Bimetallic zwitterionic complexes with an ambident stanna-closo- dodecaborate ligand: [1-{M(CO)5}-2,7,8-(μ-H)3- {Fe(triphos)}·SnB11H11] (M = Cr, Mo, W)

Article abstract of DOI:10.1021/om060328m

Starting from FeBr₂ the zwitterionic stannaborate complex [1-{Fe(MeCN)₂(triphos)}-SnB₁₁H₁₁] (1) could be obtained in a straightforward one-pot synthesis. Via a facile η¹(Sn) to η³(BH) rearrangement reaction 1 can be converted into [2,7,8-(μ-H)₃-{Fe(triphos)}-SnB₁₁H ₁₁] (2). The nucleophilicity of the tin atom in compound 2 is strongly reduced compared to the dianionic parent stannaborate cluster [SnB ₁₁H₁₁]^2-. Methylation at the tin atom using standard methods is not feasible. Transition metal fragments can be coordinated at the tin atom of 2 if reactive species such as M(CO)₅(THF) (M = Cr, Mo, W) are employed. Reaction of these fragments with 2 yields the bimetallic zwitterions [1-{M(CO)₅}-2,7,8-(μ-H)₃-{Fe(triphos)}- SnB₁₁H₁₁] (M = Cr, Mo, W) (3,4,5), which contain an ambident stannaborate moiety. All new compounds have been characterized using ¹H, ¹¹B, ¹³C, ³¹P, and ¹¹⁹Sn NMR spectroscopy as well as ³¹P and ¹¹⁹Sn MAS NMR experiments. Single-crystal X-ray diffraction analyses have been carried out for all novel compounds.

Full text of DOI:10.1021/om060328m

3904
Organometallics 2006, 25, 3904-3911
Bimetallic Zwitterionic Complexes with an Ambident
Stanna-closo-dodecaborate Ligand:
[1-{M(CO)5}-2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11] (M ) Cr, Mo, W)
Torben Ga¨dt, Klaus Eichele, and Lars Wesemann*
Institut fu¨r Anorganische Chemie der UniVersita¨t Tu¨bingen, Auf der Morgenstelle 18,
Tu¨bingen, D-72076, Germany
ReceiVed April 13, 2006
Starting from FeBr2 the zwitterionic stannaborate complex [1-{Fe(MeCN)2(triphos)}-SnB11H11] (1)
could be obtained in a straightforward one-pot synthesis. Via a facile η1(Sn) to η3(BH) rearrangement
reaction 1 can be converted into [2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11] (2). The nucleophilicity of the
tin atom in compound 2 is strongly reduced compared to the dianionic parent stannaborate cluster
[SnB11H11]2-. Methylation at the tin atom using standard methods is not feasible. Transition metal fragments
can be coordinated at the tin atom of 2 if reactive species such as M(CO)5(THF) (M ) Cr, Mo, W) are
employed. Reaction of these fragments with 2 yields the bimetallic zwitterions [1-{M(CO)5}-2,7,8-(µ-
H)3-{Fe(triphos)}-SnB11H11] (M ) Cr, Mo, W) (3, 4, 5), which contain an ambident stannaborate moiety.
1
All new compounds have been characterized using H, 11B, 13C, 31P, and 119Sn NMR spectroscopy as
well as 31P and 119Sn MAS NMR experiments. Single-crystal X-ray diffraction analyses have been carried
out for all novel compounds.
pentaanionic square planar gold complex [Au(SnB11H11)4]5-
from AuCl3 and [Bu3MeN]2[SnB11H11] is a striking example.6
As a general trend, the heteroborate coordinates at late transition
metal fragments via tin-metal bonds. The remarkable variety
of the tin-metal coordination modes with different gold
fragments is exemplified by the µ2 coordination in the dimeric
complex [Au2(SnB11H11)2(PPh3)2]2-, the µ3 coordination in the
triangular complex [{(Et3P)Au(SnB11H11)}3]3-, and µ4 coordina-
tion in [{(dppm)Au2(SnB11H11)2}2]4-.7 More recently, it was
shown that the stannaborate ligand employs η3(BH) coordination
at ruthenium fragments and can behave as an ambident ligand
employing both η3(BH) and η1(Sn) coordination in ruthenium
compounds such as [{(PPh3)2Ru(SnB11H11)}2].8 Furthermore,
examples have been reported for η1(Sn) to η3(BH) rearrange-
ment reactions of the heteroborate, including one example for
a reversible η1(Sn) to η3(BH) rearrangement between the
complexes [Ru(2,7,8-(µ-H)3-exo-SnB11H11)(SnB11H11)(dppb)]2-
Introduction
There is ongoing interest in the chemistry of monocarba-
dodecaborate [CB11H12]- and its derivatives, which have been
shown to behave as weakly coordinating anions1 because of
their very low basicity, polarizability, and high chemical
stability. The growing interest in substituted derivatives of closo-
boranes and carbaboranes is connected with the search for the
least-coordinating derivative of [CB11H12]- 2 and has also
stimulated work directed toward the understanding of substituent
effects in this class of compounds.3
The monostannadodecaborate [SnB11H11]2- is a heavier
homologue of the deprotonated borate [CB11H11]2-. The nu-
cleophilicity of the stannaborate at the tin atom has been
described by the group of Todd, who showed that [SnB11H11]2-
can be methylated with methyliodide to yield [1-CH3-SnB11H11]-.4
This is in contrast to the electrophilicity of stannacarbaboranes
such as [2,3-Me-1-Sn-2,3-C2B9H9] and derivatives of 1-Sn-2,3-
C2B4H6 and 1-Sn-2,4-C2B4H6, which are readily coordinated
by Lewis bases such as 2,2′-bipyridine at the tin vertex.5 On
the other hand, stanna-closo-dodecaborate [SnB11H11]2- does
not show electrophilicity but reacts as a nucleophile with alkyl
halides and transition metal halides. The synthesis of the
and [Ru(SnB11H11)2(dppb)(MeCN)2]2- 9
.
Here we present the synthesis of novel stannaborate iron
compounds containing the triphos ligand as well as the synthesis
and detailed characterization of bimetallic zwitterionic com-
plexes featuring an ambident stanna-closo-dodecaborate ligand.
Furthermore, the influence of the exo-polyhedral iron fragment
on the coordinated stannaborate moiety is discussed.
* To whom correspondence should be addressed. E-mail:
lars.wesemann@uni-tuebingen.de.
(1) For recent reviews see: (a) Krossing, I.; Raabe, I. Angew. Chem.
2004, 116, 2116-2142. (b) Reed, C. A. Chem. Commun. 2005, 1669-
1677.
(5) (a) Jutzi, P.; Galow, P.; Abu-Orabi, S.; Arif, A. M.; Cowley, A. H.;
Norman, N. C. Organometallics 1987, 6, 1024-1031. (b) Hosmane, N. S.;
de Meester, P.; Maldar, N. N.; Potts, S. B.; Chu, S. S. C.; Herber, R. H.
Organometallics 1986, 5, 772-778. (c) Hosmane, N. S.; Jia, L.; Zhang,
H.; Maguire, J. A. Organometallics 1994, 13, 1411-1423.
(6) Marx, T.; Mosel, B.; Pantenburg, I.; Hagen, S.; Schulze, H.;
Wesemann, L. Chem. Eur. J. 2003, 9, 4472-4478.
(7) (a) Hagen, S.; Pantenburg, I.; Weigend, F.; Wickleder, C.; Wesemann,
L. Angew. Chem. 2003, 115, 1539-1543; Angew. Chem., Int. Ed. 2003,
42, 1501-1505. (b) Hagen, S.; Wesemann, L.; Pantenburg, I. Chem.
Commun. 2005, 1013-1015.
(8) Ga¨dt, T.; Grau, B.; Eichele, K.; Pantenburg, I.; Wesemann, L. Chem.
Eur. J. 2006, 12, 1036-1045.
(9) Ga¨dt, T.; Wesemann, L. Dalton Trans. 2006, 328-329.
(2) Stasko, D.; Reed, C. A. J. Am. Chem. Soc. 2002, 124, 1148-1149.
(3) See for example: (a) Teixidor, F.; Barbera`, G.; Vaca, A.; Kiveka¨s,
R.; Sillanpa¨a¨, R.; Oliva, J.; Vin˜as, C. J. Am. Chem. Soc. 2005, 127, 10158-
10159. (b) McKee, M. L. Inorg. Chem. 2002, 41, 1299-1305. (c) Zharov,
I.; Weng, T. C.; Orendt, A. M.; Barich, D. H.; Penner-Hahn, J.; Grant, D.
M.; Havlas, Z.; Michl, J. J. Am. Chem. Soc. 2004, 126, 12033-12046. (d)
Clarke, A. J.; Ingleson, M. J.; Kociok-Ko¨hn, G.; Mahon, M. F.; Patmore,
N. J.; Rourke, J. P.; Ruggiero, G. D.; Weller, A. S. J. Am. Chem. Soc.
2004, 126, 1503-1517. (d) Saxena, A. K.; Maguire, J. A.; Hosmane, N. S.
Chem. ReV. 1997, 97, 2421-2461.
(4) Chapman, R. W.; Kester, J. G.; Folting, K.; Streib, W. E.; Todd, L.
J. Inorg. Chem. 1992, 31, 979-983.
10.1021/om060328m CCC: $33.50 © 2006 American Chemical Society
Publication on Web 06/29/2006

Bimetallic Zwitterionic Complexes
Scheme 1. One-Pot Synthesis of
Organometallics, Vol. 25, No. 16, 2006 3905
[1-{Fe(MeCN)2(triphos)}-SnB11H11] (1) from FeBr2
Scheme 2. Synthesis of
[2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11] (2) via an η1(Sn) to
η3(B-H) Rearrangement
Figure 1. Molecular structure of [1-{Fe(MeCN)2(triphos)}-
SnB11H11], 1. The hydrogen atoms and the phenyl rings except the
ipso-carbon atoms have been omitted for clarity. Selected bond
distances [Å] and angles [deg]:C(1)-N(1) 1.132(7), C(3)-N(2)
1.134(7), B(2)-Sn 2.310(6), B(3)-Sn 2.327(5), B(4)-Sn 2.329(6),
B(5)-Sn 2.343(6), B(6)-Sn 2.329(6), N(1)-Fe 1.953(4), N(2)-
Fe 1.942(4), Fe-P(1) 2.264(1), Fe-P(2) 2.249(1), Fe-P(3) 2.276(1),
Fe-Sn 2.587(1), N(2)-Fe-N(1) 83.63(17), N(1)-Fe-P(1)
96.96(13), N(1)-Fe-P(2) 171.43(13), N(1)-Fe-P(3) 93.43(13),
P(2)-Fe-P(1) 90.26(5), P(2)-Fe-P(3) 91.67(5), P(1)-Fe-P(3)
86.11(5), N(1)-Fe-Sn 80.60(12), N(2)-Fe-Sn 79.85(11), P(1)-
Fe-Sn 172.96(5), P(2)-Fe-Sn 91.70(4), P(3)-Fe-Sn 100.59(4).
Results and Discussion
Synthesis. The successful synthesis of the zwitterionic
ruthenium stannaborate complex [1-{Ru(MeCN)2(triphos)}-
SnB11H11] motivated us to synthesize the corresponding iron
analogue.10 The reaction is carried out as a one-pot synthesis
using FeBr2 as starting material, which is reacted with triphos
in acetonitrile. Subsequent addition of an acetonitrile solution
of [Bu3MeN]2[SnB11H11] leads to the formation of a purple
precipitate, which can easily be isolated by filtration. The purple
zwitterionic compound [1-{Fe(MeCN)2(triphos)}-SnB11H11] (1)
is insoluble in common solvents.
A number of examples for η1(Sn) to η3(BH) rearrangement
reactions under the loss of acetonitrile ligands in ruthenium
complexes of stannaborate have recently been described.9,10 It
was thus of interest to find out about the feasibilty of such
rearrangements for iron complexes. In fact, the rearrangement
proceeds smoothly when a suspension of [1-{Fe(MeCN)2-
(triphos)}-SnB11H11] in THF is heated for 3 h, during which
time the purple solid dissolves under the formation of a dark
violet solution of [2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11] (2),
which can be isolated by evaporation of the solvent. The
obtained violet solid is stable toward air.
Now that we had an air-stable compound at hand that can be
prepared on a multigram scale in a convenient way, we were
interested in the properties of the stannaborate moiety. The
objective was to compare the nucleophilicity of the η3(B-H-
Fe)-coordinated stannaborate with the parent heteroborate
[SnB11H11]2-. It is known from Todd’s work on the synthesis
of [SnB11H11]2- that the stannaborate behaves as a nucleophile
and can easily be methylated at the tin atom at room temperature
using MeI.4 Thus we attempted the methylation of the tin atom
of the η3(B-H-Fe)-coordinated stannaborate using an excess
of methyliodide in THF. No reaction occurs at room tempera-
ture, as monitored by 31P NMR and 11B NMR spectroscopy.
To probe whether the tin atom would still coordinate to
transition metal fragments, we decided to react metal fragments
with a labile ligand such as the readily available series of
M(CO)5(THF) (M ) Cr, Mo, W) with 2. As monitored by IR
spectroscopy, addition of 2 to a freshly prepared THF solution
of M(CO)5(THF) (M ) Cr, Mo, W) yields the bimetallic
complexes [1-{M(CO)5}-2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11]
(M ) Cr, Mo, W) (3, 4, 5) within minutes. Evaporation of the
solvent and subsequent recrystallization from THF/hexane or
CH2Cl2/hexane gives dark red crystalline materials in good
yields.
Solid-State Structure. To elucidate the solid-state structure
of the obtained compounds, we carried out single-crystal X-ray
diffraction analyses. Carefully layering a solution of FeBr2 and
triphos in acetonitrile with an acetonitrile solution of [Bu3MeN]2-
[SnB11H11] leads to the formation of single crystalline material
within 2 days. Remarkably, the structure contains four aceto-
nitrile solvent molecules in addition to the two coordinated
acetonitrile ligands. The molecular structure of compound
[1-{Fe(MeCN)2(triphos)}-SnB11H11] (1) is depicted in Figure
1 together with selected bond lengths and angles. The iron-tin
bond length amounts to Fe-Sn 2.587(1) Å, which is within
the range of known tin-iron separations of 2.41-2.77 Å11 and
somewhat longer than the Fe-Sn bond in [NBu4][CpFe(CO)2-
(SnB11H11)], with a value of 2.479 Å.12a All three phosphorus-
iron separations are similar, ranging from Fe-P(2) 2.249(1) Å
to Fe-P(3) 2.276(1) Å. Interestingly, the iron-phosphorus bond
in trans position to the stannaborate ligand of Fe-P(1) 2.264(1)
Å is not elongated due to the trans influence of the stannaborate
ligand as in the corresponding ruthenium complex.10 The tin-
boron distances lie in the range 2.310-2.342 Å, and the average
separation is 2.328 Å, which is in accord with previously
reported distances ([CpFe(CO)2(SnB11H11)]-: 2.289-2.342 Å,12a
[(dppp)Pt(SnB11H11)2]2-: 2.285-2.322 Å,12b [Au(SnB11H11)4]5-
2.293-2.321 Å 6).
:
Dark violet crystals suitable for X-ray diffraction analysis of
2 can be grown by layering a dichloromethane solution with
hexane. The molecular structure is depicted in Figure 2 and
(11) Holt, M.; Wilson, W.; Nelson, J. H. Chem. ReV. 1989, 89, 11-49.
(12) (a) Wesemann, L.; Marx, T.; Englert, U.; Ruck, M. Eur. J. Inorg.
Chem. 1999, 1563-1566. (b) Wesemann, L.; Hagen, S.; Marx, T.;
Pantenburg, I.; Nobis, M.; Driessen-Ho¨lscher, B. Eur. J. Inorg. Chem. 2002,
2261-2265.
(10) Ga¨dt, T.; Eichele, K.; Wesemann, L. Dalton Trans. 2006, 2706-
2713.

3906 Organometallics, Vol. 25, No. 16, 2006
Ga¨dt et al.
Scheme 3. The Reduced Nucleophilicity of the η3(B-H-Fe)-Coordinated Stannaborate Prevents Methylation
Scheme 4. Synthesis of Bimetallic, Zwitterionic Compounds
are similar for all three compounds and are in the range 2.230-
2.309 Å for the Fe-B separations and 2.200-2.238 Å for the
Fe-P distances. These values are similar to those of 2 and
indicate that the bonding situation around the iron fragment is
not affected significantly by the tin coordination. The B(2)-
Sn separation is smaller than the other four B(3-6)-Sn
separations for all three compounds, and the average distances
from the tin atom to the boron atoms of the first B5-belt are
2.341 Å (3), 2.357 Å (4), and 2.347 Å (5). These values lie
between those of the exclusively η3(B-H-Fe)- and η1(Sn-
Fe)-coordinated stannaborate moieties and thus demonstrate that
the cluster geometry is significantly affected by both coordina-
tion forms: η1(Sn) coordination reduces the separation of the
tin atom to the first B5-belt compared to exclusive η3(B-H)
coordination. The metal-tin bond lengths in compounds 3-5
are similar to those in the octahedral tin closo-clusters
with [SnB11H11]2- as Ambident Ligand
Scheme 5. The Two Isomers of 2 Present in the Solid State
with Occupancies of 95.7:4.3 According to the Structure
Refinement
[{(OC)5M}6Sn6]2- 13
. Finally, the carbon metal distances in trans
position to the stannaborate moiety are slightly smaller than
those in cis position, as one would expect.
IR Spectroscopy. The infrared spectra of the compounds
containing M(CO)5 fragments exhibit the characteristic pattern
for pentacarbonyl complexes of approximate C4V symmetry
consisting of four bands, namely, A1(2), B1, E, and A1(1). The
(1)
A1 vibration is mainly localized in the CO ligand in trans
establishes the η3(B-H-Fe) coordination of the stannaborate
moiety. A special feature of the crystal structure is the disorder
of the heteroborate which is coordinated at the iron fragment
in two different modes with occupancies of 95.7:4.3. The major
isomer employs one B-H vertex from the first B5-belt and two
B-H vertexes from the second B5-belt for the η3(B-H-Fe)
coordination, while the minor isomer uses two B-H vertexes
from the first B5-belt and one vertex from the second B5-belt
(Scheme 5). Recently reported stannaborate ruthenium com-
pounds exhibit analogous disorder of the heteroborate cluster.8-10
The three boron-iron separations in the major isomer are similar
(B-Fe: 2.227-2.267 Å), which is also true for the iron-
phosphorus separations (Figure 2), which are somewhat shorter
than in 1. Compared to 1 the tin-boron distances from the first
B5-belt to the tin atom are elongated and lie in the range 2.360-
2.423 Å with an average separation of 2.401 Å, the Sn-B(2)
2.360(3) Å distance being smaller than the other four tin-boron
separations from the first B5-belt.
Figure 2. Molecular structure of [2,7,8-(µ-H)3-{Fe(triphos)}-
SnB11H11], 2. Only the major isomer is shown. The hydrogen atoms
and the phenyl rings except the ipso-carbon atoms have been
omitted for clarity. Selected bond distances [Å] and angles [deg]:
Sn-B(2) 2.360(3), Sn-B(3) 2.419(3), Sn-B(4) 2.400(3), Sn-B(5)
2.403(3), Sn-B(6) 2.423(3), B(2)-Fe 2.267(3), B(7)-Fe 2.271(3),
B(8)-Fe 2.237(3), Fe-P(1) 2.219(1), Fe-P(2) 2.200(1), Fe-P(3)
2.220(1), Fe-H(2) 1.79(3), Fe-H(7) 1.80(3), Fe-H(8) 1.78(3),
P(2)-Fe-P(1) 90.97(2), P(2)-Fe-P(3) 90.21(2), P(1)-Fe-P(3)
90.73(2), P(1)-Fe-H(2) 174.0(10), P(2)-Fe-H(2) 83.1(10), P(3)-
Fe-H(2) 89.1(10).
The molecular structure of [1-{Cr(CO)5}-2,7,8-(µ-H)3-
{Fe(triphos)}-SnB11H11] (3) is depicted in Figure 3, and
structural parameters of 3, 4, and 5 are given in Table 1. Again,
the η3(B-H-Fe) coordination is clearly established, but there
is no disorder of the η3(B-H-Fe)-coordinated moiety in the
crystal structures of 3, 4, and 5. The Fe-B and Fe-P distances

Bimetallic Zwitterionic Complexes
Organometallics, Vol. 25, No. 16, 2006 3907
ity of the compound in common solvents. Fortunately, the
solubility of the other zwitterionic compounds was large enough
to carry out multinuclear NMR measurements in solution. The
η3(B-H-Fe) coordination of the stannaborate moiety of 2 is
1
corroborated by the H, 11B, and 119Sn NMR spectra, which
closely resemble the respective spectra of the analogous
ruthenium complex.10 All characteric features are present,
1
namely, the occurrence of broad hydridic H signals in the
1H{11B} NMR spectrum at -9.8 and -10.3 ppm and the
presence of five signals in the 11B NMR spectrum, reflecting
the reduced local symmetry, as well as the low-frequency shift
of the 119Sn NMR signal, which appears at -623 ppm compared
to free stannaborate (-546 ppm). Interestingly, the 31P{1H}
NMR spectrum reveals a broad singlet at 54.2 ppm at room
temperature, which implies equivalent phosphorus atoms (Figure
4). However, upon cooling, new signals appear, giving rise to
an A2B spin system with a coupling constant of 2J(P,P) ) 55.7
Hz. Since there is no line-broadening involved in the appearance
of new signals, one can exclude coalescence, and therefore the
singlet at room temperature is not caused by a dynamic process
that would render the three phosphorus atoms equivalent but
by accidental isochrony.
Figure 3. Molecular structure of [1-{Cr(CO)5}-2,7,8-(µ-H)3-
{Fe(triphos)}-SnB11H11], 3. The hydrogen atoms and the phenyl
rings except the ipso-carbon atoms have been omitted for clarity.
Table 1. Structural Parameters of 3, 4, and 5
3 (M ) Cr)
4 (M ) Mo)
2.735(1)
5 (M ) W)
The pentacarbonyl derivatives exhibit similar H, 11B{1H},
1
and 31P{1H} NMR spectra, which are in close analogy to those
of 2. There is no accidental isochrony present at room
temperature in the 31P{1H} NMR spectra, which show signals
due to A2B spin systems around 52.1 and 53.5 ppm with
coupling constants of 2J(P,P) ) 56.8 Hz. Thus the 1H, 11B{1H},
and 31P{1H} NMR spectra confirm that the bonding situation
around the iron atom remains essentially unchanged. Suitable
nuclei to probe the coordination of the tin atom are the 119Sn
and 13C nucleus. In fact, the chemical shift of the tin atom is
moved to higher frequency compared to 2, with values of -228
(3), -328 (4), and -439 ppm (5). The shift toward higher
frequencies upon coordination of the tin atom is a general trend
M-Sn
2.578(1)
2.286(7)
2.372(7)
2.341(7)
2.355(6)
2.349(7)
1.843(6)
1.152(7)
1.884(8)
1.136(9)
2.309(7)
2.252(6)
2.230(6)
2.204(2)
2.206(2)
2.238(1)
87.5(2)
2.750(1)
2.310(6)
2.357(6)
2.367(6)
2.372(6)
2.381(6)
1.989(6)
1.146(7)
2.007(9)
1.138(10)
2.292(6)
2.255(6)
2.236(5)
2.202(2)
2.212(1)
2.231(1)
93.9(2)
2.743(1)
2.296(5)
2.367(6)
2.364(6)
2.353(6)
2.357(6)
1.984(7)
1.157(8)
2.036(7)
1.145(8)
2.272(5)
2.249(5)
2.260(5)
2.205(1)
2.224(1)
2.216(1)
93.8(2)
B(2)-Sn
2.300(6)
2.381(6)
2.369(7)
2.352(6)
2.352(6)
1.999(7)
1.144(7)
2.051(8)
1.130(9)
2.271(6)
2.246(6)
2.247(6)
2.200(2)
2.219(2)
2.212(2)
92.8(2)
B(3)-Sn
B(4)-Sn
B(5)-Sn
B(6)-Sn
C(5)-M
C(5)-O(5)
C(1)-M
C(1)-O(1)
B(2)-Fe
B(7)-Fe
B(8)-Fe
P(1)-Fe
P(2)-Fe
P(3)-Fe
in the coordination chemistry of [SnB11H11]2- 8,12
. Since 3 and
C(1)-M-Sn
C(5)-M-Sn
P(1)-Fe-H(2)
P(1)-Fe-H(7)
P(1)-Fe-H(8)
5 are the first stannaborate complexes of chromium and tungsten,
a reference value is available only for 4 at the moment, which
is the 119Sn chemical shift of [(C7H7)Mo(CO)2(SnB11H11)]- with
a resonance at -257 ppm.12a Due to the very large line-width
(ν1/2 ≈ 400 Hz) of the 119Sn NMR resonance of 5, the tungsten-
tin coupling constant could not be resolved. The 13C{1H} NMR
spectra of the three pentacarbonyl compounds reveal two peaks
in the CO region exhibiting tin satellites with cis coupling
177.3(2)
170(2)
93(2)
170.8(2)
171(2)
82(2)
171.6(2)
171(2)
95(2)
170.4(2)
174(2)
84(2)
81(2)
93(2)
83(2)
96(2)
position to the stannaborate, and it is commonly accepted that
the wavenumber of this vibration may serve as a rough gauge
of the π-bonding ability of the respective trans-standing ligand.14
The low wavenumbers of the A1(1) vibrations are similar for 3,
4, and 5 (1890-1896 cm-1) and lie below those of stannylene
fragments or SnCl3 bonded to M(CO)5.15,16 They can be
compared to the A1(1) frequencies of pentacarbonyl complexes
of amines such as cyclohexylamine,14b indicating the weak
π-acceptor character of the stannaborate ligand. The broad B-H
stretching band is present in the IR spectra of all compounds
and is accompanied by the B-H-M band at lower wave-
numbers for compounds 2 and 3, which is masked by the CO
bands in compounds 4 and 5.
2
constants of J(117/119Sn,13C) ) 69 (3), 108 (4), and 57 Hz (5)
and a trans coupling constant of 2J(117/119Sn,13C) ) 80 Hz (5).
Due to the limited solubility of the zwitterionic compounds,
the trans 2J(117/119Sn,13C) coupling could not be obtained for 3
and 4.
Solid-State NMR Spectroscopy. Because of the insolubility
of 1, we decided to carry out solid-state NMR experiments on
1 and the other compounds presented in this study. Phosphorus-
31 and tin-119 magic-angle-spinning (MAS) NMR experiments
not only provide isotropic chemical shifts that can be compared
to chemical shifts obtained from solution NMR but also allow
the characterization of the 31P and 119Sn chemical shift tensors
via analysis of spinning sideband intensities.17 In the case of 1,
the crystalline material was dried under reduced pressure. Its
31P variable-amplitude cross-polarization (VACP) MAS NMR
spectrum reveals three signals with tin satellites at 48.5, 30.5,
and 19.4 ppm. The analogous ruthenium complex also shows
three peaks, at 48.7, 22.9, and 5.1 ppm, and we were able to
assign the peak at lowest frequency to the phosphorus trans to
tin because of the large 2J(Sn,P) coupling constant of 1597 Hz,
NMR Spectroscopy in Solution. The NMR spectroscopic
characterization of 1 in solution was hampered by the insolubil-
(13) (a) Schiemenz, B.; Huttner, G. Angew. Chem. 1993, 105, 295-
296; Angew. Chem., Int. Ed. Engl. 1993, 32, 297-298. (b) Renner, G.;
Kircher, P.; Huttner, G.; Rutsch, P.; Heinze, K. Eur. J. Inorg. Chem. 2001,
973-980.
(14) (a) Cotton, F. A.; Kraihanzel, C. S. J. Am. Chem. Soc. 1962, 84,
4432-4438. (b) Kraihanzel, C. S.; Cotton, F. A. Inorg. Chem. 1963, 2,
533-540.
(15) (a) Marks, T. J. J. Am. Chem. Soc. 1971, 93, 7090-7091. (b) Petz,
W. Chem. ReV. 1986, 86, 1019-1047.
(16) Ruff, J. K. Inorg. Chem. 1967, 6, 1502-1504.

3908 Organometallics, Vol. 25, No. 16, 2006
Table 2. Crystal Data and Structure Refinement Parameters for 1, 2, 3, 4, and 5
Ga¨dt et al.
1
2
3
4
5
formula
fw
cryst syst
space group
a (Å)
C53H68B11FeN6P3Sn C42H52B11Cl2FeP3Sn C54H66B11CrFeO7P3Sn C96H108B22Cl8Fe2Mo2O10P6Sn2 C48H54B11Cl4FeO5P3SnW
1175.49
orthorhombic
P212121
16.7406(6)
17.8630(5)
19.7267(7)
90
90
90
5899.0(3)
4
1014.10
monoclinic
P21/n
14.4482(5)
19.7150(9)
16.8746(7)
90
102.968(3)
90
4684.1(3)
4
1265.43
triclinic
P1h
2670.02
monoclinic
P21/a
23.1640(8)
20.2790(9)
27.1721(10)
90
112.210(3)
90
1422.92
monoclinic
P21/n
13.7646(6)
20.3159(9)
21.7745(11)
90
102.298(4)
90
12.0705(9)
13.2630(10)
21.0976(16)
76.283(6)
77.687(6)
70.274(6)
3055.7(4)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
11816.9(8)
4
5949.3(5)
4
D(calc) (g/cm3)
1.324
1.438
1.375
1.501
1.589
µ (mm-1
F(000)
)
0.791
1.091
0.941
1.175
2.889
2416
2056
1292
5344
2800
size (mm3)
0.36 × 0.15 × 0.13 0.26 × 0.24 × 0.20
0.27 × 0.19 × 0.13
3.15-29.61
35 963
0.31 × 0.26 × 0.15
2.95-31.20
131 701
0.29 × 0.17 × 0.14
3.04-31.19
34 640
θ range (deg)
total no. of reflns
no. of unique reflns
3.19-29.24
38 597
3.23-29.29
80 114
15 055 [R(int) )
0.0682]
12 640 (R(int) )
0.0537)
15 920 [R(int) )
0.0805]
35 188 [R(int) )
0.0979]
17 490 [R(int) )
0.0424]
no. of data/restraints/ 15 055/0/679
params
12 640/0/561
15 920/0/687
35 188/6/1384
17 490/22/697
GOF
1.142
1.100
1.160
1.055
1.052
final Rind [I>2σ(I)]
R1 ) 0.0644,
wR2 ) 0.1166
1.058 and -1.024
R1 ) 0.0433,
wR2 ) 0.1007
1.984 and -1.756
R1 ) 0.0812,
wR2 ) 0.1503
0.961 and -0.931
R1 ) 0.0808,
wR2 ) 0.1256
1.319 and -0.921
R1 ) 0.0605,
wR2 ) 0.1148
3.751 and -2.054
residual F (e Å-3
)
Table 3. Wavenumbers (cm-1) of Selected Bands
B-H CO
At present, we cannot rationalize this observation, but given
that the M-P distances in 1 are similar (vide supra), in contrast
to the ruthenium analogue, it seems another indication that there
are distinct electronic differences between the iron and ruthe-
nium complexes. On the other hand, the 31P chemical shift
tensors of 1 and the ruthenium analogue are similar. The 119Sn
VACP/MAS NMR spectrum of 1 shows a resonance at -383
ppm (Figure 5), which is shifted toward lower frequency
compared to [NBu4][CpFe(CO)2(SnB11H11)], with a value of
-208 ppm,12a and to Ru(MeCN)2(triphos)(SnB11H11), with
-304 ppm.10 A comparison of the principal components of the
119Sn chemical shift tensor in 1 with the Ru analogue10 indicates
that all three components are shifted by about 100 ppm to lower
frequencies in the iron complex.
1
2
3
4
5
2468
2497, 2055 (B-H-Fe)
2527, 2080 (B-H-Fe) 2051 (A1(2)), 1977 (B1), 1932 (E), 1892 (A1
)
)
)
(1)
(1)
(1)
2519
2529
2067 (A1(2)), 1989 (B1), 1943 (E), 1896 (A1
2066 (A1(2)), 1981 (B1), 1934 (E), 1890 (A1
Table 4. 31P MAS NMR Data
δiso
δ11
δ22
δ33
Ωa
κb
2J(Sn,P)
1
2
48.5
30.5
19.4
62.1
54.0
48.5
57.7
43.1
58.2
43.7
58.2
43.6
170
120
119
166
141
134
164
127
162
128
163
130
45
26
10
66
71
57
64
57
65
58
66
55
-69
-55
-71
-46
-49
-45
-55
-53
-52
-54
-54
-53
239
175
190
211
190
179
219
180
214
182
217
183
-0.05
-0.07
-0.12
0.06
0.26
0.13
0.09
0.22
0.09
0.23
693
561
415
The 31P VACP/MAS NMR spectrum of 2 shows three peaks
that are shifted to higher frequencies by 14-28 ppm compared
to 1, mainly due to changes in δ22 and δ33 (Table 4).
Interestingly, the 119Sn VACP/MAS NMR spectrum of 2
exhibits two sets of signals belonging to isomeric species present
3
4
5
0.11
0.18
a Span of the chemical shift tensor, Ω ) δ11 - δ33. b Skew of the
chemical shift tensor, κ ) 3(δ22 - δiso)/Ω.
Table 5. 119Sn MAS NMR Data
δiso
δ11
δ22
δ33
Ωa
κb
1
-383
-645
-617
-208
-303
-411
-205
-221
-201
270
137
-23
-205
-742
-689
42
-132
-294
-740
-973
-962
-935
-915
-917
535
752
761
1205
1052
894
1.00
-0.39
-0.28
0.62
0.49
0.39
2a
2b
3
4
5
a Span of the chemical shift tensor, Ω ) δ11 - δ33. b Skew of the
chemical shift tensor, κ ) 3(δ22 - δiso)/Ω.
compared to the much smaller 350 Hz for the peak at 48.7 ppm;
the satellites for the peak at 22.9 ppm were not resolved.10 Such
an assignment is not possible in the case of 1 because the
2J(Sn,P) coupling constants are of similar magnitude (Table 4).
(17) (a) Herzfeld, J.; Berger, A. E. J. Chem. Phys. 1980, 73, 6021-
6030. (b) Maricq, M. M.; Waugh, J. S. J. Chem. Phys. 1979, 70, 3300-
3316.
Figure 4. Variable-temperature 31P{1H} NMR measurements of
2 in CD2Cl2.

Bimetallic Zwitterionic Complexes
Organometallics, Vol. 25, No. 16, 2006 3909
studies.20 As Figure 5 demonstrates, the 119Sn chemical shift
tensors appear to be very sensitive to the coordination mode of
the stannaborate unit. Exclusive η1(Sn) coordination as in 1 leads
to the lowest span and a positive skew, while exclusive η3(B-
H) coordination as in 2 enlarges the span and, more dramatically,
changes the sign of the skew. Simultaneous employment of both
coordination modes affords a positive skew and the largest span
of the chemical shift tensor.
Conclusions. The η3(B-H) coordination of a (triphos)Fe2+
fragment at the stanna-closo-dodecaborate cluster leads to a
significant change in the NMR properties and structural
parameters of the heteroborate cluster. The iron-stannaborate
complex 2 displays a strongly reduced nucleophilicity at the
tin atom. Coordination at the tin atom can be achieved by
reacting metal fragments with labile ligands, which establishes
a general pathway to bimetallic complexes with [SnB11H11]2-
as ambident ligand.
Experimental Section
General Procedures. All manipulations were carried out under
dry argon in Schlenk glassware. Solvents were dried and purified
by standard methods and stored under argon. Elemental analyses
were performed by the Institut fu¨r Anorganische Chemie Universita¨t
Tu¨bingen using a Vario EL analyzer. Chemicals were purchased
commercially except [Bu3MeN]2[SnB11H11], which was synthesized
using a modified protocol of Todd’s original work.4
NMR. NMR spectra were obtained using a Bruker DRX-250
NMR spectrometer equipped with a 5 mm ATM probe head and
operating at 250.13 (1H), 80.25 (11B), 62.90 (13C), 101.25 (31P),
and 93.25 MHz (119Sn). Chemical shifts are reported in δ values
relative to external TMS (1H, 13C), BF3‚Et2O (11B), 85% aqueous
H3PO4 (31P), or SnMe4 (119Sn) using the chemical shift of the solvent
2H resonance frequency. Simulations of NMR spectra obtained from
solution were done using WINDAISY.21 NMR spectra of solid
samples were obtained on a Bruker DSX-200 NMR spectrometer
operating at 200.13 (1H), 81.01 (31P), and 74.60 MHz (119Sn). The
powdered samples were spinning about the magic angle at 10 kHz
in 4 mm o.d. zirconia rotors. Phosphorus-31 NMR spectra were
obtained after variable-amplitude cross-polarization (VACP) from
protons and under high-power 1H decoupling. Tin-119 NMR spectra
were obtained after single-pulse excitation, or VACP, and under
Figure 5. Solid-state 119Sn VACP/MAS NMR spectra obtained at
4.7 T and a spinning rate of 10 kHz; isotropic peaks are indicated
by arrows: (a) 1; (b) 2 (the asterisk denotes signals belonging to
the minor isomer); (c) 3.
in the solid state with a ratio of 68% (2a) to 32% (2b) (Table
5, Figure 5). The occurrence of two species in the solid-state
NMR spectrum is in agreement with the structure refinement
of the X-ray diffraction data (Scheme 5). A similar finding has
recently been reported for the analogous ruthenium complex.10
The 119Sn isotropic chemical shifts of -617 and -645 ppm are
shifted to lower frequencies, characteristic of a η3(B-H)-
coordinated stannaborate moiety.8,10
Although the crystal structures of 3-5 do not show molecular
symmetry, the 31P VACP/MAS NMR spectra of 3-5 reveal
two resonances, with the peak around 58 ppm twice as intense
as the peak around 43 ppm. The peak at 58 ppm actually shows
a spinning-rate-dependent splitting.18 It is not surprising that
the 31P isotropic chemical shifts as well as the respective tensor
components are very similar (Table 4). The 119Sn isotropic
chemical shifts of 3-5 are in good agreement with the chemical
shifts in solution (Table 5), and the spectra exhibit only one set
of signals, as one would expect for a system without any
disorder of the stannaborate cluster. The increasing shift of δiso
to lower frequency by roughly 100 ppm increments on changing
the metal from chromium in 3 to molybdenum in 4 to tungsten
in 5 is caused by changes in δ11 and δ22, while δ33 remains
relatively invariant. Similar trends are known for the 31P
chemical shift tensors of phosphines coordinated to those
transition metals19 and have also been the subject of theoretical
1
high-power H decoupling. Chemical shifts are referenced with
respect to external 85% aqueous H3PO4 (31P) or SnMe4 (119Sn) using
the chemical shift of ammonium dihydrogen phosphate, 0.81 ppm,
or SnCy4, -97.35 ppm, as secondary chemical shift reference. MAS
spectra were analyzed using the program HBA.22 Errors in chemical
shifts and coupling constants are estimated to be 0.5 ppm and 40
Hz (31P) or 2 ppm and 100 Hz (119Sn), because of the greater line
widths in the 119Sn MAS spectra (0.8-1.0 kHz) attributed to 119Sn-
10,11B spin-spin interactions. Principal components of the chemical
shift tensors are accurate to about 2% of Ω.
Crystallography. X-ray data for compounds 1-5 were collected
on a Stoe IPDS 2T diffractometer and were corrected for Lorentz
and polarization effects and absorption by air. Numerical absorption
correction based on crystal-shape optimization was applied for all
data. The programs used in this work are Stoe’s X-Area23 and the
WinGX suite of programs24 including SHELXS and SHELXL25
for structure solution and refinement.
(18) (a) Wu, G.; Wasylishen, R. E. Inorg. Chem. 1994, 33, 2774-2778.
(b) Wu, G.; Eichele, K.; Wasylishen, R. E. In Phosphorus-31 NMR Spectral
Properties in Compound Characterization and Structural Analysis; Quin,
L. D., Verkade, J. G., Eds.; VCH Publishers: New York, 1994; pp 441-
450.
(19) (a) Wosnick, J. H.; Morin, F. G.; Gilson, D. F. R. Can. J. Chem.
1998, 76, 1280-1283. (b) Eichele, K.; Wasylishen, R. E.; Kessler, J. M.;
Solujic´, L.; Nelson, J. H. Inorg. Chem. 1996, 35, 3904-3912.
(20) (a) Kaupp, M.; Malkin, V. G.; Malkina, O. L. In Encyclopedia of
Computational Chemistry, Vol. 3; von Rague´ Schleyer, Ed.; John Wiley &
Sons: Chichester, 1998; pp 1857-1866. (b) Kaupp, M. Chem. Ber. 1996,
129, 535-544.
(21) WinDaisy 4.0; Bruker Franzen Analytik, 1996.
(22) Eichele, K. HBA32 1.5.8; Tu¨bingen, 2005.
(23) X-AREA 1.26; Stoe & Cie GmbH: Darmstadt, 2004.
(24) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838.

3910 Organometallics, Vol. 25, No. 16, 2006
Ga¨dt et al.
[1-{Fe(MeCN)2(triphos)}-SnB11H11]‚4MeCN (1). All hydrogen
atoms were placed in calculated positions and refined with isotropic
thermal parameters. The acetonitrile solvate molecule C18, C19,
N6 was refined isotropically.
violet powder was recrystallized from CH2Cl2/hexane, yielding 441
mg (95%). IR (KBr): 2497 (s, BH), 2055 (w, B-H-Fe). 1H NMR
(CD2Cl2): δ 6.8-7.2 (m, 30H, C6H5), 2.55 (s, 2H, CH2), 2.45 (s,
4H, CH2), 1.78 (s, 3H, CH3), -9.8 (br, 1H, B-H-Fe), -10.3 (br,
2H, B-H-Fe). 11B NMR (CD2Cl2): δ -0.4, -6.1, -7.9, -14.3,
-24.7 (3B, 1J(B,H) ) 78.3 Hz, B-H-Fe). 13C{1H} NMR
(CD2Cl2): δ 135.2-136.5 (m, q-aromat. C), 128.3-132.0 (m,
aromat. C), 39.2 (m, CH3), 37.2 (m, q-C), 35.3-35.8 (br m, CH2).
31P{1H} NMR (CD2Cl2, RT): δ 54.2 (s). 31P{1H} NMR (CD2Cl2,
-70 °C): δ 58.1 (m, 2P, 2J(P,P) ) 55.7 Hz), 57.6 (m, 1P, 2J(P,P)
) 55.7 Hz). 119Sn{1H} NMR (CD2Cl2): δ -623. Anal. Calcd (%)
for C41H50B11FeP3Sn‚CH2Cl2: C, 49.74; H, 5.17. Found: C, 49.61;
H, 5.02.
[2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11]‚CH2Cl2 (2). All hydro-
gen atoms except the hydrogen atoms H2, H7, and H8 were placed
in calculated positions and refined with isotropic thermal parameters.
The B-H-Fe protons H2, H7, and H8 were located on difference
maps and allowed to refine freely. The stannaborate moiety
displayed disorder over two positions with an occupancy of 95.7:
4.3 and was refined by constraining the minor heteroborate
icosahedron to a variable-metric rigid group using the AFIX 9
constraint. The boron atoms and the tin atom of the minor isomer
were kept isotropic, and the hydrogen atoms were omitted. H3 of
the major isomer was also omitted because of its close proximity
to the tin atom of the minor heteroborate.
[1-{Cr(CO)5}-2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11]‚2THF (3).
All hydrogen atoms except the hydrogen atoms H2, H7, and H8
were placed in calculated positions and refined with isotropic
thermal parameters. H2, H7, and H8 were located on difference
maps and allowed to refine freely. The THF solvent carbons atoms
C15, C16, C17, and C18 were refined isotropically.
2 [1-{Mo(CO)5}-2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11]‚4CH2Cl2
(4). There are two independent molecules and four solvent
molecules in the asymmetric unit. All hydrogen atoms except
the hydrogen atoms H2, H7, and H8 were placed in calculated
positions and refined with isotropic thermal parameters. H2, H7,
and H8 were located on difference maps and allowed to refine
freely. The phenyl ring C29-C34 is disordered over two positions
with a ratio of 56.3:43.7, and the disordered atoms were refined
isotropically. Two CH2Cl2 molecules showed disorder and were
refined over two positions with occupancies of 76.5:23.5 and 74.3:
25.7. Two DFIX and one DANG restraint were applied for the
dichloromethane molecule C89, Cl3, and Cl4. C89 was refined
isotropically.
[1-{Cr(CO)5}-2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11] (3). A so-
lution of 66 mg (0.300 mmol) of Cr(CO)6 in 150 mL of THF was
irradiated for 90 min using a medium-pressure Hg-UV lamp. To
the resulting yellow solution was added 279 mg (0.300 mmol) of
[2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11], and stirring was continued
for 15 min. The dark red solution was concentrated in vacuo to 30
mL and layered with hexane. Within 2 days dark red crystals of
X-ray diffraction quality formed and were collected via filtration.
Yield: 283 mg (84%). IR (KBr): 2527 (m, BH), 2080 (w, B-H-
Fe), 2051 (s, CO, A1(2)), 1977 (m, CO, B1), 1932 (vs, CO, E), 1892
(m, CO, A1(1)). 1H{11B} NMR (CD2Cl2): δ 6.8-7.2 (m, 30H, C6H5),
2.54 (m, 6H, CH2), 1.82 (s, 3H, CH3) -9.95 (br, 1 H, B-H-Fe),
-10.21 (br, 2H, B-H-Fe). 11B NMR (CD2Cl2): δ -3.7 (br), -9.3
(br), -16.4 (br), -25.7 (2B, 1J(B,H) ) 84.1 Hz, B-H-Fe), -28.2
1
(1B, J(B,H) ) 86.1 Hz, B-H-Fe). 13C{1H} NMR (d6-DMSO):
δ 211.8 (trans CO), 206.6 (cis CO, 2J(117/119Sn,13C) ) 69 Hz)
134.8-136.0 (m, q-aromat. C), 128.6-132.0 (m, aromat. C), 39.2
(m, CH3), 37.1 (m, q-C), 35.7 (br m, CH2). 31P{1H} NMR
(CD2Cl2): δ 53.6 (m, 1P, 2J(P,P) ) 56.8 Hz), 52.1 (m, 2P, 2J(P,P)
) 56.8 Hz). 119Sn{1H} NMR (CD2Cl2): δ -228. Anal. Calcd (%)
for C46H50B11CrFeO5P3Sn: C, 49.27; H, 4.49. Found: C, 49.76;
H, 4.20.
[1-{W(CO)5}-2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11]‚2CH2Cl2
(5). All hydrogen atoms except the hydrogen atoms H2, H7, and
H8 were placed in calculated positions and refined with isotropic
thermal parameters. H2, H7, and H8 were located on difference
maps and allowed to refine freely. The phenyl ring C29-C34 is
disordered over two positions with a ratio of 55.3:44.7, and the
disordered atoms were refined isotropically.
[1-{Mo(CO)5}-2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11] (4). A
solution of 79 mg (0.300 mmol) of Mo(CO)6 in 150 mL of THF
was irradiated for 90 min using a UV lamp. To the resulting yellow
solution was added 279 mg (0.300 mmol) of [2,7,8-(µ-H)3-
{Fe(triphos)}-SnB11H11], and stirring was continued for 15 min.
The dark red solution was concentrated in vacuo to 30 mL and
layered with hexane. Within 2 days dark red crystals formed and
were collected via filtration, yielding 259 mg (74%). Recrystalli-
zation from CH2Cl2/hexane yielded crystals suitable for X-ray
diffraction. IR (KBr): 2519 (m, BH), 2067 (s, CO, A1(2)), 1989
(m, CO, B1), 1943 (vs, CO, E), 1896 (m, CO, A1(1)). 1H{11B} NMR
(CD2Cl2): δ 6.9-7.3 (m, 30H, C6H5), 2.63 (m, 6H, CH2), 1.92 (s,
3H, CH3), -9.82 (br, 1H, B-H-Fe), -10.10 (br, 2H, B-H-Fe).
11B NMR (CD2Cl2): δ -3.2 (br), -8.9 (br), -16.3 (br), -25.6
Syntheses. [1-{Fe(MeCN)2(triphos)}-SnB11H11] (1). To a solu-
tion of 216 mg (1.00 mmol) of FeBr2 in 20 mL of MeCN was
added 625 mg (1.00 mmol) of triphos. After 15 min 650 mg (1
mmol) of [Bu3MeN]2[SnB11H11] in 20 mL of MeCN was added
dropwise via syringe. Immediately the color of the reaction mixture
changed from red to violet and a pink precipitate formed. The
precipitate was isolated by filtration and washed with MeCN (3 ×
5 mL), yielding 627 mg (62%) of a pink solid. Single-crystals
suitable for X-ray diffraction analysis were grown by carefully
layering the acetonitrile solution of FeBr2 and triphos with an
acetonitrile solution of [Bu3MeN]2[SnB11H11]. IR (KBr): 2468 (s,
BH), 2268 (vw, MeCN). Anal. Calcd (%) for C45H56B11FeN2P3Sn:
C, 53.44; H, 5.58; N, 2.77. Found: C, 52.57; H, 4.83; N, 2.72.
Repeated elemental analyses of the crystalline material as well as
the powder consistently gave rather poor results, which might be
caused by the acetonitrile solvent molecules (four solvent molecules
are present in the crystal structure) and the lability of the acetonitrile
ligands.
1
1
(2B, J(B,H) ) 84.1 Hz, B-H-Fe), -27.9 (1B, J(B,H) ) 87.1
Hz, B-H-Fe). 13C{1H} NMR (d6-DMSO): δ 212.5 (trans CO),
207.4 (cis CO, 2J(117/119Sn,13C) ) 108 Hz), 135.0-136.5 (m,
q-aromat. C), 128.3-132.0 (m, aromat. C), 39.4 (m, CH3), 36.2
(m,q-C), 35.0 (br m, CH2). 31P{1H} NMR (CD2Cl2): δ 53.7 (A2B,
2
2
1P, J(P,P) ) 56.7), 52.4 (A2B, 2P, J(P,P) ) 56.7). 119Sn{1H}
NMR (CD2Cl2): δ -328. Anal. Calcd (%) for C46H50B11-
FeMoO5P3Sn: C, 47.42; H, 4.33. Found: C, 47.29; H, 4.55.
[1-{W(CO)5}-2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11] (5). A so-
lution of 106 mg (0.300 mmol) of W(CO)6 in 150 mL of THF was
irradiated for 90 min using a UV lamp. To the resulting yellow
solution was added 279 mg (0.300 mmol) of [2,7,8-(µ-H)3-
{Fe(triphos)}-SnB11H11], and stirring was continued for 15 min.
The dark red solution was concentrated in vacuo to 30 mL and
layered with hexane. Within 2 days dark red crystals formed and
were collected via filtration, yielding 331 mg (88%). Recrystalli-
zation from CH2Cl2/hexane yielded crystals suitable for X-ray
diffraction. IR (KBr): 2529 (m, BH), 2066 (s, CO, A1(2)), 1981
[2,7,8-(µ-H)3-{Fe(triphos)}-SnB11H11] (2). A suspension of 506
mg (0.50 mmol) of 1 in 40 mL of THF was refluxed for 3 h. The
solid dissolved and formed a dark violet solution. Afterward the
solvent was removed under reduced pressure and the remaining
(25) (a) Sheldrick, G. M. SHELXS-97, Program for the Solution of
Crystal Structures; Go¨ttingen, 1997. (b) Sheldrick, G. M. SHELXL-97,
Program for Crystal Structure Refinement; Go¨ttingen, 1997.

Bimetallic Zwitterionic Complexes
Organometallics, Vol. 25, No. 16, 2006 3911
(m, CO, B1), 1934 (vs, CO, E), 1890 (m, CO, A1(1)). H NMR
(CD2Cl2): δ 6.82-7.17 (m, 30H, C6H5), 2.54 (m, 6H, CH2), 1.81
(m, 3H, CH3) -9.94 (br, 1H, B-H-Fe), -10.20 (br, 2H, B-H-
Fe). 11B NMR (CD2Cl2): δ -3.5 (br), -9.3 (br), -16.6 (br), -25.8
119Sn{1H} NMR (CD2Cl2): δ -439. Anal. Calcd (%) for C46H50B11-
1
FeO5P3SnW: C, 44.09; H, 4.02. Found: C, 44.15; H, 3.93.
Acknowledgment. Financial support from the Deutsche
Forschungsgemeinschaft is gratefully acknowledged.
1
1
(2B, J(B,H) ) 83.6 Hz, B-H-Fe), -28.5 (1B, J(B,H) ) 87.5
Hz, B-H-Fe). 13C{1H} NMR (d6-DMSO): δ 203.5 (trans CO,
1J(183W,13C) ) 169.1 Hz, 2J(117/119Sn,13C) ) 80 Hz), 200.3 (cis CO,
1J(183W,13C) ) 123.9 Hz, 2J(117/119Sn,13C) ) 56.8 Hz), 137.9-138.8
(m, q-aromat. C), 131.2-134.6 (m, aromat. C), 42.1 (m, CH3), 38.8
(m, q-C), 37.5-38.0 (br m, CH2). 31P{1H} NMR (CD2Cl2): δ
Supporting Information Available: Full details of crystal-
lographic analyses in CIF format and ORTEP structures of 4 and
5. This material is available free of charge via the Internet at
http://pubs.acs.org.
2
2
53.7 (A2B, 1P, J(P,P) ) 56.9), 52.2 (A2B, 2P, J(P,P) ) 56.9).
OM060328M