Octaethyldiphosphaferrocene: An efficient ligand in the palladium-catalyzed suzuki cross-coupling reaction

Article abstract of DOI:10.1021/om0005699

Syntheses of octaethyldiphosphaferrocene 4 and tetraethylphosphaferrocene 5 are presented. Tetraethylzirconacyclopentadiene 1 reacts with PCl₃ in dichloromethane to yield the 1-chlorotetraethylphosphole 2, which upon reduction by lithium in excess, yields the teraethylphospholide anion 3. Anion 3 was subsequently converted into 4 or 5 by treatment with FeCl₂ or with [Fe(η⁶-C₉H₁₂)(η⁵-C₅H₅)][PF₆] respectively. The structure of diphosphaferrocene 4 was determined. Two conformations are present in the cell: a C₂ conformation (α = 51.1°) in which the P atom of each ring is located above the α-carbon atom of the other ring, and a C_2h conformation (α = 180°) in which P atoms point in opposite directions. Reaction of ligand 4 with [Pd(dba)₂] yields the bis(octaethyldiphosphaferrocene)palladium(0) complex 6. An X-ray crystallographic study reveals that the overall geometry around palladium is nearly tetrahedral and that both ligands, whose geometry is not significantly perturbed, adopt a bridging mode involving a side-on coordination of the lone pairs. Complex 6 behaves as an efficient catalyst for the coupling reaction between phenylboronic acid and 4-bromoacetophenone in refluxing toluene. A conversion of 98% was obtained with 1×10^-4% of catalyst (TON = 9.80×10⁵). The catalytic activity of 6 in coupling reactions between phenylboronic acid and 3-bromothiophene, 2-bromoanisole, and bromobenzene was also investigated.

Full text of DOI:10.1021/om0005699

Organometallics 2000, 19, 4899-4903
4899
Octa eth yld ip h osp h a fer r ocen e: An Efficien t Liga n d in
th e P a lla d iu m -Ca ta lyzed Su zu k i Cr oss-Cou p lin g
Rea ction
Xavier Sava, Louis Ricard, Franc¸ois Mathey,* and Pascal Le Floch*
Laboratoire “He´teroe´le´ments et Coordination”, UMR CNRS 7653, Ecole Polytechnique,
91128 Palaiseau Cedex, France
Received J uly 3, 2000
Syntheses of octaethyldiphosphaferrocene 4 and tetraethylphosphaferrocene 5 are pre-
sented. Tetraethylzirconacyclopentadiene 1 reacts with PCl3 in dichloromethane to yield
the 1-chlorotetraethylphosphole 2, which upon reduction by lithium in excess, yields the
teraethylphospholide anion 3. Anion 3 was subsequently converted into 4 or 5 by treatment
with FeCl2 or with [Fe(η6-C9H12)(η5-C5H5)][PF6] respectively. The structure of diphospha-
ferrocene 4 was determined. Two conformations are present in the cell: a C2 conformation
(R ) 51.1°) in which the P atom of each ring is located above the R-carbon atom of the other
ring, and a C2h conformation (R ) 180°) in which P atoms point in opposite directions.
Reaction of ligand 4 with [Pd(dba)2] yields the bis(octaethyldiphosphaferrocene)palladium-
(0) complex 6. An X-ray crystallographic study reveals that the overall geometry around
palladium is nearly tetrahedral and that both ligands, whose geometry is not significantly
perturbed, adopt a bridging mode involving a side-on coordination of the lone pairs. Complex
6 behaves as an efficient catalyst for the coupling reaction between phenylboronic acid and
4-bromoacetophenone in refluxing toluene. A conversion of 98% was obtained with 1 × 10-4
%
of catalyst (TON ) 9.80 × 105). The catalytic activity of 6 in coupling reactions between
phenylboronic acid and 3-bromothiophene, 2-bromoanisole, and bromobenzene was also
investigated.
Ch a r t 1
In tr od u ction
There is a continuing interest in the chemistry of
phosphaferrocenes because of their use as ligands in
homogeneous catalysis.1 Many reports have emphasized
the unique combination between their strong π-acceptor
properties, which makes them attractive ligands for soft
catalytic centers, and the planar-chiral type structure
provided by the ferrocene backbone.2 On the other hand,
diphosphaferrocenes have attracted much less attention
so far, and to the best of our knowledge, no report deals
with their use as ligands in catalytic processes. Three
bonding modes of phosphaferrocenes are known (Chart
1). Classical modes A and B, in which the ligand binds
one or two metals, are by far the most widespread.
Interestingly, only one example of the chelate mode C
is known. In 1993, Cowley et al. reported the X-ray
structure of a bis-chelate silver complex of the octa-
methyldiphosphaferrocene which was obtained by an
electrochemical oxidation of the ligand on a silver
anode.3
Assuming that the nondirectional coordination of the
lone pairs would probably activate the metallic center
by weakening P-metal bonds, we launched a program
aimed at studying syntheses and reactivities of these
diphosphaferrocene chelate complexes. In this article,
we report on results obtained with palladium(0) com-
plexes.
Resu lts a n d Discu ssion
A first series of experiments conducted with the
readily available 3,3′,4,4′-tetramethyldiphosphafer-
rocene showed that the substitution scheme of the
ligand plays a decisive role in the formulation of
complexes. Whatever the experimental conditions used,
reactions of this ligand with Pd(dba)2 exclusively led to
the isolation of highly insoluble black compounds, most
probably polymeric. To improve the solubility of com-
plexes formed, we investigated the use of octa-alkyl-
substituted derivatives. Two synthetic approaches are
available for the synthesis of 1-P chloro and 1-P phenyl
(1) (a) Mathey, F. New J . Chem. 1987, 11, 585. (b) Mathey, F. Coord.
Chem. Rev. 1994, 137, 1. (c) Dillon, K. B.; Mathey, F.; Nixon, J . F.
Phosphorus: The Carbon Copy; Wiley: Chichester, 1998, and refer-
ences therein.
(2) For the use of phosphaferrocenes in homogeneous catalysis, see:
(a) Deschamps, B.; Ricard, L.; Mathey, F. J . Organomet. Chem. 1997,
548, 17. (b) Ganter, C.; Brassat, L.; Glinsbo¨ckel, C.; Ganter, B.
Organometallics 1997, 16, 2862. (c) Ganter, C.; Brassat, L. Ganter, B.
Chem. Ber./ Recl. 1997, 130, 1771. (d) Ganter, C.; Brassat, L. Ganter,
B. Tetrahedron: Asymmetry 1997, 8, 2607. (e) Ganter, C.; Glinsbo¨ckel,
C.; Ganter, B. Eur. J . Inorg. Chem. 1998, 1163. (f) Garrett, C. E.; Fu,
G. C.; J . Org. Chem. 1997, 62, 4534. (g) Qiao, S.; Fu, G. C. J . Org.
Chem. 1998, 63, 4168. (h) Qiao, S.; Hoic, D. A.; Fu, G. C. Organome-
tallics 1998, 17, 773.
(3) Atwood, D. A.; Cowley, A. H.; Dennis, S. M. Inorg. Chem. 1993,
32, 1527.
10.1021/om0005699 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 10/21/2000

4900 Organometallics, Vol. 19, No. 23, 2000
Sava et al.
Sch em e 1
tetramethyl derivatives of phosphole: an aluminum-
mediated route4 and the classical metallacycle transfer
reaction from the corresponding zirconacyclopentadiene
complex,5 a methodology that proved to be successful
for syntheses of various group 14, 15, and 16 heteroles.6
This second approach was preferred using hexyne as
starting alkyne. The synthesis of diphosphaferrocene 4
was achieved via a two-step sequence. The first step is
the synthesis of 1-chloro-tetraethylphoshole 2 from the
tetraethylzirconacyclopentadiene 17 (prepared according
to Negishi’s procedure)8 using PCl3 as transfer reagent.
Phosphole 2 is highly moisture sensitive and was
characterized only by NMR techniques. Its data com-
pare with those reported for the tetramethyl derivative.5
In the second step, 2 was reacted with an excess of
lithium to yield the phospholide anion 3 (characterized
only by 31P NMR), which subsequently converted into
diphosphaferrocene upon reaction with FeCl2 as de-
picted in Scheme 1. We also investigated the synthesis
of the tetraethylphosphaferrocene 5. Reaction of phos-
pholide 3 with the commercially available (cumene)-
cyclopentadienyliron(II) hexafluorophosphate salt yielded
5 in satisfactory yield (Scheme 1). All NMR data, mass
spectroscopy, and elemental analyses support formula-
tion proposed in both cases.
F igu r e 1. ORTEP drawings of the (a) C2 and (b) C2h
conformation of 4. Hydrogen atoms are omitted for clarity.
Ellipsoids are scaled to enclose 50% of the electron density.
The crystallographic labeling is arbitrary and different
from the numbering used for assignments of 13C NMR
spectrum.
eclipses the carbon adjacent to the P atom of the other
ring (θ ) 51.1°) and a C2h conformation in which the
two P atoms point in opposite directions (θ ) 180°). The
presence of these two conformations9 lead us to propose
that the barrier to rotation is probably very weak as
usually observed.9h Another interesting feature is the
location of two ethyl substituents located at the CR
carbon atoms in conformer C2. As can be seen in Figure
1, one methyl group of a CR ethyl substituent of each
phospholyl subunit is coplanar, probably to relieve
congestion with its direct ethyl neighbor. These par-
ticular structural arrangements are not maintained in
solution, and NMR spectra (31P, 1H, 13C) show that both
phosphorus atoms and ethyl groups are magnetically
equivalent. Apart from these particular details, the
structure of 4 deserves no special comment, and bond
distances and angles are quite similar in both confor-
mations and compare with those reported for other
diphosphaferrocenes.9 One ORTEP view of each of these
two conformation is presented in Figure 1, whereas the
most relevant bond distances and bond angles are listed
in Table 1.
Definite proof of the structure of diphosphaferrocene
4 was given by an X-ray crystallographic study. Two
different conformations are present in the unit cell: a
C2 conformation in which the P atom of each ring nearly
(4) (a) Fongers, K. S.; Hogeveen, H.; Kingma, R. F. Tetrahedron Lett.
1983, 24, 1423. (b) Nief, F.; Mathey, F.; Ricard, L.; Robert, F.
Organometallics 1988, 7, 921.
(5) Douglas, T.; Theopold, K. H. Angew. Chem., Int. Ed. Engl. 1989,
28, 1367.
(6) For pertinent articles including leading references, see: (a)
Buchwald, S. L.; Nielsen, R. B. Chem. Rev. 1988, 88, 1047. (b) Fagan,
P. J .; Nugent, W. A. J . Am. Chem. Soc. 1988, 110, 2310. (c) Broene, R.
D.; Buchwald, S. L. Science 1993, 261, 1696. (d) Fagan, O. J .; Nugent,
W. A.; Calabrese, J . C. J . Am. Chem. Soc. 1994, 116, 1880. (e) Doxsee,
K. M.; Mouser, J . K. M.; Farahi, J . B. Synlett 1992, 13. (f) Breen, T.
L.; Stephan, D. W. Organometallics 1997, 16, 365. (g) Miquel, Y.; Igau,
A.; Donnadieu, B.; Majoral, J . P.; Dupuis, L.; Meunier, P. J . Chem.
Soc., Chem. Commun. 1997, 279.
(7) Various synthetic approaches leading to 1 have been studied,
see: (a) Yoshifuji, M.; Gell, K. I.; Schwartz, J . J . Organomet. Chem.
1978, 153, C15. (b) Buchwald, S. L.; Watson, B. T.; Huffman, J . C. J .
Am. Chem. Soc. 1987, 109, 2544. (c) Takahashi, T.; Hara, R.; Nishihara,
Y.; Kotova, M. J . Am. Chem. Soc. 1996, 118, 5154.
(9) For discussions regarding conformational problems in phospha-
and diphosphaferrocenes, see: (a) De Lauzon, G.; Deschamps, B.
Fischer, J .; Mathey, F.; Mitschler, A. J . Am. Chem. Soc. 1980, 102,
994. (b) Kostic, N. M.; Fenske, R. F. Organometallics 1983, 2, 1008.
(c) Guimon, G.; Gonbeau, D.; Pfister-Guillouzo, G.; De Lauzon, G.;
Mathey, F. Chem. Phys. Lett. 1984, 104, 560. (d) Ashe, A. J ., III; Kampf,
J . W.; Pilotek, S.; Rousseau, R. Organometallics 1994, 13, 4067. (e)
Hitchcock, P. B.; Lawless, G. A.; Marziano, I. J . Organomet. Chem.
1997, 527, 305. (f) Al-Taweel, S. M. Phosphorus, Sulfur Silicon 1997,
130, 203. (g) Sava, X.; Me´zailles, N.; Maigrot, N.; Nief, F.; Ricard, L.;
Mathey, F.; Le Floch, P. Organometallics 1999, 18, 4205. (h) Su, M.-
D.; Chu, S.-Y. J . Phys. Chem. 1989, 93, 6043.
(8) Neigishi, E. I.; Cederbaum, F. E.; Takahashi, T. Tetrahedron Lett.
1986, 27, 829.

Octaethyldiphosphaferrocene
Organometallics, Vol. 19, No. 23, 2000 4901
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Liga n d 4
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 6
Conformation C2h
P1-C1
C1-C2
C2-C3
C3-C4
C4-P1
P1-Pd1
P2-Pd1
P3-Pd1
P4-Pd1
Ct-FeI
1.787(2)
1.424(3)
1.434(3)
1.424(3)
1.790(2)
2.3852(6)
2.3667(6)
2.3680(6)
2.3615(6)
1.684(3)
Pd1-Fe1
3.0382(3)
3.0573(3)
89.4(1)
100.18(2)
99.63(2)
108.95(2)
105.15(2)
122.05(2)
122.52(2)
P1′-C1
C1-C2
C2-C3
C3-C4
1.778(2)
1.418(2)
1.445(2)
1.426(2)
P1′-C4
1.773(2)
1.656(2)
89.83(7)
Pd1-Fe2
Ct-Fe
C1-P1-C4
P1-Pd1-P2
P3-Pd1-P4
P1-Pd1-P4
P2-Pd1-Pd3
P4-Pd1-P2
P1-Pd1-P3
C1-P1′-C4
Conformation C2
P2′-C13
C13-C14
C14-C15
C15-C16
1.783(2)
1.431(2)
1.432(2)
1.430(2)
C16-P2′
1.782(1)
1.662(2)
89.92(7)
Ct-Fe
C13-P2′-C16
d10 complex, the overall geometry around palladium is
nearly tetrahedral (θ ) 77.3, θ being the angle between
planes P1-Pd1-P2 and P3-Pd1-P4). Like in the Ag+
complex, both ligands act as chelate and the deviation
from the ideal in-plane coordination of the lone pair at
phosphorus is very important (θ ) 50°). This particular
bonding implies that P-Pd-P angles are unusually
large (about 100°) compared with those of complexes
with classical phosphorus bidentate ligands. Though no
theoretical calculations have been carried out yet, one
may propose that this type of nondirectional bonding
mode is probably very specific of molecules containing
sp2-hybridized phosphorus atoms. Indeed, in such com-
pounds, as well as in their heavier congeners (As, Sb,
Bi), the lone pair at the heteroatom shows a pronounced
spherical character due to a less favored orbital mixing
between 3s and 3p orbitals than between 2s and 2p as
in nitrogen compounds.10 A similar nondirectional bond-
ing mode has already been observed in a 2,2′-biphos-
phinine Cu(I) complex.11 This particular electronic
situation complicates the analysis of P-Pd bond dis-
tances, and comparisons with other known complexes
involving a classical axial bonding would be inappropri-
ate. Nevertheless, at 2.3815(6)-2.3852(6) Å, these bonds
appear to be quite long. Another interesting question
concerns the possible existence of a Pd-Fe dative
bonding between nonbonding orbitals at iron and vacant
orbitals of similar symmetry at the metal, as frequently
observed in ferrocene derivatives.12 Although there is a
close analogy between MO diagrams of both compounds9a
F igu r e 2. ORTEP drawing of one molecule of X. Hydrogen
atoms and methyl groups are omitted for clarity. Ellipsoids
are scaled to enclose 50% of the electron density. The
crystallographic labeling is arbitrary and different from the
numbering used for assignments of 13C NMR spectra.
Sch em e 2
The coordinating behavior of ligand 4 toward Ni and
Pd(0) precursors was then investigated. In the case of
Ni complexes best results were obtained using [Ni-
(COD)2] as starting material. In THF at room temper-
ature, with 2 equiv of 4, a clean exchange takes place
leading to the formation the bis(octaethyldiphospha-
ferrocene) nickel(0) complex. Unfortunately this species
turned out to be too oxygen sensitive to be isolated in
satisfactory yields, and characterizations were limited
to 31P NMR data (singlet, δ (THF) ) -107.9 ppm). More
convincing results were obtained with Pd complexes.
The reaction of 2 equiv of 4 with [Pd(dba)2] (dba )
dibenzylidene acetone) in THF at room temperature
yielded complex 6, which was isolated as a green powder
(see Experimental Section) (Scheme 2). The formulation
of 6 was unambiguously established on the basis of
NMR data. The most surprising feature is given by the
31P NMR chemical shift, which is highly shielded (δ )
-125.5, ∆δ ) 59.5 ppm) compared to other diphospha-
ferrocene complexes. Unfortunately, no comparison
could be drawn with the isoelectronic Ag+ chelate
species since NMR data were not reported.3
2
2
(degenerated e2g in ferrocenes, dx -y and dxy in diphos-
phaferrocenes), the fact that Pd-Fe bond distances in
6 (3.0282(3) and 3.0273 (3) Å) appear to be quite long
and that no orbitals at the metal (d10) are available leads
us to propose that such interactions are not found here.
A chemical consequence of this particular bonding
situation is that ligand 4 is not a very efficient chelate.
Thus, when bidentate ligands such as dppe or dppp are
reacted with complex 6, the two ligands 4 are displaced
and [Pd(dppe)2] or [Pd(dppp)2] is formed quantitatively
(eq 1).
These very particular features led us to postulate that
diphosphaferrocene 4 would certainly behave as a
(10) Schoeller, W. W. In Multiple Bonds and Low Coordination in
Phosphorus Chemistry; Regitz, M., Scherer, O. J ., Eds.; Thieme
Verlag: Stuttgart, Germany, 1990; p 5.
(11) Le Floch, P.; Ricard, L.; Mathey, F. Bull. Soc. Chim. Fr. 1996,
133, 691.
(12) (a) Seyferth, D.; Hames, B. W.; Rucker, T. G.; Cowie, M.;
Dickson, R. S. Organometallics 1983, 2, 472. (b) Akabori, S.; Kumagai,
T.; Shirahige, T.; Sato, S.; Kawazoe, K.; Tamura, D. Organometallics
1987, 6, 526. (c) Akabori, S.; Kumagai, T.; Shirahige, T.; Sato, S.;
Kawazoe, K.; Tamura, D. Organometallics 1987, 6, 2105. (d) Sato, M.;
Suzuki, K.; Akabori, S. Chem. Lett. 1987, 2239. (e) Cowie, M.; Dickson,
R. J . Organomet. Chem. 1987, 326, 269. (f) Sato, M.; Sekino, M. J .
Organomet. Chem. 1988, 344, C31.
The molecular structure of complex 6 was confirmed
by X-ray crystallography. An ORTEP view of 6 is
presented in Figure 2. Most significant bond distances
and bond angles are listed in Table 2. As expected for a

4902 Organometallics, Vol. 19, No. 23, 2000
Sava et al.
Ta ble 3. Su zu k i Cou p lin g of Ar yl Br om id esa
aryl bromide
mol % Pd t/h conversion (%)
TON
4-bromoacetophenone
4-bromoacetophenone
3-bromothiophene
3-bromothiophene
2-bromoanisole
0.0001
0.0001
0.005
0.005
0.005
0.005
0.0001
1
20
1
20
1
77
98
80
96
67
96
46
770 000
980 000
16 000
19 200
13 400
19 200
460 000
hemilabile ligand in complex 6. We therefore attempted
to test its catalytic activity on the catalyzed Suzuki
cross-coupling reaction,13 which has been thoroughly
studied with various palladium-phosphines systems.14
As a model reaction, we first investigated the coupling
between phenylboronic acid and 4-bromoacetophenone
in the presence of K2CO3 as base (eq 2).
2-bromoanisole
bromobenzene
20
1
a
Reaction conditions: 1.0 equiv of aryl bromide, 1.5 equiv of
phenylboronic acid, 2.0 equiv of K2CO3. Temperature: 110 °C. TON
are expressed in mol product (mol Pd)-1
.
complex [Pd(4)] involving the axial-coordination of only
one phosphorus atom. Recently, Fu et al. proposed that
the bulkiness of P(t-Bu)315,16 favors the formation of the
12-electron species [PdP(t-Bu)3], which can be consid-
ered as the active species in the Suzuki cross-coupling
reaction of arylboronic acid with aryl and vinyl halides
All our experiments were conducted in toluene, as
usually experimented by other authors. Various experi-
mental conditions were tested, and the best results were
obtained when preparing separately complex 6 and
adding it to the mixture of arenes (see Experimental
Section). Complex 6 was indeed very efficient as cata-
lyst, and a reproducible conversion of 77% to 4′-acetyl-
biphenyl was obtained using 1 × 10-4% of Pd catalyst
at 110 °C for 1 h (TON ) 7.70 × 105, TOF ) 213.9 (mol
product(mol Pd)-1 s-1). Prolonged heating for 20 h led
to a nearly quantitative conversion under the same
conditions. Although less effective than the remarkable
o-(tert-butylphosphino)biphenyl/Pd(OAc)2 system re-
cently developed by Buchwald et al.14a (TON ) 9.1 ×
107 for the same reaction, 24 h heating), our result
approaches the second highest TON reported by Bedford
using the tris(2,4-di-tert-butylphenyl)phosphite (TON )
8.70 × 105 for 1 h reaction).14c As stated by other
authors, the coupling between phenylboronic acid and
4′-bromoacetophenone efficiently proceeds and generally
leads to high turnovers. Consequently, we extended our
study to the coupling of phenylboronic acid to other
substrates such as 3-bromothiophene, 2-bromoanisole,
and bromobenzene (eq 2).
14i
and triflates.
In conclusion, we anticipate that diphosphaferrocene
chelate complexes may display quite an unusual cata-
lytic chemistry due to their unique combination between
electronic properties and geometry. Investigations aimed
at expanding the use of complexes such as 6 in catalyzed
Csp2-Csp2 bond formation processes as well as in other
catalytic transformations of importance are currently
underway in our laboratories.
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions were routinely per-
formed under an inert atmosphere of nitrogen by using
Schlenk techniques and dry deoxygenated solvents. Dry hex-
anes was obtained by distillation from Na/benzophenone and
dry CH2Cl2 from P2O5. Dry Celite was used for filtration.
Nuclear magnetic resonance spectra were recorded on
a
Bruker AC-200 SY spectrometer operating at 200.13 MHz for
1H, 50.32 MHz for 13C, and 81.01 MHz for 31P. Chemical shifts
are expressed in parts per million downfield from external
TMS (1H and 13C) and 85% H3PO4 (31P), and coupling constants
are given in hertz. Mass spectra were obtained at 70 eV with
a HP 5989 B spectrometer coupled a with HP 5890 chromato-
graph by the direct inlet method. The following abbreviations
are used: s, singlet; d, doublet; t, triplet; m, multiplet.
Elemental analyses were performed by the “Service d’Analyse
du CNRS”, at Gif sur Yvette, France. [Pd(dba)2] was prepared
according to a published procedure.17
Also in these cases, high TONs were recorded (for 1
h reaction), thus demonstrating the versatility of our
system. Results of these catalytic tests are summarized
in Table 3.
Tetr a eth yl-1-ch lor op h osp h ole (2). To a cooled (0 °C)
dichloromethane (50 mL) solution of complex 1 (5.78 g, 15
mmol) was added via a syringe 3.4 mL of phosphorus trichlo-
ride (15 mmol). The solution was allowed to warm, and the
formation of 2 was monitored by 31P NMR. After 20 min the
transformation was completed. After evaporation to dryness,
hexane (30 mL) was added and the resulting solution was
filtered over dried Celite. No further purification was under-
taken, and phosphole 2 was isolated as a highly moisture
sensitive yellow oil. Yield: 3.35 g (96%). 31P NMR (CDCl3): δ
73.4. 1H NMR (CDCl3): δ 1.05 (t, 6H, 3J (H-H) ) 7.60, 2 ×
CH3), 1.19 (t, 6H, 3J (H-H) ) 6.50, 2 × CH3), 2.31 (m, 4H, 2 ×
CH2), 2.47 (m, 4H, 2 × CH2). 13C NMR (CDCl3): δ 15.05 (d,
4J (P-C) ) 4.6, Me), 16.65 (d, 3J (P-C) ) 6.2, Me), 21.05 (d,
2J (P-C) ) 21.4, CH2), 22.25 (s, CH2), 144.55 (d, 1J (P-C) )
The efficiency of complex 6 is difficult to rationalize
without knowing the nature of the active species. Three
intermediates are plausible: 14-electron complexes [Pd-
(4)2] and [Pd(4)], in which the ligand coordinates pal-
ladium either through the lone pair of one P atom (η1)
or in a chelate fashion, respectively, and a 12-electron
(13) (a) Suzuki, A. In Metal-Catalyzed Cross-Coupling Reactions:
Diedrich, F., Stang, P. J ., Eds.; Wiley-VCH: Weinheim, Germany, 1998;
Chapter 2. (b) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457. (c)
Stanforth, S. P. Tetrahedron 1998, 54, 263. (d) Stu¨rmer, R. Angew.
Chem., Int. Ed. Engl. 1999, 38, 3307.
(14) For relevant references, see: (a) Wolfe, J . P.; Singer, R. A.; Yang,
B. H.; Buchwald, S. L. J . Am. Chem. Soc. 1999, 121, 9550. (b) Wolfe,
J . P.; Buchwald, S. L. Angew. Chem., Int. Ed. Engl. 1999, 38, 2413. (c)
Albisson, D. A.; Bedford, R. B.; Lawrence, S.; Scully, P. N. J . Chem.
Soc., Chem. Commun. 1998, 2095. (d) Beller, M.; Fischer, H.; Her-
rmann, W. A.; O¨ fele, K.; Brossmer, Angew. Chem., Int. Ed. Engl. 1995,
34, 1848. (e) Wallow, T. I.; Novak, B. M. J . Org. Chem. 1994, 59, 5034.
(f) Bei, X.; Crevier, T.; Guram, A. S.; J andeleit, B.; Powers, T. S.;
Turner, H. W.; Uno, T.; Weinberg, W. H. Tetrahedron Lett. 1999, 40,
3855. (g) Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. 1998, 37, 3387.
(h) Zapf, A.; Beller, M. Chem. Eur. J . 2000, 6, 1830. (i) Littke, A. F. ;
Dai, C. ; Fu, G. C. J . Am. Chem. Soc. 2000, 122, 4020.
(15) The cone angle of P(t-Bu)3 is 182°. For references see: (a)
Tolman, C. A. Chem. Rev. 1977, 77, 313. (b) Rahman, M. M.; Liu, H.-
Y.; Eriks, K.; Prock, A.; Giering, W. P. Organometallics 1989, 8, 1.
(16) This value does not represent the genuine cone angle but the
“cone” swept out by ligand 4 when it rotates around the P-Pd bond,
which was approximated to 2.25 Å.
(17) Rettig, M. F.; Maitlis, P. M. Inorg. Synth. 1990, 28, 110.

Octaethyldiphosphaferrocene
Organometallics, Vol. 19, No. 23, 2000 4903
2
Ta ble 4. Cr ysta llogr a p h ic Da ta a n d Exp er im en ta l
P a r a m eter s for 4 a n d 6
21.2, C2,5), 150.35 (d, J (P-C) ) 11.4, C3,4). MS (EI, m/z (ion,
relative intensity)): 230 (M+).
Octa eth yl-1,1′-d ip h osp h a fer r ocen e (4). To a solution of
chlorophosphole 2 (3.35 g, 14.5 mmol) in 50 mL of THF was
added about 3 equiv of lithium wire (0.3 g). The formation of
phospholide anion 3 was then monitored by 31P NMR. After 1
h, 0.5 equiv of anhydrous iron dichloride (0.9 g, 7.2 mmol) was
added at room temperature to the resulting red solution. The
mixture was then allowed to stir for 30 min at 30 °C to help
completion. The volume of solvents was then strongly reduced
to about 5 mL, and salts were precipitated by addition of 20
mL of hexanes. After filtration over dried Celite and evapora-
tion of the volatiles, the mixture was quickly purified by silica
gel flash chromatography using a 90:10 hexanes/dichloro-
methane mixture. After evaporation of solvents, complex 4 was
isolated as an orange-red powder. Yield: 2.65 g (81%). 31P
NMR (CDCl3): δ -66.0. 1H NMR (CDCl3): δ 1.08 (t, 12H,
4
6
molecular formula
molecular wt
cryst description
(habit/size (mm))
cryst syst
space group
a (Å)
C
24H40FeP2
C62H96Fe2P4Pd
1183.37
deep green needle
446.35
orange cube
(0.20 × 0.20 × 0.20) (0.18 × 0.14 × 0.10)
monoclinic
C2/c
triclinic
P1h
16.7440(5)
8.9870(2)
31.9560(11)
90.0000(17)
101.2270(16)
90.0000(17)
4716.7(2)
8
12.6860(4)
14.9980(4)
16.8110(5)
103.7540(14)
97.6040(13)
11.3291(15)
2808.13(14)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
d (g cm-3
F(000)
)
1.257
1920
0.782
150.0(1)
30.04
1.400
1252
0.980
150.0(1)
30.04
3
3J (H-H) ) 7.60, 4 × CH3), 1.09 (t, 12H, J (H-H) ) 7.50, 4 ×
µ (cm-1
T (K)
)
CH3), 2.00 (m, 8H, 2 × CH2), 2.32 (m, 4H, 4 × 1H of CH2),
2.58 (m, 4H, 4 × 1H of CH2). 13C NMR (CDCl3): δ 16.65 (s,
Me), 18.90 (m, Me), 21.40 (s, CH2), 22.65 (m, CH2), 100.40 (s,
max θ (deg)
hkl ranges
0 23; 0 12; -44 44
0 17; -21 19; -23 23
C
3,4), 102.20 (d, 1J (P-C) ) 55.9, C2,5). MS (CI, m/z (ion, relative
no. of reflns measd
no. of indep reflns
no. of reflns used
Rint
refinement type
hydrogen atoms
23 052
5537
5080
25 704
16 294
12 808
intensity)): 446 (M+). Anal. Calcd for C24H40Fe1P2: C, 64.58;
H, 9.03. Found: C, 64.80; H, 9.25.
Tetr a eth yl-1-m on op h osp h a fer r ocen e (5). The prepara-
tion of the phospholide anion 3 was carried out as described
above, starting from 2.76 g of chlorophosphole 2 (12.0 mmol).
After checking the univocal formation of 3, 1 equiv of iron(II)
cyclopentadienyl cumene hexafluorophosphate salt (4.6 g, 12.0
mmol) was added at room temperature. The mixture was then
allowed to stir for 30 min at 35 °C to help completion. The
volume of solvents was then strongly reduced to about 5 mL,
and salts were precipitated by addition of 30 mL of hexanes.
After filtration over dried Celite and evaporation of the
volatiles, the mixture was purified by silica gel flash chroma-
tography, using a 95:5 hexane/dichloromethane mixture. After
evaporation of the volatiles, complex 5 was obtained as a red
0.032
0.027
F2
F2
mixed
mixed
638
no. of params refined 260
Flack parameter
reflns/params
wR2
R1
criterion
GOF
not applicable
not applicable
20
19
0.1228
0.0380
>2σ(Ι)
1.052
0.0952
0.0392
>2σ(Ι)
1.026
difference peak/hole 0.311 (0.060)/
1.632 (0.084)/
-1.996 (0.084)
(e Å-3
)
-0.288 (0.060)
Cou p lin g R ea ct ion s of 2-Br om oa n isole, 3-Br om o-
th ioph en e, an d Br om oben zen e with P h en ylbor on ic Acid .
The same procedure was employed, with identical molar
equivalents and temperature. Only the volume of the Pd
complex solution taken and time of reaction were adapted.
X-r a y Cr ysta l Str u ctu r e Deter m in a tion s. Crystals of 4
were obtained by cooling a hexane solution of the compound
at -20 °C and crystals of 6 by a slow diffusion of hexanes into
a dichloromethane solution of the complex at room tempera-
ture. Data were collected on a Nonius Kappa CCD diffracto-
meter using an Mo KR (λ ) 0.71070 Å) X-ray source and a
graphite monochromator. Experimental details are described
in Table 4. The crystal structures were solved using SIR 9718
and SHELXL-97.19 ORTEP drawings were made using ORTEP
III for Windows.20
1
powder. Yield: 2.70 g (71%). 31P NMR (CDCl3): δ -74.9. H
NMR (CDCl3): δ 1.14 (t, 12H, 3J (H-H) ) 7.50, 2 × CH3), 2.20
(m, 4H, 2 × CH2), 2.54 (m, 2H, 2 × 1H of CH2), 2.77 (m, 2H,
2 × 1H of CH2). 13C NMR (CDCl3): δ 16.70 (s, Me), 17.59 (d,
3J (P-C) ) 11.2, Me), 23.05 (s, CH2), 23.70 (d, 2J (P-C) ) 18.4,
1
CH2), 99.50 (s, C3,4), 100.10 (d, J (P-C) ) 53.8, C2,5). MS (CI,
m/z (ion, relative intensity)): 316 (M+). Anal. Calcd for C17H25
-
FeP: C, 64.57; H, 7.97. Found: C, 64.75; H, 7.85.
Bis(octa eth yld ip h osp h a fer r ocen e)p a lla d iu m (0) Com -
p lex (6). To a solution of diphosphaferrocene 4 (89 mg, 0.2
mmol) in 5 mL of THF was added 0.5 equiv of [Pd(dba)2] (57
mg, 0.1 mmol). After 30 min stirring, the solution turned green.
The volatiles were evaporated, and dibenzylilidene acetone was
extracted with acetonitrile (3 mL). Complex 6 was isolated as
a green powder. Yield: 80 mg (80%). 31P NMR (C6D6):
δ
Ack n ow led gm en t. The authors are grateful to the
CNRS and the Ecole Polytechnique for financial support
of this research.
1
3
-125.20. H NMR (C6D6): δ 1.20 (t, 24H, J (H-H) ) 7.10, 8
3
× CH3), 1.22 (t, 24H, J (H-H) ) 7.00, 8 × CH3), 1.40 (m, 8H,
8 × 1H of CH2), 1.97 (m, 8H, 8 × 1H of CH2), 2.04 (m, 8H, 8
× 1H of CH2), 2.35 (m, 8H, 8 × 1H of CH2). 13C NMR (C6D6):
δ 17.50 (s, Me), 20.40 (s, Me), 21.60 (m, CH2), 22.05 (s, CH2),
99.85 (m, C2,5), 100.90 (s, C3,4). Anal. Calcd for C48H80Fe2P4-
Pd: C, 57.70; H, 8.07. Found: C, 57.58; H, 8.13.
Su p p or tin g In for m a tion Ava ila ble: Listings containing
tables of crystal data, atomic coordinates and equivalent
isotropic parameters, bond lengths and bond angles, anisotro-
pic displacement parameters, and hydrogen coordinates for
structures of compounds 4 and 6. This material is available
free of charge via the Internet at http://pubs.acs.org.
Gen er a l P r oced u r e for Ca ta lytic Cr oss-Cou p lin g Re-
a ction s. Cou p lin g of 4-Br om oa cetop h en on e w ith P h en -
ylbor on ic Acid . In a Schlenk flask under inert atmosphere
were added 2 equiv of octaethyldiphosphaferrocene (8.9 mg, 2
× 10-2 mmol) in 20 mL of toluene and 1 equiv of Pd(dba)2 (5.7
mg, 10-2 mmol). The solution was allowed to stir for 1 h. With
a microsyringe, 20 µL of this solution was poured in 30 mL of
toluene in a separate Schlenk flask. Then were successively
added 2.0 g (10 mmol) of 4-bromoacetophenone, 1.83 g (15
mmol) of phenylboronic acid, and 2.76 g (20 mmol) potassium
carbonate. The mixture was then allowed to stir for 1 h, at
110 °C.
OM0005699
(18) SIR97, an integrated package of computer programs for the
solution and refinement of crystal structures using single-crystal
data: Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R.
(19) Sheldrick, G. M. SHELXL-97, Programs for Crystal Structure
Analysis (Release 97-2); Universita¨t Go¨ttingen: Go¨ttingen, Germany,
1998.
(20) Farrugia, L. J . ORTEP-3 for Windows, v.1.062; J . Appl.
Crystallogr. 1997, 30, 565.