Synthesis of the germanium(I) compounds [Ge2Hal4]2- and their reductive condensation to octahedral [Ge6]2- clusters in an organometallic environment

Article abstract of DOI:10.1002/(SICI)1099-0682(200005)2000:5<879::AID-EJIC879>3.0.CO;2-S

GeI₂ reacts with [M₂(CO)₁₀]^2- (M = Cr, W) leading to reductive coupling of two GeI₂ units to produce the [Ge₂I₄]^2- ligands of [{(OC)₅M}I₂Ge-GeI₂{M(CO)₅}]^2- (1a and 2a). The [Ph₄P] salts of these anions have been characterised by X-ray structure analyses as have the [Ph₄P] salts of [{(OC)₅M}Cl₂Ge-GeCl₂{M(CO)₅}]^2- (lb and 2b) obtained from the iodo derivatives la and 2a by halide metathesis with [Ph⁴P]Cl. Treatment of GeI₂ with [W₂(CO)₁₀]^2- in the presence of 2,2'- bipyridine leads to [{(OC)₅W}I₂GeGe(bipy){W(CO)₅}] (3). The digermanium ligands in 1-3 contain germanium in the unconventional formal oxidation state +I. Reductive condensation of [{(OC)₅Cr}I₂GeGeI2{Cr(CO)₅}]^2- (1a) by addition of [Cr₂(CO)₁₀]^2- leads to the octahedral cluster [{(OC)₅Cr}₆Ge₆]^2- (4) in a yield of 40%. The sequence of reactions as reported describes the first systematic approach to the synthesis of [E₆]^2- clusters.

Full text of DOI:10.1002/(SICI)1099-0682(200005)2000:5<879::AID-EJIC879>3.0.CO;2-S

FULL PAPER
Synthesis of the Germanium(I) Compounds [Ge2Hal4]2– and Their Reductive
Condensation to Octahedral [Ge6]2– Clusters in an Organometallic
Environment
Gerd Renner,[a] Peter Kircher,[a] Gottfried Huttner,*[a] Peter Rutsch,[a] and Katja Heinze[a]
Dedicated to Professor Jürgen Felsche on the occasion of his 60th birthday
Keywords: Germanium(I) / Tetrahalgenodigermanate(2–) / Octahedral [Ge6]2– clusters / Organometallic derivatives /
Carbonyl complexes / Chromium / Tungsten
2–
GeI2 reacts with [M2(CO)10
]
(M = Cr, W) leading to reduct-
ence
of
2,2Ј-bipyridine
leads
to
[{(OC)5W}I2Ge–
ive coupling of two GeI2 units to produce the [Ge2I4]2– li-
gands of [{(OC)5M}I2Ge–GeI2{M(CO)5}]2– (1a and 2a). The
[Ph4P] salts of these anions have been characterised by X-
ray structure analyses as have the [Ph4P] salts of
[{(OC)5M}Cl2Ge–GeCl2{M(CO)5}]2– (1b and 2b) obtained
Ge(bipy){W(CO)5}] (3). The digermanium ligands in 1–3 con-
tain germanium in the unconventional formal oxidation state
+I.
Reductive
condensation
of
[{(OC)5Cr}I2Ge–
]
GeI2{Cr(CO)5}]2– (1a) by addition of [Cr2(CO)10
2– leads to the
octahedral cluster [{(OC)5Cr}6Ge6]2– (4) in a yield of 40%.
The sequence of reactions as reported describes the first sys-
tematic approach to the synthesis of [E6]2– clusters.
from the iodo derivatives 1a and 2a by halide metathesis with
2–
[Ph4P]Cl. Treatment of GeI2 with [W2(CO)10
]
in the pres-
Introduction
Ge2H6 might be a potential candidate as it is known that
Ge–H bonds may be broken in the presence of organomet-
It has recently been shown that mononuclear SnII or GeII allic entities,[3] although Ge2H6 is not easy to handle and is
species may be transformed by group-16 carbonylmetallates thus perhaps not the best choice.[4] Moreover, the estab-
to produce the octahedral [E6]2– clusters (E ϭ Ge, Sn) at lished procedures for the syntheses of [{(OC)5M}6E6]2–
the core of the well-characterised compounds clusters all start from mononuclear EHal2 compounds with
[{(OC)5Cr}6E6]2–.[1] By statistical reasoning, the selective the anionic pentacarbonylmetal entities [Cr2(CO)10]2– [5] or
formation of such six-atom aggregates [E6]2– from six indi- [Cr(CO)5]2–
acting as halide abstractors and reducing
[6]
vidual constituents – each of which contains only one single agents at the same time.[1] The ideal precursors in this re-
element E – is a highly improbable process. Thermodyn- spect would therefore be the compounds Ge2Cl2 or Ge2Cl6;
amic and kinetic control along the reaction pathway must the former compound is still unknown while the latter has
play an important role if, as observed, six mononuclear en- been characterised as a rather unstable species.[7] Since these
tities aggregate to form an octahedral species. Because of precursors are not available or not suitable as such, one
the high number of oligonuclear intermediates that neces- might try to produce them in an organometallically pro-
sarily line out the pathway of such a process, these thermo- tected form. Since base-stabilised germylene compounds
dynamic and kinetic factors are difficult to control. An ex- [(OC)5M–GeHal2base] (M ϭ Cr, W) are known,[8] a con-
tended series of experiments is needed to find the proper ceptual approach would consist of the reductive coupling
conditions for such selective aggregation procedures.
of two such entities to give [{(OC)5M}Hal2Ge–
The number of potential steps involved in this type of GeHal2{M(CO)5}]2–. This approach receives some addi-
reaction might be considerably reduced if oligonuclear pre- tional credit from the observation that PhPCl2 as well as
cursors could be used in the condensation process. With PCl3 undergo reductive coupling with [Cr2(CO)10]2– to pro-
this in mind we have tried to prepare dinuclear precursors duce the corresponding diphosphane coordination com-
that, when appropriately functionalised, would allow better pounds [{(OC)5Cr}Cl(R)P–P(R)Cl{Cr(CO)5}] (R ϭ Ph,[9]
control of the condensation process and a suitable proced- Cl[10]).
ure has in fact been developed in the case of germanium.
With germanium as the main-group centre it is known
Compounds Containing a [Ge2Hal4]2– Ligand
that dinuclear species Ge2R6 are intrinsically stable entit-
ies.[2] Such organically substituted digermanes do, however,
lack the reactive functionalisation necessary to produce di-
element E2 building blocks for the formation of E6 clusters.
It is shown in this paper that GeI2 may be reductively
coupled by its reaction with [M2(CO)10]2– (M ϭ Cr, W) to
produce [{(OC)5M}I2Ge–GeI2{M(CO)5}]2– (1a and 2a,
Table 1). Halide exchange by [Ph4P]Cl leads to the corres-
ponding tetrachlorodigermanate compounds 1b and 2b
(Table 1).
[a]
Anorganisch-Chemisches Institut der Universität Heidelberg
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: (internat.) ϩ 49-(0)6221/545707
E-mail: g.huttner@indi.aci.uni-heidelberg.de
Eur. J. Inorg. Chem. 2000, 879Ϫ887
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ1948/00/0505Ϫ0879 $ 17.50ϩ.50/0
879

G. Renner, P. Kircher, G. Huttner, P. Rutsch, K. Heinze
FULL PAPER
Table 1. Complexes of type 1 and 2
Na2[{(OC)5Cr}I2Ge–GeI2{Cr(CO)5}] ([Naϩ]2 1a) as a red
oil (Scheme 1).
Scheme 1. Reaction of Na2[M2(CO)10] (M ϭ Cr, W) with GeI2
The compound [Ph4Pϩ]2 1a is obtained as a crystalline
derivative upon metathesis with [Ph4P]I in ethanol
(Scheme 2).
These compounds contain the unconventional and hith-
erto unknown [Ge2Hal4]2– ligands with the formal oxida-
tion state of Ge corresponding to ϩI. In assigning this ox-
idation state the Cr(CO)5 entities are seen as neutral six-
teen-electron Lewis acids with chromium in an oxidation
state of zero.
In agreement with the conceptual model, it is further
found that Na2[{(OC)5Cr}I2Ge–GeI2{Cr(CO)5}] ([Naϩ]2
1a) undergoes transformation to the octahedral cluster an-
ion [{(OC)5Cr}6Ge6]2– (4) by reaction with [Cr2(CO)10]2– in
an overall yield of 40%.
Scheme 2. Salt metathesis reaction
The anionic constituent of the sodium salt [Naϩ]2 1a is
the same as that of the phosphonium salt [Ph4Pϩ]2 1a, as
evidenced by the ν˜CO-IR spectra of these compounds
Syntheses and Structures
When a THF solution of Na2[Cr2(CO)10] is treated with (Table 2). The properties of 1a were therefore fully charac-
an equimolar amount of GeI2, the solution immediately terised with [Ph4Pϩ]2 1a as the example studied (Tables 5
changes colour from orange to red. Chromatography gives and 6).
Table 2. ν˜CO-IR spectroscopic data for the compounds 1–2
[a]
[b]
[c]
[d]
EtOH. – DMA. – CsI. – THF.
880
Eur. J. Inorg. Chem. 2000, 879Ϫ887

Germanium(I) Compounds [Ge2Hal4]2Ϫ
FULL PAPER
The constitution of 1a, as given, is in agreement with the Ge(bipy)] and [{(OC)5Cr}2Ge (phen)] (bipy ϭ 2,2Ј-bipyrid-
spectroscopic data as well as with the microanalytical data. ine; phen ϭ 1,10-phenanthroline).[12]
Proof of the constitution of 1a comes from the X-ray ana-
The mean Ge–I bond length of 264.5 pm (Table 3) is sim-
ilar to that observed for [{CpЈ(CO)2Mn}GeI3]– (261.6
pm).[13] Corresponding to the inversion symmetry of the
molecule, the bonds radiating from the two Ge atoms are
in a perfectly staggered arrangement. The pentacarbonyl-
chromium entities are in their conventional idealised octa-
hedral geometry with an overall slight umbrella effect for
the equatorial carbonyl groups (Table 3). The CO group
C1–O1 – equivalent to C1A–O1A by symmetry – is found
to bend in an obverse sense (Table 3). These latter two
groups are in close proximity to the GeI2 entity in the sym-
metry-related part of the molecule.
lysis of [Ph4Pϩ]2 1a (Figure 1, Tables 3 and 7).
The halide functionalities in 1a are substitutionally labile:
treatment of the sodium salt of 1a (vide supra) with
[Ph4P]Cl results in an exchange of the iodine substituents
of 1a versus chlorine substituents to give 1b (Scheme 3).
Complex 1b is obtained as a yellow microcrystalline mat-
erial. The ν˜CO-IR pattern observed for 1b is very similar to
that shown by 1a (Table 2). Elemental analysis indicates
that halide exchange is not complete under the experimental
conditions and the presence of 5 to 10% of unexchanged
Figure 1. Structure of compound [Ph4Pϩ]2 1a
The anion has crystallographically imposed inversion iodine substituents is inferred from these data (Table 5).
symmetry (Table 7). The Ge–Ge bond length is 244.8 pm
X-ray analysis of [Ph4Pϩ]2 1b substantiates this hypo-
(Table 3) and is thus well within the range of Ge–Ge dis- thesis. Crystals of [Ph4Pϩ]2 1b are isotypic with those of
tances reported for Ge2R6 compounds and their derivat- [Ph4Pϩ]2 1a (Table 7). The volume of the cell is reduced by
ives.[2] The Ge–Cr distances (Table 3) compare favourably about 4% upon substitution of iodine (1a) with chlorine
with the corresponding distances reported for (1b). The two anions 1a and 1b are isostructural in a qualit-
[{(OC)5Cr}GeR2(Donor)],[11] as well as with those observed ative sense. The Ge–Ge bond length of 245.5 pm in 1b
for the mononuclear chelate compounds [{(OC)5Cr}2- (Table 3) is almost equal to that observed for 1a (244.8 pm,
Table 3. Selected bond lengths [pm], angles [°], and torsion angles [°] for the compounds 1–2
Eur. J. Inorg. Chem. 2000, 879Ϫ887
881

G. Renner, P. Kircher, G. Huttner, P. Rutsch, K. Heinze
FULL PAPER
tern is in accord with this finding. Nevertheless, the struc-
tures of all four compounds (1a, 1b, 2a, and 2b) are qualit-
atively identical with that shown in Figure 1, which illus-
trates the general arrangement with the structure of 1a
shown as the specific example. In a quantitative respect, the
essential difference between the pairs of structures 1a/2a
and 1b/2b results from the replacement of the Cr(CO)5
groups in compounds 1 by W(CO)5 groups in compounds
2 (Tables 1, 3, and 7). The torsion angles within the molec-
ules are not affected to a great extent by this replacement
and, in particular, the Ge–Ge bond lengths are almost
identical in all four compounds within the limits of error,
with an average value of 245.2 pm (Table 3). As already
observed for 1b, some of the chlorine positions in 2b are
affected by an incomplete substitution of iodine versus
chlorine, with the numerical values of the distances for
Ge1–Hal2 in compounds 1b and 2b being too large. The
remaining distances and angles (Table 3) agree favourably
within the set of compounds 1 and 2. The W–Ge distances
observed for 2 are also within the range of W–Ge single
bond lengths known to date.[14]
Scheme 3. Salt metathesis reaction combined with an exchange of
the iodine versus chlorine substituents
Table 3). The observed discrepancy of the Ge–Cl distances
(Table 3), however, as well as the region of residual electron
density of 1.6 electrons 10–6 pm–3 in the neighbourhood of
the chlorine substituent Cl2 with the Ge1–Cl2 bond that is
apparently too long (Table 3), have to be interpreted in
terms of a partial occupancy of the chlorine position by
an iodine substituent. Values of individual parameters will
therefore be subject to errors and hence do not warrant a
detailed discussion. The overall structure of 1b is neverthe-
less unequivocally clear from the X-ray analysis.
[Hal2Ge–Ge(bipy)] as a Ligand
It has been observed that formation of the cluster
[{(OC)5Cr}6Ge6]2– from Na2[Cr2(CO)10] and GeI2 is pro-
moted by the presence of bipy (2,2Ј-bipyridine)[1a] and so
the reactions leading to 1 and 2 were repeated in the pres-
ence of bipy. It was hoped that some bipy derivative could
be detected that would help to explain the role of the bipy
ligand in cluster formation.[1a] However, treatment of
Na2[Cr2(CO)10] in THF solution with equimolar amounts
of GeI2 and bipy did not produce any new insight into the
process. The only products isolated were [{(OC)5Cr}2-
Ge(bipy)] and [{(OC)5Cr}6Ge6]2–, both of which have al-
ready been reported.[1a,12] However, the use of
Na2[W2(CO)10] as the starting material, under otherwise
identical conditions, gave the digermanium compound 3
(Scheme 4).
The mass-spectrometric analyses of [Ph4Pϩ]2 1a and
[Ph4Pϩ]2 1b show fragmentation patterns which that are in
accordance with their assigned constitution (Table 5).
The synthetic strategy leading to the pentacarbonylchro-
mium derivatives 1a and 1b works equally well for the pen-
tacarbonyltungsten derivatives 2a and 2b (Schemes 1, 2, and
3; Table 1). The anions 2a and 2b are isolated as their re-
spective [Ph4Pϩ] or [nBu4Nϩ] salts. Single crystals suitable
for X-ray analysis could be obtained for their [Ph4Pϩ] salts
(Tables 3 and 7). As seen from Table 7, the phosphonium
salts of 1a, 1b, and 2b form a set of isotypic crystals. The
corresponding salt of 2a also crystallises in a triclinic space
group. The cell parameters (Table 7) are, however, numeri-
cally quite different from those characterising the above iso-
typic series. The unit cell observed for [Ph4Pϩ]2 2a cannot
be transformed to a unit cell showing distances and angles
that would be in close numerical agreement with those for
the isotypic series of the phosphonium salts 1a, 1b, and 2b.
Transformation of the cell data of the phosphonium salt of
2a by {00–1, 100, 0–10} leads to a cell with dimensions
Scheme 4. Reaction of Na2[W2(CO)10] with GeI2 and 2,2Ј-bipyrid-
ine
˚
(12.76, 12.06, 12.26 [A]; 69.00, 90.39, 69.09 [°]). On using
this transformed unit cell for comparison, the centres of the
molecules are seen to have rather similar coordinates in all
four salts. In the salt of 2a the anionic part is, however, at
a different rotational position as compared to the orienta-
tions of the anions in 1a, 1b, and 2b with respect to the unit
cells. By comparing the volumes of the cells (Table 7) it is
clear that within the series of phosphonium salts the pack-
ing is least efficient in 2a. This may explain the observation
Compound 3 was purified by column chromatography
and the side products [(OC)4W(bipy)] and W(CO)6 were
separated by this procedure.[17] Compound 3 was eluted
with THF as a broad red band. Some additional red mat-
erial was obtained by elution with ethanol and this, by ana-
logy, is thought to contain [{(OC)5W}6Ge6]2–. Compound
3 was obtained as a red oil by evaporation of the solvent
from the combined THF fractions whose ν˜CO-IR spectra
that crystals of [Ph4Pϩ]2 2a crack when cooled down to showed only the bands due to 3 (Table 2) with no indication
200 K. A phase transition to the more closely packed pat- of by-products. Compound 3 could be obtained in a crystal-
882
Eur. J. Inorg. Chem. 2000, 879Ϫ887

Germanium(I) Compounds [Ge2Hal4]2Ϫ
FULL PAPER
line form from its concentrated solutions by a vapour phase
diffusion process (see Experimental Section). The red crys-
tals are stable over several days when retained in the mother
liquor in the dark. Handling of the crystals is nevertheless
problematic since they are found to produce an amorphous
material under the conditions of evaporation. It is not yet
clear whether this disintegration is due to the reduced pres-
sure – a possibility that is not highly probable since com-
pound 3 is found to crystallise without inclusion of solv-
ent – or whether the material is sensitive to daylight. When
the amorphous material that remained after evaporation of
the solvent was redissolved, red solutions were obtained
1
and the H-NMR spectra of these indicate the presence of
a minimum of three different types of coordinated bipy
ligands. By comparison with spectra of authentic samples
it appears that one of these products is [(OC)4W(bipy)];[17]
the identity of the two other compounds is as yet unknown.
The only way to identify the nature of the primary product
3 is therefore by X-ray analysis. Single crystals of 3 were
Figure 2. Structure of compound 3
immediately transferred from the mother liquor into perflu- length of which (248.2 pm) is close to the Ge–Ge bond
orinated oil and then placed onto a diffractometer in as lengths observed for 1 and 2 (Tables 3 and 4).
short a period of time as possible while keeping the temper-
The Ge–N and Ge–I bond lengths are also within the
ature below –70 °C. This procedure ensured that the crys- usual range,[12,13] as are the Ge–W distances[14] (compare
tals survived without disintegration. The structure of 3, as Tables 3 and 4). The arrangement of the substituents
determined by crystal structure analysis, is depicted in Fig- around the Ge–Ge axis corresponds to that observed for 1
ure 2 (Table 4).
and 2, with the bonds radiating from the two germanium
Crystals of 3 contain discrete molecular entities, the cent- centres being staggered with respect to one another
ral part of which is the digermanium-derived constituent (Table 4). Even though there is no crystallographically im-
[I2Ge–Ge(bipy)] (Figure 2). Each of the germanium centres posed molecular symmetry for 3, the effective molecular
is coordinated to a W(CO)5 group. One of the germanium symmetry is close to CS (for torsion angles, see Table 4). In
centres (Ge1) has two iodine substituents, while the other contrast to the structures of 1 and 2, the rotation of the
germanium is coordinated to the bipy ligand (Figure 2). M(CO)5 groups around their respective Ge–M axis is close
The germanium centres are linked by a Ge–Ge bond, the to an eclipsed arrangement in 3 (Table 4, Figure 2); it ap-
Table 4. Selected bond lengths [pm], angles [°], and torsion angles [°] for the compound 3
Eur. J. Inorg. Chem. 2000, 879Ϫ887
883

G. Renner, P. Kircher, G. Huttner, P. Rutsch, K. Heinze
FULL PAPER
proximates a staggered orientation in the structures 1 and metathesis with [Ph4P]Cl in ethanol. The salt [Ph4Pϩ]2 4
2 (Table 3, Figure 1). was obtained as a microcrystalline red-brown material in
Compound 3 contains the digermanium species [I2Ge– fair yields (40%). Crystals were obtained by layering a solu-
Ge(bipy)], which is unknown in the free state and stabilised tion of [Ph4Pϩ]2 4 in DMA (N,N-dimethylacetamide) with
in 3 by protection with bulky W(CO)5 groups. This diger- ethanol. The identity of 4 has been inferred by comparison
manium entity may be interpreted in terms of a Lewis base/ of the unit-cell data obtained for [Ph4Pϩ]2 4 by X-ray ana-
Lewis acid interaction with the organometallically pro- lysis with the authentic data.[1a] X-ray analysis of these crys-
tected eight electron species LnMGe(bipy) acting as the tals proved that the sample is identical with authentic
base and the equivalently protected six-electron species [Ph4P]2[{(OC)5Cr}6Ge6].[1a]
LnMGeI2 as the Lewis acid.[15] This type of interpretation is
appealing since the protected six electron species [(OC)5M–
GeR2][16] are known as such and also in their base-stabilised
form.[8] Lewis acid adducts of [(OC)5M–Ge(bipy)] are
equally well known and are well characterised as having
[M(CO)5] as the Lewis acidic group.[12] By whatever elec-
tron-counting approach the bonding situation in [I2Ge–Ge-
(bipy)] is analysed, it is found that it is in a formal sense
isoelectronic to the [Ge2Hal4]2– entities of 1 and 2.
The unsymmetrical substitution of the Ge–Ge entity in 3
might form the basis of its reactivity. To date, however, no
attempt to transform 3 into the cluster [{(OC)5W}6Ge6]2–
has been successful and it may therefore be assumed that
compounds of type 3 do not play a key role in the bipy-
mediated[1a] synthesis of [{(OC)5W}6Ge6]2–.
Scheme 5. Reaction of 1a with [Cr2(CO)10]2– to produce 4
A Straightforward Synthesis of the [Ge6]2– Core
Even though 3 could not be transformed to produce a Conclusions
[Ge6]2– cluster, an efficient synthesis of the [Ge6]2– core has
nevertheless been found by following a different strategy
(Scheme 5). When THF solutions of Na2[{(OC)5Cr}I2Ge–
GeI2{Cr(CO)5}] ([Naϩ]2 1a) (vide supra) are treated with
two equivalents of Na2[Cr2(CO)10][5] dissolved in THF, a
continuous change of the ν˜CO-IR spectra of the reaction
mixture is observed. While the long-wavelength region is
obscured by the bands that are characteristic of
[Cr2(CO)10]2–, in the short-wavelength range the bands
characteristic of the reaction products are observed to
evolve. The band pattern at 2053/2030 cm–1 indicates the
formation of [Cr2(CO)10H]–.[5,18] The assignment of this
pattern to [Cr2(CO)10H]– was corroborated by the inde-
pendent synthesis of [Ph4P][Cr2(CO)10H], which was char-
acterised by single-crystal analysis and comparison with the
known structure of this compound,[18] by its proton-NMR
signal in CD2Cl2 solution at δ ϭ –19.4 and its ν˜CO-IR spec-
trum in THF solution.[5,18] A band characteristic of the
cluster [{(OC)5Cr}6Ge6]2– (4) (2043 cm–1)[1a] was also found
to increase in intensity during the reaction. After complete
addition of the two equivalents of Na2[Cr2(CO)10] during a
period of three hours, the band at 2043 cm–1 was found not
to increase any further when an additional 0.3 equivalents
of Na2[Cr2(CO)10] were added. These findings indicate that
the formation of the compound that gives rise to the band
at 2043 cm–1 requires two equivalents of Na2[Cr2(CO)10]
for completion. The red-brown solution was concentrated,
filtered through Kieselgur, and chromatographed on silica
gel. Na2[{(OC)5Cr}6Ge6] {[Naϩ]2 4} was obtained as a red
In the presence of M(CO)5 moieties (M ϭ Cr, W) ger-
manium(II) halides may be reductively coupled to produce
[Ge2Hal4]2– ligands. In a formal sense these ligand entities
contain germanium in its unconventional ϩI oxidation
state and are formally isoelectronic to P2R4 ligands,[9,10]
which act as bridging entities in several well-characterised
organometallic derivatives. In contrast to P2R4, their an-
ionic equivalents [Ge2R4]2– are not known but they are
found to be stable in their M(CO)5-protected form
[{(OC)5M}I2Ge–GeI2{M(CO)5}]2– (1 and 2).
In the presence of bipy, the organometallically protected
ligands of the type [Hal2Ge–Ge(bipy)] may be obtained un-
der otherwise similar conditions. Here again the formal
average oxidation state of germanium is ϩI and the ligands
are not known in the free state but are stable under organo-
metallic protection, as shown for [{(OC)5W}I2Ge–
Ge(bipy){W(CO)5}] (3).
Starting from the digermanium precursor [{(OC)5Cr}-
Hal2Ge–GeHal2{Cr(CO)5}]2– (1), a reductive condensation
procedure produces [{(OC)5Cr}6Ge6]2– (4), which has a
[Ge6]2– core. This type of process is the first straightforward
approach to the selective synthesis of the [Ge6]2– core.
Experimental Section
General: All manipulations were carried out under argon by means
of standard Schlenk techniques at 20 °C unless mentioned other-
ethanolic eluate from which 4 could be precipitated by wise. All solvents were dried by standard methods and distilled
884 Eur. J. Inorg. Chem. 2000, 879Ϫ887

Germanium(I) Compounds [Ge2Hal4]2Ϫ
FULL PAPER
under argon. The [D6]DMSO and [D6]acetone used for the NMR-
spectroscopic measurements were degassed by three successive
‘‘freeze-pump-thaw’’ cycles and dried over 4-A molecular sieves.
Silica gel (Kieselgel z. A. 0.06–0.2 mm, J. T. Baker Chemicals B.
V.) used for chromatography and Kieselgur (Kieselgur, gereinigt,
spectroscopic data are given in Table 2, Table 5, and Table 6. X-ray
data are given in Tables 3, 4, and 7.
˚
Na2[{(OC)5M}I2Ge–GeI2{M(CO)5}] ([Na؉]2 1a,
[Na؉]2 2a, M ؍ W): To a stirred orange solution of Na2[M2(CO)10]
M
؍
Cr;
geglüht, Erg. B.6, Riedel de Hae¨n AG) used for filtration were de- (M ϭ Cr: 430 mg, 1 mmol; M ϭ W: 694 mg, 1 mmol) in THF
gassed at 1 mbar at 130 °C for 12 h and saturated with argon. –
(50 mL) was added solid GeI2 (326 mg, 1 mmol) in one portion.
The orange solution turned red immediately. After stirring for 1 h,
NMR: Bruker Avance DPX 200 at 200.13 MHz (1H), 50.323 MHz
(13C{1H}), 81.015 MHz (31P{1H}); chemical shifts (δ) in ppm with the GeI2 had completely dissolved and a clear red solution had
respect to [D6]DMSO (1H: δ ϭ 2.50; 13C: δ ϭ 39.4) and [D6]acetone
(1H: δ ϭ 2.05; 13C: δ ϭ 206.2), respectively, as internal standards
and to 85% H3PO4 (31P: δ ϭ 0) as external standard. – IR: Bruker
formed. The reaction mixture was filtered through Kieselgur
(3 cm). The resulting red solution was concentrated in vacuo
(5 mL) and chromatographed on silica gel (15 cm, Ø ϭ 3 cm;
FT-IR IFS-66; CaF2 cells. – UV/Vis/NIR: Perkin–Elmer Lambda THF). Elution with THF gave one yellow band that contained
19; cells (0.2 cm; Hellma 110 suprasil). – MS (FAB): Finnigan
MAT 8400; Nibeol matrix (4-nitrobenzyl alcohol). – Elemental
analysis: Microanalytical Laboratory of the Organisch-Chemisches
Institut, Universität Heidelberg. – Melting points: Gallenkamp
[M(CO)6] and Na[M(CO)5I] (M ϭ Cr, W: identification by IR spec-
troscopy[20]). A red band remained on the top of the column that
was eluted with ethanol. The resulting solution was taken to dry-
ness. [Naϩ]2 1a and [Naϩ]2 2a, respectively, were obtained as deep
orange oils. The identity of the sodium salts 1a and 2a is inferred
from metathesis to the corresponding [Ph4P] salts, which may be
MFB-595 010; the values are not corrected. – Chemicals: The
metallates Na2[M2(CO)10][5] (M ϭ Cr, W) and GeI2
were pre-
[19]
pared by literature methods. All other chemicals were commercially fully characterised by various methods, including elemental ana-
obtained and used without further purification. – Analytical and
lysis. The ν˜CO-IR patterns of the sodium salts and the phosphon-
Table 5. Analytical data for the compounds 1–2
[a]
Partial substitution of Cl by I: calculated formula for [Ph4Pϩ]2 1b: C58H40Cl3.6Cr2Ge2I0.4O10P2; calculated formula for [Ph4Pϩ]2 2b:
C58H40Cl3.6Cr2Ge2I0.4O10P2
1
Table 6. H-, 31P{1H}-, and 13C{1H}-NMR spectroscopic data for the compounds 1–2
[a]
[b]
[c]
[d]
[e]
[f]
[g]
[h]
[i]
[D6]DMSO. – [D6]acetone. – CD3CN. – Non-resolved multiplets. – t, 2 H. – m, 2 H. – m, 2 H. – t, 3 H. – In case
of [PPh4] salts: Cpara [d, J(31P,13C) ϭ 3 Hz]; Cortho [d, 4J(31P,13C) ϭ 10 Hz]; Cmeta [d, 4J(31P,13C) ϭ 13 Hz]; Cipso [d, 4J(31P,13C) ϭ 13 Hz];
in case of [nBu4N] salts: Cα, Cβ, Cγ, Cδ: carbon atoms of n-butyl substituent.
4
Eur. J. Inorg. Chem. 2000, 879Ϫ887
885

G. Renner, P. Kircher, G. Huttner, P. Rutsch, K. Heinze
FULL PAPER
Table 7. Crystal structure data for the compounds 1–3
ium salts are similar enough to leave no doubt about the nature of
the organometallic anions 1a and 2a.
(30 mL) was added solid [nBu4N]I (739 mg, 2 mmol). The corres-
ponding yellow [nBu4N] salt of 2a precipitated immediately. The
subsequent workup followed the method described for [Ph4Pϩ]2 2a.
Yield: [nBu4Nϩ]2 2a: 482 mg, 0.27 mmol, 54% (with respect to
GeI2).
[Ph4P]2[{(OC)5M}I2Ge–GeI2{M(CO)5}] ([Ph4P؉]2 1a, M ؍ Cr;
[Ph4P؉]2 2a, M ؍ W): To a stirred orange solution of [Naϩ]2 1a
(541 mg, 0.5 mmol) or [Naϩ]2 2a (673 mg, 0.5 mmol), respectively,
in ethanol (10 mL) was added a suspension of [Ph4P]I (933 mg,
2 mmol) in ethanol (30 mL). The corresponding yellow [Ph4P] salts
of 1a or 2a precipitated immediately. After stirring for 30 min, the
solid was separated from the mother liquor by filtration and
washed with ethanol (2 ϫ 5 mL), diethyl ether (2 ϫ 5 mL) and
dried in vacuo leaving the salts of [Ph4Pϩ]2 1a and [Ph4Pϩ]2 2a as
yellow powders. Yield: [Ph4Pϩ]2 1a: 394 mg, 0.23 mmol, 46%;
[Ph4Pϩ]2 2a: 456 mg, 0.23 mmol, 46% (with respect to GeI2). In
order to grow single crystals of [Ph4Pϩ]2 1a and [Ph4Pϩ]2 2a the
yellow powder was dissolved in DMA (5 mL) and overlayered with
ethanol (20 mL). Within 5 d at 20 °C yellow single crystals suitable
for X-ray analysis were obtained.
[{(OC)5W}I2Ge–Ge(bipy){W(CO)5}] (3): Na2[W2(CO)10] (694 mg,
1 mmol) was dissolved in THF (50 mL) and solid GeI2 (326 mg,
1 mmol) and solid 2,2Ј-bipyridine (156 mg, 1 mmol) were added in
one portion. The initially clear orange solution turned deep red
immediately (GeI2 dissolved in a period of minutes). After stirring
for 1 h, the reaction mixture was filtered through Kieselgur (3 cm).
The resulting red solution was concentrated to 5 mL in vacuo and
chromatographed on silica gel (15 cm, Ø ϭ 3 cm; diethyl ether).
Elution with diethyl ether gave a red band, which was identified by
IR spectroscopy to consist of [W(CO)6] and [(OC)4W(bipy)].[17,20]
Elution with THF gave a second red band containing 3. This frac-
tion was taken to dryness to leave 3 as a red oil. Single crystals of
3 were obtained by the following procedure: A concentrated THF
solution of 3 (348 mg in 5 mL of THF) was shared out between
three test tubes (Ø ϭ 1 cm), which were each placed into a Schlenk
tube (250 mL). Diethyl ether (30 mL), which was in the Schlenk
tube, was allowed to diffuse through the gas phase into the THF
solutions (12 h at 20 °C). After this period of time the diethyl ether
was replaced by petroleum ether (boiling range 40–60 °C; 50 mL).
Vapour diffusion of the petroleum ether for 4 d gave red single
crystals of 3 that were suitable for X-ray structure analysis. All
operations were carried out in the dark. While the identity of 3
could be determined by X-ray analysis of these crystals at 200 K,
dissolving these crystals in CD2Cl2 or [D6]acetone at 20 °C resulted
in red solutions that contained bipy ligands in three different coor-
dination environments. The 1H-NMR spectra show three sets of
[Ph4P]2[{(OC)5M}Cl2Ge–GeCl2{M(CO)5}] ([Ph4P؉]2 1b, M ؍ Cr;
[Ph4P؉]2 2b, M ؍ W): To a stirred orange solution of [Naϩ]2 1a
(541 mg, 0.5 mmol) or [Naϩ]2 2a (673 mg, 0.5 mmol) in ethanol
(30 mL) was added solid [Ph4P]Cl (750 mg, 2 mmol). The corres-
ponding yellow [Ph4P] salts of 1b or 2b precipitated immediately.
Further workup and the growth of single crystals of [Ph4Pϩ]2 1b
or [Ph4Pϩ]2 2b were achieved following the methods described for
[Ph4Pϩ]2 1a. Yield: [Ph4Pϩ]2 1b: 310 mg, 0.23 mmol, 46%;
[Ph4Pϩ]2 2b: 370 mg, 0.23 mmol, 46% (with respect to GeI2). The
exchange of iodide versus chloride is almost complete under these
conditions, as shown by elemental analysis and X-ray analysis.
[nBu4N]2[{(OC)5W}I2Ge–GeI2{W(CO)5}] ([nBu4N؉]2 2a): To
a
stirred orange solution of [Naϩ]2 2a (673 mg, 0.5 mmol) in ethanol
886
Eur. J. Inorg. Chem. 2000, 879Ϫ887

Germanium(I) Compounds [Ge2Hal4]2Ϫ
FULL PAPER
GeCl2{Si(SiMe3)3}] (Ge–Ge ϭ 242.1 pm): S. P. Mallela, R. A.
signals that, although not individually resolved, provide evidence
that compound 3 disintegrates at least in part under the given ex-
perimental conditions. In addition, a satisfactory elemental analysis
could not be obtained for 3.
[2d]
Geanangel, Inorg. Chem. 1991, 30, 1480–1482.
–
[{Cp(CO)2Fe}R2Ge–GeR2{Fe(CO)2Cp}] (Ge–Ge: 244.8 pm,
R2 ϭ 2,3-dimethylbut-2-ene-1,4-diyl): G. Barsuaskas, D. Lei,
M. L. Hampden-Smith, E. N. Duesler, Polyhedron 1990, 9,
773–779.
[Ph4P]2[{(OC)5Cr}6Ge6] ([Ph4P؉]2 4): To a stirred orange solution
of [Naϩ]2 1a (541 mg, 0.5 mmol) in THF (30 mL) was added a solu-
tion of Na2[Cr2(CO)10] (430 mg, 1 mmol) in THF (30 mL) in 10-
mL portions during a period of 3 h. During the addition the colour
of the solution turned to red-brown. The reaction mixture was fil-
tered through Kieselgur (3 cm), concentrated to 5 mL in vacuo and
chromatographed on silica gel (15 cm, Ø ϭ 3 cm; THF). Elution
with THF gave a broad yellow band containing Na[Cr2(CO)10H],
which was identified by IR spectroscopy.[5,18] A deep red band re-
mained on top of the column and this was eluted with ethanol.
The resulting deep red solution was taken to dryness in vacuo and
redissolved in ethanol (10 mL). Addition of solid [Ph4P]Cl (375 mg,
1 mmol) led to the corresponding red-brown [Ph4P] salt of 4, which
precipitated immediately. The solid was separated from the mother
liquor by filtration, washed with ethanol (2 ϫ 5 mL), diethyl ether
(2 ϫ 5 mL) and dried in vacuo. Yield: [Ph4Pϩ]2 4: 151 mg,
0.07 mmol, 40% (with respect to GeI2). Single crystals of [Ph4Pϩ]2 4
could be obtained by layering a concentrated DMA solution of
[Ph4Pϩ]2 4 (3 mL) with ethanol (20 mL).
[3] [3a]
[3b]
W. Gäde, E. Weiss, Chem. Ber. 1981, 114, 2399–2404. –
W. Gäde, E. Weiss, Chem. Ber. 1984, 117, 2464–2468.
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M. Scheer, K. Schuster, A. Krug, H. Hartnung, Chem.
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[12]
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P. Kircher, G. Huttner, K. Heinze, B. Schiemenz, L. Zsolnai,
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X-ray Structure Determinations: The measurements for [Ph4Pϩ]2 1a,
[Ph4Pϩ]2 2b, and 3 were carried out with a Siemens P4 four-circle
diffractometer, data for [Ph4Pϩ]2 2a were collected with a Nonius
Kappa CCD diffractometer, all using Mo-Kα radiation. In the case
of the Siemens P4 four-circle diffractometer, measurements of the
intensities of three check reflections (measured every 100
reflections) remained constant throughout the data collection, thus
indicating crystal and electronic stability. The data collected using
a scintillation counter measuring device (Siemens P4) were cor-
rected in the usual way including experimental absorption correc-
tion. The data from the CCD device (Nonius Kappa CCD) were
processed by the standard Nonius software.[21] All calculations were
performed using the SHELXT PLUS software package. Structures
were solved by direct methods with the SHELXS-86 program and
refined with the SHELXL-93 program.[22] The program XPMA[23]
was used for graphical handling of the data. The structures were
refined in fully or partially anisotropic models by full-matrix least-
squares calculations. Hydrogen atoms were introduced at calculated
positions. Table 7 compiles the data for the structure determina-
tions. Crystallographic data for the structures reported in this paper
have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication nos. CCDC-135292
([Ph4Pϩ]2 1a), -135293 ([Ph4Pϩ]2 1b), -135291 ([Ph4Pϩ]2 2a),
-135295 ([Ph4Pϩ]2 2b), -135294 (3). Copies of the data can be ob-
tained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax: int. code ϩ 44-1223/336-033; E-
mail: deposit@ccdc.cam.ac.uk].
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G. Huttner, U. Weber, B. Sigwarth, O. Scheidsteger, H.
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[14b]
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D. J. Brauer, C. Krüger, Eur.
[14d]
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[16b]
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[16c]
Okazaki, Organometallics 1994, 13, 167–171. –
M. F. Lap-
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[17b]
M. H. B. Stiddard, J. Chem. Soc. 1962, 4712–4715. –
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[18b]
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[19]
[20]
[21]
G. Brauer, Handbuch der Präparativen Anorganischen Chemie,
3rd ed., Ferdinand Enke Verlag, Stuttgart, 1981, vol. 2, p. 727.
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Collect data collection software, Nonius, 1998; http://
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[22] [22a] G. M. Sheldrick, SHELXS-86 – Program for Crystal Struc-
ture Solution, Universität Göttingen, 1986; http://
[22b]
www.shelx.uni-ac.gwdg.de/shelx/index.html. –
G. M. Shel-
[1]
[1a] P. Kircher, G. Huttner, K. Heinze, G. Renner, Angew. Chem.
drick, SHELXL-93 – Program for Crystal Structure Refine-
ment, Universität Göttingen, 1993; http://www.shelx.uni-
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295–296; Angew. Chem. Int. Ed. Engl. 1993, 32, 297–298.
[22c]
ac.gwdg.de/shelx/index.html. –
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ray Crystallography, vol. 4, Kynoch Press, Birmingham, 1974.
L. Zsolnai, G. Huttner, XPMA, Universität Heidelberg, 1998;
http://www.rzuser.uni-heidelberg.de/~v54/xpm.html
Received October 19, 1999
[2] [2a]
[23]
Ph3Ge–GePh3 (Ge–Ge: 243.7 pm): M. Dräger, L. Ross, Z.
[2b]
Anorg. Allg. Chem. 1980, 490, 207–216. –
PhCl2Ge–
GeCl2Ph (Ge–Ge: 242.1 pm): K. Häberle, M. Dräger, Z. Nat-
[2c]
urforsch. 1987, 42b, 323–329.
–
[{(Me3Si)3Si}Cl2Ge–
[I99370]
Eur. J. Inorg. Chem. 2000, 879Ϫ887
887