Mono-and di-borylated [3]ferrocenophanes

Article abstract of DOI:10.1016/j.jorganchem.2013.03.051

Treatment of [3]ferrocenophane (1) with 0.7 eq. or 3 eq. of BBr3 in hexane at reflux temperature gives the corresponding dibromoboryl (2) or 1,1′-bis(dibromoboryl) derivative (3) in good yields. Compounds 2 and 3 can be transformed into the corresponding

Full text of DOI:10.1016/j.jorganchem.2013.03.051

Accepted Manuscript
Mono- and diborylated [3]ferrocenophanes
Adelina Reichert, Michael Bolte, Hans-Wolfram Lerner, Matthias Wagner
PII:
S0022-328X(13)00253-2
10.1016/j.jorganchem.2013.03.051
JOM 17961
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 1 March 2013
Revised Date: 25 March 2013
Accepted Date: 26 March 2013
Please cite this article as: A. Reichert, M. Bolte, H.-W. Lerner, M. Wagner, Mono- and
diborylated [3]ferrocenophanes, Journal of Organometallic Chemistry (2013), doi: 10.1016/
j.jorganchem.2013.03.051.
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ACCEPTED MANUSCRIPT

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Synopsis:
3]Ferrocenophane readily undergoes electrophilic borylation with BBr ; the resulting
[
3
mono- and diborylated species provide facile access to the corresponding brominated
3]ferrocenophanes, which serve as useful starting materials for Stille-coupling reactions.
[

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Mono- and diborylated [3]ferrocenophanes
Adelina Reichert, Michael Bolte, Hans-Wolfram Lerner, Matthias Wagner*
th
Dedicated to Professor W. A. Herrmann on the occasion of his 65 birthday
Institut für Anorganische und Analytische Chemie, J. W. Goethe-Universität Frankfurt,
Max-von-Laue-Strasse 7, D-60438 Frankfurt (Main), Germany.
Corresponding author: Matthias.Wagner@chemie.uni-frankfurt.de
1

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Abstract
Treatment of [3]ferrocenophane (1) with 0.7 eq. or 3 eq. of BBr
temperature gives the corresponding dibromoboryl (2) or 1,1’-bis(dibromoboryl) derivative
3) in good yields. Compounds 2 and 3 can be transformed into the corresponding di(tert-
3
in hexane at reflux
(
butoxy)boryl (4, 5) and pinacolboryl [3]ferrocenophanes (6, 7). Reaction of 6 and 7 with
i
aqueous CuBr
2
in MeOH/ PrOH at reflux temperature leads to the formation of the mono- and
1
,1’-dibrominated [3]ferrocenophanes 8 and 9; subsequent Stille-type C−C-coupling reactions
n
with Bu
3
SnPh yield mono- and 1.1’-diphenylated [3]ferrocenophanes. Treatment of 6 with
O at −78 °C provides access to the monotopic lithium trihydridoborate 12.
Li[AlH ] in Et
4
2
Keywords: boron, [3]ferrocenophane, iron, Lewis acids, organoborane, planar chirality.
2

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1
. Introduction
Borylated ferrocenes[1] are widely applied building blocks for the preparation of ferrocenes
with switchable interannular bridges,[2] redox-active poly(pyrazol-1-yl)borate ligands,[3]
ferrocene-containing macrocycles,[4] multiple-decker sandwich complexes,[5] boron-bridged
poly(ferrocenylene)s,[6] redox-active and planar-chiral Lewis acids,[7] and anion sensors.[8]
With respect to bonding theory, ferrocenes bearing three-coordinate boryl substituents reveal
an intriguing common characteristic: In these compounds, the boryl group tends to bend out of
the plane of the cyclopentadienyl ring toward the Fe(II) ion. Experimental investigations
augmented by quantum-chemical calculations have led to the conclusion that the phenomenon
is caused by strongly delocalized orbital interactions involving the empty p orbital at the
boron atom, the ipso-carbon atom of the adjacent C
and a through-space interaction with the second cyclopentadienyl ring. The degree of bending
is quantified using the dip angle * = 180° – , whereby is the angle between the centroid
of the C ring, the ipso-carbon atom and the boron atom. The dip angle * generally
5 4
H ring, filled d orbitals at the iron center,
α
α
α
5
H
4
α
decreases (i) when the Lewis acidity of the boryl group decreases, (ii) when an increasing
number of boryl substituents is attached to the same ferrocene backbone, and (iii) upon
oxidation of the Fe(II) center to its Fe(III) state.
Given the continuing interest in ferrocenylboranes, both with regard to fundamental science
and to applied chemistry, it is surprising to note that no borylated ansa-ferrocenes have been
studied so far, even though the introduction of an interannular bridge should lead to
significantly new features: (i) Its inductive effect will influence the degree of FeꢀꢀꢀB through-
space interaction, (ii) its steric requirements will influence the site selectivity of the borylation
reaction, and (iii) the restricted conformational freedom of ansa-ferrocenes will modify the
preferred supramolecular structure of ferrocenylborane-containing macromolecules or
polymers.
Herein we describe a systematic investigation into the electrophilic mono- and diborylation of
[
3]ferrocenophane 1 (Scheme 1), the transformation of the primary products into
corresponding ferrocenyl(trihydrido)borates, and the convenient synthesis of brominated
3]ferrocenophanes from borylated [3]ferrocenophanes. Brominated [3]ferrocenophanes,
[
which are difficult to prepare by other methods, are promising platforms for the development
of planar-chiral ligands[9] and liquid-crystalline materials.[10]
3

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2
. Results and discussion
.1. Borylation of [3]ferrocenophane 1
2
We chose [3]ferrocenophane 1[11, 12] for our borylation study, because it is comparatively
easily accessible and its inert hydrocarbon bridge is compatible with the use of BBr as
borylation reagent (Scheme 1). Under the conditions usually applied for the selective
monoborylation of parent ferrocene (0.95 eq. BBr , hexane, reflux temperature, 5 h), 1 gave a
:1 mixture of the mono- and diborylated species 2 and 3. Lowering the reaction temperature
3
3
4
to room temperature or –78 °C with concomitantly increasing the reaction time to 12 h did not
lead to the expected higher product selectivity, but, on the contrary, favored the formation of
the diborylated species 3 (NMR spectroscopic control; considerable amounts of starting
material 1 remained undissolved in these reaction mixtures). Working with 3 eq. of BBr
3
(hexane, reflux temperature, 5 h) yielded 2 and 3 in a stoichiometric ratio of 1:9; quantitative
diborylation, however, could not be achieved, even when the amount of BBr
3
was raised to 10
eq.
-
-- Scheme 1 ---
These experiments lead to the following conclusions: (i) Compared to ferrocene, 1 is more
prone to electrophilic borylation with BBr , most likely because of its electron-donating 1,3-
3
propanediyl bridge (a similarly enhanced reactivity has also been observed for
ethylferrocene[13] and 1,2,3,4,5-pentamethylferrocene[14]). (ii) At elevated temperatures, an
equilibrium 2 + BBr
3
↔ 3 + HBr leads to the observed ratio of 2:3 = 1:9, largely independent
employed (3 eq.–10 eq.). We assume that steric repulsion between
from the amount of BBr
3
the two dibromoboryl substituents, which approach each other because of the ansa-ferrocene
structure, facilitates the proto-deborylation of 3. Given this background, we used 0.7 eq. / 3
3
eq. of BBr to synthesize 2 (yield: 86%) / 3 (yield: 63%; contaminated with 10% of 2) on a
preparative scale.
1
The H NMR spectrum of 2 (C
6
D
6
) shows a multiplet for the six 1,3-propanediyl protons and
four multiplets, each of them integrating 1 H, for the cyclopentadienyl protons H2’–H5’. The
borylated cyclopentadienyl ring gives rise to a virtual triplet (4.12 ppm; H2) and two doublets
of doublets (4.34 ppm; H4 / 4.22 ppm; H5). This signal pattern suggests that the interannular
bridge is dynamic at room temperature, because otherwise two sets of signals would have to
2 2
be present depending on whether CH -b is pointing to the same side as the BBr group or to
the opposite side.[15] Moreover, an inspection of the coupling constants, which possess one
4

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3
4
larger value (2.6 Hz = JHH) and two smaller values (1.4 Hz, 1.3 Hz = JHH), indicates that the
boryl substituent is located at the β-position relative to the 1,3-propanediyl bridge. This
conclusion is further supported by the X-ray crystal structure analysis of 2 (Fig. 1) and in line
with previous reports on the regioselectivity of borylation reactions of ethylferrocene, 1,1’-
dibromoferrocene, and 1,1’-bis(dibromoboryl)ferrocene.[1, 13]
Compound 3 shows only three proton resonances for its two cyclopentadienyl rings with
chemical shift values of 4.08 ppm (vt; H2), 4.58 ppm (dd; H4), and 4.03 ppm (dd; H5). This
result points towards a highly symmetric structure (on the NMR timescale) with a dynamic
three-carbon bridge and magnetically equivalent cyclopentadienyl ligands (cf. also the X-ray
crystal structure analysis of 3; Fig. 2).
1
1
1
The B{ H} NMR resonances of 2 and 3 appear at 41.0 ppm and 48.8 ppm, respectively, in
agreement with the chemical shift values of dibromoborylferrocene (46.7 ppm) and 1,1’-
bis(dibromoboryl)ferrocene (50.0 ppm).[1]
1
Compound 2 crystallizes as a racemic mixture in the monoclinic space group P2 /n. As had
1
already been deduced from the H NMR spectrum of 2, the X-ray crystal structure analysis
(
Fig. 1) proved the BBr
2
substituent to be located at C(3).
-- Figure 1 ---
The bond lengths and angles about the boron atom possess the same values in 2 and in its
unbridged congener FcBBr (Fc = ferrocenyl).[16] However, we note a revealingly greater
degree of cyclopentadienyl–BBr bending in 2 (α* = 26.1°) as compared to FcBBr (α* =
7.7°/18.9°;[16] two crystallographically independent molecules in the asymmetric unit). The
-
2
2
2
1
dip angle of 2 thus approaches the highest values found so far for any ferrocenylborane
derivatives (e.g. FcBH : α*(calcd) = 26.5°;[17] FcBC H : α* = 25.5°;[18] FcBC Ph : α* =
2
12
8
4
4
2
9.4°[19]). Two reasons can be envisaged for the short contact Fe(1)ꢀꢀꢀB(1) = 2.698(5) Å in
compound 2: (i) The +I effect of the hydrocarbon bridge renders the iron center more electron-
rich[20] and, in turn, strengthens the FeꢀꢀꢀB interaction. (ii) The carbon atoms C(13), C(14),
and C(15) are pulled away from the boryl substituent in the ansa-ferrocenyl fragment as
evidenced by the angle between the centroids (COG) of the two cyclopentadienyl rings and
the iron atom (COG(Cp(1))−Fe(1)−COG(Cp(11)) = 169.7° (2) vs. 175.3°/175.9°
2
(FcBBr )[16]). Ligand bending is consequently less hampered by unfavorable interannular
steric interactions in 2 than in FcBBr2.
5

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X-ray crystallography on 3 provided conclusive evidence for the structural assignment as
chiral 3,3’-bis(dibromoboryl)[3]ferrocenophane rather than as meso-diastereomer 3,4’-
bis(dibromoboryl)[3]ferrocenophane (Scheme 1). Compound 3 crystallizes as a racemic
mixture in the orthorhombic space group Pna2
molecular structure of 3 are the same as in 2 (Fig. 2).
-- Figure 2 ---
1
. Most key metrical parameters of the
-
The discussion can therefore be restricted to the dip angles α* = 10.2° (both at C(3) and at
C(13)), which possess less than half the value of the dip angle of 2. Also in the cases of
2 2 2
FcBBr and fc(BBr ) (fc = 1,1’-ferrocenediyl), α* decreases upon going from the mono-
(17.7°/18.9°)[16] to the diborylated species (9.1°)[21], which has been attributed to the fact
that the electron-donor capacity of the iron atom needs to be divided between two boron
acceptors in the latter molecule.[16, 17]
With the aim to generate less air- and moisture-sensitive derivatives of 2 and 3, the
3
compounds were first treated with MeOSiMe in pentane at −78 °C (Scheme 1). However,
after warming to room temperature, an NMR spectroscopic investigation of the reaction
mixture revealed nearly quantitative deborylation with formation of [3]ferrocenophane 1.
t
Better results were obtained by adding KO Bu to 2 and 3 in C
6
H
6
at room temperature. The
target molecules 4 and 5 formed as orange-colored oils, which were contaminated by 1 (in the
case of 4) and 4 (in the case of 5). Purification by column chromatography was not an option,
because both 4 and 5 are still prone to hydrolysis. The problem was finally solved by
transforming 4 and 5 into the pinacol derivatives 6 and 7 (Scheme 1), which could
subsequently be isolated in analytically pure form after column chromatography. In spite of
numerous efforts, we found no direct way leading from 2/3 to 6/7 without having to pass 4/5.
Yet, this will usually pose no major inconvenience if the entire reaction sequence is carried
out as a one-pot procedure.
1
The H NMR spectrum of 6 contains the signals characteristic of the ansa-ferrocenyl moiety
together with one resonance at 1.16 ppm (integrating 12H) for the four Bpin methyl
1
3
1
substituents. The C{ H} NMR spectrum, however, shows two methyl resonances (24.9 ppm,
2
5.0 ppm) as a result of the planar-chiral structure of 6. In line with this interpretation, the
1
diborylated species 7 gives rise to two methyl signals both in the H (1.22 ppm, 1.27 ppm; 2 ×
1
3
1
1
2H) and in the C{ H} NMR spectrum (25.0 ppm, 25.2 ppm). The structural assignment of
6

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6
and 7 was further confirmed by X-ray crystal structure analyses (cf. the Supporting
Information for more details).
We wish to emphasize in this context that the borylation of (substituted) ferrocenes via C−H
2
activation using pinB−Bpin and the catalytic system [Ir(OMe)(cod)] /dtbpy has been
investigated by Plenio et al. (pinBH = pinacolborane; dtbpy = 4,4’-di-tert-butyl-2,2’-
bipyridine).[22] The reactions were carried out in octane for 24 h at reflux temperature. The
authors note that: (i) The reactivity of parent ferrocene is significantly lower than that of
benzene, (ii) the yield of fc(Bpin)
employed (fc = 1,1’-ferrocenediyl), and (iii) electron-poor ferrocenes are more reactive than
electron-rich ferrocenes. Most importantly, fc(Me) gave only 12% of the monoborylated
2
was only 8%, even when 3 eq. of pinB−Bpin were
2
product and no diborylated ferrocene at all. We therefore conclude that this method most
likely is no option for the preparation of borylated [3]ferrocenophanes.
2
.2. Transformation of borylated into brominated [3]ferrocenophanes
Ferrocene derivatives find widespread use as (planar-chiral) ligands in coordination chemistry,
but also as building blocks of thermotropic liquid crystals.[9] Another field of continuing
interest is the preparation of oligoferrocenes and the detailed investigation of intramolecular
electron-transfer processes in their mixed-valence states.[9] In all three cases mentioned,
ansa-ferrocenes play important roles along with their unbridged congeners. Convenient access
routes to mono- and dibrominated [3]ferrocenophanes are therefore in demand, because these
compounds could serve as versatile starting materials for further transformations through, e.g.,
Ullmann or Pd-catalyzed C−C-coupling reactions.
The monobrominated [3]ferrocenophane 8 (Scheme 2) has previously been prepared in low
2
yields through the mercuration of 1 with Hg(OAc) , subsequent conversion of the primary
product [3]FcHg(OAc) into [3]FcHg(Cl) with LiCl and finally Hg(Cl)/Br exchange with N-
bromosuccinimide ([3]FcH = [3]ferrocenophane).[23] Apart from the use of toxic
(organo)mercury compounds, the synthesis protocol requires extended reaction times and
repeated chromatographic separations.
The chiral dibrominated [3]ferrocenophane 9 (Scheme 2) is unknown. Only its meso-
diastereomer 3,4’-dibromo[3]ferrocenophane[24] has been made accessible via the dilithiation
2 4 2
of 1 (n-BuLi/TMEDA), followed by the addition of C F Br .[25] The rationale behind this
synthesis approach was that the lithiated intermediate holds the lithium ions as part of a bridge
spanning the two cyclopentadienyl rings, which should, in turn, place the bromine atoms on
7

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corresponding positions of each ring.[25] However, the 3,4’-dibromo[3]ferrocenophane,
isolated in 20% yield after chromatographic workup, formed as a mixture with 2,5’-
dibromo[3]ferrocenophane, 2-bromo[3]ferrocenophane, and 8.
In a recent publication, Hartwig et al. have shown that bromoarenes can readily be prepared
2
from aryl−Bpin compounds by treatment with CuBr .[26, 27] We therefore decided to extend
this approach to the transformation of the ferrocenyl−Bpin derivatives 6 and 7 to
bromoferrocenes 8 and 9 (Scheme 2). Indeed, solutions of the starting materials in
i
MeOH/ PrOH provided 8 and 9 in yields of 66% and 91%, respectively, upon reaction with
2
aqueous solutions of CuBr at reflux temperature (Scheme 2).[28] The constitution of 9 as
3
,3’-dibromo[3]ferrocenophane was confirmed by X-ray crystallography (cf. the Supporting
Information for more details). The NMR spectra of 8 and 9 are according to expectations (cf.
the published NMR spectra of 3,4’-dibromo[3]ferrocenophane[23]) and therefore do not merit
a detailed discussion.
--- Scheme 2 ---
2
.3. Compounds 6−9 as starting materials for C−C-coupling and hydride-transfer reactions
It has been reported that Pd-catalyzed cross-coupling reactions of bromoaromatics and
ferrocenylboronic acids often suffer from mere deborylation as a serious side reaction.[29, 30]
For example, attempts to couple fc(B(OH)
2
)
2
and PhBr provided fc(Ph)
, [Pd(PPh ]) or 60% (DME, 3 M aqueous NaOH,
(dppf)]). The yields improved to 25% or 90% when PhBr was replaced by PhI.[30]
2
in yields of only 10%
(
toluene, 2 M aqueous Na
PdCl
2
CO
3
3 4
)
[
2
Moreover, the reaction of FcBpin with 4-bromoacetophenone under Suzuki-Miyaura
conditions gave the cross-coupling product in 55% yield.[22]
In order to test the behavior of 6 and 7 in Suzuki-Miyaura reactions, we tried to couple both
compounds with 4-iodotoluene, applying the reaction conditions and the catalyst system that
2 2
had shown the best performance in the case of fc(B(OH) ) (i.e., DME, 3 M aqueous NaOH,
[
PdCl (dppf)]). Employing 6 as the starting material, we isolated compound 10a in 33% yield
2
after a reaction time of 6 d at reflux temperature (Scheme 2); the use of 7 led to the partly
deborylated species 6 as the major product and was therefore of no synthetic value.
We next turned our attention to the synthetic potential of 8 and 9. A literature report on the
2 2 2
reaction between fc(Br) and PhB(OH) , which affords fc(Ph) in marginal yields of 10%,[30]
led us to switch from Suzuki-Miyaura- to Stille-type protocols. Indeed, 8 and 9 can readily be
n
t
3 3 2
transformed into 10b and 11 upon treatment with Bu SnPh in the presence of [Pd(P Bu ) ]
8

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under microwave conditions (170 °C, 30 min; Scheme 2). The isolated yields were 73% and
1
5
2%, respectively. The H NMR spectra of 10b and 11 reveal similar signal patterns for the
[
3]ferrocenophane moieties as in the cases of 6/8 and 7/9. In addition, each of the spectra
contains three resonances for the phenyl rings; the overall proton integral ratios are in accord
with the presence of one (10b) and two (11) phenyl substituents per molecule.
The molecular structures of 10b and 11 have also been confirmed by X-ray crystallography
(Fig. 3; cf. the Supporting Information for more details on the X-ray crystal structure analysis
A
B
A
B
C
of 10b). The compounds crystallize with two (10b , 10b ) and three (11 , 11 , 11 )
crystallographically independent molecules in the asymmetric units. The dihedral angles
between the phenyl substituents and the attached cyclopentadienyl rings are comparatively
small in both compounds (average values: 28° (10b), 13° (11)). For steric reasons, it can be
assumed that the solid-state conformation of 11 will largely be maintained also in solution.
One proton on each cyclopentadienyl ligand (i.e. H(4), H(14) in Fig. 3) should thus be
influenced by the ring-current effect of the phenyl substituent residing on the other
cyclopentadienyl ligand. Similar arguments hold for compound 10b. Indeed, we find one
1
unusually upfield-shifted resonance both in the H NMR spectrum of 10b (3.42 ppm) and 11
(
3.91 ppm). Related ring-current effects have also been described for FcPh and fc(Ph)
are, however, less pronounced as a result of cyclopentadienyl spinning.[31]
-- Figure 3 ---
2
. They
-
Recently, we have shown that ferrocenylboronic acids and boronic acid esters are excellent
precursors for the preparation of lithium ferrocenyl(trihydrido)borate salts.[32] As an
example, the ditopic borate A is shown in Fig. 4. The so far most important applications of A
have been (i) its polymerization to the boron-bridged poly(ferrocenylene) B[32] through
Me SiCl-induced condensation reactions and (ii) the synthesis of oligonuclear transition-metal
3
complexes like C[33] (Fig. 4).
--- Figure 4 ---
In both cases it would be desirable to possess also A-type [3]ferrocenophanes in order to be
able (i) to influence the tertiary structure of polymers B by restricting the conformational
freedom of certain repeat units or (ii) to promote metal−metal interactions in C-type
aggregates by forcing the peripheral complex fragments into closer proximity. For an
optimization of the experimental conditions, we first studied the reaction of 6 with Li[AlH4]
1
1
and finally isolated the target [3]ferrocenophane 12 in excellent yields (Scheme 3). The B
1
NMR spectrum of 12 is characterized by a quartet at −28.7 ppm ( JBH = 77 Hz), which nicely
9

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1
1
fits to the corresponding data of Li[FcBH
3
] (−30.6 ppm; JBH = 77 Hz)[34]. In the H NMR
spectrum, the BH
3
3
protons of 12 give rise to a 1:1:1:1 quartet at 0.81 ppm (Li[FcBH ]: 0.86
ppm)[34]. Moreover, we found that 12 still contained approximately 0.5 eq. of (most likely
+
Li -coordinated) Et
2
O even though the sample had been stored under dynamic vacuum for 12
h.
--- Scheme 3 ---
Single crystals were grown in the presence of 12-crown-4; the molecular structure of the
+
adduct 12ꢀ(12-c-4) is shown in Fig. 5. The Li ion coordinates not only to the crown-ether
molecule, but also to hydrogen atoms of the trihydridoborate fragment. A more detailed
discussion of the crystal structure is precluded by the fact that the contact ion pair is located
on a crystallographic mirror plane which results in severe disorder not only of the 1,3-
propanediyl bridge, but also of the crown-ether ligand.
The reaction protocol, that had worked faithfully in the case of 6, failed, however, when
applied to the diborylated [3]ferrocenophane 7. According to NMR spectroscopy, the product
mixture contained only a small amount of the target A-type ansa-ferrocene. Instead, we
obtained mainly 12, Li[BH ], and a mixed [3]ferrocenophane bearing one Bpin and one
4
trihydridoborate substituent.
3
. Conclusion
Treatment of [3]ferrocenophane (1) with BBr
3
in hexane at reflux temperature provides access
to mono- (2) and diborylated [3]ferrocenophanes (3). The electrophilic substitution reaction
proceeds more readily than in the case of pristine ferrocene, most likely because of the
positive inductive effect of the 1,3-propanediyl bridge. Diborylation thus already occurs as a
side reaction of the monoborylation process even when only 0.95 eq. of BBr
first BBr substituent is selectively introduced into the β-position relative to the interannular
bridge. The second BBr substituent gets attached to the second cyclopentadienyl ring, again
3
are used. The
2
2
2
at the β-position and at the maximum distance to the first BBr group that is possible under
these prerequisites. Compound 3 consequently forms as racemic mixture (rac-3) rather than as
meso-diastereomer. Most likely due to steric congestion, diborylation of 1 was never
quantitative, even in the presence of 10 eq. of BBr
borylation step is not irreversible but part of an equilibrium system.
The primary BBr products 2 and 3 can be converted into the corresponding pinacolboryl
derivatives 6 and 7, which are readily obtained in analytically pure form by column
3
. We therefore assume that the second
2
1
0

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chromatography. Reaction of 6 and 7 with CuBr
2
provides the brominated [3]ferrocenophanes
8
and rac-9 in good yields. Compounds 8 and rac-9 are highly useful starting materials for
the preparation of more complex [3]ferrocenophanes through Stille-type C−C-coupling
reactions. The synthesis approach to rac-9 via the electrophilic borylation of 1 is conceptually
unique, because other methods providing dibrominated [3]ferrocenophanes via
dilithiation/bromination protocols have the inherent disadvantage that they lead to meso-9 and
thus cannot be used as starting materials for chiral [3]ferrocenophane derivatives.
1
1

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4
. Experimental
4
.1. General Considerations
Unless otherwise specified, all reactions and manipulations were carried out under dry
nitrogen or argon with carefully dried and degassed solvents, flame-dried glassware, and
Schlenk or glove-box techniques. Hexane, C H , C D , Et O, THF, THF-d were dried over
6
6
6
6
2
8
Na/benzophenone and distilled prior to use. Column chromatography was performed by using
silica gel 60 (Macherey–Nagel). 1D and 2D NMR spectra were recorded on Bruker AM 250,
Avance 300, or Avance 400 spectrometers at room temperature. Chemical shifts are
1
13
1
referenced to (residual) solvent signals ( H/ C{ H}; C
6
D
6
: 7.15/128.0; THF-d
8
: 1.72/25.3) or
1
1
11
1
external BF ꢀEt O ( B, B{ H}). J values are given in Hz. Abbreviations: s = singlet, dd =
3 2
doublet of doublets, vt = virtual triplet, q = quartet, m = multiplet, n.r. = not resolved
multiplet, Cp = cyclopentadienyl. Mass spectra were recorded with a PerSeptive Biosystems
Mariner Biospectrometry Workstation spectrometer. Combustion analyses were performed by
the Microanalytical Laboratory of the Goethe-University Frankfurt. [3]Ferrocenophane was
t
synthesized according to literature procedures.[11, 12] KO Bu was sublimed at 260 °C and
stored in a glove box. Pinacol was recrystallized from dry C
6 6
H and stored in a glove box. All
other chemicals are commercially available and were used as received.
4
.2. Synthesis of 2
Neat BBr (0.21 mL, 0.55 g, 2.2 mmol) was added at room temperature via syringe to a stirred
3
clear solution of 1 (0.700 g, 3.10 mmol) in hexane (40 mL), whereupon an orange precipitate
formed. Upon heating to reflux temperature, the precipitate redissolved within minutes. After
the solution had been kept at reflux temperature for 5 h, small amounts of a greenish insoluble
material were removed by filtration using a Schlenk frit while the mixture was still hot. The
crystallization of the product from the filtrate started already at room temperature and was
completed by storing the vessel at –30 °C overnight. The crystals obtained were suitable for
1
3
X-ray crystallography. Yield: 0.747 g (86%). H NMR (300.0 MHz, C
6
D
6
): δ 4.34 (dd, JHH
=
4
3
4
2
=
×
.6 Hz, JHH = 1.3 Hz, 1H; Cp-H4), 4.24 (m, 1H; Cp-H3ʼ /4ʼ ), 4.22 (dd, JHH = 2.6 Hz, JHH
1.4 Hz, 1H; Cp-H5), 4.12 (vt, 1H; Cp-H2), 3.85 (m, 1H; Cp-H3ʼ /4ʼ ), 3.63, 3.55 (2 × m, 2
1
1
1
2 6 6
1H; Cp-H2ʼ /5ʼ ), 1.63–1.22 (m, 6H; CH ); B{ H} NMR (96.3 MHz, C D ): δ 41.0 (h1/2
1
2

ACCEPTED MANUSCRIPT
1
3
1
=
120 Hz); C{ H} NMR (75.4 MHz, C
8.9 (Cp-C2), 78.6 (Cp-C3ʼ /4ʼ ), 78.4 (Cp-C4), ≈ 76* (Cp-C3), 72.9, 72.0 (2 × Cp-
C2ʼ /5ʼ ), 71.0 (Cp-C3ʼ /4ʼ ), 34.5 (CH -b), 23.9 (CH -a), 23.5 (CH -a’). *This resonance
was not observed in the C{ H} NMR spectrum; its chemical shift value was taken from the
6 6
D ): δ 96.9 (Cp-C1), 89.6 (Cp-C1ʼ ), 81.2 (Cp-C5),
7
2
2
2
1
3
1
cross peaks in an HMBC spectrum. Anal. Calcd (%) for C13
H 3.31. Found: C 39.27, H 3.42.
2
H13BBr Fe (395.71): C 39.46,
4
.3. Synthesis of 3
3
Neat BBr (1.02 mL, 2.65 g, 10.6 mmol) was added at room temperature via syringe to a
stirred clear solution of 1 (0.800 g, 3.54 mmol) in hexane (40 mL), whereupon an orange
precipitate formed. Upon heating to reflux temperature, the precipitate redissolved within
minutes. After the solution had been kept at reflux temperature for 5 h, small amounts of a
greenish insoluble material were removed by filtration using a Schlenk frit while the mixture
was still hot. X-ray quality crystals of 3 grew together with crystals of 2 upon storage of the
1
filtrate at –30 °C overnight. The relative amounts 3:2 = 9:1 were determined by H NMR
1
3
spectroscopy. Yield of 3: 1.27 g (63%). H NMR (300.0 MHz, C
6
D
6
): δ 4.58 (dd, JHH = 2.6
4
3
4
Hz, J = 1.3 Hz, 2H; Cp-H4), 4.08 (vt, 2H; Cp-H2), 4.03 (dd, J = 2.6 Hz, J = 1.4 Hz,
HH
HH
HH
1
1
1
2
H; Cp-H5), 1.39–1.21 (m, 6H; CH
2
); B{ H} NMR (96.3 MHz, C
6
D
6
): δ 48.8 (h1/2 = 220
1
3
1
Hz); C{ H} NMR (75.4 MHz, C
6
D
6
): δ 98.1 (Cp-C1), 81.7 (Cp-C4), 79.5 (Cp-C2),
-b), 23.4 (CH -a). *This resonance was not observed
in the C{ H} NMR spectrum; its chemical shift value was taken from the cross peaks in an
HMBC spectrum. Anal. Calcd (%) for C13 Br Fe (565.34): C 27.62, H 2.14. Found: C
7.64, H 2.24. Note: The combustion analysis was performed on manually selected crystals.
7
9.3 (Cp-C5), ≈ 76* (Cp-C3), 33.6 (CH
2
2
1
3
1
H
12
B
2
4
2
4
.4. Synthesis of 4
t
Neat solid KO Bu (0.355 g, 3.16 mmol) was added at room temperature to a solution of 2
(
0.626 g, 1.58 mmol) in C
6
H
6
(25 mL). The reaction mixture was stirred overnight, the
(2 × 5 mL). The filtrate
precipitate (KBr) was collected on a frit (G4), and washed with C
6
H
6
was evaporated in vacuo to obtain an orange oil which consisted of a mixture of 4 and
1
deborylated [3]ferrocenophane 1 in a stoichiometric ratio of 3:1 ( H NMR spectroscopic
1
control). Yield of 4: 0.452 g (75%). H NMR (400.1 MHz, C
6
D
6
): δ 4.48 (vt, 1H; Cp-H2),
1
3

ACCEPTED MANUSCRIPT
3
4
4
.43 (dd, JHH = 2.3 Hz, JHH = 1.4 Hz, 1H; Cp-H4), 4.11, 4.08 (2 × m, 2 × 1H; C
5
H
4
), 4.07
), 1.84–1.74
): δ 27.2 (h1/2 = 190 Hz);
): δ 88.5 (Cp-C1), 85.6 (Cp-C1’), 78.0 (Cp-C2), 76.4 (Cp-
), 71.0, 70.3, 69.6, 69.1 (C ), ≈ 67* (Cp-C3), 35.3 (CH -b),
1.0 (CH ), 24.9, 24.8 (CH -a,a’). *This resonance was not observed in the C{ H} NMR
3
4
(
5 4
dd, JHH = 2.3 Hz, JHH = 1.5 Hz, 1H; Cp-H5), 4.02, 3.82 (2 × m, 2 × 1H; C H
1
1
1
(
m, 6H; CH
2
), 1.44 (s, 18H; CH
3 6 6
); B{ H} NMR (96.3 MHz, C D
1
3
1
C{ H} NMR (100.6 MHz, C D
6
6
C4), 73.4 (Cp-C5), 72.6 (CCH
3
5
H
4
2
1
3
1
3
3
2
spectrum; its chemical shift value was taken from the cross peaks in an HMBC spectrum.
4
.5. Synthesis of 5
t
Neat solid KO Bu (0.783 g, 6.98 mmol) was added at room temperature to a solution of a 9:1
mixture of 3 and 2 (1.021 g) in C
6 6
H (30 mL). The reaction mixture was stirred overnight, the
precipitate (KBr) was collected on a frit (G4), and washed with C H (2 × 5 mL). The filtrate
6
6
was evaporated in vacuo to obtain an orange oil which consisted of a mixture of 5 and 4 in a
1
stoichiometric ratio of 4:1 ( H NMR spectroscopic control). Yield of the 1:4 mixture of 4 and
1
3
4
5
: 0.97 g. H NMR (400.1 MHz, C
6
D
6
): δ 4.42 (dd, JHH = 2.2 Hz, JHH = 1.4 Hz, 2H; Cp-H4),
3
4
4
.36 (vt, 2H; Cp-H2), 4.23 (dd, JHH = 2.2 Hz, JHH = 1.5 Hz, 2H; Cp-H5), 1.87–1.76 (m, 6H;
1
1
1
13
1
CH ), 1.47 (s, 36H; CH ); B{ H} NMR (96.3 MHz, C D ): δ 28.4 (h = 390 Hz); C{ H}
2
3
6
6
1/2
NMR (100.6 MHz, C
6
D
6
): δ 88.5 (Cp-C1), 78.1 (Cp-C2), 77.3 (Cp-C4), 73.0 (Cp-C5), 72.7
-b), 31.2 (CH ), 24.9 (CH -a). *This resonance was not
(CCH
3
), ≈ 70* (Cp-C3), 35.1 (CH
2
3
2
1
3
1
observed in the C{ H} NMR spectrum; its chemical shift value was taken from the cross
peaks in an HMBC spectrum.
4
.6. Synthesis of 6
Neat pinacol (0.154 g, 1.30 mmol) was added at room temperature to 4 (0.603 g;
contaminated with 25% of 1) in THF (30 mL) and the resulting clear orange solution was
stirred for 24 h. All volatiles were removed under reduced pressure and the residue was
treated with Et
separation funnel and the aqueous phase was extracted with Et
organic phases were washed with brine and dried over anhydrous MgSO
2
O (30 mL) and H
2
O (20 mL). The ethereal phase was separated using a
O (2 × 10 mL). The combined
. After filtration, the
2
4
filtrate was evaporated to dryness in vacuo and the crude product was purified by column
chromatography. Yield: 0.361 g of 6 and 0.070 g of 1 (which can be re-used). 6 crystallized
1
4

ACCEPTED MANUSCRIPT
upon slow evaporation of a C
6 6
H solution in the form of yellow plates that were suitable for
X-ray crystal structure analysis; mp = 93–95 °C. R
f
= 0.42 (silica gel, hexane/EtOAc = 15:1).
1
3
4
H NMR (300.0 MHz, C D ): δ 4.63 (dd, J = 2.3 Hz, J = 1.2 Hz, 1H; Cp-H4), 4.46 (vt,
6
6
HH
HH
3
4
1
H; Cp-H2), 4.21, 4.15 (2 × m, 2 × 1H; Cp-H3’/4’), 4.02 (dd, JHH = 2.3 Hz, JHH = 1.3 Hz,
1
H; Cp-H5), 3.98, 3.75 (2 × m, 2 × 1H; Cp-H2’/5’), 1.76–1.62 (m, 6H; CH ), 1.16 (s, 12H;
2
1
1
1
13
1
CH ); B{ H} NMR (96.3 MHz, C D ): δ 33.3 (h = 270 Hz); C{ H} NMR (75.4 MHz,
3
6
6
1/2
C
6
D
6
): δ 89.5 (Cp-C1), 85.9 (Cp-C1ʼ ), 82.9 (CCH
3
), 75.7 (Cp-C2), 74.6 (Cp-C4), 74.0 (Cp-
-b), 25.0, 24.9
CH ), 24.7, 24.6 (CH -a). *This resonance was not observed in the C{ H} NMR spectrum;
C5), 70.0, 69.8 (Cp-C2’/5’), 69.7, 68.7 (Cp-C3’/4’), ≈ 61* (Cp-C3), 35.1 (CH
2
1
3
1
(
3
2
its chemical shift value was taken from the cross peaks in an HMBC spectrum. ESI-MS: m/z
+
(
%) = 352 [M] (100). Anal. Calcd (%) for C19
H
25BFeO
2
(352.05): C 64.82, H 7.16. Found: C
6
4.65, H 7.10.
4
.7. Synthesis of 7
Neat pinacol (0.395 g, 3.34 mmol) was added at room temperature to a 4:1 mixture of 5 and 4
0.970 g) in THF (30 mL). The resulting clear orange solution was stirred for 24 h, all
volatiles were removed under reduced pressure, and the residue was treated with Et O (30
(
2
mL) and H
2
O (20 mL). The ethereal phase was separated using a separation funnel and the
O (2 × 10 mL). The combined organic phases were
aqueous phase was extracted with Et
2
washed with brine and dried over MgSO . After filtration, the filtrate was evaporated to
4
dryness in vacuo and the crude product was purified by column chromatography. Yield: 0.258
g of 7 and 0.118 g of 6. 7 crystallized upon slow evaporation of a C
6 6
H solution in the form of
orange plates that were suitable for X-ray crystal structure analysis; mp = 172–174 °C. R
f
=
1
3
0
.28 (silica gel, hexane/EtOAc = 15:1). H NMR (300.0 MHz, C
6
D
6
): δ 4.64 (dd, JHH = 2.3
4
3
4
Hz, JHH = 1.2 Hz, 2H; Cp-H4), 4.39 (vt, 2H; Cp-H2), 4.15 (dd, JHH = 2.3 Hz, JHH = 1.3 Hz,
1
1
1
2
H; Cp-H5), 1.67–1.58 (m, 6H; CH
2
), 1.27, 1.22 (2 × s, 2 × 12H; CH
3
); B{ H} NMR (96.3
1
3
1
MHz, C D ): δ 33.4 (h = 480 Hz); C{ H} NMR (75.4 MHz, C D ): δ 89.8 (Cp-C1), 82.9
6
6
1/2
6
6
(
CCH
CH
3
), 75.8 (Cp-C4), 75.5 (Cp-C2), 74.2 (Cp-C5), 34.9 (CH
2
-b), 25.2, 25.0 (CH
3
), 24.5
+
(
2
-a). ESI-MS: m/z (%) = 478 [M] (100). Anal. Calcd (%) for C25
H
36
B
2
FeO (478.01): C
4
6
2.82, H 7.59. Found: C 63.24, H 7.60.
1
5

ACCEPTED MANUSCRIPT
4
.8. Synthesis of 8
i
Neat 6 (0.163 g, 0.463 mmol) was dissolved in a MeOH/ PrOH mixture (3:2; 10 mL) and a
2 2
solution of CuBr (0.310 g, 1.39 mmol) in deionized H O (5 mL) was added. The stirred
reaction mixture was heated to reflux temperature for 16 h, cooled to room temperature, and
extracted with CHCl (3 × 15 mL). The combined organic phases were washed with H O (2 ×
3
2
1
5 mL) and dried over anhydrous MgSO
4
. After filtration, all volatiles were removed from the
filtrate in vacuo. The crude product was purified by flash column chromatography to give 8 as
a yellow solid. Yield: 0.093 g (66%); mp = 67–69 °C. R
f
= 0.74 (silica gel, hexane/EtOAc =
1
3
4
1
5:1). H NMR (250.1 MHz, C
6
D
6
): δ 4.25 (dd, JHH = 2.3 Hz, JHH = 1.3 Hz, 1H; Cp-H4),
4
.17 (m, 1H; Cp-H3ʼ /4ʼ ), 4.06 (vt, 2H; Cp-H2), 4.01 (m, 1H; Cp-H2ʼ /5ʼ ), 3.83 (m, 1H;
3
4
Cp-H3ʼ /4ʼ ), 3.66 (m, 1H; Cp-H2ʼ /5ʼ ), 3.56 (dd, J = 2.3 Hz, J = 1.5 Hz, 1H; Cp-
HH
HH
1
3
1
H5), 1.65–1.46 (m, 6H; CH
2
); C{ H} NMR (75.4 MHz, C
6
D
6
): δ 86.1 (Cp-C1ʼ ), 84.5 (Cp-
C1), 78.2 (Cp-C3), 75.4 (Cp-C3ʼ /4ʼ ), 71.7 (Cp-C2), 71.2 (Cp-C2ʼ /5ʼ ), 70.7 (Cp-C4), 70.3
Cp-C3ʼ /4ʼ ), 70.1 (Cp-C2ʼ /5ʼ ), 68.4 (Cp-C5), 35.3 (CH -b), 24.3, 24.3 (CH -a,a’). ESI-
(
2
2
+
MS: m/z (%) = 304 [M] (100).
4
.9. Synthesis of 9
i
Neat 7 (0.220 g, 0.460 mmol) was dissolved in a MeOH/ PrOH mixture (3:2; 15 mL) and a
solution of CuBr (0.617 g, 2.76 mmol) in deionized H O (10 mL) was added. The stirred
reaction mixture was heated to reflux temperature for 16 h, cooled to room temperature, and
extracted with CHCl (3 × 20 mL). The combined organic phases were washed with H O (2 ×
0 mL) and dried over anhydrous MgSO . After filtration, all volatiles were removed from the
filtrate in vacuo to give 9 as an orange solid in pure form. Yield: 0.161 g (91%); mp = 152–
2
2
3
2
2
4
1
3
4
1
54 °C. H NMR (250.1 MHz, C D ): δ 4.06 (dd, J = 2.4 Hz, J = 1.3 Hz, 2H; Cp-H4),
6 6 HH HH
3
4
3
.91 (vt, 2H; Cp-H2), 3.72 (dd, JHH = 2.4 Hz, JHH = 1.5 Hz, 2H; Cp-H5), 1.35–1.29 (m, 6H;
1
3
1
CH
2
); C{ H} NMR (75.4 MHz, C
6
D
6
): δ 85.0 (Cp-C1), 78.4 (Cp-C3), 77.4 (Cp-C4), 72.0
+
(Cp-C2), 69.9 (Cp-C5), 35.1 (CH
2
-b), 23.8 (CH
2
-a). ESI-MS: m/z (%) = 384 [M] (100). Anal.
Calcd (%) for C13 Fe (383.90): C 40.67, H 3.15. Found: C 40.63, H 3.19.
H
12Br
2
1
6

ACCEPTED MANUSCRIPT
4
.10. Synthesis of 12
A solution of Li[AlH ] in Et O (1 M, 0.37 mL, 0.37 mmol) was diluted with Et O (5 mL) and
4
2
2
added dropwise with stirring at –78 °C to a solution of 6 (0.130 g, 0.369 mmol) in Et
mL). After 30 min, the mixture was allowed to warm to room temperature and stirred for
another 1 h. The insolubles were removed by filtration (G4 frit) and washed with Et O (2 × 5
mL). The solvent was removed from the filtrate under reduced pressure and the solid residue
2
O (15
2
was further dried under dynamic vacuum overnight to obtain 12ꢀ(Et
compound; the amount of Et
spectroscopy. Yield: 0.089 g (85%). 12 crystallized from Et
2
O)0.5 as a yellow
1
2
O present in the sample after drying was determined by H NMR
2
O/THF in the presence of 12-
1
crown-4 at room temperature as crown-ether adduct 12ꢀ(12-c-4). H NMR (300.0 MHz, THF-
d8): δ 3.81 (m, 1H; Cp-H2ʼ /5ʼ ), 3.77 (m, 1H; Cp-H3ʼ /4ʼ ), 3.65 (n.r., 1H; Cp-H2),
3
.63 (n.r., 1H; Cp-H4), 3.59 (m, 1H; Cp-H2ʼ /5ʼ ), 3.57 (m, 1H; Cp-H5), 3.38 (m, 1H; Cp-
1
11
1
H3ʼ /4ʼ ), 1.91–1.78 (m, 6H; CH
2
), 0.81 (q, JBH = 77 Hz, 3H; BH
3
); B{ H} NMR (96.3
1
1
1
MHz, THF-d ): δ –28.7 (h = 12 Hz); B NMR (96.3 MHz, THF-d ): δ –28.7 (q, J = 77
8
1/2
8
BH
1
3
1
1
Hz); C{ H} NMR (100.6 MHz, THF-d
8
): δ 93.7 (q, JBC = 60 Hz; Cp-C3), 84.2 (m; Cp-C1),
2
2
8
2.8 (Cp-C1ʼ ), 77.4 (q, JBC = 3.5 Hz; Cp-C2), 75.5 (q, JBC = 3.5 Hz; Cp-C4), 72.8 (Cp-
3
C3ʼ /4ʼ ), 69.5 (Cp-C2ʼ /5ʼ ), 69.1 (q, J = 2.5 Hz; Cp-C5), 67.7 (Cp-C3ʼ /4ʼ ), 67.5 (Cp-
BC
2 2
C2ʼ /5ʼ ), 36.0 (CH -b), 26.5, 26.2 (CH -a,a’).
4
.11. Crystal structure determinations of 2, 3, 11, and 12.
Data for 3 were collected on a STOE IPDS II two-circle diffractometer with graphite-
monochromated MoK radiation (λ = 0.71073 Å). An empirical absorption correction with the
α
program PLATON[35] was performed. Data for 2, 11, and 12 were collected on a STOE IPDS
II two-circle diffractometer using a Genix Microfocus X-ray source with mirror optics and
α
MoK radiation. The data of 2, 11, and 12 were corrected for absorption with the frame-
scaling procedure contained in the X-AREA package. Equivalent reflections were averaged.
The structures were solved by direct methods using the program SHELXS[36] and refined
2
with full-matrix least-squares on F using the program SHELXL-97.[37] H atoms were
geometrically positioned and refined applying a riding model.
1
7

ACCEPTED MANUSCRIPT
The absolute structure of 3 was determined: Flack-x-parameter = 0.06(4). The crystal of 3 was
of minor quality, which explains the rather large standard deviations of the bond lengths and
angles.
Compound 11 crystallized with three crystallographically independent molecules in the
A
B
C
asymmetric unit (11 , 11 , 11 ). In one of these molecules, one methylene group is disordered
over two positions with a site occupation factor of 0.787(6) for the major occupied site. The
disordered atoms were anisotropically refined and the C–C bonds of the disordered atoms
were restrained to be equal.
The molecule of 12 is located on a crystallographic mirror plane. As a result, the 1,3-
propanediyl chain is disordered over two equally occupied positions. The crown-ether ring is
also affected by the disorder and consequently its atoms show enlarged displacement
ellipsoids.
CCDC reference numbers: 926726 (2), 926727 (3), 926728 (11) 926729 (12).
5
. Acknowledgements
M.W. acknowledges financial support by the Beilstein Institute, Frankfurt/Main, Germany,
within the research collaboration NanoBiC.
1
8

ACCEPTED MANUSCRIPT
6
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1
9

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(
[
(
2
0

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(
(
(
(
(
b) S. Aldridge, C. Bresner, I.A. Fallis, S.J. Coles, M.B. Hursthouse, Chem. Commun.
2002) 740–741;
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Hursthouse, Dalton Trans. (2006) 3660–3667;
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(
Chem. Eur. J. 14 (2008) 7525–7529.
[
[
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582;
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15] A rapidly flipping 1,3-propanediyl chain has been postulated already for the
[
[
(
[
(
3]ferrocenophane 1.
a) M. Rosenblum, A.K. Banerjee, N. Danieli, R.W. Fish, V. Schlatter, J. Am. Chem.
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(
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1
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18] L. Kaufmann, H. Vitze, M. Bolte, H.-W. Lerner, M. Wagner, Organometallics 27 (2008)
6
215–6221.
2
1

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1
226–1229.
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and 7 and thereby increases the yields of 8 and 9.
i
[
[
6
29] S. Gronowitz, A.B. Hörnfeldt, Y. Yang, in O. Chizhov (ed.) Organic Synthesis: Modern
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[
[
[
[
[
[
[
[
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University of Göttingen, Göttingen, Germany, 1997.
2
2

ACCEPTED MANUSCRIPT
Scheme 1
(MeO)2B
Fe
R
R = H
R = B(OMe)2
(ii)
2
Br2B
3
1
a
(i)
4
5
Fe
'Fe
b
4
5'
3'
R
a'
1'
2'
1
2 R = H
R = BBr2
3
(iii)
(tBuO)2B
Fe
R
4
5
R = H
R = B(O Bu)2
t
(iv)
pinB
R
Fe
6
7
R = H
R = Bpin
Scheme 1. Synthesis of compounds 2–7. Reagents and conditions: (i) 2: 0.7 eq. BBr
3
, hexane,
reflux temperature, 5 h; 3: 3 eq. BBr , hexane, reflux temperature, 5 h. (ii) exc. MeOSiMe ,
3
3
t
6 6
pentane, –78 °C to room temperature, 2 h. (iii) 4: 2 eq. KO Bu, C H , room temperature, 12 h;
t
5
: 4 eq. KO Bu, C
6
H
6
, room temperature, 12 h. (iv) 6: 1 eq. pinacol, THF, room temperature,
2
4 h; 7: 2 eq. pinacol, THF, room temperature, 24 h.
2
3

ACCEPTED MANUSCRIPT
Scheme 2
2
pinB
3
1
a
4
(ii)
5
Fe
b
Fe
4'
5'
(R = H)
3'
R
a'
1'
2'
6
7
R = H
R = Bpin
10a
(i)
Br
R
Fe
8
9
R = H
R = Br
(iii)
Fe
R
1
0b R = H
R = Ph
11
Scheme 2. Synthesis of compounds 8–11. Reagents and conditions: (i) 8: 3 eq. CuBr2,
i
i
H
2
O/MeOH/ PrOH, reflux temperature, 16 h; 9: 6 eq. CuBr
2 2
, H O/MeOH/ PrOH, reflux
temperature, 16 h. (ii) 1.5 eq. 4-Iodotoluene, 0.04 eq. [PdCl
2
(dppf)], 3 M aqueous NaOH,
n
t
DME, reflux temperature, 6 d. (iii) 10b: 2 eq. Bu
3
SnPh, 0.1 eq. [Pd(P Bu
3
)
2
], toluene,
], toluene,
n
t
microwave irradiation (170 °C, 30 min); 11: 4 eq. Bu
3
SnPh, 0.2 eq. [Pd(P Bu
3
)
2
microwave irradiation (170 °C, 30 min).
2
4

ACCEPTED MANUSCRIPT
Scheme 3
Scheme 3. Synthesis of compound 12. Reagents and conditions: (i) 1 eq. Li[AlH
4 2
], Et O, –78
°C to room temperature, 1.5 h.
2
5

ACCEPTED MANUSCRIPT
Figure 1
Fig. 1. Molecular structure of 2 in the solid state. Hydrogen atoms have been omitted for
clarity; displacement ellipsoids are drawn at the 50% probability level. Selected bond lengths
(Å), atomꢀꢀꢀatom distance (Å), bond angles (°), and dihedral angles (°): B(1)−C(3) 1.478(7),
B(1)−Br(1) 1.937(5), B(1)−Br(2) 1.938(5), Fe(1)ꢀꢀꢀB(1) 2.698(5); C(3)−B(1)−Br(1) 121.8(3),
C(3)−B(1)−Br(2) 122.3(4), Br(1)−B(1)−Br(2) 115.6(3), COG(Cp(1))−Fe(1)−COG(Cp(11))
1
69.7;
Cp(C(1))//Cp(C(11))
9.7(3),
B(1)Br(1)Br(2)//Cp(C(1))
22.4(2),
C(1)Fe(1)C(11)//C(6)C(7)C(8) 57.3(3); α* 26.1. COG(Cp(X)): centroid of the
cyclopentadienyl ring containing the carbon atom C(X).
2
6

ACCEPTED MANUSCRIPT
Figure 2
Fig. 2. Molecular structure of 3 in the solid state. Hydrogen atoms have been omitted for
clarity; displacement ellipsoids are drawn at the 50% probability level. Selected bond lengths
(Å), atomꢀꢀꢀatom distances (Å), bond angles (°), torsion angle (°), and dihedral angles (°):
B(1)−C(3) 1.46(2), B(1)−Br(1) 1.96(2), B(1)−Br(2) 1.92(2), B(2)−C(13) 1.53(2), B(2)−Br(3)
1
1
1
.92(2), B(2)−Br(4) 1.92(2); Fe(1)ꢀꢀꢀB(1) 2.99(2), Fe(1)ꢀꢀꢀB(2) 3.05(2); C(3)−B(1)−Br(1)
21.1(12), C(3)−B(1)−Br(2) 123.7(12), Br(1)−B(1)−Br(2) 115.2(9), C(13)−B(2)−Br(3)
21.9(12),
C(13)−B(2)−Br(4)
120.9(13),
Br(3)−B(2)−Br(4)
117.2(9),
COG(Cp(1))−Fe(1)−COG(Cp(11)) 168.8; C(3)−COG(Cp(1))−COG(Cp(11))−C(13) –75.4;
Cp(C(1))//Cp(C(11)) 11.2(6), B(1)Br(1)Br(2)//Cp(C(1)) 11.4(7), B(2)Br(3)Br(4)//Cp(C(11))
9
.0(8), C(1)Fe(1)C(11)//C(6)C(7)C(8) 59(1); α* 10.2 (at C(3)), 10.2 (at C(13)).
2
7