd, J(PH0) 14.3 Hz,
2J(HH0) 14.3 Hz, PCHH0P], 4.18 [1H, dd, J(HH0) 18.6 Hz, 2J(PH)
6.1 Hz, C5CHH0C6F4], 3.96 [1H, d, J(HH0) 18.6 Hz, C5CHH0C6F4],
2
2
1.94 [3H, d, 4J(PH) 7.6 Hz, CH3], 1.86 [3H, d, 4J(PH) 5.6 Hz, CH3],
1.83 (3H, s, CH3), 1.40 [3H, d, 4J(PH) 0.9 Hz, CH3]. 19F NMR
(282.25 MHz, (CD3)2CO, 25 ꢁC): d = ꢀ 121.25 (1F, m), ꢀ129.61 (2F,
m), ꢀ130.14 (2F, m), ꢀ 132.61 (2F, m), ꢀ136.99 (1F, m), ꢀ149.29
(1F, td, J 20.2 Hz, J 9.0 Hz), ꢀ150.26 (1F, m), ꢀ152.23 (1F, m),
ꢀ152.43 (1F, m), ꢀ 158.43 (1F, t, J = 20.2 Hz), ꢀ162.37 (2F, m),
ꢀ163.02 (2F, m), ꢀ 163.54 (2F, m). 31P{1H} NMR (121.45 MHz,
(CD3)2CO, 25 ꢁC): d = 43.1 [ddm, 1J(RhP) 170 Hz, 2J(PP) 185 Hz,
PC6F4CH2], ꢀ66.6 [dquint, 2J(PP) = 185 Hz, 3J(PF) 38 Hz, P(C6F5)2].
[11] Crystal data for 1: C35H16Cl2F19P2Rh, M = 1033.23, orthorhombic,
Supplmentary data
CCDC No. 294507 contains the supplementary crystal-
lographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
˚
˚
˚
Pna21, a = 14.6421(13) A, b = 12.4541(11) A, b = 19.7153(17) A,
3
˚
V = 3595.2(5) A , Z = 4, final
R
indices R1 = 0.0447 and
wR2 = 0.0856 [I P 2r(I)], and R1 = 0.0705 and wR2 = 0.0955 (all
data). Flack parameter = 0.61(3). Data collection was performed at
153(2) K on a Bruker SMART diffractometer (Mo Kak = 0.71073 A).
Acknowledgements
˚
The structure was solved by direct methods and all non-hydrogen
atoms were subjected to anisotropic refinement by full matrix least
squares on F2 using the SHELXTL package. An empirical absorption
correction was applied using the SADABS program. All hydrogen
atoms were included in calculated positions.
We thank the E.U. European Social Fund for funding
(to C.L.P.) and V. Lennox for initial synthetic studies.
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