The inverse sandwich complex [(K(18-crown-6))2Cp][CpFe(CO) 2] - Unpredictable redox reactions of [CpFe(CO)2]I with the silanides Na[SiRtBu2] (R = Me, tBu) and the isoelectronic phosphanyl borohydride K[PtBu2BH3]

Article abstract of DOI:10.1039/c2dt00031h

The dimeric iron carbonyl [CpFe(CO)₂]₂ and the iodosilanes tBu₂RSiI were obtained from the reaction of [CpFe(CO)₂]I with the silanides Na[SiRtBu₂] (R = Me, tBu) in THF. By the reactions of [CpFe(CO)₂]I and Na[SiRtBu₂] (R = Me, tBu) the disilanes tBu₂RSiSiRtBu₂ (R = Me, tBu) were additionally formed using more than one equivalent of the silanide. In this context it should be noted that reduction of [CpFe(CO)₂]₂ with Na[SitBu₃] gives the disilanes tBu₃SiSitBu ₃ along with the sodium ferrate [(Na(18-crown-6))₂Cp] [CpFe(CO)₂]. The potassium analogue [(K(18-crown-6)) ₂Cp][CpFe(CO)₂] (orthorhombic, space group Pmc2 ₁), however, could be isolated as a minor product from the reaction of [CpFe(CO)₂]I with [K(18-crown-6)][PtBu₂BH₃]. The reaction of [CpFe(CO)₂]₂ with the potassium benzophenone ketyl radical and subsequent treatment with 18-crown-6 yielded the ferrate [K(18-crown-6)][CpFe(CO)₂] in THF at room temperature. The crown ether complex [K(18-crown-6)][CpFe(CO)₂] was analyzed using X-ray crystallography (orthorhombic, space group Pna2₁) and its thermal behaviour was investigated.

Full text of DOI:10.1039/c2dt00031h

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PAPER
The inverse sandwich complex [(K(18-crown-6))2Cp][CpFe(CO)2] –
unpredictable redox reactions of [CpFe(CO)2]I with the silanides Na[SiRtBu2]
(R = Me, tBu) and the isoelectronic phosphanyl borohydride K[PtBu2BH3]†
Inge Sänger, Theresa I. Kückmann, Franz Dornhaus, Michael Bolte, Matthias Wagner and
Hans-Wolfram Lerner*
Received 5th January 2012, Accepted 27th March 2012
DOI: 10.1039/c2dt00031h
The dimeric iron carbonyl [CpFe(CO)2]2 and the iodosilanes tBu2RSiI were obtained from the reaction
of [CpFe(CO)2]I with the silanides Na[SiRtBu2] (R = Me, tBu) in THF. By the reactions of [CpFe(CO)2]I
and Na[SiRtBu2] (R = Me, tBu) the disilanes tBu2RSiSiRtBu2 (R = Me, tBu) were additionally formed
using more than one equivalent of the silanide. In this context it should be noted that reduction of
[CpFe(CO)2]2 with Na[SitBu3] gives the disilanes tBu3SiSitBu3 along with the sodium ferrate
[(Na(18-crown-6))2Cp][CpFe(CO)2]. The potassium analogue [(K(18-crown-6))2Cp][CpFe(CO)2]
(orthorhombic, space group Pmc21), however, could be isolated as a minor product from the reaction of
[CpFe(CO)2]I with [K(18-crown-6)][PtBu2BH3]. The reaction of [CpFe(CO)2]2 with the potassium
benzophenone ketyl radical and subsequent treatment with 18-crown-6 yielded the ferrate
[K(18-crown-6)][CpFe(CO)2] in THF at room temperature. The crown ether complex [K(18-crown-6)]-
[CpFe(CO)2] was analyzed using X-ray crystallography (orthorhombic, space group Pna21) and its
thermal behaviour was investigated.
The purpose of this paper is now to examine the reactivity of
Introduction
[CpFe(CO)2]I towards the silanides Na[SiRtBu2] (R = Me,
tBu)5,10,11 and to make a comparison with the chemical behaviour
In the past few decades cyclopentadienyliron dicarbonyl com-
plexes have gained significant importance as model systems
in organometallic chemistry. On the one hand the [CpFe(CO)2]-
fragment is an ideal candidate to investigate substitution reac-
tions because it can act as a nucleophile (e.g. M[CpFe(CO)2];
M = alkali metal), as an electrophile (e.g. [CpFe(CO)2]X;
X = halogen) or as a radical (e.g. [CpFe(CO)2]2),1 on the other
hand its electronic properties can be related to the carbonyl IR
stretching frequencies2 as well as to the 13C NMR shifts of the
carbonyl3 and cyclopentadienido4 carbon atoms.
of the isoelectronic phosphanyl borohydride K[PtBu2BH3]. In the
course of these investigations we studied additionally the thermal
and chemical behaviour of the ferrate [K(18-crown-6)][CpFe(CO)2].
Results and discussion
Recently we have reported that preparation of the phosphanyl
borohydride homologue can best be achieved by introducing the
In a preceding study5 we have already made a comparison of
cyclopentadienyliron dicarbonyl complexes with two series of
isoelectronic and largely isosteric ligands, namely PPh2Me,6
[PPh2BH3]−,6 and [SiPh2Me]−7 and SPtBu3,8 [SPtBu2BH3]−8
and [SSitBu3]−.9 In this report we have concluded that, with
respect to electron donor strength, phosphanyl borohydrides
occupy an intermediate position between phosphanes (weakest
donors) and silyl ligands (strongest donors).5 The same is true
for the thio derivatives, although the differences are smaller.5
Institut für Anorganische Chemie, Goethe-Universität, Max-von-Laue-Str.
7, D-60438 Frankfurt, Germany. E-mail: lerner@chemie.uni-frankfurt.de;
Fax: ++49 69 79829260; Tel: ++49 69 79829152
†CCDC 832033 ([(K(18-crown-6))2Cp][5]), 832034 ([K(18-crown-6)]-
[5]), 832031 (6). For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c2dt00031h
Scheme 1 Reactivity of [CpFe(CO)2]I towards the silanides Na
[SiRtBu2] (R = Me, tBu) and the isoelectronic phosphanyl borohydride
K[PR2BH3] (R = Ph, tBu). (i) K[E] (2, E = PPh2BH3; 3, E = PtBu2BH3.
(ii) M[E]; M[E] = Na[SiRtBu2] (R = Me, tBu), K[PtBu2BH3]).
This journal is © The Royal Society of Chemistry 2012
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preformed ligands, rather than assembling them with the phos-
phorus atom connected to a metal fragment.5 Therefore treatment
of [CpFe(CO)2]I with K[PPh2BH3]6 in THF resulted in nearly
quantitative formation of the desired compound (Scheme 1).5
In pursuit of complexes of the type [CpFe(CO)2]SiR3 (R =
alkyl), [CpFe(CO)2]I (1) was first treated with one equivalent of
the sodium silanides Na[SiMetBu2]5 and Na[SitBu3].10,11 The
NMR spectra of these reactions, however, indicate that it is not
practical to prepare the cyclopentadienyliron dicarbonyl silanides
[CpFe(CO)2]SiRtBu2 by the same routes as applied for isoelec-
tronic phosphanyl borohydrides. The spectroscopically identifi-
as the cyclopentadienide anion (Scheme 2). Apparently, these
products are formed by an β-addition of Na[SitBu3] to 4 (oxi-
dative addition of Na[SitBu3] to dinuclear 4) and a subsequent
substitution reaction with the liberation of the cyclopentadienide
anion (Scheme 2). In this context it should be noted that
Fe(II) compounds with bulky σ-donating substituents are para-
magnetic and undergo easily a reductive elimination by which
16
elementary iron is formed (e.g. Fe(SitBu3)2 decomposes at
temperatures below −20 °C). It has been shown that demetalla-
tion of half-sandwich complexes with liberation of the [Cp]−
anion takes place in the presence of strong reduction agents such
as sodium metal in hexamethylphosphoramide or potassium in
the presence of 18-crown-6 and naphthalene.17 We reported on
the successful decomplexation of cyclopentadienide from cym-
antrene, which is the analogous Mn complex of 4, by treatment
with potassium metal in the presence of naphthalene and
tetramethylethylenediamine.18
In order to prove the stability of the cyclopentadienyl dicarbo-
nyl ferrate anion we decided to examine additionally the thermal
behaviour of [K(18-crown-6)][5]. At first we synthesized the
ferrate [K(18-crown-6)][5] from 4 and potassium benzophenone
ketyl radical by a slightly modified literature procedure19
(Scheme 2). Single crystals of [K(18-crown-6)][5] were grown
from a 1 : 1 mixture of K[5] and 18-crown-6 in THF at room
temperature.
Upon heating of [K(18-crown-6)][5] to 120 °C no decompo-
sition was observed either in benzene nor in THF, we can there-
fore conclude that [K(18-crown-6)][5] is thermostable under the
conditions by which we observed [Cp]− liberation during the
reaction of 4 with Na[SitBu3].
We have reported that the silyl complex [CpFe(CO)2]SiMePh2
(6) can be obtained in moderate yield by the reaction of K[5]
with Ph2MeSiCl.5 However, when K[5] was treated with the
sterically hindered bromosilanes tBu2MeSiBr12 and tBu3SiBr11
as well as with supersilyl triflate tBu3SiO3SCF3,20 no substi-
tution reaction could be detected even after two months at room
temperature.
The inverse sandwich complex [(K(18-crown-6))2Cp][5]
(shown in Fig. 1; selected bond lengths and angles see figure
caption), crystallizes in the orthorhombic space group Pmc21
with a half molecule of the ferrate and a half molecule of
benzene in the asymmetric unit (Fig. 2). The inverse sandwich
cation in [(K(18-crown-6))2Cp][5] consists of two [K(18-crown-
6)] units and one Cp ring.21 The central cyclopentadienyl ring is
η5-coordinated to the two crown ether-encapsulated potassium
cations (Fig. 1). Therefore each K atom is connected to the six O
atoms of the crown ether and to five C atoms of the Cp ring. The
K–C distances range from 3.055(13) to 3.081(12) Å.22 The dis-
tances between the centre of gravity of the Cp ring and the two
K atoms are 2.841 and 2.849 Å, respectively.23 These distances
are comparable to those reported for other compounds containing
KCp units. The averaged C–C bond lengths of the Cp ligand of
[(K(18-crown-6))2Cp]+ is 1.398(19) Å. The structural parameters
of the ferrate anion in [(K(18-crown-6))2Cp][5] are related to
those found in [K(18-crown-6)][5] and the determined values
are typical for the anion [CpFe(CO)2]−.24
able silicon-containing products are tBu2RSiI11–13 and
14,15
tBu2RSiSiRtBu2
(R = Me, tBu), respectively, indicating that
a redox reaction took place. The identity of tBu2RSiI and tBu2R-
SiSiRtBu2 (R = Me, tBu), respectively, was confirmed by com-
parison with authentic samples. The 13C NMR spectra of both
reaction solutions showed that 1 had been completely consumed,
and new signals appeared which could be assigned to the dimer
[CpFe(CO)2]2 (4), Na[Cp], the corresponding disilane tBu2RSi-
SiRtBu2 (R = Me, tBu), and the related iodo silane tBu2RSiI
(R = Me, tBu). Due to the presence of paramagnetic species, the
signals which were observable in the 1H NMR spectra of
the reaction solutions are broadened. Moreover, by varying the
molar ratio of 1 and Na[SitBu3] from 1 : 1 to 1 : 5, the NMR
signals of the dimer 4 could not be detected any more while the
amount of paramagnetic components increased. The dimer 4 was
isolable in 42% yield by a 1 : 1 reaction of Na[SiMetBu2] and 1.
It is remarkable that treatment of 1 with 0.5 molar equivalents
of Na[SitBu3] already gave tBu3SiI and 4 that had been produced
in 1 : 1 reactions, but in contrast to equimolar reactions, no
disilane tBu3SiSitBu3 was thereby formed.
The reaction of 1 with [K(18-crown-6)][PtBu2BH3] which
represents a stronger and a sterically more demanding phospha-
nyl borohydride than [PPh2BH3]− gives 3 however along with
the ferrate [(K(18-crown-6))2Cp][5] as its minor product.
Obviously, a fragmentation reaction of the [CpFe(CO)2] moiety
with liberation of K[Cp] had additionally taken place. Thus the
question arises as to what are the factors leading to this
decomposition. Interestingly, a very similar degradation of the
[CpFe(CO)2] moiety takes place when 4 is treated with Na
[SitBu3]. We found that the reaction of 4 with Na[SitBu3] gives
the disilane tBu3SiSitBu3 and the ferrate [CpFe(CO)2]− as well
X-Ray quality crystals of the ferrate [K(18-crown-6)][5]
were grown from a THF solution of a 1 : 1 mixture of unsup-
ported [K][5] and 18-crown-6 at room temperature. Complex
Scheme 2 Reduction behaviour of [CpFe(CO)2]2 (4). (i) Potassium
benzophenone ketyl radical. (ii) M[SitBu3] (M = Na); M[PtBu2BH3]
(M = K).
6672 | Dalton Trans., 2012, 41, 6671–6676
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Fig. 2 Crystal packing diagram of [(K(18-crown-6))2Cp][4] together
with one benzene molecule .
Fig. 1 Molecular structure of [(K(18-crown-6))2Cp][5] in the solid
state. Selected bond lengths [Å] and bond angles [°]: K(1)–O(17) 2.840
(3), K(1)–O(11) 2.906(4), K(1)–O(14) 2.929(3), K(1)–O(20) 2.969(4),
K(1)–C(31) 3.064(13), K(1)–C(32) 3.073(8), K(1)–C(31′) 3.080(12),
K(1)–C(33) 3.081(7), K(2)–O(27) 2.853(3), K(2)–O(21) 2.892(5), K(2)–
O(24) 2.939(3), K(2)–O(30) 2.941(4), K(2)–C(31) 3.055(13), K(2)–C(32′)
3.073(8), K(2)–C(32) 3.078(8), K(2)–C(31′) 3.081(12), O(11)–C(12)
1.432(5), Fe(1)–C(2) 1.727(6), Fe(1)–C(1) 1.735(7), Fe(1)–C(41′) 2.089
(12), Fe(1)–C(43′) 2.104(7), Fe(1)–C(42′) 2.117(7), Fe(1)–C(41) 2.120
(14), Fe(1)–C(42) 2.122(11), Fe(1)–C(43) 2.131(10), C(1)–O(1) 1.187
(8), C(2)–O(2) 1.188(7), C(2)–Fe(1)–C(1) 89.5(3), O(1)–C(1)–Fe(1)
178.8(6), O(2)–C(2)–Fe(1) 178.9(5).
[K(18-crown-6)][5] crystallizes in the orthorhombic space group
Pna21 with one molecule in the asymmetric unit (Fig. 3). In con-
trast to the structure of [(K(18-crown-6))2Cp][5], the ferrate
[K(18-crown-6)][5] displays contact ion pairs in the solid state.
Each K atom is surrounded by one ferrate anion and one crown
ether molecule. In summary, the ferrate [K(18-crown-6)][5] fea-
tures one contact of a K centre with the carbonyl group and six
strong K–O interactions with the crown ether, which gives a
coordination number of seven for the K centre. It is remarkable
that the distance between the K atom and the C atom of the car-
bonyl ligand is shorter than that to the O atom. The distances
between the O atoms of the crown ether and the K centre are in
good agreement with those observed in other 18-crown-6 com-
plexes of related potassium salts.25 The K–Fe distance in [K(18-
crown-6)][5] (K–Fe 3.576 Å) is shorter than that found in the
potassium ferrate [(K(18-crown-6))2Cp][5] (K–Fe 7.722 Å).
The metrical parameters of [K(18-crown-6)][5] are listed in the
caption of Fig. 3.
Fig. 3 Molecular structure of [K(18-crown-6)][5] in the solid state.
The displacement ellipsoids are drawn at the 50% probability level.
Selected bond lengths [Å] and bond angles [°]: Fe(1)–C(1) 1.714(2),
Fe(1)–C(2) 1.719(2), Fe(1)–C(11) 2.086(2), Fe(1)–C(13) 2.104(3),
Fe(1)–C(15) 2.104(2), Fe(1)–C(14) 2.113(2), Fe(1)–C(12) 2.119(2),
Fe(1)–K(1) 3.5764(5), K(1)–O(24) 2.8523(17), K(1)–O(21) 2.8549(17),
K(1)–O(33) 2.8697(16), K(1)–O(36) 2.8819(17), K(1)–O(27) 2.8843
(15), K(1)–O(30) 2.9214(17), K(1)–C(2) 3.288(2), C(1)–O(1) 1.179(3),
C(2)–O(2) 1.184(3), C(1)–Fe(1)–C(2) 90.40(11), C(2)–Fe(1)–K(1) 66.33
(8), O(1)–C(1)–Fe(1) 178.6(2), O(2)–C(2)–Fe(1) 178.3(2), O(2)–C(2)–
K(1) 93.29(15).
X-Ray quality crystals of a new polymorph of 6 were grown
from a pentane solution at ambient temperature. The complex 6
crystallizes in two crystallographically independent molecules in
the asymmetric unit of the monoclinic space group P2/c from
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grown from the filtrate after 5 days at room temperature. Yield:
73 mg (76%). [K(18-crown-6)][5]: IR: ν˜ = 1727, 1874 cm−1
(CO). Found: C, 47.38; H, 6.24. C19H29FeKO8 requires C,
47.51; H, 6.08.
Reaction of 1 with Na[SiMetBu2]
A solution of Na[SiMetBu2] (A: 63 mg, 0.36 mmol; B: 162 mg,
0.92 mmol) in THF (A: 1 cm3, B: 3 cm3) was added to a cooled
solution (−78 °C) of 1 (A: 218 mg, 0.72 mmol; B: 278 mg,
0.92 mmol) in THF (5 cm3). After warming to room temperature
1
overnight, an NMR sample was taken. In the H NMR spectrum
of mixture A, resonances were observable which could be
assigned to tBu2MeSiI and 3. The signals of the disilane tBu2-
MeSiSiMetBu2 were additionally found in the 1H NMR and
29Si NMR spectrum of approach B (tBu2MeSiSiMetBu2:
δSi{1H} (49.7 MHz; C6D6; Me4Si) 7.1). Due to paramagnetic
components in mixture B, the signals in the NMR spectra are
broadened.
Work-up of 4 from mixture B: All volatiles were removed
in vacuo. The residue was extracted into pentane. After filtering,
4 was crystallized from pentane. Yield: 137 mg (42%).
Fig. 4 Solid-state structure of one of two crystallographic independent
molecules of 6 in the solid state. The displacement ellipsoids are drawn
at the 50% probability level. Selected bond lengths [Å] and bond angles
[°]: Fe(1)–C(2) 1.748(14), Fe(1)–C(3) 1.751(17), Fe(1)–C(35)
2.082(17), Fe(1)–C(31) 2.083(19), Fe(1)–C(33) 2.108(16), Fe(1)–C(34)
2.122(14), Fe(1)–C(32) 2.124(19), Fe(1)–Si(1) 2.326(5), Si(1)–C(11)
1.884(16), Si(1)–C(1) 1.888(15), Si(1)–C(21) 1.938(15), C(2)–O(2)
1.145(18), C(3)–O(3) 1.156(19), O(2)–C(2)–Fe(1) 178.4(16), O(3)–
C(3)–Fe(1) 176.6(17), C(2)–Fe(1)–C(3) 98.4(8).
Preparation of an authentic sample of tBu2MeSiI
pentane (Fig. 4; selected bond lengths and angles see caption of
Fig. 4).26 The structural parameters of this polymorph are com-
parable with those of 6 which was crystallized from benzene.5
To an ice-cooled solution of tBu2MeSiH (430 mg, 2.71 mmol)
in CH2Cl2 (8 cm3) was added dropwise a solution of I2 (720 mg,
2.84 mmol) in CH2Cl2 (8 cm3). The solution was warmed to
room temperature and stirred overnight. Volatiles were removed
at room temperature/70 torr to give a solid. tBu2MeSiI: δH
(250.1 MHz; C6D6; Me4Si) 0.48 (3 H, s, Me), 0.99 (18 H, s,
tBu). δC{1H} (62.9 MHz; C6D6; Me4Si) −2.3 (SiMe), 21.1
(CMe3), 28.1 (CMe3). δSi{1H} (49.7 MHz; C6D6; Me4Si) 40.7
(tBu2MeSiI). Found: C, 38.03; H, 7.45. C9H21ISi requires C,
37.53; H, 7.22.
Experimental section
General procedures
All experiments were carried out under dry argon or nitrogen
with strict exclusion of air and moisture using standard Schlenk
techniques or a glove box. The solvents (benzene, diethylether,
hexane, pentane, tetrahydrofuran) were distilled from sodium/
benzophenone prior to use. The NMR spectra were recorded on
a Bruker AM 250, a Bruker DPX 250, a Bruker Avance 300 and
a Bruker Avance 400 spectrometer. A JASCO FT/IR 4200 spec-
trometer was used for the IR spectra.
Reaction of 1 with Na[SitBu3]
A solution of Na[SitBu3] (A: 8 mg, 0.036 mmol; B: 23 mg,
0.104 mmol; C: 89 mg, 0.401 mmol) in THF (A: 0.1 cm3; B:
0.3 cm3; C: 1 cm3) was added to a solution of 1 (A: 20 mg,
0.066 mmol; B: 31 mg, 0.102 mmol; C: 24 mg, 0.079 mmol) in
Synthesis of [K(18-crown-6)][5]
1
THF (5 cm3) at room temperature. In the H NMR spectrum of
Potassium pieces (156 mg, 4 mmol) were added to a solution of
benzophenone (728 mg, 4 mmol) in THF (20 cm3) at room
temperature. Immediately the potassium benzophenone ketyl
radical was formed. Addition of an excess of 3 (759 mg,
2.2 mmol) to this solution resulted in disappearance of the
characteristic deep blue colour of the potassium benzophenone
ketyl radical. The reaction mixture was stirred for a further 12 h
at room temperature, during which an orange-red precipitate
formed. The orange-red solid was isolated by filtration. After
washing the precipitate with benzene (8 × 3 cm3), analytically
pure K[5] remained as an orange-red microcrystalline solid
(362 mg, 47% yield).
method A, resonances were observable which could be assigned
to tBu3SiI11 and 4. Additionally the signals of the disilane tBu3-
15
1
SiSitBu3 were found in the H NMR and in the 29Si NMR
spectrum of method B (tBu3SiSitBu3: δSi{1H} (49.7 MHz;
C6D6; Me4Si) 35.0). Due to paramagnetic components, no
signals were observable for method C, whereas the signals in the
NMR spectra of mixture B were broadened.
Formation of [(K(18-crown-6))2Cp][5]
When the reaction solution of
1 with [K(18-crown-6)]-
[PtBu2BH3] in 1 : 1 stoichiometry was left to stand for several
weeks, a few crystals of the composition [(K(18-crown-6))2Cp]-
[CpFe(CO)2] ([(K(18-crown-6))2Cp][5]) could be isolated. Due
to the low yield of these species, no further characterization
could be undertaken.
At room temperature 18-crown-6 (106 mg, 0.40 mmol) was
added to a slurry of unsupported K[5] (42 mg, 0.20 mmol) in
THF (10 cm3). The mixture was stirred for 1 h at room tempera-
ture. After filtering, single crystals of [K(18-crown-6)][5] were
6674 | Dalton Trans., 2012, 41, 6671–6676
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Table 1 Crystal data and experimental details for [(K(18-crown-6))2-
Cp][5] and [K(18-crown-6)][5]
CCDC reference numbers: CCDC 832033 ([(K(18-crown-
6))2Cp][5]), 832034 ([K(18-crown-6)][5]), 832031 (6).
[(K(18-crown-6))2Cp][5] [K(18-crown-6)][5]
Empirical formula
Formula weight
Temperature/K
Crystal size/mm3
Crystal system
Space group
a/Å
b/Å
c/Å
α/°
β/°
C42H64FeK2O14
926.98
173(2)
0.35 × 0.33 × 0.32
Orthorhombic
Pmc21
11.4260(13)
9.8741(8)
21.0967(16)
90
90
90
2380.2(4)
2
1.293
C19H29FeKO8
480.37
173(2)
0.28 × 0.26 × 0.23
Orthorhombic
Pna21
14.9080(5)
10.4189(4)
14.3622(6)
90
Conclusions
The dimeric iron carbonyl 4 and the iodosilanes tBu2RSiI were
obtained from the reaction of [CpFe(CO)2]I with the silanides
Na[SiRtBu2] (R = Me, tBu) in THF. In the case of 1 : 1
approaches the disilanes tBu2RSiSiRtBu2 (R = Me, tBu) were
additionally formed. Reduction of 4 with Na[SitBu3] gives the
disilanes tBu3SiSitBu3 along with the ferrate [(Na(18-crown-
6))2Cp][5]. The inverse sandwich complex [(K(18-crown-
6))2Cp][5] was isolated as a minor product from the reaction of
1 with [K(18-crown-6)][PtBu2BH3]. In addition we prepared
[K(18-crown-6)][5] and investigated its thermal behaviour. The
paramagnetic ferrate [K][5] was obtained from the reaction of 4
with the potassium benzophenone ketyl radical in THF at room
temperature. Subsequent treatment of the reaction mixture with
18-crown-6 yielded [K(18-crown-6)][5]. The solid-state struc-
ture of [K(18-crown-6)][5] features contact ion pairs of the com-
plexed potassium cation and the ferrate anion. It is remarkable
that the distance between the K cation and the C atom of the car-
bonyl ligand is shorter than that between the K atom and O atom
of the carbonyl group of ferrate anion.
90
90
γ/°
V/Å3
2230.81(15)
4
1.430
Z
Calcd. density/
Mg m−3
μ/mm−1
0.552
0.903
Index ranges
−13 ≤ h ≤ 13,
−10 ≤ k ≤ 11,
−25 ≤ l ≤22
3.57 to 25.57
8991
−16 ≤ h ≤ 18,
−12 ≤ k ≤ 12,
−17 ≤ l ≤ 17
3.36 to 25.67
26 783
θ-range/°
No. of reflns
Collected
No. of indep. reflns
Rint
4207
0.0355
4176
0.0770
0.972
R1 = 0.0267,
wR2 = 0.0554
R1 = 0.0311,
wR2 = 0.0565
0.172 and −0.162
Goodness-of-fit (F2) 1.037
R1, wR2 [I > 2σ(I)]
R1 = 0.0499,
wR2 = 0.1317
R1 = 0.0547,
wR2 = 0.1352
0.555 and −0.482
R1, wR2 indices
(all data)
Notes and references
Largest diff. peak
and hole/e Å−3
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A solution of Na[SitBu3] (124 mg, 0.56 mmol) in THF
(1.4 cm3) was added to a solution of 4 (89 mg, 0.25 mmol) and
18-crown-6 (119 mg, 0.45 mmol) in 5 cm3 benzene at ambient
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crown-6))2Cp][5]: IR: ν˜ = 1786, 1876 cm−1 (CO). m/z (ESI+)
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6676 | Dalton Trans., 2012, 41, 6671–6676
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