Reactions of K2[Fe(CO)3(PPh3)]: Reductive Sb-Sb coupling with Ph2SbCl to form trans-[Fe(CO) 3(PPh3)(Sb2Ph4)] and salt metathesis with Me3SbCl2 to yield trans-[Fe(CO)3(PPh 3)(SbMe3)]

Article abstract of DOI:10.1002/ejic.200400683

In contrast to the ferrate K₂[Fe(CO)₄], the phosphane-substituted ferrate K₂[Fe(CO)₃(PPh₃)] (1) reacts with the stibane derivative Ph₂SbCl by metal-assisted reductive Sb-Sb coupling to give the distibane complex trans-[Fe(CO) ₃(PPh₃)-(Sb₂Ph₄)] (3). The distibane ligand in 3 is terminally η¹-coordinated trans to the phosphane ligand. However, the stiborane derivative Me₃SbCl₂ reacts with 1 in a metathetical substitution reaction to form the monostibane complex trans-[Fe(CO)₃(PPh₃)(SbMe₃)] (5). Both compounds have been characterized by spectroscopic (IR, NMR, MS), analytical (C, H) and X-ray diffraction analyses. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.

Full text of DOI:10.1002/ejic.200400683

SHORT COMMUNICATION
Reactions of K2[Fe(CO)3(PPh3)]: Reductive Sb؊Sb Coupling with Ph2SbCl To
Form trans-[Fe(CO)3(PPh3)(Sb2Ph4)] and Salt Metathesis with Me3SbCl2 To
Yield trans-[Fe(CO)3(PPh3)(SbMe3)]
Ingo-Peter Lorenz,*[a] Stefan Rudolph,[a] Holger Piotrowski,[a] and Kurt Polborn[a]
Dedicated to Professor Dr. Hubert Schmidbaur on the occasion of his 70th birthday
Keywords: Antimony / Coupling reactions / Iron / Metathesis
In contrast to the ferrate K2[Fe(CO)4], the phosphane-substi-
tion reaction to form the monostibane complex trans-[Fe-
tuted ferrate K2[Fe(CO)3(PPh3)] (1) reacts with the stibane (CO)3(PPh3)(SbMe3)] (5). Both compounds have been charac-
derivative Ph2SbCl by metal-assisted reductive Sb−Sb coup-
ling to give the distibane complex trans-[Fe(CO)3(PPh3)-
(Sb2Ph4)] (3). The distibane ligand in 3 is terminally η1-coord-
inated trans to the phosphane ligand. However, the stiborane
derivative Me3SbCl2 reacts with 1 in a metathetical substitu-
terized by spectroscopic (IR, NMR, MS), analytical (C, H) and
X-ray diffraction analyses.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
Introduction
ample of a mixed bispentelane complex. We also report the
synthesis of a second mixed bispentelane complex by the
metathetical reaction of K2[Fe(CO)3(PPh3)] with Me3SbCl2.
Molecules containing transition metalϪphosphorus
frameworks are among the most frequently reported in co-
ordination and cluster chemistry. The most common ex-
amples show terminal metalϪPR3, -PR2- and -PR- modu-
lar systems, as well as their metal-bridging analogs.[1] Sim-
ple diphosphanes of the type R2XϪXϪPR2 (X ϭ CH2,
NH, O) considerably increase the potential variety and ap-
plicability of these compounds. While the analogous arsane
and diarsane homologues exist in great numbers with simi-
lar structural motifs, analogous examples of antimony and
bismuth species are much less common.[2,3] Weaker σ-donor
and π-acceptor interactions in antimony and bismuth com-
pounds may be a reason for this. Therefore, only monostib-
ane and methylidene-bridged distibane complexes (X ϭ
CH2) obtained by substitution reactions, as in the case of
phosphorus and arsenic compounds, have been structurally
characterized. Mixed bispentelane complexes with Sb par-
ticipation are not, to the best of our knowledge, known.
We report here the synthesis and structural characteriz-
ation of the distibane ligand Sb2Ph4 bound to iron; it is
produced by a metal-assisted reductive SbϪSb coupling re-
action in the presence of a coordinated phosphane ligand
(PPh3). Thus, we have successfully synthesized the first η1-
(Sb2Ph4)-coordinated complex as well as a very rare ex-
Results and Discussion
One synthetic route to pentelane complexes of iron(0) is
the catalytic reaction of Fe(CO)5 with the pentelanes ER3
(E ϭ P, As, Sb).[4Ϫ6] A similar route is the reaction of
Na2[Fe(CO)4] with one equivalent of Ph2ECl (E ϭ P, As),
which gives first the monosubstituted ferrate Na[Fe(CO)4-
(EPh2)] and then, upon reaction with a second equivalent
of Ph2ECl, the neutral dipentelane complex [Fe(CO)4-
(E2Ph4)] by EϪE coupling.[7] Thus, mixed phosphanylar-
sane complexes can be obtained. Attempts to form distib-
ane complexes of iron(0) have thus far been unsuccessful.
Similarly, the reaction of the phosphane-substituted ferrate
K2[Fe(CO)3(PPh3)] (1) with two equivalents of Ph2SbCl
proceeds with elimination of KCl to yield the first η1-coor-
dinated tetraphenyldistibane ligand by ferrate-assisted re-
ductive SbϪSb coupling of two Ph2SbCl molecules. The re-
sulting complex, trans-[Fe(CO)3(PPh3)(Sb2Ph4)] (3), was
structurally characterized by X-ray analysis.
The first mononuclear distibane complexes of the type
[M(CO)5(Sb2R4)] (M ϭ Cr, W; R ϭ CH3, C2H5, C6H5)
were synthesized by photochemically induced substitution
of M(CO)6 (in THF) with the intact distibanes, but were
only spectroscopically characterized.[8] The analogous di-
phosphane complexes, however, have already been synthe-
sized and structurally characterized by Vahrenkamp et
al.[9,10]
[a]
Ludwig-Maximilians University Munich, Department of
Chemistry,
Butenandtstraße 5Ϫ13, 81377 München, Germany
Fax: (internat.) ϩ49 89-2180-77867
E-mail: ipl@cup.uni-muenchen.de
82
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejic.200400683
Eur. J. Inorg. Chem. 2005, 82Ϫ85

Coupling and Salt Metathesis Reactions of K2[Fe(CO)3(PPh3)]
In our case, the distibane molecule is synthesized from
SHORT COMMUNICATION
Comparison of 3 and 5 is best achieved by single-crystal
monostibane derivatives bound to a metal by template-con- X-ray diffraction analysis.[12] Relevant bond lengths and
trol and is incorporated as an η1-bound ligand trans to the angles are tabulated in the legends of the corresponding fig-
PPh3 ligand (see a in Scheme 1). Attempts to obtain mixed ures. As expected, the Fe center is trigonal-bipyramidally
bispentelane complexes of the type R3EFe(CO)3EЈR3 were configured with the phosphane and distibane ligands in
previously unsuccessful because of symmetrization reac- trans-axial positions. The Fe1ϪP1 and Fe1ϪSb1 bond
˚
tions.
lengths are 2.188(2) and 2.457(1) A, respectively, and the
P1ϪFe1ϪSb1 bond angle of 177.99(6)° indicates a nearly
linear P1ϪFeϪSb1 arrangement (Figure 1). The three CO
ligands surround the central iron in a trigonal planar
grouping with the sum of angles at Fe(1) being exactly 360°.
As Figure 2 shows, the Sb2Ph4 ligand exists in the gauche
conformation, and differs by approximately 4° from the
˚
trans conformation. The Sb1ϪSb2 bond length of 2.828 A
is slightly shorter than that of the free stibane Sb2Ph4 (2.844
A).[13] The SbϪCPh bond lengths around the two Sb centers
˚
are quite different. The bonds to Sb1 are 2.130(6) and
˚
2.132(7) A, whereas bonds to Sb2 are distinctly longer
˚
[2.138(9) and 2.145(7) A], although both pairs are shorter
˚
than those in free tetraphenyldistibane (2.16 and 2.18 A).
Both Sb centers show a strongly distorted tetrahedral con-
figuration. The steric demand of the nonbonding Sb2 MO
Scheme 1. Synthesis of 3 and 5
The reductive SbϪSb coupling reaction of 1 is similar to
the Wurtz reaction and proceeds by two steps: electrophilic
attack on the iron(iiϪ) center of 1 by the first stibane
(Sb3ϩ), followed by elimination of KCl. The monoanionic
stibane complex 2, with the negative charge located mainly
on antimony, may be formed as an intermediate. As a re-
sult, the electrophilic attack of the second stibane occurs at
the coordinated antimony, and leads to the formation of a
neutral tetraphenyldistibane complex, 3, with one Fe(0) and
two SbII centers, and thus the formal redox reaction is com-
pleted.
The energy (1883 cmϪ1) of the single ν(CO) absorption
in the IR spectrum of 3 (EЈ symmetry) is similar to the
single ν(CO) absorption of the symmetrical species trans-
[Fe(CO)3(PPh3)2] (1886 cmϪ1).[11] The signal in the 31P{1H}
NMR spectrum of 3 is found at δ ϭ 86.4 ppm. The 1H and
13C{1H} NMR spectra show only the multiplets due to the
phenyl protons (δ ϭ 7.26Ϫ7.59 ppm) and phenyl-C atoms
(δ ϭ 126Ϫ131 ppm), in addition to one signal for the CO
ligand (δ ϭ 212 ppm).
Figure 1. Molecular structure of 3 in the solid state; selected bond
˚
lengths (A) and angles (°): Fe1ϪP1 2.188(2), Fe1ϪSb1 2.457(1),
Sb1ϪSb2 2.8282(7), Fe1ϪC1 1.752(7), Fe1ϪC2 1.758(7), Fe1ϪC3
1.776(8), Sb1ϪC22 2.130(6), Sb1ϪC28 2.132(7), Sb2ϪC40
2.138(9),
Sb2ϪC34
2.145(7);
P1ϪFe1ϪSb1
177.99(6),
Fe1ϪSb1ϪSb2 125.62(3), C1ϪFe1ϪC2 119.6(3), C1ϪFe1ϪC3
118.3(3), C2ϪFe1ϪC3 122.1(3), C22ϪSb1ϪC28 100.5(2),
C22ϪSb1ϪSb2 98.6(2), C22ϪSb1ϪFe1 113.7(2), C28ϪSb1ϪFe1
114.5(2), C28ϪSb1ϪSb2 100.0(2), C40ϪSb2ϪC34 98.4(3),
C40ϪSb2ϪSb1 94.9(2), C34ϪSb2ϪSb1 98.1(2)
If the ferrate 1 is treated with an excess of the stiborane
derivative Me3SbCl2 no coupling reaction occurs; instead,
a simple salt-metathesis reaction results in the formation of
the novel mixed-dipentelane complex trans-[Fe(CO)3-
(PPh3)(SbMe3)] (5). As in the case of 3, the formation of 5
can also occur via the intermediate 4, which is formed by an
electrophilic attack of Me3SbClϩ on the nucleophilic ferrate
dianion (Scheme 1b).
The spectroscopic data of 5 (IR: ν(CO) ϭ 1877 cmϪ1
;
31P{1H} NMR: δ ϭ 85.5 ppm) are similar to those of 3,
except for the methyl-group signals in the NMR spectra (1H
NMR: δ ϭ 1.31 ppm; 13C{1H} NMR: δ ϭ 40.1 ppm).
Figure 2. Conformation of the Sb2Ph4 ligand in 3 [Newman projec-
tion along the Sb1ϪSb2 axis with dihedral angles (°)]
Eur. J. Inorg. Chem. 2005, 82Ϫ85
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
83

I.-P. Lorenz, S. Rudolph, H. Piotrowski, K. Polborn
SHORT COMMUNICATION
leads to an 11Ϫ14° reduction of the bond angles compared and distibane formation, as well as FeϪSb bond formation,
to those of coordinated Sb1. In the same fashion, the Fe- are not possible. When the monoanionic metalates
(CO)3(PPh3) group bound to Sb1 forces a greater defor- [CpM(CO)n]Ϫ (M ϭ Fe, n ϭ 2; M ϭ Mo, W, n ϭ 3) are
mation from an ideal tetrahedral configuration about Sb1, reacted with Me2SbBr, for example, a simple salt-metathesis
with the Fe1ϪSb1ϪSb2 angle of 126° differing most of all. reaction to form the metallostibanes [{Cp(CO)nM}SbMe2]
is observed.[14] An SbϪSb coupling reaction similar to the
Wurtz reaction was recently reported in the reaction of
Ph2SbI with the metals Sm or Y in THF.[15] Further investi-
gations with respect to the general application of this simple
and elegant synthesis using other substituted phosphanes
(PR3 where R ϶ Ph) or coupling different pentelanes [e.g.
SbϪE (E ϭ P, As)] are in progress.
Experimental Section
All operations were carried out under an Argon atmosphere with
complete exclusion of oxygen and moisture (Schlenk techniques).
Solvents were dried and then saturated with argon. The following
instruments were used for the spectroscopic and analytical meas-
urements: IR: Nicolet 520 FT-IR spectrometer. 31P NMR: Jeol 6SX
Figure 3. Molecular structure of 5 in the solid state; selected bond
˚
lengths (A) and angles (°): Fe1ϪP1 2.199(1), Fe1ϪSb1 2.463(6),
Fe1ϪC1 1.769(5), Fe1ϪC2 1.778(5), Fe1ϪC3 1.778(4), Sb1ϪC4
2.094(5), Sb1ϪC5 2.118(5), Sb1ϪC6 2.114(5), P1ϪCPh 1.835(4);
P1ϪFe1ϪSb1 177.56(4), C1ϪFe1ϪC2 121.8(2), C1ϪFe1ϪC3
119.5(2), C2ϪFe1ϪC3 118.4(2), C4ϪSb1ϪFe1 116.62(15),
C5ϪSb1ϪFe1 117.54(15), C6ϪSb1ϪFe1 118.46(16), CPhϪP1ϪFe1
ca. 115.7, CPhϪFe1ϪC5 ca. 102.6
Table 1. X-ray structure analysis of 3 and 5[12]
3
5
Empirical formula
Molecular weight
C45H35FeO3Sb2
1038.98
C24H24FeO3PSb
569.024
(g molϪ1
)
Crystal size (mm)
Crystal color, habit
Crystal system
Space group
0.37 ϫ 0.33 ϫ 0.10
yellow-brown
monoclinic
P21/c (No. 14)
12.999(2)
10.462(2)
32.805(4)
90
98.274(2)
90
4412.5(12)
4
0.34 ϫ 0.23 ϫ 0.14
The molecular structure of 5 (Figure 3) is similar to that
of 3; the analogous bond lengths and angles at the central
iron are practically identical. The Newman projection of 5
shows the almost perfectly staggered conformation of the
Me, CO, and Ph substituents along the Sb1ϪFe1ϪP1 axis
(Figure 4).
red-brown prism
orthorhombic
Pbca
10.897(1)
16.6396(1)
26.7645(2)
90
˚
a (A)
˚
b (A)
˚
c (A)
α (°)
β (°)
γ (°)
90
90
3
˚
Volume (A )
4853.30(6)
8
1.558
Z
Density calcd. (g cmϪ3
Absorption coefficient
)
1.564
1.736
1.798
(mmϪ1
)
F(000)
2056
Index ranges
Ϫ14 Յ h Յ 0
Ϫ11 Յ k Յ 0
Ϫ37 Յ l Յ 37
2.51Ϫ23.98
7221
Ϫ14 Յ h Յ 11
Ϫ21 Յ k Յ 21
Ϫ34 Յ l Յ 34
1.52Ϫ27.49
70393
θ Range (°)
Reflections collected
Figure 4. Newman projection of 5 along the Sb1ϪFe1ϪP1 axis
Our new reductive SbϪSb coupling reaction of two mol-
Independent reflections 6885
5563
3959
274/0
0.0747/0.1418
0.0402/0.1004
1.173
Ϫ1.184/1.404
200(2)
Observed reflections
Parameter/restraints
R1/wR2 (all data)
5081
525/42
0.0745/0.1077
0.0467/0.0928
1.133
0.7242/0.9995
293(2)
ecules of Ph2SbCl to give the η1-ligand Sb2Ph4 in 3 is ex- R1/wR2 (final)
plained by the presence of [Fe(CO)3(PPh3)]2Ϫ (1) (as suit-
GOOF
3
˚
Min./max. ρe (e A )
Temperature (K)
Diffractometer
able reducing agent) and by the activating and at the same
time stabilizing effect of the complex fragment
Fe(CO)3(PPh3). The trans-directing influence of PPh3 may
also play a positive role in the formation of the mixed di-
pentelane complex 3. An analogous effect is also found in
the reaction of 1 with the stiborane Me3SbCl2 to give 5.
However, in the case of the nonsubstituted ferrate
Na2[Fe(CO)4], the corresponding SbϪSb coupling reaction
ENRAF
Nonius
Kappa CCD
Nonius CAD-4
Radiation
Scan type
Solution
Mo-Kα, λ ϭ 0.71073 Mo-Kα, λ ϭ 0.71073
ω-scan
SHELXS 86
area detection
SIR 97,
direct methods
SHELXL-97
Refinement
SHELXL-93
84
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 82Ϫ85

Coupling and Salt Metathesis Reactions of K2[Fe(CO)3(PPh3)]
SHORT COMMUNICATION
N. R. Champness, W. Levason, Coord. Chem. Rev. 1994, 133,
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185Ϫ189.
CCDC-246697 (for 3) and -246325 (for 5) contain the sup-
plementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data request/
cif.
G. Becker, H. Freudenkamp, C. Witthauer, Z. Anorg. Allg.
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Organikum, VEB Deutscher Verlag der Wissenschaften,
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[2]
[3]
270 (85% H3PO4 as standard). X-ray analysis: ENRAF-Nonius
CAD 4-diffractometer and Nonius Kappa CCD-diffractometer. El-
emental analysis: Elementar vario EL (W. C. Heraeus). Melting
Print: Büchi-510 (m.p. were not corrected).
[4]
[5]
Synthesis of 3: K2[Fe(CO)3(PPh3)] (1; 124 mg, 0.259 mmol) and
Ph2SbCl (353 mg, 0.518 mmol) were dissolved in 10 mL of THF,
upon which the solution immediately turned deep red. After stir-
ring for 2 h and filtering, the solvent was distilled off in vacuo to
yield a viscous brownish oil. Repeated recrystallization from
CH2Cl2/n-hexane resulted in a microcrystalline solid, which was
dried in vacuo. Yield: 154 mg (63%), orange brown crystals, m.p.
[6]
[7]
[8]
137 °C. IR (KBr): ν(CO) ϭ 1883 cmϪ1 13C NMR ([D6]acetone):
.
[9]
δ ϭ 126Ϫ131 (Ph), 212 (CO) ppm. 31P{1H} NMR: δ ϭ 86.4 ppm.
[10]
[11]
[12]
C46H37FeO3PSb2 (954.09): calcd. C 57.9, H 3.9; found C 57.9, H
3.8.
Synthesis of 5: K2[Fe(CO)3(PPh3)] (1; 275 mg, 0.573 mmol) was dis-
solved in 20 mL of THF containing Me3SbCl2 (136 mg,
0.573 mmol). The color of the solution changed to red, and a fine,
light-colored precipitate of KCl formed. After stirring for 2 h and
careful decantation, the solvent was distilled off in vacuo. The red-
brown residue was recrystallized several times to give analytically
pure 5. Yield: 179 mg (55%), red-brown crystals, m.p. 121 °C. IR
(KBr): ν(CO) ϭ 1877 cmϪ1. 1H NMR ([D6]acetone): δ ϭ 1.31 (s, 9
H, Me), 7.22Ϫ7.63 (m, 15 H, Ph) ppm. 13C{1H} NMR ([D6]ace-
tone): δ ϭ 40.1 (s, Me), 126Ϫ131 (m, Ph), 209 (s, CO) ppm.
31P{1H} NMR ([D6]acetone): δ ϭ 85.5 ppm. C24H24FeO3PSb
(567.99): calcd. C 50.7, H 4.3; found C 51.6, H 3.7.
[13]
[14]
[15]
[16]
[17]
[18]
J. E. Ellis, Y.-S. Chen, Organometallics 1989, 8, 1350Ϫ1361.
M. Nunn, D. B. Sowerby, D. M. Wesolek, J. Organomet. Chem.
1983, 251, C45ϪC46.
[1]
C. A. McAuliffe, W. Levason, Phosphine, Arsine and Stibine
Complexes of the Transition Elements, Elsevier 1979.
Received August 6, 2004
Eur. J. Inorg. Chem. 2005, 82Ϫ85
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
85