Synthesis, structure and electrochemical properties of a ferrocene-bridged bis[tris(arylselenolato)stannyl] compound

Article abstract of DOI:10.1002/ejic.200900664

Two ferrocene-bridged bis[tris(arylselenolate)stannyl] compounds with the general formula (RSe)₃Sn-Fc-Sn(SeR)₃ [Fc = ferrocene; R = Ph (1), 1-Np (2)] were synthesized and characterized by means of NMR spectroscopy (1, 2) as well as X

Full text of DOI:10.1002/ejic.200900664

SHORT COMMUNICATION
DOI: 10.1002/ejic.200900664
Synthesis, Structure and Electrochemical Properties of a Ferrocene-Bridged
Bis[tris(arylselenolato)stannyl] Compound
Hari Pada Nayek,[a] Gerhard Hilt,[a] and Stefanie Dehnen*[a]
Keywords: Ferrocene / Selenium / Tin / X-ray diffraction / Cyclic voltammetry / DFT calculations
Two ferrocene-bridged bis[tris(arylselenolate)stannyl] com- in the presence of an Fc bridge between the two tin atoms.
pounds with the general formula (RSe)3Sn–Fc–Sn(SeR)3 [Fc
= ferrocene; R = Ph (1), 1-Np (2)] were synthesized and char-
acterized by means of NMR spectroscopy (1, 2) as well as X-
ray diffraction (1). It was shown by DFT calculations that the
observed mixed cis/trans conformation of the SePh groups in
1 represents the global minimum on the energy hyperface
Investigation of the electrochemical behavior of 1 indicated
the electrochemically driven conversion under cleavage of
the tin–selenium bond.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
thesized by treating bis(trichlorostannyl)butane with
Na2S·9H2O and [CuCl(Ph3P)3] under solvothermal condi-
tion.[20] The Corrigan group used ferrocene-bridged chalco-
genido ligands to synthesize several nanoclusters.[21] How-
ever, the reactivity of ferrocene-bridged ditin compounds
towards arylchalcogenolate or chalcogenide was not investi-
gated so far.
In this paper, we report the syntheses, characterization,
optical and electrochemical properties of two novel aryl-
selenolato-substituted tinorganyl compounds according to
the general formula (RSe)3Sn–Fc–Sn(SeR)3, (Fc = ferro-
cene; 1: R = Ph; 2: R = 1-Np). The title compounds are
currently being explored with respect to their applicability
as synthons in the preparation of heterometallic, mixed co-
ordination/organometallic polymers.
Introduction
During the last decades, organotin and (organochalcog-
enolato)tin compounds have been extensively developed
due to their interesting catalytic or biological activities, as
well as their precursor function for the generation of tin
chalcogenide films for opto-electronic applications.[1–11]
Stannoxanes, for example, catalyze the formation of acetals
or esters from alcohols and ketones[12] or acids and
alcohols,[13] respectively. [Ph3Sn(SR)] (HSR = 2-mercapto-
benzoxazole or 5-chloro-2-mercaptobenzothiazole) exhibits
lipoxygenase inhibitory activities.[14] Tetrakis(thiophenol-
ato)tin was used for the syntheses of thin films of SnS and
SnS2.[15] Additionally, organotin chlorides were used as
starting materials for the synthesis of a number of cyclic
compounds R6Sn3S3 or adamantine-type structures (RSn)4-
S6 (e.g. R = C6F5, C6H4F, Ph, C6H4Me, Me, CMe2CH2-
COMe, C2H4COOH) by reactions with S(SiMe3)2 or
Na2S·9H2O.[16] The employment of tin thiolates recently re-
sulted in the formation of ternary clusters like [Cu4Sn3(edt)6-
Results and Discussion
Syntheses
(µ3-O)(PPh3)4](ClO4)2·3CH2Cl2,
[(Ph3P)2Cu]2SnS(edt)2·
1,1Ј-Bis[tris(arylselenolato)stannyl]ferrocene compounds
were prepared by treating 1,1Ј-bis(trichlorostannyl)ferro-
cene with NaSeR, generated in situ by sodium borohydride
reduction of diphenyl diselenide (1) or dinaphthyl diselenide
(2) in ethanol (Scheme 1). Compounds 1 and 2 were charac-
2CH2Cl2·H2O, [(Ph3P)2Cu]2SnS(edt)2·2DMF·H2O and
[(Ph3P)Cu]2Sn(SPh)6·3H2O, synthesized by reactions of
[Cu(PPh3)2(MeCN)2]ClO4 with Sn(edt)2 (edt = ethane-1,2-
dithiolate),[17] by reaction of [(PPh3)3CuBr] with (Bu4N)2-
[Sn3S4(edt)3], or by reaction of Sn(SPh)4 with CuCN and
PPh3.[18] Bis(trichlorostannyl)organyl compounds were used
to synthesize a series of bis[tris(arylchalcogenolato)stannyl]
derivatives, and their reactivity was studied by our group.[19]
We have also reported a heterometallic, heterovalent CuI/
SnII/IV/S cluster, [(Ph3PCuI)6{(CH2)4SnIVS2}6CuI4SnII], syn-
[a] Fachbereich Chemie und Wissenschaftliches Zentrum für Mate-
rialwissenschaften (WZMW) der Philipps-Universität Marburg
Hans-Meerwein-Straße, 35032 Marburg, Germany
Fax: +49-6421-28-25653
Scheme 1. Syntheses of compounds 1 and 2.
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H. P. Nayek, G. Hilt, S. Dehnen
SHORT COMMUNICATION
terized by means of NMR spectroscopy. Details of the ex- with a gauche-type conformation, a more trans-like arrange-
perimental procedures are given in the Experimental Sec- ment of four selenophenolato ligands is observed: those
tion.
containing Se2, Se3, Se2Ј, Se3Ј are oriented away from the
bridging ferrocene residue with dihedral angles C1–Sn–Se–
CPh of 137.20 or 162.30°. The remaining two selenophe-
nolato groups at Se1 and Se1Ј atoms are oriented rather cis-
like toward the bridging ferrocene residue with a dihedral
angle of 72.48°. This cis/trans mixed conformation of the
C1–Sn–Se–CPh connections in 1 does not only seem to be
favorable for a dense packing of the rod-like molecules
within the crystal; according to density functional theory
(DFT)[24] calculations of the isolated molecules, using the
program system Turbomole,[25] the all-trans-type conformer
is by 340 kJmol–1 higher in energy for the most stable ar-
rangement of the three Ph rings upon rotation about the
Se–CPh bonds. This significant energetic disadvantage is the
result of a systematically observed distortion of the geome-
try at the Sn atoms away from a trigonal pyramid toward
a less favorable see-saw geometry, which is driven by the
incongruent tendency to form intramolecular Cp–H···Se in-
teractions and to minimize the steric interaction between
the three SePh groups at the same time. Conformers with
more than one cis-type SePh ligand per Sn atom evolved
not to be a local minimum on the energy hypersurface ow-
ing to unacceptable steric repulsions between the Cp rings
and the backward orientated Ph substituents.
Crystal Structures
Compound 1 was structurally characterized by means of
single-crystal X-ray diffraction,[22,23] whereas for 2, no crys-
tals were obtained. However, the congruence of all analyti-
cal data served to identify the composition. Figure 1 shows
the molecular structure and provides selected interatomic
distances and angles of compound 1. A fragment of the
packing of the molecules within the crystal lattice is shown
in Figure 2.
Figure 1. (a) Molecular structure of 1, selected distances [pm] and
angles [°] in 1: Sn–C 210.40(7), Sn–Se 250.58(11)–254.13(11), C–Se
191.5(8)–194.2(7); C–Sn–Se 104.85(19)–113.20(2), Se–Sn–Se
106.47(3)–111.83(4), C–Se–Sn 92.00(2)–96.00(2).
Electrochemical Behavior
Cyclovoltammetric measurements were performed in or-
der to investigate both the influence of the substitution of
ferrocene by two Sn(SR)3 groups and to explore the electro-
chemical stability of 1. The cyclic voltammogram is given
in Figure 3.
Figure 2. Fragment of the packing of the molecules of 1 within the
crystal, viewed along crystallographic b axis.
Compound 1 crystallizes as orange needles in the mono-
clinic space group P21/n (No. 14) with two formula units in
the unit cell. The two [Sn(SePh)3] units bind to different
cyclopentadienyl rings of the bridging ferrocene entity. Ac-
cording to the inversion symmetry of the molecule, both
Figure 3. Multiple cyclic voltammogram of compound 1 at a scan
rate of 200 mVs–1 in dichloromethane.
The figure shows the electrochemical behavior of com-
the Cp rings and the [Sn(SePh)3] groups adopt a staggered pound 1 in dichloromethane. The strong oxidation peak of
conformation. This way, the steric hindrance of the bulky the first scan at +860 mV seems to have its quasi-reversible
substituents is minimized. The coordination geometry counter peak at a reduction potential of +660 mV. A second
around the tin atoms is distorted tetrahedral with distances reduction peak at +485 mV overlaps with the first peak. In
Sn–C 210.40(7) and Sn–Se 250.58(11)–254.13(11) pm. Al- the second cycle, we observed that the previous shoulder at
though all six connections C1–Sn–Se–CPh are in accord +510 mV increases, while a strong decrease of the firstly
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Ferrocene-Bridged Bis[tris(arylselenolato)stannyl] Compound
observed oxidative peak at +860 mV occurs. On the reverse
scan the first reduction peak at +660 mV decreases, while
the peak at +485 mV increases. In the third cycle isosbestic
points are clearly recognizable indicating that compound 1
is electrochemically transformed into a new product. In
control experiments we were able to show that PhSn-
(SePh)3 did not produce any eletroanalytically relevant
Experimental Section
General: All manipulations were performed under purified argon
by using a double manifold Schlenk line, or under dry N2 within a
glove box. Solvents were dried by standard methods and freshly
distilled prior to use. 1H, 13C and 119Sn NMR spectra were re-
corded with a Bruker Avance DRX 400 spectrometer. Commer-
cially available reagents were used as received. Cl3Sn–Fc–SnCl3 was
peaks in the region in question. The electroanalytical inves- prepared according to the literature.[26]
tigation of FcSnCl3 showed an almost reversible redox cou-
Synthesis of (RЈSe)3Sn–Fc–Sn(SeRЈ)3: 1,1Ј-Bis(trichlorostannyl)fer-
ple at +705 mV for the oxidation peak and +475 mV for
the corresponding reduction peak vs. Ag/AgCl. Therefore,
rocene (0.16 mmol) was dissolved in degassed absolute ethanol
(5 mL) and added to an ethanolic solution (5 mL) of NaSePh pre-
we propose that the carbon–tin bond is not cleaved during pared from R2Se2 (0.48 mmol) and Na[BH4] (1.06 mmol) in situ.
The mixture was stirred for 24 h. The orange solid was isolated by
filtration, washed with ethanol and n-hexane, and dried in vacuo.
Crystals of 1, suitable for single-crystal X-ray diffraction were ob-
tained by slow evaporation of a dichloromethane/n-hexane (1:1)
mixture.
the cyclic voltammograms of 1. The cleavage of a tin–sele-
nium bond seems most likely. Another weak reduction peak
is observed at ca. –950 mV. It may arise from the decompo-
sition process of 1 or be due to further impurities. The na-
ture of the electrochemically generated product could not
be elucidated so far.
1,1Ј-Bis[tris(selenophenolato)stannyl]ferrocene (1): Yield: 0.085 g,
1
0.063 mmol, 40%. H NMR (400 MHz, CDCl3): δ = 3.75 (s, 4 H,
CpH), 4.28 (s, 4 H, CpH), 7.14–7.50 (m, 30 H, ArH) ppm. 13C
NMR (100 MHz, CDCl3): δ = 70.30, 72.47, 74.16 (Cp), 124.23,
129.00, 131.53, 137.08 (Ar) ppm. 119Sn NMR (CDCl3): δ = –49.27
(s) ppm. C46H38Se6Sn2Fe (1357.75): C 40.69, H 2.82; found C
40.52, H 2.79.
UV/Vis Spectroscopy
The solid-state optical properties of compounds 1 and 2
were investigated by recording UV/Vis spectra (Figure 4).
One observes a smooth onset of absorption at 2.23 eV
(556 nm; 1) and 2.29 eV (541 nm; 2), respectively, which re-
flect Se(p)ǞSn(p)-based LMCT transitions within the crys-
tals. No bands are observed that can be assigned to dǞd
transitions, which indicates that even the modification of
the Cp rings by two bulky Sn(SePh)3 groups does not pro-
voke a high-spin situation at the transition-metal center.
1,1Ј-Bis[tris(selenonaphthylato)stannyl]ferrocene (2): Yield: 0.175 g,
1
0.106 mmol, 32%. H NMR (400 MHz, CDCl3): δ = 3.23 (s, 4 H,
CpH), 3.83 (s, 4 H, CpH), 7.1–7.76 (m, 42 H, ArH) ppm. 13C NMR
(100 MHz, CDCl3): δ = 71.79, 73.57, 74.32, 124.78, 125.60, 126.19,
126.71, 128.50, 129.02, 129.39, 134.14, 136.15, 136.97 (Ar) ppm.
119Sn (CDCl3): δ = –49.92 (s) ppm. C70H50Se6Sn2Fe (1658.17):
calcd. C 50.70, H 3.04; found C 50.78, H 3.00.
UV/Vis Spectroscopy: UV/Vis spectra were recorded with a Varian
Cary 5000 UV/Vis/NIR spectrometer in the range of 800–200 nm
using the double-beam technique. The samples were measured as
suspensions in nujol between two quartz plates. The mixture was
placed between two quartz plates and rapidly brought into the UV/
Vis beam.
Electrochemical Investigations: The voltammetric investigations
were carried out with a BAS-100 B/W Electrochemical Analyzer
(Bioanalytical Systems, West Lafayette, Indiana, U.S.A.). Potentials
were measured against an Ag/AgCl “leek-free” reference electrode
(Cypress Systems, Inc., Lawrence, Kansas, U.S.A.); glassy carbon
working electrode (3 mm diameter); anhydrous dichloromethane
containing tetra-n-butylammonium perchlorate as supporting elec-
trolyte (0.1 ) under nitrogen; scan rate: 200 mVs–1; automatic IR
compensation.
Figure 4. UV/Vis spectra of compounds 1 and 2, recorded as sus-
pension of single crystals in nujol oil.
Conclusions
Methods of the Quantum Chemical Investigations: All calculations
were conducted with the Turbomole[25] software package in the ver-
sion 5.10. The calculations were performed on the DFT level[24] by
employing a B88 exchange functional 3-5 and a P86 correlation
functional[27] and the Ridft program.[28] Basis sets def2-SV(P)[29]
were employed with an effective core potential (ECP-28) at the Sn
atoms.[30] All data were taken from optimized local minimum struc-
tures, rationalized by analytical calculation of the second deriva-
tives with respect to the vibrational normal modes.[31]
Two ferrocene-bridged bis[tris(arylselenolato)stannyl]
compounds were prepared and characterized. The molecu-
lar structure of compound 1 was additionally optimized by
DFT calculations. In accordance with these investigations,
a cis/trans mixed orientation of the selenophenolate groups
is favored. We were able to show by cyclic voltammery that
the compound is electrochemically converted into another
species, probably under Sn–Se bond cleavage. We are about
to study the reactivity of such compounds containing
Lewis-basic chalcogenolato groups towards transition-
metal complexes in order to produce novel ternary metal-
organic frameworks.
Acknowledgments
This work was financially supported by the Deutsche Forschungs-
gemeinschaft (DFG).
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Published Online: August 25, 2009
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