Towards cationic gallium derivatives: Metallacycles from the reactions of organogallium compounds with tetraorganodichalcogenoimidodiphosphinates and a new N-(diphenylthiophosphinyl)thioureato ligand

Article abstract of DOI:10.1002/ejic.200400087

The organometallic complexes of general formulae [Me₂Ga{η ²-E,E′-[R₂P(E)NP(E′)R′₂]}] [R = R′ = Ph, E = E′ = O (1); R = R′ = Ph, E = E′ = S (2); R = R′ = Ph, E = E′ = Se (3); R = R′ = Ph, E = O, E′ = S (4); R = Me, R′ = Ph, E = S, E′ = O (5)] and [Me ₂Ga{η²-S,S′-[Ph₂P(S)NC(S)(C ₉H₁₀N)]}] (6) were obtained by facile methane elimination reactions from GaMe₃ and the acidic ligands L¹H [(XPPh₂)₂NH (X = O, S, Se)1 (OPPh₂)(SPPh ₂)NH, and (OPMe₂)(SPPh₂)NH] and L²H [Ph₂P(S)NHC(S)(C₉H₁₀N)] in toluene. Replacement of one phosphorus atom by a carbon atom in the ligand skeleton of L ¹H gave the new ligand L²H, which, upon reaction with GaMe₃, gave compound 6, which shows no significant structural differences with respect to 1-5. Therefore, L²H does not induce partial planarity in the six-membered ring, indicating the necessity for replacing both phosphorus atoms of the ligand by carbon atoms, as in the β-diketonate-type derivatives, in order to impose ring planarity. Thus, despite originating from a variety of ligands with differing donor atoms and substituents at the phosphorus atoms, all complexes show little structural differences. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200400087

FULL PAPER
Towards Cationic Gallium Derivatives: Metallacycles from the Reactions of
Organogallium Compounds with Tetraorganodichalcogenoimidodiphosphinates
and a New N-(Diphenylthiophosphinyl)thioureato Ligand
[a]
[a]
[a]
´
´
´
Virginia Montiel-Palma, Estefanıa Huitron-Rattinger, Sara Cortes-Llamas,
[a]
[b]
[b]
´
´
´
´
´
˜
Miguel-Angel Munoz-Hernandez,* Veronica Garcıa-Montalvo, Eddie Lopez-Honorato,
and Cristian Silvestru[c]
Keywords: Cationic catalysts / Chelating ligands / Gallium / Metallacycles / Phosphorus
The organometallic complexes of general formulae
[Me2Ga{η2-E,EЈ-[R2P(E)NP(EЈ)RЈ2]}] [R = RЈ = Ph, E = EЈ = O
(1); R = RЈ = Ph, E = EЈ = S (2); R = RЈ = Ph, E = EЈ = Se (3);
R = RЈ = Ph, E = O, EЈ = S (4); R = Me, RЈ = Ph, E = S, EЈ = O
(5)] and [Me2Ga{η2-S,SЈ-[Ph2P(S)NC(S)(C9H10N)]}] (6) were
obtained by facile methane elimination reactions from
GaMe3 and the acidic ligands L1H [(XPPh2)2NH (X = O, S,
Se), (OPPh2)(SPPh2)NH, and (OPMe2)(SPPh2)NH] and L2H
[Ph2P(S)NHC(S)(C9H10N)] in toluene. Replacement of one
phosphorus atom by a carbon atom in the ligand skeleton
of L1H gave the new ligand L2H, which, upon reaction with
GaMe3, gave compound 6, which shows no significant struc-
tural differences with respect to 1−5. Therefore, L2H does not
induce partial planarity in the six-membered ring, indicating
the necessity for replacing both phosphorus atoms of the li-
gand by carbon atoms, as in the β-diketonate-type derivati-
ves, in order to impose ring planarity. Thus, despite origina-
ting from a variety of ligands with differing donor atoms and
substituents at the phosphorus atoms, all complexes show
little structural differences.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
bility of the six-membered M{η2-E,EЈ-(EPNPEЈ)} (M ϭ
main group or transition metal) ring derived from L1 that
has been credited for the variety of structural and coordi-
nation modes encountered, a number of which have even
given rise to supramolecular structures or proved to be po-
tential building blocks for the design of new materials;
others have found prospective industrial use in catalytic sys-
tems or biological applications.[3,4] Accordingly, the last
decade has seen a considerable growth in the investigations
of complexes bearing this kind of ligands, yet surprisingly
only a discrete number of organometallic gallium deriva-
tives have been isolated.
Comparisons between the bonding in organic and inor-
ganic (carbon-free) analogs are widely sought throughout
chemistry and have led to a higher understanding of elec-
tronically related systems. In particular, the consequences of
π-electron delocalization in planar chelate rings have been
traditionally assessed by comparison of their properties
with those of their nonplanar counterparts arising from
atom substitution.[1,2]
In this light, tetraorganodichalcogenoimidodiphos-
phinato {[R2P(E)NP(EЈ)RЈ2]Ϫ (E ϭ EЈ ϭ chalcogen) (L1)}
and N-(diorganothiophosphinyl)thioureato {[R2P(S)NC-
(S)RЈЈ2]Ϫ (L2)} ligands can be regarded as inorganic anal-
ogs of the much used β-diketonate ligands. It is the flexi-
From the first organogallium derivative of L1, [Et2Ga{η2-
Se,SeЈ-[Ph2P(Se)NP(Se)Ph2]}][5] (3-Et), to Uhl’s organo-
digallium() compounds, [{(Me3Si)2HC}2Ga{η2-O,OЈ-
[Ph2P(O)NP(O)Ph2]}],
[{(Me3Si)2HC}Ga{µ-η2-O,OЈ-
[Ph2P(O)NP(O)Ph2]}]2, and [{(Me3Si)2HC}Ga{η2-S,SЈ-
[Ph2P(S)NP(S)Ph2]}]2,[6] this class of compounds has given
insights into the feasibility of preparation and stability
towards ligand-redistribution reactions.
[a]
´
´
Centro de Investigaciones Quımicas, Universidad Autonoma
del Estado de Morelos,
Av. Universidad 1001, Col. Chamilpa, Cuernavaca, Morelos
62210, Mexico
Fax: (internat.) ϩ 52-777-329-7997
Perhaps more importantly, however, cationic gallium
species with chelating ligands are desirable for applications
in homogeneous catalytic reactions such as alkene polymer-
ization to prevent undesirable ligand exchange/redistri-
bution reactions. Amongst some of the most representative
examples are those gallium cations supported by sal-
E-mail: mamund2@buzon.uaem.mx
[b]
[c]
´
´
Instituto de Quımica, Universidad Nacional Autonoma de
´
Mexico. Circuito Exterior, Ciudad Universitaria,
´
Mexico 04510, D. F., Mexico
Facultatea de Chimie si Inginerie Chimica, Universitatea
Babes-Bolyai,
3400 Cluj-Napoca, Romania
Eur. J. Inorg. Chem. 2004, 3743Ϫ3750
DOI: 10.1002/ejic.200400087
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3743

´
´
M.-A. Mun˜oz-Hernandez et al.
FULL PAPER
omphen,[7] amidinate,[8,9] β-diketonate[10] and more recently
terphenyl[11] ligands. In these systems, ligand bite angles
and steric protection play a crucial role in the prevention
of nucleophilic attack, besides allowing electronic and
steric control. Indeed, Jordan has demonstrated that along
the cationic amidinate series [{MeC(NiPr)2}2Ga2Me3]ϩ,
[{tBuC(NiPr)2}GaMe2{tBuC(NiPr)2}GaMe]ϩ and [{tBuC-
(NtBu)2}GaMe]ϩ, susceptibility to dimerization decreases,
as does nucleophilic addition.[8,9]
In our search for new organogallium cations we recently
started a program to systematically explore the incorpor-
ation of bulky wide-bite-angle tetraorganodichalcogenoimi-
dodiphosphinato (L1) and N-(diorganothiophosphinyl)thi-
oureato (L2) ligands at organogallium centers. The ligands
in these complexes are closely related to the bis(iminophos-
phorano)methanide ligand system, which has been used to
prepare the monomeric aluminum complexes [κN,κNЈ-
{[Ph2P(Me3SiN)]2CH}AlR2] (R ϭ Me, Bu) and [κN,κNЈ-
{[Ph2P(Me3SiN)]2CH}Al(Cl)Et], and the dimetallic com-
plex [κC,κCЈ,κN,κNЈ-{[Ph2P(Me3SiN)]2C}(Me2Al)2]. These
complexes show catalytic activity towards ethylene poly-
merization when activated by trityl tetrafluoroborate, pre-
sumably due to formation of a cationic species.[12] Herein
we report the facile synthesis and characterization of
complexes of general formulae [Me2Ga{η2-E,EЈ-
[R2P(E)NP(EЈ)RЈ2]}] and [Me2Ga{η2-S,SЈ-[Ph2P(S)NC-
(S)RЈЈ)]}] which were envisioned to be good precursors of
organometallic cationic species.
Figure 1. Molecular structure of L2H with thermal ellipsoids at
50% probability level
The organogallium compounds of general formulae
[Me2Ga{η2-E,EЈ-[R2P(E)NP(EЈ)RЈ2]}] [R ϭ RЈ ϭ Ph, E ϭ
EЈ ϭ O (1); R ϭ RЈ ϭ Ph, E ϭ EЈ ϭ S (2); R ϭ RЈ ϭ Ph,
E ϭ EЈ ϭ Se (3); R ϭRЈ ϭ Ph, E ϭ O, EЈ ϭ S (4); R ϭ
Me, RЈ ϭ Ph, E ϭ S, EЈ ϭ O (5)] and [Me2Ga{η2-S,SЈ-
[Ph2P(S)NHC(S)(C9H10N)]}] (6) were obtained in good
yields by room temperature methane elimination reactions
between GaMe3 and the ligands L1H or L2H in toluene, as
depicted in Scheme 2.
Results and Discussion
The synthesis of the new proligand L2H was carried out
in two steps. First, diphenyl isothiocyanide was synthesized
according to reported general procedures for the synthesis
of similar types of ligands from Ph2P(S)Cl and
KNCS.[13Ϫ15] The purified product was then treated with
tetrahydroquinoline in CH2Cl2, yielding L2H after treat-
ment with hexane (Scheme 1). Crystals suitable for X-ray
diffraction analysis were deposited from hexane at Ϫ20 °C.
The molecular structure is shown in Figure 1 and the collec-
tion and crystal data are given in the Exp. Sect.
Scheme 2. General synthesis of complexes 1Ϫ6
Apart from the organogallium complexes mentioned in
the introduction, only one other Ga derivative bearing this
Scheme 1. The synthesis of the new ligand L2H
3744
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 3743Ϫ3750

Towards Cationic Gallium Derivatives
FULL PAPER
type of ligand has been structurally characterized. The inor- ment is found to coordinate in a bidentate fashion to the
ganic tris(chelate) [Ga{η2-O,OЈ-[Ph2P(O)NP(O)PPh2]3}] ex- L1 or L2 ligands (Tables 2 and 3). Although the crystals of
hibits a slightly distorted octahedral GaO6 core as well as 3 diffracted, we were unable to obtain an acceptable refine-
three six-membered Ga(OPNPO) rings.[16] On the other ment of the data, which, however, show good similarities
hand, the coordination chemistry with thiophosphorylthi- with those of the already reported diethyl analogue
oureato (L2) type ligands is much less developed. Only a [Et2Ga{η2-Se,SeЈ-[Ph2P(Se)NP(Se)Ph2]}] (3-Et).[5]
few complexes of this kind have been reported and, to the
best of our knowledge, no group-13 derivatives have been
isolated. Interestingly, the formation of a cavity that would
host an alkaline metal ion led to the X-ray diffraction study
of cadmium and palladium dinuclear N-thiophosphoryl-
ated thiourea complexes from α,ω-diamines that allow the
connection of two units of tetracoordinate transition me-
tal centers.[15]
Complexes 1Ϫ6 were characterized by physical (m.p.),
chemical (C, H and N analysis), and spectroscopic tech-
niques (multinuclear NMR and IR spectroscopy). In ad-
dition, solid-state structures of 1, 2, 4, 5 and 6 were ob-
tained by single-crystal X-ray diffraction.
The first indications of the complexation of L1 and L2
were given by the absence of ν(NH) bands in the IR spectra
and of the NH resonances in the 1H NMR solution spectra
of the products, particularly in complexes 2Ϫ6.[3] Moreover,
as expected for metal coordination, the 31P{1H} NMR
spectra show a high-field shift of the resonance signals for
the homoleptic complexes 2 and 3, and for the PϪO reson-
ance of the mixed-chalcogen species. Furthermore, in the
Figure 2. Molecular structure of 1 with thermal ellipsoids at 30%
probability level
case of the selenium derivative 3 there is a considerable de-
1
crease in the JP,Se coupling constant with respect to the
free ligand (Table 1). On the contrary, there is a small
down-field change in the chemical shift of the 31P{1H}
NMR resonance of 1, although it should be noted that in
the tetraphenylimidodiphosphinic acid (L1H) used as pre-
cursor, the acidic hydrogen atom is probably located in an
intermolecular OϪH···O bridge[17] which does not permit
straightforward deductions.
Table 1. Selected spectroscopic parameters of complexes 1Ϫ6 com-
pared to acidic ligands L1H and L2H
31P{1H} NMR of complex
31P{1H} NMR of acidic ligand
1
2
3
4
26.4 (s)[a]
36.7 (s)[b]
19.4 (s)[3][b]
55.7 (s)[18][c]
1
1
29.3 (s, JP,Se ϭ 534 Hz)[c]
53.0 (s, JP,Se ϭ 793 Hz)[19][b]
2
2
27.1 (d, JP,P ϭ 3.6 Hz, PS)
56.1 (d, JP,P ϭ 17.5 Hz, PS)
2
2
34.8 (d, JP,P ϭ 3.6 Hz, PO)[a] 23.1 (d, JP,P ϭ 17.5 Hz, PO)[20][b]
Figure 3. Molecular structure of 2 with thermal ellipsoids at 30%
probability level
2
2
5
39.2 (d, JP,P ϭ 7.3 Hz, PS)
63.0 (d, JP,P ϭ 19.5 Hz, PS)
2
2
24.7 (d, JP,P ϭ 7.3 Hz, PO)[a] 23.9 (d, JP,P ϭ 19.5 Hz, PO)[21][b]
6
41.1 (s)[a]
56.9 (s)[b]
Compared to the free acidic ligands, the structural fea-
tures of the complexes are as expected, with the PϪE and
PϪEЈ distances enlarged and the PϪN distances shortened
[a]
[b]
[c]
C6D6. CDCl3. [D6]THF.
evidencing changes in bond orders. The PϪO distances in
˚
Crystals of complexes 1Ϫ6 (Figures 2Ϫ6, respectively) the complexes — 1.526(3) and 1.527(3) A (1), 1.530(3) (4)
˚
suitable for X-ray analysis were grown from saturated hex- and 1.527(1) A (5) — are longer than typical PϭO distances
ane solutions at Ϫ20 °C. The molecular structures of the [cf. Ph2P(O)OH:[22] PϪO 1.526(6), PϭO 1.486(6) A]. Ac-
˚
˚
five complexes show a six-membered metallacycle with the cordingly, the PϪS distances — 2.037(2) and 2.040(1) A (2),
˚
˚
geometry around the gallium center being that of a dis- 2.030(2) A (4), and 2.011(1) A (6) — are also longer than
˚
torted tetrahedron (see below). The dimethylgallium frag- the distances of typical PϭS bonds (1.89Ϫ1.96 A). The
Eur. J. Inorg. Chem. 2004, 3743Ϫ3750
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3745

´
´
M.-A. Mun˜oz-Hernandez et al.
FULL PAPER
Figure 4. Molecular structure of 4 with thermal ellipsoids at 30% probability level
Figure 6. Molecular structure of 6 with thermal ellipsoids at 50%
probability level
Figure 5. Molecular structure of 5 with thermal ellipsoids at 30%
probability level
˚
PϪN bond lengths range from 1.59 to 1.61 A and are some-
As demonstrated by the X-ray analysis, the confor-
what shorter than typical PϪN bond lengths {cf. [2- mations of the six-membered metallacycles are diverse: 1 is
(Me2NCH2)C6H4]TeSPPh2ϭNPPh2ϭS:[23] PϪS 2.057(1), a chair with the Ga and N(1) atoms at the apices, 2 adopts
˚
PϭS 1.945(1), PϪN 1.612(3), PϭN 1.557(3) A} as expected an envelope conformation with Ga out of the plane, 4 has
due to a higher bond order.
a twist-boat conformation also with Ga and N(1) at the
In contrast, along the series, the CϪGaϪC angles of the apices, and 5 and 6 are both boats with Ga and N(1), and
dimethylgallium fragments are practically the same, ranging P(1) and S(2), respectively, at the apices. The closely related
from 125.3(2)° in 6 to 127.6(3)° in 4. Additionally, apart selenium derivative [Et2Ga{η2-Se,Se-[Ph2P(Se)NP(Se)-
from the dioxo derivative, comparisons of the PϪNϪP (or Ph2]}] (3-Et)[5] shows a distorted boat conformation with
PϪNϪC) angles of the complexes with respect to those of Se and P atoms at the apices. A nonplanar ring is a com-
the free ligands show little tendency to variation, with the mon feature of complexes derived from tetraorganodichal-
largest difference being 6.4° in complex 2. Amongst all the cogenoimidodiphosphinato ligands, as demonstrated by the
complexes, these angles differ very little as they range only variety of examples encountered in main-group and tran-
˚
˚
from 123.4(1) A in 1 to 138.1(2) A in 2 (Table 3).
sition-metal chemistry. On the contrary, replacing phos-
3746
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 3743Ϫ3750

Towards Cationic Gallium Derivatives
FULL PAPER
˚
phorus with carbon in the ligand skeleton, as in the tetra-
hedral imidoylamidinato complex [Me2Ga{η2-N,NЈ-
[HNC(CF3)NC(CF3)NH]}][27] leads to all atoms of the ring
being coplanar. In addition, a small number of planar galla-
cycle rings have been structurally characterized as deriva-
tives of β-diketonate ligands. For example, four-coordinate
[GaCl2(bdk)][10] [bdk ϭ (2,4-pentanedionato), acac and
Table 2. Selected bond lengths [A] and angles [°] for complexes 1,
2, 4, 5 and 6
1
2
4
5
6
Ga(1)ϪC(25) 1.938(5)
Ga(1)ϪC(26) 1.994(7)
O(2)ϪGa(1)ϪO(1)
C(25)ϪGa(1)ϪC(26) 126.0(4)
O(1)ϪGa(1)ϪC(26)
O(1)ϪGa(1)ϪC(25)
O(2)ϪGa(1)ϪC(25)
O(2)ϪGa(1)ϪC(26)
97.9(1)
Ga(1)ϪO(1)
Ga(1)ϪO(2)
O(1)ϪP(1)
O(2)ϪP(2)
P(1)ϪN(1)
P(2)ϪN(1)
1.951(3)
1.953(3)
1.527(3)
1.526(3)
1.590(3)
1.591(3)
107.7(3)
107.7(3)
107.7(3)
106.9(3)
(2,2,6,6-tetramethylheptanedionato)],
[GaMeCl(acac)][28]
and [GaCl{N(SiMe3)2}(acac)][28] all show planar six-mem-
bered GaO2C3 rings with OϪGaϪO bite angles ranging
from 96.1 to 99.3°. It is thus significant that in complex 6
replacement of one phosphorus atom by a carbon atom
does not induce partial planarity in the ring.
Ga(1)ϪC(25) 1.958(5)
Ga(1)ϪC(26) 1.978(5)
S(2)ϪGa(1)ϪS(1)
C(25)ϪGa(1)ϪC(26) 126.1(2)
S(1)ϪGa(1)ϪC(26)
S(1)ϪGa(1)ϪC(25)
S(2)ϪGa(1)ϪC(25)
S(2)ϪGa(1)ϪC(26)
99.2(1)
Ga(1)ϪS(1)
Ga(1)ϪS(2)
S(1)ϪP(1)
S(2)ϪP(2)
P(1)ϪN(1)
P(2)ϪN(1)
2.380(1)
2.416(2)
2.040(1)
2.037(2)
1.593(3)
1.588(3)
104.5(2)
110.8(2)
110.9(2)
101.9(2)
Perhaps the most striking feature is the fact that along a
series of chemically differing ligands, the structural varia-
tion is not as large as expected, despite the well-documented
versatility of the PNP ligand.
The fact that the bite angles of the ligands in the com-
plexes studied are in the range 96.3Ϫ108.4° (see Table 3)
is indicative of their prospective good potential as cationic
precursors. Steric protection for catalytically active metal
centers can be provided by bulky multidentate ligands, and
various examples have been reported with late transition
metals[29] as well as aluminum.[30] Indeed, large bite angles
in cationic, three-coordinate aluminum complexes have
proved to be an effective approach to stabilize these highly
reactive species. Bulky aluminum amidinate complexes
[{RC(NRЈ)2}AlMe]ϩ with small bite angles (NϪAlϪN
angle of about 70° in neutral derivatives) are thermally
unstable but the N,NЈ-diaryldiketiminate complex
[{HC(CMeNAr)2}AlMe2] (Ar ϭ 2,6-iPr2C6H3) with a
larger bite angle (NϪAlϪN angle of about 96°) and bulky
N-aryl substituents yield a stable, three-coordinate cation
upon abstraction of the alkyl group.[31] Moreover, in con-
trast to most precursors documented in the literature, the
family of complexes reported herein is easily accessible and
requires little purification. Current work in our laboratory
is focused in this direction, treating complexes 1Ϫ6 and
others with strong Lewis acids. The results of this work will
be reported shortly.
Ga(1)ϪC(25) 1.957(5)
Ga(1)ϪC(26) 1.963(5)
O(1)ϪGa(1)ϪS(1)
C(25)ϪGa(1)ϪC(26) 127.6(3)
O(1)ϪGa(1)ϪC(26)
O(1)ϪGa(1)ϪC(25)
S(1)ϪGa(1)ϪC(25)
S(1)ϪGa(1)ϪC(26)
99.1(1)
Ga(1)ϪO(1)
Ga(1)ϪS(1)
O(1)ϪP(1)
S(1)ϪP(2)
P(1)ϪN(1)
P(2)ϪN(1)
1.945(3)
2.389(1)
1.530(3)
2.030(2)
1.596(3)
1.601(3)
107.3(2)
106.8(2)
102.1(2)
110.3(2)
Ga(1)ϪC(15) 1.942(3)
Ga(1)ϪC(16) 1.937(3)
O(1)ϪGa(1)ϪS(1)
C(15)ϪGa(1)ϪC(16) 127.1(2)
O(1)ϪGa(1)ϪC(15)
O(1)ϪGa(1)ϪC(16)
S(1)ϪGa(1)ϪC(15)
S(1)ϪGa(1)ϪC(16)
96.3(1)
Ga(1)ϪO(1)
Ga(1)ϪS(1)
O(1)ϪP(1)
S(1)ϪP(2)
P(1)ϪN(1)
P(2)ϪN(1)
1.932(2)
2.377(1)
1.527(2)
2.041(1)
1.577(2)
1.612(2)
108.3(1)
104.8(1)
109.8(1)
106.2(1)
Ga(1)ϪC(24) 1.960(4)
Ga(1)ϪC(23) 1.961(4)
S(2)ϪGa(1)ϪS(1)
C(24)ϪGa(1)ϪC(23) 125.3(3)
103.4(1)
Ga(1)ϪS(1)
Ga(1)ϪS(2)
S(1)ϪP(1)
S(2)ϪC(22)
P(1)ϪN(1)
C(22)ϪN(1)
2.3886(9) S(1)ϪGa(1)ϪC(24)
2.3535(9) S(1)ϪGa(1)ϪC(23)
110.7(1)
104.8(1)
109.3(1)
101.4(1)
2.011(1)
1.758(3)
1.614(2)
1.325(4)
S(2)ϪGa(1)ϪC(23)
S(2)ϪGa(1)ϪC(24)
Table 3. Selected structural features of organogallium metallacycles 1, 2, 4, 5, 6 and [Et2Ga{η2-Se,SeЈ-[Ph2P(Se)NP(Se)Ph2]}] (3-Et)[5]
PϪNϪP or
PϪNϪC angle
in ligand
[°]
PϪNϪP or
PϪNϪC angle
in complex
[°]
EϪGaϪEЈ
angle
MeϪGaϪMe
angle
(PENPEЈ)Ga or
(PSNCS)Ga ring
conformation
Nonbonding EϪEЈ
length
˚
[°]
[°]
[A]
1
180[17]
123.4(1)
138.1(2)
129.8(3)[5]
125.4(2)
131.1(1)
124.1(2)
97.9(1)
99.2(1)
126.0(4)
126.1(2)
125.5(4)[5]
127.6(3)
127.1(2)
125.3(2)
chair
O(1)ϪO(2)
S(1)ϪS(2)
Se(1)ϪSe(2) 4.09
O(1)ϪS(1)
O(1)ϪS(1)
S(1)ϪS(2)
2.94
3.65
2
131.7(5)[24]
132.3(2)[25]
131.4(3)[26]
126.5[20]
envelope-
boat[5]
twist boat
boat
3-Et[5]
4
5
6
108.4(1)[5]
99.1(1)
3.31
3.22
3.72
96.3(1)
103.4(1)
128.8(1)
boat
Eur. J. Inorg. Chem. 2004, 3743Ϫ3750
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3747

´
´
M.-A. Mun˜oz-Hernandez et al.
FULL PAPER
2336 (w), 200.22 (w), 1959 (w), 1893 (w), 1814 (w), 1674 (w), 1590
Conclusion
(w), 1482 (m), 1436 (s), 1126 (s), 691 (s) 590 (s) cmϪ1
.
C26H26GaNO2P2 (516.14): calcd. C 60.50, H 5.08, N 2.71; found
C 60.43, H 5.03, N 2.72.
Gallium metallacycles derived from dichalcogenoimido-
diphosphinato ligands were obtained by facile methane
elimination reactions. In the new complexes, the Ga center
is in a distorted tetrahedral environment forming part of a
six-membered metallacycle. The conformations of these
rings do not correlate with the nature of the chalcogen nor
with the substituents at the phosphorus or carbon atoms,
but in all cases a nonplanar ring was observed. Exchanging
a phosphorus atom by a carbon atom in the metallacycle
ring does not result, even partially, in a planar structure of
complex 6.
Compounds 2Ϫ6 were prepared in a similar manner to 1.
[Me2Ga{η2-S,S-[Ph2P(S)NP(S)Ph2]}] (2): (SPPh2)2NH (0.30 g,
0.67 mmol) and trimethylgallium (0.08 g, 0.70 mmol) afforded 2 as
a white solid. Yield 0.30 g (82%), m.p. 103Ϫ105 °C. 1H NMR
(CDCl3, 400 MHz): δ ϭ Ϫ0.25 (s, 6 H, CH3Ga), 7.35 (m, 12 H,
C6H5), 7.83 (m, 8 H, C6H5P) ppm. 13C NMR (CDCl3, 100.6 MHz):
1
δ ϭ Ϫ0.79 (s, GaCH3), 128.41Ϫ131.36 (C6H5), 137.31 (d, JC,P
ϭ
140 Hz, ipso-C6H5) ppm. 31P{1H} NMR (CDCl3, 161.8 MHz): δ ϭ
36.71 (s) ppm. IR: ν˜ ϭ 3069.3 (w), 2962.3 (m), 2901.4 (w), 1999.5
(w), 1892.5 (w), 1809.7 (w), 1674 (w), 1582.8 (w), 1476.7 (m), 1433
(m),1258.9 (m), 1196.4 (s), 1104.7 (s), 1022.8 (s), 807.5 (s), 743.7
(s), 694.8 (s), 577.5 (s), 530.3 (s) cmϪ1. C26H26GaNP2S2 (548.26):
calcd. C 56.96, H 4.78, N 2.55, S 11.70; found C 57.01, H 4.79, N
2.60, S 11.87.
Experimental Section
General Remarks: All glassware was rigorously dried in an oven at
130 °C for 24 h, assembled hot, and then allowed to cool under
argon. All the manipulations of the air-sensitive compounds were
conducted using standard inert-gas bench-top and glove-box tech-
niques. Solvents were dried with sodium or potassium/benzo-
phenone and freshly distilled prior to use. The L1H ligands
were synthesized according to literature methods: (XPPh2)2NH
[Me2Ga{η2-Se,Se-[Ph2P(Se)NP(Se)Ph2]}] (3): (SePPh2)2NH (0.3 g,
0.55 mmol) and trimethylgallium (0.063 g, 0.55 mmol) generated 3
as a white solid. Yield 0.31 g (88%), m.p. 143 °C. 1H NMR (CDCl3,
400 MHz): δ ϭ Ϫ0.11 (s, 1JC,H ϭ 162, 3JSe,H ϭ 4 Hz, 6 H, GaCH3),
7.34Ϫ7.44 (m, 12 H, C6H5), 7.81 (m, 8 H, C6H5) ppm. 13C{1H}
(CDCl3, 100.6 MHz): δ ϭ 0.20 (GaCH3), 128.2Ϫ131.4 (C6H5),
(X
ϭ
O,[32] S,[33] Se[33]), (OPPh2)(SPPh2)NH,[34] and
1
2
136.8 (dd, JP,C ϭ 98.49, JC,Se 4.19 Hz, ipso-C6H5) ppm. 31P{1H}
NMR (CDCl3, 81 MHz): δ ϭ 29.3 (s, 1JP,Seϭ 525 Hz) ppm. IR:
ν˜ ϭ 3060 (w), 1583 (w), 1477 (w), 1433 (m), 1210 (s), 1108 (s), 1025
(OPMe2)(SPPh2)NH.[35] NMR spectroscopic data (1H, 13C and
31P) were obtained with Varian-Inova 400 MHz and Varian-
Gemini-200 MHz instruments at 19 °C. Chemical shifts are re-
(w), 925 (w), 803 (m), 691 (s), 562 (s), 516 (m), 486 (m) cmϪ1
.
ported relative to SiMe4 for H and 13C, 85% H3PO4 for 31P and
1
C26H26GaNP2Se2 (642.08): calcd. C 48.64, H 4.08, N 2.18; found
C 48.85, H 4.11, N 2.14.
are in ppm. Microanalyses were obtained with an Elementar Vario
EL III instrument in the CHNS operation mode. Infrared spectra
were recorded as KBr pellets with a Bruker Equinox 55 Spec-
[Me2Ga{η2-S,O-[Ph2P(S)NP(O)Ph2]}] (4): Compound 4 was ob-
tained as a white solid from (SPPh2)NH(OPPh2) (0.3 g, 0.69 mmol)
and trimethylgallium (0.08 g, 0.70 mmol). Yield 0.27 g, 73%, m.p.
trometer and are reported in cmϪ1
.
Synthesis of Ph2P(S)NHC(S)(C9H10N) (L2H): Tetrahydroquinoline
(0.65 mL, 5.1 mmol) was added to stirred solution of
1
83Ϫ85 °C. H NMR (200 MHz, C6D6): δ ϭ 0.22 (s, 6 H, GaCH3),
a
6.98 (m, 12 H, C6H5), 7.96 (m, 8 H, C6H5) ppm. 13C NMR
Ph2P(S)NCS (1.42 g, 5.1 mmol) in CH2Cl2 (20 mL). After 4 h, the
solvent was removed under vacuum, hexane (30 mL) was added
and the mixture stirred for a further 2 h. The white solid deposited
was filtered and dried under vacuum. Yield: 1.89 g (90%), m.p.
71Ϫ73 °C. Selected 1H NMR data (CDCl3, 300 MHz): δ ϭ 3.97 (s,
1 H, NH) ppm. 13C NMR (CDCl3, 75.4 MHz): δ ϭ 150.50 (CϭS)
ppm. 31P NMR (CDCl3, 121.4 MHz): δ ϭ 56.89 (s) ppm. IR: ν˜ ϭ
3309 (νNH), 1445 (νCN), 1103 (νCS), 957, 882 (νPN), 647 (νPS)
cmϪ1. Crystals suitable for X-ray diffraction analysis were grown
from hexane solution.
(50.3 MHz, C6D6): δ ϭ Ϫ1.50 (s, GaCH3), 128.59 (m, and C6H5),
1
131.58 (m, C6H5), 136.23 (d, JC,P ϭ 105 Hz, ipso-C6H5), 139.32
1
(d, JC,P ϭ 83 Hz, ipso-C6H5) ppm. 31P{1H} NMR (161.8 Hz,
2
2
C6D6): δ ϭ 27.07 (d, JP,P ϭ 3.56 Hz, GaOPPh2), 34.78 (d, JP,P
ϭ
3.56 Hz, GaSPPh2) ppm. IR: ν˜ ϭ 3053.2 (m), 2966 (s), 2909 (m),
2712 (w), 1968 (w), 1890 (w), 1825 (w), 1775 (m), 1674 (w), 1591
(m), 1482 (m), 1433 (s), 1410 (s), 1050 (s), 867 (s), 700 (s), 549 (s)
cmϪ1. C26H26GaNOP2S (532.20): calcd. C 58.67, H 4.92, N 2.63,
S 6.03; found C 58.68, H 5.01, N 2.62, S 5.98.
[Me2Ga{η2-S,O-[Me2P(S)NP(O)Ph2]}] (5): White compound 5 was
synthesized from (SPMe2)(OPPh2)NH (0.22 g, 0.71 mmol) and tri-
methylgallium (0.08 g, 0.70 mmol). Yield 0.25 g (87%), m.p.
116Ϫ118 °C. 1H NMR (400 MHz, C6D6): δ ϭ 0.35 (s, 6 H,
Synthesis of [Me2Ga{η2-O,OЈ-[Ph2P(O)NP(O)Ph2]}] (1): A solution
of trimethylgallium (0.08 g, 0.70 mmol) in toluene (10 mL) was ad-
ded to a stirred suspension of (OPPh2)2NH (0.3 g, 0.72 mmol) in
toluene (20 mL), causing vigorous gas evolution and the formation
of a clear colorless solution which was stirred for 4 h. Removal of
the volatiles under reduced pressure produced a viscous substance,
which was treated with hexane (5 mL) and stirred until the depo-
sition of a white solid. The solid was separated from the solution
by cannula filtration and dried under high vacuum. The remaining
hexane solution at Ϫ20 °C deposited suitable crystals for X-ray
analysis. Yield 0.27 g (87%), m.p. 77Ϫ78 °C. 1H NMR (CDCl3,
400 MHz): δ ϭ Ϫ0.31 (s, 6 H, GaCH3), 7.34Ϫ7.40 (m, 12 H, C6H5),
2
GaCH3), 1.39 (d, JP,H ϭ 26.4 Hz, 6 H, GaPCH3), 7.03 (m, 6 H,
C6H5), 7.90 (m, 4 H, C6H5) ppm. 13C NMR (50.3 Hz, C6D6): δ ϭ
1
3
Ϫ1.17 (s, GaCH3), 26.37 (dd, JC,P ϭ 122.56, JC,P ϭ 5.01 Hz,
PCH3), 128.64 (m, C6H5), 131.63 (m, C6H5) ppm. 31P{1H} NMR
(161.82 MHz, C6D6): δ ϭ 25.61 (d, JP,P ϭ 7.29 Hz, GaOPPh2),
39.18 (d, JP,P ϭ 7.29 Hz, GaSPMe2) ppm. IR: ν˜ ϭ 3053 (m),
2
2
2966.0 (s), 2909 (m), 2712 (w), 1968 (w), 1890 (w), 1825 (w), 1755
(w), 1674 (w), 1591 (w), 1482 (m), 1433 (s), 1410 (s), 1050 (s), 867
(s), 700 (s), 549 (s) cmϪ1. C16H22GaNOP2S (408.07): calcd. C 47.09,
H 5.43, N 3.43, S 7.86; found C 47.13, H 5.51, N 3.39.
7.75 (m, 8 H, C6H5) ppm. 13C NMR (CDCl3, 100.6 MHz): δ ϭ
1
Ϫ4.52 (s, CH3Ga), 128.30Ϫ131.26 (C6H5), 136.04 (d, JC,P
ϭ
140 Hz, ipso-C6H5) ppm. 31P{1H} NMR (C6D6, 161.8 MHz): δ ϭ
[Me2Ga{η2-S,S-[Ph2P(S)N(C)NC9H10]}] (6): White compound 6
26.43 (s) ppm. IR: ν˜ ϭ 3072 (m), 2960 (m), 2718 (w), 2365 (w), was synthesized from C9H10NC(S)NHP(S)(C6H5)2 (0.27 g,
3748  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org
Eur. J. Inorg. Chem. 2004, 3743Ϫ3750

Towards Cationic Gallium Derivatives
FULL PAPER
Table 4. Summary of crystallographic data for complexes L2H, 1, 2, 4, 5 and 6
L2H
1
2
4
5
6
Empirical formula
Formula mass
Crystal system
Space group
C22H21N2PS2
408.50
monoclinic
P21/c
10.4437(8)
22.2312(16)
9.1690(7)
90
106.6740(10)
90
C26H26GaNO2P2
C26H26GaNP2S2
548.26
monoclinic
P21/c
14.257(6)
8.852(4)
21.635(9)
90
101.881(7)
90
C26H26GaNOP2S
C16H22GaNOP2S
408.07
C24H26GaN2PS2
507.28
orthorhombic
P212121
8.481(2)
16.596(4)
17.078(4)
90
516.14
orthorhombic
Cc
9.645(1)
14.842(1)
17.743(2)
90
90
90
2539.8(6)
4
1.350
532.20
orthorhombic
Pbca
16.687(4)
15.943(4)
19.526(5)
90
90
90
5195(2)
8
1.361
triclinic
¯
P1
˚
a [A]
9.162(1)
9.308(1)
12.921(1)
106.216(1)
93.480(1)
111.178(1)
970.30(14)
2
˚
b [A]
˚
c [A]
α [°]
β [°]
γ [°]
90
90
3
˚
V [A ]
2039.3(3)
4
1.331
2671.9(19)
4
1.363
2403.8(10)
4
1.402
Z
Dcalcd. ([g/cm3]
F(000)
1.397
420
856
1064
1128
2192
1048
Crystal size [mm]
Temperature [K]
2θ range [°]
No. of reflections
collected
No. of independent
reflections
No. of observed
reflections
No. of parameters
R
0.12 ϫ 0.23 ϫ 0.26 0.14 ϫ 0.26 ϫ 0.29 0.13 ϫ 0.18 ϫ 0.26 0.13 ϫ 0.18 ϫ 0.27 0.18 ϫ 0.17 ϫ 0.11 0.15 ϫ 0.18 ϫ 0.24
293
3.6Ϫ55
22836
293
5.6Ϫ50
8938
293
2.9Ϫ50
12838
293
4.1Ϫ50
45930
100
3.3Ϫ52
10895
100
3.4Ϫ50
8640
4662 (Rint ϭ 0.0342) 4380 (Rint ϭ 0.0209) 4645 (Rint ϭ 0.0591) 4569 (Rint ϭ 0.0569) 4199 (Rint ϭ 0.0171) 4150 (Rint ϭ 0.0330)
3706 [F Ͼ 4.0σ(F)] 4225 [F Ͼ 4.0 σ(F)] 3439 [F Ͼ 4.0 σ(F)] 3978 [F Ͼ 4.0 σ(F)] 3763 [F Ͼ 4.0 σ(F)] 3687 [F Ͼ 4.0 σ(F)]
244
291
291
291
203
273
0.0295
0.0598
0.958
0.0442
0.1138
1.038
0.0377
0.0984
1.084
0.0631
0.1559
0.969
0.0604
0.1369
1.230
0.0368
0.1032
1.080
Rw
GOF
Largest difference
electron density [e/A ]
0.449/Ϫ0.311
0.711/Ϫ0.496
1.056/Ϫ0.927
0.545/Ϫ0.244
0.667/Ϫ0.165
0.416 and Ϫ0.220
3
˚
[5]
[6]
´
M. A. Mun˜oz-Hernandez, A. Singer, D. A. Atwood, R. Cea-
Olivares, J. Organomet. Chem. 1998, 571, 15Ϫ19.
W. Uhl, T. Spies, W. Saak, Z. Anorg. Allg. Chem. 1999, 625,
2095Ϫ2102.
0.66 mmol) and trimethylgallium (0.076 g, 0.66 mmol). Yield 0.25 g
(75%). Selected H NMR data (80.96 MHz, C6D6): δ ϭ 0.35 (s, 6
1
H, GaCH3), 2.23 (m, 2 H, CH2), 3.94 (m, 2 H, CH2), 4.27 (m, 2
H, CH2), 6.89Ϫ7.91 (m, 13 H, aromatic H) ppm. 31P{1H} NMR
(80.96 MHz, C6D6): δ ϭ 41.07 (s). C24H26GaN2PS2 (507.28): calcd.
C 56.54, H 5.10, N 2.75, S 12.57; found C 56.81, H 5.21, N 2.64,
S 12.43.
[7]
[8]
M. S. Hill, D. A. Atwood, Eur. J. Inorg. Chem. 1998, 67Ϫ72.
S. Dagorne, I. A. Guzei, M. P. Coles, R. F. Jordan, J. Am.
Chem. Soc. 2000, 122, 274Ϫ289.
A. V. Korolev, F. Delpech, S. Dagorne, I. A. Guzei, R. J. Jor-
dan, Organometallics 2001, 20, 3367Ϫ3369.
O. T. Beachley Jr., J. R. Gardinier, M. R. Churchill, Organome-
tallics 2003, 22, 1145Ϫ1151.
R. J. Wehmschulte, J. M. Steele, J. D. Young, M. A. Khan, J.
Am. Chem. Soc. 2003, 125, 1470Ϫ1471.
[9]
X-ray Crystallographic Study: Crystals suitable for X-ray diffrac-
tion for compounds L2H, 1, 2, 4, 5 and 6 were obtained from
saturated hexane solutions as described above. X-ray data were col-
lected with a Bruker APEX CCD diffractometer with Mo-Kα radi-
ation. The structures were refined using the software package
SHELXTL vers. 6.1.[36] All of the non-hydrogen atoms were refined
anisotropically. The hydrogen atoms were put into calculated posi-
tions. Absorption correction in all cases was applied using SAD-
ABS.[37] Further details of the structure analyses are given in
Table 4.[38]
[10]
[11]
[12]
[13]
[14]
[15]
R. G. Cavell, K. Aparna, R. P. K. Babu, Q. Wang, J. Mol.
Catal. A: Chem. 2002, 189, 137Ϫ143.
A. Ziegler, V. P. Botha, I. Haiduc, Inorg. Chim. Acta 1975,
15, 123Ϫ128.
R. A. Spence, J. M. Swan, S. H. B. Wright, Aust. J. Chem.
1969, 22, 2359Ϫ2370.
N. G. Zabirov, V. V. Brus’ko, S. V. Kashevarov, F. D. Sokolov,
V. A. Shcherbakova, A. Y. Verat, R. A. Cherkasov, Russ. J.
Gen. Chem. 2000, 70, 1214Ϫ1221.
V. G a r c ıa-Montalvo, R. Cea-Olivares, D. J. Williams, G. Espi-
nosa-Perez, Inorg. Chem. 1996, 35, 3948Ϫ3953.
H. Nöth, Z. Naturforsch., Teil B 1982, 37, 1491.
A. M. Z. Slawin, J. Ward, D. J. Williams, J. D. Woolins, J.
Chem. Soc., Chem. Commun. 1994, 421Ϫ422.
P. Bahttacharyya, A. M. Z. Slawin, D. J. Williams, J. D. Wool-
ins, J. Chem. Soc., Dalton Trans. 1995, 2489Ϫ2495.
R. Rösler, M. Stanciu, J. Yang, J. E. Drake, C. Silvestru, I.
Haiduc, Phosphorus, Sulfur Silicon 1998, 132, 231.
R. Rösler, M. Stanciu, J. Yang, I. Haiduc, J. Chem. Soc., Dalton
Trans. 1996, 391Ϫ399.
[16]
Acknowledgments
´
´
´
We are indebted to CONACYT-Mexico (Grant J30234-E) and
[17]
[18]
UCMEXUS-CONACYT for generous support. We also thank
CONACYT for a PhD grant to S. C.-L. and an undergraduate
studentship to E. H.-R.
[19]
[20]
[21]
[22]
[23]
[1]
J. E. Huheey, E. A. Keiter, R. L. Keiter, Inorganic Chemistry,
4th ed., Harper Collins College Publishers, New York, 1993.
I. Haiduc, The Chemistry of Inorganic Ring Systems, Wiley In-
[2]
terscience, New York, 1970, vols. I and II.
[3]
D. Fenske, R. Mattes, J. Löns, K. F. Tebbe, Chem. Ber. 1973,
C. Silvestru, J. E. Drake, Coord. Chem. Rev. 2001, 223,
106, 1139Ϫ1144.
117Ϫ216 and references cited therein.
P. Bhattacharyya, J. D. Woollins, Polyhedron 1995, 14,
3367Ϫ3388.
[4]
J. E. Drake, M. B. Hursthouse, M. Kulcsar, M. E. Light, A.
Silvestru, J. Organomet. Chem. 2001, 623, 153Ϫ160.
Eur. J. Inorg. Chem. 2004, 3743Ϫ3750
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3749

´
´
M.-A. Mun˜oz-Hernandez et al.
FULL PAPER
[24]
[33]
P. B. Hitchcock, J. F. Nixon, I. Silaghi-Dumitrescu, I. Haiduc,
P. Bahttacharyya, J. Novasad, J. Phillips, A. M. Z. Slawin, D.
J. Williams, J. D. Woollins, J. Chem. Soc., Dalton Trans. 1995,
1607Ϫ1613.
Inorg. Chim. Acta 1985, 96, 77.
P. Bahttacharyya, J. Novasad, J. Phillips, A. M. Z. Slawin, D.
[25]
[34]
[35]
[36]
[37]
[38]
J. Williams, J. D. Woolins, J. Chem. Soc., Dalton Trans. 1995,
J. Yang, J. E. Drake, S. Hernandez-Ortega, R. Rösler, C. Silves-
tru, Polyhedron 1997, 16, 4061Ϫ4071.
R. Rösler, M. Stanciu, J. Yang, J. E. Drake, C. Silvestru, I.
Haiduc, Phosphorus, Sulfur Silicon 1998, 132, 231Ϫ250.
G. M. Sheldrick, SHELXTL, version 6.0, Bruker AXS, Inc.,
Madison, WI, USA, 2000.
1607Ϫ1613.
[26]
J. Yang, J. E. Drake, S. Hernandez-Ortega, R. Rösler, C. Silves-
tru, Polyhedron 1996, 16, 4061.
D. R. Aris, J. Barker, P. R. Philips, N. W. Alcock, M. G. H.
Wallbridge, J. Chem. Soc., Dalton Trans. 1997, 909Ϫ910.
O. T. Beachley Jr, J. R. Gardinier, M. R. Churchill, D. G. Chur-
[27]
[28]
G. M. Sheldrick, SAINT-Plus, version 6.0, Bruker AXS, Inc.,
Madison, WI, USA, 2000.
chill, K. M. Keil, Organometallics 2002, 21, 946Ϫ951.
[29]
S. D. Ittel, L. K. Johnson, M. Brookhart, Chem. Rev. 2000,
CCDC-236532 (1), -236533 (2), -236534 (4), -236535 (5),
-236536 (6) and -236537 (L2H) contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or
from the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; Fax: (internat.) ϩ 44-1223-
336033; E-mail: deposit@ccdc.cam.ac.uk].
100, 1169Ϫ1204.
[30]
See for example: M. P. Coles, R. F. Jordan, J. Am. Chem. Soc.
1997, 119, 8125Ϫ8126.
A. V. Korolev, E. Ihara, I. A. Guzei, V. G. Young Jr., R. F.
Jordan, J. Am. Chem. Soc. 2001, 123, 8291Ϫ8309.
F. T. Wang, J. Najdzionek, K. L. Leneker, H. Wasserman, D.
[31]
[32]
M. Braitsch, Synth. React. Inorg. Met.-Org. Chem. 1978, 8,
119Ϫ125.
Received February 3, 2004
Early View Article
Published Online July 12, 2004
3750
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 3743Ϫ3750