Microwave-assisted and PdII-mediated nitrile-oxime coupling

Article abstract of DOI:10.1002/ejic.200500287

Refluxing PdCl₂ with the ketoximes R¹R ²C=NOH (R¹R² = MeMe, MeEt, C₅H ₁₀) in RCN (R = Me, Et, nPr, Ph) for 2-3 h results in precipitation of the oxime complexes [PdCl₂(R¹R²C=NOH) ₂], whereas further reflux of the reaction mixture for an additional 6-12 h leads to formation of the chelated species [PdCl₂{NH=C(R)ON= CR¹R²-κ²N}] (R/R¹R² = Me/MeMe 1; Et/MeMe 2; nPr/MeMe 3; Me/MeEt 4; Me/ C₅H₁₀ 5; Ph/MeMe 6) by a Pd^II-mediated coupling between the oximes and the nitriles; complexes 1-6 were isolated in the solid state in 60-75 % yields. The reaction time could be drastically reduced, to 15-30 min, when the system was additionally irradiated with microwaves (100 W, about 60°C). Compounds 1-6 can also be obtained without isolation of the intermediate oxime complexes either by refluxing for 8-15 h or by microwave irradiation (100 W, about 60°C) for 15-30 min. The formulation of 1-6 is based upon satisfactory C, H, and N elemental analyses, FAB mass spectrometry, and IR, ¹H and ¹³C{¹H} NMR spectroscopy, while the structures of 1·(Me₂CO), 1·(CHCl₃), 2·(H ₂O), and 6·1/2(H₂O) were determined by X-ray single-crystal diffraction. Wiley-VCH Verlag GmbH & Co. KGaA 2005.

Full text of DOI:10.1002/ejic.200500287

FULL PAPER
Microwave-Assisted and PdII-Mediated Nitrile–Oxime Coupling
Dmitrii A. Garnovskii,[a] Nadezhda A. Bokach,[b] Armando J. L. Pombeiro,*[a]
Matti Haukka,[c] João J. R. Fraústo da Silva,[a] and Vadim Yu. Kukushkin*[b]
Keywords: Microwave synthesis / Metal-mediated synthesis / Nitriles / Oximes / Nitrile–oxime coupling / Palladium com-
plexes
Refluxing PdCl2 with the ketoximes R1R2C=NOH (R1R2
=
ditionally irradiated with microwaves (100 W, about 60 °C).
Compounds 1–6 can also be obtained without isolation of the
intermediate oxime complexes either by refluxing for 8–15 h
or by microwave irradiation (100 W, about 60 °C) for 15–
30 min. The formulation of 1–6 is based upon satisfactory C,
H, and N elemental analyses, FAB mass spectrometry, and
IR, 1H and 13C{1H} NMR spectroscopy, while the structures
of 1·(Me2CO), 1·(CHCl3), 2·(H2O), and 6·½(H2O) were deter-
mined by X-ray single-crystal diffraction.
MeMe, MeEt, C5H10) in RCN (R = Me, Et, nPr, Ph) for 2–3 h
results in precipitation of the oxime complexes
[PdCl2(R1R2C=NOH)2], whereas further reflux of the reaction
mixture for an additional 6–12 h leads to formation of the
chelated species [PdCl2{NH=C(R)ON=CR1R2-κ2N}] (R/R1R2 =
Me/MeMe 1; Et/MeMe 2; nPr/MeMe 3; Me/MeEt 4; Me/
C5H10 5; Ph/MeMe 6) by a PdII-mediated coupling between
the oximes and the nitriles; complexes 1–6 were isolated in
the solid state in 60–75% yields. The reaction time could be
drastically reduced, to 15–30 min, when the system was ad-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
another system by applying MWI for the nitrile–oxime
coupling to form the imino species HN=C(R)ON=CRЈRЈЈ.
In a series of previous papers,[26] we have found that these
processes are especially efficient when metal centers are in
high oxidation states, for example PtIV,[27] ReIV,[28] or
Introduction
In the past five years, microwave irradiation (MWI) has
become an increasingly useful tool in synthetic chemis-
try.[1–12] The major advantages of microwave-assisted syn-
theses are associated with a substantial decrease of reaction
times, an increase of the selectivities of the processes,
and, consequently, better purity of the products
formed.[2,4,6–8,10–12] In the overwhelming majority of cases,
MWI has been applied in organic synthesis. However, some
reports on the application of MWI in the synthesis of coor-
dination compounds are also present in the literature.[13–25]
In particular, microwave syntheses have been used for the
preparation of nanophases and nanocrystalline materials
starting from metal complexes,[16,19,20] for preparations by
substitution,[17,18,21] and for phthalocyanine synthe-
ses.[13–15,22,23] Recently, some of us have demonstrated that
MWI also efficiently promotes reactions of coordinated li-
gands, such as in the [2+3]-cycloaddition[24] and the ad-
dition of hydroxamic acids to metal-bound nitriles.[25]
In the current work, we have extended our previous re-
sults on microwave-assisted reactions of ligated nitriles to
RhIII [29]
whereas low-oxidation-state metal centers, such as
,
PtII,[30] are insufficiently strong activators to provide the
coupling under conventional conditions. Hence, we believed
that MWI could provide an additional activation for the
addition of oximes to nitriles complexed by low-oxidation-
state metal centers and to expand, in this way, the number
of this type of compounds with their potential application
in organic[31] and phthalocyanine syntheses.[32]
Results and Discussion
In organic chemistry, oximes are known as ambidentate
nucleophiles and their reactions with electrophilic reagents,
such as acylation, have been extensively studied and re-
viewed.[33] Metal-mediated oxime–nitrile coupling (or, in
other words, iminoacylation by complexed nitriles), is a lit-
tle-explored area and only recently have publications on this
subject started to appear in the literature. The largest frac-
tion of these reports is devoted to the coupling induced by
high-oxidation-state metal centers, while reactions at low-
oxidation-state metal centers, such as PdII, are scarce. It is
important to note that the first data on metal-mediated imi-
noacylation, reported at a conference,[34] deal with the reac-
tion between 3,3-dimethyl-2-butanone oxime and
[PdCl2(PhCN)2] to yield, among other products, the imino
[a] Centro de Química Estrutural, Complexo I, Instituto Superior
Técnico, Av. Rovisco Pais,
1049-001 Lisboa, Portugal
E-mail: pombeiro@ist.utl.pt
[b] Department of Chemistry, St. Petersburg State University,
198904 Stary Petergof, Russian Federation
E-mail: kukushkin@VK2100.spb.edu
[c] Department of Chemistry, University of Joensuu,
P. O. Box 111, 80101 Joensuu, Finland
E-mail: matti.haukka@joensuu.fi
Eur. J. Inorg. Chem. 2005, 3467–3471
DOI: 10.1002/ejic.200500287
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A. J. L. Pombeiro, V. Yu. Kukushkin et al.
FULL PAPER
complex [PdCl2{NH=C(Ph)ON=CMetBu}2]. The latter a broad peak for the =NH group at δ = 9.01–9.44 ppm.
observation, which was not developed further, prompted us This range is specific for imino hydrogens involved in hy-
to investigate the coupling at a PdII center under both mi- drogen bonding.[27] The latter was unambiguously deter-
crowave and conventional thermal conditions. For this mined in the solid state for the solvates 1·(Me2CO),
work we used PdCl2 in neat RCN (R = Me, Et, nPr, Ph) 2·(H2O), and 6·½(H2O) (see below). We anticipate that
and the ketoximes R1R2C=NOH (R1R2 = MeMe, MeEt, complexes 1–6 should also exhibit a similar type of H-bond
C5H10).
with either [D6]acetone or with traces of water in the com-
Refluxing PdCl2 with the ketoximes R1R2C=NOH in mercially available solvent. In the 1H NMR spectrum, com-
RCN for 2–3 h results in precipitation of the known[35] ox- plex 4 displays two set of signals for the alkyl groups (two
ime complexes [PdCl2(R1R2C=NOH)2] (Scheme 1, route Me’s and Et) of the chelated ligand [the latter derived from
A). However, further reflux of the reaction mixture for an the coupling with a mixture of syn/anti-MeC(=NOH)Et]
additional 6–12 h leads to formation of the chelated species due to syn/anti-isomers of the ligand.
[PdCl2{NH=C(R)ON=CR1R2-κ2N}] (1–6) (route C); these
The structures of 1·(Me2CO), 1·(CHCl3), 2·(H2O), and
complexes were isolated in the solid state in 60–75% yields. 6·½(H2O) were determined by single-crystal X-ray diffrac-
tion; the molecular structure of 1·(Me2CO) is depicted in
Figure 1. The atoms in the other similar structures are num-
bered correspondingly and bond lengths and angles are
given in Table 1.
Figure 1. Thermal ellipsoid view of [PdCl2{NH=C(Me)-
ON=CMe2-κ2N}]·(Me2CO) (1·Me2CO) with the atomic numbering
scheme. Thermal ellipsoids are drawn with 50% probability.
Scheme 1.
N(2)···O(99) = 2.954(6) Å.
The reaction time could be drastically reduced, to 15–
30 min, when the system was additionally irradiated with
microwaves (100 W, about 60 °C). The yields of the com-
plexes for both conventional and microwave methods were
almost identical. Compounds 1–6 can also be obtained by
Table 1. Selected bond lengths [Å] and angles [°] 1·(Me2CO),
1·(CHCl3), 2·(H2O), and 6·½(H2O).
1·(Me2CO) 1·(CHCl3) 2·(H2O) 6·½(H2O)
route B without isolation of the intermediate oxime com- Pd(1)–Cl(1)
2.2769(14) 2.2883(4) 2.2846(13) 2.2810(10)
2.3058(13) 2.3022(4) 2.3054(14) 2.3119(11)
Pd(1)–Cl(2)
plexes.
Pd(1)–N(1)
We believe that a plausible mechanism for the oxime–
Pd(1)–N(2)
2.068(4) 2.0622(15) 2.052(4)
1.968(4) 1.974(2) 1.965(4)
1.463(5) 1.4615(19) 1.454(5)
2.069(3)
1.980(4)
1.454(4)
1.260(5)
1.352(5)
88.48(4)
nitrile coupling at the PdII center involves the formation of
N(1)–O(1)
N(2)–C(4)
C(4)–O(1)
the bis(oxime) complexes [PdCl2(R1R2C=NOH)2], which,
1.271(7)
1.342(6)
1.267(2)
1.339(2)
88.87(2)
1.262(6)
1.333(5)
87.38(5)
in neat RCN, can form an equilibrium concentration of
[PdCl2(R1R2C=NOH)(RCN)] by displacement of one ox-
ime ligand. In the latter intermediate, the ligated nitrile is
subject to intramolecular attack by the adjacent oxime (or
Cl(1)–Pd(1)–Cl(2) 88.93(5)
N(1)–Pd(1)–N(2)
Pd(1)–N(1)–O(1)
Pd(1)–N(2)–C(4)
79.2(2)
79.20(6) 78.80(15) 79.12(13)
110.0(3) 109.66(10) 110.3(2)
117.0(4) 117.05(13) 117.6(3)
113.0(4) 113.57(13) 113.3(3)
109.5(2)
117.6(3)
114.4(3)
oximato ligand formed upon deprotonation). In general, C(4)–O(1)–N(2)
the coupling between electrophilically activated species and
nucleophiles is highly probable when the two species are
bound to a common metal center,[36] and, moreover, the lengths and angles of the four complexes agree with each
chelate effect also drives the reaction. other within 3σ and they are also well-coherent with the
All isolated compounds (1–6) gave satisfactory C, H, and normal bond lengths and angles.[37]
Inspection of Table 1 shows that the relevant bond
N elemental analyses and the expected molecular ion and
In conclusion, one should note that (i) the observed ox-
fragmentation patterns in the FAB+ mass spectra. The IR ime coupling is metal-mediated (as we have shown pre-
spectrum of each product displays two strong ν(C=N) viously,[1] the addition of oximes to nonactivated orga-
bands in the range between 1672 and 1613 cm–1 and a nonitriles RCN, i.e. those with a donor group R, does not
strong band in the high frequency region between 3265 and proceed in the absence of any metal complex even under
3217 cm–1 that can be attributed to the ν(N–H) stretching rather harsh reaction conditions) and (ii) the reaction is
vibration. The 1H NMR spectra of 1–6 in [D6]acetone show dramatically accelerated by microwave irradiation, thus al-
3468
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2005, 3467–3471

Microwave-Assisted and PdII-Mediated Nitrile–Oxime Coupling
FULL PAPER
+ H – Cl]+. M.p. 174–175 °C. IR (KBr): ν = 3222 s cm–1 ν(N–H),
lowing the formation of (imino)PdII complexes in a short
time.
˜
1667 s and 1620 s ν(C=N). 1H NMR ([D6]acetone): δ = 0.98 (t,
3
3JH,H = 6.6 Hz, 3 H, CH3), 1.76 (q, JH,H = 6.6 Hz, 2 H, CH2),
3
2.37 (s, 3 H, Me), 2.69 (s, 3 H, Me), 2.77 (t, JH,H = 6.6 Hz, 2 H,
Experimental Section
CH2), 9.11 (br. s, 1 H, NH) ppm.
6: C10H12Cl2N2OPd (353.5): calcd. C 34.09, H 3.44, N 7.96; found
Materials and Instrumentation: All reagents and solvents were ob-
tained from commercial sources and used as received. C, H, and N
elemental analyses were carried out by the Microanalytical Service
of the Instituto Superior Técnico. Melting points were determined
on a Kofler Table. For TLC, Merck UV 254 SiO2 plates were used.
Positive-ion FAB mass spectra were obtained on a Trio 2000 instru-
ment by bombarding 3-nitrobenzyl alcohol (NBA) matrices of the
samples with 8 keV (ca. 1.28×1015 J) Xe atoms. Mass calibration
for the data system acquisition was achieved with CsI. IR spectra
(4000–400 cm–1) were recorded on a JASCO FT/IR-430 instrument
in KBr pellets. 1H NMR spectra were measured on a Varian
UNITY 300 spectrometer at ambient temperature. The microwave
irradiation experiments were undertaken in a focused microwave
CEM Discover®LabMate reactor (100 W, 2.45 Hz) fitted with a
rotational system and an IR temperature detector; reactions were
performed in 10-mL pressure-rated reaction tubes, volumes of reac-
tion mixtures were about 3 mL. Detailed information on the reac-
tor is given at http://www.combichemlab.com/website/files/Combi-
chem/Microwave/cem.htm.
[PdCl2{NH=C(R)ON=CMe2-κ2N}] (R = Me 1, Et 2, nPr 3, Ph 6):
PdCl2 (20.0 mg, 0.11 mmol) and 2-propanone oxime (17.0 mg,
0.23 mmol) were suspended in the corresponding RCN (1 mL) and
the reaction mixture was heated under reflux conditions for 2–3 h
until the yellow solid complex [PdCl2(HON=CMe2-κN)2] had
formed. However, if the reaction mixture was refluxed for an ad-
ditional 6 (1), 8 (2), or 9 h (3), it leads to (i) R = Me: the release
of orange complex 1, which was filtered off, washed three times
with a small amount of acetonitrile and dried in vacuo. Yield:
25 mg (76%). The latter reaction was also performed under MW
irradiation (100 W, about 60 °C) and was complete in 15 min (yield:
24 mg, 73%). (ii) R = Et and nPr: formation of an orange solution.
The solvent was removed under a gentle stream of nitrogen and
the orange solid was washed with diethyl ether and dried in vacuo.
Yields: 23 mg (67%; 2) and 25 mg (69%; 3). The latter reaction was
also performed under MW irradiation (100 W, about 60 °C) and
was complete in 30 min. Yields: 22 mg (64%; 2) and 27 mg (74%;
3). (iii) After refluxing for more than 10 h (R = Ph), the dissolution
of the oxime complex was complete and the solution turned orange.
The solvent was removed under a gentle stream of nitrogen and
the orange crystalline residue was washed three times with diethyl
ether and dried in vacuo. Yield: 23.5 mg (59%; 6). The use of MW
irradiation (100 W, about 60 °C) allowed the completion of this re-
action in 30 min.
C 34.17, H 3.23, N 8.25. FAB+-MS: m/z = 319 [M – Cl + 3H]+,
317 [M – Cl + H]+, 316 [M – Cl]+. M.p. 169–170 °C. IR (KBr): ν
˜
= 3218 s cm–1 ν(N–H), 1649 s and 1617 s ν(C=N), 1579 s ν(C=C).
1H NMR ([D6]acetone): δ = 2.55 (s, 3 H, CH3), 2.76 (s, 3 H, CH3),
7.61–8.13 (m, 5 H, Ph), 9.44 (br. s, 1 H, NH) ppm.
[PdCl2{NH=C(Me)ON=CMeEt-κ2N}] (4): PdCl2 (20.0 mg,
0.11 mmol) and 2-butanone oxime (20.0 mg, 0.23 mmol; a mixture
of syn and anti isomers) were suspended in acetonitrile (1 mL). The
reaction mixture was refluxed for 9 h until the complete dissolution
of PdCl2 to give an orange solution, whereupon acetonitrile was
evaporated with a flow of nitrogen and the yellow oily residue was
crystallized under a layer of diethyl ether to give an orange yellow
solid that was filtered off and dried in air at room temperature.
Yield: 23 mg (67%). The latter reaction was also performed under
MW irradiation (100 W, about 60 °C) and was complete in 15 min.
Yield: 22 mg (63%). C6H12Cl2N2OPd (305.5): calcd. C 23.60, H
3.93, N 9.18; found C 22.97, H 3.91, N 9.13. FAB+-MS: m/z = 305
[M]+, 269 [M – HCl]+. IR (KBr): ν = 3237 s cm–1 ν(N–H), 1670 s
˜
1
and 1617 s ν(C=N). H NMR ([D6]acetone): two syn-anti isomers
3
in ca. 3:2 ratio. Major isomer: δ = 1.16 (t, JH,H = 7.2 Hz, 3 H)
3
and 3.16 (q, JH,H = 7.2 Hz, 2 H) (C2H5), 2.37 (s, 3 H, CH3), 2.44
(s, 3 H, CH3 from oxime), 9.05 (br. s, 1 H, NH); minor isomer: δ
3
3
= 1.22 (t, JH,H = 7.2 Hz, 3 H) and 2.75 (q, JH,H = 7.2 Hz, 2 H)
(C2H5), 2.68 (s, 3 H, CH3 from oxime), 2.45 (s, 3 H, CH3), 9.05
(br. s, 1 H, NH) ppm.
[PdCl2{NH=C(Me)ON=C(C5H10)-κ2N}] (5): PdCl2 (20.0 mg,
0.11 mmol) and cyclohexanone oxime (26.0 mg, 0.23 mmol) were
suspended in acetonitrile (1 mL) and refluxed for 4 h, whereupon
a yellow, crystalline precipitate of [Pd{HON=C(C5H10)}2] formed.
If this suspension was refluxed for an additional 11 h, the oxime
complex gradually dissolved to give an orange solution. The sol-
vent was removed under a stream of nitrogen and the orange solid
was washed with diethyl ether and dried in vacuo. Yield: 26 mg
(69%). The latter reaction was also performed under MW irradia-
tion (100 W, 60 °C) for 30 min. Yield: 25 mg (68%).
C8H14Cl2N2OPd (331.5): calcd. C 29.00, H 4.22, N 8.45; found C
28.72, H 3.71, N 8.69. FAB+-MS: m/z = 331 [M]+, 330 [M – H]+,
260 [M – 2Cl]+. M.p. 191–193 °C. IR (KBr): ν = 3265 s cm–1 ν(N–
˜
H), 1658 s and 1613 s ν(C=N). 1H NMR ([D6]acetone): δ = 1.65
(m, 2 H, C5H10), 1.85 (m, 4 H, C5H10), 2.46 (s, 3 H, CH3), 2.50
(m, 2 H, C5H10), 2.60 (m, 2 H, C5H10), 9.20 (br. s, 1 H, NH) ppm.
1: C5H10Cl2N2OPd (291.5): calcd. C 20.60, H 3.46, N 9.61; found
X-ray Structure Determinations. Crystals were immersed in cryo-
oil, mounted in a Nylon loop, and measured at a temperature of
100 K or 110 K. The X-ray diffraction data were collected with
a Nonius KappaCCD diffractometer using Mo-Kα radiation (λ =
0.71073 Å). The Denzo-Scalepack[38] or EvalCCD[39] program
packages were used for cell refinements and data reduction. The
structures were solved by direct methods using SIR2000[40] or by
the Patterson method with DIRDIF-99.[41] A multiscan absorption
correction based on equivalent reflections (XPREP in SHELXTL
v. 6.14)[42] was applied to all of the data (the Tmin/Tmax values were
0.7411/0.8986, 0.5614/0.8510, 0.5097/0.8461, and 0.4884/0.8636 for
C 20.80, H 3.42, N 9.31. FAB+-MS: m/z = 313 [M – H + Na]+,
289 [M – 2H]+, 255 [M – HCl]+. M.p. 187–188 °C. IR (KBr): ν =
˜
3239 s cm–1 ν(N–H), 1672 s and 1625 s ν(C=N). 1H NMR ([D6]-
acetone): δ = 2.36 (s, 3 H, Me), 2.44 (s, 3 H, Me), 2.68 (s, 3 H,
Me), 9.01 (br. s, 1 H, NH) ppm.
2: C6H12Cl2N2OPd (305.5): calcd. C 23.60, H 3.93, N 9.18; found
C 23.82, H 3.69, N 9.19. FAB+-MS: m/z = 306 [M + H]+, 271 [M
+ H – Cl]+, 235 [M + H – 2Cl]+. M.p. 194–195 °C. IR (KBr): ν =
˜
3217 s cm–1 ν(N–H), 1665 s and 1621 s ν(C=N). 1H NMR ([D6]-
3
acetone): δ = 1.27 (t, JH,H = 6.8 Hz, 3 H, Me from Et), 2.38 (s, 3
H, Me), 2.69 (s, 3 H, Me), 2.95 (q, 3JH,H = 6.8 Hz, 2 H, CH2 from 1·(Me2CO), 1·(CHCl3), 2·(H2O), and 6·½(H2O), respectively).
Et), 9.13 (br. s, 1 H, NH) ppm.
Structural refinements were carried out with SHELXL-97 with the
WinGX graphical user interface.[43,44] NH and H2O were located
from the difference Fourier map but not refined in 6·½(H2O) [N(2)
3: C7H14Cl2N2OPd (319.5): calcd. C 26.33, H 4.38, N 8.77; found
C 25.98, H 4.06, N 8.81. FAB+-MS: m/z = 320 [M + H]+, 285 [M
Eur. J. Inorg. Chem. 2005, 3467–3471
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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A. J. L. Pombeiro, V. Yu. Kukushkin et al.
FULL PAPER
Table 2. Crystallographic data for 1·(Me2CO), 1·(CHCl3), 2·(H2O), and 6·½(H2O).
1·(Me2CO)
1·(CHCl3)
2·(H2O)
6·½(H2O)
Empirical formula
Formula mass
Temperature [K]
λ [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C8H16Cl2N2O2Pd
349.53
100(2)
0.71073
monoclinic
C2/m
20.8502(12)
6.8143(3)
9.2995(5)
90
100.117(3)
90
1300.72(12)
4
1.785
1.821
C6H11Cl5N2OPd
410.82
100(2)
C6H14Cl2N2O2Pd
323.49
110(2)
0.71073
monoclinic
P21/n
7.112(2)
11.014(3)
14.391(3)
90
101.245(17)
90
1105.6(5)
4
1.944
2.134
C10H13Cl2N2O1.5Pd
362.52
100(2)
0.71073
0.71073
triclinic
triclinic
¯
¯
P1
P1
7.7792(2)
8.9921(3)
10.4116(3)
105.127(2)
96.913(2)
105.504(2)
663.19(3)
2
2.057
2.382
0.0181
0.0425
7.1582(6)
8.1661(7)
11.5194(11)
110.343(5)
90.897(5)
95.358(6)
627.77(10)
2
1.918
1.888
0.0388
0.0993
γ [°]
V [Å3]
Z
ρcalcd. [Mgm–3]
µ(Mo-Kα) [mm–1]
[a]
R1 [I Ն 2σ(I)]
0.0277
0.0705
0.0375
0.0666
[b]
wR2 [I Ն 2σ(I)]
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = [Σ{w(Fo – Fc ) }/Σ{w(Fo2)2}]1/2
.
2
2 2
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and O(99)] but refined as riding atoms with a fixed distance of
0.85 Å. Other hydrogens were placed in idealized position and con-
strained to ride on their parent atom. The crystal water in
6·½(H2O) is disordered over two sites with equal occupancy of 0.5.
The crystallographic data are summarized in Table 2, with selected
bond lengths and angles given in Table 1. CCDC-267621 to
-267624 [for 1·(Me2CO), 1·(CHCl3), 2·(H2O), and 6·½(H2O),
respectively] contain the supplementary crystallographic data
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This work was supported by the Fundação para a Ciência e a Tec-
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43415/2001 project, which is FEDER funded). D. A. G. expresses
gratitude to the FCT and the POCTI program for a fellowship
(grant SFRH/BPD/11685/2002). M. H. and V. Yu. K. would like
to thank the Academy of Finland for financial support. V. Yu. K.
thanks FCT for a grant for Cientista Convidado/Professor at the
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