Synthesis and characterization of cationic palladium (6,6′-dimethoxybiphenyl-2,2′-diyl)bis(diphenylphosphine) complexes

Article abstract of DOI:10.1021/om960445p

For compounds of the type [(MeO-BIPHEP)PdX₂] (where MeO-BIPHEP is (6,6′-dimethoxybiphenyl-2,2′-diyl)bis(diphenylphosphine) and X is an anion with low coordination ability) one or both anions X, depending on their nature, are displaced in an out

Full text of DOI:10.1021/om960445p

5196
Organometallics 1996, 15, 5196-5201
Syn th esis a n d Ch a r a cter iza tion of Ca tion ic P a lla d iu m
(6,6′-Dim eth oxybip h en yl-2,2′-d iyl)bis(d ip h en ylp h osp h in e)
Com p lexes
Martin Sperrle,† Volker Gramlich,‡ and Giambattista Consiglio*,†
Laboratorium fu¨r Technische Chemie and Laboratorium fu¨r Kristallographie, Eidgeno¨ssische
Technische Hochschule, ETH Zentrum, CH-8092 Zu¨rich, Switzerland
Received J une 4, 1996X
For compounds of the type [(MeO-BIPHEP)PdX2] (where MeO-BIPHEP is (6,6′-dimethoxy-
biphenyl-2,2′-diyl)bis(diphenylphosphine) and X is an anion with low coordination ability)
one or both anions X, depending on their nature, are displaced in an outer coordination
sphere due to water coordination. The compounds are easily reduced in methanolic solution.
With the diaquo complex [{(S)-MeO-BIPHEP}Pd(H2O)2](OTf)2 as starting material, the
formation of the dimeric palladium(I) complex [{(S)-MeO-BIPHEP}Pd]2(OTf)2 is observed.
In contrast, under CO pressure, the µ-hydrido µ-carbonyl binuclear palladium(I) complex
[{(S)-MeO-BIPHEP}Pd(µ-H)(µ-CO)Pd{(S)-MeO-BIPHEP}]OTf is formed. The molecular
structures of [{(S)-MeO-BIPHEP}Pd(H2O)(THF)](OTf)2 and [{(S)-MeO-BIPHEP}Pd(OTfa)2]
were determined by X-ray diffraction.
In recent years cationic palladium(II) complexes have
substrates such as nitroaromatics18 and alkylphenyl-
iodonium salts.19 Furthermore, oxidations,20 different
types of rearrangements,21,22 dimerization (of methyl
acrylate),23,24 acetalization and transacetalization,25
hydration,26 and carbon-carbon bond-forming reactions,
such as the Heck27,28 and aldol reactions,29 have been
catalyzed by cationic palladium complexes.
An important aspect of the chemistry of such com-
plexes is related to the coordination of water.30 In fact,
the aquo complexes can give the binuclear µ-hydroxo
species 2 (Scheme 1),31-36 which could lead to palladium
hydride species in the presence of reducing agents (e.g.
when CO is present, CO2 is formed).11,34,37,38 Palladium
attracted a great deal of attention in organometallic
chemistry, particularly due to their catalytic reactions
and to their application in the self-assembly of various
metallamacrocycles. In the field of catalysis, the most
important process which deserves mention is the co-
polymerization of olefins with carbon monoxide;1-3 this
is even more so if the possibility of extending the
copolymerization process to functionalized olefin sub-
strates is taken into account.4,5 Other useful applica-
tions, reported in the literature, include the carbony-
lation of olefinic substrates to form aldehydes,6,7
monoesters,8 ketones,9-12 and diesters,13-17 the water-
gas shift reaction,12 and the carbonylation of other
(18) Bontempi, A.; Alessio, E.; Chanos, G.; Mestroni, G. J . Mol.
Catal. 1987, 42, 67-80.
† Laboratorium fu¨r Technische Chemie.
(19) Kitamura, T.; Mihara, I.; Taniguchi, H.; Stang, P. J . J . Chem.
Soc., Chem Commun. 1990, 614-615.
‡ Laboratorium fu¨r Kristallographie.
X Abstract published in Advance ACS Abstracts, November 1, 1996.
(1) Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663-681.
(2) Amevor, E.; Bronco, S.; Consiglio, G.; Di Benedetto, S. Macromol.
Symp. 1995, 89, 443-454.
(20) Wenzel, T. T. J . Chem. Soc., Chem. Commun. 1989, 932-933.
(21) Murahashi, S.-I.; Makabe, Y.; Kunita, K. J . Org. Chem. 1988,
53, 4489-4495.
(22) Hirai, K.; Fuchikami, T.; Hirose, H.; Ojima. I. Eur. Patent Appl.
153,692, 1984; Chem. Abstr. 1986, 104, 70677.
(23) Oehme, G.; Pracejus, H. J . Organomet. Chem. 1987, 320, C56-
C58 and references therein.
(3) Sen, A. Acc. Chem. Res. 1993, 26, 303-310.
(4) Drent, E. Eur. Patent Appl. 251,373, 1987; Chem. Abstr. 1988,
109, 23531.
(5) J ohnson, L. K.; Mecking, S.; Brookhart, M. J . Am. Chem. Soc.
1996, 118, 267-268.
(6) Mrowca, J . J . U.S. Patent 3,876,672, 1972; Chem. Abstr. 1976,
84, 30432; cf. also Bel. Patent 825,835, 1975.
(7) Drent, E. Eur. Patent Appl. 220,767, 1985; Chem. Abstr. 1987,
107, 39199.
(8) Waller, F. J . Prepr. Am. Chem. Soc. Div. Pet. Chem. 1982, 27,
611-613.
(9) Zudin, V. N.; II’inich, G. N.; Likholobov, V. A.; Yermakov, Y. I.
J . Chem. Soc., Chem. Commun. 1984, 545-546.
(10) Drent, E. U.K. Patent Appl. 2,183,631, 1985; Chem. Abstr. 1987,
107, 153941.
(11) Pisano, C.; Consiglio, G. Gazz. Chim. Ital. 1994, 124, 393-401.
(12) Zudin, V. N.; Chinakov, V. D.; Nekipelov, V. M.; Rogov, V. A.;
Likholobov, V. A.; Yermakov, Y. I. J . Mol. Catal. 1989, 52, 27-48.
(13) Drent, E. Eur. Patent Appl. 121,965, 1983; Chem. Abstr. 1985,
102, 46423.
(14) Nefkens, S. C. A.; Sperrle, M.; Consiglio, G. Angew. Chem. 1993,
105 (32), 1837-1838; Angew. Chem., Int. Ed. Engl. 1993, 32, 1719-
1720.
(24) Guibert, I.; Neibecker, D.; Tkatchenko, I. J . Chem. Soc., Chem.
Commun. 1989, 1850-1852.
(25) Gorla, F.; Venanzi, L. M. Helv. Chim. Acta 1990, 73, 690-697.
(26) Ganguly, S.; Roundhill, D. M. J . Chem. Soc., Chem. Commun.
1991, 639-640.
(27) Cabri, W.; Candiani, I. Acc. Chem. Res. 1995, 28, 2-7.
(28) Brown, J . M.; Hii, K. K. Angew. Chem. 1996, 108, 679-682;
Angew. Chem., Int. Ed. Engl. 1996, 35, 657-659.
(29) Sodeoka, M.; Ohrai, K.; Shibasaki, M. J . Org. Chem. 1995, 60,
2648-2649.
(30) Stang, P. J .; Cao, D. H.; Poulter, G. T.; Arif, A. M. Organome-
tallics 1995, 14, 1110-1114.
(31) Bushnell, G. W.; Dixon, K. R.; Hunter, R. G.; McFarland, J . J .
Can. J . Chem. 1972, 50, 3694-3699.
(32) Longato, B.; Pilloni, G.; Valle, G.; Corain, B. Inorg. Chem. 1988,
27, 956-958.
(33) Wimmer, S.; Castan, P.; Wimmer, F. L.; J ohnson, N. P. Inorg.
Chim. Acta 1988, 142, 13-15.
(34) Pisano, C.; Consiglio, G.; Sironi, A.; Moret, M. J . Chem. Soc.,
Chem. Commun. 1991, 421-423.
(15) Sperrle, M.; Consiglio, G. J . Organomet. Chem. 1996, 506, 177-
180.
(16) Sperrle, M.; Consiglio, G. J . Am. Chem. Soc. 1995, 117, 12130-
12136.
(17) Ukaji, Y.; Miyamoto, M.; Mikuni, M.; Takeuchi, S.; Inomata,
K. Bull. Chem. Soc. J pn. 1996, 69, 735-742.
(35) Bandini, A. L.; Banditelli, G.; Demartin, F.; Manassero, M.;
Minghetti, G. Gazz. Chim. Ital. 1993, 123, 417-423.
(36) Li, J . J .; Li, W.; Sharp, P. R. Inorg. Chem. 1996, 35, 604-613.
(37) Consiglio, G.; Nefkens, S. C. A.; Pisano, C. Inorg. Chim. Acta
1994, 220, 273-281.
(38) Cavinato, G.; Toniolo, L. J . Mol. Catal. A 1996, 105, 9-15.
S0276-7333(96)00445-1 CCC: $12.00 © 1996 American Chemical Society

Pd Biphenyldiyl-Phosphine Complexes
Organometallics, Vol. 15, No. 24, 1996 5197
Sch em e 1
isomeric diphosphine ligands has been described re-
cently.42 Moreover, it was observed that the high
binding constant of water to palladium can lead to
displacement of ligands even if water is present at an
impurity level.28
The cation-anion separation of the complexes 1
corresponds to that expected for the various anions on
the basis of their σ-donor strength reported in the
literature.43 The stoichiometry of 1 is also supported
by conductivity measurements showing increased values
of conductivity ΛM with decreasing coordination ability
of the anion. This shows that cationic complexes must
be present in acetone solution for 1a -c. In contrast,
the low value of ΛM for 1d indicates that almost no
dissociation of the trifluoroacetate anions from the
palladium center takes place.
All complexes mentioned in Table 1 showed only one
31P NMR signal at room temperature.
A
31P NMR
variable-temperature study of 1a showed no line broad-
ening down to -80 °C. Attempts to recognize the
anisochronicity of the two phosphorus atoms of 1c
through low-temperature NMR spectroscopy failed.
However, the singlets of the methyl protons belonging
to the tosylate anion and to the methoxy substituent of
the MeO-BIPHEP ligand at room temperature split into
two signals with a ratio of ∼2:1 at -80 °C (2.17, 2.31
ppm and 3.40, 3.51 ppm). Correspondingly, the 31P
NMR spectrum contains two signals at 29.89 and 33.81
ppm in the same ratio of ∼2:1. The less intense set of
signals might be due to the diaquo complex, as indicated
by comparison of the NMR data. The species corre-
sponding to the second set of signals must, therefore,
contain coordinated tosylate anions as reported for 1c
in Table 1. However, whether the signals are due to
[{(S)-MeO-BIPHEP}Pd(OTs)2] or to a still dynamic
equilibrium at -80 °C between [{(S)-MeO-BIPHEP}-
Pd(OTs)2] and [{(S)-MeO-BIPHEP}Pd(OTs)(H2O)](OTs)
is not obvious. An equilibrium between the coordination
of water (present at an impurity level), the solvent
(THF), and a triflate anion toward a cationic aryl-
(diphosphine)palladium(II) fragment has been reported
recently.28 A rapid exchange of THF and water was
observed that could be slowed down at -98 °C. The
corresponding complex with coordinated triflate, how-
ever, has not been observed. Analogously, we observed
that complex 1a crystallized out from a THF solution
with exchange of one water molecule as [{(S)-MeO-
BIPHEP}Pd(H2O)(THF)](OTf)2.
In an attempt to determine the conductivity of 1a -d
in methanol, a color change of the solutions from yellow
to red was observed. The rate of the development of
the red color was enhanced by increasing the temper-
ature. The conductivity ΛM of 1d after stirring a 10-3
M methanolic solution for 30 min is 64 Ω-1 cm2 mol-1
as compared to 4 Ω-1 cm2 mol-1 in acetone (see Table
1). A methanolic solution of 1a was heated overnight
at 50 °C. The 31P NMR spectrum showed the appear-
ance of an AA′XX′ pattern as well as the original singlet
of unreacted 1a (∼60%). The red color and the NMR
data imply the formation of the dimeric palladium(I)
complex [{(S)-MeO-BIPHEP}Pd]2(OTf)2, to which struc-
ture 3 (Scheme 1; P-P ) (S)-MeO-BIPHEP, X ) OTf) is
Ta ble 1. 31P NMR a n d Con d u ctivity Da ta for 1a -d
31P conductivity
b
complex
NMRa
ΛM
[{(S)-MeO-BIPHEP}Pd(H2O)2](OTf)2 (1a )
[{(S)-MeO-BIPHEP}Pd(H2O)2](BF4)2 (1b)
[{(S)-MeO-BIPHEP}Pd(H2O)(OTs)]OTs (1c) 30.7
[{(S)-MeO-BIPHEP}Pd(OTfa)2] (1d ) 27.5
33.7
33.3
157
171
55
4
a
b
δ (ppm) in CDCl3. In a 10-3 M acetone solution (Ω-1 cm2
mol-1).
hydrides are believed to be part of the catalytic cycle in
most of the aforementioned reactions.
In view of the growing interest in cationic palladium
complexes containing chiral atropisomeric diphosphine
ligands, both for highly enantioselective catalytic
reactions14-16,29,39 and for the self-organizing assembly
of high-molecular weight species,40 we report here the
preparation of some palladium(II) complexes of the
MeO-BIPHEP ligand (MeO-BIPHEP is (6,6′-dimethoxy-
biphenyl-2,2′-diyl)bis(diphenylphosphine)) with different
anions as well as their characterization in solution and,
for two of them, in the solid state. Furthermore, their
reactivity under conditions relevant to carbonylation
catalysis is discussed.
With [{(S)-MeO-BIPHEP}PdCl2] as starting mate-
rial,16 the addition of the corresponding silver salts AgX
(X- ) OTf-, BF4-, OTs-, OTfa-) in tetrahydrofuran or
acetone led to the formation of the complexes 1 as yellow
microcrystalline solids. Table 1 shows the 31P NMR
data and the conductivity in a 10-3 M acetone solution
of the complexes. The reported composition of the
complexes is based on those data as well as on elemental
1
analysis and H NMR data.
All manipulations were carried out under a dry
nitrogen atmosphere using Schlenk techniques and
dried solvents; however, with the exception of the
trifluoroacetato compound 1d , the aquo complex was
isolated. A possible source of water may be the silver
salt, which was used, as purchased, for the synthesis.
This was already observed for the preparation of cationic
aquocarbonylmanganese and -rhenium complexes with
weakly coordinating anions.41 The high hygroscopicity
of anhydrous palladium bis(triflates) containing atrop-
(39) Yamaguchi, M.; Yabuki, M.; Yamagishi, T.; Sakai, K.; Tsubo-
mura, T. Chem. Lett. 1996, 241-242.
(40) Stang, P. J .; Olenyuk, B. Angew. Chem. 1996, 108, 798-802.
(41) Horn, E.; Snow, M. R. Aust. J . Chem. 1984, 37, 1375-1393.
(42) Stang, P. J .; Olenyuk, B.; Arif, A. M. Organometallics 1995,
14, 5281-5289.
(43) Beck, W.; Su¨nkel, K. Chem. Rev. 1988, 88, 1405-1421.

5198 Organometallics, Vol. 15, No. 24, 1996
Sperrle et al.
ascribed in analogy to a recently described similar
binuclear Pd(I) compound.44 Attempts to isolate 3
through crystallization were unsuccessful.
The fact that the reduction of palladium occurs but
carbonyl complexes do not form, as was expected,45-47
prompted us to study this reaction in the presence of
carbon monoxide, i.e. under conditions in which com-
pounds 1 are catalyst precursors for carbonylation
reactions. The NMR spectra show that, after 20 h at
50 °C under a CO pressure of 50 bar, about half of 1a
is transformed into the µ-hydrido µ-carbonyl binuclear
palladium(I) complex [{(S)-MeO-BIPHEP}Pd(µ-H)(µ-
CO)Pd{(S)-MeO-BIPHEP}]OTf (4; Scheme 1; P-P ) (S)-
MeO-BIPHEP, X ) OTf). 4 represents a dynamic
system at room temperature as analogous com-
pounds.45-47 Thus, the 1H NMR spectrum exhibits a
quintet for the bridging hydride centered at -5.22 ppm
F igu r e 1. ORTEP diagram of [{(S)-MeO-BIPHEP}Pd-
(H2O)(THF)](OTf)2.
2
with a J PH coupling of 44 Hz at 25 °C changing into a
triplet of triplets at -50 °C (2J PH(trans) ) 92 Hz and
2J PH(cis) ) 6 Hz). On the other hand, the 31P NMR
spectrum shows a broad signal at room temperature at
22 ppm, which splits into two doublets at 25.22 and
19.92 ppm (J PP ) 37 Hz) at -40 °C. The IR spectrum
of 4 shows a strong band at 1835 cm-1 in accordance
with the literature.46,47
The oxidation of methanol by palladium(II) complexes
has been observed to occur over a π-bonded palladium-
(II) formaldehyde hydride complex, which eventually
decarbonylates to form a Pd(0) carbonyl compound.46
Thus, the formation of 3 in the absence of carbon
monoxide could imply that, in the present reaction, the
decarbonylation of formaldehyde is not favored.46 On
the other hand, in the presence of carbon monoxide, the
palladium hydride intermediate can be stabilized by CO,
thereby forming 4 through combination with an unsat-
urated Pd(0) intermediate.
F igu r e 2. ORTEP diagram of [{(S)-MeO-BIPHEP}Pd-
(OTfa)2].
Suitable single crystals for X-ray structure determi-
nations were obtained by vapor diffusion of n-pentane
into 10-5 M THF solutions of 1a and 1d at room
temperature. Selected crystallographic data are sum-
marized in Table 2, and ORTEP diagrams of [{(S)-MeO-
BIPHEP}Pd(H2O)(THF)](OTf)2 and [{(S)-MeO-BIPHEP}-
Pd(OTfa)2] with the atom-numbering scheme are dis-
played in Figures 1 and 2, respectively. Both com-
pounds crystallize in the orthorhombic space group
P212121 as yellow platelets. Two cis positions are
occupied by the (S)-MeO-BIPHEP ligand for both com-
pounds. In [{(S)-MeO-BIPHEP}Pd(OTfa)2] the trifluo-
roacetate anions are directly coordinated to the palla-
dium atom, whereas in [{(S)-MeO-BIPHEP}Pd(H2O)-
(THF)](OTf)2 the triflates act as counteranions. In the
latter case the other two cis positions in the first
coordination sphere of the palladium are occupied by
one molecule of water and one of THF.
configuration of the chiral diphosphine and the confor-
mation of the chelating seven-membered ring corre-
sponds to that reported in the sole X-ray structure of a
compound containing the MeO-BIPHEP ligand.50 In
that compound, the R enantiomeric ligand formed a
seven-membered ring including a palladium atom with
a λ skew(v) boat conformation.
The least-squares planes of the two phenyl rings of
the biphenyl system in MeO-BIPHEP exhibit an inter-
planar angle θ of 71.1° for [{(S)-MeO-BIPHEP}Pd(H2O)-
(THF)](OTf)2 and 71.4° for [{(S)-MeO-BIPHEP}Pd-
(OTfa)2]. These values are similar to the 70.3° angle
reported for θ of the above-mentioned palladium com-
plex bearing the (R)-MeO-BIPHEP ligand and an ortho-
metalated dimethyl(R-methylbenzyl)amine.50 Moreover,
the quasi-axial phenyl rings of the diphenylphosphino
groups possess a roughly parallel orientation with
apparent π-π stacking interactions with respect to one
phenyl ring of the biphenyl system. The interplanar
angles of the best-squares planes of 18.6 and 23.2° are
slightly higher than the values of 12.4 and 14.1°
reported for the aforementioned ortho-metalated pal-
ladium complex.50
In both compounds the seven-membered hetero-
metallacyclic ring involving the (S)-MeO-BIPHEP ligand
adopts a skew(v) boat conformation with δ absolute
configuration.48,49 This correlation between the absolute
(44) Budzelaar, P. H. M.; van Leeuwen, P. W. N. M.; Roobeek, C.
F.; Orpen, A. G. Organometallics 1992, 11, 23-25.
(45) Portnoy, M.; Frolow, F.; Milstein, D. Organometallics 1991, 10,
3960-3962.
(46) Portnoy, M.; Milstein, D. Organometallics 1994, 13, 600-609.
(47) Toth, I.; Elsevier, C. J . Organometallics 1994, 13, 2118-2122.
(48) Inorg. Chem. 1970, 9, 1-5.
(49) Kashiwabara, K.; Hanaki, K.; Fujita, J . Bull. Chem. Soc. J pn.
1980, 53, 2275-2280.
In both complexes the Pd(II) has a distorted-square-
planar coordination. While in [{(S)-MeO-BIPHEP}Pd-
(H2O)(THF)](OTf)2 the oxygen atoms O(7) and O(8) are
(50) Schmid, R.; Foricher, J .; Cereghetti, M.; Scho¨nholzer, P. Helv.
Chim. Acta 1991, 74, 370-389.

Pd Biphenyldiyl-Phosphine Complexes
Organometallics, Vol. 15, No. 24, 1996 5199
Ta ble 2. Exp er im en ta l Da ta for th e X-r a y
Diffr a ction Stu d y of
[{(S)-MeO-BIP HEP }P d (H2O)(THF )](OTf)2 a n d
[{(S)-MeO-BIP HEP }P d (OTfa )2]
with the corresponding bond length in related Pd-OH2
complexes.30,51
Different bond lengths Pd-O were observed for the
coordinated trifluoroacetate anions in [{(S)-MeO-
BIPHEP}Pd(OTfa)2]. As already mentioned, O(8) is out
of the P(1)-Pd-P(2) plane having the longer distance.
Therefore, the angles P(2)-Pd-O(8) and O(8)-Pd-P(1)
differ remarkably with respect to the corresponding
angles P(1)-Pd-O(7) and O(7)-Pd-P(2). The bite
angles of the MeO-BIPHEP ligand in both crystal
structures with values of 90.7 and 92.9° are similar to
the 91.7° angle reported by Schmid et al.50
[{(S)-MeO-
BIPHEP}Pd(H2O)-
(THF)](OTf)2
[{(S)-MeO-
BIPHEP}-
Pd(OTfa)2]
mol formula
mol wt
C44H40F6O10P2PdS2 C42H32F6O6P2Pd
1075.2
915.0
cryst dimens (mm)
data collecn T (°C)
cryst syst
space group
a (Å)
0.1 × 0.2 × 0.4
0.1 × 0.1 × 0.3
20
20
orthorhombic
P212121
10.994(2)
11.453(2)
36.307(7)
4571.6(15)
4
1.562
6.48
2184
orthorhombic
P212121
13.856(14)
13.929(15)
21.12(3)
4077(9)
4
1.491
6.07
1848
b (Å)
The coordinated O(8) water molecule in [{(S)-MeO-
BIPHEP}Pd(H2O)(THF)](OTf)2 forms intermolecular
hydrogen bonds to two oxygen atoms of two different
triflate anions. The distances of Pd-O(11) and Pd-
O(22) are 2.74(1) and 2.72(1) Å, respectively. A similar
hydrogen-bonding pattern was recently observed for the
monoaquo and diaquo cationic palladium(II) complexes
bearing the chelating DPPP diphosphine ligand.30 Hy-
drogen bonding seems to be a common feature in aquo-
transition-metal complexes55 due to its importance in
the stabilization of the solid-state structure of these
molecules.56,57
c (Å)
V (Å3)
Z
Dcalcd (g cm-3
)
abs coeff (cm-1
F(000)
)
diffractometer
radiation
Siemens R3m/V
Syntex P21
Mo KR (graphite monochrom);
λ ) 0.710 73 Å
scan range, 2θ (deg)
scan type
no. of indep data collected 2446
3.0-40.0
2θ-θ
3.0-40.0
2θ-θ
2179
no. of obsd rflns (n0)
abs cor
1988
N/A
1149
N/A
no. of params refined (nv) 467
weighting scheme
174
Particularly noteworthy are the nonbonding inter-
actions in [{(S)-MeO-BIPHEP}Pd(H2O)(THF)](OTf)2 be-
tween the palladium center and an oxygen atom of an
uncoordinated triflate anion. Thus, a Pd-O(13) dis-
tance of about 3.35(1) Å was observed.
w-1 ) σ2(F) +
0.0000F2
0.0449
w-1 ) σ2(F) +
0.0000F2
0.0852
0.0651
2.42
R
Rw
GOF
0.0450
3.04
Recently, Seebach et al. established the existence of
two categories of transition-metal complexes containing
chelating bis(diphenylphosphino) ligands by superim-
posing a large number of X-ray structures: one has
approximate C2 symmetry with respect to the two
diphenylphosphino groups, and the other has C1 sym-
metry.58 Both [{(S)-MeO-BIPHEP}Pd(H2O)(THF)](OTf)2
and [{(S)-MeO-BIPHEP}Pd(OTfa)2] belong to the former
class, having two of the four phosphorus-phenyl rings
oriented quasi-axially and the other two phenyl groups
quasi-equatorially with respect to the P(1)-Pd-P(2)
plane. Note that the quasi-axial rings are at the rear,
while the quasi-equatorial phenyl groups are pushed
toward the palladium center.
Ta ble 3. Selected Bon d Dista n ces a n d An gles
[{(S)-MeO-BIPHEP}- [{(S)-MeO-BIPHEP}-
Pd(H2O)(THF)](OTf)2
Pd(OTfa)2]
Bond Distances (Å)
2.248(4)
2.256(4)
2.130(12)
2.147(9)
Pd-P(1)
Pd-P(2)
Pd-O(7)
Pd-O(8)
2.256(13)
2.240(12)
2.076(20)
2.239(31)
Bond Angles (deg)
90.7(2)
91.8(3)
91.6(3)
87.1(4)
P(1)-Pd-P(2)
P(1)-Pd-O(7)
P(2)-Pd-O(8)
O(7)-Pd-O(8)
O(7)-Pd-P(2)
O(8)-Pd-P(1)
92.9(4)
93.5(6)
80.8(8)
93.3(9)
173.6(6)
156.7(9)
173.4(3)
169.4(3)
A schematic superimposition of the two structures,
as shown in Figure 3, revealed virtually identical
conformations in the solid state of the [{(S)-MeO-
BIPHEP}Pd} fragments.
situated above and below the P(1)-Pd-P(2) plane with
distances of 0.23(1) and 0.39(1) Å, respectively, only O(8)
of one trifluoroacetate ligand is positioned 0.85(1) Å
outside the P(1)-Pd-P(2) plane in [{(S)-MeO-BIPHEP}-
Pd(OTfa)2]. The relatively strong deviation of O(8) in
the latter case resulted in a elongated Pd-O(8) bond
length.
The steric requirement of the quasi-equatorial phenyl
groups around the coordination sphere of the metal in
addition to the rigidity of the axially dissymmetric
biphenyl system is believed to be responsible for the very
high enantioface discrimination observed in the forma-
tion of optically active dimethyl 2-phenylbutanedioate14
and optically active dimethyl 2-oxo-3-phenyl-pentanedio-
ate.15 If we take into account the possible interactions
of the substituent of the olefin substrate during the
insertion into a [Pd]-COOCH3 bond and the secondary
Relevant bond lengths and angles for both structures
are reported in Table 3. The palladium-phosphorus
distances are similar for both complexes, and the values
of 2.240-2.256 Å are in the normal range for cis-
chelated phosphorus at a palladium(II) center.30,51-54
The Pd-OH2 distance in 1a of 2.147 Å is comparable
(51) Benetollo, F.; Bertani, R.; Bombieri, G.; Toniolo, L. Inorg. Chim.
Acta 1995, 233, 5-9.
(55) Boyer, P. M.; Roy, C. P.; Bielski, J . M.; Merola, J . S. Inorg. Chim.
Acta 1996, 245, 7-15.
(52) Ozawa, F.; Kubo, A.; Matsumoto, Y.; Hayashi, T.; Nishioka, E.;
Yanagi, K.; Moriguchi, K. Organometallics 1993, 12, 4188-4196.
(53) Hayashi, T.; Konishi, M.; Kobori, Y.; Kumada, M.; Higuchi, T.;
Hirotsu, K. J . Am. Chem. Soc. 1984, 106, 158-163.
(54) Steffen, W. L.; Palenik, G. J . Inorg. Chem. 1976, 15, 2432-
2439.
(56) Braga, D.; Grepioni, F. Acc. Chem. Res. 1994, 27, 51-56.
(57) Braga, D.; Grepioni, F.; Sabatino, P.; Desiraju, G. R. Organo-
metallics 1994, 13, 3532-3543.
(58) Seebach, D.; Devaquet, E.; Ernst, A.; Hayakawa, M.; Ku¨hnle,
F. N. M.; Schweizer, W. B.; Weber, B. Helv. Chim. Acta 1995, 78, 1636-
1650.

5200 Organometallics, Vol. 15, No. 24, 1996
Sperrle et al.
completed after 24 h at 4 °C. The yellow precipitate was
filtered off and dried under reduced pressure. The crude
product was recrystallized from acetone/n-pentane. Yield:
86% (0.225 g, 0.25 mmol). 1H NMR (300 MHz, CDCl3, 25 °C):
δ 2.8 (s, 4H, H2O), 3.51 (s, 6H, OCH3), 6.57-6.60 (m, 2H),
6.84-6.90 (m, 2H), 7.02-7.08 (m, 2H), 7.40-7.92 (m, 20H,
H
arom). 31P{1H} NMR (121.02 MHz, CDCl3, 25 °C): δ 33.3.
Anal. Calcd for C38H36P2O4F8B2Pd (898.7): C, 50.79; H, 4.04.
Found: C, 50.55; H, 4.25.
P r epar ation of [{(S)-MeO-BIP HEP }P d(H2O)(OTs)](OTs)
(1c). The procedure is the same as that for 1a , except that
AgOTs (0.293 g, 1.05 mmol) dissolved in THF (50 mL) was
stirred for 5 h with [((S)-MeO-BIPHEP)PdCl2] (0.399 g, 0.525
mmol) in THF (150 mL) to give a yellow solid of 1c. Yield:
87% (0.481 g, 0.458 mmol). 1H NMR (200 MHz, CDCl3, 25
°C): δ 2.22 (s, 6H, PhCH3), 3.44 (s, 6H, OCH3), 4.54 (s, 2H,
H2O), 6.45-6.49 (m, 2H), 6.71-6.85 (m, 6H), 6.92-7.02 (m,
2H), 7.26-8.03 (m, 24H, Harom). 31P{1H} NMR (81.02 MHz,
CDCl3, 25 °C): δ 30.7. Anal. Calcd for C52H48P2O9S2Pd
(1049.5): C, 59.51; H, 4.61. Found: C, 59.65; H, 4.74.
P r ep a r a tion of [{(S)-MeO-BIP HEP }P d (OTfa )2] (1d ).
The same procedure as described for 1a was applied, except
that AgOTfa (0.385 g, 1.74 mmol) in THF (20 mL) and [((S)-
MeO-BIPHEP)PdCl2] (0.662 g, 0.87 mmol) dissolved in THF
(100 mL) led to 1d as a yellow solid. Yield: 84% (0.664 g,
0.73 mmol). 1H NMR (200 MHz, CDCl3, 25 °C): δ 3.43 (s, 6H,
OCH3), 6.42-6.46 (m, 2H), 6.74-6.83 (m, 2H), 6.93-7.01 (m,
2H), 7.26-7.97 (m, 20H, Harom). 31P{1H} NMR (81.02 MHz,
CDCl3, 25 °C): δ 27.5. Anal. Calcd for C42H32P2O6F6Pd
(915.1): C, 55.13; H, 3.52; F, 12.46. Found: C, 54.86; H, 3.74;
F, 12.54. Single crystals suitable for X-ray structure deter-
mination were obtained by vapor diffusion of n-pentane into
a THF solution of 1d at room temperature.
F igu r e 3. Schematic superposition of the [{(S)-MeO-
BIPHEP}PdO2] fragments of the two crystal structures.
insertion established for styrene59,60 as the substrate,
the prevailing formation of the l enantiomer (with
respect to the absolute configuration of the ligand) can
be rationalized.
Exp er im en ta l Section
Sta r tin g Ma ter ia ls. Silver tetrafluoroborate (AgBF4),
silver trifluoromethanesulfonate (AgSO3CF3 or AgOTf), silver
p-toluenesulfonate (AgCH3C6H4SO3 or AgOTs), silver trifluo-
roacetate (AgCF3CO2/AgOTfa), and MeOH (crown cap) were
obtained from Fluka. [{(S)-MeO-BIPHEP}PdCl2] was pre-
pared according to the literature.16
Gen er a l P r oced u r es. All reactions and manipulations
were carried out under a purified nitrogen atmosphere using
either Schlenk techniques or a glovebox (MBraun MB 150BG-
I). 1H and 13C NMR data were reported with tetramethylsilane
and 85% H3PO4 as the standard. THF was distilled over
sodium/benzophenone ketyl and acetone over Drierite (Fluka
product) prior to use.
P r ep a r a t ion of [{(S)-MeO-BIP H E P }P d (H2O)2](OTf)2
(1a ). A solution of AgOTf (0.632 g, 2.46 mmol) in THF (25
mL) was added dropwise in the dark to a solution of [((S)-MeO-
BIPHEP)PdCl2] (0.936 g, 1.23 mmol) in THF (125 mL). The
reaction mixture was stirred for 2 h at room temperature. The
precipitated AgCl was filtered off on Celite and washed twice
with THF (15 mL). The filtrate was concentrated to a total
volume of about 30 mL by evaporation under reduced pressure.
Pentane was added to initiate crystallization, which was
completed within 24 h at 4 °C. The yellow precipitate was
filtered off and dried under reduced pressure. The crude
product was recrystallized from THF/hexane. Yield: 77%
(0.971 g, 0.95 mmol). 1H NMR (300 MHz, CDCl3, 25 °C): δ
3.51 (s, 6H, OCH3), 4.05 (s, 4H, H2O), 6.58-6.60 (m, 2H), 6.79-
6.86 (m, 2H), 7.02-7.09 (m, 2H), 7.37-7.88 (m, 20H, Harom).
31P{1H} NMR (121.02 MHz, CDCl3, 25 °C): δ 33.4. Anal.
Calcd for C40H36P2O10F6S2Pd (1023.4): C, 46.95; H, 3.55.
Found: C, 46.74; H, 3.63. Suitable single crystals for X-ray
structure determination were obtained by vapor diffusion of
n-pentane into a THF solution of 1a at room temperature.
P r epar ation of [{(S)-MeO-BIP HEP }P d(H2O)2](BF4)2 (1b).
A solution of AgBF4 (0.111 g, 0.58 mmol) in acetone (20 mL)
was added in the dark to a solution of [((S)-MeO-BIPHEP)-
PdCl2] (0.218 g, 0.29 mmol) in acetone (60 mL). The reaction
mixture was stirred for 2 h at room temperature. The
precipitated AgCl was filtered off on Celite and washed twice
with acetone (5 mL). The filtrate was concentrated to a total
volume of about 25 mL by evaporation under reduced pressure.
Diethyl ether was added to initiate crystallization, which was
Rea ction of 1a w ith Meth a n ol. A solution of 1a (0.067
g, 0.065 mmol) was stirred in methanol (3 mL) under a
nitrogen atmosphere at 50 °C for 12 h. The red residue
obtained after evaporation was dried in vacuo for 12 h. The
1H NMR spectrum shows the formation of [{(S)-MeO-BIPHEP}-
Pd]2(OTf)2 (3) in 35% yield based on the integration of the
methoxy signals of the MeO-BIPHEP ligand, in addition to
1a (60%) and 5% of a complex as yet unidentified. The latter
shows a singlet at 23.6 ppm in the 31P NMR (81.02 MHz, CD2-
Cl2, 25 °C) and a singlet at 4.03 ppm in the 1H NMR (200 MHz,
CD2Cl2, 25 °C) for the methoxy groups. Selected data for 3
(simulated with PANIC from Bruker Spectrospin AG): 31P{1H}
NMR (81.02 MHz, CD2Cl2, 25 °C) δA 29.76, δX 5.80, J AA′ ) 226.3
1
Hz, J XX′ ) 9.5 Hz, J AX ) -57.1 Hz, J AX′ ) 125.8 Hz; H NMR
(500 MHz, CD2Cl2, 25 °C) δ 3.06 (s, 3H, OCH3), 3.29 (s, 3H,
OCH3).
Rea ction of 1a w ith Meth a n ol in th e P r esen ce of
Ca r bon Mon oxid e. A solution of 1a (0.087 g, 0.085 mmol)
in methanol (12 mL) was transferred under
a nitrogen
atmosphere into a 150 mL steel autoclave. The autoclave was
heated to 50 °C under a CO pressure of 50 bar for 20 h. After
the gas was released, the resulting red solution was evaporated
in vacuo, and the red residue was dried overnight. The NMR
spectra show the formation of 4 as well as unreacted 1a (50%).
Selected data for 4: 1H NMR (200 MHz, CD2Cl2, 25 °C) δ -5.22
1
ppm (2J PH ) 44 Hz); H NMR (200 MHz, CD2Cl2, -50 °C) δ
2
-5.22 ppm (2J PH(trans) ) 92 Hz, J PH(cis) ) 6 Hz); 31P NMR
(81.02 MHz, CD2Cl2, 25 °C) δ 22 ppm; 31P NMR (81.02 MHz,
CD2Cl2, -40 °C): δ 19.92 ppm (d, J PP ) 37 Hz), 25.22 (d, J PP
) 37 Hz); IR (νCO) 1835 cm-1
.
X-r ay Cr ystallogr aph ic Stu dies of [{(S)-MeO-BIP HEP }-
P d(H2O)(THF)](OTf)2 an d [{(S)-MeO-BIP HEP }P d(OTfa)2].
Data were measured with variable scan speed to ensure
constant statistical precision on the collected intensities. One
standard reflection was measured every 120 reflections; no
significant variation was detected. The structures were solved
by direct methods and refined by full-matrix least squares
using anisotropic displacement parameters for all non-
hydrogen atoms. The contribution of the hydrogen atoms in
(59) Pisano, C.; Nefkens, S. C. A.; Consiglio, G. Organometallics
1992, 11, 1975-1978.
(60) Barsacchi, M.; Consiglio, G.; Medici, L.; Petrucci, G.; Suter, U.
W. Angew. Chem. 1991, 103, 992-994; Angew. Chem., Int. Ed. Engl.
1991, 30, 989-991.

Pd Biphenyldiyl-Phosphine Complexes
Organometallics, Vol. 15, No. 24, 1996 5201
their idealized positions (riding model with fixed isotropic U)
was taken into account but not refined. All calculations were
carried out by using the Siemens SHELXTL PLUS system.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and refinement details, all bond distances and angles,
and anisotropic displacement coefficients for the non-carbon
atoms of [{(S)-MeO-BIPHEP}Pd(H2O)(THF)](OTf)2 and [{(S)-
MeO-BIPHEP}Pd(OTfa)2] (18 pages). Ordering information
is given on any current masthead page.
Ack n ow led gm en t. We are very grateful to Hoff-
mann-La Roche AG for providing the MeO-BIPHEP
ligand and to A. Mezzetti for the simulation of the 31P
NMR spectra of 3.
OM960445P