Complexes of N-thiophosphorylthioureas (HL) with copper(I). Crystal structures of [Cu3L3] and [Cu(PPh3) 2L] chelates

Article abstract of DOI:10.1039/b709551a

Reaction of the potassium salts of N-thiophosphorylated thioureas of common formula RC(S)NHP(S)(OiPr)₂ [R = morpholin-N-yl (HL^a), piperidin-N-yl (HL^b), NH₂ (HL^c), PhCH ₂NH (HL^d)] with Cu(PPh₃)₃I in aqueous EtOH/CH₂Cl₂ leads to mononuclear [Cu(PPh ₃)₂L-S,S′] complexes. Using copper(i) iodide instead of Cu(PPh₃)₃I, polynuclear complexes [Cu _n(L-S,S′)_n] were obtained. The structures of these compounds were investigated by ES-MS, elemental analyses, ¹H and ³¹P NMR in solution, IR and ³¹P solid-state MAS NMR spectroscopy. The crystal structures of [Cu₃L₃ ^a] and [Cu(PPh₃)₂L^b] were determined by single-crystal X-ray diffraction. The Royal Society of Chemistry 2007.

Full text of DOI:10.1039/b709551a

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Complexes of N-thiophosphorylthioureas (HL) with copper(I). Crystal
structures of [Cu3L3] and [Cu(PPh3)2L] chelates†
Felix D. Sokolov,*a Maria G. Babashkina,a Damir A. Safin,*a Aydar I. Rakhmatullin,b Franck Fayon,b
Nail G. Zabirov,a Michael Bolte,c Vasiliy V. Brusko,a Joanna Galezowskad and Henryk Kozlowskid
Received 25th June 2007, Accepted 13th August 2007
First published as an Advance Article on the web 22nd August 2007
DOI: 10.1039/b709551a
Reaction of the potassium salts of N-thiophosphorylated thioureas of common formula
RC(S)NHP(S)(OiPr)2 [R = morpholin-N-yl (HLa), piperidin-N-yl (HLb), NH2 (HLc), PhCH2NH
(HLd)] with Cu(PPh3)3I in aqueous EtOH/CH2Cl2 leads to mononuclear [Cu(PPh3)2L–S,Sꢀ] complexes.
Using copper(I) iodide instead of Cu(PPh3)3I, polynuclear complexes [Cun(L–S,Sꢀ)n] were obtained. The
structures of these compounds were investigated by ES-MS, elemental analyses, 1H and 31P NMR in
solution, IR and 31P solid-state MAS NMR spectroscopy. The crystal structures of [Cu3L3 ] and
a
[Cu(PPh3)2Lb] were determined by single-crystal X-ray diffraction.
Introduction
The chelates of phosphorus-, sulfur- or selenium-containing
ligands with coinage metal cations are of great importance due
to their photophysical properties,1,2 application for the creation
of chalcogenide nanoparticles,3 and use as models for biolog-
ical systems.4 Therefore, complexes of dithio(seleno)phosphinic
acids [RRꢀP(X)YH] (X, Y = S, Se) and imidodithio(seleno)-
diphosphinate ligands [R2P(X)NHP(X)Rꢀ2] (IDP) with coinage
metal cations have recently drawn considerable attention.5–7 There
is a growing family of IDP polynuclear aggregates of com-
mon formula [M3{R2P(X)NP(X)Rꢀ2}3] (1) (M = Cu(I), Ag(I);
X = S, Se) with a cyclic M3X3 core3a,8,9 and ionic complexes
[M4{Ph2P(X)NP(X)Ph2}3]+An− (2) with a tetrahedral M4 core
surrounded by six chalcogen atoms (Chart 1).6 Contrary to the
previously mentioned ligands, there is a lack of information about
structures of the polynuclear copper(I) complexes containing N-
thiophosphorylated thioureas and thioamides, RC(S)NHP(S)Rꢀ2
(3) (R = Rꢀ2N, Alk, Ar), which are IDP’s asymmetrical analogues
containing the thiocarbonyl group instead of one thiophos-
Chart 1
phinic unit. The structures of only two species, a cyclic trimer
[Cu3{Et2NC(S)NP(S)(OPh)2}3] (4),10 and an ionic aggregate with
crown-ethers, aza-macrocycles, etc. can be easily obtained.12,13 It
unusual “tent-like” structure [Cu10{PhNHC(S)NP(S)(OEt)2}9]-
opens interesting perspectives for the further application of these
complexes in selective catalysis and crystal engineering.
ClO4 (5),11 have been reported.
The IDP ligands have mostly simple substituents R, Rꢀ =
In this work, we describe the synthesis and the structural charac-
Ar, Alk, OAr or OAlk. Presence of the sp2-carbon atom in the
terization of several new polynuclear complexes of the Cu(I) cation
S–C–N–P–Y ligand backbone of (3) facilitates modification of
the ligands. Multifunctional molecules containing fragments of
with N-thiophosphorylthiourea ligands RC(S)NHP(S)(OiPr)2
[R = morpholin-N-yl (HLa), piperidin-N-yl (HLb), NH2 (HLc),
PhCH2NH (HLd)] (Chart 2) and their mononuclear analogues
aA. M. Butlerov Chemistry Institute, Kazan State University, Kremlevskaya
containing triphenylphosphine ligands.
Str. 18, 420008, Kazan, Russian Federation. E-mail: felix.sokolov@
ksu.ru, damir.safin@ksu.ru; Fax: +7-843-2543734
bCRMHT-CNRS, 1D avenue de la Recherche Scientifique, 45071, Orle´ans
Results and discussion
cedex 2, France
cInstitut fu¨r Anorganische Chemie J.-W.-Goethe-Universita¨t, Frankfurt/
Main, Germany
N-thiophosphorylated thioureas HLa-d were prepared by addition
of the corresponding amine to O,O-diisopropylthiophosphoric
acid isothiocyanate (iPrO)2P(S)NCS. Reaction of the potassium
salts of HLa–d with [Cu(PPh3)3I] in aqueous EtOH/CH2Cl2
leads to mononuclear [Cu(PPh3)2La–d] complexes (6a–d). When
dFaculty of Chemistry, University of Wroclaw, F. Joliot-Curie Str. 14, 50383,
Wroclaw, Poland
† CCDC reference numbers [CCDC NUMBER(S)]. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/b709551a
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spectra of the chelates containing anionic forms of La,b. Presence
of the NH2 group in HLc and its complexes is seen in the IR
spectra by its mas, ms and dNH2 absorption bands. A unique band
at 3320 cm−1 related to the AlkNH group was observed in the
spectrum of 6d.
1
The 31P{ H} NMR spectra of HLa,b in a CDCl3 solution
show a single resonance around 60 ppm. The corresponding 31P
resonance in HLc,d is high-field shifted by approximately 6.5 ppm.
This difference in the 31P NMR chemical shifts is typical for
N-thiophosphorylated thioureas with the tertiary amine group
R (HLa,b) relative to HLc,d ligands containing secondary amine
1
substituents RꢀNH, where Rꢀ = H, Alk, Ar.12 In the 31P{ H}
NMR spectra of mononuclear complexes 6, the resonances in
the range 51.8–55.3 ppm correspond to the phosphorus atoms
of the thiophosphoryl group. The signals of triphenylphosphine
groups are shifted downfield relative to the free PPh3 and exhibit
31P NMR chemical shifts at about −1 ppm. In solution, the fast
exchange between free and bound triphenylphosphine groups of
Chart 2
using CuI instead of Cu(PPh3)3I polynuclear [CunLna–c] complexes
(7a–c) were formed (Scheme 1). Thiourea HLb decays when stored
for several days, therefore the one pot synthesis was used to yield
its complexes.
1
complexes 6 results in a signal broadening of the 31P{ H} NMR
spectra, as it was previously observed for the Cu(I) complexes
with N-thioacylamidothiophosphates.13 Formation of polynuclear
complexes 7a–c leads to a high-field shift of the 31P resonance of
1
the thiophosphoryl group. For complexes 7a,b, the 31P{ H} NMR
spectra recorded at 25 and −50 ◦C show a single narrow peak
1
(fwhm of 3–5 Hz) at arou◦nd 50 ppm. For 7c the 31P{ H} NMR
spectrum, obtained at 25 C, shows a single slightly-wider reso-
nance in the same region (Fig. 1), while several additional peaks
are observed in the low-temperature spectrum. Further analyses
are required to unambiguously assign these additional signals.
It could be assumed, however, that at low temperature several
polynuclear compounds having various structures and different
values of n occur. The range of observed 31P NMR chemical
shifts would suggest that both thiocarbonyl and thiophosphoryl
groups form bridging bonds involving sulfur atoms. In the case of
complexes 7a,b, steric effects due to the demanding substituents
would interfere with such association processes.
Scheme 1
Reaction of the potassium salt of HLd with CuI does not lead
to stable Cu(I) chelates. It is known that N-phosphorylthiourea
complexes bearing AlkNH groups easily react with nucleophiles
to form phosphorylated guanidines, ureas and isoureas.13a The
−1
=
C N group stretching vibration band at 1600–1650 cm in the
IR spectra of the reaction mixture and 31P NMR signals in the
range of 58–60 ppm confirm the decomposition of the ligand.
The chelates obtained are colourless crystalline powders, soluble
in acetone, benzene, dichloromethane and insoluble in water and
n-hexane. 1H, 31P{ H} NMR in solution and IR data indicated that
1
thioureas HL are 1,5-S,Sꢀ-ligands in all the present cases studied.
Conductometric analyses in acetone have shown an absence of
conductivity for complexes 6 and 7.
The ES-MS spectra obtained are similar for all polynuclear
complexes of 7. The strongest peaks correspond to the [Cu4L3]+
cations. Mass-spectra also contain the peaks of the [Cu3L3 + Na]+
and [Cu3L2]+ ions. [Cu4L3]+ and [Cu3L2]+ species are observed
in the spectra of the compounds 6, however, in these cases the
maximum intensity belongs to the peaks of [Cu(PPh3)2]+.
The IR spectra of HL contain weak bands centered at 620–
Fig. 1 31P{ H} NMR spectra of [Cun(Lc)n] (7c) (−50 ◦C (A), 25 ◦C (B))
1
in CDCl3.
The 1H NMR spectra of complexes 6 and 7 in CDCl3 contain the
signals expected for the proposed structure only (chemical shifts
and J-coupling constants are given in the Experimental section).
676 cm−1 assigned to the P S groups. They are shifted to low
=
frequencies (580–608 cm−1) in the spectra of complexes 6 and 7
due to the coordination with the Cu(I) ion. Occurrence of the new
broad and strong absorption peak at 1460–1568 cm−1, related to
the conjugated SCN group,12 also proves the formation of S,Sꢀ-
chelates. There are no NH group absorption bands in the IR
The H signal of the NHP(S) group is absent in the H NMR
1
1
spectra, confirming the anionic form of La–d
.
In the 1H NMR spectrum of HLc, the signals of the two
nonequivalent protons of the NH2 group are observed. These two
1H resonances are also evidenced in the 1H NMR low-temperature
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spectrum (−50 ◦C) of the 6c complex. The downfield shift of the
Hb proton of 6c, observed at low temperature (Fig. 2B) is caused
by the intermolecular H-bonding in solution. The spectrum of 6c,
recorded at 25 ◦C, exhibits a motional-averaged signal of the NH2
group with an intensity corresponding to two protons (see Fig. 2A
and 2B). This is caused by dissociation of the weak intermolecular
H-bonds and a decrease in the H2N–C bond rotation barrier at
the higher temperature.
Chart 3
Variation of the chemical shift for the Ha proton of the NH2
group in complexes 6c and 7c could be assigned to the formation
of intramolecular hydrogen bonds in molecules of the polynuclear
aggregate (Chart 3B). This is confirmed by the 1H NMR spectrum
of 7c in d6-acetone which shows a weak shift of the Ha resonance
(DdH + 0.3 ppm ) whereas the Hb peak is strongly downfield shifted
(DdH + 1.5) due to the formation of hydrogen bonds with the
solvent.
Thus, comparative analysis of the 1H NMR spectra of the NH2
moieties in 6c and 7c clearly demonstrates the preservation of the
bonding between [CuLc] units of [CunLn ] aggregates in a CDCl3
c
solution.
Crystal structures of mononuclear 6b and trimeric 7a complexes
were determined by single crystal X-ray diffraction. The complexes
obtained have been crystallized from dichloromethane–n-hexane
solution, 1 : 2 (v/v). In the structure of 6b (Fig. 3), the copper(I)
cation is in a P2S2 tetrahedral environment. The weak distortions
relative to a perfect tetrahedron (Table 1) reveal the absence of
major steric hindrance. According to the X-ray data, complex
7a is a cyclic trimer (Fig. 4), in which the Cu–S–Cu bridging
Fig. 2 NH2 group proton resonance of complexes [Cu(PPh3)2Lc] (6c) at
25 ◦C (A), −50 ◦C (B), and [CunLn ] (7c) at 25 ◦C (C) in CDCl3 without
c
(C), and with (D) phosphorus decoupling.
It should be noted that the signals of the Ha and Hb protons of
the NH2 groups in 6c and 7c have different scalar coupling with the
phosphorus atom (Chart 3). The high-field resonance of the NH2
group in 6c clearly shows a splitting due to the 4JPNCNH spin–spin
interaction. Similar splitting is observed for the downfield NH2 sig-
nal in 7c. Rather high 4JPNCNH coupling constants are measured for
mononuclear 6c (7.7 Hz) and polynuclear 7c (8.6 Hz) complexes.
This was previously reported for other N-phosphorylthiourea
complexes13,14 and attributed to the fact that the P–N–C–N–
H chain matches the so-called W-criterion (Chart 3).15 The
4
contribution of the observed splitting to the presence of JPNCNH
spin–spin coupling was unambiguously confirmed by recording
1H NMR spectra with 31P decoupling (e.g. Fig. 2D).
For complex 7c in CDCl3, a comparative analysis of 1H NMR
data gives evidence for the existence of a polynuclear chelate at
room temperature. The H NMR spectrum, obtained at 25 ◦C,
1
shows two signals of equal intensity corresponding to the two
nonequivalent protons of the NH2 group (Fig. 2C). This is
=
explained by the participation of the sulfur atom of the C S
groups in the bridging bonds resulting in a decrease of the
electronic density in the conjugated chelate cycle and, hence, to
the increase of the conjugation degree of the lone electron pair
of the NH2 group and an increase of the H2N–C bond rotation
barrier.
Fig. 3 Molecular structure of complex [Cu(PPh3)2Lb] (6b).
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Table 1 Selected bond lengths, bond angles, and torsion angles for
complex [Cu(PPh3)2Lb] (6b)
Table 2 Selected bond lengths, bond angles, and torsion angles for
a
complex [Cu3L3 ] (7a)
˚
˚
Bond lengths/A
Bond lengths/A
C(1)–S(2)
C(1)–N(1)
C(1)–N(11)
N(1)–P(1)
P(1)–S(1)
1.746(2)
1.325(3)
1.364(3)
1.590(2)
1.9821(8)
Cu(1)–P(2)
Cu(1)–P(3)
Cu(1)–S(1)
Cu(1)–S(2)
2.2970(6)
2.3162(6)
2.3479(6)
2.3051(6)
Cu(1)–S(31)
Cu(1)–S(11)
Cu(1)–S(1)
S(11)–Cu(2)
Cu(2)–S(21)
Cu(2)–S(2)
S(21)–Cu(3)
P(2)–N(2)
2.2443(5)
2.2469(5)
2.2507(6)
2.2634(5)
2.2437(5)
2.2624(6)
2.2653(5)
1.610(2)
P(3)–N(3)
Cu(3)–S(31)
Cu(3)–S(3)
S(1)–P(1)
P(1)–N(1)
N(1)–C(1)
C(1)–S(11)
S(2)–P(2)
1.593(2)
2.2032(5)
2.2406(6)
1.9899(7)
1.604(2)
1.307(3)
1.787(2)
1.9847(7)
1.308(2)
1.791(2)
Bond angles/◦
N(2)–C(2)
C(2)–S(21)
S(3)–P(3)
1.312(2)
1.786(2)
1.9950(8)
N(3)–C(3)
C(3)–S(31)
S(1)–Cu(1)–S(2)
109.19(2)
53.8(2)
P(2)–Cu(1)–P(3)
110.12(2)
Torsion angles/◦
Bond angles/◦
S(1)–P(1)–N(1)–C(1)
Cu(1)–S(11)–Cu(2)
Cu(2)–S(21)–Cu(3)
Cu(3)–S(31)–Cu(1)
78.53(2)
75.53(2)
87.62(2)
Torsion angles/◦
S(1)–P(1)–N(1)–C(1)
S(3)–P(3)–N(3)–C(3)
S(2)–P(2)–N(2)–C(2)
53.8(2)
−27.8(3)
58.1(2)
the polynuclear complex 7a, the C–S bonds, participating in the
formation of bridges, are especially strongly lengthened to the
˚
values 1.787(2), 1.7858(18) and 1.7910(18) A characteristic for
single bonds.16
The data presented clearly show that increasing the coordination
number of the thiocarbonyl sulfur atoms in polynuclear chelates
4, 5, 7a leads to a lengthening of the CS and CN bonds
and a shortening of the Cu–S bonds in comparison with the
mononuclear analog 6b. In our opinion, it could be caused by
the more effective overlap of copper(I) and sulfur orbitals in the
CuS3 and CuS4 environments than in the CuP2S2 complex core.
Comparison of polynuclear complexes 4, 5, 7a shows, that the
conjugated SCNPS moiety in the ligand anions possesses sufficient
structural flexibility due to the presence of the phosphorus
atom in it. A low rotation barrier around the PN bond in the
chelate cycles provides realization of various types of the folded
conformations.10,11
Thiocarbonyl and thiophosphoryl sulfur atoms are capable to
form bridging bonds between the [CuL] units. However, the ability
of such association essentially depends on the structure of the
substituents at the chelate units. The lack of experimental data
means a law of such aggregates formation can not be formulated
at the moment. However, it is possible to assume that a reduction
of the sterical demands at the chetate unit facilitates increasing
the coordination numbers of the sulfur and copper(I) atoms. The
increase in association degree in the aggregates 5 and 7c confirms
this assumption.
a
Fig. 4 Molecular structure of complex [Cu3L3 ] (7a).
=
bonds are formed by the sulfur atoms of the C S groups.
The Cu3S3 cyclic backbone is in a chair conformation and the
copper atoms are in a S3 trigonal-planar environment. In the
crystal structure, the molecular unit is distorted and does not
possess a C3 symmetry axis. The distances Cu(1)–Cu(2) 2.8546(4)
and Cu(2)–Cu(3) 2.7614(3) indicate lack of any distinct Cu–Cu
interactions11 and the Cu(1)–Cu(3) distance is the longest one
˚
(3.0789 A). This variation in the Cu–Cu distances leads to an
increase of the Cu(1)–S(31)–Cu(3) bond angle relative to the
Cu(1)–S(11)–Cu(2) and Cu(2)–S(21)–Cu(3) angles (Table 2). The
cyclic Cu(1)–S(11)–C(1)–N(1)–P(1)–S(1) moiety is almost flat.
The Cu(2)–S(21)–C(2)–N(2)–P(2)–S(2) and Cu(3)–S(31)–C(3)–
N(3)–P(3)–S(3) six-membered chelate rings are similar to that
in the mononuclear analogue 6b which adopts a distorted boat
conformation with the maximal distortion of the thiophosphoryl
sulfur atoms from the N–C(S)–N–P–O plane. In these chelate
rings, the C–S and P–S bonds are lengthened, while C–N and
P–N bonds are shortened (Table 2) in comparison to the typical
values for N-thiophosphorylated thioureas and thioamides.12 In
The structures of the crystalline mononuclear 6a–c and polynu-
clear 7a–c complexes were also characterized by 31P solid-state
magic angle spinning (MAS) NMR spectroscopy.
According to the X-ray data, there are four equivalent molecules
in the asymmetric unit of the mononuclear complex 6b, each of
them containing three crystallographically inequivalent P sites.
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1
The 31P{ H} CPMAS spectra with 1H decoupling is in agreement
the fast exchange between free and bound triphenylphosphine
groups. Table 3 gives the 31P NMR isotropic chemical shifts and
isotropic J-coupling constants determined from the simulations
of the CPMAS spectra. The coupling constants obtained are
comparable to values found previously for complexes with the
same complex core CuP2S2,20 but slightly smaller because of
longer Cu–P bond distances. The P-site quantification obtained
from a single pulse spectrum is in agreement with the expected
multiplicities and the 63,65Cu isotopic abundances. The simulation
of the J-multiplet patterns takes into account “residual dipolar”
effects due to the dipolar and anisotropic scalar couplings
between 31P and the quadrupolar copper nucleus.21–23 However,
only the magnitude of this term was fitted since both the 63,65Cu
quadrupolar coupling constants and J-coupling anisotropy are
with the X-ray diffraction data (Fig. 5A). In this spectrum, the
resonance of the P atom of the thiophosphoryl group appears as
a single peak with a 31P NMR chemical shift of −52.8 ppm, while
the two inequivalent triphenylphosphine P sites give rise to four
multiplets owing to the direct J-couplings with the 63Cu and 65Cu
isotopes. These multiplets appear as a quadruplet (63,65Cu, I = 3/2)
of doublets due to the presence of a homonuclear 2JPCuP coupling
of about 98 Hz, which was also measured using a two-dimensional
spin echo MAS experiment17–19 (not shown). These 1JPCu and 2JPCuP
couplings were not observed in the solution NMR spectra due to
1
unknown. The 31P{ H} CPMAS spectra of the mononuclear
complex 6a is shown in Fig. 5B, As for 6b, this spectrum shows
a single resonance for the thiophosphoryl group and four partly
overlapping quadruplets of doublets for the triphenylphosphine
groups, indicating that the crystal structure of this complex
contains one distinct molecular unit with three inequivalent P
sites. For mononuclear complex 6a, the 31P isotropic chemical
shifts and J-coupling constants are very similar to those measured
for 6b. The spectrum of 6c shows a single narrow resonance for
the thiophosphoryl group (Fig. 5C). However, the complex J-
multiplet patterns of the triphenylphosphine resonances are not
resolved and only a broad asymmetric quadruplet is observed. The
lack of the spectral resolution could be due to a more pronounced
“residual dipolar effect”, which would arise from a very large
63,65Cu quadrupolar coupling constant and would result in a second
order broadening of the 31P J-multiplets.21–23 In order to get a more
detailed interpretation of this spectrum, additional 63,65Cu and 31
P
NMR experiments at very high magnetic fields are in progress.
The 31P{ H} CPMAS spectra of polynuclear copper(I) com-
plexes 7 are also shown in Fig. 5. In the case of 7a, the spectrum
contains three resolved resonances at 45.4, 52.8 and 53.4 ppm
with relative intensities in the ratio ∼1 : 1 : 1, corresponding to the
three crystallographically inequivalent PS groups per molecule, in
1
1
Fig. 5 31P{ H} solid state CPMAS NMR spectra of mononuclear
complexes [Cu(PPh3)2L] 6b (A), 6a (B), 6c (C) and polynuclear complexes
[CunLn] 7a (n = 3) (D), 7b (E), 7c (F) (top). Expansion of the experimental
and simulated J-multiplet patterns of the mononuclear samples (A) and
(B) (bottom).
1
agreement with the X-ray diffraction data. The 31P{ H} CPMAS
spectrum of 7b (Fig. 5E) exhibits two partly resolved peaks with an
Table 3 31P isotropic chemical shifts and 1JP–Cu and 2JP–P coupling constants of Cu(I) complexes. Estimation of errors according to Dmfit 2007 is 6 Hz.
(nm: not measured)
Complex
P site
diso (ppm)
1J(63Cu–31P)/Hz
1J(65Cu–31P)/Hz
2J(31P–31P)/Hz
I (%)
6a
[PPh3]
[PPh3]
[CuL]
−8.6
−1.1
54.5
933
1082
999
1158
94
94
30.2
33.8
36.0
6b
[PPh3]
[PPh3]
[CuL]
−9.0
−0.7
52.8
913
1085
978
1161
98
98
35.3
33.4
31.3
6c
7a
[CuL]
[PPh3]
−8.6
39.4
60.6
nm
nm
nm
nm
[CuL]
[CuL]
[CuL]
45.4
52.8
53.4
33.4
31.9
34.7
7c
[CuL]
[CuL]
54.9
55.5
32.5
67.5
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intensity ratio 2 : 1. In this spectrum, the most intense peak shows
a slightly asymmetric lineshape that would suggest the presence
of two overlapping resonances. This spectrum would therefore
be consistent with the presence of three inequivalent P sites, two
of them having very similar 31P NMR isotropic chemical shifts
85% H3PO4 (31P) solutions. All MAS NMR spectra were modeled
using the Dmfit program.27
Synthesis of HLa. A solution of morpholine (1.044 g, 12 mmol)
in CH2Cl2 (25 mL) was added dropwise to a solution of
SCNP(S)(OiPr)2 (3.155 g, 13.2 mmol) in the same solvent (15 mL).
The mixture was stirred at room temperature for 3 h. The solvent
was then removed in vacuum. The residue was recrystallized from
a dichloromethane–n-hexane mixture 1 : 5 (v/v). The product was
b
and with the formation of a trimeric associate [Cu3L3 ]. For 7c,
the 31P CPMAS spectrum is much more complex and exhibits
at least 8 partly overlapping thiophosphoryl resonances with
different relative intensities. In this case, the 31P NMR spectrum
could indicate the presence of several polynuclear complexes
having different n values and/or the presence of different isomeric
structures.
◦
obtained as colorless crystals. Yield: 3.129 g, 80%. mp = 84 C.
3
1H NMR (d6-acetone) 1.31 (d, JH,H = 6.0 Hz, 12H, CH3), 3.66
3
(m, 4H, OCH2), 3.89 (m, 4H, NCH2), 4.87 (d. sept, JPOCH
=
3
10.9 Hz, JH,H = 6.0 Hz, 2H, OCH), 6.06 (br. s, 1H, NH) ppm;
31P{ H} NMR (CDCl3) 59.5 ppm; 31P{ H} NMR (d6-acetone)
1
1
−1
Conclusions
=
61.5 ppm; IR (cm ): 3232 (NH), 1496 (S C–N), 1112 (COC),
=
960, 1000,1040 (POC), 623 (P S). Anal. Calcd for C11H23N2O3PS2
(326.42): C, 40.48; H, 7.10; N, 8.58. Found: C, 40.41; H, 7.06; N,
8.60.
Reaction of [Cu(PPh3)3I] with the potassium salts of the N-
thiophosphorylated thioureas HLa–d has allowed us to obtain
complexes of composition [Cu(PPh3)2L] (6a–d) containing tetraco-
ordinated atoms of copper(I). A similar reaction using CuI instead
of [Cu(PPh3)3I] yields the [CunLn] polynuclear analogues 7a–c.
NMR experiments in solution and IR have shown that HLa–d are
1,5-S,Sꢀ-ligands in all cases.
HLb. This was prepared similar to that described for HLa but
with piperidine (1.020 g, 12 mmol). The product was obtained
as colorless crystals. Yield: 3.499 g, 90%. mp = 101 ◦C. 1H NMR
(CDCl3) 1.36 (br. s, 12H, CH3), 1.65 (br. s, 6H, b,c-CH2, c-C5H10N),
3.81 (br. s, 4H, a-CH2, c-C5H10N), 4.89 (br. s, 2H, OCH), 5.93 (br. s,
Crystal structures of mononuclear 6b and polynuclear 7a
complexes were determined by single crystal X-ray diffraction.
1
1H, NH) ppm; 31P{ H} NMR (CDCl3) 59.9 ppm; IR (cm−1): 3200
a
=
=
According to the X-ray data, [Cu3L3 ] (7a) is a cyclic trimer, formed
(NH), 1502 (S C–N), 1000,1008 (POC), 624 (P S). Anal. Calcd
for C12H25N2O2PS2 (324.44): C, 44.42; H, 7.77; N, 8.63. Found: C,
44.45; H, 7.73; N, 8.59.
by the bridging bonds with participation of the thiocarbonyl sulfur
atoms. Additionally 31P solid state NMR experiments indicate the
b
formation of the polynuclear associate [CunLn ] (7b) with n =
HLc. This was prepared similar to that described for HLa but
with a 30% water solution of ammonia (0.680 g, 12 mmol). The
product wa◦s obtained as colorless crystals.28 Yield: 2.673 g, 87%.
3, while for [CunLn ] (7c) the 31P NMR spectrum suggests the
c
formation of several polynuclear complexes having different n
values and/or different isomeric structures.
1
3
mp = 111 C. H NMR (CDCl3) 1.33 (d, JH,H = 6.2 Hz, 12H,
CH3), 4.78 (d. sept, 3JPOCH = 10.5 Hz, 3JH,H = 6.2 Hz, 2H, OCH),
4.91 (d, 2JHNP = 10.1 Hz, 1H, NH), 7.03 (s, 1H, NH2), 7.55 (s, 1H,
Experimental
◦
1
1
NH2) ppm; 31P{ H} NMR (t = 25 C, CDCl3) 53.3 ppm; 31P{ H}
General procedures
◦
NMR (t = −50 C, CDCl3) 53.1 ppm; IR (cm−1): 3208, 3180,
=
3060 (NH + NH2), 1628 (NH2), 1492 (S C–N), 976 (POC), 676
Tris-triphenylphosphine copper(I) iodide [Cu(PPh3)3I] was synthe-
sised using a previously described method.24 Elemental analyses
were performed on a Perkin-Elmer 2400 CHN microanalyser.
Electrospray ionization mass spectra were measured with a
Finnigan-Mat TCQ 700 mass spectrometer on a 10−6 M solution
in CH3OH. The speed of sample submission was 2 lL min−1. The
ionization energy was 4.5 kV and the capillary temperature was
200 ◦C. Infrared spectra (Nujol) were recorded with a Specord M-
=
(P S). Anal. Calcd for C7H17N2O2PS2 (256.33): C, 32.80; H, 6.68;
N, 10.93. Found: C, 32.81; H, 6.62; N, 10.88.
HLd. This was prepared similar to that described for HLa but
with benzylamine (1.284 g, 12 mmol). The product ◦was obtained
as colorless crystals. Yield: 3.446 g, 83%. mp = 125 C. 1H NMR
(CCl4 + C6D6) 1.36 (d, 3JH,H = 6.4 Hz, 6H, CH3), 1.38 (d, 3JH,H
=
6.4 Hz, 6H, CH3), 4.86 (d. sept, 3JPOCH = 10.7 Hz, 3JH,H = 6.4 Hz,
80 spectrometer in the frequency range 400–3600 cm−1. 1H and 31
P
3
2H, OCH), 4.91 (d, JHCNH = 5.4 Hz, 2H, CH2), 7.32–7.44 (m,
NMR experiments in solution were performed on a Bruker AMX-
300 NMR spectrometer. 31P NMR spectra with continuous wave
1H decoupling were acquired using a single pulse of 7 ls duration
(p/4) and a recycle delay varying between 1 to 5 s to ensure no
saturation. 31P solid-state magic angle spinning (MAS) NMR were
carried out on a Bruker Avance 400 (9.4 T) spectrometer using
5H, C6H5), 8.32 (s, 1H, NHP), 8.49 (t, 3JHCNH = 4.9 Hz, 1H, NH)
1
ppm; 31P{ H} NMR (CCl4 + C6D6) 53.0 ppm; IR (cm−1): 3255,
=
=
3070 (NH), 1548 (S C–N), 980 (POC), 620 (P S). Anal. Calcd
for C14H23N2O2PS2 (346.45): C, 48.54; H, 6.69; N, 8.04. Found: C,
48.51; H, 6.72; N, 8.08.
1
a 4 mm probe-head. The 31P{ H} cross-polarization (CP) MAS
Synthesis of [Cu(PPh3)2La] (6a). A suspension of HLa (0.978 g,
3 mmol) in aqueous ethanol (25 mL) was mixed with an ethanol
solution of KOH (0.185 g 3.3 mmol). A dichloromethane (25 mL)
solution of [Cu(PPh3)3I] (2.931 g, 3 mmol) was added dropwise
under vigorous stirring to the resulting potassium salt. The
mixture was stirred at room temperature for a further hour and
a precipitate was filtered off. The filtrate was concentrated until
the crystallization began. The residue was recrystallized from a
NMR spectra were recorded at a spinning frequency of 14 kHz
using a ramped cross-polarization25 with a contact time of 1 ms
1
and a recycle delay of 2 s. H decoupling was achieved using the
SPINAL-64 sequence26 with a 1H nutation frequency of about 60
kHz. Quantitative MAS spectra were acquired (with and without
1H decoupling) using a single pulse of 0.5 ls duration (p/12) and a
recycle delay of 1 s. Chemical shifts are referred to SiMe4 (1H) and
4698 | Dalton Trans., 2007, 4693–4700
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dichloromethane–n-hexane mixture 1 : 5 (v/v). Complex 6a was
obtained as colorless crystals. Yield: 1.917 g, 70%. mp = 151 ◦C.
Anal. Calcd for C50H52CuN2O2P3S2 (933.56): C, 64.33; H, 5.61; N,
3.00. Found: C, 64.36; H, 5.57; N, 3.05.
3
1H NMR (CDCl3) 1.26 (d, JH,H = 6.2 Hz, 6H, CH3), 1.31 (d,
3JH,H = 6.2 Hz, 6H, CH3), 3.60–3.74 (m, 4H, OCH2), 3.80–4.22
(m, 4H, NCH2), 4.71 (d. sept, 3JPOCH = 10.8 Hz, 3JH,H = 6.2 Hz, 2H,
Synthesis of [Cu3L3 ] (7a). A suspension of HLa (0.978 g,
a
3 mmol) in aqueous ethanol (25 mL) was mixed with an ethanol
solution of KOH (0.185 g, 3.3 mmol). The resulting mixture
was added dropwise to a suspension of CuI (0.570 g, 3 mmol)
in aqueous ethanol (20 mL). The mixture was stirred at room
temperature for 1.5 h. The resulting precipitate of KI was filtered
and the solvent was then removed in vacuum. The residue
was recrystallized from a dichloromethane–n-hexane mixture 1 :
5 (v/v). Complex 7a was ◦obtained as light yellow crystals. Yield:
1
OCH), 7.27–7.43 (m, 30H, C6H5) ppm; 31P{ H} NMR (CDCl3)
−1.2 (PPh3), 53.3 (L) ppm; IR (cm−1): 1460 (SCN), 1100 (COC),
=
960, 1015 (POC), 598 (P S). ES-MS (positive ion): m/z (%) =
1230 (28) [Cu4L3]+, 1189 (1) [Cu3L3 + Na]+, 841 (5) [Cu3L2]+,
589 (100) [Cu(PPh3)2]+. Anal. Calcd for C47H52CuN2O3P3S2
(913.52): C, 61.79; H, 5.74; N, 3.07. Found: C, 61.81; H,
5.78; N, 3.02.
1
3
2.605 g, 72%. mp = 140 C. H NMR (CDCl3) 1.30 (d, JH,H
=
Synthesis of [Cu(PPh3)2Lb] (6b). A solution of piperidine
(0.507 g, 5.9 mmol) in CH2Cl2 (25 mL) was added dropwise to a
solution of SCNP(S)(OiPr)2 (1.410 g, 5.9 mmol) in CH2Cl2 (20 mL)
under vigorous stirring. After 3 h, the solution was removed in
vacuum and a potassium hydroxide solution (0.364 g, 6.5 mmol)
in aqueous ethanol (20 mL) was added to the residue and the
mixture was stirred until the ligand was completely dissolved. The
steps which follow are similar to those used in the synthesis of
6.2 Hz, 36H, CH3), 3.66–3.75 (m, 12H, OCH2), 3.82–3.87 (m,
3
6H, NCH2), 4.13–4.17 (m, 6H, NCH2), 4.67 (d. sept, JPOCH
=
10.6 Hz, JH,H = 6.2 Hz, 6H, OCH) ppm; 31P{ H} NMR (t =
3
1
25 ◦C, CDCl3) 50.1 ppm; 31P{ H} NMR (t = −50 ◦C, CDCl3)
1
50.7 ppm; IR (cm−1): 1520 (SCN), 1084 (COC), 980, 1000, 1020
=
(POC), 602 (P S). ES-MS (positive ion): m/z (%) = 1230 (100)
[Cu4L3]+, 1189 (21) [Cu3L3 + Na]+, 841 (69) [Cu3L2]+. Anal. Calcd
for C33H66Cu3N6O9P3S6 (1166.86): C, 33.97; H, 5.70; N, 7.20.
Found: C, 33.92; H, 5.66; N, 7.15.
6a. Complex 6b was obtained as colorless crystals. Yield: 3.228 g,
◦
1
3
60%. mp = 137 C. H NMR (CDCl3) 1.26 (d, JH,H = 6.2 Hz,
3
b
6H, CH3), 1.30 (d, JH,H = 6.2 Hz, 6H, CH3), 1.50–1.67 (m, 6H,
[CunLn ] (7b). A solution of piperidine (0.507 g, 5.9 mmol)
CH2), 3.75–3.90 (m, 2H, NCH2), 4.00–4.15 (m, 2H, NCH2), 4.71
in CH2Cl2 (25 mL) was added dropwise to a solution of
SCNP(S)(OiPr)2 (1.410 g, 5.9 mmol) in the same solvent (20 mL)
under vigorous stirring. After 3 h, the solution was removed in
vacuum and a potassium hydroxide (0.364 g, 6.5 mmol) solution
in aqueous ethanol (20 mL) was added to the residue and the
mixture was stirred until the ligand dissolved completely. The
following steps are similar to those used in the synthesis of 7a.
Complex 7b was obtained as yellow crystals. Yield◦: 1.911 g, 84%
(d. sept, 3JPOCH = 10.8 Hz, 3JH,H = 6.2 Hz, 2H, OCH), 7.28–7.44
(m, 30H, C6H5) ppm; 31P{ H} NMR (CDCl3) −0.9 (PPh3), 51.8
1
−1
=
(L) ppm; IR (cm ): 1485 (SCN), 980, 1010 (POC), 590 (P S).
ES-MS (positive ion): m/z (%) = 837 (56) [Cu3L2]+, 712 (15)
[CuL2 + 2H]+, 651 (33) [Cu(PPh3)L + H]+, 589 (100) [Cu(PPh3)2]+,
387 (24) [CuL + H]+. Anal. Calcd for C48H54CuN2O2P3S2
(911.55): C, 63.25; H, 5.97; N, 3.07. Found: C, 63.21; H, 6.01;
N, 3.08.
1
([CuLb] relative to SCNP(S)(OiPr)2). mp = 133 C. H NMR
3
(CDCl3) 1.29 (d, JH,H = 6.2 Hz, 12H, CH3), 1.52–1.71 (m, 6H,
[Cu(PPh3)2Lc] (6c). was prepared similar to that described for
6a but with HLc (0.768 g, 3 mmol). Complex 6c was obtained as
CH2), 3.75–3.85 (m, 2H, NCH2), 4.05–4.15 (m, 2H, NCH2), 4.68
3
3
(d. sept, JPOCH = 10.6 Hz, JH,H = 6.2 Hz, 2H, OCH) ppm;
◦
◦
1
1
1
colorless crystals. Yield: 2.074 g, 82%. mp = 119 C. H NMR
31P{ H} NMR (t = 25 C, CDCl3) 48.9 ppm; 31P{ H} NMR (t =
(CDCl3) 1.27 (d, JH,H = 6.1 Hz, 6H, CH3), 1.28 (d, JH,H
=
−50 ◦C, CDCl3) 49.3 ppm; IR (cm−1): 1510 (SCN), 990, 1010, 1020
3
3
6.1 Hz, 6H, CH3), 4.70 (d. sept, 3JPOCH = 10.6 Hz, 3JH,H = 6.2 Hz,
(POC), 595 (P S). ES-MS (positive ion): m/z (%) = 1225 (100)
=
2H, OCH), 5.72 (br. s, 2H, NH2), 7.24–7.39 (m, 30H, C6H5)
[Cu4L3]+, 1185 (12) [Cu3L3 + Na]+, 837 (56) [Cu3L2]+. Anal. Calcd
for C12H24CuN2O2PS2 ([CuLb], 386.98): C, 37.24; H, 6.25; N, 7.24.
Found: C, 37.17; H, 6.26; N, 7.28.
ppm; 31P{ H} NMR (t = 25 ◦C, CDCl3) −0.7 (PPh3), 55.3 (L)
1
◦
ppm; 31P{ H} NMR (t = −50 C, CDCl3) −2.8 (PPh3), 57.8 (L)
1
ppm; IR (cm−1): 3504, 3256, 3120, 1610 (NH2), 1520 (SCN), 1000
c
=
(POC), 608 (P S). ES-MS (positive ion): m/z (%) = 1021 (50)
[CunLn ] (7c). was prepared similar to that described for 7a
[Cu4L3]+, 701 (23) [Cu3L2]+, 589 (100) [Cu(PPh3)2]+. Anal. Calcd
for C43H46CuN2O2P3S2 (843.43): C, 61.23; H, 5.50; N, 3.32. Found:
C, 61.26; H, 5.47; N, 3.38.
but with HLc (1.307 g, 5.1 mmol). Complex 7c was obtained as
beige crystals. Yield: 1.213 g, 75% ([CuLc] relative to HLc). mp =
151–153 ◦C. 1H NMR (CDCl3) 1.34 (d, 3JH,H = 6.4 Hz, 12H, CH3),
3
4.73 (d. sept, 3JPOCH = JH,H = 6.0 Hz, 2H, OCH), 5.84 (br. s, 1H,
[Cu(PPh3)2Ld] (6d). was prepared similar to that described for
6a but with HLd (1.038 g, 3 mmol). Complex 6d was obtained as
Hb, NH2), 6.42 (br. d, JPNCNH = 8.6 Hz, 1H, Ha, NH2) ppm; H
NMR (d6-acetone) 1.30 (t, 3JH,H = 6.0 Hz, 12H, CH3), 4.72 (d. sept,
4
1
◦
1
3
4
colorless crystals. Yield: 2.186 g, 78%. mp = 110 C. H NMR
3JPOCH = 10.7 Hz, JH,H = 6.1 Hz, 2H, OCH), 6.70 (d, JPNCNH
=
(CDCl3) 1.24 (d, 3JH,H = 6.2 Hz, 6H, CH3), 1.29 (d, 3JH,H = 6.2 Hz,
9.8 Hz, 1H, Ha, NH2), 7.31 (s, 1H, Hb, NH2) ppm; 31P{ H} NMR
1
◦
◦
6H, CH3), 4.53 (d, 3JH,H = 5.5 Hz, 2H, CH2), 4.69 (d. sept, 3JPOCH
=
(t = 25 C, CDCl3) 50.7 ppm; 31P{ H} NMR (t = −50 C, CDCl3)
1
◦
10.7 Hz, 3JH,H = 6.2 Hz, 2H, OCH), 6.17 (d. t, 4JPNCNH = 8.2 Hz,
40.9, 43.1, 46.9, 51.5, 51.9, 52.3 ppm; 31P{ H} NMR (t = 25 C,
1
1
3JH,H = 5.5 Hz, 1H, NH), 7.23–7.41 (m, 35H, C6H5) ppm; 31P{ H}
d6-acetone) 52.4 ppm; IR (cm−1): 3445, 3280, 3160, 1628 (NH2),
NMR (CDCl3) −0.9 (PPh3), 54.9 (L) ppm; IR (cm−1): 3320 (NH2),
1568, 1504 (SCN), 1000 (POC), 595 (P S). ES-MS (positive ion):
=
1530 (SCN), 990, 1010, 1030 (POC), 580 (P S). ES-MS (positive
m/z (%) = 1021 (100) [Cu4L3]+, 701 (16) [Cu3L2]+. Anal. Calcd
for C7H16CuN2O2PS2 ([CuLc], 318.86): C, 26.37; H, 5.06; N, 8.79.
Found: C, 26.33; H, 5.09; N, 8.72.
=
ion): m/z (%) = 1290 (24) [Cu4L3]+, 881 (5) [Cu3L2]+, 672 (22)
[Cu(PPh3)L + L]+, 589 (100) [Cu(PPh3)2]+, 410 (18) [CuL + H]+.
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X-Ray crystallography
6 (a) H. Liu, N. A. G. Bandeira, M. J. Calhorda, M. G. B, Drew, V. Felix,
J. Novosad, F. Fabrizi, de Biani and P. Zanello, J. Organomet. Chem.,
2004, 689, 2808–2819; (b) S. Canales, O. Crespo, M. Concepcion,
Gimeno, P. G. Jones, A. Laguna, A. Silvestru and C. Silvestru, Inorg.
Chim. Acta, 2003, 347, 16–22.
7 (a) D. Rusanova, W. Forsling, O. N. Antzutkin, K. J. Pike and R.
Dupree, J. Magn. Reson., 2006, 179, 140–145; (b) D. Rusanova, W.
Forsling, O. N. Antzutkin, K. J. Pike and R. Dupree, Langmuir, 2005,
21, 4420–4424; (c) W. Shi, M. Shafaei-Fallah, C. E, Anson and A.
Rothenberger, Dalton Trans., 2006, 3257–3262; (d) M. C. Aragoni, M.
Arca, M. B. Carrea, F. Demartin, F. A. Devillanova, A. Garau, M. B.
Hursthouse, S. L. Huth, F. Isaia, V. Lippolis, H. R. Ogilvie and G.
Verani, Eur. J. Inorg. Chem., 2006, 200–206.
X-Ray crystal structure determination was carried out us-
ing a Stoe-IPDS-II two-circle diffractometer with graphite-
monochromated Mo-Ka radiation. An empirical absorption cor-
rection was performed. The structures were solved by direct meth-
ods and refined with full-matrix least-squares on F2. Hydrogen
atoms were placed on ideal positions, and refined with fixed
isotropic displacement parameters using a riding model.
Crystal data for 6b. C48H54CuN2O2P3S2, Mr = 911.50 g mol−1,
colorless prisms, monoclinic, space group P21/n, a = 12.9095(7),
8 D. J. Birdsall, A. M. Z. J. Slawin and D. Woollins, Inorg. Chem., 1999,
38, 4152–4155.
9 P. Moore, W. Errington and S. P. Sangha, Helv. Chim. Acta, 2005, 88,
782–795.
◦
˚
−3
b = 21.2619(8), c = 17.5378(9) A, b = 109.403(4) , V =
3
−1
˚
4540.4(4) A , Z = 4, q = 1.333 g cm , l(Mo-Ka) = 0.719 mm ,
reflections: 51 935 collected, 8369 unique, Rint = 0.0623, R1(all) =
0.0482, wR2(all) = 0.0806.
10 E. Herrmann, R. Richter and N. T. T. Chau, Z. Anorg. Allg. Chem.,
1997, B. 623, 403–408.
11 M. L. Niven, P. Kyriacou and T. A. Modro, J. Chem. Soc., Dalton
Trans., 1988, 1915–1920.
12 F. D. Sokolov, V. V. Brusko, N. G. Zabirov and R. A. Cherkasov, Curr.
Org. Chem., 2006, 10, 27–42.
13 (a) A. Y. Verat, F. D. Sokolov, N. G. Zabirov, M. G. Babashkina, D. B.
Krivolapov, V. V. Brusko and I. A. Litvinov, Inorg. Chim. Acta, 2006,
359, 475–483; (b) D. A. Safin, M. G. Babashkina, F. D. Sokolov, N. G.
Zabirov, J. Galezowska and H. Kozlowski, Polyhedron, 2007, 26(5),
1113–1116.
14 (a) V. V. Brusko, A. I. Rakhmatullin and N. G. Zabirov, Russ. J. Gen.
Chem., 2000, 70, 1603–1609; (b) F. D. Sokolov, D. A. Safin, N. G.
Zabirov, P. V. Zotov and R. A. Cherkasov, Russ. J. Gen. Chem., 2005,
12, 1919–1926.
15 H. Gu¨nter, NMR Spectroscopy: An Introduction, Wiley, Chichester,
1980.
Crystal data for 7a. C33H66Cu3N6O9P3S6, Mr = 1166.81 g
mol−1, colorless prisms, triclinic, space group P-1, a = 10.4622(5),
◦
˚
3
b = 12.3431(5), c = 21.1918(9) A, a = 88.634(3), b = 81.852(3) ,
−3
˚
c = 75.398(3), V = 2621.3(2) A , Z = 2, q = 1.478 g cm , l(Mo-
Ka) = 1.586 mm−1, reflections: 58264 collected, 12 072 unique,
Rint = 0.0313, R1(all) = 0.0342, wR2(all) = 0.0766.
CCDC reference numbers are 619482 (6b) and 619483 (7a),
respectively.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b709551a
16 V. N. Solov’ev, N. G. Zabirov, R. A. Cherkasov and I. V. Martynov,
Zh. Strukt. Khim., 1991, 32, 80–84.
Acknowledgements
17 (a) G. Wu and R. E. Wasylishen, Organometallics, 1992, 11, 3242–3248;
(b) G. Wu and R. E. Wasylishen, Inorg. Chem., 1992, 31, 145–148.
18 S. P. Brown, M. Pe´rez-Torralba, D. Sanz, R. M. Claramunt and L.
Emsley, Chem. Commun., 2002, 1852–1853.
19 F. Fayon, I. J. King, R. K. Harris, R. K. B. Gover, J. S. O. Evans and
D. Massiot, Chem. Mater., 2003, 15, 2234–2239.
This work was supported by the Russian Foundation for Basic Re-
search (grant no. 03-03-32372-a, 03-03-96225-r2003tatarstan_a)
and the joint programme of CRDF and the Russian Ministry of
Education (BRHE 2004 Y2-C-07-02, grant no. REC-007). D. A. S.
and M. G. B. thank Faculty of Chemistry of University of Wroclaw
for scholarships.
20 (a) F. Asaro, A. Camus, R. Gobetto, A. C. Olivieri and G. Pellizer,
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Hart, P. C. Healy, B. W. Skelton and A. H. White, J. Chem. Soc., Dalton
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