Methoxycarbonylation of ethene by palladium(II) complexes with 1,1′-bis(diphenylphosphino)ferrocene (dppf) and 1,1′-bis(diphenylphosphino)octamethylferrocene (dppomf)

Article abstract of DOI:10.1021/om021049b

The square-planar bis(aquo) palladium(II) complexes [Pd(H₂O)₂(dppf)](OTs)₂ and [Pd(H₂O)₂-(dppomf)](OTs)₂ are effective catalysts for the methoxycarbonylation of ethene, yet they exhibit quite different selectivity: the dppf-modified catalyst produces several low molecular weight oxygenates, spanning from methyl propanoate to alternating oligomers of carbon monoxide and ethene, while the dppomf catalyst yields exclusively methyl propanoate (dppf = 1,1′-bis(diphenylphosphino)ferrocene; dppomf = 1,1′-bis(diphenylphosphino)octamethylferrocene; OTs = p-toluenesulfonate). In an attempt to rationalize the different selectivities of the two catalytic systems, the methoxycarbonylation of ethene has been carried out under various experimental conditions in both autoclaves and high-pressure NMR tubes. Also, a number of model compounds have been synthesized with the aim of elucidating the structure of intermediate species observed by NMR during catalysis. Model reactions for the initiation, propagation, and chain-transfer steps in either alternating copolymerization or selective production of methyl propanoate have been performed. On the basis of all of these studies, it can be concluded that the behavior of the dppf precursor is similar to that of any other Pd^II catalyst modified with a chelating diphosphine. In particular, the formation of β-chelate intermediates from either Pd-H or Pd-OMe and their importance in controlling the perfect alternation of monomers have been experimentally demonstrated. The selective production of methyl propanoate with the use of the dppomf-modified catalyst has been attributed to the greater propensity of dppomf versus dppf to form Pd^II complexes with a dative Fe-Pd bond, which forces the P atoms to be trans to each other, yielding Pd-acyl species that do not react with ethene in MeOH. β-Chelate species are not formed by the dppomf-modified catalyst.

Full text of DOI:10.1021/om021049b

Organometallics 2003, 22, 2409-2421
2409
Meth oxyca r bon yla tion of Eth en e by 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 e
(d p p f) a n d
1,1′-Bis(d ip h en ylp h osp h in o)octa m eth ylfer r ocen e
(d p p om f)
Claudio Bianchini,* Andrea Meli, and Werner Oberhauser
Istituto di Chimica dei Composti Organometallici (ICCOM-CNR), Via J . Nardi 39,
50132 Firenze, Italy
Piet W. N. M. van Leeuwen,* Martin A. Zuideveld, Zoraida Freixa, and
Paul C. J . Kamer
Institute of Molecular Chemistry, University of Amsterdam, Nieuwe Achtergracht 166,
1018 WV Amsterdam, The Netherlands
Anthony L. Spek
Department of Crystal and Structural Chemistry, Utrecht University, Padualaan 8,
3584 CH Utrecht, The Netherlands
Oleg V. Gusev* and Alexander M. Kal’sin
N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences,
Vavilov St. 28, 119991 Moscow, Russian Federation
Received December 27, 2002
The square-planar bis(aquo) palladium(II) complexes [Pd(H2O)2(dppf)](OTs)2 and [Pd(H2O)2-
(dppomf)](OTs)2 are effective catalysts for the methoxycarbonylation of ethene, yet they
exhibit quite different selectivity: the dppf-modified catalyst produces several low molecular
weight oxygenates, spanning from methyl propanoate to alternating oligomers of carbon
monoxide and ethene, while the dppomf catalyst yields exclusively methyl propanoate
(dppf ) 1,1′-bis(diphenylphosphino)ferrocene; dppomf ) 1,1′-bis(diphenylphosphino)octa-
methylferrocene; OTs ) p-toluenesulfonate). In an attempt to rationalize the different
selectivities of the two catalytic systems, the methoxycarbonylation of ethene has been carried
out under various experimental conditions in both autoclaves and high-pressure NMR tubes.
Also, a number of model compounds have been synthesized with the aim of elucidating the
structure of intermediate species observed by NMR during catalysis. Model reactions for
the initiation, propagation, and chain-transfer steps in either alternating copolymerization
or selective production of methyl propanoate have been performed. On the basis of all of
these studies, it can be concluded that the behavior of the dppf precursor is similar to that
of any other PdII catalyst modified with a chelating diphosphine. In particular, the formation
of â-chelate intermediates from either Pd-H or Pd-OMe and their importance in controlling
the perfect alternation of monomers have been experimentally demonstrated. The selective
production of methyl propanoate with the use of the dppomf-modified catalyst has been
attributed to the greater propensity of dppomf versus dppf to form PdII complexes with a
dative Fe-Pd bond, which forces the P atoms to be trans to each other, yielding Pd-acyl
species that do not react with ethene in MeOH. â-Chelate species are not formed by the
dppomf-modified catalyst.
In tr od u ction
It was found that the dppf catalyst leads to a variety
of low molecular weight oxygenates spanning from
methyl propanoate to perfectly alternating oligoketones,
while dppomf generates a selective catalyst for methyl
propanoate (Scheme 1).
The methoxycarbonylation of ethene catalyzed by the
bis(aquo) palladium(II) complexes [Pd(H2O)2(dppf)]-
(OTs)2 (1) and [Pd(H2O)2(dppomf)](OTs)2 (2) has been
recently investigated by some of us (dppf ) 1,1′-bis-
(diphenylphosphino)ferrocene; dppomf ) 1,1′-bis(diphen-
ylphosphino)octamethylferrocene; OTs ) p-toluenesul-
fonate).1
(1) Gusev, O. V.; Kalsin, A. M.; Peterleitner, M. G.; Petrovskii, P.
V.; Lyssenko, K. A.; Akhmedov, N. G.; Bianchini, C.; Meli, A.;
Oberhauser, W. Organometallics 2002, 21, 3637.
10.1021/om021049b CCC: $25.00 © 2003 American Chemical Society
Publication on Web 05/15/2003

2410 Organometallics, Vol. 22, No. 12, 2003
Bianchini et al.
Sch em e 1
No attempt was made to rationalize the different
selectivity of the two catalytic systems, apart from
suggesting a correlation between chemoselectivity and
P-Pd-P bite angles in the bis(aquo) precursors. Single-
crystal X-ray analyses showed a significantly larger
P-Pd-P bite angle for [Pd(H2O)2(dppomf)]2+ (101.32-
(5)°) as compared to [Pd(H2O)2(dppf)]2+ (96.38(4)°).1
Therefore, we decided to study the mechanistic aspects
of the methoxycarbonylation of ethene using 1 and 2
by in situ NMR spectroscopy in conjunction with the
isolation and characterization of intermediates and
resting states related to catalysis. The results of this
investigation are reported in this paper. We are confi-
dent to have elucidated the role of the dppf and dppomf
ligands in governing the chemoselectivity of the ethene
methoxycarbonylation catalyzed by 1 and 2. Our study
may also contribute to a better understanding of the
general mechanisms involved in the alkoxycarbonyla-
tion of olefins2 by diphosphine-palladium(II) complexes
and expand the knowledge of the coordination chemistry
of 1,1′-bis(diorganylphosphino)ferrocenes,3 whose ap-
plications in metal-catalyzed homogeneous reactions are
increasingly numerous and successful.1,4
Table 1 reports data for reactions carried out in the
presence of p-toluenesulfonic acid (TsOH) varying from
0 to 160 equiv with respect to palladium. In some
reactions, the oxidant p-benzoquinone (BQ) was em-
ployed, alone or in conjunction with TsOH.2 The pro-
moting effects of protic acids and oxidants in olefin
alkoxycarbonylation catalyzed by PdII complexes with
chelating diphosphines are well known.2,5c,d,g Strong
protic acids with weakly coordinating conjugated bases
such as TsOH serve to remove strongly bound ligands
from palladium, oxidize Pd0 species to PdII species, and
deliver active PdII that might have been entrapped into
less active compounds, such as µ-hydroxo complexes [Pd-
2+
(µ-OH)(P-P)]2 (P-P ) chelating diphosphines) into
the catalytic cycle. The formation of the latter complexes
is generally observed in reactions performed in reagent
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Resu lts
Ca r bon yla tion of Eth en e in Meth a n ol w ith th e
Ca ta lyst P r ecu r sor s 1 a n d 2. To achieve a more
profound knowledge of the catalytic activity of 1 and 2,
the methoxycarbonylation of ethene with these two
catalyst precursors was reinvestigated using a wider
range of experimental conditions than previously done.
Common to all reactions were a constant 600 psi
pressure of 1:1 CO/C2H4, 85 °C, and a catalyst concen-
tration of 10-4 M. Under these typical conditions,1,2,5
1
and 2 generated catalytic systems with almost constant
activity within 1 h of reaction time. At longer reaction
times, the conversion of ethene, estimated experimen-
tally by measuring the gas uptake, slowed regularly, but
all the systems were still active after 3 h. Appreciable
formation of inactive Pd metal, as a black powder, was
observed in all reactions lasting more than 1 h.
(5) (a) Bianchini, C.; Meli, A.; Muller, G.; Oberhauser, W.; Passaglia,
E. Organometallics 2002, 21 4965. (b) Bianchini, C.; Lee, H. M.;
Mantovani, G.; Meli, A.; Oberhauser, W. New J . Chem. 2002, 26, 387.
(c) Bianchini, C.; Lee, H. M.; Meli, A.; Oberhauser, W.; Peruzzini, M.;
Vizza, F. Organometallics 2002, 21, 16. (d) Bianchini, C.; Mantovani,
G.; Meli, A.; Oberhauser, W.; Bru¨ggeller, P.; Stampfl, T. J . Chem. Soc.,
Dalton Trans. 2001, 690. (e) Bianchini, C.; Lee, H. M.; Meli, A.;
Oberhauser, W.; Vizza, F.; Bru¨ggeller, P.; Haid, R.; Langes, C. Chem.
Commun. 2000, 777. (f) Bianchini, C.; Lee, H. M.; Barbaro, P.; Meli,
A.; Moneti, S.; Vizza, F. New J . Chem. 1999, 23, 929. (g) Bianchini,
C.; Lee, H. M.; Meli, A.; Moneti, S.; Vizza, F.; Fontani, M.; Zanello, P.
Macromolecules 1999, 32, 4183. (h) Bianchini, C.; Lee, H. M.; Meli,
A.; Moneti, S.; Patinec, V.; Petrucci, G.; Vizza, F. Macromolecules 1999,
32, 3859.
(2) (a) Sen, A. Acc. Chem. Res. 1993, 26, 303. (b) Drent, E.;
Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663. (c) Drent, E.; van
Broekhoven, J . A. M.; Budzelaar, P. H. M. In Applied Homogeneous
Catalysis with Organometallic Compounds; Cornils, B., Herrmann, W.
A., Eds.; VCH: Weinheim, 1996; Vol. 1, p 333. (d) Sommazzi, A.;
Garbassi, G. Prog. Polym. Sci. 1997, 22, 1547. (e) Nozaki, K.; Hijama,
T. J . Organomet. Chem. 1999, 576, 248. (f) Bianchini, C.; Meli, A.
Coord. Chem. Rev. 2002, 225, 35. (g) Robertson, R. A. M.; Cole-
Hamilton, D. J . Coord. Chem. Rev. 2002, 225, 67.

Methoxycarbonylation of Ethene by Pd(II) Complexes
Organometallics, Vol. 22, No. 12, 2003 2411
Ta ble 1. 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 or Dp p om f Liga n d sa
TOFb
amt of TsOH
(equiv)
amt of BQ
(equiv)
a lt-E-CO
entry no.
precursor
productivity/TOFb
A
B
C
De
1f
1
1
1
1
1
1
1
0
20
40c
80c
160c
0
20
20
20
0
20
0
20
0
20
40
80
160
0
20
20
20
0
0
0
0
0
0
80
80
0
80
0
110/214
580/1069
949/1804
1107/2103
1748/3321
263/500
940/1785
326/619
470/893
traces
338/643
0
340
1378
2264
2610
2838
194
1085
749
825
69
1170
171
1224
139
550
406
1780
2994
3210
1664
104
1274
541
1234
23
5
29
72
60
35
21
40
20
62
traces
17
traces
63
0
411
1887
3679
2905
1478
107
1280
650
1851
53
2f
3
4
5
6
7f
8
9
1d
1d
3
3
3
3
2
10
11
12
13
14f
15f
16
17
18
19
20f
21
22
23
24
0
1187
79
1632
0
299
286
2210
0
80
80
0
0
0
376/714
0
0
0
0
0
0
0
0
0
0
0
2
2
2
2
2
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
732
0
0
1202
1665
95
513
370
460
131
560
80
80
0
80
0
2d
2d
4
0
0
0
0
0
0
4
20
0
a
b
Catalyst (0.01 mmol); 1:1 CO/C2H4 (600 psi); MeOH (100 mL); 85 °C; 1 h; 1400 rpm. Productivity as g of product (g of Pd × h)-1
;
TOF as moles of ethene incorporated (moles of cat × h)-1
.
c This reaction produced also diethyl ketone. 3 h. e Three higher homologues
d
of D are also included (overall 20% of D). f Reference 1.
grade methanol, especially when the catalyst precursors
contain water molecules, as is the case of 1 and 2.2,3f,n,5a,6
The organic oxidant, here BQ, is commonly used to
oxidize inactive PdI or Pd0, which may form during the
catalysis,2,5a,d,g to PdII and also transform (P-P)PdII-H
into (P-P)PdII-OMe (eq 1). Protons are consumed in the
course of the latter process.
Some reactions were also carried out using the
µ-hydroxo complex [Pd(µ-OH)(dppf)]2(OTs)2 (3), which
was shown to be a chain-transfer product by in situ
HPNMR spectroscopy (see below).3f,n Complex 3 gener-
ated an effective catalyst only in the presence of TsOH
as co-reagent (entry 11), while the concomitant presence
of both acid and organic oxidant gave an overall TOF
that was almost twice as high. Recent studies have
shown that µ-hydroxo PdII complexes with chelating
diphosphines are active catalyst precursors for the
alternating CO/C2H4 copolymerization due to their
capability to react with CO, forming mononuclear PdII-H
moieties via a water gas shift mechanism.5a,7
In the absence of BQ, with or without TsOH, the
oligoketone products were featured by a 1:1 ratio
between ketone and ester end groups and an average
molecular weight of ca. 0.5 kg mol-1 (1H and 13C{1H}
NMR analysis). When BQ was used in conjunction with
the acid (entry 7), a slight prevalence of ester over
ketone end groups (6:4 ratio) was observed (molecular
weight of 0.6 kg mol-1), while, in the presence of 80
equiv of BQ with no added acid (entry 6), the end groups
were prevalently constituted by ester groups (8:2 ratio)
The catalytic activities of 1 and 2 increased steadily
with the TsOH concentration with no significant change
in the chemoselectivity up to 80 equiv of acid (entries
1-4 and 14-17). The dppf-based catalysts gave several
carbonylation products (Scheme 1), from alternating
oligoketones (a lt-E-CO) to a variety of low molecular
weight oxygenates including methyl propanoate (A),
methyl 4-oxohexanoate (B), dimethyl succinate (C), and
dimethyl 4-oxoheptanedioate (D). Three other oligomeric
diesters with higher molecular weight were also de-
tected by GC in small amounts (overall 20% of D). In
contrast, the dppomf-based catalyst produced A exclu-
sively. Irrespective of the reaction conditions, the overall
and the average molecular weight was 0.7 kg mol-1
.
Like observed for 1, the catalytic activity of 2 did not
improve by using BQ as co-reagent (entries 19, 20), yet
the presence of the organic oxidant improved the
catalyst stability (entries 15, 20 vs entries 21, 22).
The last two entries of Table 1 refer to reactions
performed with the catalyst precursor [Pd2(µ-H)(µ-CO)-
(dppomf)2]OTs (4), which was actually intercepted by
NMR spectroscopy during the methoxycarbonylation
TOFs (moles of ethene incorporated (moles of cat × h)-1
)
obtained with the dppf-modified catalysts were signifi-
cantly higher than those with dppomf.
In the case of 1, the production of diethyl ketone was
observed under acidic conditions only, with a maximum
TOF of 190 in the presence of 160 equiv of TsOH. The
addition of BQ decreased the activity of 1 (entries 6 and
7 vs 1 and 2), yet the organic oxidant improved the
selectivity in a lt-E-CO as well as the catalyst stability,
as is evident from a comparison between reactions
lasting 1 h (entries 2 and 7) and 3 h (entries 8 and 9).
(6) (a) Ledford, J .; Shultz, C. S.; Gates, D. P.; White, P. S.; DeSimone,
J . M.; Brookhart, M. Organometallics 2001, 20, 5266. (b) Pisano, C.;
Consiglio, G. Gazz. Chim. Ital. 1994, 124, 393. (c) Pisano, C.; Consiglio,
G.; Sironi, A.; Moret, M. J . Chem. Soc., Chem. Commun. 1991, 421.
(7) Verspui, G.; Schanssema, F.; Sheldon, R. A. Appl. Catal. A: Gen.
2000, 198, 5.

2412 Organometallics, Vol. 22, No. 12, 2003
Bianchini et al.
1
ca. 4 by H NMR integration.2,3f,5c,12-19 A minor species
(5-10%) featured by a broad signal at δ 19.6 was also
observed that was assigned to the µ-hydrido-µ-carbonyl
complex [Pd2(µ-D/H)(µ-CO)(dppf)2]OTs (6) (Chart 1).6b,8-12
In addition to the formation of these well-defined
species, appreciable catalyst degradation occurred, as
shown by the high noise level of the baseline and the
appearance of traces of black palladium in the NMR
1
tube. The H NMR spectrum of 6 contained a weak, yet
unambiguously identifiable signal due to the µ-H hy-
drogen (quintet at δ -6.01), which suggests the involve-
ment of the water molecules contained in both 1 and
solvent in the formation of Pd-H moieties. Alternatively,
the proton may stem from H/D scrambling with ethene
via â-hydride elimination of palladium alkyl intermedi-
ates. Increasing the temperature led to the disappear-
ance of 5 and 6; species in fast dynamic exchange were
formed in their place (see the spectra recorded in the
temperature range from 50 to 70 °C, traces c and d).
After 30 min at 70 °C, the probe-head was cooled to
room temperature. The 31P{1H} NMR spectrum at this
temperature showed the formation of a mixture of
products that denied first-order analysis. The only
complex that we could assign was the known µ-OH(OD)
complex 3 (Chart 1) (trace e, singlet at δ 33.1).3f,n
Analysis of the solution by GC showed the formation of
deuterated samples of A, B, C, and D. The formed co-
oligomer was similar to the samples obtained in the
batch experiments under comparable experimental
conditions with n˜ values of ca. 8 and both ketonic and
ester end groups.1
F igu r e 1. Variable-temperature 31P{1H} NMR study
(sapphire tube, MeOH-d4, 81.01 MHz) of the carbonylation
reaction of ethene catalyzed by 1: (a) dissolving 1 in MeOH-
d4 under nitrogen at room temperature; (b) after the tube
was pressurized with 40 bar of CO/C2H4 (1:1) at room
temperature; (c) after 10 min at 50 °C; (d) after 10 min at
70 °C; (e) after the tube was cooled to room temperature.
Ch a r t 1. Com p lexes Seen in th e HP NMR
Stu d y of th e Meth oxyca r bon yla tion of Eth en e
Ca ta lyzed by 1
A different 31P{1H} NMR picture was observed when
the methoxycarbonylation of ethene was performed in
the presence of 16 equiv of BQ with respect to the
catalyst. In this case the PdI-PdI complex 6 did not form
at any stage of the reaction, while the µ-OH species was
again seen at the end of the reaction. Along the whole
experiment, the spectral noise was much lower than
that observed in the absence of oxidant, which reflects
a minor degradation of the PdII catalyst to palladium
metal.
reactions catalyzed by 2 (see below).6b,8-12 Precursor 4
was as efficient and selective as the parent complex 2
under comparable experimental conditions. A few re-
ports showing a catalytic role for µ-H(µ-CO) PdI com-
plexes in alkene carbonylation reactions have appeared
in the relevant literature.6b,8b
In the reaction performed in the presence of 4 equiv
of TsOH, no other palladium complex than 1 was seen
by NMR spectroscopy, besides the protonolysis termina-
tion product 3.3f Moreover, the signal of the precursor
1 persisted up to 50 °C. Apparently, the formation of
the â-chelates 5 from either Pd-H or Pd-OMe is inhibited
at room temperature by the tosylate ions, which may
compete with monomers for coordination to palladium.
Above 50 °C, when the methoxycarbonylation products
started to form, all the species were in rapid chemical
exchange on the NMR time scale and therefore unde-
tectable.
In Situ High -P r essu r e NMR Stu d y of th e Meth -
oxyca r bon yla tion of Eth en e Ca ta lyzed by 1. The
reaction catalyzed by 1 was followed by variable-
1
temperature 31P{1H} and H HPNMR spectroscopy in
MeOH-d4. A sequence of selected 31P{1H} NMR spectra
is reported in Figure 1.
A 10 mm sapphire HPNMR tube was charged under
nitrogen with a solution of 1 in MeOH-d4 and then
placed into the NMR probe at room temperature (δ 47.9,
trace a). Pressurizing with a 1:1 mixture of CO/C2H4 to
40 bar at room temperature (trace b) converted 1 into
the â-chelate complexes [Pd(CH2CH2C(O)(CH2CH2C-
(O))nR)(dppf)]OTs (5; doublets at ca. δ 40 and 16 with
J (PP) of ca. 36 Hz) (Chart 1). R in 5 may be either OCD3
or C2H4D(H) depending on whether the reaction starts
with Pd-D/H or Pd-OCD3, respectively. The average
repeating units of the chain in 5 were estimated to be
Syn th esis a n d Ch a r a cter iza tion of In ter m ed i-
a tes a n d Restin g Sta tes in th e Meth oxyca r bon -
yla tion of Eth en e Ca ta lyzed by 1. The model â-che-
late complex [Pd(CH2CH2C(O)Me)(dppf)]OTf3f,12 (7) was
synthesized by sequential bubbling of CO and ethene
into a solution of [PdMe(NCMe)(dppf)]OTf3l in CH2Cl2
(9) (a) Perez, P. J .; Calabrese, J . C.; Bunel, E. E. Organometallics
2001, 20, 337. (b) Portnoy, M.; Milstein, D. Organometallics 1994, 13,
600. (c) Portnoy, M.; Frolow, F.; Milstein, D. Organometallics 1991,
10, 3960.
(8) (a) Siedle, A. R.; Newmark, R. A.; Gleason, W. B. Inorg. Chem.
1991, 30, 2005. (b) Zudin, V. N.; Chinakov, V. D.; Nekipelov, V. M.;
Rogov, V. A.; Likholobov, V. A.; Yermakov, Yu. I. J . Mol. Catal. 1989,
52, 27.
(10) To´th, I.; Elsevier: C. J . Organometallics 1994, 13, 2118.

Methoxycarbonylation of Ethene by Pd(II) Complexes
Organometallics, Vol. 22, No. 12, 2003 2413
Sch em e 2
square-planar geometry with cis coordinating phospho-
rus atoms (P1-Pd-P2 angle of 98.47(9)°). This P1-Pd-
P2 angle is similar to that of other palladium complexes
of dppf.20 The structure shows the chelate ring with the
oxygen atom of the carbonyl group coordinated to the
metal center. The Pd-P1 distance is much shorter
(2.220(3) Å) than the Pd-P2 distance (2.395(3) Å), as
this bond is trans-located to the Pd-alkyl bond, whereas
the P2 phosphorus is trans-coordinated to the coordinat-
ing oxygen atom. The Pd-O bond length of 2.123(4) Å
is in accordance with a dative bond.19,21
The (carbonyl)acyl complex [Pd(CO)(C(O)CH2CH2C-
(O)Me)(dppf)]OTf (8) and the â-ketoalkyl derivative [Pd-
(CH2CH2C(O)CH2CH2C(O)Me)(dppf)]OTf (9) were pre-
pared in CD2Cl2 and characterized by NMR spectroscopy
at low temperature. The reaction of CO with 7 gave the
carbonyl(acyl) 8, which was transformed into the â-che-
late 9 by reaction with ethene (Scheme 3). In the
reaction leading to 9, the formation of a minor species
featured by two doublets with chemical shifts and
F igu r e 2. ORTEP drawing (30% displacement ellipsoids)
of the cation of 7‚0.5CH2Cl2. Hydrogen atoms, triflate
anion, and CH2Cl2 have been omitted for clarity.
2
coupling constants (δ 39.1 and 15.4, J (PP) ) 35.8 Hz)
2
Ta ble 2. Selected Geom etr ica l P a r a m eter s for
very close to those of 9 (δ 38.7 and 15.8, J (PP) ) 35.7
7‚0.5CH2Cl2
Hz) was observed. On the basis of these NMR data and
the presence of two IR bands at 1629 and 1710 cm-1
,
bond lengths (Å)
bond angles (deg)
which are typical of coordinated and free carbonyl
groups, respectively,22 we suggest that this minor spe-
cies is a higher â-ketoalkyl homologue of 9 formed by
reaction of the latter with residual CO and ethene in
the solution.
Multinuclear NMR analysis allowed for the identifi-
cation of the acyl(carbonyl) complex 8; in particular, the
13C{1H} NMR spectrum showed an acyl carbon signal
at δ 229.3 (d, 2J (CP) ) 86.7 Hz) and ketone carbon
signal at δ 208.1 (s).
Pd-P1
2.220(3)
2.395(3)
2.123(7)
2.032(12)
1.490(15)
1.476(16)
1.466(14)
1.229(13)
P1-Pd-P2
98.47(9)
89.9(2)
90.5(3)
Pd-P2
Pd-O1
Pd-C1
C1-C2
C2-C3
C3-C4
C3-O1
P2-Pd-O1
P1-Pd-C1
O1-Pd-C1
O1-C3-C2
O1-C3-C4
Pd-O1-C3
C1-C2-C3
Pd-C1-C2
81.1(4)
119.9(9)
119.5(10)
114.1(7)
113.3(10)
110.3(8)
at low temperature, followed by solvent evaporation
(Scheme 2).
The µ-H, µ-CO complex 6 was independently synthe-
sized by two different methods, involving either the
treatment of the aquo complex 1 with CO in CH2Cl2
(water-gas shift reaction)2 (route a in Scheme 4) or the
methanolysis of the Pd-acetyl complex [Pd(COMe)-
(NCMe)(dppf)]OTs3l under a CO atmosphere (route b).
The NMR features of 6 are in line with those of other
µ-hydrido, µ-carbonyl binuclear Pd8-12 and Pt23 com-
plexes stabilized by phosphine ligands.
The synthesis of 6 from an acetyl complex in the
presence of CO (route b) resembles closely the chain-
transfer mechanism by methanolysis in real copolym-
erization reactions catalyzed by PdII precursors with
chelating diphosphines where the acetyl group is sub-
The coordination of the â-keto group was inferred by
the low-field 13C{1H} NMR signal of the carbonyl carbon
atom (δ 238.9) and the low-frequency ν(CO) stretch
(1630 cm-1).15-19 Conclusive evidence of the â-chelate
structure was obtained by a single-crystal X-ray analy-
sis of 7‚0.5CH2Cl2 (Figure 2 and Table 2).
The structure consists of [Pd(CH2CH2C(O)Me)(dppf)]+
complex cations and triflate counteranions with inter-
spersed CH2Cl2 molecules. The metal center exhibits a
(11) Sperrle, M.; Gramlish, V.; Consiglio, G. Organometallics 1996,
15, 5196.
(12) Zuideveld, M. A. Thesis, University of Amsterdam, 2001.
(13) Dekker, G. P. C. M.; Elsevier, C. J .; Vrieze, K.; van Leeuwen,
P. W. N. M.; Roobeek, C. F. J . Organomet. Chem. 1992, 430, 357
(14) (a) Ozawa, F.; Hayashi, T.; Koide, H.; Yamamoto, A. J . Chem.
Soc., Chem. Commun. 1991, 1469. (b) Reddy, K. R.; Surekha, K.; Lee,
G.-H.; Peng, S.-M.; Chen, J .-T.; Liu, S.-T. Organometalllics 2001, 20,
1292.
(15) Shultz, C. S.; Ledford, J .; DeSimone, J . M.; Brookhart, M. J .
Am. Chem. Soc. 2000, 122, 6351.
(16) Rix, F. C.; Brookhart, M. J . Am. Chem. Soc. 1995, 117, 1137.
(17) Parlevliet, F. J .; Zuideveld, M. A.; Kiener, C.; Kooijman, H.;
Spek, A. L.; Kamer, P. C. J .; van Leeuwen, P. W. N. M. Organometallics
1999, 18, 3394.
(20) Dierkes, P.; van Leeuwen, P. W. N. M. J . Chem. Soc., Dalton
Trans. 1999, 1519.
(21) Reddy, K. R.; Chen, C.-L.; Hung Liu, Y.-H.; Peng, S.-M.; Chen,
J .-T.; Liu, S.-T. Organometalllics 1999, 18, 2574.
(22) Mul, W. P.; Oosterbeek, H.; Beitel, G. A.; Kramer, G.-J .; Drent,
E. Angew. Chem., Int. Ed. 2000, 39, 1848.
(23) (a) Minghetti, G.; Bandini, A. L.; Banditelli, G.; Bonati, F.,
Szostak, R.; Strouse, C. E.; Knobler, C. B.; Kalst, H. D. Inorg. Chem.
1983, 22, 2332. (b) Bandini, A. L.; Banditelli, G.; Cinellu, M. A.; Sanna,
G.; Minghetti, G.; Demartin, F.; Manassero, M. Inorg. Chem. 1989,
28, 404. (c) Bandini, A. L.; Banditelli, G.; Demartin, F.; Manassero,
M.; Minghetti, G. Gazz. Chim. Ital. 1993, 123, 417.
(18) Aeby, A.; Consiglio, G. J . Chem. Soc., Dalton Trans. 1999, 655.
(19) Green, M. J .; Britovsek, G. J . P.; Cavell, K. J .; Skelton, B. W.;
White, A. H. J . Chem. Soc., Chem. Commun. 1996, 1563.

2414 Organometallics, Vol. 22, No. 12, 2003
Bianchini et al.
Sch em e 3
Sch em e 4
Ch a r t 2. Com p lexes Seen in th e HP NMR
Stu d y of th e Meth oxyca r bon yla tion of Eth en e
Ca ta lyzed by 2
Sch em e 5
the palladium(I) binuclear complex [Pd(dppomf)]2(OTs)2
(10) (δ -1.3) (Chart 2).11,25,26 Additional NMR spectra
were acquired every 30 min at room temperature. The
ratio between 2 and 10 did not appreciably vary with
time, yet the concentration of these two compounds
slowly decreased, becoming, altogether, one-fifth of the
Sch em e 6
1
initial one over 2 days. The H NMR spectra acquired
during this experiment showed a small downfield shift
of the resonances of both p-toluenesulfonate ions and
adventitious water, which is consistent with the pres-
ence of protons in solution (vide infra). In separate NMR
experiments, treating a freshly prepared solution con-
taining 2 and 10 with 4 equiv of either TsOH or BQ
resulted in re-formation of 2 as the exclusive complex.
In Situ High -P r essu r e NMR Stu d y of th e Meth -
oxyca r bon yla tion of Eth en e Ca ta lyzed by 2 w ith -
ou t Co-r ea gen t. A 10 mm sapphire HPNMR tube was
charged under nitrogen with a solution prepared by
dissolving a solid sample of 2 in MeOH-d4 and then
placed into the NMR probe at room temperature. A
sequence of selected 31P{1H} NMR spectra is reported
in Figure 3.
As already observed in the stability study of 2 in
methanol, the first spectrum (trace a) showed the partial
conversion (15%) of the precursor into 10. The NMR
tube was pressurized with a 1:1 mixture of CO/C2H4 to
40 bar at room temperature (trace b) and then heated
to 40 °C. As shown by the first spectrum acquired at
this temperature (trace c), both complexes converted
into a new complex featured by a singlet at δ 5.6, which
we suggest to be the Pd0 µ-CO binuclear complex Pd2-
(µ-CO)(dppomf)2 (11) (Chart 2) on the basis of its NMR
characteristics (see below).27 Increasing progressively
the temperature to 50 (trace d), 60 (trace e), and 70 °C
(trace f) decreased the concentration of 11; in its place
stituted by a generic acyl group (Scheme 5).2 Following
the methanolysis of Pd-COR with production of the
corresponding ester, the resultant [PdIIH(P-P)] frag-
ment is not stable in the presence of CO.2,9a,24 Part of it
disproportionates to give H+ and [Pd0(CO)(P-P)]. The
combination of the latter Pd0 fragment with residual
[PdIIH(P-P)] eventually generates the PdI-PdI µ-H,
µ-CO species.
The µ-OH complex 3 was previously synthesized by
Longato3n and later shown by van Leeuwen to be the
chain-transfer product by protonolysis with water in CO/
C2H4 copolymerizations catalyzed by PdII-dppf com-
plexes.3f The formation of 3 involves â-chelates, struc-
turally similar to 6, that isomerize to enolates prior to
undergoing regioselective attack by water at the C2
carbon atom. This mechanism is exemplified for 7 in
Scheme 6.3f
Sta bility of 2 in Meth a n ol. Syn th esis a n d Ch a r -
a cter iza tion of [P d (d p p om f)]2(OTs)2. The starting
solution employed in this study was obtained by dis-
solving a sample of 2 in MeOH-d4 at room temperature.
Within a few minutes, the green solution of 2 turned
brownish red. The reaction was followed by 31P{1H} and
1H NMR spectroscopy. The first 31P{1H} NMR spectrum
showed a 14% conversion of the precursor (δ 71.6) into
(25) Budzelaar, P. H. M.; van Leeuwen, P. W. N. M.; Roobeek, C. F.
Organometallics 1992, 11, 23.
(26) Davies, J . A.; Hartley, F. R.; Murray, S. G.; Marshall, G. J . Mol.
Catal. 1981, 10, 171.
(24) Di Bugno, C.; Pasquali, M.; Leoni, P.; Sabatino, P.; Braga, D.
Inorg. Chem. 1989, 28, 1390.
(27) Trebbe, R.; Goddard, R.; Rufinska, A.; Seevogel, K.; Porschke,
K.-R. Organometallics 1999, 18, 2466.

Methoxycarbonylation of Ethene by Pd(II) Complexes
Organometallics, Vol. 22, No. 12, 2003 2415
F igu r e 4. Variable-temperature 31P{1H} NMR study
(sapphire tube, MeOH-d4, 81.01 MHz) of the carbonylation
reaction of ethene catalyzed by 2: (a) dissolving 2 in MeOH-
d4 under nitrogen at room temperature; (b) after the
addition of 16 equiv of BQ; (c) after the tube was pressur-
ized with 40 bar of CO/C2H4 (1:1) at room temperature;
(d) at 40 °C; (e) at 50 °C; (f) at 60 °C; (g) at 70 °C.
F igu r e 3. Variable-temperature 31P{1H} NMR study
(sapphire tube, MeOH-d4, 81.01 MHz) of the carbonylation
reaction of ethene catalyzed by 2: (a) dissolving 2 in MeOH-
d4 under nitrogen at room temperature; (b) after the tube
was pressurized with 40 bar of CO/C2H4 (1:1) at room
temperature; (c) at 40 °C; (d) at 50 °C; (e) at 60 °C; (f) at
70 °C; (g) after the tube was cooled to room temperature.
12 into the µ-CO dimer 11 (trace d). Upon a further
increase of the temperature to 70 °C, 11 converted to
the µ-hydride, µ-CO complex 4 (traces e-g), while
methyl propanoate began to form. After 30 min at 70
°C, the tube was allowed to cool to room temperature.
The 31P{1H} NMR spectrum at this temperature showed
exclusively 4, yet traces of black palladium metal proved
a new complex was formed (singlet at δ 23.7) featured
by a quintet at δ -6.31 (J (HP) ) 42.1 Hz) in the 1H
NMR spectrum. On the basis of an independent syn-
thesis, the new complex was identified as the µ-hydrido,
µ-carbonyl complex [Pd2(µ-H)(µ-CO)(dppomf)2]OTs (4)
(Chart 2). After 30 min at 70 °C, the probe-head was
cooled to room temperature. The 31P{1H} NMR spec-
trum at this temperature showed that compound 4 was
the only phosphorus-containing species visible in solu-
tion (trace g). Palladium metal in the tube indicated the
1
the occurrence of some catalyst degradation. H NMR
and GC/MS analyses confirmed the formation of methyl
propanoate-d4.
In Situ High -P r essu r e NMR Stu d y of th e Meth -
oxyca r bon yla tion of Eth en e Ca ta lyzed by 2 in th e
P r esen ce of 4 Equ iv of TsOH. A 10 mm sapphire
HPNMR tube was charged with a solution of 2 in
MeOH-d4 under nitrogen. The first spectrum at room
temperature showed the presence of both 2 and 10 in a
ca. 5:1 ratio. Upon addition of TsOH (4 equiv), 10
converted immediately to 2 completely. Pressurizing
with a 1:1 mixture of CO/C2H4 to 40 bar at room
temperature caused the quantitative formation of the
µ-hydride, µ-CO complex 4, which was also the only
phosphorus-containing complex visible on the NMR time
scale during the carbonylation reaction (1 h, 50-70 °C).
After 30 min at 70 °C, the probe-head was cooled to
room temperature. The 31P{1H} NMR spectrum at this
1
occurrence of partial catalyst decomposition. H NMR
spectra acquired during the experiment showed that the
formation of methyl propanoate-d4 (multiplets at δ 1.05
and 2.27) had started at ca. 60 °C.
In Situ High -P r essu r e NMR Stu d y of th e Meth -
oxyca r bon yla tion of Eth en e Ca ta lyzed by 2 in th e
P r esen ce of 16 Equ iv of BQ. A sequence of selected
31P{1H} NMR spectra is reported in Figure 4. A 10 mm
sapphire HPNMR tube was charged under nitrogen
with a solution of 2 in MeOH-d4 and then placed into
the NMR probe at room temperature.
As in the previous experiment, the first spectrum
(trace a) showed the presence of both 2 and 10 in a ca.
5:1 ratio. Adding BQ (16 equiv) led to the immediate
oxidative conversion of 10 into 2 (trace b). Pressurizing
with a 1:1 mixture of CO/C2H4 to 40 bar at room
temperature caused the complete transformation of 2
into a new complex featured by a 31P{1H} NMR reso-
nance at δ -19.1 (trace c). On the basis of an in situ
NMR characterization in methanol (see below) this
complex was assigned the η1-carbomethoxy complex [Pd-
(C(O)OCD3)(dppomf)]OTs (12), where the metal center
is coordinated in a square-planar environment by two
trans phosphorus atoms from dppomf, a carbomethoxy
group, and a dative Fe-Pd bond (Chart 2).1,3a,c,k In-
creasing the temperature to 40 °C caused the consump-
tion of BQ (eq 1) with concomitant transformation of
1
temperature showed only 4, while H NMR and GC/MS
analyses revealed the formation of methyl propanoate-
d4.
In Situ High -P r essu r e NMR Stu d y of th e Meth -
oxyca r bon yla tion of Eth en e Ca ta lyzed by 2 in th e
P r esen ce of 4 Equ iv of TsOH a n d 16 Equ iv of BQ.
A 10 mm sapphire HPNMR tube was charged under
nitrogen with a solution of 2, TsOH (4 equiv), and BQ
(16 equiv) in MeOH-d4 (2 mL) and then placed into the
NMR probe at room temperature. The first spectrum
showed only 2. Pressurizing to 40 bar with a 1:1 mixture
of CO/C2H4 at room temperature caused no change in
both the 1H and 31P{1H} NMR spectra. However,
increasing the temperature to 50 °C decreased the

2416 Organometallics, Vol. 22, No. 12, 2003
Bianchini et al.
Sch em e 7
Sch em e 8
constant 2/10 ratio observed in the stability experiment
described above.
concentration of 2 and gave both 11 and 4, albeit in
small amounts. At 60 °C, only 11 and 4 were visible,
with a higher concentration of the former complex. With
time, the signal of 11 decreased in intensity. At 70 °C,
4 was the only visible phosphorus-containing species
during the carbonylation reaction. After 30 min at 70
°C, the probe-head was cooled to room temperature. The
31P{1H} NMR spectrum at this temperature showed the
exclusive presence of 4. As usual, palladium metal
deposited on the bottom of the NMR tube. 1H NMR and
GC/MS analyses showed the formation of methyl pro-
panoate-d4.
Like 10, the µ-CO binuclear complex 11 was neither
isolated nor prepared through an independent proce-
dure. All our efforts to prepare 11 led to the formation
of either unidentified species or well-defined (dppomf)-
Pd0 complexes, such as [Pd(dppomf)2] and the bis-
(carbonyl) complex [Pd(CO)2(dppomf)],28 none of which
showing the spectral characteristics of 11. Indirect
support for the proposed structure of 11 was provided
by the following experiment: a 10 mm sapphire HP-
NMR tube was charged under nitrogen with a solution
of 2 in MeOH-d4 and pressurized to 40 bar with 1:1 CO/
C2H4 at room temperature. The tube was introduced
into a spectrometer and heated to 40 °C. Already the
first spectrum at this temperature showed the quantita-
tive formation of 11 (see Figure 3, trace c). The tube
was then removed from the probe head, frozen in liquid
nitrogen, and subjected to vacuum to remove the
gaseous phase. One equivalent of TsOH was added to
the frozen solution. The tube was allowed to reach room
temperature, where the quantitative formation of the
µ-hydride, µ-CO complex 4 was observed by NMR
spectroscopy.
Complex 4 was synthesized by the procedure de-
scribed above for the dppf derivative 6, namely, the
reaction of the aquo complex 2 with CO in CH2Cl2.
Alternatively, 4 was prepared by pressurizing a mixture
of 2 and TsOH (4 equiv) in methanol with 1:1 CO/C2H4
in a HPNMR tube. Under these conditions, 4 can form
according to the reaction sequence proposed in Scheme
5 for the dppf analogue 6, i.e., partial disproportionation
of the PdII system [PdH(dppomf)]+ in the presence of
CO to give H+ and [Pd(CO)(dppomf)], followed by
combination of the latter Pd0 fragment with residual
[PdH(dppomf)]+.
Syn th esis a n d Ch a r a cter iza tion of In ter m ed i-
a tes a n d Ter m in a tion P r od u cts of th e Meth oxy-
ca r bon yla tion of Eth en e by 2. Complex 10 was
obtained by simply dissolving 2 in methanol. After 5
min, ca. 14% 2 converted to 10, while the color of the
solution turned from green to brownish red. An in situ
experiment monitored by NMR spectroscopy showed
that both 2 and 10 were intrinsically unstable in
methanol under N2, where they decomposed with time
to unknown species, under release of protons. During
this decomposition, the 2/10 ratio remained constant.
All our attempts to isolate a sample of 10 by fractional
crystallization were unsuccessful. Likewise, we were
unable to develop an independent synthetic procedure
to this PdI-PdI dimer. Therefore, 10 was characterized
by 1H and 31P{1H} NMR spectroscopy in situ. Two
magnetically equivalent phosphorus atoms and two
largely separated signals for the methyl hydrogen atoms
of the Cp* rings (∆δ ) 1.35) are strongly diagnostic for
a structure in which the phosphorus atoms are trans to
each other, and iron forms a dative bond to palladium
using its e2g electron density.3a,c,k Recent studies have
demonstrated that the formation of dative iron-pal-
ladium bonds in dppf and dppomf palladium complexes
causes a tilting of the Cp rings. As a consequence of this
Like 6 and other µ-hydrido, µ-carbonyl binuclear Pd
complexes with chelating diphosphines, 4 is fluxional
on the NMR time scale: the hydride resonance in the
1H NMR spectrum appears as a quintet with δ -6.02
(J (HP) ) 42.6 Hz) at 20 °C and as a triplet of triplets
with δ -5.72 (2J (HP) ) 80.8, 5.2 Hz) at -70 °C.8,12
Pressurizing a methanol solution of 2 with CO gave
the carbomethoxy complex 12 quantitatively, likely
through CO insertion into a PdII methoxy intermediate
that was not intercepted (Scheme 8).2,29
1
tilting, the H NMR ∆δ of the R- and â-hydrogen atoms
(H in Cp, Me in Cp*) is larger than that in the free
ligand.3a,c,k
Indirect support for the proposed structure for 10 was
provided by its reactivity toward protic acids and
oxidants. Indeed, treatment of methanol solutions of 10
with either TsOH or BQ regenerated 2 cleanly.
The dissolution of mononuclear (P-P)PdII complexes
in MeOH (P-P ) chelating diphosphine) is a known
procedure to prepare binuclear PdI complexes structur-
ally similar to 10.11,25,26 The formation of these PdI-PdI
compounds has been proposed to involve the coupling
of (P-P)PdII and (P-P)Pd0 moieties, the latter being
generated by palladium-promoted methanol oxidation
to formaldehyde.9,25 Scheme 7 illustrates this process
for 10.
A carbon resonance at 209.9 in the 13C{1H} NMR
spectrum was diagnostic for the presence of a car-
bomethoxy group in 12, while the lack of additional P-C
couplings in the 31P{1H} NMR spectrum, when 13CO
was used in the place of 12CO, was consistent with a
trans arrangement of the phosphorus atoms.3a,c,k Fi-
(28) Bianchini, C.; Meli, A.; Oberhauser, W., manuscript in prepara-
The protons formed during the oxidation of methanol,
converting 10 into 2, are likely to be responsible for the
tion.
(29) Milstein, D. Acc. Chem. Res. 1988, 212, 428.

Methoxycarbonylation of Ethene by Pd(II) Complexes
Organometallics, Vol. 22, No. 12, 2003 2417
Sch em e 9
nally, a strong argument in favor of the η3-P,P,Fe
bonding mode of dppomf in 12 was provided by the large
difference between the chemical shifts of the R and â
methyl hydrogen atoms of the Cp* rings (∆δ ) 0.87).3a,c,k
Under CO atmosphere, 12 underwent methanolysis
at room temperature very slowly (t1/2 ca. 12 h), yielding
dimethyl carbonate (GC/MS analysis) and the (hydrido)-
carbonyl complex 4.
Some possible intermediates in Scheme 8 have been
represented with arbitrary molecular structures. Our
preference for a chelating η2-P,P dppomf ligand in these
compounds stems from the nature of the co-ligands,
which are neither sterically demanding nor electron-
withdrawing (H, OMe, OTs). Indeed, both characteris-
tics disfavor the formation of a dative Fe-Pd, which
requires either bulky or electron-withdrawing co-
ligands.3a,c
tion catalyzed by 1 as well as rationalize the different
selectivity of the dppf and dppomf catalysts.
Scheme 10 shows mechanistic details for the reactions
assisted by the dppf-modified catalyst.
On the basis of the experimental results and model
studies described in the section above, one may conclude
that the behavior of the dppf precursor 1 in the
methoxycarbonylation of ethene is quite similar to that
of any other PdII catalyst modified with a chelating
diphosphine.2 In particular, the formation of â-chelate
intermediates from either Pd-H or Pd-OMe has been
experimentally determined (Figure 1), and their impor-
tance in controlling the perfect alternation of monomers
has been demonstrated in the model studies illustrated
in Schemes 2 and 3.
The formation of the µ-OH binuclear complex 3 during
the catalysis together with that of diethyl ketone
demonstrate that the chain transfer can proceed by
protonolysis of Pd-alkyl, most likely through the enolate
mechanism reported by van Leeuwen et al. (Scheme 6).3f
The chain transfer by protonolysis seems to be much
less important than that by methanolysis of Pd-acyl,
however. In fact, the production of diethyl ketone
occurred in very low yield and only in the presence of
an excess of protic acid. Upon methanolysis of Pd-acyl,
the Pd-H moiety is regenerated, which can initiate the
next catalytic cycle; however, this species is unstable
and can also degrade to the hydride(carbonyl) complex
6 through the mechanism reported in Scheme 5. The
termination product 3 is not a dead-end for the catalytic
reaction, as it may be considered a resting state for
Mod el Stu d y of th e Meth oxyca r bon yla tion of
Eth en e by P d II-d p p om f Ca ta lysis. The methyl com-
plex [Pd(Me)(H2O)(dppomf)]OTs (14) was straightfor-
wardly prepared by reaction of [PdCl(Me)(dppomf)] (13)
with AgOTs in CH2Cl2 solution. In the presence of 1 bar
of CO at room temperature, 14 converted immediately
into the acyl complex [Pd(COMe)(dppomf)]OTs (15)
(Scheme 9). The different hapticity of dppomf in 14 and
15 was unequivocally put in evidence by the corre-
sponding 31P{1H} NMR patterns: AM system with δ
48.8 (br) and 12.6 (2J (PP) ) 20.5 Hz), and A2 system
1
with δ -13.3, respectively. The H NMR resonances of
the Cp* methyl groups were in line with the different
hapticity of dppomf in the two compounds, showing four
close signals for 14 and two well-separated signals for
15.
catalytically active PdII (Table 1, entries 10-13). The
2+
mechanism by which [Pd(µ-OH)(P-P)]2
complexes
The acyl complex 15 in CD2Cl2 underwent fast
methanolysis at room temperature, yielding the µ-hy-
dride, µ-CO complex 4 (see Scheme 5) and methyl
acetate (Scheme 9). Complex 4 and methyl acetate were
selectively produced also when MeOH was added to a
CD2Cl2 solution of 15 previously saturated with a 1:1
CO/C2H4 mixture at room temperature. It is worth
noticing that the carbomethoxy complex 12, containing
a dative Fe-Pd bond like 15, undergoes alcoholysis very
slowly even in neat MeOH (vide infra), which reflects
the lower electrophilic character of the CO2R carbon
atom as compared to the COR carbon atom.
may re-enter the copolymerization cycle has been pro-
posed to involve the cleavage of the binuclear structure
by CO, followed by a water-gas-shift process to generate
Pd-H moieties.5c,7
In contrast to 1, the dppomf precursor 2 yields methyl
propanoate exclusively, irrespective of the experimental
conditions (Table 1), which means that the whole
activity of the dppomf-modified catalyst is confined in
the reaction sequence reported in Scheme 11. Indeed,
the alternative path to generate methyl propanoate via
protonolysis of a possible â-chelate complex of the
formula [Pd(CH2CH2C(O)OMe)(dppomf)]+ can be ruled
out on the basis of both direct evidence and model
studies.
Discu ssion
The overall mechanism accounting for the nature of
the oxygenated products obtained by methoxycarbon-
ylation of ethene with 1 and 2 (Scheme 1) has been
reported previously.1 The results of the present study
highlight mechanistic details regarding the propagation
and termination steps of the alternating copolymeriza-
The HPNMR studies did not reveal the formation of
any â-chelate species with dppomf at any stage of the
carbonylation reaction under a CO/C2H4 pressure of 40
bar, while methyl propanoate was selectively and ef-
ficiently produced under conditions that do not allow
for the formation of Pd-C(O)OMe initiators (i.e., in the

2418 Organometallics, Vol. 22, No. 12, 2003
Bianchini et al.
Sch em e 10
criteria, established in the course of previous studies,3a,c,k
for the formation of a dative Fe-Pd bond in [PdL-
(ferrocenyldiphosphine)]+ complexes; that is, L must be
bulky or have an electron-withdrawing character to
make the Pd center susceptible to accept e2g electron
density from iron. Consistent with this rule, the methyl
derivative 14 exhibits a chelating dppomf ligand, while
the acyl complex 15 contains a dative Fe-Pd bond and
trans P atoms.
Sch em e 11
The overall TOFs obtained with 2 are by far lower
than those obtained with 1 under comparable conditions
(Table 1). The propensity of the precursor 2 to degrade
spontaneously to the PdI-PdI binuclear complex 10 and,
under CO/C2H4, to the Pd0 µ-CO complex 11 may well
account for the low productivity of the dppomf-modified
catalyst. Another factor that can contribute to decrease
the catalytic activity of 2 is the formation of a propionyl
intermediate with a dative Fe-Pd bond and trans P
atoms (Scheme 11). In fact, the methanolysis of the
propionyl intermediate may be rate limiting in the
catalysis cycle shown in Scheme 11, as it involves the
reaction of MeOH with a coordinatively saturated
square-planar PdII complex. To accomplish this reaction,
a change in the hapticity of dppomf from η3-P,P,Fe
(trans P atoms) to η2-P,P (cis P atoms) is required to
provide a free coordination site for MeOH coordination
and to allow for the nucleophilic attack by the oxygen
atom to the acyl carbon atom. The energy barrier to this
hapticity change is presumably high. Moreover, as
recently shown by van Leeuwen et al.,30 under acidic
conditions methanol is a too weak a nucleophile to give
direct attack from solution.
presence of a large excess of acid, see Table 1, entry 18).
The occurrence of the Pd-OMe mechanism is unlikely
on the basis of the results of the model study with the
acyl complex 15 that showed the methanolysis of 15,
yielding methyl acetate and 4, to be much faster than
the insertion of ethene into Pd-COMe to give a Pd-alkyl
(Scheme 9). Studies underway in this laboratory confirm
that the insertion of ethene into the Pd-COMe bond of
15 is a thermodynamically allowed process in CH2Cl2,
yet kinetically disfavored over alcoholysis by MeOH
even under a high pressure of ethene (20 bar).28 In this
respect, the behavior of the η3-P,P,Fe-dppomf acyl
complex 15 contrasts dramatically with that of the η2-
P,P-dppf analogues [Pd(COR)(S)(dppf)]+ (S ) MeOH,
monomer), which convert to â-chelate species by reac-
tion with C2H4 even in neat MeOH (Figure 1).12,30
The Pd-H initiator in Scheme 11 has been drawn as
containing an η2-chelating dppomf ligand. Although this
representation is arbitrary, as no spectroscopic evidence
whatsoever was obtained for a mononuclear Pd-H
complex during the catalysis, the probability that such
an intermediate contains a η2-P,P-dppomf ligand is
indeed very high. The hydride ligand lacks all important
The stabilizing effect of the η3-P,P,Fe-dppomf bonding
mode seems to be particularly important in the meth-
oxycarbonylation reactions carried out in the presence
of an excess of BQ, yielding a TOF of 95 only (Table 1,
entry 19). The organic oxidant, promoting the conver-
sion of Pd-H into Pd-C(O)OMe (eq 1), increases the
concentration of the η3-P,P,Fe-dppomf carbomethoxy
(30) van Leeuwen, P. W. N. M.; Zuideveld, M. A.; Swennenhuis, B.
H. G.; Freixa, Z.; Kamer, P. C. J .; Goubitz, K.; Fraanje, J .; Lutz, M.;
Spek, A. L., submitted for publication.

Methoxycarbonylation of Ethene by Pd(II) Complexes
Organometallics, Vol. 22, No. 12, 2003 2419
The product composition of the catalytic reactions was deter-
mined by using dimethyl oxalate as the internal standard. GC/
MS analyses were performed on a Shimadzu QP 5000 appa-
ratus equipped with a column identical with that used for GC
analysis.
complex 12 (Figure 4), which is not a good catalyst
precursor to form Pd-H due to its reluctance to undergo
methanolysis.
Con clu sion s
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 BQ and/or 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 over all 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 bath. After the unreacted gases
were released, the insoluble CO/C2H4 material, 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.
The square-planar palladium(II) complexes [Pd(H2O)2-
(dppf)](OTf)2 and [Pd(H2O)2(dppomf)](OTf)2 are effective
catalysts for the methoxycarbonylation of ethene, yet
they exhibit quite different selectivity: the dppf-modi-
fied catalyst produces several low molecular weight
oxygenates, spanning from methyl propanoate to alter-
nating oligoketones, while the dppomf catalyst yields
exclusively methyl propanoate. Batch catalytic reac-
tions, in situ high-pressure NMR experiments, and
model studies with isolated compounds agree to indicate
the greater propensity of dppomf versus dppf to form
palladium(II) complexes with a dative Fe-Pd bond as
the factor leading to the selective production of methyl
propanoate. In fact, the presence of an Fe-Pd bond
forces the P atoms to be trans to each other and
ultimately results in Pd-acyl species that do not react
with ethene in MeOH.
Ch a r a cter iza tion of th e Co-oligom er s. The elemental
analysis values were in agreement with a CO/C2H4 ratio of 1.
Spectroscopically (IR and NMR), the oligomers showed chemi-
cal-physical properties comparable to those reported in the
literature for perfectly alternating copolymers obtained by CO/
C2H4 copolymerization in methanol by PdII-diphosphine ca-
talysis.2 In general, all samples showed the presence of both
ketonic and ester end groups; however, a different ratio of
these groups was observed depending on the reaction condi-
tions. 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).
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions and manipulations
were carried out under an atmosphere of nitrogen using
Schlenk-type techniques. All reagents and solvents were used
as purchased from commercial suppliers. The complexes PdCl-
(Me)(COD) (COD ) cycloocta-1,5-diene),31 [Pd(H2O)2(dppf)]-
(OTs)2,1 [Pd(H2O)2(dppomf)](OTs)2,1 [Pd(µ-OH)(dppf)]2(OTs)2,3n
[Pd(Me)(NCMe)(dppf)]OTf,3l and [Pd(COMe)(NCMe)(dppf)]-
OTs3l were synthesized according to published procedures. All
the isolated solid samples were collected on sintered-glass frits
and washed with appropriate solvents before being dried under
a stream of nitrogen. Elemental analyses were performed
using a Carlo Erba Model 1106 elemental analyzer. Infrared
spectra were recorded on a Perkin-Elmer 1600 Series FT-IR
spectrophotometer. Conductivities were measured with an
ORION model 990101 conductance cell connected to a model
101 conductivity meter. The conductivity data32 were obtained
at sample concentrations of ca. 10-3 M in nitroethane solutions.
In Situ HP NMR Stu d y of th e Meth oxyca r bon yla tion
of Eth en e Ca ta lyzed by 1. A 10 mm sapphire HPNMR tube
was charged under nitrogen with a solution of 1 (13.5 mg,
0.013 mmol) in MeOH-d4 (2 mL) and then pressurized with a
1:1 mixture of CO/C2H4 to 40 bar at room temperature. The
Carbonylation reactions were performed with
a 250 mL
1
reaction was followed by variable-temperature 31P{1H} and H
stainless steel autoclave, constructed at the ICCOM-CNR
(Firenze, Italy), equipped with a magnetic drive stirrer and a
Parr 4842 temperature and pressure controller. The autoclave
was connected to a gas reservoir to maintain a constant
pressure over all the catalytic reactions. Deuterated solvents
for routine NMR measurements were dried over molecular
NMR spectroscopy. A sequence of selected 31P{1H} NMR
spectra is reported in Figure 1. NMR data for 1: 31P{1H} NMR
(MeOH-d4, 20 °C): δ 47.9 (s). 1H NMR (MeOH-d4, 20 °C): δ
8.0-7.0 (m, 28H, Ar-PPh2 + Ar-OTs), 4.69 (s, 4H, H-Cp), 4.55
(s, 4H, H-Cp), 2.23 (s, 6H, Me-OTs).
1
sieves. H, 13C{1H}, and 31P{1H} NMR spectra were obtained
Syn th esis of 6. A. A solution of 1 (130 mg, 0.13 mmol) in
CH2Cl2 (20 mL) was introduced into a 100 mL autoclave and
pressurized with CO to 20 bar at room temperature. After 2
h, the unreacted gas was released and the contents were
transferred into a round-bottomed flask and concentrated to
half the volume under vacuum. The solution was filtered on
Celite to eliminate precipitated palladium, and a 3:1 mixture
of n-hexane/diethyl ether (10 mL) was added to precipitate 6,
which was collected on a sintered-glass frit, washed with
n-hexane, and dried under a stream of nitrogen. Yield: 70%.
Anal. Calcd for C76H64Fe2O4P4Pd2S: C, 59.98; H, 4.24. Found:
C, 59.89; H, 4.22. 31P{1H} NMR (20 °C): δ (MeOH-d4) 19.6 (br
s); (CD2Cl2): 18.5 (br s). 31P NMR (CD2Cl2, 20 °C): δ 18.5 (d,
a Bruker ACP 200 spectrometer (200.13, 50.32, and 81.01
MHz, respectively). 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). The 10 mm sapphire NMR tube was
purchased from Saphikon, Milford, NH, while the titanium
high-pressure charging head was constructed at the ICCOM-
CNR (Firenze, Italy).33 Caution: Since high gas pressures are
involved, safety precautions must be taken at all stages of
studies involving high-pressure NMR tubes. 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.
1
2J (PH) ) 42.1 Hz). H NMR (20 °C): δ (CD2Cl2) 8.0-6.9 (m,
44H, Ar-PPh2 + Ar-OTs), 4.38 (s, 8H, H-Cp), 4.11 (s, 8H, H-Cp),
2.32 (s, 3H, Me-OTs), -6.08 (quintet, J (HP) ) 41.9 Hz, 1H,
2
(31) (a) Drew, D.; Doyle, J . R. Inorg. Synth. 1972, 13, 52. (b) Ru¨lke,
R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier, C. J .; van Leeuwen, P. W.
N. M.; Vrieze, K. Inorg. Chem. 1993, 16, 9, 5972.
(32) (a) Geary, W. J . Coord. Chem. Rev. 1971, 7, 81. (b) Morassi, R.;
Sacconi, L. J . Chem. Soc. A 1971, 492.
µ-H); (MeOH-d4) 8.0-7.0 (m, 44H, Ar-PPh2 + Ar-OTs), 4.69
(s, 8H, H-Cp), 4.54 (s, 8H, H-Cp), 2.23 (s, 3H, Me-OTs), -6.01
2
(quintet, J (HP) ) 42.0 Hz, 1H, µ-H). 13C{1H} NMR (CD2Cl2,

2420 Organometallics, Vol. 22, No. 12, 2003
Bianchini et al.
20 °C): δ 229.7 (quintet, 2J (CP) ) 34.1 Hz, µ-CO). IR (CH2-
Cl2, cm-1): 1841 (CO).
1.56 (tdd, 3J (HH) ) 6.3 Hz, 3J (HP) ) 7.4, 2.7 Hz, 2H, PdCH2).
13C{1H} NMR (CD2Cl2, -20 °C): δ 239.4 (dd, 3J (CP) ) 12.8,
1.3 Hz, CH2C(O)CH2), 207.2 (s, CH2C(O)CH3), 135-123 (m,
Ph), 78-71 (m, Cp), 51.6 (d, 3J (CP) ) 6.0 Hz, PdCH2CH2), 39.2
B. Methanol (10 equiv) was syringed into a 5 mm NMR tube
containing a 3.3 × 10-2 M solution of [Pd(COMe)(NCMe)(dppf)]-
OTs in CD2Cl2 (0.7 mL) under 1 bar of CO at room tempera-
ture. 1H and 31P{1H} NMR spectra showed the quantitative
2
(d, J (CP) ) 86.0 Hz, PdCH2CH2), 37.5 (s, CH2CH2C(O)CH3),
34.7 (s, CH2C(O)CH3), 30.0 (s, C(O)CH3). IR (CD2Cl2, cm-1):
ν(CO) 1629, 1710.
1
formation of the dimer 5 (31P{1H} NMR singlet at δ 18.5; H
quintet for the hydride at -6.08 (2J (HP) ) 41.9 H)) and methyl
acetate.12 The use of 13CO resulted in an additional P-C
Sta bility Stu d y of 2 in Meth a n ol by NMR Sp ectr os-
cop y. Syn th esis a n d Ch a r a cter iza tion of 10. The starting
solutions employed in this study were obtained by dissolving
samples of 2 (8 mg, 0.007 mmol) in MeOH-d4 (1 mL) at room
temperature. A 5 mm NMR tube was charged under nitrogen
with one of these solutions and then placed into the NMR
probe at room temperature. The reaction was followed by 31P-
2
coupling in the 31P{1H} NMR spectrum (d, J (PC) ) 34.1 Hz)
and an additional H-C coupling for the hydride signal (quintet
of d, 2J (CH) ) 4.5 Hz) in the 1H NMR spectrum. When MeOH-
d4 was added to the solution of the starting acyl complex, the
deuterated analogue [Pd2(dppf)2(µ-D)(µ-CO)]OTs formed; three
signals were observed in the 31P{1H} NMR spectrum in an
intensity ratio of 1:1:1 due to the phosphorus-deuterium
coupling (2J (PD) ) 6.1 Hz).
1
{1H} and H NMR spectroscopy. The results of this investiga-
tion are discussed in a previous section. NMR data for 2:
1
31P{1H} NMR (MeOH-d4, 20 °C): δ 71.6 (s). H NMR (MeOH-
Syn th esis of 7. A stream of CO was bubbled through a
solution of [PdMe(NCMe)(dppf)]OTf (162 mg, 0.19 mmol) in
CH2Cl2 (2 mL) at -60 °C for 10 min, then ethene was
substituted for CO. After bubbling ethene for 1 min, the
resulting solution was allowed to warm to -20 °C. After 20
min, evaporation of the solvent at -20 °C gave an orange solid
residue that was washed with cold diethyl ether and n-
pentane. Yield: 80%. Anal. Calcd for C39H35F3FeO4P2PdS: C,
53.17; H, 4.00. Found: C, 52.65; H, 4.19. 31P{1H} NMR (CD2-
d4, 20 °C): δ 6.9-8.3 (m, 28H, Ar-PPh2 + Ar-OTs), 2.23 (s,
6H, Me-OTs), 1.49 (s, 12H, Me-Cp*), 1.32 (s, 12H, Me-Cp*).
NMR data for 10: 31P{1H} NMR (MeOH-d4, 20 °C): δ -1.3
1
(s). H NMR (MeOH-d4, 20 °C): 8.3-6.9 (m, 48H, Ar-PPh2
+
Ar-OTs), 2.23 (s, 6H, Me-OTs), 1.86 (br s, 24H, Me-Cp*),
0.51 (br s, 24H, Me-Cp*). 31P{1H} NMR (MeOH-d4, -40 °C):
δ -1.4 (s). 1H NMR (-40 °C, MeOH-d4): 8.3-6.9 (m, 48H, Ar-
PPh2 + Ar-OTs), 2.22 (s, 6H, Me-OTs), 1.87 (s, 24H, Me-Cp*),
0.50 (s, 24H, Me-Cp*).
2
1
Cl2, -20 °C): δ 38.7 (d, J (PP) ) 35.7 Hz), 15.8 (d). H NMR
(CD2Cl2, -20 °C): δ 7.8-7.3 (m, 20H, Ar-PPh2), 4.65 (m, 2H,
Cp), 4.56 (m, 2H, Cp), 4.36 (m, 2H, Cp), 3.79 (m, 2H, Cp), 3.19
In Situ HP NMR Stu d y of th e Meth oxyca r bon yla tion
of Eth en e Ca ta lyzed by 2. A 10 mm sapphire HPNMR tube
was charged under nitrogen with a solution of 2 (15 mg, 0.013
mmol) in MeOH-d4 (2 mL) and then pressurized with a 1:1
mixture of CO/C2H4 to 40 bar at room temperature. TsOH (10
mg, 0.052 mmol, 4 equiv) and/or BQ (23 mg, 0.208 mmol, 16
equiv), if any, were also added. The reactions were followed
by variable-temperature 31P{1H} and 1H NMR spectroscopy.
Selected 31P{1H} NMR spectra are reported in Figures 3
and 4.
3
4
(dt, J (HH) ) 6.2 Hz, J (HP) ) 7.8 Hz, 2H, PdCH2CH2), 2.31
(s, 3H, C(O)CH3), 1.39 (dtd, 3J (HH) ) 6.2 Hz, 3J (HP) ) 7.4,
3.2 Hz, 2H, PdCH2CH2). 13C{1H} NMR (CD2Cl2, -20 °C): δ
4
238.9 (d, J (CP) ) 12.6 Hz, C(O)CH3), 136-130 (m, Ph), 76-
69 (m, Cp), 52.5 (d, 3J (CP) ) 6.0 Hz, PdCH2CH2), 39.0 (d,
2J (CP) ) 85.2 Hz, PdCH2CH2), 28.9 (s, C(O)CH3). IR (KBr
pellet, cm-1): 1630 (CO).
Single crystals of 7‚0.5CH2Cl2 suitable for an X-ray analysis
were obtained by crystallization from CH2Cl2/Et2O in a Schlenk
tube stored at -20 °C. Anal. Calcd for C39H35F3FeO4P2PdS‚
0.5CH2Cl2: C, 51.37; H, 3.93. Found: C, 51.02; H, 3.89.
Syn th esis of 8. A solution of 7 (52.8 mg, 0.06 mmol) in CD2-
Cl2 (2 mL) was maintained under a stream of CO at -40 °C
for 15 min and then transferred into a 5 mm NMR tube at
-40 °C. The tube was inserted into a NMR probe-head
precooled at -40 °C. 1H and 31P{1H} NMR spectra showed the
quantitative formation of the carbonyl acyl complex 8. 31P{1H}
NMR (CD2Cl2, -40 °C): δ 23.0 (d, 2J (PP) ) 62.1 Hz), 11.3 (d).
1H NMR (CD2Cl2, -40 °C): δ 7.8-7.3 (m, 20H, Ar-PPh2), 4.77
(m, 2H, Cp), 4.66 (m, 2H, Cp), 4.34 (m, 2H, Cp), 3.70 (m, 2H,
Cp), 2.56 (br s, 2H, PdC(O)CH2CH2), 2.12 (br s, 2H, PdC(O)-
CH2CH2), 1.97 (s, 3H, C(O)CH3). 13C{1H} NMR (CD2Cl2, -40
°C): δ 229.3 (d, 2J (CP) ) 86.7 Hz, PdC(O)CH2), 208.1 (s,
CH2C(O)CH3), 177.0 (br s, Pd(CO)), 136-130 (m, Ph), 78-69
(m, Cp), 49.9 (m, PdC(O)CH2), 39.6 (s, CH2C(O)CH3), 30.2 (s,
C(O)CH3).
Syn th esis of 4. A. A solution of 2 (150 mg, 0.13 mmol) in
CH2Cl2 (20 mL) was introduced into a 100 mL autoclave and
pressurized with CO to 20 bar at room temperature. After 2
h, the unreacted gas was released and the contents were
transferred into a round-bottomed flask and concentrated to
half of the volume under vacuum. The solution was filtered
over Celite to eliminate black palladium, and a 3:1 mixture of
n-hexane/diethyl ether (10 mL) was added to precipitate the
product, which was collected on a sintered-glass frit, washed
with n-hexane, and dried under a stream of nitrogen. Yield:
75%.
B. A solution of 2 (150 mg, 0.13 mmol) and TsOH (100 mg,
0.52 mmol) in MeOH (20 mL) was introduced into a 100 mL
autoclave and pressurized with 1:1 CO/C2H4 to 40 bar at room
temperature. After 30 min, the unreacted gases were released
and the contents was concentrated to dryness under vacuum.
The solid residue was dissolved in THF and filtered over Celite
to give an organic phase that was concentrated again to
dryness. The solid residue was washed with n-pentane, filtered
off, and dried under a stream of nitrogen. Yield: 60%. Anal.
Calcd for C92H96Fe2O4P4Pd2S: C, 63.28; H, 5.54. Found: C,
63.14; H, 5.51. 31P{1H} NMR δ: (CD2Cl2, 20 °C) 23.7 (s); (THF-
d8, 20 °C) 22.2 (s); (THF-d8, -70 °C) 27.3 (d, 2J (PP) ) 36.1
On using 13CO, the resonance at δ 11.3 in the 31P{1H} NMR
2
spectrum became a doublet of doublets with J (PC) ) 87.0 Hz.
Syn th esis of 9. Ethene was bubbled for 10 min through a
solution of 7 (54.5 mg, 0.06 mmol) obtained as above in CD2-
Cl2 (2 mL) at -60 °C. A sample of the resulting solution (1
mL) was transferred into a 5 mm NMR tube at -20 °C, and
the tube was inserted into a NMR probe-head precooled at -20
°C. Another sample of the solution was transferred into a KBr
cell for IR measurements. 1H, 13C{1H}, and 31P{1H} NMR and
IR spectra showed the quantitative formation of 9. 31P{1H}
NMR (CD2Cl2, -20 °C): δ 39.1 (d, 2J (PP) ) 35.9 Hz), 15.1 (d).
1H NMR (CD2Cl2, -20 °C): δ 7.8-7.3 (m, 20H, Ar-PPh2), 4.65
(m, 2H, Cp), 4.56 (m, 2H, Cp), 4.34 (m, 2H, Cp), 3.79 (m, 2H,
Cp), 3.18 (dt, 3J (HH) ) 6.6 Hz, 4J (HP) ) 7.7 Hz, 2H,
PdCH2CH2), 2.87 (t, 3J (HH) ) 5.6 Hz, 2H, C(O)CH2CH2), 2.31
(t, 3J (HH) ) 5.6 Hz, 2H, C(O)CH2CH2), 1.64 (s, 3H, C(O)CH3),
2
Hz), 19.4 (d, J (PP) ) 36.1 Hz). 31P NMR δ: (THF-d8, 20 °C)
22.2 (d, 2J (PH) ) 40.1 Hz); (THF-d8, -70 °C) 27.3 (dd,
2J (PP) ) 36.1 Hz, 2J (PH) ) 82.1 Hz), 19.4 (d, 2J (PP) ) 36.1
1
Hz). H NMR δ: (CD2Cl2, 20 °C) 8.1-6.8 (m, 44H, Ar-PPh2
+
Ar-OTs), 2.36 (s, 3H, Me-OTs), 1.62 (s, 24H, Me-Cp*), 1.25 (s,
24H, Me-Cp*), -6.18 (quintet, 2J (HP) ) 42.4 Hz, 1H, µ-H);
(THF-d8, 20 °C) -6.02 (quintet, J (HP) ) 42.6 Hz, 1H, µ-H);
2
2
(THF-d8, -70 °C) -5.72 (tt, J (HP) ) 80.8, 5.2 Hz, 1H, µ-H).
13C{1H} NMR (CD2Cl2): δ (20 °C) 226.4 (quintet, 2J (CP) ) 34.1
Hz, µ-CO). IR (Nujol mull, KBr plates/CH2Cl2, cm-1): ν(CO)
1848/1846.

Methoxycarbonylation of Ethene by Pd(II) Complexes
Organometallics, Vol. 22, No. 12, 2003 2421
NMR experiments in MeOH-d4 showed 4 to decompose into
2 and several unknown species when treated with TsOH or
BQ.
Me), 2.31 (s, 3H, Me-OTs), 1.74 (s, 12H, Me-Cp*), 1.21 (s, 12H,
Me-Cp*).
Rea ction of 15 w ith MeOH. A solution of 15 in CD2Cl2
was prepared as above and transferred into a 5 mm NMR tube
equipped with a rubber cap. A 100 µL sample of MeOH was
injected by syringe into the tube at room temperature. 1H and
31P{1H} NMR spectroscopy showed the formation of 4 and
methyl acetate already in the first spectra.
Rea ction of 15 w ith CO/C2H4. A 1:1 CO/C2H4 mixture was
bubbled for 15 min at room temperature into a CD2Cl2 solution
of 15 in a 5 mm NMR tube equipped with a rubber cap. Then,
the tube was closed and allowed to stand for 15 min at room
temperature. A 100 µL sample of MeOH was injected by
syringe into the tube. 1H and 31P{1H} NMR spectra showed
the formation of 4 and methyl acetate. GC/MS confirmed the
exclusive formation of methyl acetate.
Syn th esis of 11. A 10 mm sapphire HPNMR tube was
charged under nitrogen with a solution of 2 (15 mg, 0.013
mmol) in MeOH-d4 (2 mL) and pressurized to 40 bar with 1:1
CO/C2H4 at room temperature. The tube was introduced into
a spectrometer and heated to 40 °C. The first spectrum
acquired at this temperature showed the presence of the 11.
The tube was removed from the probe-head, frozen in liquid
nitrogen, and subjected to high vacuum. To the frozen solution
was added 1 equiv of TsOH. This mixture was allowed to thaw
and reach room temperature. The formation of the µ-hydride,
µ-CO complex 4 was determined by NMR spectroscopy. 31P-
1
{1H} NMR (MeOH-d4, 20 °C): δ 5.6 (s). H NMR (MeOH-d4,
40 °C): δ 7.9-7.0 (m, 40H, Ar-PPh2), 1.62 (s, 24H, Me-Cp*),
1.11 (s, 24H, Me-Cp*).
X-r a y Da ta Collection a n d Str u ctu r e Deter m in a tion
of [C38H 35F eOP 2P d +][SO3CF 3-]‚0.5(CH 2Cl2). X-ray data
were collected at 150 K on an Enraf-Nonius TurboCAD4
(Rotating Anode, Mo KR, θ max ) 26.5°). Reflection profiles
turned out to be broad and highly structured. Pertinent data:
monoclinic, space group P21/c (No. 14), a ) 11.057(2) Å, b )
23.767(4) Å, c ) 16.203(3) Å, â ) 116.78(1)°, Z ) 4. The
structure was solved by direct methods (SIR97)34 and refined
on F2 with SHELXL9635 to a final R ) 0.0813 for 3287
reflections with I > 2σ(I) [wR2 ) 0.167 for 7763 reflections].
The main cation structure contains two solvent-accessible voids
at 0,1/2,0 and 0,0,1/2 of 419 Å3, each containing disordered
OTf- and CH2Cl2. Their contribution to the structure factors
was taken into account by back-Fourier transformation using
the PLATON/SQUEEZE36 procedure. A total of 189 electrons/
per void were accounted for (corresponding with two OTf- and
one CH2Cl2 per void). Data were corrected for absorption with
the PLATON/DELABS36 procedure. Hydrogen atoms were
taken into account at calculated positions and refined riding
on their carrier atoms.
Syn th esis of 12. A 10 mm sapphire HPNMR tube was
charged under nitrogen with a solution of 2 (15 mg, 0.013
mmol) in MeOH-d4 (2 mL) and pressurized to 10 bar with CO
at room temperature. 1H and 31P{1H} NMR spectra showed
the quantitative formation of 12. On standing at room tem-
perature, this complex slowly undergoes methanolysis (t1/2
)
12 h), decomposing to 4 and dimethyl carbonate-d6 (GC/MS
analysis). Attempts to isolate 12 failed due to its decomposition
to 2 when the CO pressure was released and nitrogen was
added. 31P{1H} NMR (MeOH-d4, 20 °C): δ -19.1 (s). 1H NMR
(MeOH-d4, 20 °C): δ 8.1-6.9 (m, 24H, Ar-PPh2 + Ar-OTs),
2.28 (s, 3H, Me-OTs), 1.71 (s, 12H, Me-Cp*), 0.84 (s, 12H, Me-
Cp*). 13C{1H} NMR (MeOH-d4, 20 °C): δ 209.9 (br s, C(O)-
OCD3).
Syn th esis of 13. To a solution of dppomf (292 mg, 0.438
mmol) in THF (30 mL) was added a solution of PdCl(Me)(COD)
(116 mg, 0.439 mmol) under stirring. After 15 min, the solution
was concentrated to half volume and n-hexane (15 mL) was
added. The formed yellow solid was filtered off, washed with
n-hexane, and dried in a stream of nitrogen. Yield: 86%. Anal.
Calcd for C43H47ClFeP2Pd: C, 62.72; H, 5.75. Found: C, 62.70;
H, 5.69. 31P{1H} NMR (CD2Cl2, 20 °C): δ 45.2 (d, 2J (PP) )
24.5 Hz), 12.8 (d). 1H NMR (CD2Cl2, 20 °C): δ 8.3-7.2 (m, 20H,
Ar-PPh2), 1.56 (s, 6H, Cp*), 1.52 (s, 6H, Cp*), 1.28 (s, 6H, Cp*),
Ack n ow led gm en t. Thanks are due to the following
institutions: European Community (contracts HPRN-
CT-2000-00010 and HPRN-CT-2002-00196; COST Ac-
tion D17 with the Working Groups 0007/2000 and 0002/
2000); a CNR-RAS bilateral agreement; the Russian
Foundation for Basic Research (Grants 00-03-32855 and
01-03-06145); Haldor Topsøe A/S (Denmark); the Shell
Research and Technology Centre, Amsterdam (M.A.Z.);
the National Research School Combination Catalysis
(Z.F.). A.L.S. wishes to thank The Netherlands Founda-
tion for Chemical Sciences (CW) with financial aid from
the Netherlands Organization for Scientific Research
(NWO).
3
1.10 (s, 6H, Cp*), 0.96 (dd, J (HP) ) 7.0, 3.8 Hz, 3H, Me).
Syn th esis of 14. To a solution of 13 (150 mg, 0.182 mmol)
in CH2Cl2 (10 mL) was added AgOTs (51 mg, 0.182 mmol).
After the resulting mixture was stirred overnight, it was
filtered over Celite and the filtrate was concentrated to 5 mL.
Addition of Et2O caused the precipitation of a yellow micro-
crystalline solid, which was filtered off, washed with Et2O, and
dried in a vacuum. Yield: 87%. Anal. Calcd for C50H56FeO4P2-
PdS: C, 61.45; H, 5.78. Found: C, 61.38; H, 5.79. 31P{1H} NMR
2
(CD2Cl2): (20 °C) δ 48.8 (br), 12.6 (d, J (PP) ) 20.5 Hz); (-80
°C) δ 50.8 (d, 2J (PP) ) 24.6 Hz), 12.7 (d). 1H NMR (CD2Cl2, 20
°C): δ 8.2-6.7 (m, 24H, Ar-PPh2 + Ar-OTs), 1.55 (s, 12H, Cp*),
1.28 (s, 6H, Cp*), 1.12 (s, 6H, Cp*), 0.88 (br t, 3J (HP) ) 6.4
Hz, 3H, Me). This complex behaves as a 1:1 electrolyte in both
CH2Cl2 (ΛM: 8 Ω-1 cm2 mol-1) and nitroethane (ΛM: 38 Ω-1
cm2 mol-1).32
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and collection parameters, bond lengths and angles, and
positional and thermal parameters for compound 7‚0.5CH2-
Cl2. This material is available free of charge via the Internet
at http://pubs.acs.org.
Rea ction of 14 w ith CO: Syn th esis of 15. Carbon
monoxide was bubbled for 5 min through a solution of 14 (15
mg, 0.015 mmol) in CD2Cl2 (1.5 mL) at 0 °C. A 1 mL sample
of the resultant solution was transferred by syringe into a 5
mm NMR tube at room temperature. 1H and 31P{1H} NMR
spectra showed the quantitative formation of 15. 31P{1H} NMR
(CD2Cl2, 20 °C): δ -13.3 (s). 1H NMR (CD2Cl2, 20 °C): δ 7.8-
7.0 (m, 24H, Ar-PPh2 + Ar-OTs), 3.09 (t, 4J (HP) ) 1.7 Hz, 3H,
OM021049B
(33) Bianchini, C.; Meli, A.; Traversi, A. Ital. Pat. FI A000025, 1997.
(34) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J . Appl. Crystallogr. 1999, 32, 115.
(35) Sheldrick, G. M. SHELXL96 Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1996.
(36) Spek, A. L. Acta Crystallogr. 1990, A46, C34.