Formal insertion of o-carborynes into ferrocenyl C-H bonds: A simple access to o-carboranylferrocenes

Article abstract of DOI:10.1021/om300324n

Insertion of o-carborynes (1,2-dehydro-o-carboranes) into ferrocenyl C-H bonds has been described, providing a convenient methodology for the preparation of functionalized ferrocenyl o-carboranes. Reaction of the carboryne precursors 1-I-2-Li-9,12-Me₂-1,2-C₂B₁₀H₈ or 1-I-2-Li-3-R-1,2-C₂B₁₀H₉ (R = H, Ph, Me, Cl, Br, and I) with 2.5 equiv of ferrocene at 80 °C in cyclohexane afforded [1-(η⁵-C₅H₄)(9,12-Me₂-1,2-C ₂B₁₀H₉)]Fe(η⁵-C ₅H₅) and [1-(η⁵-C₅H ₄)(3-R-1,2-C₂B₁₀H₁₀)] Fe(η⁵-C₅H₅) (R = H, Ph, Me, Cl, Br, and I) in 19-44% isolated yields. On the other hand, in addition to the desired C-H bond insertion products [1-(η⁵-C₅H₄)(3-X-1, 2-C₂B₁₀H₁₀)]Fe(η⁵-C ₅H₅), bis(ferrocenyl)-o-carboranes 1,2- [(η⁵-C₅H₅)Fe(η⁵-C ₅H₄)]₂-3-X-1,2-C₂B ₁₀H₉ were isolated from the reactions of 1-I-2-Li-3-X-1,2-C₂B₁₀H₉ (X = Cl, Br, and I) in 12%, 15%, and 8% yields, respectively. Treatment of 1,2-dilithio-o-carborane or 1-lithio-2-methyl-o-carborane with ferrocenium hexafluorophosphate in cyclohexane also generated [1-(η⁵-C₅H ₄)(1,2-C₂B₁₀H₁₁)] Fe(η⁵-C₅H₅) and [1-(η⁵- C₅H₄)(2-Me-1,2-C₂B₁₀H ₁₀)]Fe(η⁵-C₅H₅) in 17% and 31% isolated yields, respectively. On the basis of these observations, it is suggested that the single-electron oxidation of ferrocene to the electrophilic ferrocenium cation by o-carborynes is crucial for the insertion reaction. Accordingly, a reaction mechanism is proposed.

Full text of DOI:10.1021/om300324n

Article
pubs.acs.org/Organometallics
Formal Insertion of o-Carborynes into Ferrocenyl C−H Bonds:
A Simple Access to o-Carboranylferrocenes
Sunewang Rixin Wang and Zuowei Xie*
Department of Chemistry and State Key Laboratory on Synthetic Chemistry, The Chinese University of Hong Kong, Shatin,
New Territories, Hong Kong, China
S
* Supporting Information
ABSTRACT: Insertion of o-carborynes (1,2-dehydro-o-
carboranes) into ferrocenyl C−H bonds has been described,
providing a convenient methodology for the preparation of
functionalized ferrocenyl o-carboranes. Reaction of the
carboryne precursors 1-I-2-Li-9,12-Me2-1,2-C2B10H8 or 1-I-2-
Li-3-R-1,2-C2B10H9 (R = H, Ph, Me, Cl, Br, and I) with
2.5 equiv of ferrocene at 80 °C in cyclohexane afforded [1-(η5-C5H4)(9,12-Me2-1,2-C2B10H9)]Fe(η5-C5H5) and [1-(η5-C5H4)-
(3-R-1,2-C2B10H10)]Fe(η5-C5H5) (R = H, Ph, Me, Cl, Br, and I) in 19−44% isolated yields. On the other hand, in addition
to the desired C−H bond insertion products [1-(η5-C5H4)(3-X-1,2-C2B10H10)]Fe(η5-C5H5), bis(ferrocenyl)-o-carboranes
1,2-[(η5-C5H5)Fe(η5-C5H4)]2-3-X-1,2-C2B10H9 were isolated from the reactions of 1-I-2-Li-3-X-1,2-C2B10H9 (X = Cl, Br, and I)
in 12%, 15%, and 8% yields, respectively. Treatment of 1,2-dilithio-o-carborane or 1-lithio-2-methyl-o-carborane with ferrocenium
hexafluorophosphate in cyclohexane also generated [1-(η5-C5H4)(1,2-C2B10H11)]Fe(η5-C5H5) and [1-(η5-C5H4)(2-Me-1,2-
C2B10H10)]Fe(η5-C5H5) in 17% and 31% isolated yields, respectively. On the basis of these observations, it is suggested that the
single-electron oxidation of ferrocene to the electrophilic ferrocenium cation by o-carborynes is crucial for the insertion reaction.
Accordingly, a reaction mechanism is proposed.
Scheme 1. Reaction of o-Carboryne (3a) with Organic
Aromatics
INTRODUCTION
■
o-Carboryne (1,2-dehydro-o-carborane) (3a), a very reactive
intermediate reported first in 1990,1 reacts readily with alkenes,
dienes, alkynes, and polycyclic or heteroaromatics in [2 + 2] and
[4 + 2] cycloaddition and ene reaction patterns,2 similar to that of
benzyne.3 It can be generated in situ from either 1-Br-2-Li-1,2-
C2B10H101 or 1-Me3Si-2-[IPh(OAc)]-1,2-C2B10H10.4
Recently, we reported a more efficient precursor, 1-I-2-Li-1,2-
C2B10H10 (2a), readily prepared from o-carborane (1a), for the
production of 3a.5a Our preliminary results show that 3a can exist
in two resonance forms, a bonding form vs a biradical form,
which exhibit significantly different reactivity patterns.6,7 The
biradical form can insert regioselectively into α-C−H bond of
aliphatic ethers, affording α-carboranylated ethers.6 On the other
hand, the bonding form undergoes both [4 + 2] and [2 + 2]
cycloaddition reactions with anisole and its derivatives. The
resulting [2 + 2] cycloaddition intermediates simultaneously
rearrange to cyclooctatetraenocarboranes via thermal [3,3]
sigmatropic rearrangement.7 Further studies show that 3a can
undergo [4 + 2] cycloaddition reaction, benzyl C−H bond
insertion, and ene reaction with toluene8 and exocyclic [4 + 2]
cycloaddition reaction with styrenes,9 in which the reactions
exhibit a remarkable substituent effect (Scheme 1). As an
ongoing project, we extended our research to include ferrocene,
an intriguing aromatic organometallic complex.10 Ferrocene
consists of two cyclopentadienyls that can be viewed as carbanion
species stabilized by aromaticity.11,12 It is speculated that
dearomatization of ferrocene with 3a would generate energeti-
cally unstable species, from which new reaction patterns
retaining the aromatic system would be anticipated. Indeed,
o-carborynes 3 insert readily into the aromatic C−H bond
of ferrocene, providing a simple access to ferrocenyl-substituted
o-carboranes.13 It is noted that no C−H bond insertion occurs
between benzyne and ferrocene. These findings suggest that
o-carboryne has unique properties of its own due to its higher
electron deficiency, which is detailed in this article.
RESULTS
■
A suspension of 2a in cyclohexane, prepared in situ according to
the reported procedures,8,9 was heated at 110 °C for 24 h in the
Received: April 19, 2012
Published: June 5, 2012
© 2012 American Chemical Society
4544
dx.doi.org/10.1021/om300324n | Organometallics 2012, 31, 4544−4550

Organometallics
Article
presence of 1.25 equiv of ferrocene (4). A new species (5a) was
formed together with the regenerated o-carborane (1a) in a
molar ratio of 45/55, as indicated by the 1H NMR spectrum of
the crude product mixture. They were inseparable by flash
column chromatography on silica gel. However, 1a was readily
removed from the crude product mixture by sublimation.
Accordingly, an unexpected C−H bond insertion product,
1-ferrocenylcarborane (5a), was obtained in 27% isolated yield
(Table 1, entry 1). The characterization of 5a was done by full
Table 2. Effects of Cage B-Substituents on C−H Bond
Insertion
Table 1. Screening of Reaction Conditions
entry
conditions
isolated yield (5a, %)
1
2
3
4
5
4 (1.25 equiv), 110 °C
4 (1.25 equiv), 80 °C
4 (2.5 equiv), 80 °C
4 (2.5 equiv), in the dark, 80 °C
4 (2.5 equiv), one-pot reaction, 80 °C
27
31
36
35
38
Interestingly, treatment of a cyclohexane solution of 1-methyl-
o-carborane (1i) and 4 with 1 equiv of nBuLi followed by addition
of 0.5 equiv of I2 and heating at 80 °C for 24 h afforded
1-ferrocenyl-2-methyl-o-carborane (5i) in 37% isolated yield
based on I2. In contrast, 5i was not formed if ferrocene (4)
was added after the consumption of elemental I2, as shown in
Scheme 2. This result may indicate that the oxidation of
comparison with the reported NMR data.13 Lowering the
reaction temperature to 80 °C or addition of a large excess of
ferrocene (4) resulted in improved product yields (Table 1,
entries 2 and 3). This reaction also proceeded smoothly in the
dark under the same conditions (Table 1, entry 4). Alternatively,
mixing ferrocene (4) and 1a before adding nBuLi and I2 gave an
analogous result (Table 1, entry 5). Since the cage C−H proton
of o-carborane (with a pKa value of ∼2314) is more acidic than
the ferrocenyl C−H proton (with a pKa value of ∼39),15 the
competitive deprotonation of ferrocene by nBuLi is not
anticipated. It has also been documented that ferrocene was
readily oxidized to the deep blue species once elemental I2 was
added.16 The above results may shed some light on the reaction
mechanism (vide infra).
Scheme 2. Reaction of 1-Methyl-o-Carborane (1i) with
Ferrocene
No corresponding C−H bond insertion product was obtained
when benzyne was generated by treatment of 2-(trimethylsilyl)-
phenyl trifluoromethanesulfonate with CsF in CH3CN in the
presence of 2.5 equiv of ferrocene (4), showing that o-carboryne
has unique properties of its own.
ferrocene to the ferrocenium cation by I2 is crucial for the
formation of 5i (vide infra).16
Under the reaction conditions shown in entry 5, Table 1,
o-carborynes bearing B-substituents such as phenyl, halo, and
methyl groups were subject to the above reaction. The results are
summarized in Table 2. 9,12-Dimethyl-o-carboryne showed
a similar reactivity to that of its parent o-carboryne (Table 2,
entry 1). 3-Substituted o-carborynes exhibited various reactivities
dependent on the substituents. 3-Phenyl-o-carboryne underwent
a C−H insertion with 4 to give 5c in an isolated yield of 44%,
while 3-methyl-o-carboryne afforded the desired product 5d in
only 19% isolated yield (Table 2, entries 2 and 3). Interestingly,
in addition to the C−H bond insertion products 5 in yields
comparable to that of o-carboryne, reaction of ferrocene (4) with
3-halocarborynes generated bis(ferrocenyl)-o-carboranes 6 in
8−15% yields (Table 2, entries 4−6). These results suggested
that electron-withdrawing substituents at the 3-position favor
the insertion reactions. It is noteworthy that disubstituted
o-carboranes were also produced from the C−H bond insertion
reaction of o-carboryne with aliphatic ethers,6 which may indicate
that both reactions share some common features in the reaction
mechanism.
Accordingly, reactions of 1,2-dilithio-o-carborane, 1,7-dilithio-
m-carborane, or 1-lithio-2-methyl-o-carborane with a commercially
available ferrocenium salt, ferrocenium hexafluorophosphate
(4+[PF6]−), were carried out (Scheme 3). In addition to the
reduction product ferrocene and o-carboranes, the anticipated
ferrocenylcarboranes 5a and 5i were isolated in 17% and 31%
yields, respectively. However, no coupling product was generated
in the reaction of 1,7-dilithio-m-carborane with 4+[PF6]−.
All new compounds were purified by flash column
chromatography on silica gel and characterized by various
1
spectroscopic data. The H NMR spectra of 5b showed two
doublets of doublets at 4.35 and 4.19 ppm corresponding to the
η5-C5H4 group, one singlet at 4.22 ppm of η5-C5H5, one broad
singlet at 3.52 ppm attributable to the cage C−H proton, and two
singlets at 0.24 and 0.18 ppm assignable to two B−CH3 units. For
1-ferrocenyl-3-phenyl-o-carborane (5c), three multiplets, at 4.06,
3.99, and 3.94 ppm, corresponding to the η5-C5H4 unit were
observed. These protons were slightly shielded by the 3-phenyl
group. The other B(3)-substituted ferrocenyl o-carboranes, 5d to
5g, displayed four multiplets of the η5-C5H4 group at 4.36, 4.24,
4545
dx.doi.org/10.1021/om300324n | Organometallics 2012, 31, 4544−4550

Organometallics
Article
Scheme 3. Reaction of Lithiocarboranes with 4+[PF6]−
redox reaction between the two substrates is likely to occur
(Scheme 4),24 which can be viewed as the reverse process of one-
electron oxidation of 4 by o-carboryne (Scheme 5). The resulting
carboranyl radicals then undergo hydrogen abstraction with
solvents to regenerate o-carborane (1a).2,9 Such a redox reaction
predominates in the reaction of the m-carborane system, and
thus only ferrocene (4) was regenerated in high yield together
with 1h (Scheme 3). This result suggests that m-lithiocarborane
is a stronger reducing agent than its ortho counterpart, which
is consistent with the observations for the nido species of
carboranes.25
Theoretical calculations show that the LUMO (lowest
unoccupied molecular orbital) energy of o-carboryne is much
lower than that of benzyne;26 that is, o-carboryne can more easily
accommodate another external electron than benzyne. This may
account for the different reactivities in their reactions with
ferrocene. On the basis of the above results, a plausible
mechanism is thus proposed in Scheme 5. Elimination of LiI
from 2a gives the reactive intermediate o-carboryne (3a), which
is best described as a resonance hybrid of both bonding and
biradical forms.6 3a undergoes one-electron oxidation with
ferrocene (4) to afford the ferrocenium cation 4+ and the
carboranyl radical anion 7a, which may be a reversible process.
Nucleophilic exo-attack of 7a on one of the cyclopentadienyl
rings in 4+ results in the formation of adduct 8a′,21,22 which can
be viewed as the reduced form of the protonated ferrocene.27
There are two possible pathways from 8a′ to the C−H bond
insertion product 5a: direct radical-induced hydrogen shift of 8a′
generating 5a (path I) or an intramolecular single-electron
transfer of 8a′ giving the protonated ferrocene 9a,27 which is
rapidly deprotonated by the neighboring carboranyl anion to
afford 5a (path II). It should be pointed out that the carboranyl
anion of 1 or 7 can deprotonate the insertion product 5 as well to
give the 1-ferrocenyl-o-carboranyl anion, which can react with
the electrophilic species 4+ in a similar manner to that of the
reaction of 1-lithio-2-methyl-o-carborane with 4+[PF6]−
(Scheme 4), yielding 1,2-bis(ferrocenyl)-o-carboranes 6. For
example, the reactions of 3-halo-o-carborynes 3e,f,g with 4 gave 6
(Table 2, entries 4−6).
4.21, and 4.02 ppm (5d), 4.48, 4.30, 4.28, and 4.18 ppm (5e),
4.48, 4.30, 4.28, and 4.14 ppm (5f), and 4.47, 4.30, 4.28, and 4.09
ppm (5g), respectively. Such a splitting pattern was also found in
the spectra of their corresponding 1,2-bis(ferrocenyl)-o-carbor-
anes 6e,f,g. For 5i, two multiplets at 4.41 and 4.28 ppm of the
η5-C5H4 group were observed, similar to that of [1-(η5-C5H4)-(2-
Me-1,2-C2B10H10)]2Fe.13
Molecular structures of 5b,c,e,f,i and 6e were further
confirmed by single-crystal X-ray analyses (Figure 1). The
measured cage C−C bond distances from 1.637(4) to 1.775(4) Å
fall in the range normally observed in o-carboranes.17 The cage
C−C(Cp) distances vary from 1.480(4) to 1.495(4) Å, which are
very close to the corresponding values found in the documented
carboranyl metallocene complexes, for example, 1.487(7) Å in
[1-(η5-C5H4)(1,2-C2B10H11)]Fe(η5-C5H5),13 1.492(2) Å in
[1-(η5-C5D4)(2-Me-1,2-C2B10H10)]RuD(PPh3)2,18a and
1.495(6) Å in [1,2-(η5-MeHC-C5H3)(1,2-C2B10H10)]RuH-
(PPh3)2.19b
DISCUSSION
■
A formal nucleophilic attack of 1-Li-2-Me-1,2-C2B10H10 on the
Cp ring bound to a ruthenium(II) center was reported.18a
Further studies suggested the coupling between carboranyl and
cyclopentadienyl groups resulted from the reductive elimination
of a CpRu(C2B10H10R) complex promoted by sterically
demanding coordinating ligands.18b,19 Ferrocene, an electron-
rich species, is susceptible to the exo-attack of electrophiles rather
than nucleophiles.20 Indeed, nucleophilic 1,2-dilithio-o-carbor-
ane did not react with ferrocene. On the other hand, electron-
deficient cationic half-sandwich iron(II) complexes have been
documented to undergo nucleophilic substitution on the cyclo-
pentadienyl ring, inducing the hapticity change from η5-Cp
bonding mode to η4-cyclopentadiene complexation.21,22
CONCLUSION
■
Insertion of o-carborynes into the ferrocenyl C−H bond has
been described. It is suggested that the oxidation of ferrocene to
the electrophilic ferrocenium cation via a single electron transfer
by o-carborynes is crucial for the insertion reaction, which is
confirmed by the reactions of lithiocarboranes with ferrocenium
hexafluorophosphate. Such an aromatic C−H bond insertion
reaction serves as a convenient methodology for the preparation
of a series of functionalized ferrocenyl o-carboranes. This work
demonstrates that carborynes not only have very rich reaction
chemistry but also have unique properties of their own, which is
different from that of benzyne.
In the reaction of 1,2-dilithio-o-carborane with 4+[PF6]−
(Scheme 3), 1 equiv of ferrocenium hexafluorophosphate
functions as the electrophile and the other one may act as
the oxidant to oxidize the nucleophilic adducts 8a; meanwhile,
1,2-dilithio-o-carborane also serves as a base to accept the leaving
proton from the cyclopentadiene of 9a (Scheme 4). After initial
oxidation of ferrocene by I2,16 one-pot reaction with 1-methyl-o-
carborane in Scheme 2 would enter the same reaction pathway,
which can be regarded as oxidative activation of ferrocene for
nucleophilic reaction.23
EXPERIMENTAL SECTION
■
General Procedures. All reactions were carried out in flame-dried
glassware under an atmosphere of dry N2 or Ar with the rigid exclusion
of air and moisture using standard Schlenk techniques unless otherwise
specified.8 All organic solvents were freshly distilled from Na−K alloy
immediately prior to use. All other chemicals were purchased from
either Aldrich or Acros Chemical Co. and used as received unless
otherwise specified. 1H NMR spectra were recorded on a Bruker DPX
400 spectrometer at 400 MHz. 13C{1H} NMR spectra were recorded on
either a Bruker DPX 300 spectrometer at 75 MHz or a Bruker DPX 400
In view of a much higher yield of ferrocene (4) over the
coupling product 5a (52% vs 17%) in the reaction of 1,2-dilithio-
o-carborane with 4+[PF6]− (Scheme 3), a competitive direct
4546
dx.doi.org/10.1021/om300324n | Organometallics 2012, 31, 4544−4550

Organometallics
Article
Figure 1. Molecular structures of (a) 5b, (b) 5c, (c) 5e, (d) 5f, (e) 5i, and (f) 6e. All hydrogen atoms are omitted for clarity.
spectrometer at 100 MHz. 11B NMR spectra were recorded on a Bruker
DPX 300 spectrometer at 96 MHz or a Varian Inova 400 spectrometer at
128 MHz. Chemical shifts were reported in ppm with references to the
residual solvent resonances of the deuterated solvents for proton and
carbon chemical shifts and to external BF3·OEt2 (0.0 ppm) for boron
chemical shifts. The data were reported as follows: chemical shift,
multiplicity (s = singlet, d = doublet, t = triplet, q = quadruplet, m =
multiplet or unresolved, br = broad), coupling constant(s) in Hz,
integration, and assignment. Mass spectra were obtained on a Thermo
Finnigan MAT 95 XL spectrometer.
Reaction of 2a with Ferrocene (4). To an in situ prepared
cyclohexane solution (5 mL) of 2a (0.4 mmol) at room temperature was
added ferrocene (186.1 mg, 1.0 mmol). The reaction mixture was heated
at 80 °C for 24 h and then quenched with wet n-hexane. The resulting
suspension was quickly passed through a short column of silica gel to
remove the inorganic salts and washed with ether (5 mL × 3). The
organic portions were combined. After removal of solvents in vacuo,
the residue was analyzed by 1H NMR spectroscopy (5a/1a = 45/55).
The regenerated o-carborane (1a) was removed by sublimation in
vacuo, and the resulting residue was then subjected to flash column
4547
dx.doi.org/10.1021/om300324n | Organometallics 2012, 31, 4544−4550

Organometallics
Article
CH), 3.52 (br, 1H) (cage CH), 0.24 (s, 3H), 0.18 (s, 3H) (CH3).
13C{1H} NMR (100 MHz, CDCl3): δ 85.7, 70.03, 69.87, 68.4, 58.3 (cage
C), −0.1 (br), one cage carbon was not observed. 11B NMR (128 MHz,
CDCl3): δ 7.6 (s, 1B), 4.5 (s, 1B), −7.8 (d, J = 145 Hz, 2B), −10.2 (d, J =
164 Hz, 2B), −13.2 (d, J = 161 Hz, 4B). HRMS (EI): calcd for
C14H2411B810B2Fe+ 356.2232, found 356.2229.
Scheme 4. Possible Pathways for Reaction of 1,2-Dilithio-o-
carborane with 4+[PF6]−
1-Ferrocenyl-3-phenyl-o-carborane, 5c. Yellow crystals. Yield:
1
71.2 mg (44%). H NMR (400 MHz, CDCl3): δ 7.29 (m, 3H), 7.19
(m, 2H) (aromatic CH), 4.21 (s, 5H), 4.06 (m, 1H), 3.99 (m, 1H), 3.94
(m, 2H) (ferrocenyl CH), 3.92 (br, 1H) (cage CH). 13C{1H} NMR
(100 MHz, CDCl3): δ 133.5, 129.0, 127.6, 85.2, 70.3, 70.0, 68.1, 67.8,
67.7, 63.2 (cage C), one cage carbon was not observed. 11B NMR
(128 MHz, CDCl3): δ −2.4 (s, 1B), −4.6 (d, J = 147 Hz, 2B), −8.4 (d,
J = 143 Hz, 2B), −11.4 (d, J = 152 Hz, 4B), −14.9 (d, J = 163 Hz, 1B).
HRMS (EI): calcd for C18H2411B810B2Fe+ 404.2234, found 404.2240.
1-Ferrocenyl-3-methyl-o-carborane, 5d. Yellow crystals. Yield: 26.3
mg (19%). 1H NMR (400 MHz, CDCl3): δ 4.36 (m, 1H), 4.27 (s, 5H),
4.24 (m, 1H), 4.21 (m, 1H), 4.02 (m, 1H) (ferrocenyl CH), 3.43 (br,
1H) (cage CH), 0.17 (s, 3H) (CH3). 13C{1H} NMR (100 MHz,
CDCl3): δ 86.1, 75.3 (cage C), 70.2, 69.4, 68.5, 68.1, 66.8, 65.6 (cage C).
11B NMR (128 MHz, CDCl3): δ −2.1 (s, 1B), −4.9 (d, J = 137 Hz, 2B),
−8.6 (d, J = 138 Hz, 1B), −9.5 (d, J = 142 Hz, 1B), −10.9 (d, J = 154 Hz,
2B), −11.9 (d, J = 140 Hz, 2B), −15.2 (d, J = 163 Hz, 1B). HRMS (EI):
calcd for C13H2211B810B2Fe+ 342.2075, found 342.2079.
Scheme 5. Possible Pathways for Insertion of 3a into a
Ferrocenyl C−H Bond
3-Chloro-1-ferrocenyl-o-carborane, 5e. Yellow crystals. Yield:
1
61.0 mg (42%). H NMR (400 MHz, CDCl3): δ 4.48 (m, 1H), 4.30
(m, 1H), 4.28 (m, 6H), 4.18 (m, 1H) (ferrocenyl CH), 3.73 (br, 1H)
(cage CH). 13C{1H} NMR (100 MHz, CDCl3): δ 84.4, 70.21, 70.16,
68.8, 68.6, 67.9, 67.1 (cage C), one cage carbon was not observed. 11B
NMR (128 MHz, CDCl3): δ −3.2 (s, 1B), −5.0 (d, J = 143 Hz, 1B), −5.4
(d, J = 148 Hz, 1B), −8.8 (d, J = 147 Hz, 1B), −9.7 (d, J = 134 Hz, 1B),
−11.0 (m, 3B), −13.5 (d, J = 157 Hz, 1B), −15.3 (d, J = 172 Hz, 1B).
HRMS (EI): calcd for C12H1911B810B2ClFe+ 363.1503, found 363.1503.
3-Chloro-1,2-bis(ferrocenyl)-o-carborane, 6e. Red-brown crystals.
Yield: 26.4 mg (12%). 1H NMR (400 MHz, CDCl3): δ 4.60 (m, 2H),
4.18 (s, 10H), 4.13 (m, 2H), 4.09 (m, 2H), 4.06 (m, 2H) (ferrocenyl
CH). 13C{1H} NMR (100 MHz, CDCl3): δ 82.0, 72.3, 70.4, 70.3, 68.6,
68.2, cage carbons were not observed. 11B NMR (128 MHz, CDCl3): δ
−1.8 (s, 1B), −5.0 (d, J = 146 Hz, 2B), −8.5 (d, J = 159 Hz, 3B), −9.6 (d,
J = 141 Hz, 3B), −14.9 (d, J = 149 Hz, 1B). HRMS (EI): calcd for
C22H2711B810B2ClFe2+ 547.1486, found 547.1486.
3-Bromo-1-ferrocenyl-o-carborane, 5f. Yellow crystals. Yield: 55.5
mg (34%). 1H NMR (400 MHz, CDCl3): δ 4.48 (m, 1H), 4.30 (m, 1H),
4.28 (m, 6H), 4.14 (m, 1H) (ferrocenyl CH), 3.78 (br, 1H) (cage CH).
13C{1H} NMR (100 MHz, CDCl3): δ 85.3, 70.24, 70.18, 68.8, 68.5, 67.6,
67.1 (cage C), one cage carbon was not observed. 11B NMR (128 MHz,
CDCl3): δ −4.5 (d, J = 142 Hz, 1B), −5.1 (d, J = 150 Hz, 1B), −8.0 (br,
1B), −8.9 (br, 2B), −10.7 (br, 3B), −12.0 (br, 1B), −14.8 (d, J = 165 Hz,
1B). HRMS (EI): calcd for C12H1911B810B2BrFe+ 407.1010, found
407.1012.
chromatography on silica gel (230−400 mesh) using n-hexane as eluent
1
to give 5a as yellow crystals (47.3 mg, 36%). H NMR (400 MHz,
CDCl3): δ 4.37 (m, 2H), 4.24 (s, 5H), 4.21 (m, 2H) (ferrocenyl CH),
3.72 (br, 1H) (cage CH). 13C{1H} NMR (100 MHz, CDCl3): δ 86.0,
75.8 (cage C), 70.03, 69.98, 68.7, 65.0 (cage C). 11B{1H} NMR (128
MHz, CDCl3): δ −2.2 (1B), −5.5 (1B), −10.0 (4B), −11.8 (2B), −13.1
(2B). These data are the same as the reported ones.13
Reaction of o-Carborane (1a) with Ferrocene (4) in the
Presence of nBuLi and I2. To a cyclohexane solution (5 mL) of
o-carborane (57.6 mg, 0.4 mmol) and ferrocene (186.1 mg, 1.0 mmol) at
n
room temperature was slowly added BuLi (0.5 mL, 1.6 M in hexane,
3-Bromo-1,2-bis(ferrocenyl)-o-carborane, 6f. Red-brown crystals.
Yield: 35.6 mg (15%). 1H NMR (400 MHz, CDCl3): δ 4.71 (m, 2H),
4.18 (s, 10H), 4.16 (m, 2H), 4.11 (m, 2H), 4.03 (m, 2H) (ferrocenyl
CH). 13C{1H} NMR (100 MHz, CDCl3): δ 86.1 (cage C), 82.6, 72.3,
70.8, 70.4, 68.5, 68.2. 11B NMR (128 MHz, CDCl3): δ −4.5 (d, J = 145
Hz, 2B), −7.3 (s, 1B), −8.2 (br, 4B), −9.1 (d, J = 154 Hz, 2B), −13.5 (d,
0.8 mmol) with stirring. After stirring for 6 h, iodine (101.6 mg,
0.4 mmol) was added and a deep blue mixture was obtained after stirring
at room temperature overnight. The reaction mixture was heated at
80 °C for 24 h and then quenched with wet n-hexane. The resulting
suspension was quickly passed through a short column of silica gel to
remove the inorganic salts and washed with ether (5 mL × 3). The
organic portions were combined. After removal of solvents in vacuo,
+
J = 147 Hz, 1B). HRMS (EI): calcd for C22H2611B810B2BrFe2 ([M −
H]+) 591.0895, found 591.0875.
1
1-Ferrocenyl-3-iodo-o-carborane, 5g. Yellow crystals. Yield: 60.3
mg (33%). 1H NMR (400 MHz, CDCl3): δ 4.47 (m, 1H), 4.30 (m, 1H),
4.28 (m, 6H), 4.09 (m, 1H) (ferrocenyl CH), 3.81 (br, 1H) (cage CH).
13C{1H} NMR (100 MHz, CDCl3): δ 87.2, 70.3, 70.2, 68.8, 68.4, 67.4,
67.3 (cage C), one cage carbon was not observed. 11B NMR (128 MHz,
CDCl3): δ −3.5 (d, J = 143 Hz, 1B), −4.6 (d, J = 146 Hz, 1B), −6.7 (d,
J = 160 Hz, 1B), −9.8 (br, 5B), −13.9 (d, J = 162 Hz, 1B), −23.1 (s, 1B).
HRMS (EI): calcd for C12H1911B810B2IFe+ 454.0885, found 454.0893.
1,2-Bis(ferrocenyl)-3-iodo-o-carborane, 6g. Red-brown crystals.
the residue was analyzed by H NMR spectroscopy. The regenerated
o-carborane (1a) was removed by sublimation in vacuo, and the
resulting residue was then subjected to flash column chromatography on
silica gel (230−400 mesh) using n-hexane as eluent to give 5a as yellow
crystals (49.6 mg, 38%).
n
Reaction of 4 with 1b−g,i in the Presence of BuLi and I2.
These reactions were performed at a scale of 1.0 mmol of 4 and
0.4 mmol of 1 using the same procedures reported for 5a.
1-Ferrocenyl-9,12-dimethyl-o-carborane, 5b. Yellow crystals.
1
1
Yield: 49.9 mg (35%). H NMR (400 MHz, CDCl3): δ 4.35 (dd, J =
Yield: 20.5 mg (8%). H NMR (400 MHz, CDCl3): δ 4.83 (m, 2H),
2.0, 1.6 Hz, 2H), 4.22 (s, 5H), 4.19 (dd, J = 2.0, 1.6 Hz, 2H) (ferrocenyl
4.20 (m, 12H), 4.14 (m, 2H), 4.01 (m, 2H) (ferrocenyl CH). 13C{1H}
4548
dx.doi.org/10.1021/om300324n | Organometallics 2012, 31, 4544−4550

Organometallics
Article
NMR (100 MHz, CDCl3): δ 85.7 (cage C), 83.4, 72.1, 71.5, 70.4, 68.4,
68.3. 11B NMR (128 MHz, CDCl3): δ −3.6 (d, J = 141 Hz, 2B), −6.7 (d,
J = 131 Hz, 3B), −8.1 (br, 3B), −11.4 (d, J = 154 Hz, 1B), −21.3 (s, 1B).
HRMS (EI): calcd for C22H2711B810B2IFe2+ 638.0865, found 638.0871.
1-Ferrocenyl-2-methyl-o-carborane, 5i. Yellow crystals. Yield: 50.6
mg (37%). 1H NMR (400 MHz, CDCl3): δ 4.41 (m, 2H), 4.28 (m, 2H),
4.26 (s, 5H) (ferrocenyl CH), 1.49 (s, 3H) (CH3). 13C{1H} NMR (100
MHz, CDCl3): δ 83.4, 81.0 (cage C), 71.2, 70.6, 69.0, 22.7, one cage
carbon was not observed. 11B{1H} NMR (128 MHz, CDCl3): δ −4.7
(2B), −9.5 (6B), −11.6 (2B). HRMS (EI): calcd for C13H2211B810B2Fe+
342.2075, found 342.2081.
China (973 Program) (Project No. 2012CB821600), and
NSFC/RGC Joint Research Scheme (No. N_CUHK470/10).
We thank Ms. Hoi-Shan Chan for single-crystal X-ray analyses.
REFERENCES
■
(1) Gingrich, H. L.; Ghosh, T.; Huang, Q.; Jones, M., Jr. J. Am. Chem.
Soc. 1990, 112, 4082−4083.
(2) (a) Ghosh, T.; Gingrich, H. L.; Kam, C. K.; Mobraaten, E. C.;
Jones, M., Jr. J. Am. Chem. Soc. 1991, 113, 1313−1318. (b) Gingrich, H.
L.; Huang, Q.; Morales, A. L.; Jones, M., Jr. J. Org. Chem. 1992, 57,
3803−3806. (c) Gingrich, H. L.; Ghosh, T.; Huang, Q.; Li, J.; Jones, M.,
Jr. Pure Appl. Chem. 1993, 65, 65−71. (d) Ho, D. M.; Cunningham, R. J.;
Brewer, J. A.; Bian, N.; Jones, M., Jr. Inorg. Chem. 1995, 34, 5274−5278.
(e) Atkins, J. H.; Ho, D. M.; Jones, M., Jr. Tetrahedron Lett. 1996, 37,
7217−7220. (f) Barnett-Thamattoor, L.; Zheng, G.-X.; Ho, D. M.;
Jones, M., Jr.; Jackson, J. E. Inorg. Chem. 1996, 35, 7311−7315.
(3) (a) Hoffmann, R. W. Dehydrobenzene and Cycloalkynes; Academic:
New York, 1967. (b) Pellissier, H.; Santelli, M. Tetrahedron 2003, 59,
701−730.
Reaction of 1,2-Dilithio-o-carborane with Ferrocenium
Hexafluorophosphate (4+[PF6]−). To a cyclohexane solution
n
(5 mL) of o-carborane (57.6 mg, 0.4 mmol) was slowly added BuLi
(0.5 mL, 1.6 M in hexane, 0.8 mmol) with stirring at room temperature.
After the mixture was stirred for 6 h at room temperature, ferrocenium
hexafluorophosphate (331.0 mg, 1.0 mmol) was added with stirring.
The reaction mixture was heated at 80 °C for 24 h and then quenched
with wet n-hexane. The resulting suspension was quickly passed through
a short column of silica gel to remove the inorganic salts and washed
with ether (5 mL × 3). The organic portions were combined. After
1
(4) (a) Jeon, J.; Kitamura, T.; Yoo, B.-W.; Kang, S. O.; Ko, J. Chem.
Commun. 2001, 2110−2111. (b) Lee, T.; Jeon, J.; Song, K. H.; Jung, I.;
Baik, C.; Park, K.-M.; Lee, S. S.; Kang, S. O.; Ko, J. Dalton Trans. 2004,
933−937.
removal of solvents in vacuo, the residue was analyzed by H NMR
spectroscopy and then subjected to flash column chromatography on
silica gel (230−400 mesh) using n-hexane as eluent to give 5a (22.6 mg,
17%) as yellow crystals and ferrocene (39.0 mg, 52%).
Reaction of 1,7-Dilithio-m-carborane or 1-Lithio-2-methyl-o-
carborane with 4+[PF6]−. These reaction were performed at a scale
of 1.0 mmol of 4+[PF6]− using the same procedures reported for
1,2-dilithio-o-carborane.
4: This compound was isolated from the reaction of 1,7-dilithio-m-
carborane as yellow crystals (72.2 mg, 49%).
5i: This compound was isolated from the reaction of 1-lithio-2-
methyl-o-carborane as yellow crystals (42.5 mg, 31%).
X-ray Structure Determination. All single crystals were immersed
in Paraton-N oil. Data were collected at 293 K on a Bruker SMART 1000
CCD diffractometer using Mo Kα radiation (0.71073 Å). An empirical
absorption correction was applied using the SADABS program.28 All
structures were solved by direct methods and subsequent Fourier
difference techniques and refined anisotropically for all non-hydrogen
atoms by full-matrix least-squares on F2 using the SHELXTL program
package.29 All hydrogen atoms were geometrically fixed using the riding
model. Molecular structure of 5c showed a half hexane of solvation. The
chlorine atom in 6e is disordered over two sets of positions (B(3) and
B(6) positions) with 0.19:0.81 occupancies. For non-centrosymmetric
structures of 5e and 5i, the appropriate enantiomorph was chosen by
refining Flack’s parameter x toward zero.30 Crystal data and details of
data collection and structure refinements are given in Table S1 in the
Supporting Information. Further details are also included in the
Supporting Information.
(5) (a) Qiu, Z.; Wang, S. R.; Xie, Z. Angew. Chem., Int. Ed. 2010, 49,
4649−4652. For metal−carboryne chemistry developed in our lab, see:
(b) Deng, L.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2005, 127, 13774−
13775. (c) Deng, L.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2006, 128,
7728−7729. (d) Qiu, Z.; Xie, Z. Angew. Chem., Int. Ed. 2008, 47, 6572−
6575. (e) Qiu, Z.; Xie, Z. J. Am. Chem. Soc. 2009, 131, 2084−2085.
(f) Ren, S.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2009, 131, 3862−3863.
(g) Qiu, Z.; Xie, Z. J. Am. Chem. Soc. 2010, 132, 16085−16093. (h) Ren,
S.; Qiu, Z.; Xie, Z. Angew. Chem., Int. Ed. 2012, 51, 1010−1013. (i) Ren,
S.; Qiu, Z.; Xie, Z. J. Am. Chem. Soc. 2012, 134, 3242−3254. (j) Qiu, Z.;
Ren, S.; Xie, Z. Acc. Chem. Res. 2011, 44, 299−309.
(6) Wang, S. R.; Qiu, Z.; Xie, Z. J. Am. Chem. Soc. 2011, 133, 5760−
5763.
(7) Wang, S. R.; Qiu, Z.; Xie, Z. J. Am. Chem. Soc. 2010, 132, 9988−
9989.
(8) Wang, S. R.; Xie, Z. Organometallics 2012, 31, 3316−3323.
(9) Wang, S. R.; Xie, Z. Tetrahedron 2012, 68, 5269−5278.
(10) Woodward, R. B.; Rosenblum, M.; Whiting, M. C. J. Am. Chem.
Soc. 1952, 74, 3458−3459.
(11) (a) Fischer, E. O.; Pfab, W. Z. Naturforsch. 1952, 7B, 377−379.
(b) Ruch., E.; Fischer, E. O. Z. Naturforsch. 1952, 7B, 676. (c) Wilkinson,
G.; Rosenblum, M.; Whiting, M. C.; Woodward, R. B. J. Am. Chem. Soc.
1952, 74, 2125−2126.
(12) (a) Lauher, J. W.; Hoffmann, R. J. Am. Chem. Soc. 1976, 98, 1729−
1742. (b) Takusagawa, F.; Koetzle, T. F. Acta Crystallogr. B 1979, 35,
1074−1081. (c) Seiler, P.; Dunitz, J. D. Acta Crystallogr. B 1982, 38,
1741−1745.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H, 13C, and 11B NMR spectra of all new compounds, Table S1,
and crystallographic data in CIF format for 5b,c,e,f,i and 6e. This
material is available free of charge via the Internet at http://pubs.
acs.org.
(13) Ferrocenyl o-carboranes were prepared from the reaction of
alkynyl ferrocenes and decaborane; see: Beckering, C. L.; Rosair, G. M.;
Weller, A. S. J. Organomet. Chem. 1998, 556, 55−66.
(14) Hermansson, K.; Woj
6039−6048.
́
cik, M.; Sjoberg, S. Inorg. Chem. 1999, 38,
̈
(15) Denisovich, L. I.; Gubin, P. S. Russ. Chem. Rev. 1977, 46, 27−45.
(16) Salman, H. M. A.; Mahmoud, M. R.; Abou-El-Wafa, M. H. M.;
Rabie, U. M.; Crabtree, R. H. Inorg. Chem. Commun. 2004, 7, 1209−
1212.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: zxie@cuhk.edu.hk.
(17) (a) Oliva, J. M.; Allan, N. L.; Schleyer, P. v. R.; Vinas, C.; Teixidor,
̃
Notes
F. J. Am. Chem. Soc. 2005, 127, 13538−13547. (b) Wang, H.; Li, H.-W.;
Xie, Z. Organometallics 2003, 22, 4522−4531. (c) Wang, S.; Yang, Q.;
Mak, T. C. W.; Xie, Z. Organometallics 1999, 18, 4478−4487.
(18) (a) Basato, M.; Biffis, A.; Tubaro, C.; Graiff, C.; Tiripicchio, A.
Dalton Trans. 2004, 4092−4093. (b) Basato, M.; Biffis, A.; Buscemi, G.;
Callegaro, E.; Polo, M.; Tubaro, C.; Venzo, A.; Vianini, C.; Graiff, C.;
Tiripicchio, A.; Benetollo, F. Organometallics 2007, 26, 4265−4270.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by grants from the Research Grants
Council of the Hong Kong Special Administration Region
(Project No. 404011), National Basic Research Program of
4549
dx.doi.org/10.1021/om300324n | Organometallics 2012, 31, 4544−4550

Organometallics
Article
(19) (a) Sun, Y.; Chan, H.-S.; Dixneuf, P. H.; Xie, Z. Chem. Commun.
2004, 2588−2589. (b) Sun, Y.; Chan, H.-S.; Xie, Z. Organometallics
2006, 25, 4188−4195.
(20) Rosenblum, M.; Abbate, F. W. J. Am. Chem. Soc. 1966, 88, 4178−
4184.
(21) (a) Reger, D. L.; Belmore, K. A.; Atwood, J. L.; Hunter, W. E. J.
Am. Chem. Soc. 1983, 105, 5710−5711. (b) Reger, D. L.; Belmore, K. A.
Organometallics 1985, 4, 305−311. (c) Reger, D. L.; Klaeren, S. A.;
Lebioda, L. Organometallics 1986, 5, 1072−1079. (d) Reger, D. L. Acc.
Chem. Res. 1988, 21, 229−235.
(22) (a) Liu, L.-K.; Luh, L.-S. Organometallics 1994, 13, 2816−2824.
(b) Luh, L.-S.; Eke, U. B.; Liu, L.-K. Organometallics 1995, 14, 440−447.
(c) Liu, L.-K.; Luh, L.-S. Organometallics 1996, 15, 5263−5265.
(d) Deng, L.; Chan, H.-S.; Xie, Z. Inorg. Chem. 2007, 46, 2716−2724.
(23) Valyaev, D. A.; Peterleitner, M. G.; Leont’eva, L. I.; Novikova, L.
N.; Semeikin, O. V.; Khrustalev, V. N.; Antipin, M. Y.; Ustynyuk, N. A.;
Skelton, B. W.; White, A. H. Organometallics 2003, 22, 5491−5497.
(24) Karpinski, Z. J.; Nanjundiah, C.; Osteryoung, R. A. Inorg. Chem.
1984, 23, 3358−3364.
(25) (a) Deng, L.; Chan, H.-S.; Xie, Z. Angew. Chem., Int. Ed. 2005, 44,
2128−2131. (b) Deng, L.; Xie, Z. Organometallics 2007, 26, 1832−1845.
(c) Zhang, J.; Xie, Z. Chem. Asian J. 2010, 5, 1742−1757.
(26) (a) Jemmis, E. D.; Kiran, B. J. Am. Chem. Soc. 1997, 119, 4076−
4077. (b) Kiran, B.; Anoop, A.; Jemmis, E. D. J. Am. Chem. Soc. 2002,
124, 4402−4407.
(27) Buhl, M.; Grigoleit, S. Organometallics 2005, 24, 1516−1527.
̈
(28) Sheldrick, G. M. SADABS: Program for Empirical Absorption
Correction of Area Detector Data; University of Gottingen: Germany,
̈
1996.
(29) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure
Determination Software Programs; Bruker Analytical X-ray Systems, Inc.:
Madison, WI, USA, 1997.
(30) Flack, H. D. Acta Crystallogr. 1983, A39, 876−881.
4550
dx.doi.org/10.1021/om300324n | Organometallics 2012, 31, 4544−4550