Palladium(II) complexes with 1,1′-bis(diphenylphosphino)ferrocenes [Fe(η5-C5R4PPh2)2] n+ (dppf, R = H, n = 0; dppomf, R = Me, n = 0; dppomf+, R = Me, n = 1). Synthesis, characterization, and catalytic activity in ethene methoxycarbonylation

Article abstract of DOI:10.1021/om020300k

Several palladium(II) complexes with 1,1′-bis(diphenylphosphino)octamethylferrocene (dppomf) and its oxidized form 1,1′-bis(diphenylphosphino)octamethylferrocenium (dppomf) have been synthesized and characterized by spectroscopic and electrochemical methods. For comparative purposes, analogous Pd(II) derivatives with 1,1′-bis(diphenylphosphino)ferrocene (dppf) have been also prepared. Single-crystal X-ray analyses have been carried out for the square-planar mononuclear compounds [Pd(H₂O)₂(dppf)](OTf)₂ and [Pd(H₂O)₂(dppomf)](OTf)₂ and for the binuclear complex [Pd(μ-OPF₂O)(dppomf⁺)]₂(BF₄) ₄·6CH₂Cl₂ in which two [Pd(dppomf⁺)]³⁺ moieties are held together by the oxygen atoms of two bridging PO₂F₂ groups derived from the oxidative degradation of PF₆ ions. Selected dppf and dppomf Pd(II) complexes have been employed as catalyst precursors for the methoxycarbonylation of ethene (600 psi, 1:1 CO/C₂H₄, 85 °C). It has been found that dppomf generates selective catalysts for the production of methyl propanoate, while dppf leads to a variety of low-molecular-weight oxygenates spanning from methyl propanoate to alternating oligoketones.

Full text of DOI:10.1021/om020300k

Organometallics 2002, 21, 3637-3649
3637
P a lla d iu m (II) Com p lexes w ith
1,1′-Bis(d ip h en ylp h osp h in o)fer r ocen es
[F e(η5-C5R4P P h 2)2]n + (d p p f, R ) H, n ) 0; d p p om f, R ) Me,
n ) 0; d p p om f+, R ) Me, n ) 1). Syn th esis,
Ch a r a cter iza tion , a n d Ca ta lytic Activity in Eth en e
Meth oxyca r bon yla tion
Oleg V. Gusev,* Alexander M. Kalsin, Mikhail G. Peterleitner,
Pavel V. Petrovskii, and Konstantin A. Lyssenko
N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences,
Vavilov St. 28, 119991 Moscow, Russian Federation
Novruz G. Akhmedov
Department of Chemistry, M. V. Lomonosov Moscow State University, Leninskie Gory,
119899 Moscow, Russian Federation
Claudio Bianchini,* Andrea Meli, and Werner Oberhauser*
Istituto di Chimica dei Composti Organometallici (ICCOM-CNR), Via J . Nardi 39,
50132 Firenze, Italy
Received April 16, 2002
Several palladium(II) complexes with 1,1′-bis(diphenylphosphino)octamethylferrocene
(dppomf) and its oxidized form 1,1′-bis(diphenylphosphino)octamethylferrocenium (dppomf+)
have been synthesized and characterized by spectroscopic and electrochemical methods. For
comparative purposes, analogous Pd(II) derivatives with 1,1′-bis(diphenylphosphino)ferrocene
(dppf) have been also prepared. Single-crystal X-ray analyses have been carried out for the
square-planar mononuclear compounds [Pd(H2O)2(dppf)](OTf)2 and [Pd(H2O)2(dppomf)](OTf)2
and for the binuclear complex [Pd(µ-OPF2O)(dppomf+)]2(BF4)4‚6CH2Cl2 in which two [Pd-
(dppomf+)]3+ moieties are held together by the oxygen atoms of two bridging PO2F2- groups
-
derived from the oxidative degradation of PF6 ions. Selected dppf and dppomf Pd(II)
complexes have been employed as catalyst precursors for the methoxycarbonylation of ethene
(600 psi, 1:1 CO/C2H4, 85 °C). It has been found that dppomf generates selective catalysts
for the production of methyl propanoate, while dppf leads to a variety of low-molecular-
weight oxygenates spanning from methyl propanoate to alternating oligoketones.
In tr od u ction
The wealth of Pd(II) coordination compounds and
relative catalytic applications contrasts dramatically
Since its discovery in the early 1970s,1 the metallo-
phosphine 1,1′-bis(diphenylphosphino)ferrocene (dppf)
has been widely used in organometallic chemistry and
homogeneous catalysis.2,3 Palladium(II) complexes are
relatively numerous4 and have also proved to be effec-
tive catalysts in a variety of homogeneous processes.3
Among the applications of Pd(II)-dppf complexes in
catalysis, carbon-carbon and carbon-nitrogen bond-
forming reactions are of particular importance. Repre-
sentative examples include cross-coupling reactions,5
the Heck reaction,6 carbonylation of chloroarenes,7 aryl
halide amination,8 hydroamination of alkynes,9 and the
glyoxylate-ene reaction with chiral controllers.10
(4) (a) Butler, I. R.; Cullen, W. R.; Kim, T.-J .; Rettig, S. J .; Trotter,
J . Organometallics 1985, 4, 972. (b) Brown, J . M.; Guiry, P. J ., Inorg.
Chim. Acta 1994, 220, 149. (c) Stang, P. J .; Olenyuk, B.; Fan, J .; Arif,
A. M. Organometallics 1996, 15, 904. (d) Corain, B.; Longato, B.;
Favero, G.; Ajo, D.; Pilloni, G.; Russo, U.; Creissl, F. R. Inorg. Chim.
Acta 1989, 157, 259. (e) Vasapollo, G.; Toniolo, L.; Cavinato, G.; Bigoli,
F.; Lanfranchi, M.; Pellinghelli, M. A. J . Organomet. Chem. 1994, 481,
173. (f) Dekker, G. P. C. M.; Elsevier, C. J .; Vrieze, K.; van Leeuwen,
P. W. N. M. Organometallics 1992, 11, 1598. (g) Longato, B.; Pilloni,
G.; Valle, G.; Corain, B. Inorg. Chem. 1988, 27, 956. (h) Clemente, D.
A.; Pilloni, G.; Corain, B.; Longato, B.; Tiripicchio-Camellini, M. Inorg.
Chim. Acta 1986, 115, L9. (i) Sato, M.; Shigeta, H.; Sekino, M.; Akabori,
S. J . Organomet. Chem. 1993, 458, 199 and references therein. (j) Fang,
Z.-G.; Low, P. M. N.; Ng, S.-C.; Hor, T. S. A. J . Organomet. Chem.
1994, 483, 17. (k) Li, G.; Tan, A. L.; Yip, W.-H.; Mak, T. C. W.; Hor, T.
S. A. J . Chem. Soc., Dalton Trans. 1996, 4315.
(5) (a) Hayashi, T.; Konishi, M.; Kobori, Y.; Kumada, M.; Higuchi,
T.; Hirotsu, K. J . Am. Chem. Soc. 1984, 106, 158. (b) Bosch, B. E.;
Bru¨mmer, I.; Kunz, K.; Erker, G.; Fro¨lich, R.; Kotila, S. Organome-
tallics 2000, 19, 1255. (c) Ogasawara, M.; Yoshida, K.; Hayashi, T.
Organometallics 2000, 19, 1567.
(6) Boyes, A. L.; Butler, I. R.; Quayle, S. C. Tetrahedron Lett. 1998,
39, 7763.
(1) Bishop, J . J .; Davidson, A. J . Organomet. Chem. 1971, 27, 241.
(2) (a) Rudie, A. W.; Lichtenberger, D. W.; Katcher, M. L.; Davison,
A. Inorg. Chem. 1978, 17, 2859. (b) Dierkes, P.; van Leeuwen, P. W.
N. M. J . Chem. Soc., Dalton Trans. 1999, 1519.
(3) Colacot, T. J . Platinum Met. Rev. 2001, 45, 22.
10.1021/om020300k CCC: $22.00 © 2002 American Chemical Society
Publication on Web 07/25/2002

3638 Organometallics, Vol. 21, No. 17, 2002
Gusev et al.
13C{1H} NMR spectra were recorded on Bruker AMX 400 and
Varian VXR 400 spectrometers. Chemical shifts are reported
in ppm (δ) with reference to either TMS as an internal
standard (1H and 13C{1H} NMR spectra) or 85% H3PO4 as an
external standard (31P{1H} NMR spectra). IR spectra were
obtained with a Specord M-82 spectrometer. Microanalyses
were performed in the Laboratory of Microanalysis of the A.
N. Nesmeyanov Institute of Organoelement Compounds. Con-
ductivities were measured with an ORION Model 990101
conductance cell connected to a Model 101 conductivity meter.
The conductivity data15 were obtained at sample concentra-
tions of ca. 10-3 M in nitroethane solutions. The following
compounds were synthesized according to published proce-
dures: dppf,1 PdCl2(dppf) (1a),4a,5a [Pd(H2O)2(dppf)](OTf)2 (2a),4c
dppomf,11 and cis-PdCl2(PhCN)2.16 Slow diffusion of Et2O into
a saturated CH2Cl2 solution of 2a at room temperature gave
crystals suitable for an X-ray analysis. Cyclic voltammetry
(CV) data were obtained in CH2Cl2 solutions at room temper-
ature under Ar using a PI-50-1 potentiostat. A three-electrode
cell was used with an SCE reference electrode, a glassy-carbon
working electrode, and a platinum auxiliary electrode. The
scan rate was 200 mV s-1 in each experiment. The solutions
of electroactive substance were 2 × 10-3 M in 0.1 M [Bu4N]-
PF6 as supporting electrolyte. Peak potentials were calibrated
against the ferrocene/ferrocenium (+0.46 V) couple by adding
ferrocene directly to the solution of the complexes under
investigation. Bulk electrolysis experiments were carried out
with a P-5827M potentiostat in CH2Cl2 solutions with stirring
in the presence of 0.1 M [Bu4N]BF4. In the electrolysis cell,
the cathodic and anodic areas were separated by a G4 frit.
The working electrode was a cylindrical glassy-carbon elec-
trode (S ) 35 cm2), and the auxiliary electrode was a platinum
plate. An aqueous SCE served as reference electrode, in which
the KCl phase was separated from the solution by a G4 frit.
Carbonylation reactions were performed at constant pressure
with a 250 mL stainless steel autoclave, constructed at the
ISSECC-CNR (Firenze, Italy), equipped with a magnetic drive
stirrer and a Parr 4842 temperature and pressure controller.
GC analyses were performed on a Shimadzu GC-14 A gas
chromatograph equipped with a flame ionization detector and
a 30 m (0.25 mm i.d., 0.25 µm film thickness) SPB-1 Supelco
fused silica capillary column. The product composition was
determined by using dimethyl oxalate as the internal standard.
GC/MS analyses were performed on a Shimadzu QP 5000
apparatus equipped with a column identical with that used
for GC analysis.
Ch a r t 1
with the absence of reports on Pd(II) complexes contain-
ing 1,1′-bis(diphenylphosphino)octamethylferrocene (dp-
pomf) (Chart 1).11
We have recently initiated a study of the organome-
tallic chemistry of palladium(II) with dppomf and its
oxidized form 1,1′-bis(diphenylphosphino)octameth-
ylferrocenium (dppomf+). In comparison to the dppf
analogues, a different behavior is expected for both
dppomf and dppomf+ Pd(II) complexes, in particular as
regards the influence of the ligands on the catalytic
activity, due to the steric and electronic properties of
the methyl groups and, in the case of dppomf+, also due
to the different iron oxidation state and positive charge
of the complexes.
This article describes the preparation and character-
ization of several mononuclear and binuclear Pd(II)
complexes stabilized by either dppomf or dppomf+. For
comparative purposes, dppf analogues have been syn-
thesized by known or improved procedures.
Selected dppf and dppomf Pd(II) complexes have been
scrutinized for the first time as catalyst precursors for
the methoxycarbonylation of ethene, which is an indus-
trially relevant reaction efficiently catalyzed in the
homogeneous phase by palladium(II) bis(phosphine)
complexes.12,13 Minor changes in these latter species
and/or in the experimental conditions can affect re-
markably the selectivity of the alkoxycarbonylation
reaction, leading to the formation of a variety of
products spanning from alternating polyketones to
methyl propanoate.12-14
It is shown in this work that dppomf generates
selective catalysts for methyl propanoate, while dppf
leads to a variety of low-molecular-weight oxygenates
spanning from methyl propanoate to alternating oli-
goketones.
Syn th esis of P d Cl2(d p p om f) (1b). To a solution of dppomf
(1.05 g, 1.58 mmol) in benzene (20 mL) was added a solution
of cis-PdCl2(PhCN)2 (0.61 g, 1.58 mmol) in benzene (30 mL).
The resulting solution was stirred overnight to give purple
crystals of 1b‚C6H6, which were filtered off, washed with
benzene, and dried under vacuum. Yield: 1.28 g (96%). Anal.
Calcd for C48H50Cl2FeP2Pd: C, 62.60; H, 5.48. Found: C, 62.85;
H, 5.59.
Exp er im en ta l Section
Gen er a l P r oced u r es. All experiments were performed
under Ar in solvents purified by standard methods. 1H and
(7) Ma¨gerlein, W.; Indolese, A. F.; Beller, M. Angew. Chem., Int. Ed.
2001, 40, 2856.
(8) Driver, M. S.; Hartwig, J . F. J . Am. Chem. Soc. 1996, 118, 7217.
(9) Mu¨ller, T. E.; Berger, M.; Grosche, M.; Herdtweck, E.; Schmidt-
chen, F. P. Organometallics 2001, 20, 4384.
(10) Mikami, K.; Aikawa, K. Org. Lett. 2002, 4, 99.
(11) (a) Ninoreille, S.; Broussier, R.; Amardeil, R.; Kubicki, M. M.;
Gautheron, B. Bull. Soc. Chim. Fr. 1995, 132, 128. (b) Szymoniac, J .;
Besanc¸on, J .; Dormond, A.; Mo¨ıse, C. J . Org. Chem. 1990, 55, 1429.
(c) Trouve´, G.; Broussier, R.; Gautheron, B.; Kubicki, M. M. Acta
Crystallogr. 1991, C47, 1966.
(12) (a) Robertson, R. A.; Cole-Hamilton, D. J . Coord. Chem. Rev.
2002, 225, 67. (b) Bianchini, C.; Meli, A. Coord. Chem. Rev. 2002, 225,
35.
Syn th esis of [P d (H2O)2(d p p om f)](OTf)2 (2b). To a solu-
tion of 1b (0.42 g, 0.50 mmol) in CH2Cl2 (30 mL) cooled to -78
°C was added AgOTf (0.26 g, 1.02 mmol) with stirring. This
mixture was warmed to room temperature and then was
stirred overnight. During this time the color slowly changed
from violet-blue to green. AgCl was filtered off through Celite,
and the filtrate was concentrated to 10 mL and then stored at
0 °C for 30 min. After a small amount of a yellow-green solid
was separated by filtration, 15 mL of Et2O was added to the
filtrate. Green prisms were formed on standing overnight at
room temperature, which were filtered off, washed with Et2O
and dried under vacuum. Yield: 0.42 g (78%). Suitable crystals
for X-ray analysis were obtained by slow diffusion of Et2O into
(13) (a) Drent, E.; Budzelaar, H. M. Chem. Rev. 1996, 96, 663. (b)
Drent, E.; van Broekhoven, J . A. M.; Doyle, M. J . J . Organomet. Chem.
1991, 417, 235.
(14) (a) Clegg, W.; Eastman, G. R.; Elsegood, M. R. J .; Tooze, R. P.;
Wang, X. L.; Whiston, K. J . Chem. Soc., Chem. Commun. 1999, 1877.
(b) Eastman, G. R.; Heaton, B. T.; Iggo, J . A.; Tooze, R. P.; Whyman,
R.; Zacchini, S. Chem. Commun. 2000, 609.
(15) (a) Geary, W. J : Coord. Chem. Rev. 1971, 7, 81. (b) Morassi,
R.; Sacconi, L. J . Chem. Soc. A 1971, 492.
(16) Anderson, G. K.; Lin, M. Inorg. Synth. 1989, 28, 60.

PdII-1,1′-Bis(diphenylphosphino)ferrocenes
Organometallics, Vol. 21, No. 17, 2002 3639
a saturated CH2Cl2 solution of 2b at room temperature. IR
(powder sample in KBr pellet): ν(OH2) 3440 (br m) cm-1. Anal.
Calcd for C44H48F6FeO8P2PdS2: C, 47.73; H, 4.37. Found: C,
47.62; H, 4.39. This complex behaves as a 1:1 electrolyte in
nitroethane (ΛM ) 74 Ω-1 cm2 mol-1),15 which is consistent
with the formula [Pd(H2O)(OTf)(dppomf)]OTf.
Syn th esis of [P d (H2O)2(d p p f)](OTs)2 (3a ). To a solution
of 1a (0.36 g, 0.49 mmol) in CH2Cl2 (40 mL) was added AgOTs
(0.32 g, 1.05 mmol). This mixture was stirred overnight at
room temperature to give a cherry-colored solution, which was
filtered through Celite and then concentrated to 10 mL.
Benzene (30 mL) was added, and the resulting solution was
evaporated to half volume until reddish brown needles pre-
cipitated. These were filtered off, washed with benzene and
Et2O, and dried under vacuum. Yield: 0.44 g (85%). IR (powder
sample in KBr pellet): ν(OH2) 3440 (br m) cm-1. Anal. Calcd
for C48H46FeO8P2PdS2: C, 55.48; H, 4.46. Found: C, 55.40; H,
4.24. This complex behaves as a 1:1 electrolyte in nitroethane
(ΛM ) 30 Ω-1 cm2 mol-1),15 which is consistent with the
formula [Pd(H2O)(OTs)(dppf)]OTs.
Syn th esis of [P d (H2O)2(d p p om f)](OTs)2 (3b). To a solu-
tion of 1b (0.41 g, 0.49 mmol) in CH2Cl2 (20 mL) was added
AgOTs (0.30 g, 1.07 mmol). After it was stirred overnight, this
mixture was filtered through Celite and the filtrate was
concentrated to 5 mL. The addition of 1 mL of Et2O caused
the precipitation of green crystals. An additional amount of
Et2O (5 mL) was slowly added with stirring to complete the
precipitation of the desired product, which was filtered off,
washed with Et2O, and dried under vacuum. Yield: 0.51 g
(92%). IR (powder sample in KBr pellet): ν(OH2) 3450 (br m)
cm-1. Anal. Calcd for C56H62FeO8P2PdS2: C, 58.43; H, 5.43.
Found: C, 58.22; H, 5.29. This complex behaves as a 1:1
electrolyte in nitroethane (ΛM ) 31 Ω-1 cm2 mol-1),15 which is
consistent with the formula [Pd(H2O)(OTs)(dppomf)]OTs.
Syn th esis of [P d (NCMe)2(d p p f)](BF 4)2 (4a ). AgBF4 (0.33
g, 1.70 mmol) was added to a solution of 1a (0.57 g, 0.78 mmol)
in a mixture of CH2Cl2 (40 mL) and MeCN (5 mL) cooled to
-78 °C. This mixture was warmed to room temperature slowly,
and then it was stirred for 1 h to give a deep violet solution
and an off-white precipitate of AgCl. The solution was filtered
through Celite, and the solvent was removed in vacuo. The
solid residue was dissolved in CH2Cl2 (15 mL). To the resulting
solution was added dropwise Et2O (60 mL) until dark violet-
blue crystals precipitated, which were filtered off, washed with
Et2O several times, and dried under vacuum. Yield: 0.64 g
Syn th esis of [P d (P P h 3)(d p p f)](BF 4)2 (5a ).4i,17 To a solu-
tion of 4a (0.45 g, 0.49 mmol) in CH2Cl2 (30 mL) was added
triphenylphosphine (0.13 g, 0.50 mmol). This solution was
stirred for 1 h until the color became red-brown and then was
concentrated to 15 mL. THF (40 mL) was added, and the
resulting solution was cooled to 0 °C until dark red needles
precipitated, which were filtered off, washed with THF, and
dried in vacuo. The mother liquor was evaporated to half its
original volume to collect further product. Overall yield: 0.41
g (76%). Anal. Calcd for C52H43B2F8FeP3Pd: C, 56.95; H, 3.95.
Found: C, 56.75; H, 3.89.
Syn th esis of [P d (P P h 3)(d p p om f)](BF 4)2 (5b). To a solu-
tion of 4b (0.44 g, 0.43 mmol) in CH2Cl2 (20 mL) was added
neat triphenylphosphine (0.12 g, 0.45 mmol). The resulting
mixture was stirred for 1 h, during which time the color turned
dark blue. Et2O (20 mL) was added to this solution, which was
stored at 0 °C for 15 min to give a greenish blue microcrys-
talline solid. Further Et2O (10 mL) was added to favor the
precipitation of this product, which was washed with Et2O and
dried under vacuum. Yield: 0.42 g (81%). Anal. Calcd for
C60H59B2F8FeP3Pd: C, 59.59; H, 4.92. Found: C, 59.20; H, 5.08.
Syn th esis of P d (OAc)2(d p p f) (6a ). To a solution of dppf
(1.48 g, 2.67 mmol) in benzene (50 mL) was added a solution
of Pd(OAc)2 (0.60 g, 2.67 mmol) in benzene (40 mL). The
solution was stirred overnight, during which time a yellow
precipitate was formed. The solvent was evaporated under
reduced pressure to half volume, and the brownish yellow
precipitate was filtered off and washed with benzene (2 × 5
mL). This crude product was recrystallized from CH2Cl2 (30
mL) and benzene (60 mL). Bright yellow microcrystals were
filtered off, washed with benzene, and dried under vacuum.
Yield: 1.14 g (55%). IR (CH2Cl2): ν(OAc) 1612, 1590, 1371,
1319 cm-1. Anal. Calcd for C38H34FeO4P2Pd: C, 58.60; H, 4.40.
Found: C, 58.85; H, 4.45. This complex behaves as a nonelec-
trolyte in nitroethane (ΛM ) 6 Ω-1 cm2 mol-1).15
Rea ction of 3a w ith Ce(NO3)6(NH4)2. To a solution of 3a
(0.20 g, 0.20 mmol) in acetone (20 mL) were added sodium
tetrafluoroborate (0.1 g, 0.9 mmol) and cerium(IV) ammonium
nitrate (0.10 g, 0.19 mmol). The resulting mixture was stirred
at room temperature for 15 min, and then the solvent was
removed under reduced pressure. The residue was extracted
with CH2Cl2 (5 × 10 mL), and the resulting solution was
filtered through a glass frit and then concentrated to 5 mL to
give red crystals of Pd(NO3)2(dppf)‚CH2Cl2 (7) that were
filtered off, washed with CH2Cl2 (5 mL), and dried under
vacuum. Yield: 0.12 g (73%). IR (CH2Cl2): ν(NO3) 1487, 1275
cm-1. Anal. Calcd for C35H30Cl2FeN2O6P2Pd: C, 48.33; H, 3.48;
N, 3.22. Found: C, 48.54; H, 3.46; N, 3.22.
(90%). IR (Nujol, KBr): ν(NCMe) 2322 (w), 2292 (w) cm-1
;
ν(BF4) 1054 (s) cm-1. Anal. Calcd for C38H34B2F8FeN2P2Pd: C,
49.80; H, 3.74; N, 3.06. Found: C, 49.70; H, 3.71; N, 2.91. This
complex behaves as a 1:2 electrolyte in nitroethane (ΛM ) 139
Ω-1 cm2 mol-1).15
Syn th esis of [(d p p om f+)]P F 6 (8a ) a n d [(d p p om f+)]BF 4
(8b). [FeCp2]PF6 (0.39 g, 1.18 mmol) was added to a solution
of dppomf (0.80 g, 1.20 mmol) in CH2Cl2 (20 mL). The resulting
solution was stirred for 1 h, and then the solvent was
evaporated to dryness. The solid residue was filtered off,
washed repeatedly with benzene until the filtrate was color-
less, and dried under vacuum to give green microcrystals of
8a . Yield: 0.95 g (99%). Anal. Calcd for C42H44F6FeP3: C,
Syn th esis of [P d (NCMe)2(d p p om f)](BF 4)2 (4b). A solu-
tion of AgBF4 (0.44 g, 2.26 mmol) in MeCN (10 mL) was added
with stirring to a solution of PdCl2(MeCN)2 (0.29 g, 1.12 mmol)
in MeCN (10 mL). After 30 min of stirring, this mixture was
filtered through a glass frit and the filtrate was then added
dropwise to a solution of dppomf (0.74 g, 1.11 mmol) in CH2-
Cl2 (20 mL) cooled to -40 °C. The resulting mixture was
warmed to room temperature and then was stirred overnight.
The green slurry obtained was filtered through a glass frit to
remove some black product. The solvent was evaporated, and
the solid residue was dissolved in CH2Cl2 (20 mL). After this
solution was filtered through Celite, the filtrate was concen-
trated to 10 mL. The addition of 10 mL of Et2O led to the
formation of an orange sticky solid that was separated by
filtration. Treatment of the mother liquor with 5 mL of Et2O
gave green crystals that were filtered off, washed with Et2O,
and dried under vacuum. Yield: 0.55 g (50%). IR (Nujol,
1
62.13; H, 5.47. Found: C, 62.24; H, 5.52. H NMR (CD3NO2)
for 8a : δ 15.2 (br s, 8H, o-Ph), 9.0 (br s, 8H, m-Ph), 7.9 (s, 4H,
p-Ph), -38.6 (br s, 12H, C5Me4), -40.3 (br s, 12H, C5Me4). 31P-
{1H} NMR (CD3NO2) for 8a : δ 25.7 (br s, 2P, PPh2), -143.7
(sept, 1P, J (PF) ) 707 Hz, PF6-).
Complex 8b was prepared analogously from dppomf (0.49
g, 0.73 mmol) and [FeCp2]BF4 (0.20 g, 0.73 mmol). Yield: 0.54
g (98%). Anal. Calcd C42H44BF4FeP2: C, 66.91; H, 5.89.
Found: C, 66.81; H, 5.84.
Syn th esis of [P d Cl2(d p p om f+)]P F 6 (9a ) a n d [P d Cl2-
(d p p om f+)]BF 4 (9b). To a solution of 8a (0.34 g, 0.40 mmol)
in CH2Cl2 (20 mL) was added a solution of cis-PdCl2(PhCN)2
KBr): ν(NCMe) 2326 (w), 2299 (w) cm-1; ν(BF4) 1055 (s) cm-1
.
Anal. Calcd for C46H50B2F8FeN2P2Pd: C, 53.69; H, 4.90; N,
2.72. Found: C, 53.43; H, 4.82; N, 2.68. This complex behaves
as a 1:2 electrolyte in nitroethane (ΛM ) 129 Ω-1 cm2 mol-1).15
(17) Sato, M.; Sekino, M.; Akabori, S. J . Organomet. Chem. 1988,
344, C31.

3640 Organometallics, Vol. 21, No. 17, 2002
Gusev et al.
(0.16 g, 0.42 mmol) in CH2Cl2 (10 mL). The resulting mixture
was stirred overnight until yellowish brown crystals of 9a ‚
CH2Cl2 precipitated. These were filtered off, washed with CH2-
Cl2, and dried under vacuum. Yield: 0.36 g (91%). Anal. Calcd
for C43H46Cl4F6FeP3Pd: C, 48.10; H, 4.32. Found: C, 48.35;
H, 4.29.
Complex 9b was prepared analogously from 8b (0.41 g, 0.54
mmol) and cis-PdCl2(PhCN)2 (0.21 g, 0.55 mmol). Yield: 0.40
g (92%). Anal. Calcd for C42H44BCl2F4FeP2Pd: C, 54.25; H,
4.77. Found: C, 54.28; H, 4.71.
Syn th esis of [P d (µ-OP F 2O)(d p p om f+)]2(OTf)4 (10a ) a n d
[P d (H2O)2(d p p om f+)](OTf)2(BF 4) (11). To a solution of 9a
(0.30 g, 0.30 mmol) in nitromethane (20 mL) was added solid
AgOTf (0.16 g, 0.62 mmol). This mixture was stirred overnight
at room temperature. After AgCl was filtered off through
Celite, the solvent was evaporated under reduced pressure and
the solid product was dissolved in CH2Cl2 (20 mL) to give a
solution which was further filtered through Celite to remove
any trace of Ag(I) salts. The filtrate was stored at 0 °C
overnight to give yellow-brown crystals of 10a ‚CH2Cl2, which
were filtered off, washed with CH2Cl2 and dried in a vacuum.
Yield 0.25 g (71%). Anal. Calcd for C89H90Cl2F16Fe2O16P6-
Pd2S4: C, 44.01; H, 3.73. Found: C, 43.67; H, 3.99.
product obtained was filtered off, washed with CH2Cl2 (5 mL),
and dried under reduced pressure to give [Ag (dppomf)](BF4)2
(13). Yield: 0.78 g (70%). Anal. Calcd for C42H44B2FeF8P2Ag:
C, 53.23; H, 4.64. Found: C, 53.00; H, 4.50. This complex
behaves as a 1:2 electrolyte in nitroethane (ΛM ) 141 Ω-1 cm2
mol-1).15 1H NMR (CD3NO2): δ -46.3 (br s, 12H), -34.5 (br s,
12H), 8.4 (s, 4H, p-Ph), 9.6 (br s, 16H, o-Ph + m-Ph). 31P{1H}
NMR (CD3NO2): δ -65.2 (br d, ω1/2 ) 100 Hz, J (AgP) ) 472
Hz).
Electr och em ica l Oxid a tion of 1a . The oxidation of 1a
(0.20 g, 0.027 mmol) was carried out at a glassy-carbon
electrode (+0.7 V) in CH2Cl2 (25 mL) (0.1 M [Bu4N]BF4). The
initial current was 60 mA. After consumption of one electron
(Qexptl ) 27.3 C, Qtheor ) 26.4 C) the current decreased to 5
mA. A greenish blue microcrystalline product precipitated on
the glassy-carbon electrode.
Electr och em ica l Oxid a tion of 2a . The oxidation of 2a
(0.10 g, 0.010 mmol) was carried out at a glassy-carbon
electrode (+1.0 V) in CH2Cl2 (25 mL) (0.1 M [Bu4N]BF4). The
initial current was 18 mA. After consumption of one electron
(Qexptl ) 10.8 C, Qtheor ) 9.8 C) the current decreased to 4 mA.
The color of the solution changed from violet to dark green.
Electr och em ica l Oxid a tion of 3a . The oxidation of 3a
(0.20 g, 0.020 mmol) was carried out at a glassy-carbon
electrode (+0.9 V) in CH2Cl2 (25 mL) (0.1 M [Bu4N]BF4). The
initial current was 55 mA. After consumption of one electron
(Qexptl ) 21.0 C, Qtheor ) 19.2 C) the current decreased to 8
mA. The color of the solution changed from violet to dark
green.
The procedure above was used also to prepare 11 from 9b
(0.37 g, 0.40 mmol) and AgOTf (0.21 g, 0.82 mmol). Yield 0.42
g (88%). ΛM: 107 Ω-1 cm2 mol-1. Anal. Calcd for C44H48BF10
-
FeO8P2PdS2: C, 44.26; H, 4.05. Found: C, 44.16; H, 4.00.
Syn th esis of [P d (µ-OP F 2O)(d p p om f+)]2(BF 4)4 (10b). To
a solution of 9a (0.56 g, 0.56 mmol) in MeCN (20 mL) cooled
to -78 °C was added AgBF4 (0.23 g, 1.18 mmol). This mixture
was warmed to room temperature, and the solvent was
removed under reduced pressure. The residue was dissolved
in CH3NO2 (20 mL) to give a slurry that was filtered through
a short Celite column. The filtrate was evaporated under
reduced pressure to obtain a solid residue that was dissolved
in CH2Cl2 (20 mL). This solution was rapidly passed through
Celite. Yellow-brown crystals of 10b began almost immediately
to form from the filtrate. When the precipitation was complete,
the product was filtered off, washed with CH2Cl2, and dried
under vacuum. Yield: 0.39 g (67%). Crystals of 10b‚6CH2Cl2
suitable for an X-ray structure analysis were obtained by slow
crystallization from diluted CH2Cl2 solutions of 10b at room
temperature. Anal. Calcd for C90H100B4Cl12F20Fe2O4P6Pd2: C,
41.50; H, 3.87. Found: C, 41.32; H, 3.79.
Ca ta lytic Ca r bon yla tion of Eth en e in Meth a n ol. Typi-
cally, MeOH (100 mL) was introduced by suction into a 250
mL autoclave, previously evacuated by a vacuum pump,
containing 0.01 mmol of catalyst precursor along with the
desired amounts of 1,4-benzoquinone (BQ) and/or p-toluene-
sulfonic acid (TsOH). The autoclave was then pressurized with
1:1 CO/C2H4 (600 psi) at room temperature and heated to 85
°C. As soon as the reaction mixture in the autoclave reached
the desired temperature, stirring (1400 rpm) was applied for
the desired time (1-3 h). A constant pressure was maintained
all over the experiments by a continuous feeding of the same
mixture of CO/C2H4 from a gas reservoir. The reaction was
stopped by cooling the autoclave to room temperature by
means of an ice-acetone bath. After the unreacted gases were
released, the insoluble ethene/CO copolymer, if any, was
filtered off, washed with cold MeOH, and dried overnight
under reduced pressure at 70 °C. The filtrate was analyzed
by GC using dimethyl oxalate as the internal standard.
Ch a r a cter iza tion of th e Cop olym er . The elemental
analysis values are in agreement with an ethene/CO ratio of
1. Spectroscopically (IR and NMR), the polyketones obtained
are identical with those previously isolated in methanol and
for which a perfectly alternating structure was assigned.12,13
Rea ction of d p p om f w ith 1 Equ iv of AgOTf. To a yellow
solution of dppomf (0.24 g, 0.36 mmol) in CH2Cl2 (20 mL)
cooled to -78 °C was added AgOTf (0.09 g, 0.35 mmol). A green
solution was obtained. This mixture was stirred for 2 days at
room temperature to give a yellow solution. The solvent was
evaporated, and the residue was dissolved in benzene (50 mL).
The resulting solution was filtered with a glass frit to remove
some green crystals. The filtrate was concentrated to 5 mL to
obtain a yellow-orange solid product. This was filtered off,
washed with benzene (5 mL), and dried in vacuo to give Ag-
1
In particular, the H and 13C{1H} NMR spectra of the samples
show the contemporaneous presence of both ketonic and ester
end groups. Anal. Calcd for (COCH2CH2)n: C, 64.27; H, 7.19.
Found: C, 64.21; H, 7.16. IR (powder sample in KBr pellet):
3391 (w), 2912 (m), 1694 (vs), 1408 (s), 1333 (s), 1259 (m), 1056
(s), 811 (m), 592 (m) cm-1. 1H NMR (HFIP-d2): δ 3.73 (s, CH2-
CO2CH3), 2.83 (s, CH2COCH2), 2.55 (q, J (HH) ) 7.4 Hz,
COCH2CH3), 1.09 (t, J (HH) ) 7.4 Hz, COCH2CH3). 13C{1H}
NMR (HFIP/CDCl3, 9:1, v:v): δ 217.2 (COCH2CH3), 213.0
(CH2COCH2), 176.6 (CH2CO2CH3), 52.6 (CH2CO2CH3), 36.1
(CH2COCH2), 27.9 (CH2CO2CH3), 7.1 (COCH2CH3).
X-r a y Da ta Collection a n d Str u ctu r e Deter m in a tion
of 2a ,b a n d 10b‚6CH2Cl2. Single crystals were analyzed with
a Bruker Smart 1000 CCD diffractometer. X-ray diffraction
data were collected at 110 K. A set of 994 reflections for 2a
and 10b and a set of 100 reflections for 2b with 4° e θ e 25°
were used to determine the lattice constants. Atomic scattering
with anomalous dispersion corrections were taken from ref 19.
All structures were solved by direct methods and refined by
(OTf)(dppomf) (12). Yield: 0.25 g (75%). Anal. Calcd for C43H44
-
FeF3O3P2Ag: C, 54.13; H, 4.61. Found: C, 54.01; H, 4.57. This
complex behaves as a nonelectrolyte in nitroethane (ΛM ) 8
1
Ω-1 cm2 mol-1). H NMR (CDCl3): δ 1.33 (br s, 12H), 1.62 (br
s, 12H), 7.35 (br s, 12H, p-Ph + m-Ph), 7.60 (br s, 8H, o-Ph).
31P{1H} NMR (CDCl3): δ -4.3 (d, J (107AgP) ) 458 Hz,
J (109AgP) ) 526 Hz).18
Rea ction of d p p om f w ith 2 Equ iv of AgBF 4. To a
solution of dppomf (0.78 g, 1.17 mmol) in CH2Cl2 (20 mL) was
added AgBF4 (0.47 g, 2.41 mmol), and the mixture was stirred
overnight to give a green solution that separated a green
precipitate. The slurry was filtered through a glass frit, and
the solid product was washed with CH2Cl2 (4 × 10 mL). The
filtrate was concentrated to 10 mL, and the microcrystalline
(18) Barrow, M.; Bu¨rgi, H.-B.; Camalli, M.; Caruso, F.; Fischer, E.;
Venanzi, L. M.; Zambonelli, L. Inorg. Chem. 1983, 22, 2356.

PdII-1,1′-Bis(diphenylphosphino)ferrocenes
Organometallics, Vol. 21, No. 17, 2002 3641
Sch em e 1
Sch em e 3
Sch em e 2
(BF4)2 (5b), both containing an Fe-Pd bond, were
conveniently prepared by reaction of the bis-MeCN
precursors with PPh3 in CH2Cl2 (Scheme 3).
The synthesis20 of [Pd(OAc)2{Fe(η5-C5R4PPh2)2}] (6a ,
R ) H; 6b, R ) Me) by treatment of dichloride precur-
sors with Pd(OAc)2 in benzene was unexpectedly com-
plicated by the formation of many different products,
especially in the case of the permethylated complex 6b.
The dppf derivative 6a is appreciably more stable than
the dppomf analogue and could be isolated, although
in moderate yield (55%). As was reported by Amatore
and co-workers for Pd(PPh3)2(OAc)2,21 the degradation
of the acetate compounds might be due to intramolecu-
lar nucleophilic attack of the acetate on the phosphine
donor, followed by phosphine oxide formation.
full-matrix least squares against F2 using the SHELXTL-97
package. The data were corrected for Lorentz-polarization
effects. All of the non-hydrogen atoms were found through a
series of Fo Fourier maps and refined initially with isotropic
thermal parameters and finally with anisotropic thermal
parameters. The hydrogen atoms of the phenyl groups were
introduced at calculated positions and refined by applying the
riding model. The hydrogen atoms of the water molecules and
the methyl groups were located from
a Fourier density
All the complexes obtained were unambiguously
characterized by elemental analysis and NMR spectros-
copy (Tables 1 and 2). Moreover, the molecular struc-
tures of complexes 2a ,b were determined by single-
crystal X-ray diffractometry (see below).
synthesis and refined afterwards by applying a riding model.
Resu lts a n d Discu ssion
Syn th esis of P a lla d iu m (II) Com p lexes w ith d p p f
a n d d p p om f. Common synthetic methods developed to
prepare PdII-dppf complexes can be successfully applied
to obtain the dppomf analogues. Therefore, the straight-
forward reaction of cis-PdCl2(PhCN)2 with dppomf in
benzene gave the dichloride complex PdCl2(dppomf)
(1b), analogous to PdCl2(dppf)4a,5a (1a ).
As a general trend, the chemical shifts of the chemi-
cally equivalent -PPh2 groups reflect the charge of the
complex: the 31P resonances of the neutral dppf deriva-
tives fall in the range 30-38 ppm, while the dicationic
complexes exhibit singlets at lower field between 43 and
48 ppm. The dppomf complexes behave similarly (Table
1). It may be worth commenting that the 31P resonances
of the dppomf complexes are shifted to low field by 18-
26 ppm as compared to the dppf analogues. This effect
has been previously observed for Pd(II) complexes
containing 1,3-diphenylphosphino-like ligands and has
been attributed to the influence exerted by methyl
groups on the s orbital electron density of R-phosphorus
atoms.22 Besides the dppomf phosphorus atoms, 5b
contains a PPh3 ligand, and therefore the 31P{1H} NMR
spectrum contains a doublet (2P) and a triplet (1P). The
chemical shift of the ferrocenyl phosphorus nuclei is
remarkably high field shifted (-22.8 ppm), which is in
line with the presence of an Fe-Pd bond.4i,17
[Pd(H2O)2(dppomf)](OTf)2 (2b) was prepared using a
procedure previously designed for [Pd(H2O)2(dppf)]-
(OTf)2 (2a ): i.e., treatment of 1b with a chloride sca-
venger in a noncoordinating solvent (Scheme 1).4c The
tosylate complexes 3a ,b were synthesized analogously.
[Pd(NCMe)2(dppf)](BF4)2 (4a ) was straightforwardly
prepared in MeCN solution using a Ag(I) salt as chloride
scavenger (Scheme 2). This procedure could not be used
to prepare the dppomf derivative [Pd(NCMe)2(dppomf)]-
(BF4)2 (4b) because of the formation of paramagnetic
byproducts, most likely containing “Pd(dppomf+)” spe-
cies, that were difficult to separate from the desired
product. However, 4b was successfully obtained in pure
form by an alternative procedure involving stoichiomet-
ric addition of dppomf to a MeCN solution of [Pd-
(MeCN)4](BF4)2 generated in situ by treatment of PdCl2-
(MeCN)2 with AgBF4.
Typical of all 13C{1H} NMR spectra, signals are
multiplets corresponding to second-order ABX spin
(20) Neo, Y. C.; Vittal, J . J .; Hor, T. S. J . Chem. Soc., Dalton Trans.
2002, 337.
(21) (a) Amatore, C.; J utand, A.; M’Barki, M. A. Organometallics
1992, 11, 3009. (b) Amatore, C.; Carre, E.;. J utand, A.; M’Barki, M.
A.; Meyer, G. Organometallics 1995, 14, 5605.
The known complex [Pd(PPh3)(dppf)](BF4)2 (5a )4i,17
and the novel dppomf derivative [Pd(PPh3)(dppomf)]-
(19) (a) Wilson, A. J . C. International Tables for X-ray Crystal-
lography; Kluwer: Dordrecht, The Netherlands, 1992; p 219. (b)
Wilson, A. J . C. International Tables for X-ray Crystallography;
Kluwer: Dordrecht, The Netherlands, 1992; p 500.
(22) (a) Bianchini, C.; Lee, H. M.; Meli, A.; Moneti, S.; Vizza, F.;
Fontani, M.; Zanello, P. Macromolecules 1999, 32, 4183. (b) Phosphorus-
31 NMR Spectroscopy in Stereochemical Analysis; Verkade, J ., Quin,
L. D., Eds.; VCH: Deerfield Beach, FL, 1987; p 539.

3642 Organometallics, Vol. 21, No. 17, 2002
Gusev et al.
Ta ble 1. Selected 1H a n d 31P {1H} NMR Sp ectr a l Da ta for P d (II) Com p lexes w ith th e Dip h osp h in es d p p f,
d p p om f, a n d d p p om f+ a
1H NMR chem shift (multiplicity, J )
31P{1H} NMR
complex
C5R4
PPh2
Pd-X
chem shift (multiplicity, J )
48.1 (s)
2a
4.60 (s, 4H)
4.61 (s, 4H)
7.78 (dd, 8H, J ) 13.2, 7.6, o-Ph)
7.49 (dd, 8H, J ) 7.6, 7.2, m-Ph)
7.63 (t, 4H, J ) 7.2, p-Ph)
7.92 (dd, 8H, J ) 12.4, 7.6, o-Ph)
7.41 (dd, 8H, J ) 8.0, 7.2, m-Ph)
7.53 (t, 4H, J ) 7.2, p-Ph)
3a b
4a
4.40 (s, 4H)
4.57 (s, 4H)
44.9 (s)
43.4 (s)
4.56 (s, 4H)
4.66 (s, 4H)
7.77 (dd, 8H, J ) 13.2, 7.6, o-Ph)
7.51 (dd, 8H, J ) 7.6, 7.2, m-Ph)
7.61 (t, 4H, J ) 7.2, p-Ph)
1.85 (s, 6H, MeCN)
5a
6a
4.34 (s, 4H)
5.61 (s, 4H)
4.39 (s, 4H)
4.42 (s, 4H)
7.2-7.5 (m, 35H)
c
-15.9 (d, 2P, J ) 14.6, PPh2)
37.0 (t, 1P, J ) 14.6, PPh3)
30.4 (s)
7.93 (dd, 8H, J ) 12.4, 7.6, o-Ph)
7.40 (ddd, 8H, J ) 8.0, 7.2, 2.0, m-Ph)
7.78 (dt, 4H, J ) 7.2, 2.0, p-Ph)
7.77 (dd, 8H, J ) 12.4, 7.6, o-Ph)
7.48 (dd, 8H, J ) 7.6, 7.2, m-Ph)
7.59 (t, 4H, J ) 7.2, p-Ph)
8.27 (br dd, 8H, o-Ph)
7.42 (br dd, 8H, m-Ph)
7.40 (br t, 4H, p-Ph)
8.13 (br dd, 8H, o-Ph)
7.62 (br dd, 8H, m-Ph)
7.64 (br t, 4H, p-Ph)
8.20 (br dd, 8H, o-Ph)
7.56 (br dd, 8H, m-Ph)
7.52 (br t, 4H, p-Ph)
8.17 (br dd, 8H, o-Ph)
1.39 (br s, 6H, AcO)
7d
4.40 (s, 4H)
4.51 (s, 4H)
38.2 (s)
50.6 (s)
69.1 (s)
63.0 (s)
69.3 (s)
1b
1.21 (s, 12H)
1.51 (s, 12H)
2be
3bf
4b
1.45 (s, 12H)
1.56 (s, 12H)
1.42 (s, 12H)
1.55 (s, 12H)
1.41 (s, 12H)
1.55 (s, 12H)
1.96 (s, 6H, MeCN)
7.61 (br dd, 8H, m-Ph)
7.64 (br t, 4H, p-Ph)
5b
0.88 (s, 12H)
1.72 (s, 12H)
-16.6 (br s, 12H)
-38.1 (br s, 12H)
7.2 -7.5 (m, 35H)
c
-22.8 (d, 2P, J ) 20.3, PPh2)
19.9 (t, 1P, J ) 20.3, PPh3)
-82.4 (br s, 2P, PPh2)
9a ,bg
13.8 (br s, 8H, o-Ph)
9.3 (br s, 8H, m-Ph)
8.3 (s, 4H, p-Ph)
-
h
-143.5 (sept, 1P, J ) 707, PF6
)
10a g
10bg
11g
-10.9 (br s, 12H)
-39.4 (br s, 12H)
12.0 (br s, 8H, o-Ph)
8.7 (br s, 8H, m-Ph)
7.9 (s, 4H, p-Ph)
11.8 (br s, 8H, o-Ph)
8.7 (br s, 8H, m-Ph)
7.9 (s, 4H, p-Ph)
12.2 (br s, 8H, o-Ph)
8.9 (br s, 8H, m-Ph)
8.1 (s, 4H, p-Ph)
-145.5 (br s, 2P, PPh2)
-
-26.9 (br t, 1P, J ) 965, PO2F2
)
)
-10.8 (br s, 12H)
-40.2 (br s, 12H)
-148.8 (br s, 2P, PPh2)
-32.4 (br t, 1P, J ) 967, PO2F2
-
-10.9 (br s, 12H)
-40.0 (br s, 12H)
-148.6 (s)
a
All spectra were recorded at room temperature in CDCl3 solutions unless otherwise stated. Chemical shifts are reported in ppm (δ)
31P{1H} NMR, downfield
relative to TMS, referenced to the chemical shifts of residual solvent resonances (1H NMR) or 85% H3PO4
(
values are assumed as positive). Key: s, singlet; d, doublet; t, triplet; sept, septuplet; m, multiplet; br, broad. Coupling constants (J ) are
b
in hertz. OTs resonances: 2.24 (s, 6H, Me), 7.37 (d, 4H, J ) 8.0), 6.81 (d, 4H, J ) 8.0). c The hydrogen resonances of PPh3 are masked
d
g
by those of PPh2. CH2Cl2 singlet at 5.31. e In CD2Cl2. f OTs resonances: 2.26 (s, 6H, Me), 7.68 (br s, 4H), 6.99 (br s, 4H). In CD3NO2.
h
PF6 signal for 9a .
systems due to the Cp carbon atoms and to the ipso,
ortho, and meta phenyl carbon atoms (Table 2).11a,23
Cyclic Volta m m etr y Stu d y of 1a ,b-5a ,b a n d 6a .
The electrochemistry of Pd(II) complexes with dppf has
been scarcely investigated,4d while no report concerning
dppomf compounds is available in the relevant litera-
ture. Therefore, we have examined the cyclic voltam-
metry behavior of various dppf and dppomf Pd(II)
complexes in CH2Cl2 solution. The results obtained are
reported in Table 3.
potentials than those of the dicationic complexes 2a ,b-
4a ,b. The reduction potentials of the latter complexes
were close to each other and did not show any depen-
dence on either the nature of the coligand/counterion
or the presence of methyl groups in the ferrocenyl
moiety. Unlike 1a ,b-4a ,b, the complexes 5a ,b under-
went two chemically and electrochemically reversible
one-electron-reduction steps to form Pd(0) complexes.
These were quite stable in solution under Ar but
(26) (a) Bowyer, W. J .; Merkert, J . W.; Geiger, W. E.;. Rheingold,
A. L Organometallics 1989, 8, 191. (b) Lee, S.; Lovelace, S. R.; Cooper,
N. J . Organometallics 1995, 14, 1974. (c) Astruc, D.; Lacoste, M.;
Toupet, L. J . Chem. Soc., Chem. Commun. 1990, 558. (d) Yarmolenko,
A. I.; Kukharenko, S. V.; Novikova, L. N.; Strelets, V. V. Izv. Akad.
Nauk SSSR, Ser. Khim. 1995, 1347. (e) Bowyer, W. J .;. Geiger, W. Ε.
J . Am. Chem. Soc. 1985, 107, 5657. (f) Nielson, R. M.; Weaver, M. J .
Organometallics 1989, 8, 1636. (g) Merkert, J .; Nielson, R. M.; Weaver,
M. J .; Geiger, W. E. J . Am. Chem. Soc. 1989, 111, 7084. (h) Pierce. D.
T.; Geiger, W. E. J . Am. Chem. Soc. 1992, 114, 6063.
All the Pd(II) complexes showed an irreversible two-
electron reduction centered at the palladium met-
al.4d,22a,24-27 As expected, the neutral complexes 1a ,b
and 6a were reduced at significantly less positive
(23) Sørensen, S.; J acobsen, H. J . Org. Magn. Reson. 1977, 9, 101.
(24) Viotte, M.; Gautheron, B.; Kubicki, M. M.; Mugnier, Y.; Parish.
R. V. Inorg. Chem. 1995, 34, 3465.
(25) Pilloni, G.; Longato, B.; Corain, B. J . Organomet. Chem. 1991,
420, 57.
(27) Bianchini, C.; Lee, H. M.; Meli, A.; Moneti, S.; Patinec, V.;
Petrucci, G.; Vizza, F. Macromolecules 1999, 32, 3859.

PdII-1,1′-Bis(diphenylphosphino)ferrocenes
Organometallics, Vol. 21, No. 17, 2002 3643
Ta ble 2. Selected 13C{1H} NMR Sp ectr a l Da ta for P d (II) Com p lexes w ith th e Dip h osp h in es d p p f a n d
d p p om fa
chem shift (multiplicity, J )
complex
C5R4
PPh2
Pd-X
1
2a b
78.44 (t, J ) 5.9, R-C)
76.27 (t, J ) 4.7, â-C)
127.85 (m, | J + 2J | ) 67.6, ipso-Ph)
134.48 (t, J ) 6.2, o-Ph)
129.71 (t, J ) 6.1, m-Ph)
133.57 (s, p-Ph)
1
69.45 (m, | J + 2J | ) 75.4, ipso-C)
1
3a
77.61 (t, J ) 5.6, R-C)
74.88 (t, J ) 4.1, â-C)
128.31 (m, | J + 2J | ) 66.1, ipso-Ph)
134.37 (t, J ) 5.5, o-Ph)
128.81 (t, J ) 5.7, m-Ph)
132.25 (s, p-Ph)
1
70.65 (m, | J + 2J | ) 73.2, ipso-C)
1
4a
78.35 (t, J ) 6.2, R-C)
76.13 (t, J ) 4.7, â-C)
128.10 (m, | J + 2J | ) 60.4, ipso-Ph)
1.97 (s, MeCN)
122.77 (s, MeCN)
133.70 (t, J ) 6.2, o-Ph)
129.53 (t, J ) 6.1, m-Ph)
133.20 (s, p-Ph)
1
68.25 (m, | J + 2J | ) 74.8, ipso-C)
1
6a
76.41 (d, J ) 10.9, R-C)
73.80 (d, J ) 7.7, â-C)
130.91 (m, | J + 2J | ) 55.1, ipso-Ph)
22.9 (br s, MeCOO)
177.5 (br s, MeCOO)
134.94 (d, J ) 5.9, o-Ph)
128.82 (d, J ) 5.8, m-Ph)
131.11 (d, J ) 1.2, p-Ph)
1
76.41 (m, | J + 2J | ) 60.2, ipso-C)
1
3bb
89.45 (t, J ) 4.8, R-C)
86.80 (t, J ) 4.0, â-C)
129.78 (m, | J + 2J | ) 64.8, ipso-Ph)
135.08 (t, J ) 6.0, o-Ph)
129.42 (t, J ) 5.6, m-Ph)
132.59 (s, p-Ph)
1
75.32 (m, | J + 2J | ) 69.2, ipso-C)
12.50 (s, Me)
8.60 (s, Me)
4bb
5b
90.51 (t, J ) 6.2, R-C)
∼129 (overlapped, ipso-Ph)
134.94 (br s, o-Ph)
129.78 (br s, m-Ph)
133.25 (s, p-Ph)
2.55 (s, MeCN)
123.68 (s, MeCN)
87.61 (t, J ) 4.7, â-C)
1
76.04 (m, | J + 2J | ) 78.8, ipso-C)
12.36 (s, Me)
8.43 (s, Me)
81.58 (dd, J ) 7.1, 4.6, R-C)
103.10 (t, J ) 3.5, â-C)
45.21 (t, J ) 19.8, ipso-C)
12.53 (s, Me)
122.27 (dd, J ) 28.6, 2.8, ipso-Ph)
135.50 (t, J ) 7.0, o-Ph)
129.85 (t, J ) 4.5, m-Ph)
133.45 (s, p-Ph)
129.29 (overlapped, ipso-Ph)
129.68 (d, J ) 12.0, o-Ph)
133.53 (t, J ) 11.6, m-Ph)
132.93 (d, J ) 3.2, p-Ph)
9.14 (s, Me)
a
All spectra were recorded at room temperature in CDCl3 solutions unless otherwise stated. Chemical shifts are reported in ppm (δ)
relative to TMS, referenced to the chemical shifts of residual solvent resonances. Key: s, singlet; d, doublet; t, triplet; br, broad. Coupling
constants (J ) are in Hertz. In CD2Cl2.
b
Ta ble 3. Cyclic Volta m m etr y Da ta for d p p f,
d p p om f, a n d Rela ted P d (II) Com p lexes in CH2Cl2
Solu tion a
Sch em e 4
sample
E
p,a, V
Ep,c, V
sample Ep,a, V
Ep,c, V
dppf 0.18
dppomf -0.40
1a
2a
3a
4a
5a
6a
0.58
0.82
0.77
0.86
1.09
-1.59
1b
2b
3b
4b
0.07
0.32
0.29
0.36
0.77
-1.44
-0.77
-0.77
-0.74
-0.74
-0.77
-0.73
-0.55, -0.69 5b
-0.64, -0.78
0.56, 0.82 -1.83
a
Conditions: 2 × 10-3 M samples; 0.1 M [Bu4]NBF4; v ) 200
mV s-1; glassy-carbon working electrode. All potentials are given
with reference to the Cp2Fe+/Cp2Fe couple (+0.46 V vs SCE).
decomposed rapidly when exposed to air. For this reason
as well as the presence of the supporting electrolyte,
all our attempts to isolate the Pd(0) species were
unsuccessful. The CV profile and the small difference
(140 mV) separating the two reduction waves of 5a ,b
closely resemble the behavior of several metal complexes
that undergo a chemically reversible structural reorga-
nization only in the second electron transfer.26 For
example, [Fe(η5-C5Me5)(µ2-η10-biphenyl)Fe(η5-C5Me5)]-
(PF6)2 was reduced in two electrochemically reversible
one-electron steps separated by 130 mV undergoing
transformation of the bridging biphenyl ligand to bicy-
clohexadienylidene upon addition of the second elec-
tron.26c It is therefore likely, yet quite speculative, that
the second reduction of 5a ,b leads to the reversible
rupture of the Fe-Pd bond, as shown in Scheme 4.
Free dppf is known to undergo a quasireversible one-
electron oxidation to give the dppf+ cation which is
intrinsically unstable and undergoes a fast chemical
reaction (EC process).25 In contrast, the dppomf+ cation
is quite stable and can be prepared by bulk electrolysis
and characterized by EPR spectroscopy.24
Transition-metal complexes with either dppf or dp-
pomf reflect the behavior of the free ligands, as they
generally undergo a one-electron oxidation.4d,24,25 All the
Pd(II) complexes described in this work showed a
reversible one-electron oxidation of the ferrocenyl frag-
ments with oxidation potentials spanning from 0.07 to
1.09 V. This wide range is apparently occasioned by the
dependence of the potential on several factors: the
presence of methyl groups in the ferrocenyl moiety, the
nature of the counterions and coligands, and the exist-
ence of a FefPd bonding interaction. The oxidation
potentials of 1b-4b were ca. 0.5 V less positive than

3644 Organometallics, Vol. 21, No. 17, 2002
Gusev et al.
oxidized to dppomf+ to give the complex [Ag(dppomf+)]-
(BF4)2 (13). The direct oxidation of 1b with Ag(I) salts
produced the corresponding ferrocenium derivatives (see
below) in very low yield. Moreover, the products were
difficult to separate from the nonoxidized complexes.
Using 8a ,b in conjunction with cis-PdCl2(PhCN)2,
[PdCl2(dppomf+)]X (9a , X ) PF6; 9b, X ) BF4) were
finally obtained in good yields and then employed to
synthesize other dppomf+ Pd(II) complexes (Scheme 6).
Treatment of 9a with AgOTf in nitromethane led to
the formation of the binuclear complex [Pd(µ-OPF2O)-
(dppomf+)]2(OTf)4 (10a ), in which two Pd(II) centers are
held together by the oxygen atoms from two bridging
Sch em e 5
those of the dppf analogues 1a -4a , which is in line with
the more electron-rich character of dppomf vs dppf. The
oxidation potentials of the neutral dichloride complexes
1a ,b were less positive by ca. 0.25 V than those of the
dicationic derivatives 2a ,b-4a ,b. The triphenylphos-
phine complexes 5a ,b featured the most positive poten-
tials, irrespective of the ferrocenyl ligand. This result
is consistent with a decrease of the electron density on
the iron center occasioned by the dative bonding inter-
action with palladium.4i,17 It is noteworthy that this
donor-acceptor interaction is apparently stronger in
the methylated complex 5b than in the dppf analogue
5a (∆E ) Ep,a(5b) - Ep,a(4b) ) 0.41 V and Epa(5a ) -
-
PO2F2 groups derived from the oxidative degradation
-
of the PF6 ion.28 Similarly, the reaction of 9a with 2
equiv of AgBF4 gave the bimetallic analogue 10b, which
was authenticated by a single-crystal X-ray analysis (see
below).
A mononuclear dppomf+ Pd(II) complex was obtained
by using 9b as precursor and AgOTf as halide scaven-
ger. In this way, [Pd(H2O)2(dppomf+)](OTf)2(BF4) (11)
was isolated in good yield.
Besides elemental analysis, the complexes with dp-
1
pomf+ were characterized by H and 31P NMR spectros-
E
pa(4a ) ) 0.23 V).
copy (Table 1). All the signals were quite broad due to
the paramagnetic nature of the compounds.
Syn th eses of th e F er r ocen iu m Com p lexes [P d -
(dppom f+)(µ -OP F2O)]2X4 (10a,b) an d [P d(dppom f+)-
(H2O)2](OTf)2(BF 4) (11). On the basis of the results of
the CV study, several attempts were made to prepare
dppomf+ Pd(II) complexes by either macroelectrolysis
at controlled potential or appropriate chemical oxidants.
Bulk electrolysis of 1a in CH2Cl2 at +0.7 V resulted
in the precipitation of a greenish blue microcrystalline
material onto the glassy-carbon electrode after con-
sumption of one electron/molecule. The same product
was obtained by oxidation with NOBF4. As previously
reported by Corain and co-workers,4d the product may
have the formula [PdCl2(dppf)]BF4 (on the basis of
elemental analysis), but this cannot be proved unequivo-
cally due to the very low solubility in common organic
solvents that precluded a thorough spectroscopic analy-
sis.
Sin gle-Cr ysta l X-r a y Str u ctu r es of [P d (OH2)2-
(d p p f)](OTf)2 (2a ), [P d (OH2)2(d p p om f)](OTf)2 (2b),
a n d [P d (µ-OP F 2O)(d p p om f+)]2(BF 4)4 (10b‚6CH2Cl2).
ORTEP drawings of the complexes 2a ,b and 10b‚6CH2-
Cl2 are reported in Figures 1-3, respectively. Crystal-
lographic data are reported in Table 4. Selected bond
distances and angles are listed in Table 5.
In all complexes, the coordination geometry around
palladium can be described as a slightly distorted square
plane with cis phosphorus atoms. The distances from
the centroid of the Cp ring to iron (Cpcent-Fe) are 1.639-
(4) and 1.649(4) Å for 2a and 1.637(6) Å for 2b and
match well the values reported for PdCl2(dppf).4a The
distances Cpcent-Fe in 10b are 1.700(4) and 1.704(4) Å
and are therefore significantly longer than those in 2a ,b,
yet they are close to the value 1.710(2) Å reported for
[Fe(C5Me5)2]+[C3(CN5)]-.29
In all complexes, the Cp rings are planar and tilted
toward the palladium atom. The angle between the
plane normals related to the Cp rings are 5.3° (2a ), 2.0°
(2b), and 6.9° (10b). The analogous angle in PdCl2(dppf)
is 6.2°.4a
The dihedral angle C(1)-Cpcent(1)-Cpcent(2)-C(2) in
2a is 30.7° and is close to that reported for [Pt(H2O)2-
(dppf)](OTf)2 (30.0°)4c and larger than that in either 2b
(24.6°) or 10b (16.2°).
Bulk electrolysis of 2a and 3a was performed under
similar conditions at potentials of +1.0 and +0.9 V,
respectively. Both experiments gave dark green solu-
tions from which no Pd(II) product could be isolated in
a pure form, due to the extreme sensitivity to oxygen
as well as the presence of the supporting electrolyte.
The oxidation of 2a and 3a with NOBF4 was unsuc-
cessful, as no paramagnetic product was obtained. An
attempt was then made in acetone with (NH4)2[Ce-
(NO3)6] as oxidant, but the reaction gave exclusively
Pd(NO3)2(dppf) (7), even in the presence of NaBF4.
The best way to prepare dppomf+ Pd(II) complexes
was found to involve the use of preformed dppomf+ as
either the PF6- or BF4- salt. For this purpose, ferroce-
nium as the hexafluorophosphate or tetrafluoroborate
salt proved to be an excellent and selective oxidant that
allowed for quantitative oxidation of dppomf to dppomf+
(Scheme 5).
The phosphorus atoms deviate from the plane defined
by the Cp rings. In 2a , the deviation is toward iron by
0.02-0.04 Å, while in 2b and 10b the deviation is away
from iron by 0.10 and 0.18-0.19 Å, respectively. The
distance P-CCp increases on going from 2a (1.786(4)-
1.794(4) Å) to 2b (1.796(6)-1.802(6) Å) to 10b (1.813-
(6)-1.819(6) Å).
All our attempts to oxidize dppomf or PdII-dppomf
complexes with Ag(I) salts were partially successful. In
particular, if used stoichiometrically, AgOTf reacted
with dppomf, yielding the complex Ag(OTf)(dppomf)
(12). Only by using an excess of Ag(I) salt was dppomf
(28) Phosphorus, 5th ed.; Corbridge, D. E. C., Ed.; Elsevier
Science: Amsterdam, 1995; pp 138-168.
(29) Miller, J . S.; Calabrese, J . C.; Rommelmann, H.; Chittipeddi,
S. R.; Zhang, J . H.; Reiff, W. M.; Epstein, A. J . J . Am. Chem. Soc. 1987,
109, 769.

PdII-1,1′-Bis(diphenylphosphino)ferrocenes
Organometallics, Vol. 21, No. 17, 2002 3645
Sch em e 6
F igu r e 1. ORTEP drawing of 2a . Thermal ellipsoids are
drawn at the 50% probability level. The OTf- counteranions
have been omitted for clarity.
F igu r e 2. ORTEP drawing of 2b. Thermal ellipsoids are
drawn at the 50% probability level. The OTf- counteranions
have been omitted for clarity.
The Pd-P distances are longer in the dppomf complex
2b (2.271(2)-2.279(2) Å) than in the dppf analogue 2a
(2.263(1)-2.268(1) Å), probably due to steric effects. The
Pd-P bond lengths in 10b are 2.243(2) and 2.245(2) Å,
respectively; these distances are surprisingly short, as
the presence of a ferrocenium moiety in 10b was
expected to reduce the σ-donating ability of the phos-
phorus donors with consequent lengthening of the Pd-P
distances. This unexpected shortening of the P-Pd
distances may be rationalized in terms of either crystal
packing or an increased π-back-bonding Pd-P contribu-
tion. The latter hypothesis has been proposed earlier
to account for the stability of electrochemically gener-
ated [MCl2(dppf)]+ (M ) Pd, Pt).4d
The P-Pd-P bond angles in 2a and in the octameth-
yl-substituted complexes 2b and 10b are remarkably
different from each other: this angle in 2a is 96.38(4)°
and is therefore close to the value reported for the
cationic square-planar platinum(II) complex [Pt(OH2)2-
(dppf)](OTf)2 (97.37(7)°)4c and appreciably smaller than
the value observed in the dichloride palladium(II)
complex 1a (98.0(1)°).4d The presence of methyl groups
F igu r e 3. ORTEP drawing of 10b‚6CH2Cl2. Thermal
-
ellipsoids are drawn at the 50% probability level. The BF4
counteranions have been omitted for clarity.
in the Cp rings as in 2b leads to an enlargement of this
bond angle to 101.32(5)°. A similar effect has been
previously observed for the six-coordinate complexes
M(CO)4(dppomf)/M(CO)4(dppf) (M ) Mo, W).4a,11a Inter-
estingly, the oxidation of the ferrocenyl moiety does not

3646 Organometallics, Vol. 21, No. 17, 2002
Ta ble 4. Cr ysta l a n d Str u ctu r e Refin em en t Da ta for 2a ,b a n d 10b‚6CH2Cl2
Gusev et al.
2a
2b
10b‚6CH2Cl2
empirical formula
fw
C
36H32F6O8S2FeP2Pd
C44H48F6O8S2FeP2Pd
1107.13
C90H100B4Cl12F20O4P6Fe2Pd2
2604.66
994.93
cryst color, shape
cryst size, mm
collection temp, K
cryst syst
space group
unit cell dimens
a, Å
red, prism
0.35 × 0.30 × 0.15
110
monoclinic
P21/n
green, plate
0.30 × 0.20 × 0.10
110
orthorhombic
Pca21
yellow-brown, prism
0.35 × 0.22 × 0.15
110
monoclinic
P21/n
12.265(2)
17.796(4)
17.861(4)
20.888(5)
11.539(3)
18.889(6)
16.616(2)
18.140(3)
18.469(3)
b, Å
c, Å
â, deg
97.669(4)
3863.5(13)
4
111.356(6)
5184.7(15)
2
V, Å3
Z
4553(2)
4
F(000)
2000
1.710
Mo KR/0.710 72
1.112
1.62-29.05
-16 e h e16
-24 e k e 24
-24 e l e 124
10 280
7523 (R(int) ) 0.0427)
7523/0/521
full-matrix least squares on F2
1.093
2256
1.615
Mo KR/0.710 72
0.952
2.16-27.49
-26 e h e 27
-14 e k e 14
-24 e l e 24
10 299
7954 (R(int) ) 0.0882)
7954/0/587
full-matrix least squares on F2
1.024
2620
1.668
Mo KR/0.710 72
1.102
1.73-27.52
-21 e h e 21
-23 e k e 22
-23 e l e 23
11 801
6950 (R(int) ) 0.0581)
6950/0/639
full-matrix least squares on F2
1.077
calcd density, g/cm3
radiation/wavelength, Å
abs coeff, mm-1
θ range, deg
index ranges
no. of rflns collected
no. of unique rflns
no. of data/restraints/params
refinement method
goodness of fit on F2
final R1, wR2 indices
(I > 2σ(I))
0.0550, 0.1197
0.0556, 0.1289
0.0684, 0.1469
R1, wR2 indices (all data)
largest diff peak
0.073, 0.1275
1.060 and -0.981
0.0738, 0.1389
1.504 and -0.528
0.1263, 0.1743
1.030 and -1.040
and hole, e/Å3
affect the P-Pd-P bond angle, which is 101.78(6)° in
the dppomf+ complex 10b.
the dihedral angle between the planes P(1)Fe(1)P(2) and
P(1)Pd(1)P(2), the deviation of the phosphorus from the
planes of the Cp rings, and the Fe‚‚‚Pd distance. All
these differences cannot be clearly accounted for by
crystal packing effects; rather, they appear as a direct
consequence of the replacement of the Cp hydrogens by
methyl groups. As will be shown in the following section,
the presence of either H or Me groups on the Cp rings
affects remarkably also the chemistry of the correspond-
ing Pd(II) complexes.
Ca r bon yla tion of Eth en e in Meth a n ol. The car-
bonylation of ethene has been investigated in MeOH
(methoxycarbonylation) using 3a ,b and 5a ,b as catalyst
precursors. Compounds 3a and 5a differ from 3b and
5b by the chelating diphosphine ligand (dppf vs dppomf)
and from each other by the coligands (weakly bound
H2O molecules in 3a ,b, strongly bound PPh3 in 5a ,b).
No attempt at all has been made to optimize the
processes; studies in this direction are in progress
together with in situ NMR and IR studies.
A constant 600 psi pressure of 1:1 CO/C2H4 and 85
°C were the experimental parameters chosen to evaluate
the catalytic performance of all catalysts. Under these
typical conditions,12,13,22a,31 all the Pd complexes were
substantially stable toward decomposition within 1 h
of reaction time. For longer times, the formation of some
black precipitate of Pd metal was observed in all
experiments, yet the systems were still active after 3
h. In some reactions, TsOH was employed as cocatalyst,
alone or in conjunction with BQ as organic oxidant.12,13
The results obtained are reported in Table 6.
The O-Pd-O angles in the diaquo complexes 2a ,b
are comparable to each other (87.56(12) and 87.01(16)°)
and somewhat larger than the O-Pt-O angle in the
structurally related platinum complex [Pt(OH2)2(dppf)]-
(OTf)2 (86.02(2)°).4c The O-Pd-O angle in complex 10b
-
relative to the bridging PO2F2 group is 89.00(20)°.
The iron center in 2a significantly deviates from the
plane P(1)Pd(1)P(2), the dihedral angle between the
planes P(1)Fe(1)P(2) and P(1)Pd(1)P(2) being 38.8°. A
comparable deviation from planarity was reported for
[Pt(OH2)2(dppf)](OTf)2, which shows a dihedral angle
P(1)Fe(1)P(2)/P(1)Pt(1)P(2) of 39.1°.4c Unlike 2a , the iron
centers in 2b and 10b do not appreciably deviate from
the plane defined by P(1), Pd(1), and P(2), while the
dihedral angles between the planes P(1)Fe(1)P(2) and
P(1)Pd(1)P(2) are dramatically smaller than in 2a (4.6-
(2) and 0.7(2)°, respectively).
No bonding interaction may be envisaged between the
iron and palladium centers in 2a ,b and 10b (distances
of 4.192(1), 4.394(1), and 4.437(1) Å, respectively). No
abnormal contact was found in 2a , while the triflate
anions in 2b clearly bring about a hydrogen-bonding
interaction with both coordinated water molecules. An
agostic contact between a phenyl ortho hydrogen and
the palladium atom in both 2b (C-H‚‚‚Pd: separation
2.65(2) Å, angle 113.6(4)°) and 10b (C-H‚‚‚Pd: separa-
tion 2.55(2) Å, angle 118.1(5)°) is suggested by calcula-
tions.30
To summarize, the molecular structure of the dppf
complex 2a differs from those of the complexes 2b and
10b by several parameters: the P-Pd-P bond angle,
(31) (a) Bianchini, C.; Lee, H. M.; Meli, A.; Oberhauser, W.;
Peruzzini, M.; Vizza, F. Organometallics 2002, 21, 16. (b) Bianchini,
C.; Mantovani, G.; Meli, A.; Oberhauser, W.; Bru¨ggeller, P.; Stampfl,
T. J . Chem. Soc., Dalton Trans. 2001, 690.
(30) Yao, W.; Eisenstein, O.; Crabtree, R. H. Inorg. Chim. Acta 1997,
254, 105.

PdII-1,1′-Bis(diphenylphosphino)ferrocenes
Ta ble 5. Selected Geom etr ica l P a r a m eter s for 2a ,b a n d 10b‚6CH2Cl2
2a 2b
Organometallics, Vol. 21, No. 17, 2002 3647
10b‚6CH2Cl2
Bond Lengths (Å)
Fe(1)-Cp(1)a
Fe(1)-Cp(2)b
Fe(1)-CCp
Fe(1)‚‚‚Pd(1)
Pd(1)-P(1)
Pd(1)-P(2)
Pd(1)-O(1)
Pd(1)-O(2)
P-CCp
1.639(4)
1.649(4)
1.637(6)
1.637(6)
1.704(4)
1.700(4)
1.994(4)-2.071(4)
2.015(6)-2.077(6)
4.394(1)
2.030(6)-2.160(6)
4.437(1)
4.192(1)
2.263(1)
2.267(1)
2.117(3)
2.279(2)
2.245(2)
2.271(2)
2.244(2)
2.117(4)
2.100(5)
2.132(3)
2.169(4)
2.090(5)
1.786(4)-1.794(4)
1.804(3)-1.813(3)
1.796(6)-1.802(6)
1.821(6)-1.834(6)
1.813(6)-1.819(6)
1.806(7)-1.818(6)
1.473(5)
P-CPh
P(3)-O(1A)
P(3)-O(2)
P(3)-F
1.438(5)
1.511(5)-1.522(5)
Bond Angles (deg)
O(1)-Pd(1)-O(2)
P(1)-Pd(1)-P(2)
P(1)-Pd(1)-O(1)
P(2)-Pd(1)-O(2)
P(1)-Pd(1)-O(2)
P(2)-Pd(1)-O(1)
CCp-P-Pd(1)
87.56(12)
96.38(4)
90.27(9)
85.98(9)
175.03(9)
172.96(9)
113.1(1)-122.7(1)
105.3(1)-111.7(1)
103.0(2)-111.1(2)
106.0(2)-102.1(2)
87.01(16)
101.32(5)
85.70(12)
86.16(12)
170.70(12)
172.83(12)
124.8(1)
102.4(1)-110.8(1)
98.8(3)-113.4(3)
105.6(3)-106.2(3)
89.09(20)
101.78(6)
83.57(15)
85.68(17)
172.47(17)
174.53(15)
125.3(2)
102.8(3)-111.8(2)
97.7(3)-108.6(3)
109.1(3)-111.1(3)
120.2(3)
CPh-P-Pd(1)
CCp-P-CPh
CPh-P-CPh
O(2)-P(1)-O(1A)
F(1)-P(3)-F(2)
99.8(4)
Dihedral and Pseudotorsion Angles (deg)
P(1)Cp(1)Cp(2)P(2)
28.7(3)
19.0(2)
12.9(2)
C(1)Cp(1)Cp(2)C(2)
30.7(3)
24.6(2)
16.2(2)
O(1)O(2)Pd(1)/Pd(1)P(1)P(2)
Fe(1)P(1)P(2)/Pd(1)P(1)P(2)
5.1(1)
38.8(3)
-5.3(1)
0.043(2), 0.021(2)
5.9(1)
4.6(2)
-2.0(1)
-0.106(2), -0.102(2)
-0.021(5), -0.044(5)
1.7(1)
0.7(2)
-6.9(1)
-0.182(3), -0.186(3)
-0.025(5), -0.041(5)
c
RCp
d
∆
P
e
∆
Me
a
b
Cp(1) ) center of the C(1)-C(5) Cp ligand. Cp(2) ) center of the C(6)-C(10) Cp ligand in 2a and of C(10)-C(14) in 2b and
10b‚6CH2Cl2. c Dihedral angle between the Cp planes. The negative values correspond to the inclination of the Cp rings toward the Pd
d
atom. Deviations of the P atom from the corresponding Cp ring. The negative value corresponds to the deviation in the opposite direction
to the Fe atom. e Average value of the deviation of the Me group from the corresponding Cp ring. The negative value corresponds to the
deviation in the direction opposite to the Fe atom.
Ta ble 6. Meth oxyca r bon yla tion of Eth en e
Ca ta lyzed by P d (II) Com p lexes w ith d p p f a n d
d p p om f Liga n d sa
Scheme 8 shows the principal reaction mechanisms
reported in the relevant literature for the methoxycar-
bonylation of ethene, yielding A-D and a lt-E-CO
products by PdII-diphosphine catalysis.12,13,31 The over-
all mechanism comprises two main cycles catalyzed by
hydride and methoxy species, linked to each other by
the transformation of Pd-H into Pd-OMe. In principle,
there might be other linking reactions, for example the
protonolysis of Pd-alkyl to give Pd-OMe, yet the
results obtained allow us to rule them out.
The diaquo complex 3a was active, with no need of
added coreagents, but both the selectivity and the
overall TON, expressed as moles of ethene consumed
per mole of Pd(II) precursor, were low (entry 1). The
addition of 20 equiv of TsOH increased the TON values
by ca. 5 times without improving the selectivity, how-
ever. The coaddition of an organic oxidant in large
excess decreased the productivity and slightly favored
the production of oligoketones (940 g (g of Pd)-1) (entry
3). The absence of dialkyl ketones suggests that the
protonolysis of Pd-alkyl is disfavored over CO insertion
to give Pd-acyl, while the production of a lt-E-CO
bearing ester and ketone end groups in a ca. 1:1 ratio
is consistent with the concomitant occurrence of the
“hydride” and “methoxy” cycles (Scheme 8). The relative
concentrations of C and D and the other soluble diesters
suggest that the rate of chain transfer by methanolysis
prevails over that of propagation, even after the second
en-
amt of amt of
BQ
(equiv) (equiv)
a lt-E-CO
productivity/
TONb
TONb
try precur- TsOH
no.
sor
A
B
C
D
1
2
3
4
5
6
7
8
3a
3a
3a
5a
5a
5a
3b
3b
3b
5b
5b
5b
0
20
20
0
20
20
0
20
20
0
20
20
0
0
80
0
0
80
0
0
80
0
0
80
110/214
340 406
5
411
580/1069 1378 1780 29 1887
940/1785 1085 1274 40 1280
0
4
0
0
0
470/893
370/714
1618 2059 41 4457
799 1008 62 1310
0
0
0
0
0
0
139
550
513
4
0
0
0
0
0
0
0
0
0
0
0
0
0
5
0
9
10
11
12
0
581
629
48
0
a
Conditions: catalyst (0.01 mmol); 1:1 CO/C2H4 (600 psi);
b
MeOH (100 mL); 85 °C; 1 h; 1400 rpm. Productivity as grams of
product (grams of Pd)-1; TON as moles of ethene incorporated
(moles of cat)-1
.
Scheme 7 shows the principal reaction products
obtained with the dppf precursors 3a and 5a : alternat-
ing copolymer (a lt-E-CO) with n ) 7, 8 (1H and 13C
NMR spectroscopy), methyl propanoate (A), methyl
4-oxohexanoate (B), dimethyl succinate (C), and dimeth-
yl 4-oxoheptanedioate (D). Three other oligomeric di-
esters with higher molecular weight were detected by
GC in low amount (overall 20% of D).

3648 Organometallics, Vol. 21, No. 17, 2002
Gusev et al.
Sch em e 7
Sch em e 8. P r in cip a l Rea ction Mech a n ism s for th e Meth oxyca r bon yla tion of Eth en e w ith
P d (II)-Ch ela tin g Dip h osp h in e P r ecu r sor s Lea d in g to A-D a n d a lt-E-CO P r od u ctsa
a
[Pd] ) [(P-P)Pd]; 0 represents either a coligand or a solvent molecule.
insertion of ethene. This confirms that the observed
formation of a lt-E-CO proceeds via two mechanisms.
The promoting effects of TsOH and BQ in olefin
carbonylation by Pd(II) catalysis are well-known.12,13,22a,31
A strong protic acid with a noncoordinating conjugated
base is required to remove strongly bound ligands from
palladium as well as deliver into the catalysis cycle
active Pd(II) that might have been entrapped into less
active µ-hydroxo species [{Pd(dppf)}2(µ-OH)2]2+, whose
formation is unavoidable in reactions carried in reagent
grade methanol.4g,12,13,32,33 The ability of the protic acid
to decrease the concentration of binuclear hydroxo
species should be particularly important for 3a , as it
contains coordinated water molecules together with
tosylate counteranions. The organic oxidant, here BQ,
is used in ethene alkoxycarbonylation reactions to
oxidize inactive Pd(I) or Pd(0), which may form during
the catalysis,12,13,22a,31,32 to Pd(II) and also transform (P-
P)PdII-H into (P-P)PdII-OMe (eq 1). In the course of
the latter process, protons are consumed. J ust this
consumption may account for the decreased activity of
3a in the presence of excess BQ (entry 3), as protons
are required to destabilize the µ-OH resting state.
Unlike the diaquo complex 3a , the triphenylphos-
phine complex 5a was active only in the presence of
protic acid, which reflects the good ligating properties
of PPh3 that is most likely removed from the metal as
the phosphonium salt to allow for the coordination of
the monomers (entries 4 and 5). The use of 5a in
conjunction with 20 equiv of acid gave an overall TON
higher than that observed with 3a under analogous
conditions (entry 2 vs entry 5). This surprising effect
may be due to the absence of water in the precursor and
therefore to a more efficient action of the protic acid.
The major contribution to the TON obtained with 5a /
TsOH was provided by product D, which, like C, is
produced exclusively in the “methoxy cycle”. The con-
comitant addition of BQ and TsOH decreased substan-
tially the overall TON (by ca. 60%), most likely due to
consumption of H+ by BQ and re-formation of PPh3 in
the reaction mixture.
Interestingly, the dppomf precursor 3b generated a
selective catalyst for the production of methyl pro-
panoate (Scheme 9).
Under comparable conditions (entries 7-9), 3b gave
exclusively A, the largest TON (550) being obtained in
(32) Zuideveld, M. A.; Kamer, P. C. J .; van Leeuwen, P. W. N. M.;
Klusener, P. A. A.; Stil, H. A.; Roobeek, C. F. J . Am. Chem. Soc. 1998,
120, 7977.
(33) Ledford, J .; Shultz, C. S.; Gates, D. P.; White, P. S.; DeSimone,
J . M.; Brookhart, M. Organometallics 2001, 20, 5266.

PdII-1,1′-Bis(diphenylphosphino)ferrocenes
Organometallics, Vol. 21, No. 17, 2002 3649
Sch em e 9
that a substantial contribution to the selectivity exhib-
ited by 3a ,b is provided by the respective P-Pd-P bond
angles. The bite angles of the archetypal ligand for the
selective production of alternating polyketones by Pd-
(II) catalysis (1,3-bis(diphenylphosphino)propane) gen-
erally measure 90 ( 2°, whereas those of the ligand 1,4-
bis(diphenylphosphino)butane, which gives various esters
from methyl propanoate to oligoketones, are in the
range 93-97°.2b,4f,13,14 Therefore, the exclusive formation
of methyl propanoate is not unexpected for PdII-dppomf
catalysts, as they show P-Pd-P bond angles as large
as 101°.
the presence of TsOH. As was observed for the dppf
precursor, the PPh3 complex 5b was inactive in the
absence of acid (entry 10), while the best conversion
(TON 629) and selectivity (100%) were obtained in the
presence of both acid and organic oxidant (entry 12).
The dramatic change in selectivity on going from the
dppf precursors to the dppomf analogues is intriguing.
The selectivity in the methoxycarbonylation of ethene
by palladium catalysts with phosphine ligands is es-
sentially driven by the nature of the latter.12-14 At one
end, chelating diphosphines, particularly those with
PPh2 end groups and less than four CH2 spacers, form
selective catalysts for the alternating copolymerization
leading to polyketones. At the other end, monophos-
phines give exclusively A, irrespective of the phosphorus
substituents. In the middle, Pd(II) systems containing
chelating diphosphines with more than three carbon
spacers or containing alkyl substituents at the phos-
phorus atoms may appropriately be tuned so as to give
various products with low to high chemoselectivity.
The selectivity in A obtained with (L)2PdII precursors
(L ) monophosphine) is determined by the occurrence
of cis-trans isomerization during the catalysis at the
stage in which Pd-C(O)C2H5 may undergo either
methanolysis or ethene insertion.13 A similar cis-trans
isomerization has been also suggested to account for the
different selectivity in A obtained with 1,2-bis((di-tert-
butylphosphino)methyl)benzene (99.9%) and 1,2-bis-
((diphenylphosphino)methyl)benzene (20%).14 These two
chelating ligands differ from each other by the phos-
phorus substituents but exhibit comparable P-Pd-P
bond angles (103.9 and 104.6°).
Con clu sion s
It has been shown in this article that dppomf and its
oxidized form dppomf+ can form stable Pd(II) complexes
with primary structures that are similar to those of the
parent chelating diphosphine dppf. However, the pres-
ence of eight methyl groups in the dppomf induces
remarkable changes in the secondary structure of the
complexes (P-Pd-P bond angles, dihedral angles be-
tween the (P, Fe, P) and (P, Pd, P) planes, deviation of
the phosphorus atoms from the planes of the Cp rings).
These structural changes and the electronic changes
associated with the presence of the methyl groups
ultimately contribute to differentiate the chemistry of
dppf and dppomf palladium(II) complexes. This effect
has been proved in the methoxycarbonylation of ethene,
for which dppomf generates selective catalysts for the
production of methyl propanoate, while dppf leads to
as many as five different products, spanning from
methyl propanoate to alternating CO/C2H4 copolymer.
Ack n ow led gm en t. Thanks are due to the EC for
Contract No. HPRN-CT-2000-00010, to COST Action
D17 for sponsoring the Working Groups 0007/2000 and
0002/2000, to a CNR-RAS bilateral agreement, to the
Russian Foundation for Basic Research (Grants 00-03-
32855 and 01-03-06145), and to the Haldor Topsøe A/S.
P-M-P bite angles represent useful parameters to
categorize the catalytic activity of metal phosphine
complexes.2b,4f,33 In the present Pd(II) precursors, the
dppf and dppomf ligands bear the same aryl substitu-
ents, yet they give rise to different bond angles, as
determined crystallographically for the derivatives 2a
(96.37(1)°) and 2b (101.3(1)°). Hence, it is very likely
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
lengths and angles and positional and thermal parameters for
compounds 2a ,b and 10b‚6CH2Cl2. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM020300K