Rational synthesis and complexation behavior of the bidentate lewis acid 1,2-bis(chloromercury)ferrocene

Article abstract of DOI:10.1021/om0506567

1,2-Disubstituted ferrocenes represent an interesting, yet underdeveloped class of redoxactive bidentate Lewis acids. We describe here a new rational synthesis of 1,2-bis(tri-methylstannyDferrocene (2) and its high yield conversion to 1,2-bis(chloromercury)ferrocene (3). X-ray crystal structures for complexes of the bidentate Lewis acid 3 with DMSO, [Bu₄N]Cl, and [PPh₄]Cl were obtained. In all cases the two Hg atoms form reverse chelates with the nucleophile. With DMSO a 1:1 complex is formed, in which DMSO is coordinated from the endo side of ferrocene. Two molecules of 3 are used in the binding to the chloride anion. Different modes are realized with the two different counterions. In the complex with [Bu₄N]Cl the chloride ion is coordinated from the exo side of both ferrocenes, while with [PPh ₄]Cl the chloride ion is endo with respect to one and exo with respect to the other ferrocene moiety. Layered and channel-like supramolecular structures are realized with [Bu₄N] and [Pt₄P] counterions, respectively.

Full text of DOI:10.1021/om0506567

Organometallics 2005, 24, 6043-6050
6043
Rational Synthesis and Complexation Behavior of the
Bidentate Lewis Acid 1,2-Bis(chloromercury)ferrocene
Krishnan Venkatasubbaiah,† Jan W. Bats,‡ Arnold L. Rheingold,§ and
Frieder Ja¨kle*,†
Department of Chemistry, Rutgers University-Newark, 73 Warren Street,
Newark, New Jersey 07102, Department of Chemistry and Biochemistry,
Institut fu¨r Organische Chemie, Johann Wolfgang Goethe-Universita¨t Frankfurt,
Marie-Curie-Strasse 11, D-60439 Frankfurt am Main, Germany, and
University of California, San Diego, La Jolla, California 92093
Received July 29, 2005
1,2-Disubstituted ferrocenes represent an interesting, yet underdeveloped class of redox-
active bidentate Lewis acids. We describe here a new rational synthesis of 1,2-bis(tri-
methylstannyl)ferrocene (2) and its high yield conversion to 1,2-bis(chloromercury)ferro-
cene (3). X-ray crystal structures for complexes of the bidentate Lewis acid 3 with DMSO,
[Bu4N]Cl, and [PPh4]Cl were obtained. In all cases the two Hg atoms form reverse chelates
with the nucleophile. With DMSO a 1:1 complex is formed, in which DMSO is coordinated
from the endo side of ferrocene. Two molecules of 3 are used in the binding to the chloride
anion. Different modes are realized with the two different counterions. In the complex with
[Bu4N]Cl the chloride ion is coordinated from the exo side of both ferrocenes, while with
[PPh4]Cl the chloride ion is endo with respect to one and exo with respect to the other
ferrocene moiety. Layered and channel-like supramolecular structures are realized with
[Bu4N] and [Ph4P] counterions, respectively.
Introduction
sensors,14 luminescence enhancing materials,15 and
membrane components.16
Arylmercury compounds have long been known to
serve as highly selective precursors to other organome-
tallic compounds through transmetalation reactions.1
More recently, multifunctional arylmercury species have
attracted much interest with regard to their ability to
act as Lewis acid receptors in the recognition of anions
and neutral Lewis basic species2-8 and to serve as
building blocks for supramolecular chemistry.8-10 They
have also proven useful as chemo- and stereoselective
Lewis acid catalysts,11,12 phase transfer catalysts,13
Over the past about 20 years Wuest and co-workers
have done extensive work on the complexation behavior
and catalytic activity of 1,2-phenylenedimercury dichlo-
ride A.4a-d The respective fluorinated species B has been
explored by Gabba¨ı,5h-k,10,11 and the naphthalene de-
rivative C has been studied by Schmidbaur and Oh.6,7
However, although the related 1,2-dimercurated fer-
rocene derivative has been reported by Rausch and co-
workers as early as 1974,17 a lack of binding studies
using this metallocene-based bidentate Lewis acid is
noticeable. The latter may be attributed to difficulties
* To whom correspondence should be addressed. E-mail: fjaekle@
rutgers.edu.
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† Rutgers University-Newark.
‡ Johann Wolfgang Goethe-Universita¨t Frankfurt.
§ University of California, San Diego.
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10.1021/om0506567 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/25/2005

6044 Organometallics, Vol. 24, No. 24, 2005
Venkatasubbaiah et al.
Chart 1
in preparing this compound in high yield. Direct mer-
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monomercurated and 1,1′-dimercurated ferrocene,18-20
and the crude 1,2-dimercurated species is obtained only
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in a very low yield of ca. 2% after tedious workup
procedures including column chromatographic separa-
tion of the different isomers. On the other hand,
ferrocene-based bidentate Lewis acids of this type21-23
are particularly intriguing due to the unique three-
dimensional geometry and, maybe even more impor-
tantly, the opportunity to influence the binding strength
through the oxidation state of the central metal ion.23i,j,24
We have previously demonstrated that heteronuclear
bidentate ferrocene-based Lewis acids comprised of
boron and/or tin groups can readily be prepared through
a rearrangement reaction from 1,1′-bis(trimethylstan-
nyl)ferrocene and boron halides.22 Here we report a new
synthetic route to 1,2-bis(chloromercury)ferrocene and
the first studies on the complexation behavior of this
ferrocene-based bidentate Lewis acid with neutral and
anionic substrates.
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Results and Discussion
For the preparation of 1,2-dimetalated ferrocenes we
have chosen a new modular approach that is outlined
in Scheme 1. This method involves initial preparation
of a 1,2-distannylated ferrocene, which in itself is an
interesting molecule that may serve as a versatile
precursor to other bidentate Lewis acids. The related
compound 1,2-bis(tributylstannyl)ferrocene had been
mentioned previously by Butler and co-workers to form
upon lithiation of 1,2-dibromoferrocene and subsequent
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Complexation Behavior of 1,2-Bis(chloromercury)ferrocene
Organometallics, Vol. 24, No. 24, 2005 6045
Scheme 1. Synthesis of
1,2-Bis(chloromercury)ferrocene
Figure 1. Molecular structure of 4 with thermal ellipsoids
at the 50% probability level. Hydrogen atoms are omitted
for clarity. Selected interatomic distances (Å) and angles
(deg): Hg1-C2 2.028(4), Hg2-C1 2.021(4), Hg1-Cl1 2.3195-
(12), Hg2-Cl2 2.3341(13), Hg2-O 2.771(3), Hg1-O 2.955-
(4), C2-Hg1-Cl1 178.68(12), C1-Hg2-Cl2 173.74(12),
Cl1-Hg1-O 90.63(8), Cl2-Hg2-O 92.47(8), C2-Hg1-O
90.68(13), C1-Hg2-O 93.64(14).
1
tained in pure form and was only characterized by H
NMR spectroscopy. We chose a slightly different syn-
thetic method, where p-tolylsulfinylferrocene serves as
the starting material. The 1,2-functionalized ferrocene
species 1-trimethylstannyl-2-p-tolylsulfinylferrocene (1)
was prepared through directed lithiation followed by
treatment with trimethyltin chloride according to a
literature procedure.26,27 Subsequent reaction of 1 with
tert-butyllithium (1.1 equiv) followed by addition of
trimethyltin chloride (1.2 equiv) led to the formation of
the desired 1,2-bis(trimethylstannyl)ferrocene (2) to-
gether with a small amount of the monostannylated
species 1-trimethylstannylferrocene (Scheme 1). Re-
moval of trimethylstannylferrocene by vacuum distil-
lation gave pure 2 in 48% isolated yield. Formation of
2 was confirmed by multinuclear NMR spectroscopy and
mass spectrometry. For instance, the 1H NMR spectrum
of 2 shows a triplet at δ 4.41 (1H) and a doublet at δ
4.20 (2H) with a coupling constant of 3J ) 2.5 Hz, which
is characteristic of 1,2-disubstituted ferrocenes.17,22,28
Moreover, a single signal at δ -4.2 in the 119Sn NMR
spectrum is consistent with the symmetry of 2. The
molecular ion peak is found at m/z ) 512 in the mass
spectrum, further confirming the identity of 2.
which reveals a reversible one-electron oxidation wave
at E1/2 ) -96 mV with respect to FcH/FcH+.30 The latter
confirms that 3 may indeed act as a redox-active
bidentate Lewis acid in the recognition of anions and
neutral Lewis basic substrates.
To investigate the ability of 3 to serve as a bifunc-
tional Lewis acid, we have performed binding studies
of 3 with the neutral substrate DMSO and with chloride
as an anionic nucleophile. Recrystallization of 3 from
hot acetone in the presence of DMSO led to X-ray
quality single crystals of the DMSO adduct 4. The
incorporation of DMSO in the product was confirmed
by IR spectroscopy, which shows the expected SdO
stretching band at 1018 cm-1. Elemental analysis of 4
is consistent with incorporation of only one molecule of
DMSO. To further examine the binding of DMSO to the
bidentate Lewis acid 3, we performed a single-crystal
X-ray diffraction study.
The molecular structure of 4 confirms the formation
of a 1:1 complex, in which the oxygen atom coordinates
to both Hg atoms (Figure 1). Interestingly, the DMSO
molecule is coordinating from the endo side of the
ferrocene, which stands in contrast to what we have
previously observed for the binding of pyridine to the
heteronuclear bifunctional Lewis acid 1,2-fc(SnMe2Cl)-
(BMeCl) comprising organotin and organoboron moieties
in the 1,2-positions of the same Cp ring.22b The lower
steric demand of the DMSO molecule is probably in part
responsible for the preference for the endo side in 4, and
packing effects likely also play an important role. The
Hg‚‚‚O distances of 2.955(4) and 2.771(3) Å significantly
differ from one another, although both are shorter than
the sum of the van der Waals radii (for O, 1.54 Å;31 for
Hg, 1.73-2.00 Å32). In comparison, the Hg‚‚‚O contacts
in the related complexes 1,8-bis(chloromercurio)naph-
thalene‚DMSO,7 1,2-bis(chloromercurio)benzene‚DMF,4d
Aryltriorganotin compounds are known to react with
mercuric halides with high selectivity and under mild
conditions to give the respective arylmercury species.29
Thus, treatment of 2 with 2 equiv of HgCl2 in acetone
led to formation of 1,2-bis(chloromercury)ferrocene (3)
as a yellow solid in 96% isolated yield. Comparison of
1
the H NMR spectrum of the product with literature
data for 3 confirmed the 1,2-substitution pattern;17
compound 3 was further characterized by 13C NMR
spectroscopy and elemental analysis. We also studied
the redox properties of 3 by cyclic voltammetry in DMF,
(25) Butler, I. R.; Drew, M. G. B. Inorg. Chem. Commun. 1999, 2,
234.
(26) (a) Guillaneux, D.; Kagan, H. B. J. Org. Chem. 1995, 60, 2502.
(b) Riant, O.; Argouarch, G.; Guillaneux, D.; Samuel, O.; Kagan, H. B.
J. Org. Chem. 1998, 63, 3511.
(27) See also related work: (a) Hua, D. H.; Lagneau, N. M.; Chen,
Y.; Robben, P. M.; Clapham, G.; Robinson, P. D. J. Org. Chem. 1996,
61, 4508. (b) Lagneau, N. M.; Chen, Y.; Robben, P. M.; Sin, H.-S.;
Takasu, K.; Chen, J.-S.; Robinson, P. D.; Hua, D. H. Tetrahedron 1998,
54, 7301. (c) Bolm, C.; Kesselgruber, M.; Mun˜iz, K.; Raabe, G.
Organometallics 2000, 19, 1648.
5h
and 1,2-bis(chloromercurio)tetrafluorobenzene‚(DMSO)2
are all in the range from 2.681 to 2.804 Å. The larger
distortion from linearity for C1-Hg2-Cl2 (173.7(1)°)
relative to C2-Hg1-Cl1 (178.7(1)°) is associated with
the shorter Hg‚‚‚O contact and is tentatively attributed
to a combination of electronic effects due to nucleophile
(28) Pickett, T. E.; Richards, C. J. Tetrahedron Lett. 1999, 40, 5251.
(29) See for example: (a) Eaborn, C. J. Organomet. Chem. 1975,
100, 43. (b) Roberts, R. M. G.; Silver, J.; Azizian, J. J. Organomet.
Chem. 1986, 303, 387. (c) Rot, N.; de Kanter, F. J. F.; Bickelhaupt, F.;
Smeets, W. J. J.; Spek, A. L. J. Organomet. Chem. 2000, 593-594,
369.
(30) See also: Fernandes, J. C.; de Lima, G. M.; Filgueiras, C. A. L.
Quim. Nova 1994, 17, 17.
(31) Nyburg, S. C.; Faerman, C. H. Acta Crystallogr. Sect. B 1985,
41, 274.
(32) Canty, A. J.; Deacon, G. B. Inorg. Chim. Acta 1980, 45, L225.

6046 Organometallics, Vol. 24, No. 24, 2005
Venkatasubbaiah et al.
Cl, respectively. Slow solvent evaporation gave 5a (from
CH2Cl2) and 5b (from CHCl3) as orange crystalline
1
compounds. The H NMR spectra of the crystals indi-
cated in both cases the formation of a 2:1 complex with
Cl-, which was further confirmed by X-ray crystal-
lography and elemental analysis.
The structures of 5a and 5b are shown in Figure 3a
and Figure 3b, respectively. In both species, formation
of the complex anion [(C5H5FeC5H3Hg2Cl2)2Cl]- is evi-
dent, which consists of a chloride ion (Cl5) that is
bridged by four Lewis acidic mercury atoms from two
molecules of 1,2-bis(chloromercurio)ferrocene. Thus the
chloride anion (Cl5) is coordinated by each ferrocene
unit in a bidentate manner. This structural feature has
also been found by Wuest et al. for the chloride complex
of 1,2-phenylenedimercurydichloride.4c However, an
interesting observation is made in that the coordination
mode with respect to the central iron atom is different
for the two complexes 5a and 5b. While for the [Bu4N]+
complex 5a the chloride anion occupies positions on the
exo side with respect to both ferrocene moieties (Figure
3a), in 5b the chloride anion is bound from the exo side
of one ferrocene, but from the endo side of the other
ferrocene moiety (Figure 3b). This observation suggests
again that, in contrast to our previous work on the
pyridine binding to heteronuclear bidentate ferrocene
Lewis acids,22b there is no strong preference for the
binding mode with respect to the iron center in these
chloride complexes and that packing and counterion
effects play a decisive role. While the bond lengths
and angles for 5a and 5b are overall fairly similar,
closer inspection reveals some subtle differences. The
Cl(5)-Hg distances vary from 2.889(2) to 3.144(2) Å for
5a and from 2.934(3) to 3.141(3) Å for 5b. However, for
5a three relatively long and one shorter Hg4‚‚‚Cl5
contact of 2.889(2) Å are formed, whereas three short
and one longer contact of Hg1‚‚‚Cl5 ) 3.141(3) Å are
present in 5b. In comparison, Wuest et al. observed
similar Hg‚‚‚Cl distances of 2.857-3.335 Å for the
complex ion [(1,2-C6H4(HgCl)2)2Cl]-, although with two
short and two longer contacts.4c Interestingly, the short
Hg4‚‚‚Cl5 distance in 5a can be related to a significant
deviation from linearity of the C12-Hg4-Cl4 moiety
(170.0(3)°) and a relatively long Hg4-Cl4 bond of 2.346-
(3) Å. The long contact in 5b on the other hand is
associated with a more modest deviation from linearity
for C10-Hg1-Cl1 (175.1(4) Å) and a shorter Hg-Cl
bond of 2.310(3) Å. Overall, however, the Hg-C dis-
tances for 5a (2.032(10) to 2.051(10) Å) and 5b (2.047-
(12) to 2.071(12) Å) and the Hg-Cl distances for 5a
(2.315(3) to 2.346(3) Å) and 5b (2.310(3) to 2.359(3) Å)
are in the same range as those reported in the litera-
ture. A slight tilting of the HgCl substituents in 5a
toward Fe (CpCentroid-C-Hg of 174.4° to 177.7°) that is
similar to though less pronounced than in 4 is ob-
served. However, especially distortions for Hg2 and Hg4
are to a large extent due to displacement within the
plane, as evident from comparison of the angles
C13-C12-Hg4 and C11-C12-Hg4 (129.8(8)° and
123.8(8)°) as well as C3-C2-Hg2 and C1-C2-Hg2
(128.6(7)° and 122.8(8)°) with the expected angle of
126° in an undistorted system. In 5b only one of
the HgCl substituents for each ferrocene moiety is
tilted toward Fe (CpCentroid-C19-Hg3 ) 173.2(1)° and
Figure 2. View of the extended structure of 4 (one layer).
The DMSO molecules that are located inside the channels
are omitted for clarity.
binding to Hg and steric distortions that result from
interference between the chloro substituent and one of
the DMSO methyl groups. A slight tilting of the HgCl
substituents relative to the Cp planes (CpCentroid-C2-
Hg1 ) 174.7(1)° and CpCentroid-C1-Hg2 ) 174.8(1)°)
toward the Fe atoms may also be associated with
binding of the DMSO ligand, although a comparison
with the elusive structure of the free acid 3 would be
needed to confirm this feature. The Hg-C bond lengths
of 2.021(4) and 2.028(4) Å as well as the Hg-Cl bond
distances of 2.319(1) and 2.334(1) Å are comparable to
those found in other chloromercuryferrocene deriva-
tives.33
The packing diagram of 4 shown in Figure 2 reveals
an interesting sheet-like supramolecular structure. Infi-
nite chains arise due to weak intermolecular Hg‚‚‚Cl
contacts (Hg1‚‚‚Cl1* 3.31(2) and Hg2‚‚‚Cl2* 3.46(3) Å),
which fall within the limit of the sum of the van der
Waals radii of chlorine (1.58-1.78 Å)31 and mercury
(1.73-2.00 Å).32 Weak hydrogen-bonding interactions
(Cl‚‚‚H ) 3.07(3) and 3.14(2) Å) between these chains
lead to the formation of an extended sheet structure.
The sheets in turn are further interlinked by hydrogen-
bonding interactions that lead to formation of a 3D
network containing channels with effective diagonals of
ca. 9 and 3 Å (Figure 2). The channels are occupied by
the coordinated DMSO molecules, which can be removed
at elevated temperature, as shown by thermogravimet-
ric analysis (TGA). The TGA trace shows a 9% weight
loss at 151 °C (onset), corresponding to evaporation of
DMSO from the solid. A microporous solid with channels
(effective diagonals of ca. 10 and 7 Å), in which the walls
consist of four dimercuriobenzene species, was reported
previously for the structure of 1,2-bis(chloromercurio)-
tetrafluorobenzene by Gabba¨ı.5h While in Gabba¨ı’s
system assembly into a three-dimensional structure is
promoted by π-stacking interactions, in our case hydro-
gen bonding results in formation of extended channels.
The chloride complexes [Bu4N][(C5H5FeC5H3Hg2Cl2)2-
Cl] (5a) and [Ph4P][(C5H5FeC5H3Hg2Cl2)2Cl] (5b) were
prepared by treatment of 3 with [Bu4N]Cl and [Ph4P]-
(33) (a) Su¨nkel, K.; Kiessling, T. J. Organomet. Chem. 2001, 637-
639, 796. (b) Huo, S. Q.; Zhu, Y.; Wu, Y. J. J. Organomet. Chem. 1995,
490, 243. (c) Wu, Y. J.; Cui, X. L.; Liu, Y. H.; Yuan, H. Z.; Mao, X. A.
J. Organomet. Chem. 1997, 543, 63. (d) Lin, K.; Song, M.; Zhu, Y.;
Wu, Y. J. Organomet. Chem. 2002, 660, 139.

Complexation Behavior of 1,2-Bis(chloromercury)ferrocene
Organometallics, Vol. 24, No. 24, 2005 6047
Figure 3. (a) Two different views of the molecular structure of 5a with thermal ellipsoids at the 50% probability level
showing the chloride ion above the Cp plane of both ferrocene moieties. Hydrogen atoms and the countercation are omitted
for clarity. Selected interatomic distances (Å) and angles (deg): Hg1-C1 2.032(10), Hg2-C2 2.051(10), Hg3-C11 2.044-
(11), Hg4-C12, 2.037(11), Hg1-Cl1 2.315(3), Hg2-Cl2 2.335(3), Hg3-Cl3 2.325(3), Hg4-Cl4 2.346(3), Hg1-Cl5 3.144(2),
Hg2-Cl5 3.043(3), Hg3-Cl5 3.129(2), Hg4-Cl5 2.889(2); C1-Hg1-Cl1 173.8(3), C2-Hg2-Cl2 174.6(3), C11-Hg3-Cl3
173.2(3), C12-Hg4-Cl4 170.0(3), C12-Hg4-Cl5 99.6(3), C11-Hg3-Cl5 92.8(3), C1-Hg1-Cl5 94.2(3), C2-Hg2-Cl5 97.5-
(3), Hg1-Cl5-Hg2 76.10(6), Hg3-Cl5-Hg4 77.94(6). (b) Two different views of the molecular structure of 5b with thermal
ellipsoids at the 50% probability level showing the chloride ion (i) below the plane of the Cp ring of one of the ferrocene
moieties and (ii) above the plane of the Cp ring of the adjacent ferrocene. Hydrogen atoms and the countercation are
omitted for clarity. Selected interatomic distances (Å) and angles (deg): Hg1-C10 2.071(12), Hg2-C9 2.053(13), Hg3-
C19 2.053(12), Hg4-C20 2.047(12), Hg1-Cl1 2.310(3), Hg2-Cl2 2.343(3), Hg3-Cl3 2.359(3), Hg4-Cl4 2.322(3), Hg1-Cl5
3.141(3), Hg2-Cl5 2.985(3), Hg3-Cl5 2.934(3), Hg4-Cl5 2.957(3); C10-Hg1-Cl1 175.1(4), C9-Hg2-Cl2 175.8(4),
C19-Hg3-Cl3 172.5(4), C20-Hg4-Cl4 169.3(3), C9-Hg2-Cl5 92.7(3), C10-Hg1-Cl5 88.8(3), C19-Hg3-Cl5 97.6(4),
C20-Hg4-Cl5 95.4(3), Hg1-Cl5-Hg2 77.16(7), Hg3-Cl5-Hg4 81.91(7).
CpCentroid-C10-Hg1 ) 175.4(1)°), whereas the other one
is slightly bent away (CpCentroid-C20-Hg4 ) 179.0(1)°
and CpCentroid-C9-Hg2 ) 178.4(1)°).
While the structural parameters are quite similar for
5a and 5b on the molecular level, considerable differ-
ences are apparent in the supramolecular structures.
The packing diagram of compound 5a reveals the
formation of a sheet-like structure with layers of the
complex anion [(1,2-fc(HgCl)2)2Cl]- alternating with
layers of [Bu4N]+ counterions (Figure 4). Relatively
short intermolecular Hg‚‚‚Cl contacts (3.543(17) and
3.546(9) Å) result in chains of complex anions, which
in turn are interconnected by C-H‚‚‚Cl hydrogen-
bonding interactions (2.97(1) to 3.06(2) Å) to form the
layered structure of anions (Figure 5).
In contrast to the layered structure of 5a, a channel-
like structure is realized in the case of the phosphonium
complex 5b (Figure 6). The [(1,2-fc(HgCl)2)2Cl]- anions
form zigzag chains, in which the individual units are
connected by weak intermolecular Hg‚‚‚Cl contacts
(3.623(3) Å). Hydrogen-bonding interactions between
ferrocene H atoms and the chlorine atoms of cocrystal-
lized CHCl3 molecules (C-H‚‚‚Cl ) 2.764(4) to 2.987(4)
Figure 4. Packing diagram of 5a showing the layered
structure; green ) cations, blue ) complex anions.

6048 Organometallics, Vol. 24, No. 24, 2005
Venkatasubbaiah et al.
Figure 5. View of the sheet-like network in 5a formed through Hg‚‚‚Cl contacts within the anion layer.
Figure 6. Packing diagram of 5b showing the presence of cation-directed channels; green ) cations, blue ) complex
anions, and red ) solvent (CHCl3). One of the cations was removed to illustrate the channel diagonals.
Å) lead to the formation of channels that consist of four
[(fc(HgCl)2)2Cl]- units and two CHCl3 molecules. The
CHCl3 molecules are released only at fairly high tem-
peratures as shown by TGA analysis.34 A 6% weight loss
at 163 °C (onset) corresponds to evaporation of CHCl3
from the solid. The [Ph4P]+ cations are located inside
these channels, which have effective diagonals of ca. 10
and 9 Å.
etries are realized with different counterions (5a vs 5b)
indicate that packing effects dominate the individual
complex geometries in the case of the relatively small
nucleophiles studied here. Interestingly, the observation
that 3 undergoes reversible one-electron oxidation opens
up new possibilities for further fine-tuning of the Lewis
acid-Lewis base interactions through changes in the
oxidation state of iron. The reported 1,2-dimetalated
In conclusion, we have developed a new method for
the preparation of the redox-active bidentate Lewis acid
1,2-bis(chloromercurio)ferrocene (3). Different binding
modes are realized, where the nucleophiles are coordi-
nated from either the exo or the endo side of ferrocene.
The fact that both binding modes can be observed in
the very same structure (5b) and that different geom-
(34) A reviewer kindly pointed out that the observation that CHCl3
is released only at relatively high temperatures may be due to the fact
that the lattice is ionic, making the distortions needed for the loss of
guests in the solid state more difficult. It is also interesting to note
that the CHCl3 molecules are part of the channel framework in 5b
with the PPh4 cations inside the channels, while in the extended
structure of 4 the coordinated DMSO molecules are located inside the
channels.

Complexation Behavior of 1,2-Bis(chloromercury)ferrocene
Organometallics, Vol. 24, No. 24, 2005 6049
Table 1. Details of X-ray Structure Determinations
4
5a
5b
empirical formula
MW
C
12H14Cl2FeHg2OS
C36H52Cl5Fe2Hg4N
1590.10
C45H37Cl8Fe2Hg4P
1806.38
734.22
T, K
162(2)
161(2)
100(2)
wavelength, Å
cryst syst
space group
a, Å
0.71073
0.71073
monoclinic
P21
9.8089(18)
22.226(4)
10.107(2)
0.71073
monoclinic
P21/c
10.1136(13)
22.411(3)
21.073(3)
triclinic
P1h
7.4804(13)
7.7155(13)
13.743(3)
b, Å
c, Å
R, deg
85.591(12)
88.926(15)
80.568(18)
780.1(2)
â, deg
99.354(19)
90.195(2)
γ, deg
V, Å3
2174.2(7)
4776.4(11)
Z
2
2
4
F
calc, g cm-3
3.126
2.429
2.512
µ(Mo KR), mm-1
F(000)
21.011
15.052
13.915
660
1464
3320
cryst size, mm
θ range, deg
limiting indices
0.20 × 0.12 × 0.06
2.68-32.68
-11 e h e 11
-11 e k e 11
-20 e l e 20
13 959
0.22 × 0.20 × 0.05
0.40 × 0.30 × 0.20
1.82-26.00
-12 e h e 12
-27 e k e 27
-25 e l e 25
20 774
1.83-30.10
-13 e h e 13
-29 e k e 30
-14 e l e 13
32 673
no. of reflns collected
no. of indepe reflns
absorption correction
refinement method
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I >2σ(I)]
5086 [R(int) ) 0.0581]
numerical, SHELXTL
full-matrix least-squares on F2
5086/0/175
1.240
R1 ) 0.0295
wR2 ) 0.0602
R1 ) 0.0398
wR2 ) 0.0631
2.412 and -1.285
11 103 [R(int) ) 0.0852]
numerical, SHELXTL
full-matrix least-squares on F2
11 103/1/434
1.303
R1 ) 0.0483
wR2 ) 0.0871
R1 ) 0.0625
wR2 ) 0.0923
2.089 and -2.555
6045 [R(int) ) 0.0449]
SADABS
full-matrix least-squares on F2
6045/0/541
1.055
R1 ) 0.0444
wR2 ) 0.1029
R1 ) 0.0607
wR2 ) 0.1065
5.666 and -1.099
R indices (all data)
peakmax/holemin (e Å-3
)
atmosphere at a scan rate of 20 °C/min. Elemental analyses
were performed by Quantitative Technologies Inc., White-
house, NJ.
ferrocenes 2 and 3 represent potentially useful precur-
sors to various other bidentate Lewis acids through
transmetalation reactions with other main group and
transition metal complexes, an area of research that we
are currently further pursuing.
Synthesis of 1,2-Bis(trimethylstannyl)ferrocene (2). A
solution of t-BuLi (0.7 mL, 1.5 M in hexanes, 1.05 mmol) was
added dropwise via syringe to a solution of 1 (0.48 g, 0.98
mmol) in freshly distilled THF (20 mL) at -78 °C. The solution
was stirred for 5 min before adding Me3SnCl (0.24 g, 1.20
mmol) in THF (10 mL). The solution was stirred at the same
temperature for 1 h and subsequently quenched with a small
amount of distilled water. Standard workup and flash column
chromatography on silica gel with hexanes as the eluent gave
a mixture of 1,2-bis(trimethylstannyl)ferrocene and 1-tri-
methylstannylferrocene. Distillation under high vacuum (135
°C) yielded spectrocopically pure 1,2-bis(trimethylstannyl)-
ferrocene as an orange oil. Yield: 0.26 g (48%). 1H NMR (500
MHz, C6D6, 25 °C): δ 4.41 (t, J ) 2.5 Hz, 1H, Cp-4), 4.20 (d,
J ) 2.5 Hz, 2H, Cp-3,5), 4.07 (s, 5H, C5H5), 0.29 (s/d, J(117/119Sn,
H) ) 52/54 Hz, 18H, Sn-Me). 13C NMR (125.69 MHz, C6D6, 25
°C): δ 78.6 (s/dd, 2J(117/119Sn, C) ) 62 Hz, 3J(117/119Sn, C) ) 51
Hz, Cp-3,5), 76.5 (ipso-CpSn), 73.0 (s/d, J(117/119Sn, 13C) ) 38
Hz, Cp-4), 68.6 (C5H5), -7.3 (s/d, J(117/119Sn, C) ) 333/349 Hz,
Sn-Me). 119Sn NMR (149.1 MHz, C6D6, 25 °C): δ -4.2. GC-
Experimental Section
General Procedures. tert-Butyllithium (1.5 M in hexanes),
mercuric chloride, [Bu4N]Cl, and [Ph4P]Cl were purchased
from Acros, and trimethyltin chloride was purchased from
Strem. 1-Trimethylstannyl-2-p-tolylsulfinylferrocene was pre-
pared according to a literature procedure.26 All reactions and
manipulations were carried out under an atmosphere of
prepurified nitrogen using either Schlenk techniques or an
inert-atmosphere glovebox (Innovative Technologies). THF was
distilled from sodium/benzophenone. Hydrocarbon and chlo-
rinated solvents were purified using a solvent purification
system (Innovative Technologies), and the chlorinated solvents
were subsequently degassed via several freeze-pump-thaw
cycles. All 499.9 MHz 1H NMR, 125.7 MHz 13C NMR, and 186.4
MHz 119Sn NMR spectra were recorded on a Varian INOVA
NMR spectrometer (Varian Inc., Palo Alto, CA) equipped with
a 5 mm dual broadband gradient probe (Nalorac, Varian Inc.,
Martinez, CA). All solution 1H and 13C NMR spectra were
referenced internally to the solvent signals. 119Sn NMR spec-
tra were referenced externally to SnMe4 (δ ) 0) in C6D6.
Infrared spectra of KBr pellets were recorded on a Nicolet
IR-200 spectrometer. Cyclic voltammetry was carried out
on a CV-50W analyzer from BAS. The three-electrode sys-
tem consisted of an Au disk as working electrode, a Pt wire
as secondary electrode, and an Ag wire as the reference
electrode. The voltammogram was recorded in DMF containing
[Bu4N][PF6] (0.1 M) as the supporting electrolyte and refer-
enced relative to decamethylferrocene as an internal stand-
ard. The redox potential is reported relative to ferrocene (+480
mV vs decamethylferrocene). Thermogravimetric analyses
were performed on a Perkin-Elmer Pyris 1 analyzer under N2
MS (m/z, (%)): 512 [M+] (86), 497 [M+ - Me] (91), 467 [M+
-
3Me] (100).
Synthesis of 1,2-Bis(chloromercury)ferrocene. A solu-
tion of 2 (0.98 g, 1.90 mmol) in acetone (20 mL) was added
dropwise to a solution of HgCl2 in acetone (30 mL). The
mixture was stirred for 30 min before adding it to water. A
yellow solid precipitated, which was collected on a frit and
washed first with water and then with hexanes. The product
was dried under high vacuum at 60 °C for 6 h. Yield: 1.20 g
(96%). For 3: 1H NMR (500 MHz, DMSO-d6, 25 °C): δ 4.52 (t,
J ) 2.0 Hz, 1H, Cp-4), 4.29 (d, J ) 2.0 Hz, 2H, Cp-3,5), 4.21
(s, 5H, C5H5). 13C NMR (125.69 MHz, DMSO-d6, 25 °C): δ 90.7
(Cp-1,2), 74.5 (Cp-3,5), 70.2 (Cp-4), 68.8 (C5H5). IR (cm-1):
3087, 2920, 2850, 2372, 1654, 1106, 1026, 1001, 816, 497. Anal.

6050 Organometallics, Vol. 24, No. 24, 2005
Venkatasubbaiah et al.
Calcd for C10H8FeHg2Cl2: C 18.31, H 1.23. Found: C 18.50,
H 1.00.
Complexation of 1,2-Bis(chloromercury)ferrocene with
[PPh4]Cl. To a suspension of 1,2-bis(chloromercury)ferrocene
(42.5 mg, 65 µmol) in chloroform was added [PPh4]Cl (12.1 mg,
32 µmol) in chloroform. 1,2-Bis(chloromercury)ferrocene is
insoluble in chloroform, but forms a homogeneous solution
after the addition of [PPh4]Cl. Slow evaporation of chloroform
gave yellow single crystals of the 2:1 complex 5a. Yield: 44.3
mg (81%). For 5b: 1H NMR (500 MHz, DMSO-d6, 25 °C): δ
7.98-7.20 (m, 20H, PPh4), 4.51 (t, J ) 2.5 Hz, 2H, Cp-4), 4.28
(d, J ) 2.5 Hz, 4H, Cp-3,5), 4.20 (s, 10H, C5H5). 13C
NMR (125.69 MHz, DMSO-d6, 25 °C): δ 135.4 (Ph), 134.5 (m,
Ph), 130.4 (m, Ph), 118.8 (d, J(P,C) ) 89 Hz, ipso-Ph), 90.7
(Cp-1,2), 74.6 (Cp-3,5), 70.3 (Cp-4), 68.7 (C5H5). IR (cm-1):
3087, 3048, 2919, 2850, 2372, 1654, 1436, 1106, 995, 814, 722,
688, 526, 500, 484. Anal. Calcd for C44H36Cl5Fe2Hg4P: C 31.33,
H 2.15. Found: C 31.36, H 1.92.
Complexation of 1,2-Bis(chloromercury)ferrocene with
DMSO. DMSO (0.2 mL) was added to a suspension of 1,2-bis-
(chloromercury)ferrocene (25.1 mg, 38 µmol) in acetone (3 mL).
The mixture was heated gently to give a homogeneous solution,
from which yellow single crystals of the DMSO complex 4
formed upon cooling to room temperature. Yield: 24.9 mg
(89%). For 4: IR (cm-1): 3087, 2920, 2850, 2372, 1654, 1018,
996, 951, 822, 499. TGA analysis (20 °C/min): 9% weight loss
at 151 °C (onset) corresponding to loss of DMSO. Anal. Calcd
for C12H14FeHg2Cl2OS: C 19.63, H 1.92. Found: C 19.82, H
1.58.
Complexation of 1,2-Bis(chloromercury)ferrocene with
[Bu4N]Cl. To a suspension of 1,2-bis(chloromercury)ferrocene
(34.2 mg, 52 µmol) in dichloromethane was added [Bu4N]Cl
(7.2 mg, 26 µmol) in chloroform. 1,2-Bis(chloromercury)-
ferrocene is insoluble in dichloromethane, but forms a homo-
geneous solution after the addition of [Bu4N]Cl. Slow evapo-
ration of dichloromethane gave yellow single crystals of the
2:1 complex 5a. Yield: 30.9 mg (75%). For 5a: 1H NMR (500
MHz, DMSO-d6, 25 °C): δ 4.52 (t, J ) 2.5 Hz, 2H, Cp-4), 4.28
(d, J ) 2.5 Hz, 4H, Cp-3,5), 4.21 (s, 10H, C5H5), 3.16 (t, J )
8.5 Hz, 8H, Bu), 1.56 (m, 8H, Bu), 1.31 (m, 8H, Bu), 0.93 (t, J
) 7.5 Hz, 12H, Bu). 13C NMR (125.69 MHz, DMSO-d6, 25 °C):
δ 90.7 (Cp-1,2), 74.6 (Cp-3,5), 70.3 (Cp-4), 68.7 (C5H5), 57.5,
29.0, 19.2, 13.4 (Bu). IR (cm-1): 3083, 2953, 2929, 2871, 1637,
1487, 1458, 1102, 998, 826, 816, 736, 501. Anal. Calcd for
C36H52Cl5Fe2Hg4N: C 27.19, H 3.30, N 0.88. Found: C 28.54,
H 3.56, N 0.98.
Acknowledgment is made to the National Science
Foundation, to the donors of the Petroleum Research
Fund, administered by the American Chemical Society,
and to the Rutgers University Research Council for
support of this research.
Supporting Information Available: Crystallographic
data for compounds 4, 5a, and 5b including tables of crystal
data, atomic coordinates, bond lengths and angles, and aniso-
tropic thermal parameters. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM0506567