Palladium(II) complexes with hemilabile etherdiphos ligands in the alternating copolymerization of carbon monoxide with olefins

Article abstract of DOI:10.1016/S0020-1693(99)00323-0

The potentially hexadentate diphos ligands (ROCH₂CH₂)₂P(CH₂) ₃P(CH₂CH₂OR)₂ (1a-d) (R = Et (a), n-Bu (b), t-Bu (c), Cy (d)) are accessible by photochemically induced hy

Full text of DOI:10.1016/S0020-1693(99)00323-0

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 296 (1999) 103–113
Palladium(II) complexes with hemilabile etherdiphos ligands in the
alternating copolymerization of carbon monoxide with olefins
Ekkehard Lindner *, Markus Schmid, Peter Wegner, Christiane Nachtigal,
Manfred Steimann, Riad Fawzi
Institut fu¨r Anorganische Chemie der Uni6ersita¨t Tu¨bingen, Auf der Morgenstelle 18, D-72076 Tu¨bingen, Germany
Received 13 May 1999; accepted 30 July 1999
Abstract
The potentially hexadentate diphos ligands (ROCH2CH2)2P(CH2)3P(CH2CH2OR)2 (1a-d) (R=Et (a), n-Bu (b), t-Bu (c), Cy (d))
are accessible by photochemically induced hydrophosphination of the vinyl ethers CH2ꢀCHꢁOR with the diprimary phosphine
H2P(CH2)3PH2. Treatment of 1a–d with (PhCN)2PdCl2 in CH2Cl2 leads to the dichlorodiphospalladium(II) complexes 2a–d, from
which the dicationic palladium(II) complexes 3a–d were obtained by abstraction of the chlorides with AgBF4 in CH2Cl2. In 3a–d
the etherdiphos ligands are coordinated in a h4(O,P;O%,P%) fashion. A rapid chemical exchange between the h2-PSO chelated and
the h1-P coordinated part of the ligands in 3a–d was demonstrated by means of temperature-dependent 13C{1H} NMR
spectroscopy. Both PdꢁO bonds in 3a–d are easily cleaved by polar solvents such as acetonitrile and water resulting in the
formation of the adducts 3b · 2CH3CN, 3c · H2O, and 3c · 2H2O. The molecular structures of 2a and 3c · H2O were determined by
single crystal X-ray diffraction methods. Under a total pressure of 60 bar ethene/CO and propene/CO, respectively, 3a-d are
highly active catalysts in the copolymerization of olefins with carbon monoxide. GPC measurements revealed high molecular
weights of these polyketones. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Palladium complexes; Hemilabile ligands; Copolymerization; Ethene; Propene; Carbon monoxide
imines [5] were employed and carbon monoxide was
replaced by other polar building blocks, such as sulfur
1. Introduction
dioxide [6] or alkane-a,v-dinitrite esters [7].
The alternating copolymerization of carbon monox-
ide with a-olefins forming polyketones (Scheme 1) has
attracted both academic and industrial interest, because
The copolymerization is commonly catalyzed by
cationic palladium complexes, provided with bidentate
phosphorus [8] or nitrogen [9] ligands (LSL), weakly
of at least four reasons: (i) a plausible reaction mecha-
coordinating anions (A−) [10], and solvent molecules
nism which makes the alternation of the inserted
(solv) (Scheme 2). Diphosphines with a hydrocarbon
monomers clear [1]; (ii) an easy and cheap access of the
backbone consisting of three methylene groups belong
comonomers; (iii) the polymers engineering properties
to the most active palladium catalysts [8,11]. Upon
[2], and (iv) the potential of further derivatization of the
carbonyl group [3]. A great variety of olefins [4] or
polymerization conditions the solvent molecules are
separated and the complex fragment is then trans-
formed to the active form [1a].
Scheme 1.
* Corresponding author. Tel.: +49-7071-297 2039; fax: +49-
7071-295 306.
E-mail address: ekkehard.lindner@uni-tuebingen.de (E. Lindner)
Scheme 2.
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00323-0

104
E. Lindner et al. / Inorganica Chimica Acta 296 (1999) 103–113
1
The introduction of bifunctional ether-phosphines
NMR 101.25 MHz. Chemical shifts in the H, 31P{1H},
and 13C{1H} spectra were measured relative to partially
deuterated solvent peaks and to deuterated solvent
peaks, respectively, which are reported relative to TMS.
Mass spectra were acquired on a Finnigan MAT 711A
modified by AMD ‘Meß- und Datensysteme’ (8 kV, 303
K) and reported as mass/charge (m/z). IR spectra were
recorded on a Bruker IFS 48 FT-IR spectrometer.
Molecular weights were determined by means of gel
permeation chromatography (GPC), using a set-up con-
sisting of a Perkin–Elmer Series 10 HPLC pump, a
Perkin–Elmer LC 90 UV-detector, a PSS SDV linear
XL column (CHCl3) with a pore size of 10 mm or a PSS
PFG linear XL column (1,1,1,3,3,3-hexafluoroiso-
propanol) with a pore size of 7 mm. All molecular
weights refer to narrow distributed polymethyl-
methacrylate standards.
[12] makes the external solvent molecules unnecessary.
Hemilabile ligands of this type are provided with an
ether-oxygen donor forming only weak metal–oxygen
interactions while the phosphorus atom is strongly co-
ordinated to the central atom. The oxygen-containing
part of the ligand may be regarded as an intramolecular
solvent stabilizing vacant coordination sites. Bis(ether-
phosphine)palladium(II), ruthenium(II), and rhodi-
um(I) complexes show fluxional behavior which can be
studied by dynamic 31P NMR spectroscopy [13]. Com-
parable hybrid palladium(II) complexes with monoden-
tate phosphines have already been successfully
employed in an interphase catalysis for the copolymer-
ization of ethene with carbon monoxide [14]. Although
in dicationic bis(chelated) palladium(II) complexes the
phosphorus atoms initially are oriented in a cis fashion
[15], in the course of the copolymerization a rearrange-
ment to the inactive trans complexes takes place. Keim
and co-workers demonstrated that palladium(II) com-
plexes containing anionic hemilabile phosphine ligands
enhance the catalytic activity leading to high molecular
weight copolymers [16]. Therefore in this investigation
hemilabile diphosphines were employed in the copoly-
merization of carbon monoxide with ethene and
propene, respectively. The ability of the intramolecular
ether moiety to stabilize electron deficient palladium
species should suppress the decomposition of the cata-
lyst which is associated with the formation of
palladium.
2.2. Preparation of the phosphine ligands 1a–d.
General procedure A
In a quartz Schlenk tube 1,3-diphosphinopropane
and an excess of the corresponding olefin were magnet-
ically stirred and the mixture was irradiated with the
ultraviolet light of a mercury high pressure lamp. After
6 h excess olefin was removed under reduced pressure.
Further purification was not necessary.
Hazards: The phosphines 1a–c are pyrophoric in
contact with cellulose.
2.3. 1,3-Bis[di(2-ethoxyethyl)phosphino]propane (1a)
2. Experimental
1,3-Diphosphinopropane (891 mg, 8.25 mmol) and
ethylvinyl ether (2.617 g, 36.3 mmol) were reacted
according to procedure A to give 3.14 g (96%) of 1a.
MS (EI): m/z 396.1 (M+). Anal. Calc. for C19H42O4P2
(396.2): C, 57.56; H, 10.68. Found: C, 57.10; H,
2.1. General remarks
All experiments were carried out under an atmo-
sphere of argon, unless otherwise stated. Dichloro-
methane was distilled from calcium hydride, diethyl
ether from sodium/benzophenone, n-hexane from
LiAlH4 and acetonitrile from P4O10. PdCl2 was a gift
from Degussa AG. Ethylvinyl ether, n-butylvinyl ether,
tert-butylvinyl ether and cyclohexylvinyl ether were
purchased from Aldrich. The diprimary phosphine 1,3-
diphosphinopropane [17] and dppp [18] were synthe-
sized according to literature methods. Propene, ethene
and carbon monoxide were gifts from BASF AG. Ele-
mental analyses were carried out on a Carlo Erba
analyzer model 1106 and Elementar model Vario EL;
Cl analyses were carried out according to Dirschel and
Erne [19] and Scho¨niger [20]. Palladium was determined
on a Perkin–Elmer Model 4000 atomic absorption
spectrometer. The high resolution 1H, 13C{1H}, and
31P{1H} NMR spectra were recorded on a Bruker DRX
250 spectrometer at 296 K. Frequencies and standards
are as follows: 13C{1H} NMR 62.90 MHz, 31P{1H}
1
10.23%. H NMR (CDCl3): l (ppm) 3.4 (m, 8H4+4
OCH2CH3 ), 1.67 (m, 8H3), 1.49 (m, br, 2H1+4H2),
1
3
1.13 (t, JHH=6.9 Hz, 4CH3). 13C{1H} NMR (CDCl3):
l
(ppm) 68.2 (d, 3JPC=16.5 Hz, C4), 66.0 (s,
2
OCH2CH3), 29.4 (N=22.8 Hz
[21], C2), 28.0 (d,
1JPC=13.4 Hz, C3), 22.4 (t, 2JPC=14.5 Hz, C1), 15.1 (s,
CH3). 31P{1H} NMR (CDCl3): l (ppm) −37.4 (s). IR
(CH2Cl2, cm−1): was(C2O) 1096.
2.4. 1,3-Bis[di(2-n-butoxyethyl)phosphino]propane (1b)
1,3-Diphosphinopropane (1.012 g, 9.37 mmol) and
n-butylvinyl ether (4.133 g, 41.3 mmol) were reacted
according to procedure A to give 4.47 g (94%) of 1b.
1 For the labeling of the hydrogen and carbon atoms see Scheme 3.
1
2 AXX% pattern, N=ꢀ JPC+3JPC ꢀ.

E. Lindner et al. / Inorganica Chimica Acta 296 (1999) 103–113
105
MS (EI): m/z 508.2 (M+). Anal. Calc. for C27H58O4P2
(508.3): C, 63.75; H, 11.49. Found: C, 63.75; H,
11.38%. 1H NMR (CDCl3): l (ppm) 3.47 (m, 8H4), 3.32
(t, 3JHH=6.6 Hz, 8OCH2C3H7), 2.0 (m, 2H1), 1.69
(m, 8H3), 1.48 (m, 4H2+4CH2C2H5), 1.32 (m,
4CH2CH3), 0.85 (t, 3JHH=7.3 Hz, 4CH3). 13C{1H}
NMR (CDCl3): l (ppm) 70.6 (s, OCH2C3H7), 68.4 (d,
2JPC=18.2 Hz, C4), 31.7 (s, CH2C2H5), 29.4 (N=22.9
3×20 ml) and recrystallized from toluene/n-hexane to
give colorless, crystalline complexes.
2.8. Dichloro{1,3-bis[di(2-ethoxyethyl)phosphino]-
propane-P,P%}palladium(II) (2a)
According to procedure B, 1a (433 mg, 1.093 mmol)
was reacted with (PhCN)2PdCl2 (381 mg, 0.993 mmol)
to give 461 mg (81%) of 2a. M.p. 114°C. MS (FD,
30°C): m/z 573.8 (M+, 106Pd). Anal. Calc. for
C19H42Cl2O4P2Pd (573.6): C, 39.77; H, 7.38; Cl, 12.38;
Pd, 18.56. Found: C, 40.01; H, 7.48; Cl, 12.30; Pd,
18.05%. 1H NMR (CDCl3): l (ppm) 3.79 (m, 8H4), 3.45
(m, 4OCH2CH3), 2.60 (m, 4H3), 2.24 (m, 4H3), 2.10 (m,
2H1), 1.85 (m, 4H2), 1.13 (t, 3JHH=6.9 Hz, 4CH3).
13C{1H} NMR (CDCl3): l (ppm) 66.8 (s, C4), 66.4 (s,
2
1
2
Hz , C2), 27.9 (d, JPC=13.5 Hz, C3) 22.4 (t, JPC
=
14.3 Hz, C1), 19.3 (s, CH2CH3), 13.9 (s, CH3). 31P{1H}
NMR (CDCl3): l (ppm) −37.1 (s). IR (CH2Cl2,
cm−1): was(C2O) 1098.
2.5. 1,3-Bis[di(2-tert-butoxyethyl)phosphino]propane
(1c)
2
1,3-Diphosphinopropane (1.251 g, 11.58 mmol) and
tert-butylvinyl ether (5.104 g, 51.0 mmol) were reacted
according to procedure A to give 5.46 g (93%) of 1c.
MS (EI): m/z 507.4 (M+−H). Anal. Calc. for
C27H58O4P2 (508.3): C, 63.75; H, 11.49. Found: C,
OCH2CH3), 28.8 (N=31.7 Hz , C3), 22.9 (N=38.4
Hz 2, C2), 19.2 (s, C1), 15.2 (s, CH3). 31P{1H} NMR
(CDCl3): l (ppm) 17.1 (s). IR (KBr, cm−1): was(C2O)
1100.
1
63.25; H, 11.40%. H NMR (CDCl3): l (ppm) 3.44 (m,
2.9. Dichloro{1,3-bis[di(2-n-butoxyethyl)phosphino]-
propane-P,P%}palladium(II) (2b)
8H4), 1.9 (m, 2H1), 1.68–1.62 (m, 8H3), 1.39 (m, 4H2),
1.14 (s, 4CH3). 13C{1H} NMR (CDCl3): l (ppm) 72.8
2
(s, C(CH3)3), 59.5 (d, JPC=22.1 Hz, C4), 29.7 (N=
According to procedure B, 1b (572 mg, 1.126 mmol)
was reacted with (PhCN)2PdCl2 (390 mg, 1.024 mmol)
to give 555 mg (79%) of 2b. M.p. 85.5°C. MS (FD,
30°C): m/z 685.9 (M+, 106Pd). Anal. Calc. for
C27H58Cl2O4P2Pd (685.7): C, 47.27; H, 8.52; Cl, 10.53;
Pd, 15.53. Found: C, 47.09; H, 8.49; Cl, 10.48; Pd,
16.01%. 1H NMR (CDCl3): l (ppm) 3.76 (m, 8H4), 3.34
(m, 4OCH2C3H7), (m, 4H2), 2.28 (m, 4H2), 2.14–1.76
(m, 2H1+4H2), 1.45 (m, 4CH2C2H5), 1.27 (m,
4CH2CH3), 0.85 (t, 3JHH=7.2 Hz, 4CH3). 13C{1H}
NMR (CDCl3): l (ppm) 70.9 (s, OCH2C3H7), 66.9 (s,
2
1
22.3 Hz , C2), 28.9 (d, JPC=12.8 Hz, C3), 27.5 (s,
CH3), 22.38 (t, 2JPC=14.1 Hz, C1). 31P{1H} NMR
(CDCl3): l (ppm) −37.2 (s). IR (CH2Cl2, cm−1):
was(C2O) 1195.
2.6. 1,3-Bis[di(2-cyclohexoxyethyl)phosphino]propane
(1d)
1,3-Diphosphinopropane (974 mg, 9.02 mmol) and
cyclohexylvinyl ether (5.010 g, 39.7 mmol) were reacted
according to procedure A to give 5.4 g (98%) of 1d.
M.p. 49°C. MS (EI): m/z 611.4 (M+−H). Anal. Calc.
C35H66O4P2 (612.4): C, 68.64; H, 10.78. Found: C,
2
C4), 31.7 (s, CH2C2H5), 28.7 (N=37.7 Hz , C3), 22.7
(N=36.4 Hz 2, C2), 19.2, 19.1 (s, C1+CH2CH3), 13.8
(s, CH3). 31P{1H} NMR (CDCl3): l (ppm) 17.3 (s). IR
(KBr, cm−1): was(C2O) 1106.
1
68.60; H, 11.06%. H NMR (CDCl3): l (ppm) 3.91–
3.73 (m, 8H4+4OCH), 3.29–3.19 (m, 8H3), 2.70–1.13
(m, 46H). 13C{1H} NMR (CDCl3): l (ppm) 76.8 (s,
2.10. Dichloro{1,3-bis[di(2-tert-butoxyethyl)phosphino]-
propane-P,P%}palladium(II) (2c)
2
OCH), 64.9 (d, JPC=20.5 Hz, C4), 31.7 (s, OCHCH2),
2
1
29.0 (N=22.8 Hz , C2), 27.8 (d, JCP=13.5 Hz, C3),
25.3 (s, OCHCH2CH2), 23.5 (s, OCHCH2CH2CH2),
According to procedure B, 1c (584 mg, 1.149 mmol)
was reacted with (PhCN)2PdCl2 (397 mg, 1.035 mmol)
to give 625 mg (88%) of 2c. M.p. 175 °C. MS (FD, 30
°C): m/z 650.9 (M+−Cl, 106Pd). Anal. Calc. for
C27H58Cl2O4P2Pd (685.7): C, 47.27; H, 8.52; Cl, 10.53;
Pd, 15.53. Found: C, 47.50; H, 8.67; Cl, 10.11; Pd,
15.40%. 1H NMR (CDCl3): l (ppm) 3.78 (m, 8H4), 2.52
(m, 4H3), 2.28 (m, 4H3), 2.16–1.88 (m, 2H1+4H2),
1.14 (s, 16CH3). 13C{1H} NMR (CDCl3): l (ppm) 73.6
2
21.9 (t, JPC=15.2 Hz, C1). 31P{1H} NMR (CDCl3):
l (ppm) −36.7 (s). IR (CH2Cl2, cm−1): was(C2O)
1100.
2.7. Preparation of the dichlorodiphosphinepalladium(II)
complexes 2a–f. General procedure B
Stirred solutions of the corresponding phosphine 1a–
d and (PhCN)2PdCl2 in each 20 ml of dichloromethane
were reacted for 2 h at room temperature. Subsequently
the solvent was removed in vacuo. Finally, the com-
plexes 2a–d were washed with cold n-hexane (−30°C,
2
(s, C(CH3)3), 58.2 (s, C4), 29.5 (N=35.8 Hz , C3), 27.6
2
(s, CH3), 23.0 (N=37.9 Hz , C2), 19.1 (s, C1). 31P{1H}
NMR (CDCl3): l (ppm) 16.3 (s). IR (KBr, cm−1):
was(C2O) 1195.

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E. Lindner et al. / Inorganica Chimica Acta 296 (1999) 103–113
1
2.11. Dichloro{1,3-bis[di(2-cyclohexoxyethyl)phosphino]-
propane-P,P%}palladium(II) (2d)
Pd, 13.49. Found: C, 40.54; H, 7.09; Pd, 14.06%. H
NMR (CD2Cl2): l (ppm) 3.95–3.63 (m, 4OCH2C3H7+
8H4), 2.51 (m, 8H3), 2.37–2.22 (m, 2H1+4H2), 1.56
(m, 4OCH2CH2C2H5), 1.28 (m, 4CH2CH3), 0.86 (t,
3JHH=7.2 Hz, 4CH3). 13C{1H} NMR (CD2Cl2): l
(ppm) 74.3 (s, OCH2C3H7), 67.2 (s, C4), 31.5 (s,
According to procedure B, 1d (599 mg, 1.095 mmol)
was reacted with (PhCN)2PdCl2 (375 mg, 0.978 mmol)
to give 672 mg (87%) of 2d. M.p. 159°C. MS (FD,
30°C): m/z 650.8 (M+−Cl, 106Pd). Anal. Calc. for
C35H66Cl2O4P2Pd (789.7): C, 53.20; H, 8.42; Cl, 8.97;
Pd, 13.47. Found: C, 52.89; H, 7.90; Cl, 8.91; Pd, 13.25.
1H NMR (CDCl3): l (ppm) 3.83 (m, 8H4), 3.23 (m,
4OCH), 2.54 (m, 4H3), 2.29 (m, 4H3), 1.92–1.16 (m,
46H). 13C{1H} NMR (CDCl3): l (ppm) 77.7 (s, OCH),
OCH2CH2C2H5), 26.3 (N=31.8 Hz , C3), 20.7–20.0
2
(m, C1+C2), 19.4 (s, CH2CH3), 14.1 (s, CH3). 31P{1H}
NMR (CD2Cl2): l (ppm) 43.2 (s). 31P{1H} NMR
(CD2Cl2, −80°C): l (ppm) 45.7 (br s), 19.6 (br s). IR
(CH2Cl2, cm−1): was(C2O) 1106, w(BF4−) 1063 cm−1
.
A solution of 3b (120 mg, 0.152 mmol) in 1 ml of
dichloromethane reacts with excess acetonitrile to give
the adduct 3b · 2CH3CN. H NMR (CD2Cl2): l (ppm)
2
63.9 (s, C4), 32.1 (s, OCHCH2), 29.1 (N=34.7 Hz ,
2
1
C3), 25.6, 23.8 (s, C6H11), 22.8 (N=37.0 Hz , C2), 19.2
(s, C1). 31P{1H} NMR (CDCl3): l (ppm) 16.5 (s). IR
(KBr, cm−1): was(C2O) 1087.
3.75–3.62 (m, 8H4), 3.39 (m, 4OCH2C3H7), 2.35 (m,
8H3), 2.16–1.89 (m, 2H1+4H2+CH3CN), 1.47 (m,
4CH2C2H5), 1.28 (m, 4CH2CH3), 0.82 (t, 3JHH=7.5
Hz, 4CH3). 13C{1H} NMR (CD2Cl2): l (ppm) 117.7 (s,
CN), 71.6 (s, OCH2C3H7), 65.8 (s, C4), 32.0 (s,
CH2C2H5), 28.5 (N=43.1 Hz 2, C3), 20.5–18.9 (m,
C1+C2+CH2CH3), 14.0 (s, CH3), 1.8 (s, CH3CN).
31P{1H} NMR (CD2Cl2): 21.0 (s). IR (CH2Cl2, cm−1):
w(CN) 2325, 2297, w(C2O) 1100, w(BF−4 ) 1065.
2.12. Preparation of the dicationic palladium(II)
complexes 3a–d. General procedure C
To a solution of the corresponding dichloropalladi-
um(II) complexes 2a–d in 10 ml of CH2Cl2 a suspen-
sion of AgBF4 in 10 ml of CH2Cl2 was added and the
mixture was stirred for 1 h at room temperature. Subse-
quently the suspension was centrifuged, decanted and
the solvent was removed in vacuo. The crude product
was dissolved in CH2Cl2 and centrifuged again to re-
move traces of AgCl. Finally the solvent was removed
under reduced pressure to give the dicationic complexes
3a–d.
2.15. {1,3-Bis[di(2-tert-butoxyethyl)phosphino]propane-
O,P;O%,P%}palladium(II)bis(tetrafluoroborate) (3c)
According to procedure C, 2c (357 mg, 0.521 mmol)
was reacted with AgBF4 (203 mg, 1.043 mmol) to give
374 mg (91%) of 3c. M.p. 67.6 °C. MS (FD, 30 °C):
700.9
(M+−BF4,
106Pd).
Anal.
Calc.
for
2.13. {1,3-Bis[di(2-ethoxyethyl)phosphino]propane-
O,P;O%,P%}palladium(II)bis(tetrafluoroborate) (3a)
C27H58B2F8O4P2Pd (788.4): C, 41.12; H, 7.41; Pd,
1
13.49. Found: C, 40.56; H, 7.25; Pd, 13.81%. H NMR
(CD2Cl2): l (ppm) 3.83–3.74 (m, 8H4), 2.40 (m, 8H3),
2.27–2.05 (m, 2H1+4H2), 1.22 (s, 16CH3). 13C{1H}
NMR (CD2Cl2): l (ppm) 79.6 (s, OC(CH3)3), 59.2 (s,
According to procedure C, 2a (290 mg, 0.505 mmol)
was reacted with AgBF4 (198 mg, 1.02 mmol) to give
324 mg (95%) of 3a. M.p. 43°C. MS (FD, 30°C): m/z
2
C4), 27.4–26.7 (m, CH3+C3), 20.2 (N=41.7 Hz , C2),
588.7
(M+−BF4,
106Pd).
Anal.
Calc.
for
19.2 (s, C1). 13C{1H} NMR (CD2Cl2, −80°C): l (ppm)
84.9 (br, PdOC(CH3)3), 75.8–74.6 (br, OC(CH3)3), 62.7
(br, PdOC4), 56.0 (br, C4). 31P{1H} NMR (CD2Cl2): l
(ppm) 40.3 (s). 31P{1H} NMR (CD2Cl2, −80°C): l
(ppm) 45.7 (br s), 43.8 (br s), 37.8 (br s), 19.5 (br s). IR
(CH2Cl2, cm−1): was(C2O) 1191 cm, w(BF−4 ) 1048.
3c reacts stepwise with water to give 3c · H2O and
3c · 2H2O. Whereas 3c · H2O is obtained from a concen-
trated solution of 3c in CH2Cl2 layered with n-hexane
in a Schlenk tube which is sealed with a rubber plug,
3c · 2H2O is formed if the same solution (without n-hex-
ane) is exposed to atmospheric humidity for 5 min.
3c · H2O: MS (FD, 30°C): m/z 632.3 (M+−2BF4,
106Pd). 1H NMR (CD2Cl2): l (ppm) 3.87–3.77 (m,
8H4), 2.45 (m, 8H3), 2.32–2.22 (m, 2H1+4H2), 1.24 (s,
16CH3). 13C{1H} NMR (CD2Cl2): l (ppm) 78.9 (s,
C(CH3)3), 59.0 (s, C4), 27.5–26.8 (m, CH3+C3), 20.5
(N=41.9 Hz 2, C2), 19.2 (s, C1). 31P{1H} NMR
(CD2Cl2): l (ppm) 36.7 (s).
C19H42B2F8O4P2Pd (676.3): C, 33.73; H, 6.26; Pd,
1
15.73. Found: C, 33.71; H, 6.31; Pd, 15.45%. H NMR
(CD2Cl2): l (ppm) 3.97–3.69 (m, 8H4 + 4OCH2CH3),
2.50 (m, 8H3), 2.38–2.23 (m, 2H1+4H2), 1.22 (t,
3JHH=6.9 Hz, 4CH3). 13C{1H} NMR (CD2Cl2): l
(ppm) 70.4 (s, OCH2CH3), 67.2 (s, C4), 26.5 (N=36.5
Hz 2, C3), 20.8–20.1 (m, C2+C1), 15.0 (s, CH3).
31P{1H} NMR (CD2Cl2): l (ppm) 46.2 (s). IR (CH2Cl2,
cm−1): was(C2O) 1106, w(BF−4 ) 1061.
2.14. {1,3-Bis[di(2-n-butoxyethyl)phosphino]propane-
O,P;O%,P%}palladium(II)bis(tetrafluoroborate) (3b)
According to procedure C, 2b (336 mg, 0.49 mmol)
was reacted with AgBF4 (191 mg, 0.98 mmol) to give
375 mg (97%) of 3b. M.p. 96°C. MS (FD, 30°C): m/z
700.8
(M+−BF4,
106Pd).
Anal.
Calc.
for
C27H58B2F8O4P2Pd (788.4): C, 41.12; H, 7.41; F, 19.27;

E. Lindner et al. / Inorganica Chimica Acta 296 (1999) 103–113
107
3c · 2H2O: MS (FD, 30 °C): m/z 650.4 (M+−BF4,
monoxide copolymers were obtained by evaporation of
the solvent. The reproducibility of the catalytic activity
is about 10% (ethene/CO copolymerization) and 5%
(propene/CO copolymerization).
1
106Pd). H NMR (CD2Cl2): l (ppm) 3.77 (m, 8H4), 3.07
(m, br, H2O), 2.36 (m, 8H3), 2.19–1.97 (m, 2H1+4H2),
1.19 (s, 16CH3). 13C{1H} NMR (CD2Cl2): l (ppm) 77.4
(s, C(CH3)3), 58.9 (s, C4), 29.0 (N=31.7 Hz 2, C3),
2
28.7 (s, CH3), 22.4 (N=42.5 Hz , C2), 19.9 (s, C1).
2.18. X-ray structural determination of 2a and
3c · H2O (see Section 5)
31P{1H} NMR (CD2Cl2): l (ppm) 25.5 (s). IR (CH2Cl2,
cm−1): w(H2O) 3624, w(C2O) 1190, w(BF4−) 1076.
Single crystals of 2a were obtained by slow diffusion
of n-hexane into a concentrated solution of 2a in
CH2Cl2. Crystals of 3c · H2O were grown within several
weeks by slow diffusion of water into a Schlenk tube
sealed with a rubber plug containing a CH2Cl2 solution
of 3c layered with n-hexane. The crystals were
mounted on a glass fiber and transferred to a P4
Siemens diffractometer, using graphite-monochromated
Mo Ka radiation. The lattice constants were deter-
mined by 17 (2a) or 20 (3c · H2O) precisely centered
high-angle reflections and refined by least-squares
methods. The structures were solved by Patterson
methods [23] and refined by full-matrix least-squares
using SHELXL97 [24]. All non-hydrogen atoms were
refined anisotropically (based on F2). Hydrogen atoms
2.16. {1,3ꢁBis[di(2-cyclohexoxyethyl)phosphino]-
propane-O,P;O%,P%}palladium(II)bis(tetrafluoroborate)
(3d)
According to procedure C, 2d (311 mg, 0.508 mmol)
was reacted with AgBF4 (198 mg, 1.018 mmol) to give
438 mg (97%) of 3d. M.p. 82°C. MS (FD, 30°C): m/z
805.1 (M+−BF4, 106Pd). Anal. Calc. for C35H66B2F8-
O4P2Pd (892.4): C, 47.08; H, 7.45; Pd, 11.93. Found:
1
C, 47.19; H, 7.36; Pd, 11.50%. H NMR (CD2Cl2): l
(ppm) 3.86 (m, 8H4), 3.51 (m, 4OCH), 2.49 (m, H3),
2.25–2.13 (m, 4H2+2H1), 1.98–1.05 (m, 44H, C6H11).
13C{1H} NMR (CD2Cl2): l (ppm) 82.4 (s, OCH), 64.0
2
(s, C4), 32.4 (s, OCHCH2), 27.2 (N=31.2 Hz , C3),
2
25.7, 24.9 (s, C6H11), 20.6 (N=42.1 Hz , C2), 20.1 (s,
,
were placed in calculated positions (d(CH3)=0.98 A;
C1). 13C{1H} NMR (CD2Cl2, −80°C): l (ppm) 85.0
(br, PdOCH), 78.8 (br, OCH), 65.7 (br, PdOC4), 62.0
(br, C4). 31P{1H} NMR (CD2Cl2): l (ppm) 44.1 (s).
31P{1H} NMR (CD2Cl2, −80 °C): l (ppm) 47.6 (br s),
43.0 (br s), 19.7 (br s). IR (CH2Cl2, cm−1): was(C2O)
1099, w(BF4−) 1065.
,
,
d(CH2)=0.99 A; d(CH)=1.00 A). The H atoms of
the water molecule in 3c · H2O were located on a differ-
ence Fourier map and refined isotropically. The final
cell parameters and specific data collection parameters
for 2a and 3c · H2O are summarized in Table 1.
2.17. Copolymerization of ethene and propene with
carbon monoxide
3. Results and discussion
For all high pressure reactions a computer controlled
autoclave system was applied. A solution of the
corresponding palladium(II) complex 3a–d (0.01
mmol) in CH2Cl2 (30 ml) and CH3OH (2 ml) as activa-
tor [22] was placed in a 100-ml magnetically-stirred
steel autoclave which was charged with 30 bar of
ethene and 30 bar of carbon monoxide. The reaction
temperature was adjusted by a thermostat. Finally, the
gases were released after the appropriate reaction time.
The copolymer was collected by filtration and dried in
vacuo.
The copolymerization of propene with carbon
monoxide was carried out in a 250-ml mechanically-
stirred steel autoclave with electrical heating, and air
cooling. The evacuated autoclave was charged with a
solution of the corresponding dicationic palladium(II)
complex 3a–d (0.01 mmol) in CH2Cl2 (100 ml) and
CH3OH (2 ml) as activator. The mixture was saturated
with propene (20°C, 20 min) and pressurized with 51
bar of carbon monoxide. At the end of the reaction
period the gases were released. The propene/carbon
3.1. Synthesis of the ligands 1a–d and complexes
2a–d, 3a–d
With some modifications the etherdiphos ligands
1a–d were prepared according to Ref. [25]. The dipri-
mary phosphine H2Pꢁ(CH2)3ꢁPH2 [17] was photochem-
ically hydrophosphinated with an excess of vinyl ether
(Scheme 3). This procedure is much more convenient,
since the reaction, as monitored by 31P{1H} spec-
troscopy, is quantitative and no by-products occur. In
a simple purification step excess olefin can be removed
in vacuo. All phosphines are colorless, air-sensitive,
and oily (1a–c) or solid (1d) products, which are read-
ily soluble in common organic solvents. They were
characterized by means of MS, IR, and NMR spectra
(Section 2).
By treatment of (PhCN)2PdCl2 with 1a–d in dichloro-
methane at room temperature, the air-stable, color-
less palladium(II) complexes 2a–d are formed (Scheme
3). Recrystallization from toluene/n-hexane affords
crystalline products; the molecular structure of

108
E. Lindner et al. / Inorganica Chimica Acta 296 (1999) 103–113
Table 1
Summary of crystallographic data and parameters for data collection
and refinement of 2a and 3c · H2O
2a
3c · H2O
Formula
C19H42Cl2O4P2Pd C27H60B2F8O5P2Pd
Formula weight
Color
Crystal
573.8
colorless plate
0.45×0.20×0.10
806.1
colorless plate
0.1×0.4×0.45
dimension (mm)
Crystal system
Space group
monoclinic
P21/c No. 14
8.885(4)
22.81(2)
12.753(5)
93.10(2)
2580(2)
4
1.477
−100
1192
1.071
monoclinic
P21/n No. 14
10.126(5)
36.328(9)
11.035(4)
113.45(2)
3724(2)
4
1.439
−100
1680
0.657
,
a (A)
,
b (A)
,
c (A)
i (°)
3
,
V (A )
Z
dcalc. (g cm−1
T (°C)
F(000)
)
v(Mo Ka) (mm−1
Scan type
)
ꢀ
ꢀ
2q limits (°)
4–55
4–50
Data collected: h, k, l
−11–2, −1–29,
916
−12–3, 943,
912
Scheme 3.
Number of reflections
measured
7744
17415
for the h4(O,P;O%,P%) coordination. Instead of two
signals for each coordinated (C4%, C5%) and non-coordi-
nated (C4, C5) ether moiety, only two averaged reso-
nances for the four carbon atoms are observed. The
dynamic behavior was studied by temperature-depen-
dent 13C{1H} NMR experiments. The exchange of both
types of ether oxygen atoms is decelerated by cooling
the sample which results in a line broadening of the
above-mentioned resonances of the carbon nuclei. Be-
low the coalescence temperature of about −60°C for
3c and 3d, these signals split in pairs, revealing coordi-
nated and non-coordinated oxygen atoms (Fig. 1). In
the case of 3a and 3b, this splitting was not observed,
because of their low coalescence temperatures (below
−80°C). The inversion of the six-membered ring
formed by the ligand backbone is also affected at low
temperatures and is illustrated by the line broadening
of the bridging carbon atoms C1 and C2. Due to
chemical exchange and conformational processes the
singlets in the 31P{1H} NMR spectra of 3c and 3d split
in several resonances at −80°C, while those of 3a and
3b only broaden.
Number of unique
data with I]2|(I)
Number of variables
Goodness-of-fit
5235
5516
254
415
1.988
0.0416
0.1088
1.997
0.0474
0.1169
a
R1
wR2
b
a R1=S ꢀꢀ Fo ꢀ−ꢀ Fc ꢀꢀ/S ꢀ Fo ꢀ.
b wR2=[S[w(Fo2−Fc2)2]/S[w(Fo2)2]]0.5
.
2a was exemplarily determined by an X-ray structural
analysis (vide infra). Spectroscopic data of 2a–d are
summarized in Section 2.
Intramolecular coordination of two ether moieties to
the metal center succeeded by reacting 2a–d with two
equivalents of AgBF4 in CH2Cl2 at 20°C, leading to the
dicationic, colorless, hygroscopic etherdiphospalladi-
um(II) complexes 3a–d. Without cleavage of a PdꢁO
bond they are soluble in medium polar organic sol-
vents, like CH2Cl2. Because of the ring contribution DR
[26], the 31P resonances in the 31P{1H} NMR spectra
are shifted about 30 ppm to lower field compared to
2a–d. The h4(O,P;O%,P%) coordination mode in 3a–d is
responsible for a center of chirality at both phosphorus
atoms resulting in three diastereomers [(R,R), (S,S),
meso]. However, at room temperature only one 31P
singlet is observed, because of a rapid chemical ex-
change process between the coordinated (PSO) and the
non-coordinated (PꢀO) ether oxygen atoms. Com-
pared to 2a–d the signals of both carbon atoms adja-
cent to the ether function in the 13C{1H} NMR spectra
of 3a–d are shifted to lower field. This is a further hint
Although no kinetic parameters were determined
[13a], complexes 3a–d can be classified into two groups.
The PdꢁO bonds in 3c and 3d are much stronger
compared to 3a and 3b, leading to a higher coalescence
temperature. Obviously because of the higher basicity
the tert-butyl and cyclohexyl groups strengthen the
PdꢁO contact.
Both PdꢁO bonds in 3a–d are easily ruptured with
coordinating solvents like acetonitrile or water. If for

E. Lindner et al. / Inorganica Chimica Acta 296 (1999) 103–113
109
Fig. 1. Temperature-dependent 13C{1H} NMR spectrum of 3d.
,
,
example 3b or 3c is treated with CH3CN or exposed to
atmospheric humidity, the adducts 3b · 2CH3CN,
3c · H2O, and 3c · 2H2O are obtained, respectively.
However, these complexes cannot be isolated by simple
removal of the solvent, because of the reversibility of
the reaction, in particular in the case of the acetonitrile
complexes. Due to the PdꢁO cleavage of the five-mem-
bered chelate rings the incorporation of water and
acetonitrile in 3c and 3b, respectively results in a shift
of the singlets in the 31P{1H} NMR spectra of 3c · H2O,
3c · 2H2O, and 3b · 2CH3CN to higher field [26]. The IR
spectrum of 3b · 2CH3CN (in CH3CN) exhibits two
strong CꢂN absorptions at 2325 and 2297 cm−1, which
are typical for the expected cis configuration.
(Pd1ꢁCl1=2.365(1) A, Pd1ꢁCl2=2.365(1) A) dis-
tances are equal within experimental error. In Table 2 a
selection of bond lengths and angles of 2a is
summarized.
The formulation of 3c · H2O readily follows from the
results of the single crystal diffraction analysis (Fig. 3).
Selected interatomic parameters are collected in Table
3. The square planar coordination about the palladium
by the four donor functions P1, P2, O1, O11 is ex-
tremely distorted, caused on the one hand by the
bicyclic ring system and on the other hand by the
hydrogen bridge between O11 and O3 (O11ꢁH1E···
,
O3=2.630(5) A [27]). The six-membered ring of the
bicyclic system is arranged in a chair conformation.
,
The Pd and the C2 atoms are located 0.795(3) A
,
above and −0.721(6) A below the plane that is formed
3.2. Crystal structures of 2a and 3c · H2O
by the atoms P1, P2, C1, and C3. The five-membered
chelate ring reveals a twisted conformation. Remark-
able is the rather shortened PdꢁP1 bond length with
The resultant data of 2a best fit the centrosymmetric
monoclinic space group P21/c (No. 14). Crystallization
occurs with four formula units per unit cell (Z=4). A
perspective view of compound 2a (Fig. 2) shows the
crystallographic numbering scheme. Due to the back-
bone the square planar geometry about the Pd atom is
slightly distorted with a P1ꢁPd1ꢁP2 angle of 95.45(4)°.
Noticeable is the plane formed by the seven atoms Cl1,
Cl2, Pd1, P1, P2, C1, and C3. The distance between
,
2.205(1) A and the enlarged O1ꢁPdꢁO11 angle with
96.42(12)°.
3.3. Copolymerization of carbon monoxide with ethene
and propene
Dicationic palladium(II) complexes of the type 3a–d
proved to be highly active catalysts in the copolymer-
ization of carbon monoxide with ethene and propene,
,
atom C2 and this plane is 0.757(4) A. The PdꢁP
,
,
(Pd1ꢁP1=2.241(1) A, Pd1ꢁP2=2.243(1) A) and PdꢁCl

110
E. Lindner et al. / Inorganica Chimica Acta 296 (1999) 103–113
Fig. 3. ORTEP plot of the palladium(II) complex 3c · H2O.
Fig. 2. ORTEP plot of the palladium(II) complex 2a.
temperature leads to an overall increased activity (Fig.
4 and Table 4). While the efficiency of 3b–d and
(dppp)Pd is similar at 60°C, 3a still remains somewhat
moderate in this series. The resulting copolymer repre-
sents a colorless, flocky material with high melting
points ranging from 254–266°C [28]. The molecular
weight of the ethene/CO copolymer, obtained with
catalyst 3a is the lowest at 25°C, while with complex 3d
a much higher molecular weight was determined (Table
4, run 1–5). The expected decrease of the Mw values
was observed at 60°C. However, at this temperature
(dppp)Pd clearly produces the highest molecular weight,
followed by the more bulky etherdiphospalladium(II)
catalysts 3c–d (Table 4, run 6–10). In the IR spectra a
carbonyl absorption at 1691 cm−1 is observed. In the
respectively. However, they do not catalyze the copoly-
merization of styrene with carbon monoxide. Optimal
reaction conditions are achieved at a total pressure of
60 bar using dichloromethane as solvent and a small
amount of methanol as activator. All catalysts were
stable under the reaction conditions and no precipita-
tion of palladium occurred. In order to compare the
catalytic efficiency of 3a–d with the performance of a
standard,
the
industrially
employed
complex
[(dppp)Pd(NCCH3)2][BF4]2 [(dppp)Pd] was incorporated
in the investigations [8].
Upon copolymerization of ethene with carbon
monoxide at 25 °C the highest activities were obtained
with 3b and 3c followed by 3d and 3a. A rise of the
Table 2
Table 3
,
,
Selected interatomic distances (A) and angles (°) for 2a
Selected interatomic distances (A) and angles (°) for 3c · H2O
Bond lengths
Bond lengths
Pd(1)ꢁP(1)
Pd(1)ꢁP(2)
2.2409(11)
2.2425(10)
Pd(1)ꢁCl(1)
Pd(1)ꢁCl(2)
2.3647(11)
2.3649(11)
Pd(1)ꢁP(1)
Pd(1)ꢁP(2)
2.2055(12)
2.2327(13)
Pd(1)ꢁO(1)
Pd(1)ꢁO(11)
2.254(3)
2.154(3)
Bond angles
Bond angles
P(1)ꢁPd(1)ꢁP(2)
P(2)ꢁPd(1)ꢁCl(2)
95.45(4)
87.14(4)
P(1)ꢁPd(1)ꢁCl(1)
Cl(1)ꢁPd(1)ꢁCl(2)
86.48(4)
90.90(4)
P(1)ꢁPd(1)ꢁP(2) 89.71(5)
P(1)ꢁPd(1)ꢁO(1) 84.22(9)
P(2)ꢁPd(1)ꢁO(11)
O(1)ꢁPd(1)ꢁO(11)
92.60(10)
96.40(13)

E. Lindner et al. / Inorganica Chimica Acta 296 (1999) 103–113
111
Fig. 5. Catalytic activity (g polymer)(g Pd h)−1 in the propene/CO
copolymerization.
Fig. 4. Catalytic activity (g polymer)(g Pd h)−1 in the ethene/CO
copolymerization.
inverse gated decoupled 13C NMR spectra of the co-
polymers (in 1,1,1,3,3,3-hexafluoroisopropanol) no end
groups were found. The integrals of the 13C signals of
the carbonyl and methylene groups (212 and 35 ppm,
respectively [28]) are in a ratio of 1:2 which is consistent
with the strict alternation of the copolymers. No addi-
tional resonances were observed.
With the exception of lower reaction rates compara-
ble relations are established in the propene/carbon
monoxide copolymerization for both temperatures (25
and 60°C). However, in contrast to ethene/CO copoly-
merization at 25°C, 3d is the best catalyst in this
sequence (Fig. 5 and Table 4). With all catalysts 3a–d,
colorless, viscous solutions of the copolymers were
formed from which thin, brittle films were grown by
slow evaporation of the solvent. At 25 °C 3a–d produce
ultra-high molecular weight propene/CO copolymers.
Although (dppp)Pd is a similar active catalyst, chain
transfer reactions are more frequent, which is corrobo-
rated by the much lower molecular weight and the
broader molecular weight distribution (Table 4, run
11–15). Rising the polymerization temperature to 60°C
results in decrease of the molecular weight, but 3a–d
remain superior to (dppp)Pd. In the DSC spectra only
Table 4
Results of the copolymerization of carbon monoxide with ethene and propene, respectively
a
d
Run
Precatalyst
Olefin
Temperature
(°C)
Reaction time
(h)
Activity b
TON
(cycles)
H–T units c
(%)
Mw
Mw/Mn
(103 g mol−1
)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
3a
3b
3c
3d
(dppp)Pd
3a
3b
3c
3d
(dppp)Pd
3a
3b
3c
3d
(dppp)Pd
3a
Ethene
Ethene
Ethene
Ethene
Ethene
Ethene
Ethene
Ethene
Ethene
Ethene
Propene
Propene
Propene
Propene
Propene
Propene
Propene
Propene
Propene
Propene
25
25
25
25
25
60
60
60
60
60
25
25
25
25
25
60
60
60
60
60
2
2
2
2
2
2
2
2
2
645
1166
1189
852
840
2469
3174
2803
3007
2904
43
53
37
65
45
365
489
441
474
476
2453
4434
4520
3238
3194
9389
12072
10659
11435
11043
1563
1922
1355
2373
1643
2221
2975
2682
2885
2896
–
–
–
–
–
–
–
–
–
261.1
473.7
510.0
686.9
554.0
41.1
49.9
76.5
53.4
245.5
181.5
181.6
247.0
244.1
108.2
25.3
33.9
29.8
34.0
8.5
2.5
5.1
4.1
1.9
2.0
4.5
3.2
2.3
3.1
7.0
2.2
2.2
1.5
1.4
3.4
3.8
3.4
3.4
3.4
4.1
2
–
24
24
24
24
24
4
4
4
4
4
100
100
96
98
57
100
100
98
100
58
3b
3c
3d
(dppp)Pd
a Ethene: the polymerization was carried out in 30 ml of CH2Cl2, 2 ml of methanol and 30 bar of ethene, and CO each; propene: 100 ml of
CH2Cl2, 2 ml of methanol, saturated with 9 bar of propene in 20 min and 51 bar of CO.
b Activity in g of copolymer×(g of Pd×h)−1
.
c H–T units: regioregularity in mol% of head-to-tail units.
d Molecular weight of the ethene/CO and propene/CO copolymers determined by GPC.

112
E. Lindner et al. / Inorganica Chimica Acta 296 (1999) 103–113
weak glass transitions (−5 to 10°C) and little distinct
melting points (120–150°C) were observed. Inverse
gated decoupled 13C NMR spectra point to an almost
regioregular microstructure which is realized if alkyl
substituted diphospalladium(II) complexes are applied
in the propene/CO copolymerization [29].
and the h1-P coordinated part of the ligands in 3a–d, in
other words, the strength of the PdꢁO bond is not
responsible for the catalytic activity of these complexes
in the copolymerization of carbon monoxide with
ethene and propene, respectively. Obviously the cata-
lytic activity is influenced by steric effects, since 3b–d
with the more bulky ligands 1b–d are superior to 3a.
However, also electronic impacts can not be ruled out.
The catalytic activities of the catalysts in the copoly-
merization of carbon monoxide with ethene and
propene cannot be correlated with the dynamic behav-
ior of the complexes 3a–d. Obviously the ether oxygen
atoms do not compete with the substrate molecules for
the empty coordination sites at the palladium centers
[1]. Remarkably the complexes with the weakest PdꢁO
bonds belong to the most (3b) and least (3c) active
catalysts in this series. If one would expect a specific
effect of the hemilabile PSO ligand, the increase of the
polymerization temperature should result in a signifi-
cant enhancement of the catalytic activity of 3a–d
compared to [(dppp)Pd(NCCH3)2][BF4]2, which is not
observed. Such an implication should be observed if the
oxygen donors exert an impact on the coordination of
the comonomers. Yet the copolymerization is influ-
enced by steric effects of the ligand. From the polymer-
ization of olefins with b-diiminepalladium(II) and
-nickel(II) complexes it is known that bulky sub-
stituents are necessary to suppress chain transfer and
termination reactions [30]. The lower catalytic activity
of 3a may be attributed to the lack of steric bulk.
If the oxygen function is replaced by a methylene
group, the corresponding diphospalladium(II) com-
plexes show a higher activity in the 1-alkene/CO co-
polymerization compared to etherdiphospalladium(II)
species. In a systematic study [31], the steric and elec-
tronic properties of diphospalladium(II) complexes are
optimized with respect to the catalytic performance by
variation of the length of the phosphorus attached alkyl
chains. This observation clearly demonstrates that not
only steric, but also electronic effects play an important
role in this type of catalysis.
5. Supplementary material
Crystallographic data (excluding structural factors)
for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data
Center as supplementary publication no. CCDC 134578
(2a) and CCDC 134579 (3c · H2O). Copies of the data
can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK;
fax:
+
44-1223-336 033; e-mail: deposit@ccdc.
cam.ac.uk.
Acknowledgements
M.S. acknowledges the Land Baden-Wu¨rttemberg
for the award of
a Ph.D. Fellowship (Landes-
graduiertenfo¨rderungsgesetz). The generous support of
this research by the Fonds der Chemischen Industrie,
Frankfurt/Main, Germany, BASF Aktiengesellschaft
and by Degussa AG with valuable starting materials is
gratefully acknowledged. We thank Priv.-Doz. Dr H.
A. Mayer for helpful NMR discussions.
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