Radical-type reactivity of metalla[1.1.1]propellanes of group 14: Syntheses, structures, and reduction chemistry of transition metal-terminated bicyclo[1.1.1]pentastannanes

Article abstract of DOI:10.1021/om100779b

Two selected metalla[1.1.1]propellanes of group 14, Sn₅Dep ₆ (1) and Ge₅Mes₆ (2) (Dep = 2,6-Et ₂C₆H₃, Mes = 2,4,6-Me₃C ₆H₂), were reacted with [FeCp(CO)₂]₂ and [RuCp(CO)₂]₂. While 2 did not show any reaction with [FeCp(CO)₂]₂ or did not lead to any isolable product in the case of [RuCp(CO)₂]₂, the tin propellane 1 quantitatively (monitored by ¹H NMR) afforded the first transition metal-terminated bicyclo[1.1.1]pentastannanes, [{MCp(CO)₂} ₂{μ-Sn₅Dep₆}] (M = Fe (3), Ru = (4)), in 68% (3) and 66% (4) isolated yield. This behavior confirms the radical-type reactivity of metalla[1.1.1]propellanes, in this case 1. The title compounds 3 and 4 have been characterized in detail using various methods. X-ray structure analyses corroborated that the two ligand-free bridgehead tin atoms within the Sn₅ scaffold are bonded to the transition metal fragments. Electrochemical studies revealed the reduction chemistry of 3 and 4 in THF solutions to be very interesting. A detailed preparative and electrochemical study, including the isolation and characterization of the monosubstituted cobaltocenium salt [CoCp*₂]⁺[{FeCp(CO) ₂}{Sn₅Dep₆}]^- (5), elucidated a complex redox cycle consisting of a cascade of bond-breaking and bond-making processes.

Full text of DOI:10.1021/om100779b

6028 Organometallics 2010, 29, 6028–6037
DOI: 10.1021/om100779b
Radical-Type Reactivity of Metalla[1.1.1]propellanes of Group 14:
Syntheses, Structures, and Reduction Chemistry of Transition
Metal-Terminated Bicyclo[1.1.1]pentastannanes
Dominik Nied, Eberhard Matern, Helga Berberich, Marco Neumaier, and Frank Breher*
Institute of Inorganic Chemistry, Karlsruhe Institute of Technology (KIT), Engesserstrasse 15,
76131 Karlsruhe, Germany
Received August 11, 2010
Two selected metalla[1.1.1]propellanes of group 14, Sn5Dep6 (1) and Ge5Mes6 (2) (Dep = 2,6-
Et2C6H3, Mes = 2,4,6-Me3C6H2), were reacted with [FeCp(CO)2]2 and [RuCp(CO)2]2. While 2 did
not show any reaction with [FeCp(CO)2]2 or did not lead to any isolable product in the case of
1
[RuCp(CO)2]2, the tin propellane 1 quantitatively (monitored by H NMR) afforded the first
transition metal-terminated bicyclo[1.1.1]pentastannanes, [{MCp(CO)2}2{μ-Sn5Dep6}] (M=Fe (3),
Ru=(4)), in 68% (3) and 66% (4) isolated yield. This behavior confirms the radical-type reactivity of
metalla[1.1.1]propellanes, in this case 1. The title compounds 3 and 4 have been characterized in detail
using various methods. X-ray structure analyses corroborated that the two ligand-free bridgehead tin
atoms within the Sn5 scaffold are bonded to the transition metal fragments. Electrochemical studies
revealed the reduction chemistry of 3 and 4 in THF solutions to be very interesting. A detailed
preparative and electrochemical study, including the isolation and characterization of the mono-
substituted cobaltocenium salt [CoCp*2]þ[{FeCp(CO)2}{Sn5Dep6}]- (5), elucidated a complex
redox cycle consisting of a cascade of bond-breaking and bond-making processes.
Introduction
all-carbon [1.1.1]propellane5 has attracted renewed interest,
from both experimentalists6 and theoreticians.7 For the
heavier congeners of carbon, however, the situation is even
more complicated.3,8 They were shown to be fundamentally
different from their carbon counterparts.3,9 Several quantum
chemical calculations4 on these heavy metalla[1.1.1]-
propellanes [E5R6] (E = Si, Ge, Sn; Chart 1) predicted some
biradical character of the ground state and that “it would be
misleading to represent the structure by drawing a line
between the bridgehead atoms”.4a Clearly, the inherent
singlet ground state of these species points toward noticeable
Propellane molecules1 intrigue chemists for a number of
reasons, not at least because their core structures resemble
“eponymous macroscopic propellers”.2 In particular, the
question about the interaction between the bridgehead
atoms in propellanes has been extensively discussed in the
literature.3,4 All efforts are mainly directed toward clarifying
fundamental aspects of the nature of the interaction
between the “inverted” bridgehead atoms. Even the simplest
Eb Eb interactions, but it appears that this interaction is
*To whom correspondence should be addressed. Fax: þ49 721 608 70
21. Tel: þ49 721 608 48 55. E-mail: breher@kit.de.
3 3 3
perturbed to such an extent (“stretched bonds”) that quantum
chemistry provides evidence for some biradicaloid10 charac-
teristics. This nicely illustrates the continuous nature11 of
the conversion of an ordinary closed-shell molecule into
a biradicaloid and eventually into a “perfect” biradical12 by
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pubs.acs.org/Organometallics
Published on Web 10/11/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 22, 2010 6029
Chart 1
propellanes is considerably stretched by between 13% and
20% of a regular E-E single bond. On the basis of this
elongation, these molecules have frequently been described
as singlet biradicaloids.3 Although highly correlated CASSCF
calculations predicted the biradicaloid character24 to be fairly
small, experimental studies indeed revealed some radical-type
reactivity.22,23 To the best of our knowledge, no further
experimental studies on the biradicaloid behavior of these
species are known. Only Sita et al. studied the reactivity
of Sn5Dep6 toward MeLi and MeI and observed formation
of unstable adducts.19
Results and Discussion
the introduction of a suitable perturbation. Apart from
fundamental aspects addressing the bonding in biradicaloid
species, they have attracted considerable recent interest due to
the unusual reactivity involving main group elements.9,13
Although numerous quantum chemical calculations have
been performed for metalla[1.1.1]propellanes3,4 as well as
hetero[1.1.1]propellanes,14 synthetically accessible and struc-
turally characterized species are very rare. Apart from closely
related cluster compounds [E8R6] containing silicon,15
germanium,16 and tin,17 seminal work was performed by Sita
and co-workers in the early 1990s.18 They succeeded in
isolating the pentastanna[1.1.1]propellane Sn5Dep6 (Dep =
2,6-Et2C6H3) and a further derivative.19 Analogous group
14 metalla[1.1.1]propellanes such as Sn5R6 (R = 2,6-(i-PrO)2-
C6H3) and Ge2{Sn(Cl)R}3 (R = 2,6-Mes2C6H3; Mes = 2,4,6-
Me3C6H2) were reported later by Drost20 and Power,21 respec-
tively. To shed more light on the accessibility and stability of
metallapropellanes of this type and to study fundamental aspects
of their bonding, we have recently investigated the Mes-
substituted pentagerma-22 and pentasila[1.1.1]propellanes23 in
combined experimental and quantum chemical studies. In each
case it was found that the central distance between the “naked”
bridgehead atoms (Eb) within the [1.1.1] scaffold of heavy
In order to extend our studies in the area of biradicaloids,
we have investigated the reactivities of some selected homo-
nuclear propellanes in homolytic bond cleavage reactions by
using transition metal precusors containing M-M bonds.
For this case study we used Sn5Dep6 (1)19 and Ge5Mes6 (2)22
and reacted both with [FeCp(CO)2]2 and [RuCp(CO)2]2.
The latter were chosen because of the moderate metal-
metal bond strengths25 and their well-known electrochemical
properties.26 In addition, we have a general interest in metal-
terminated clusters/cage compounds for studies addressing
electronic communications between metal centers. Metal-
terminated bicyclo[1.1.1]pentastannanes are promising can-
didates for such investigations since the metal atoms are
arranged in close spatial proximity.
In general, homolytic M-M bond activation of these transi-
tion metal precursors and addition of two [MCp(CO)2]• frag-
ments to the bridgehead atoms should strongly depend on the
amount of interaction between the bridghead atoms in 1 and 2.
In terms of bond energies alone, it is the subtle balance between
M-M and Eb Eb bond cleavage and M-E bond forma-
3 3 3
tion that governs the overall reactivity. On the basis of our
experimental and theoretical findings,22,23 we expected the tin
propellane 1 to be more reactive in these types of reactions,
although differences in the steric accessibility of the bridge-
heads should not be neglected. Furthermore, we speculated
that the general reactivity of metallapropellanes might be
influenced by light due to the facile accessibility of the excited
singlet (1A2) and triplet states (3A2) in the UV/vis region.22,23
For this comparative case study, the tin compound
Sn5Dep6 (1), known from the seminal work of Sita et al.,19
was prepared in a modified procedure by reacting the
cyclotristannane Sn3Dep6 with 6 equiv of lithium chunks
and 3 equiv of SnCl2 as additional Sn source in THF as
solvent. We optimized the purification steps and rerecorded
the UV/vis spectrum of 1 in pentane (Figure 1). The absorp-
tion bands were assigned by using our previous TD-DFT
(13) Review on REER (E = group 14 element) showing in some cases
biradicaloid behavior: Power, P. P. Organometallics 2007, 26, 4362.
(14) See for example: (a) Nguyen, K. A.; Carroll, M. T.; Gordon,
€
M. S. J. Am. Chem. Soc. 1991, 113, 7924. (b) Sandstrom, N.; Ottosson, H.
Chem.;Eur. J. 2005, 11, 5067. (c) Wang, Y.; Ma, J.; Inagaki, S. Tetra-
hedron Lett. 2005, 46, 5567. (d) Ebrahimi, A.; Deyhimi, F.; Roohi, H.
J. Mol. Struct. (THEOCHEM) 2003, 626, 223. (e) Kitchen, D. B.; Jackson,
J. E.; Allen, L. C. J. Am. Chem. Soc. 1990, 112, 3408.
(15) (a) Fischer, G.; Huch, V.; Mayer, P.; Vasisht, S. K.; Veith, M.;
Wiberg, N. Angew. Chem. 2005, 117, 8096; Angew. Chem., Int. Ed. 2005,
44, 7884. For a Si cluster of the formula Si5Tip6 (Tip = 2,4,6-i-Pr3C6H2)
consisting of only one ligand-free Si atom see: (b) Scheschkewitz, D.
Angew. Chem. 2005, 117, 3014; Angew. Chem., Int. Ed. 2005, 44, 2954.
€
(16) (a) Schnepf, A.; Koppe, R. Angew. Chem. 2003, 115, 940; Angew.
Chem., Int. Ed. 2003, 42, 911. (b) Schnepf, A.; Drost, C. Dalton Trans.
2005, 3277. See also: (c) Schnepf, A. Chem. Soc. Rev. 2007, 36, 745.
€
(17) (a) Wiberg, N.; Lerner, H.-W.; Wagner, S.; Noth, H.; Seifert, T.
calculations.22,27 The lowest energy absorbance at λmax
=
558 nm belongs to the transition HOMO (e) f LUMO (a2)
Z. Naturforsch. B 1999, 54, 877. (b) See also: Wiberg, N.; Power, P. P. In
€
Molecular Clusters of the Main Group Elements; Driess, M.; Noth, H.,
Eds.; Wiley-VCH: Weinheim, 2004.
(18) Reviews: (a) Sita, L. R. Adv. Organomet. Chem. 1995, 38, 189.
(b) Sita, L. R. Acc. Chem. Res. 1994, 27, 191.
(19) (a) Sita, L. R.; Kinoshita, I. J. Am. Chem. Soc. 1992, 114, 7024.
(b) Sita, L. R.; Kinoshita, I. J. Am. Chem. Soc. 1991, 113, 5070. (c) Sita,
L. R.; Kinoshita, I. J. Am. Chem. Soc. 1990, 112, 8839. (d) Sita, L. R.;
Bickerstaff, R. D. J. Am. Chem. Soc. 1989, 111, 6454.
(24) It is important to note that the quantity of radical character is
fundamentally different from the theory of radical behavior. Radical
character serves as a theoretical measure, whereas radical behavior is
experimentally observed for such species.
(25) (a) Bitterwolf, T. E. Coord. Chem. Rev. 2000, 206-207, 419.
(b) Bitterwolf, T. E. J. Organomet. Chem. 2004, 689, 3939. (c) Meyer, T. J.;
Caspar, J. V. Chem. Rev. 1985, 85, 197. (d) Szacizowski, K.; Macyk, W.;
Stochel, G.; Stasicka, Z.; Sostero, S.; Traverso, O. Coord. Chem. Rev. 2000,
208, 277.
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(20) Drost, C.; Hildebrand, M.; Lonnecke, P. Main Group Met.
Chem. 2002, 25, 93.
(21) (a) Richards, A. F.; Brynda, M.; Power, P. P. Organometallics
2004, 23, 4009. See also: (b) Richards, A. F.; Brynda, M.; Olmstead, M. M.;
Power, P. P. Organometallics 2004, 23, 2841.
(22) Nied, D.; Klopper, W.; Breher, F. Angew. Chem. 2009, 121, 1439;
Angew. Chem., Int. Ed. 2009, 48, 1411.
(26) (a) Dessy, R. E.; Weissman, P. M.; Pohl, R. L. J. Am. Chem. Soc.
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1966, 88, 5117. (b) Miholova, D.; Vlcek, A. A. Inorg. Chim. Acta 1980, 41,
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6030 Organometallics, Vol. 29, No. 22, 2010
Nied et al.
photochemistry of the M-M bonded bimetallic transition
metal precursors.31 This is work in progress. Furthermore, we
noticed that only decomposition products are obtained in
these reactions in cases where we used light sources of much
higher intensities (i.e., λ < 400 nm, 200 W).
The title compounds 3 and 4 are soluble in toluene, diethyl
ether, and tetrahydrofuran and moderately soluble in pen-
tane. The thermally stable (mp>250 °C (dec)) dark green
solids form almost black crystals when recrystallized from
toluene/acetonitrile. In crystalline form, both compounds
can shortly be handled under aerobic conditions. Yellow-
green solutions of 3 and 4, however, are sensitive to oxygen
and/or moisture. In addition, both solutions are unstable at
room temperature if stored for longer periods (some weeks),
even under argon. The UV/vis spectra (THF) showed char-
acteristic absorptions at λmax(3) = 436, ∼330 (sh), 254, and
212 nm and λmax(4) = 414, ∼350 (sh), 254 (sh), and 213 nm
(see Supporting Information).32 IR spectroscopic investiga-
tions exposed in each case two characteristic vibrations in
the CO region centered at ν=1985, 1947 cm-1 (3) and 2003,
1958 cm-1 (4), respectively. Most revealingly, no bridging
CO entities could be detected, which is consistent with the
structures proposed in Scheme 1.33
Figure 1. Experimental UV/vis spectrum of 1 in pentane and
TD-DFT-calculated UV/vis transitions of A2 (HOMO-1 f
LUMO transition) and E symmetry (HOMO fLUMO transition).
The possible 3A2 transition is marked by an asterisk.
(97.8%, E in Figure 1) and the characteristic band at λ= 381 nm
to the transition HOMO-1 (a1) f LUMO (a2) (67.9%,
A2 in Figure 1).22 The broad shoulder located around
500 nm can most likely be attributed to the triplet transition
(3A2, HOMO-1 (a1) f LUMO (a2)), for which we calcu-
lated a value of λcalcd = 522.1 nm. These transitions are
usually not visible in the UV/vis spectrum but obviously are
allowed due to spin-orbit coupling effects for the heavier
propellanes. This effect is also known for other metalla-
[1.1.1]propellanes of group 14.28
1 and 2 were reacted with the iron and ruthenium com-
pounds [MCp(CO)2]2 in the stoichiometric ratio of 1:1 in
C6D6 at room temperature. The germanium compound 2 did
not show any reaction with [FeCp(CO)2]2. The analogous
reaction using the ruthenium precursor did not lead to any
isolable product. The tin popellane 1, however, quantitatively
(monitored by 1H NMR) afforded the first transition metal-
terminated bicyclo[1.1.1]pentastannanes,29 [{MCp(CO)2}2-
{μ-Sn5Dep6}] (M = Fe (3), Ru = (4), Scheme 1) in 68% (3)
and 66% (4) isolated yield (reactions in THF solution).30
Analytically pure crystals were obtained from toluene/
acetonitrile solutions. It is important to note that no reaction
is observed (or very slow) in the absence of daylight. We are
not able to comment on whether this enhanced reactivity is
due to the excited singlet or triplet A2 state of 1 or the
The 1H NMR spectra of 3 and 4 in C6D6 solutions further
corroborated the formation of metal-terminated tin clusters.
For instance, we detected two triplets for nonequivalent Me
protons with chemical shifts of δ = 0.81 and 1.00 ppm (3)
and δ = 0.81 and 1.01 ppm (4). The corresponding methy-
lene protons of the ethyl groups appear around δ ≈ 2.0 and
3.0-3.1 ppm, alongside the aromatic protons of the aryl
substituent (δ = 7.0-7.2 ppm). The Cp rings show sharp
singlets at δ = 4.54 (3) and 4.91 ppm (4). The structural
integrity in solution was confirmed by 1H-1H NOESY
experiments, showing characteristic NOEs between the
CpH and the protons of the CH2 and CH3 entities (see
Supporting Information).
For tin clusters of this type, 119Sn NMR spectroscopy is a
powerful tool to determine the connectivity between the metal
atoms. Both title compounds were analyzed in detail, show-
ing in each case the expected 119Sn-119Sn and 119Sn-117Sn
couplings between the bridgehead (Snb) and bridging (Snbr)
tin atoms. A typical example of an experimental 119Sn NMR
spectrum, showing also the simulated satellites,34 is depicted
in Figure 2. Of particular interest in this case was to compare
the J(Snb Snb) coupling constant in 1 with those observed
3 3 3
for 3 and 4. Since both bridgehead atoms are bonded to
the metal fragments and, accordingly, the formal bonding
interaction between them is eliminated, couplings may still
arise either through the bridging {SnDep2} units or via
(27) DFT calculations on D3 symmetric model compounds predicted
in each case the following order of the frontier molecular orbitals: (a)
HOMO-1: Eb Eb bonding orbital of a1 symmetry; (b) HOMO:
3 3 3
degenerate set of Eb-Ebr cluster bonding orbitals of e symmetry; (c)
(31) Photochemical investigations on M-M bonded bimetallic Cp/
carbonyl compounds like [MCp(CO)2]2 showed M-M bond homolysis
and CO-loss photochemical channels. It is by far out of the scope of this
article to cite all original papers dealing with the photochemistry of these
types of molecules. The reader is referred to excellent review articles cited
in ref 25. We thank one referee for helpful comments.
(32) Unfortunately, 3 and 4 could not be analyzed by mass spectrom-
etry because the electron impact (EI) ionization method tends to result
in decomposition of the compounds. The smoother electrospray ioniza-
tion method (ESI), however, was shown to be too gentle to ionize the
compounds.
LUMO: Eb Eb antibonding orbital of a2 symmetry (Eb: bridgehead
3 3 3
atoms; Ebr: bridging group 14 element of the {ER2} entities).
(28) Nied, D.; Klopper, W.; Breher, F. Manuscript in preparation.
(29) For a closely related bicyclo[1.1.1]pentasilane derivative see:
(a) Kabe, Y.; Kawase, T.; Okada, J.; Yamashita, O.; Goto, M.;
Masamune, S. Angew. Chem. 1990, 102, 823; Angew. Chem., Int. Ed.
1990, 29, 794. See also for some tricyclo[2.1.0.02,5]pentane derivatives:
(b) Lee, V. A.; Yokoyama, T.; Takanashi, K.; Sekiguchi, A. Chem.;
Eur. J. 2009, 15, 8401. (c) Lee, V. A.; Ichinoe, M.; Sekiguchi, A. J. Am.
Chem. Soc. 2002, 124, 9962.
(30) Moreover, 1H NMR spectroscopic monitoring of a reaction of 1
with a mixture of [FeCp(CO)2]2 and [RuCp(CO)2]2 in C6D6 provided the
typical signals of the symmetrical products 3 and 4. Furthermore, we
observed via 2D NMR spectra the unsymmetrical, heterobimetallic
Fe/Ru adduct, which exhibits the same 1H NMR chemical shifts (see
Supporting Information).
(33) For comparison: ν(CO) for [FeCp(CO)2]2 = 1958, 1936, 1771,
1757 cm-1; ν(CO) for [RuCp(CO)2]2 = 1957, 1940, 1773, 1761 cm-1
.
Fischer, R. D.; Vogler, A.; Noack, K. J. Organomet. Chem. 1967, 7, 135.
(34) (a) Programs WinNMR and WinDaisy, Bruker Daltonik: Bremen,
€
1999. (b) Hagele, G.; Engelhardt, M.; Boenigk, W. Simulation und Auto-
matisierte Analyse von NMR-Spektren; VCH: Weinheim, 1987.

Article
Organometallics, Vol. 29, No. 22, 2010 6031
Scheme 1. Reactivity of the Metalla[1.1.1]propellanes 1 and 2; Synthesis of the Transition Metal-Terminated
Bicyclo[1.1.1]pentastannanes 3 (M = Fe) and 4 (M = Ru)a
a Dep = 2,6-Et2C6H3, Mes = 2,4,6-Me3C6H2.
Figure 2. Experimental 119Sn NMR spectrum of 4 (C6D6, bottom) and the simulated34 coupling constants (top traces); only the
satellites are shown in the simulated spectra. See also Table 1 and the main text for further details.
“through-space interactions” due to the close spatial proxi-
mity of the bridgeheads.35
Table 1. Tin Coupling Constants [Hz] for 3 and 4; Those Reported
for 1 Are Given for Comparison
Table 1 summarizes and compares the coupling constants
observed for 3 and 4 with those reported for 1. Compared to
the latter, we observed smaller values for the one-bond
couplings 1J(119Snb-117/119Snbr), which in turn strongly vary
coupling
3
4
119
1J(119Snb-117Snbr
1J(119Snb-119Snbr
)
)
1623
1699
2908
1270
1230
1291
3896
1348
3975
4159
8145a
262
2J(119Snb 117Snb)
3 3 3
2J(119Snbr-117Snbr)
(35) Hoffmann, R. Acc. Chem. Res. 1971, 4, 1.
a Remeasured for completeness.

6032 Organometallics, Vol. 29, No. 22, 2010
Nied et al.
Figure 3. Molecular structures of 3 (a) and 4 (b). Displacement ellipsoids are drawn at the 30% probability level; hydrogen atoms have
been omitted and carbon atoms of the 2,6-Et2C6H3 substituents have been drawn with arbitrary radii for clarity. Selected bond lengths
[pm] and angles [deg]: (3) Sn3 Sn5 357.3(1), Sn1-Sn3 286.1(1), Sn2-Sn3 281.8(1), Sn3-Sn4 283.2(1), Sn1-Sn5 284.4(1), Sn2-Sn5
3 3 3
284.5(1), Sn4-Sn5 287.4(1), Fe1-Sn5 258.8(1), Fe2-Sn3 256.5(1), Fe-CpCentroid 171.7, Fe-CO 174.1, CO 114.7, Sn-C 217.4(6)-
219.9(6); Sn3-Sn1-Sn5 77.57(1), Sn3-Sn2-Sn5 78.25(1), Sn3-Sn4-Sn5 77.55(2), Sn1-Sn3-Sn2 85.05(1), Sn1-Sn3-Sn4 83.53(2),
Sn1-Sn5-Sn2 84.87(1), Sn1-Sn5-Sn4 83.09(1), Sn2-Sn3-Sn4 86.61(1), Sn2-Sn5-Sn4 85.32(1), C-Sn-C 106.1; (4) Sn1 Sn10
3 3 3
355.1(1) {357.4(1)}, Sn1-Sn2 283.2(1) {283.7(1)}, Sn1-Sn20 287.6(1) {285.8(1)}, Sn1-Sn3 283.7(1) {285.2(1)}, Ru1-Sn1 266.3(1)
{266.2(1)}, Ru-CpCentroid 189.7 {188.3}, Ru-CO 185.5 {184.6}, CO 114.3 {114.7}, Sn-C 219.8(7) - 220.6(7) {219.1(7)-220.6(7)};
Sn1-Sn2-Sn10 76.96(2) {77.60(3)}, Sn1-Sn3-Sn10 77.50(3) {77.74(3)}, Sn2-Sn1-Sn20 83.46(2) {85.41(3)}, Sn3-Sn1-
Sn2 85.68(2) {84.35(3)}, Sn3-Sn10-Sn2 86.51(2) {84.72(2)}, C-Sn-C 102.8 {101.6}; the values given in face brackets correspond
3
1
to the second molecule in the asymmetric unit; equivalent atoms generated by -x þ /2, y, -z þ /2; CpCentroid = centroid of the
Cp ring.
with the nature of the metal fragments (1623/1699 Hz for 3 vs
1230/1291 Hz for 4). Interestingly, the two-bond coupling
constant 2J(119Snbr-117Snbr) of 1348 Hz for 3 was revealed to
be larger than the one-bond coupling 1J(119Snb-117Snbr)
(1230 Hz). The most striking feature, however, is the com-
parably large coupling between the bridgehead tin atoms,
which were found to amount to 2908 (3) and 3896 (4) Hz
(absolute values).
The crystal structure determination of 3 (space group
Iba2) and 4 (P2/n)36 verified the formation of the metal-
terminated tin clusters (Figure 3).37 Relevant structural
parameters are given in the figure caption. As expected, the
Sn5 scaffold consisting of three bridging {SnDep2} units and
two ligand-free bridgehead tin atoms is preserved in both
compounds. The latter are coordinated to iron (3) and
ruthenium (4), which in turn consist of two CO ligands and
one η5-coordinated Cp moiety. Most importantly, the central
stretched in the direction of the bridgehead atoms. As a result
of this structural distortion, the Snb-Snbr-Snb angles are
increased (77.55(2)-78.25(1)° for 3 and 76.96(2)-77.50(3)°
(77.60(3)-77.74(3)°)38 for 4 vs 72.2(1)° for 1) and the
Snbr-Snb-Snbr angles of 83.09(1)-86.61(1)° for 3 and
83.46(2)-86.51(2)° (84.35(3)-85.41(3)°)38 for 4are decreased
with respect to the parent propellane 1 (cf. 88.2(1)-89.9(1)°).
The transition metal tin bond lengths of 256.5(1) and 258.8(1)
pm for Fe-Sn (3) and 266.3(1) pm (266.2(1) pm)38 for Ru-Sn
(4) fall within the expected ranges.39
Since redox-active transition metal atoms are present in
both compounds, it was of interest to study their electro-
chemical properties using cyclic voltammetry (CV) under
strictly anaerobic and dry conditions. In particular, we
studied the reduction chemistry of 3 and 4 in THF solutions.
As can be seen from Figure 4, the CVs of both compounds
were revealed to be much more complicated than antici-
pated. The cyclovoltammogram of 3 shows three irreversible
reduction waves centered atEpc = -1.90, -2.24, and -2.93 V.
On the basis of the peak current intensities it appears that
the first two waves correspond to one-electron processes,
while the last event comprises a two-electron reduction pro-
cess (for further studies see below). Furthermore, a broad
oxidation event between -3.0 and -2.5 V is observed in the
return sweep, followed by two electrochemically irreversible
Snb Snb distances of 357.3(1) pm (3) and 355.1(1) pm (4)
3 3 3
(357.4(1) pm)38 are significantly elongated by ca. 20 pm as
compared to the starting material 1. This observation con-
trasts earlier findings of Sita and co-workers, which showed
no structural changes upon MeI addition to the all-tin pro-
pellane 1 (cf. 336.1(1) and 336.7(1) pm).19 In 3 and 4, however,
the trigonal bipyramids composed of the five tin atoms are
(36) Hahn, T. International Tables for Crystallography, Vol. A, 5th
ed.; Kluwer Academic Publishers: Dordrecht, 2002.
(37) For a closely related structure, [{CpFe(CO)2}2Sn2Fe3(CO)9], see:
McNeese, T. J.; Wreford, S. S.; Tipton, D. L.; Bau, R. J. Chem. Soc.,
Chem. Commun. 1977, 390.
(39) See for instance Sn-Fe: 254.5 pm in [Cp(py)(CO)Fe-SnEt3].
Itazaki, M.; Kamitani, M.; Nakazawa, H. Acta Crystallogr. Sect. E
2008, 64, m1578. Sn-Ru: 265.0 pm in [Cp2Ru2(μ-CH2)(CO)2(SnMe3)2].
Akita, M.; Hua, R.; Oku, T.; Tanaka, M.; Moro-oka, Y. Organometallics
1996, 15, 4162.
(38) Values for the second independent molecule in the asymmetric
unit are given in brackets.

Article
Organometallics, Vol. 29, No. 22, 2010 6033
Scheme 2. Synthesis of 5
(CO)2}{Sn5Dep6}]- (5) and [CpFe(CO)2]2 (Scheme 2). For
the isolation of 5, the solvent THF was removed in vacuo and
the crude product washed with toluene in order to remove
the excess CoCp*2 and the byproduct [FeCp(CO)2]2. Re-
crystallization from acetonitrile at -40 °C affords analyti-
cally pure, dark red crystals of 5 (yield 85%; mp 245 °C
(dec)), which are soluble in THF and sparingly soluble in
acetonitrile and DMSO.
The 1H NMR spectrum of 5 in DMSO-d6 was consistent
with a monosubstituted cluster: the CH3 protons of the Dep
ligand appear as four triplets and the methylene protons as
several sets of multiplets. Alongside the aryl ring protons,
the Cp entity was detected as a singlet at δ = 4.68 ppm. In
contrast to 3 and 4, crystals of 5 are extremely sensitive to
air and moisture. Solutions of 5 immediately decolorize
when exposed to air. Furthermore, they turned out to be
unstable when stored at room temperature for a prolonged
time. Due to the instability of 5 in solution, we were not able
to record satisfactory 13C and 119Sn NMR spectra. How-
ever, the elemental analysis of bulk 5 was consistent with
the composition [CoCp*2][{FeCp(CO)2}{Sn5Dep6}]. In the
ESI mass spectrum we found the correct molecular ion
envelope and isotope distribution centered at m/z 1569.08
(ion envelope for the anionic cluster, see Figure 5). The
UV/vis spectrum of 5 in THF shows characteristic bands
at λmax = 492, 294, 264 (sh), and 214 nm (see the Supporting
Information).
Figure 4. Cyclic voltammetry of 3 at 15 °C in THF vs the
Fc/Fcþ couple. Scan rate 100 mV s-1, Pt/[(nBu)4N]PF6/Ag.
All redox waves show completely the same behavior in a second
CV cycle; only one is shown here for clarity. The oxidation wave
of very small intensity located at ca. -2.4 V can most likely be
attributed to the reoxidation of trace amounts of [1]2- (see text).
oxidations at Epa = -1.61 and -1.00 V (Figure 4). To put this
electrochemical behavior into perspective, it is instructive
to recall that metalla[1.1.1]propellanes such as 1 show two
An X-ray structure analysis was conducted on single
crystals of 5 (space group Pbca),36 unambiguously confirm-
ing the formation of the cobaltocenium salt of the anionic
cluster. As shown in Figure 6, only one of the bridgehead tin
atoms is bonded to the [FeCp(CO)2] entity. The tin cage is
quasi-reversible one-electron reduction waves at E0
=
1/2
-1.96 and -2.48 V (vs Fc/Fcþ). These redox couples corre-
spond to the processes 1 þ e- / [1]•- and [1]•- þ e- / [1]2-
.
stretched along the Snb Snb-Fe vector, which leads to
3 3 3
Furthermore, it is important to note that all redox waves of 3
show completely the same behavior in a second CV cycle,
which means that the overall reduction is chemically reversible,
consisting of several electrochemically irreversible couples.40
The electrochemistry of 4 is very similar (see the Supporting
Information).
a very large distance of d = 380.8(1) pm between the Snb
atoms. The Sn-Fe bond (267.3(1) pm) is 11 pm longer than
that found for 3. Other relevant distances and angles are
given in the figure caption.
With this first result in hand we were able to explain
the redox processes of 3 as follows: the first irreversible
reduction of 3 at Epc=-1.90 V (Figure 4) can be assigned to
the splitting of one Sn-Fe bond, which results in the
formation of 5 and “[FeCp(CO)2]•”. At this potential, the
resulting fragment “[FeCp(CO)2]•” immediately dimerizes
to form a half of an equivalent of [FeCp(CO)2]2. This one-
electron process is depicted in eq 1. Since the electrochem-
istry of [FeCp(CO)2]2 is very well known,26 the second
reduction process in the CV of 3 (Epc = -2.24 V) can be
assigned to the reductive splitting of [FeCp(CO)2]2 into two
anionic [FeCp(CO)2]- fragments (overall a one-electron
In order to shed more light on this fascinating electro-
chemistry, we performed some preparative reductions. As a
suitable entry point we decided to examine the first reduc-
tion event (Epc=-1.90 V). To this end, we treated a THF
solution of 3 with a slight excess of CoCp*2 (Cp* = C5Me5;
E01/2 = -1.94 V vs Fc/Fcþ), which resulted in a quantitative
formation of the cobaltocenium salt [CoCp*2]þ[{CpFe-
(40) (a) Geiger, W. E. Organometallics 2007, 26, 5738. (b) Evans, D. H.
Chem. Rev. 2008, 108, 2113.

6034 Organometallics, Vol. 29, No. 22, 2010
Nied et al.
Figure 5. Electrospray ionization (ESI) mass spectrum of 5
(inset: enlargement of the experimental and simulated molecular
ion envelope for [{FeCp(CO)2}{Sn5Dep6}]-). Since 5 is very
sensitive, the ion signals of low intensities are due to decom-
position products.
Figure 7. Cyclic voltammetry of 5 at 15 °C in THF vs Fc/Fcþ.
Scan rate: 100 mV s-1, Pt/[(nBu)4N]PF6/Ag. All redox waves
show completely the same behavior in a second CV cycle; only
one is shown here for clarity. CoCp2*: quasi-reversible redox
waves of the CoCp2* entity. Relevant redox processes of the
anion of 5 are marked with an asterisk (note the similarities to
those observed for 3, Figure 4).
the re-formation of 5 (eq 4; reverse of eq 3). The oxidation
event at Epa = -1.61 V belongs to the reoxidation of
[FeCp(CO)2]-, as known from the literature (eq 5).26
1
3 þ e- f 5 þ ½FeCpðCOÞ2ꢀ2 Epc ¼ - 1:90 V ð1Þ
2
1
2
-
½FeCpðCOÞ2ꢀ2 þ e- f ½FeCpðCOÞ2ꢀ
Epc ¼ - 2:24 V
ð2Þ
2 -
-
5 þ 2e- f ½1ꢀ þ ½FeCpðCOÞ2ꢀ
Epc ¼ - 2:93 V
ð3Þ
2 -
-
½1ꢀ þ ½FeCpðCOÞ2ꢀ f 5 þ 2e- Epa ꢁ - 2:75 V ð4Þ
Figure 6. Molecular structure of 5. Displacement ellipsoids are
drawn at the 30% probability level; the hydrogen atoms have
been omitted and carbon atoms of 2,6-Et2C6H3 and Cp* ligands
have been drawn with arbitrary radii for clarity. Selected bond
1
2
-
½FeCpðCOÞ2ꢀ
f
½FeCpðCOÞ2ꢀ2 þ e- Epa ¼ - 1:61 V
ð5Þ
lengths [pm] and angles [deg]: Sn1 Sn2 380.8(1), Sn1-Sn3
3 3 3
289.0(1), Sn1-Sn4 285.8(1), Sn1-Sn5 288.8(1), Sn2-Sn3
285.0(1), Sn2-Sn4 285.9(1), Sn2-Sn5 287.3(1), Fe1-Sn1
So far, all proposed equations comprise only diamagnetic
species. This is in accord with supplementary EPR studies.
As expected, we were not able to detect any paramagnetic
species by repeated in situ reduction of 3 within an EPR
tube. In order to fully explore the CV of 3 and to bolster the
proposed equations, we have investigated the fate of 5 a little
further by examining the electrochemistry of the latter. The
electrochemical responses of 5 (Figure 7) are very similar
to those found for 3, with some important exceptions: (a) two
quasi-reversible redox processes of the CoCp2* entity are
present (i.e., CoCp*2 / [CoCp*2]þ þ e-, E01/2 = -1.85 V;
267.3(1), Sn2 Co1 606.2, Fe1-CpCentroid 172.1, Co-
3 3 3
CpCentroid 163.1, Fe-CO 173.6, CO 115.3, Sn-C 219.3(6)-
221.2(6); Sn1-Sn3-Sn2 83.11(1), Sn1-Sn4-Sn2 83.53(1),
Sn1-Sn5-Sn2 82.76(1), Sn3-Sn1-Sn4 80.05(1), Sn3-Sn1-
Sn5 80.12(1), Sn4-Sn1-Sn5 81.23(1), Sn3-Sn2-Sn4 80.72(1),
Sn3-Sn2-Sn5 81.06(1), Sn4-Sn2-Sn5 81.47(1), C-Sn-C
103.7; CpCentroid = centroid of the Cp ring.
process, eq 2). Since it is reasonable to assume that the most
negative reduction process at Epc = -2.93 V again leads to
a splitting of the Fe-Sn bond in 5, formation of [1]2-, and a
reduction of the resulting “[FeCp(CO)2]•” fragment at this
potential, we propose eq 3 for this two-electron process.
Furthermore, we assume that the broad oxidation peak
around Epa ≈ -2.75 V in the return sweep can be assigned to
CoCp*2 þ e- / [CoCp*2]-, E0 = -3.15 V);41 (b) the
1/2
(41) Braunschweig, H.; Breher, F.; Kaupp, M.; Gross, M.; Kupfer,
T.; Nied, D.; Radacki, K.; Schinzel, S. Organometallics 2008, 27, 6427
(and cited references).

Article
Organometallics, Vol. 29, No. 22, 2010 6035
Figure 8. Proposed cascade of bond-breaking and bond-making processes during the chemically reversible though electrochemically
irreversible redox cycle of 3. The numbers correspond to the equations given in the text.
redox waves of [FeCp(CO)2]2 (eq 2) and [FeCp(CO)2]- (eq 5)
are missing. All other features, i.e., peak current intensities
and potentials for 5, directly correspond to those observed
for 3. Especially the first reduction peak at Epc=-1.90 V,
which was assigned to the splitting of one Sn-Fe bond in 3, is
also visible in the CV of 5. Furthermore, the so far unex-
plained irreversible oxidation peak centered at Epa = -1.0 V
in the CV of 3 is also present in the voltammogram of 5.
From these studies it can be concluded that identical tin
clusters species must be involved in the electrochemistry of
both compounds!
In order to clarify this last piece of the puzzle, we per-
formed some preparative oxidation experiments on an NMR
tube scale. The anionic cluster 5 was reacted with 1 equiv of
[Fc][PF] (with [PF]- = [Al{OC(CF3)3}4]-)42 in d8-THF.
Again, we were not able to detect any paramagnetic species
by EPR spectroscopy. Most revealingly, the sample gave
clean NMR signals, which were easily assigned to 3 and 1.
Hence, the most positive oxidation event at Epa=-1.0 V
corresponds to a dismutation reaction (eq 6).
Conclusions
Metal-terminated bicyclo[1.1.1]pentastannanes of the
general formula [{MCp(CO)2}2{μ-Sn5Dep6}] (M=Fe (3),
Ru =(4)) are available by reacting the heavy propellane
Sn5Dep6 (1) with the transition metal precursors [MCp-
(CO)2]2. In each case, the latter can readily be added to the
bridgehead atoms, nicely confirming the radical-type reac-
tivity of metalla[1.1.1]propellanes, in this case 1. The title
compounds 3 and 4 have been characterized in detail using
various methods. X-ray structures of both compounds cor-
roborated that the two ligand-free bridgehead tin atoms
within the Sn5 scaffold are bonded to iron (3) and ruthenium
(4). The reduction chemistry of 3 and 4 in THF solutions was
shown to be considerably more complicated than antici-
pated. A detailed preparative and electrochemical study
elucidated a complex redox cycle consisting of a cascade of
bond-breaking and bond-making processes, fully in accord
with the chemically reversible redox cycle of 3 consisting of
electrochemical irreversible couples. Further studies on this
type of metal-terminated clusters are currently in progress in
our laboratory.
1
1
5 f 1 þ 3 þ e- Epa ¼ - 1:0 V
ð6Þ
2
2
Experimental Section
The absence of the redox waves of [FeCp(CO)2]2 in the CV
of 5 can be explained as follows: once the first amounts of 3
are reduced (eq 1), the resulting [FeCp(CO)2]2 immediately
reacts with 1 to form 3 (see above), which in turn is again
reduced to 5.43 Thus, no electrochemical responses of
[FeCp(CO)2]2 and/or [FeCp(CO)2]- are visible in the cyclic
voltammogram of 5.
By summing up all equations and assumptions, we were
able to propose the redox cycle depicted in Figure 8. The
complicated though very appealing reduction chemistry of 3
consists of a cascade of bond-breaking and bond-making
processes, fully in accord with the chemically reversible
redox cycle of 3 consisting of electrochemical irreversible
couples.
General Methods and Instrumentation. All manipulations
were carried out using standard Schlenk line or drybox tech-
niques under an atmosphere of argon. Solvents were freshly
distilled under argon from the appropriate drying agent.
Deuterated solvents were refluxed over the appropriate drying
agent, distilled, and stored under argon in Teflon valve ampules.
NMR samples were prepared under an inert atmosphere
in 5 mm Wilmad 507-PP tubes, either sealed or fitted with
J. Young Teflon valves. 1H, 13C{1H}, 29Si, and 119Sn NMR
spectra were recorded on Bruker Avance 400 and Avance III
300 spectrometers and are referenced according to IUPAC
recommendations.44 1H, 13C, and 29Si chemical shifts are given
relative to TMS and 119Sn to Me4Sn. Coupling constants J are
given in Hertz as absolute values regardless of their real indivi-
dual signs. The multiplicity of the signals is indicated as s, d, t,
dq, or m for singlets, doublets, triplets, doublets of quadruplets,
(42) Krossing, I.; Raabe, I. Angew. Chem. 2004, 116, 2116; Angew.
Chem., Int. Ed. 2004, 43, 2066.
(43) Another possible mechanism: (a) reduction of 1 to [1]•-; (b)
reaction of [1]•- with “[FeCp(CO)2]•” or [FeCp(CO)2]2 to furnish 5.
(44) Harris, R. K.; Becker, E. D.; Cabral de Menezes, S. M.;
Goodfellow, R.; Granger, P. Pure Appl. Chem. 2001, 73, 1795.

6036 Organometallics, Vol. 29, No. 22, 2010
Nied et al.
and multiplets, respectively. The abbreviation br is given for
broadened signals. Assignments were confirmed as necessary
with the use of 2D correlation experiments. Cyclic voltammetry
measurements were performed with an EG&G potentiostat
(PAR model 263A) and an electrochemical cell for sensitive
compounds.45 We used a freshly polished Pt disk working
electrode, a Pt wire as counter electrode, and a Ag wire as
(pseudo) reference electrode ([n-Bu4N][PF6] (0.1 M) as electro-
lyte). Potentials were calibrated against the Fc/Fcþ couple,46
which has a potential of E01/2 = 0.35 V vs Ag/AgCl. Continuous
wave electron paramagnetic resonance spectroscopy was per-
formed at X-band on a Bruker EMXplus spectrometer (microwave
frequency 9.43 GHz) equipped with a liquid nitrogen cryostat.
The samples were measured with a modulation amplitude of
10 G and a modulation frequency of 100 kHz, and the field
was calibrated by using 2,2-diphenyl-1-picrylhydrazyl with a g
value of 2.0036. IR spectra were recorded on a Bruker Vertex
70 spectrometer in the range from 4000 to 400 cm-1 using a KBr
beamsplitter. Samples were prepared by using the ATR technique
(attenuated total reflection) on bulk material, and the data are
quoted in wavenumbers (cm-1). The intensity of the absorption
band is indicated as vw (very weak), w (weak), m (medium), s
(strong), vs (very strong), br (broad), or sh (shoulder). UV/vis
spectra were recorded on a Varian Cary 100 Scan UV/vis spectro-
meter. ESI mass spectra of 5 (THF solution under nitrogen) were
measured on a FTICR (Fourier Transform Ion Cyclotron Res-
onance) IonSpec Ultima mass spectrometer equipped with a 7 T
magnet (Cryomagnetics, Inc.). The end plate of the ESI source
was typically held at a potential of 3.25 kV while the potential of
the entrance of the metal coated quartz glass capillary was set to
3.20 kV. Dry nitrogen was used as nebulizing gas. The ions were
stored in a hexapole for 4 s prior to transfer into the ICR cell in
order to increase the signal-to-noise ratio. Elemental analyses
were recorded by the institutional technical laboratories of the
Karlsruhe Institute of Technology (KIT). The elemental analysis
(carbon) of compound 4 is slightly out of the admitted error,
which can be attributed to either the sensitivity or the varying
solvent content of the sample. As indicated by the formula
[C74H88Ru2O4Sn5 1/2toluene 1/4thf], we have consistently used
and 152.4 (Ph), 214.9 (CO). 119Sn{1H} NMR (C6D6, 149.0
MHz, ppm): δ -260 (1J(119Snbr,117/119Snb) = 1623/1699 Hz,
2J(119Snbr,117Snbr) = 1270 Hz), -296 (1J(119Snb,117/119Snbr) =
1623/1699 Hz, 2J(119Snb,117Snb) = 2908 Hz). IR-ATR (cm-1): ν
404 (w), 415 (w), 426 (m), 445 (m), 464 (m), 485 (m), 501 (m), 570
(vs), 630 (w), 694 (vw), 717 (vw), 729 (w), 756 (vw), 802 (w), 832
(w), 1010 (vw), 1371 (vw), 1413 (vw), 1429 (vw), 1448 (w),
1466 (vw), 1947 (m), 1985 (m), 2852 (w), 2921 (m), 2955 (vw).
UV/vis (nm): λmax = 436 (ε = 14 500), 368-300 shoulder, 254
(ε = 68 500 M-1 cm-1), 212 (ε = 150 500 M-1 cm-1).
[{RuCp(CO)2}2Sn5Dep6] (4). A THF solution (10 mL) of 1
(80.0 mg, 57.4 μmol) and [RuCp(CO)2]2 (26.1 mg, 57.4 μmol)
was stirred for one week at room temperature. After the solvent
of the dark yellow solution was removed in vacuo, the crude
product was redisolved in toluene (3 mL), layered with acetoni-
trile (10 mL), and stored at -40 °C to afford dark yellow-green
crystals suitable for single-crystal X-ray diffraction. Yield:
70 mg (38.1 μmol, 66%). Mp: 270 °C (dec). Anal. Found: C,
50.52; H, 5.06. Calcd for [C74H88Ru2O4Sn5 1/2toluene 1/4thf ]
3
3
[1899.1 g mol-1]: C, 49.59; H, 4.98. 1H NMR (C6D6, 400.1 MHz,
ppm): δ 0.81 (t, 3JHH = 7.4 Hz, 18 H, CH3), 1.01 (t, 3JHH = 7.4
Hz, 18 H, CH3), 2.07 (dq, 3JHH = 7.4 Hz, 2JHH = 15.5 Hz, 6 H,
CH2), 3.08 (m, 18 H, three overlapping methylene groups), 4.91
3
(s, 10 H, Cp), 6.99 and 7.01 (2d, JHH = 7.9 Hz, 12 H, H3-Ph
and H5-Ph), 7.22 (t, 3JHH = 7.6 Hz, 6 H, H4-Ph). 13C{1H} NMR
(C6D6, 100.6 MHz, ppm): δ 14.9 and 16.3 (CH3), 35.5 and
35.6 (CH2), 86.4 (Cp), 125.8, 125.9, 130.4, 150.3, 150.5,
and 152.3 (Ph), 215.2 (CO). 119Sn{1H} NMR (C6D6, 149.0
MHz, ppm): δ -285 (1J(119Snbr,117/119Snb) = 1230/1291 Hz),
2J(119Snbr,117Snb) = 1348 Hz), -287 (1J(119Snb,117/119Snbr) =
1230/1291 Hz, 2J(119Snb,117Snb) = 3896 Hz). IR-ATR (cm-1):
476 (s), 512 (s), 548 (vs), 592 (w), 694 (w), 715 (w), 729 (w), 756
(vw), 802 (m), 816 (m), 833 (vw), 1010 (w), 1038 (vw), 1062 (vw),
1091 (vw), 1170 (vw), 1225 (vw), 1320 (vw), 1351 (vw), 1372 (w),
1421 (w), 1449 (m), 1562 (vw), 1953 (s), 1962 (s), 2003 (vs),
2852 (m), 2921 (m), 2955 (w), 3044 (vw). UV/vis (nm): λmax 414
(ε = 73 500 M-1 cm-1), 382-335 shoulder, 254 shoulder, 213
(ε = 285 000 M-1 cm-1).
3
3
[CoCp*2][{FeCp(CO)2}Sn5Dep6] (5). To a THF solution
(5 mL) of 3 (20.0 mg, 11.5 μmol) was added a THF solution
(3 mL) of CoCp*2 (5 mg, 15.2 μmol) at room temperature, and
the solution was stirred for 20 min. The reaction mixture was
evaporated to dryness, and the residue was washed several times
with toluene. The ruby-colored powder was redisolved in aceto-
nitrile and stored at -30 °C to form dark red crystals suitable for
X-ray diffraction. Yield: 19 mg (9.8 μmol, 85%). Mp: 245 °C
(dec). ESI-MS (3.6 kV) m/z: 1569.08. Anal. Found: C, 55.05; H,
5.92. Calcd for [C87H113CoFeO2Sn5] [1899.2 g/mol]: C, 55.02;
H, 6.00; Co, 3.10; Fe, 2.94; O, 1.68; Sn, 31.25. 1H NMR (DMSO-
d6, 400.1 MHz, ppm): δ 0.53 (t, 3JHH = 7.4 Hz, 9 H, CH3), 0.61
the composition detected by X-ray crystallography for the calcu-
lated values.
Starting Materials. Sn3Dep6,47 Sn5Dep6 (1),19 Ge5Mes6 (2),22
and [RuCp(CO)2]2 were prepared according to literature
48
methods. [FeCp(CO)2]2 and CoCp*2 were used as purchased
from ABCR without further purification.
[{FeCp(CO)2}2Sn5Dep6] (3). A THF solution (10 mL) of 1
(100 mg, 71.8 μmol) and [FeCp(CO)2]2 (25.4 mg, 71.8 μmol)
was stirred for 48 h at room temperature. After the solvent of
the dark yellow solution was removed in vacuo, the crude
product was redisolved in toluene (3 mL), layered with acetoni-
trile (10 mL), and stored at -40 °C to afford dark yellow-
green crystals suitable for single-crystal X-ray diffraction. Yield:
85 mg (48.7 μmol, 68%). Mp: 255 °C (dec). Anal. Found:
C, 52.87; H, 5.23. Calcd for [C74H88Fe2O4Sn5 toluene
3
(2t, JHH = 7.4 Hz, 18 H, CH3), 0.96 (t, 3JHH = 7.4 Hz, 9 H,
CH3), 1.62 (m, 3 H, CH2), 1.96 (m, 3 H, CH2), 2.45 (m, 3 H,
CH2), 2.67 (m, 3 H, CH2), 2.96 (m, 12 H, CH2), 4.68 (s, 5 H, Cp),
6.43 (d, 3JHH = 7.6 Hz, 3 H,), 6.56 (d, 3JHH = 7.6 Hz, 3 H) and
6.71 (t, 3JHH = 6.4, 6 H, H3-Ph and H5-Ph), 6.91 (2t, 3JHH = 7.5
Hz, 6 H, H4-Ph). IR-ATR (cm-1): 445 (m), 490 (m), 508 (m), 572
(vs), 643 (m), 722 (m), 739 (w), 753 (m), 802 (m), 889 (wv), 1013
(w), 1021 (w), 1058 (vw), 1165 (vw), 1225 (vw), 1268 (vw), 1324
(w), 1371 (m), 1425 (m), 1447 (s), 1562 (vw), 1638 (vw), 1906 (vs),
1953 (vs), 2000 (vw), 2869 (w), 2927 (w), 2958 (w), 3040 (vw).
UV/vis (nm): λmax 492 (ε = 24 500 M-1 cm-1), 294 (ε = 140 000
M-1 cm-1), 264 shoulder, 214 (ε = 315 000 M-1 cm-1).
3
3
1
1/2CH3CN] [1859.26 g mol-1]: C, 52.97; H, 5.29; N, 0.38. H
NMR (C6D6, 400.1 MHz, ppm): δ 0.81 (t, 3JHH = 7.3 Hz, 18 H,
CH3), 1.00 (t, JHH = 7.3 Hz, 18 H, CH3), 2.02 (dq, JHH =
3
3
2
7.3 Hz, JHH = 15.4 Hz, 6 H, CH2), 3.03 (m, 12 H, two
3
overlapping methylene groups), 3.12 (dq, JHH = 7.3 Hz,
2JHH = 14.5 Hz, 6 H, CH2), 4.54 (s, 10 H, Cp), 6.98-7.02 (m,
12 H, H3-Ph and H5-Ph) 7.21 (t, 3JHH = 7.6 Hz, 6 H, H4-Ph).
13C{1H} NMR (C6D6, 100.6 MHz, ppm): δ 14.8 and 16.2 (CH3),
35.4 and 35.7 (CH2), 83,4 (Cp), 125.8, 125.9, 127.1, 150.2, 150.5,
Crystal Structure Determinations of 3, 4, and 5. Crystal data
collection and processing parameters are given in Table 2. In
order to avoid degradation, the single crystals were mounted on
glass fibers using perfluoropolyether oil and cooled rapidly in a
stream of cold N2 using an Oxford Cryosystems Cryostream
unit. Diffraction data were measured using a STOE STADI 4
diffractometer equipped with a CCD detector and graphite-
(45) (a) Hinkelmann, K.; Heinze, J.; Schacht, H.-T.; Field, J. S.;
Vahrenkamp, H. J. Am. Chem. Soc. 1989, 111, 5078. (b) Heinze, J. Angew.
Chem. 1984, 96, 823; Angew. Chem., Int. Ed. 1984, 23, 831.
(46) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877.
(47) Sita, L. R.; Bickerstaff, R. D. J. Am. Chem. Soc. 1989, 111, 3769.
(48) Doherty, N. M.; Knox, S. A. R.; Morris, M. J. Inorg. Synth.
1990, 28, 189.
˚
monochromated Mo KR (0.71073 A) radiation. All calculations

Article
Organometallics, Vol. 29, No. 22, 2010 6037
Table 2. Crystal Data, Data Collection, and Structure Refinement for 3, 4, and 5
3
4
5
empirical formula
M
cryst syst
space group
a/pm
b/pm
C
74H88O4Fe2Sn5 C7H8 1/2 CH3CN
1859.26
2 C74H88O4Ru2Sn5 C7H8 1/2C4O
C67H83O2FeSn5,C20H30Co
1899.00
orthorhombic
Pbca (no. 61)
25.077(5)
3
3
3
3
3798.22
monoclinic
P2/n (no. 13)
20.896(4)
14.802(3)
25.759(5)
107.59(3)
7595(3)
2.050
orthorhombic
Iba2 (no. 45)
21.362(4)
40.586(8)
17.613(4)
24.040(5)
26.596(5)
c/pm
β/deg
V/106 pm3
μ/mm-1
15271(5)
2.026
1.617
16033(6)
1.955
Dcalcd/g cm-3
cryst dimens/mm
Z
1.661
0.15 ꢂ 0.10 ꢂ 0.10
1.573
0.40 ꢂ 0.25 ꢂ 0.20
0.25 ꢂ 0.15 ꢂ 0.15
8
150
2
200
8
200
T/K
2θmax/deg
reflns measd
reflns unique
params/restraints
R1 [I g 2σ(I )]
wR2 (all data)
max./min.
resid electron
dens/eꢂ10-6 pm-3
52.00
54 993
14 738 (Rint = 0.0643)
858/149
0.0406
0.0906
1.534/-1.088
52.00
55 138
14 885 (Rint = 0.0638)
923/141
0.0581
0.1498
2.620/-2.020
52.00
11 1307
15 667 (Rint = 0.0890)
907/4
0.0647
0.1224
0.850/-1.074
were performed using the SHELXTL (ver. 6.12) program
suite.49,50 The structures were solved by direct methods and
successive interpretation of the difference Fourier maps, fol-
lowed by full matrix least-squares refinement (against either F
or F2). All non-hydrogen atoms were refined anisotropically
(for exceptions see below). The contribution of the hydrogen
atoms, in their calculated positions, was included in the refine-
ment using a riding model. Upon convergence, the final Fourier
difference map of the X-ray structures showed no significant
peaks.
suitably refined. Two molecules of 4 crystallize with one
toluene and
1
/ THF molecule, as indicated by the formula
2
2C74H88O4Ru2Sn5 C7H8 1/2C4O in Table 2. The latter was
3
3
located on a special crystallographic position and was refined
isotropically without hydrogen atoms. Since the toluene solvent
molecule was also located on a special crystallographic position,
it was refined by using appropriate restraints and the instruction
PART-1 in SHELXL. The toluene C atoms and two other C
atoms of the Dep ligands (disordered Et substituents) have been
refined using the ISOR restraint.
Several ethyl groups of the Dep ligands in 4 and one in 5 were
disordered over two sites. In these cases, the two positions were
refined against each other using one free variable with occupa-
tion factors of 2 ꢂ 42% and 45% (4) and 40% (5) for the
disordered position. Attempts to refine other Et groups showing
unusually large displacement ellipsoids were not successful. 3
All details of the structure solution and refinements are given
in the Supporting Information (CIF data). Full listings of
atomic coordinates, bond lengths and angles, and displacement
parameters for all the structures have been deposited at
the Cambridge Crystallographic Data Centre. See Notice to
Authors, Issue No. 1.
1
crystallizes with one toluene and /2 CH3CN molecule in the
Acknowledgment. Partial financial support by the Fonds
der Chemischen Industrie is gratefully acknowledged. M.N.
thanks the German Science Foundation (DFG) for finan-
cial support.
crystal lattice. The toluene C atoms (refined with some DFIX
restraints) and one CO oxygen atom and four C atoms of the
Dep ligands (disordered Et substituents) have been refined
using the ISOR restraint. As indicated by SHELXL (Flack x
parameter around 0.3), the structure of 3 showed racemic
twinning. By using an appropriate TWIN card in SHELXL
and a batch scale factor of BASF=0.31 the structure was
Supporting Information Available: X-ray crystallographic
data in CIF format for the structure determinations of 3, 4,
and 5. UV/vis spectra of 3, 4, and 5, NOESY and 119Sn NMR
spectra for 3, cyclic voltammetry of 4. This material is available
free of charge via the Internet at http://pubs.acs.org.
(49) SHELXTL v6.12; Bruker AXS Inst. Inc.: Madison, WI, USA, 2000.
(50) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.