Synthesis, structure, and reactivity of borate ester coordinated organobismuth compounds

Article abstract of DOI:10.1021/om7009792

A new class of hypervalent organobismuth compounds functionalized with coordinating pinacolborate esters of the nature ArBiCl₂ (2), Ar ₃Bi (3), ArPh₂Bi (4), Ar₃BiCl₂ (5), and ArPh₂BiCl₂ (6), where Ar = 3-fluoro-2- pinacolatoboronphenyl, have been prepared and structurally characterized. The Bi ... O distance is between 2.58 and 3.47 A in the solid state for all compounds, and reasonable bonding interactions are presumed to exist in compounds 2-4 and 6, where Bi ... O < 3.0 A. When ArPh ₂BiCh (6) is exposed to CsF in the presence of furan, the [4 + 2] cycloaddition product of 3-fluorobenzyne + furan, 8, is isolated in 58% yield. Mechanistic evidence is offered to support the claim that 6 undergoes an unprecedented fluoride-promoted fragmentation to generate 3-fluorobenzyne, pinacol, BF₃, and Ph₂BiF.

Full text of DOI:10.1021/om7009792

Organometallics 2008, 27, 747–752
747
Synthesis, Structure, and Reactivity of Borate Ester Coordinated
Organobismuth Compounds
Christopher C. Caires*,† and Samira Guccione‡
Departments of Chemistry and Radiology and Molecular Imaging Program at Stanford, Stanford
UniVersity School of Medicine, Lucas MRS Center, 1201 Welch Road, Stanford, California 94305
ReceiVed October 1, 2007
A new class of hypervalent organobismuth compounds functionalized with coordinating pinacolborate
esters of the nature ArBiCl2 (2), Ar3Bi (3), ArPh2Bi (4), Ar3BiCl2 (5), and ArPh2BiCl2 (6), where Ar )
3-fluoro-2-pinacolatoboronphenyl, have been prepared and structurally characterized. The Bi · · · O distance
is between 2.58 and 3.47 Å in the solid state for all compounds, and reasonable bonding interactions are
presumed to exist in compounds 2-4 and 6, where Bi · · · O < 3.0 Å. When ArPh2BiCl2 (6) is exposed
to CsF in the presence of furan, the [4 + 2] cycloaddition product of 3-fluorobenzyne + furan, 8, is
isolated in 58% yield. Mechanistic evidence is offered to support the claim that 6 undergoes an
unprecedented fluoride-promoted fragmentation to generate 3-fluorobenzyne, pinacol, BF3, and Ph2BiF.
muth compounds containing a chelating oxygen ether func-
tionality are somewhat less common, and recent examples
include the 2,6-(MeO)2C6H3-14 and O,C,O pincer ligands 2,6-
Introduction
Organobismuth compounds have broad application in multiple
areas of chemistry. They have medicinal value for the treatment
of H. pylori infections and as antifungal agents.1–3 Organobis-
muth reagents also have synthetic utility as coupling partners
in numerous reactions,4,5 including enolate arylations6 and metal-
catalyzed C-O7 and C-N8 bond-forming reactions.
Interest in bismuth chemistry has driven synthetic efforts in
recent years to prepare organobismuth compounds with greater
functional complexity.9 Notable are the new classes of arylbis-
muth compounds that are stabilized by the intramolecular
coordination of pendant Lewis bases.10 Most of the compounds
reported utilize chelating tertiary amines: for example
2-(Me2NCH2)C6H4-,11 2-(Me2N)C10H6-,12 and more recently
the N,C,N pincer ligand 2,6-(Me2NCH2)2C6H3-.13 Organobis-
t
(ROCH2)C6H3- (R ) Me, Bu).15
Our laboratory is interested in preparing organobismuth
compounds that contain hypervalent stabilizing groups with
complex functionalities to increase the diversity and ultimately
the scope of organobismuth chemistry. We chose to prepare
bismuth complexes containing a borate ester moiety because
of their relative rarity as oxygen donors in coordination
compounds and because of their importance in metal-catalyzed
cross-coupling reactions.16 We describe herein the synthesis of
a new class of organobismuth compounds bearing the ligand
3-fluoro-2-pinacolatoboronphenyl. To our knowledge, this is the
first example of an organobismuth compound that contains
organic boron groups. We report both the X-ray structures and
solution behavior of compounds 2-6. Finally, we disclose an
unprecedented fluoride-promoted fragmentation of the triaryl-
bismuthane 6 to yield products consistent with the generation
of 3-fluorobenzyne.
* To whom correspondence should be addressed. E-mail: cccaires@
stanford.edu.
† Department of Chemistry.
‡ Department of Radiology.
(1) Dahlgren, A.; Glogard, C.; Gammelsaether, M.; Aasen, A. J.;
Klaveness, J.; Berdal, B. P.; Bergan, T. Scand. J. Gastroenterol. 1999, 34,
135–137.
Results and Discussion
(2) Murafuji, T.; Miyoshi, Y.; Ishibashi, M.; Mustafizur Rahman, A. F.;
Sugihara, Y.; Miyakawa, I.; Uno, H. J. Inorg. Biochem. 2004, 98, 547–
552.
Preparation of Arylbismuthines 2–4. Compounds 2-4 were
prepared by reacting Grignard reagent 1 with BiCl3 or Ph2BiCl
at -78 °C, as depicted in Scheme 1.17 After the mixtures were
stirred overnight and warmed to room temperature, the desired
arylbismuthines were isolated in low (2, 14%) to good (3, 60%;
4, 65%) yield. Compounds 3 and 4 were purified by silica gel
chromatography (hexanes/dichloromethane) followed by re-
crystallization (3, ethyl acetate/methanol; 4, dichloromethane/
methanol), to give colorless crystals suitable for X-ray diffrac-
tion. In the crystalline state, compounds 2-4 have been stored
under air for several months without any noticeable decomposi-
(3) Murafuji, T.; Azuma, T.; Miyoshi, Y.; Ishibashi, M.; Rahman, A. F.;
Migita, K.; Sugihara, Y.; Mikata, Y. Bioorg. Med. Chem. Lett. 2006, 16,
1510–1513.
(4) Shimada, S.; Yamazaki, O.; Tanaka, T.; Rao, M. L.; Suzuki, Y.;
Tanaka, M. Angew. Chem., Int. Ed. 2003, 42, 1845–1848.
(5) Arnauld, T.; Barton, D. H.; Normant, J. F. J. Org. Chem. 1999, 64,
3722–3725.
(6) Koech, P. K.; Krische, M. J. J. Am. Chem. Soc. 2004, 126, 5350–
5351.
(7) Sheppard, G. S. Synlett 1999, 1207–1210.
(8) Combes, S.; Finet, J. P. Tetrahedron 1998, 54, 4313–4318.
(9) Suzuki, H., Matano, Y., Eds. Organobismuth Chemistry; Elsevier
Science: Amsterdam, 2001.
(10) Silvestru, C.; Breunig, H. J.; Althaus, H. Chem. ReV. 1999, 99,
(14) Ogawa, T.; Ikegami, T.; Hikasa, T.; Ono, N.; Suzuki, H. J. Chem.
Soc., Perkin Trans. 1 1994, 3479–3483.
3277–3328.
(11) Kamepalli, S.; Carmalt, C. J.; Culp, R. D.; Cowley, A. H.; Jones,
R. A.; Norman, N. C. Inorg. Chem. 1996, 35, 6179–6183.
(12) Carmalt, C. J.; Cowley, A. H.; Culp, R. D.; Jones, R. A.; Kamepalli,
S.; Norman, N. C. Inorg. Chem. 1997, 36, 2770–2776.
(13) Soran, A. P.; Silvestru, C.; Breunig, H. J.; Balazs, G.; Green, J. C.
Organometallics 2007, 26, 1196–1203.
(15) Dostal, L.; Cisarova, I.; Jambor, R.; Ruzicka, A.; Jirasko, R.;
Holecek, J. Organometallics 2006, 25, 4366–4373.
(16) Billingsley, K.; Buchwald, S. L. J. Am. Chem. Soc. 2007, 129,
3358–3366.
(17) Baron, O.; Knochel, P. Angew. Chem., Int. Ed. 2005, 44, 3133–
3135.
10.1021/om7009792 CCC: $40.75
2008 American Chemical Society
Publication on Web 01/25/2008

748 Organometallics, Vol. 27, No. 4, 2008
Caires and Guccione
1
with chelating -NMe2 groups (2.97–3.15 Å).11 The H NMR
Scheme 1
spectrum of 3 at room temperature showed a broad doublet at
1.16 ppm corresponding to the pinacol methyl groups. When
the temperature was raised to 55 °C, the doublet coalesced to a
broad singlet. The 1H NMR spectrum and coalesce temperature
was not affected by changing the solvent to CD3OD.
Organobismuth(III) complexes with intramolecularly coor-
dinated -OR or -NR2 functionalities rarely show magnetic
inequivalence of their R groups in their NMR spectra.18 The
doublet observed for the pinacol methyl groups in the 1H
spectrum of 3 is likely due to restricted rotation about the C-B
bond due to the steric bulk of three pinacolborane groups
crowded around the central bismuth atom. A consequence of
the rigidity of the C-B bond is that the borate oxygens are
forced into an ideal conformation to coordinate the bismuth
atom.
Compound 4 adopts an equatorially vacant trigonal-bipyra-
midal conformation in the solid state (Figure 4). 4 also showed
structural properties very similar to those of 3, including an
almost identical Bi-O bond distance of 2.89 Å. The C-Bi-C′
bond angles of 4 have an average of 95.3°, in comparison to 3,
which has a slightly smaller C-Bi-C′ bond angle average of
92.8°. The larger C-Bi-C′ bond angles of 4 compared to 3
reflect the reduced steric effect of having only one bulky
pinacolborane group in the ligand sphere.
Scheme 2
Compound 5 crystallized in a trigonal-bipyramidal motif with
one molecule of benzene in the asymmetric unit (Figure 5). The
Bi · · · O distances varied widely from 3.2 to 3.47 Å, and the
orientation of the pinacolborate oxygens is not ideal to form a
Bi-O bond. Therefore, it is assumed very weak, if any, Bi · · · O
bonding interactions are present in the solid state. The
Cl(1)-Bi(1)-Cl(2) bond angle is bent noticeably from the ideal
geometry of 180° to 169.7°. The bent Cl(1)-Bi(1)-Cl(2) angle
is likely the result of steric pressure of two pinacolborane groups
occupying the same face of the molecule, causing the chloride
ligands to bend in the opposite direction. Compound 6, a related
compound with only one pinacolborane moiety, has a Cl(1)-
Bi(1)-Cl(2) bond angle of 175.2°.
tion. Compound 2 has poor solubility in organic solvents, which
contributed to the low isolated yield. Despite this limitation, a
small quantity of colorless needles were collected from a
solution of 2 in dichloromethane that were suitable for X-ray
diffraction.
Preparation of Dichlorotriarylbismuthanes 5 and 6. Com-
pounds 5 and 6 were prepared by respective treatment of 3 and
4 with an excess of freshly distilled sulfuryl chloride in benzene
at ambient temperature (Scheme 2). Immediate solvent removal
followed by NMR analysis (C6D6) showed quantitative conver-
sion to the dichlorides 5 and 6 with no further purification
necessary. X-ray-quality crystals were grown by slow infusion
of pentane into concentrated benzene solutions of 5 and 6.
Compound 5 was stable in a solution of C6D6 at 4 °C over 4
days without decomposition, but both 5 and 6 showed ap-
preciable decomposition in CDCl3 within 4 h at room temperature.
Solid-State Structures of 2–6. The data collection and
structural refinement parameters for crystals of 2-6 are sum-
marized in Table 1. Select bond angles and distances for 2-6
are presented in Table 2.
Compound 2 crystallized in a square-pyramidal motif with
an infinite chain of bridging chlorides (Figures 1 and 2). The
Bi-O bond distance is 2.58 Å, which is well within the van
der Waal radii of Bi and O (3.9 Å) and is similar to the Bi-O
bond distance (2.50 Å) reported for the related complex [2,6-
(MeOCH2)C6H3]BiCl2.15 The Bi-Cl bond lengths varied de-
pending on coordination geometry and measured 2.52 Å (Cl
trans to Bi-O), 2.65 (Cl cis to Bi-O, bridging covalent), and
2.90 (bridging Bi-Cl, non-covalent).
At low temperature (-50 °C) the 1H NMR spectra of 5
showed an interesting dependence on solvent. In a nonpolar
solvent, CDCl3, two broad resonances were observed at 1.2 ppm
corresponding to the pinacol methyl groups. When the temper-
ature was raised, the peaks coalesced to a broad singlet at -20
°C and a sharp singlet at room temperature. Repetition of the
experiment using a more polar solvent, CD3OD, showed the
pinacol methyl groups as a sharp singlet down to -80 °C. This
observation supports the hypothesis that at low temperature
solvation of the pinacolborane group by methanol suppresses
intramolecular coordination of the pinacol oxygen atoms to the
bismuth center.
Compound 6 crystallized with two independent molecules
in the asymmetric unit (Figure 6). For both molecules the
geometry was observed to be pseudooctahedral, with a pina-
colborate oxygen occupying an equatorial coordination site. The
Bi-O bond distance was 2.96 Å in both molecules, which is
only a slight increase from the Bi-O bond distance of 2.89 Å
in the precursor bismuthine 4. The Cl(1,3)-Bi(1,2)-Cl(2,4)
bond angles differed between the two X-ray structures and
measured 175.2 and 172.4°. The C(1)-Bi(1)-C(13) bond angle
is bent substantially to 146.0° to accommodate the coordinating
pinacolborane group, which adopts a nearly planar configuration
with the bismuth ligand framework.
Compound 3 crystallized in a pseudo-octahedral geometry
with three pinacolborate ester oxygens coordinated to the
bismuth center (Figure 3). The Bi-O average bond distance is
2.90 Å, still within the van der Waals radii of 3.9 Å and slightly
shorter than the bond distances reported for similar structures
(18) Chen, X.; Ohdoi, K.; Yamamoto, Y.; Akiba, K. Organometallics
1993, 12, 1857–1864.

Borate Ester Coordinated Organobismuth Compounds
Organometallics, Vol. 27, No. 4, 2008 749
Figure 1. ORTEP plot of compound 2. Ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted for clarity.
Figure 3. ORTEP plot of compound 3. Ellipsoids are drawn at the
50% probability level. Hydrogen atoms and pinacol methyl groups
are omitted for clarity.
Figure 4. ORTEP plot of compound 4. Ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted for clarity.
Figure 2. ORTEP plot of 2 showing infinite chloride-bridged chains
in the crystal lattice. Ellipsoids are drawn at the 50% probability
level. Hydrogen atoms are omitted for clarity.
Solid-State Analysis. Complexes 2-4 and 6 all showed
Bi-O bond distances under 3.0 Å, which is between the
covalent radii (2.16 Å) and van der Waals radii (3.9 Å) and
consistent with the literature precedent for a Bi-O bonding
interaction.10 The structure of compound 5 did not support a
reasonable likelihood of Bi-O bonding interactions, on the basis
of long Bi · · · O distances between 3.2 and 3.47 Å.
The coordination of the chelating oxygen atoms showed a
strong preference to orient trans to the Bi-Caryl σ bonds. The
measured O · · · Bi-Caryl bond angles for complexes 2-4 and 6
were narrowly confined between 160.3 and 166.1°, whereas the
O · · · Bi-Caryl bond angles of complex 5 measured between
148.5 and 156.9°. The preference for oxygen coordination trans
to the Bi-Caryl σ bond can be attributed to donation of the
Figure 5. ORTEP plot of compound 5. Ellipsoids are drawn at the
50% probability level. Hydrogen atoms, pinacol methyl groups, and
a benzene solvent molecule are omitted for clarity.
oxygen lone pair into the Bi-Caryl σ* orbital.19 Complex 5,
with the large steric bulk of three pinacolborates and two
chlorides, cannot adopt the preferred trans confirmation to
effectively overlap with the Bi-Caryl σ* orbital.
Fluoride-Promoted Disproportionation of 6. We sought to
study the corresponding difluorotriarylbismuthanes of com-
(19) Carmalt, C. J.; Cowley, A. H.; Decken, A.; Norman, N. C. J.
Organomet. Chem. 1995, 496, 59–67.

750 Organometallics, Vol. 27, No. 4, 2008
Caires and Guccione
Figure 7. Hypothetical B · · · F · · · Bi bidentate mixed Lewis acid
complexes.
Scheme 3
Figure 6. ORTEP plot of compound 6. Only one of two of the
independent molecules in the asymmetric unit are shown. Ellipsoids
are drawn at the 50% probability level. Hydrogen atoms are omitted
for clarity.
pounds 5 and 6 to determine whether the boron atom would
engage in a bridging bond to the bismuth-bound fluoride ligand
(Figure 7).
Complexes with the ability to recognize and chelate fluoride
are an important class of molecules used as fluoride sensors.20
Bidentate complexes that rely on a mixed Lewis acid bridging
B · · · F · · · L motif, where L ) HgC6F5,21 HNC(O)CF3,22
Scheme 4
24
B(Mes)2,23 B(C6F5)2 have been reported to have enhanced
fluoride-binding properties. Since bismuth is known to be
fluorophilic, these compounds have the potential to be high-
affinity fluoride chelators.3,25
Treatment of 5 or 6 with 2 equiv of tetramethylammonium
fluoride (TMAF) in methanol did not lead to the desired
difluorobismuthane but instead resulted in rapid decomposition
and formation of an off-white precipitate (Scheme 3).26 Further
analysis of the reaction mixture of 6 with excess TMAF in
CD3OD revealed that the deuterated arene 7 was formed in 75%
yield as a single regioisomer, along with BF3, pinacol, triph-
enylbismuthine, and an insoluble solid presumed to be inorganic
bismuth salts.27 The observed products are consistent with
formation of 3-fluorobenzyne, which reacts with CD3OD to give
the expected regiochemical isomer.28 The immediate side
products of the reaction are pinacol, BF3, and transiently formed
Ph2BiF, which undergoes a well-documented transmutation to
give Ph3Bi and inorganic bismuth salts.29
conditions.30 After 4 h the reaction mixture was concentrated
in Vacuo and chromatographed to yield cycloadduct 8 in 58%
yield (Scheme 4). On the basis of this preliminary evidence,
we theorize that fluoride displaces the pinacol ester to give the
trifluoroborate salt. This intermediate eliminates to give a highly
reactive “aryne”, which then undergoes the [4 + 2] cycloaddition
with furan to give the observed product.31 The fluoride-promoted
reactions of 6 with CD3OD and furan are the first examples of
organobismuth compounds being used as precursors to generate
benzyne equivalents.
Since arynes are known to undergo [4 + 2] cycloadditions,
6 was treated with excess CsF in furan to further validate the
hypothesis that 3-fluorobenzyne is generated under the reaction
(20) Martinez-Manez, R.; Sancenon, F. Chem. ReV. 2003, 103, 4419–
4476.
(21) Melaimi, M.; Gabbai, F. P. J. Am. Chem. Soc. 2005, 127, 9680–
9681.
(22) Hudnall, T. W.; Melaimi, M.; Gabbai, F. P. Org. Lett. 2006, 8,
2747–2749.
Conclusion
(23) Melaimi, M.; Sole, S.; Chiu, C. W.; Wang, H.; Gabbai, F. P. Inorg.
Chem. 2006, 45, 8136–8143.
We have described the synthesis and structure of a new class
of organobismuth compounds that contain intramolecularly
coordinated pinacolborate esters. Probing the reactivity of these
compounds, we discovered a mild method to generate arynes
using anionic fluoride at ambient temperature. The use of
organobismuth compounds as benzyne precursors is shown as
a selective way to generate arynes that are viable as coupling
partners in both [4 + 2] cycloadditions and the addition of
(24) Williams, V. C.; Piers, W. E.; Clegg, W.; Elsegood, M. R. J.;
Collins, S.; Marder, T. B. J. Am. Chem. Soc. 1999, 121, 3244–3245.
(25) Rahman, A. F. M. M.; Murafuji, T.; Ishibashi, M.; Miyoshi, Y.;
Sugihara, Y. J. Organomet. Chem. 2004, 689, 3395–3401.
(26) Attempts to prepare 5 or 6 directly by oxidizing 3 or 4 with XeF2
were unsuccessful. Control experiments demonstrated that XeF2 is incom-
patible with the borate functionality.
(27) The yield for 7 was based on GC analysis using methanol with
4-bromoanisole as the internal standard. BF3, pinacol, and triphenylbis-
1
muthine were all identified by comparison of their H, 19F, or 11B spectra
to those of authentic samples.
(28) Heaney, H. Chem. ReV. 1962, 62, 81–97.
(29) Barton, D. H. R.; Bhatnagar, N. Y.; Finet, J. P.; Motherwell, W. B.
Tetrahedron 1986, 42, 3111–3122.
(30) Pellissier, H.; Santelli, M. Tetrahedron 2003, 59, 701–730.
(31) Masson, E.; Schlosser, M. Eur. J. Org. Chem. 2005, 4401–4405.

Borate Ester Coordinated Organobismuth Compounds
Organometallics, Vol. 27, No. 4, 2008 751
Table 1. Crystal Data Collection and Refinement Parameters for Compounds 2–6
2
3
4
5
6
chem formula
formula wt
cryst habit
cryst size (mm)
T (K)
C12H15BBiCl2FO2
500.93
colorless, needle
0.40 × 0.05 × 0.05
123(2)
C36H45B3BiF3O6
872.13
colorless, block
0.35 × 0.35 × 0.25
173(2)
C24H25BBiFO2
584.23
colorless, rod
0.40 × 0.13 × 0.10
173(2)
C42H51B3BiCl2F3O6
1021.14
colorless, plate
0.25 × 0.25 × 0.08
173(2)
C24H25BBiCl2FO2
655.13
colorless, block
0.25 × 0.15 × 0.05
173(2)
cryst syst
space group
a (Å)
b (Å)
c (Å)
orthorhombic
P212121
9.1514(7)
11.6274(9)
14.5092(11)
90
90
90
1543.9(2)
4
2.155
monoclinic
P21/n
11.6453(9)
13.4108(10)
24.5109(18)
90
94.0630(10)
90
3818.3(5)
4
triclinic
P1
monoclinic
P21/c
15.0270(16)
24.892(3)
11.7187(12)
90
93.247(2)
90
4376.4(8)
4
orthorhombic
P212121
9.4733(6)
13.9288(8)
37.941(2)
90
90
90
5006.4(5)
8
1.738
j
10.399(3)
10.701(3)
11.484(3)
94.046(4)
95.697(4)
118.484(3)
1107.6(5)
2
R (deg)
ꢀ (deg)
γ (deg)
U (Å3)
Z
Dc (g cm-3
)
1.517
4.673
1736
1.752
7.984
564
1.55
4.208
2040
abs coeff (mm-1
F(000)
)
11.769
936
7.282
2528
θ range (deg)
2.24–27.49
18 062
3525
0.0425
0.0183
0.0345
176
0
1.67–27.50
43 874
8708
0.0348
0.0245
0.0589
475
32
1.009
1.80–25.11
3928
3928
0.0425
0.0352
0.087
267
0
1.016
1.459, -1.944
1.36–25.68
38 227
8324
0.105
0.0592
0.1001
527
12
1.089
1.56–27.50
59 270
11 417
0.0517
0.0263
0.0526
567
0
no. of rflns measd
no. of unique rflns
Rint
R1a (I > 2σ(I))
wR2b (F2, all rflns)
no. of params
no. of restraints
Sc
0.903
0.724, -0.595
1.023
1.233, -0.966
max, min ∆F (e Å-3
)
1.017, -0.527
1.395, -0.857
2
2 2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo - Fc ) ]/∑[w(Fo2)2]}1/2. w ) 1/[σ2(Fo2) + (w1P)2 + w2P], where P ) [2Fc + Max(Fo2)]/3. c GOF )
S ){∑[w(Fo - Fc ) ]/(n - p)]1/2, where n is the number of reflections and p is the total number of parameters refined.
2
2 2
Synthesis of [3-F-2-BO2C2(CH3)4]BiCl2 (2). 2-(2-Fluoro-6-
methanol. We expect that this new method of generating arynes
will prove useful in organic synthesis.
iodophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (200 mg,
0.575 mmol) was dissolved in 2 mL of THF and cooled to -78
°C using a dry ice/ethanol bath. To this solution was added
dropwise isopropylmagnesium chloride · LiCl (1 M THF, 0.575
mL, 0.575 mmol). The reaction was monitored by GC/MS until
complete conversion of the starting material to the Grignard
reagent (5 h). A solution of BiCl3 (145 mg, 0.460 mmol) in 2
mL of THF was cooled to -78 °C and transferred via cannula
to the reaction flask, followed by two rinses of 1 mL of THF.
The reaction mixture was stirred for 12 h and the bath warmed
to room temperature. Upon completion the reaction mixture was
poured into saturated NH4Cl(aq) and extracted three times with
EtOAc. The organic layer was washed with brine and then dried
over Na2SO4. The organic layer was filtered and concentrated
in vacuo to give an orange semisolid. The residue was recrystal-
lized from dichloromethane to yield a small amount of white
needles (33 mg, 0.066 mmol, 14% yield). Anal. Calcd for
C12H15BBiCl2FO2: C, 29.02; H 3.21. Found: C, 28.77; H, 3.02.
1H NMR (DMSO-d6): δ 9.21 (d, 7.4 Hz, 1H, Ar H), 8.23 (m,
1H, Ar H), 7.19 (dd, 8.8 Hz, 7.4 Hz, 1H, Ar H) 1.36 (s, 12H).
19F NMR: δ -100.7 (dd, 8.4 Hz). A satisfactory 13C spectrum
was not obtained due to the small amount of material formed
from the reaction.
Synthesis of [3-F-2-BO2C2(CH3)4]3Bi (3). A procedure related
to that used to make compound 2 was used, with 2-(2-fluoro-6-
iodophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (308 mg, 0.885
mmol), and isopropylmagnesium chloride · LiCl (1 M THF, 0.885
mL, 0.885 mmol) in 3 mL of THF. Then BiCl3 (74 mg, 0.236
mmol) in 2 mL of THF was added. Upon completion the reaction
mixture was concentrated in vacuo. The solid residue was suspended
in toluene and filtered through Celite. The resulting residue was
purified by silica gel chromatography (2% diethyl ether/98%
toluene) followed by recrystallization (EtOAc/MeOH) to give
X-ray-quality white crystals (120 mg, 0.140 mmol, 60% yield).
Anal. Calcd for C36H45B3BiF3O6: C, 49.70; H 5.39. Found: C, 49.58;
H, 5.20. 1H NMR (CDCl3): δ 7.55 (d, 7.3 Hz, 3H, Ar H), 7.24 (m,
Experimental Section
General Procedures. All reagents were obtained commercially
at the highest available purity unless otherwise noted. All organo-
metallic reactions were performed using oven-dried glassware under
an inert atmosphere of argon using standard Schlenk line techniques.
Dichloromethane, tetrahydrofuran (THF), and benzene were passed
through two columns of activated alumina immediately prior to
use. Sulfuryl chloride and furan were distilled from CaH2 im-
mediately prior to use. Chromatographic purification of products
was accomplished using forced flow chromatography on Silicycle
silica gel 60 (40–63 µm). Thin-layer chromatography was performed
on EM Science silica gel 60 F254 plates (250 µm). Unless otherwise
stated, nuclear magnetic resonance (NMR) spectra were acquired
on a Varian GX-400 spectrometer and are referenced internally (1H,
13C) according to residual solvent signals or externally (19F) to
neat trifluoroacetic acid (-78.5 ppm). Elemental analyses were
performed by M-H-W Laboratories, Phoenix, AZ. Diphenylbis-
muth(III) chloride was prepared according to a literature proce-
dure.29
2-(2-Fluoro-6-iodophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane. 2-Fluoro-6-iodophenylboronic acid (1.5 g, 5.64 mmol) was
dissolved in 13 mL of toluene. Pinacol (666 mg, 5.64 mmol)
was added to the solution and stirred until dissolved. A reflux
condenser was attached to the reaction flask and the solution heated
to reflux for 1 h. After 1 h the toluene was distilled away from the
reaction mixture, facilitating the removal of water. The crude solid
was purified by silica gel column chromatography (10% dichlo-
romethane/90% hexanes) to yield the desired product as a white
crystalline solid (1.431 g, 4.17 mmol, 73% yield). Anal. Calcd for
C12H15BFIO2: C, 41.62; H 4.58. Found: C, 41.42; H, 4.35. 1H NMR
(CDCl3): δ 7.54 (ddd, 1H, 7.4 Hz, 1.3 Hz, 0.4 Hz), 6.9–7.1 (m, 2H),
1.4 (s, 12 H). 19F NMR: δ -102.1 (dd, 7.3 Hz). 13C NMR (CDCl3):
δ 166.0, 163.54, 134.20, 134.21, 132.30, 132.21, 114.40, 114.17, 98.18,
98.09, 84.93, 24.79.

752 Organometallics, Vol. 27, No. 4, 2008
Caires and Guccione
Table 2. Select Bond Distances and Angles for Compounds 2–6
yield. X-ray-quality crystals were obtained by vapor infusion
of pentane into a concentrated solution in benzene. 1H NMR
(C6D6): δ 8.13 (br d, 8.0 Hz, 3H, Ar H), 6.91 (ddd, 8.6 Hz, 8.1
Hz, 5.2 Hz, 3H, Ar H), 6.68 (dd, 8.6 Hz, 3H, Ar H), 1.01 (s,
36H). 19F NMR: δ -97.0 (br s). 13C NMR (C6D6): δ 173.99,
169.85, 167.80, 133.20, 133.14, 131.64, 128.53, 128.29, 124.13,
117.60, 117.40, 85.04, 25.02. An accurate elemental analysis
could not be obtained, due to the difficulty of removing trace
solvent from the crystalline material.
Synthesis of [3-F-2-BO2C2(CH3)4]Ph2BiCl2 (6). A procedure
related to that used to make compound 5 was used, with compound
4 (25 mg, 0.043 mmol) and SO2Cl2 (5 µL, 0.062 mmol) in 3 mL
of benzene. The desired compound was isolated in quantitative
yield. X-ray-quality crystals were obtained by vapor infusion of
pentane into a concentrated solution in benzene. Anal. Calcd for
C24H25BBiCl2FO2: C, 44.18; H 4.02. Found: C, 44.00; H, 3.85. 1H
NMR (C6D6): δ 8.92 (d, 7.8 Hz, 4H, Ar H), 7.60 (d, 7.9 Hz, 1H,
Ar H), 7.19 (m, 4H, Ar H), 6.96 (t, 7.3 Hz, 2H, Ar H), 6.74 (ddd,
8.6 Hz, 7.9 Hz, 5.2 Hz, 1H, Ar H), 6.51 (dd, 8.6 Hz, 1H, Ar H),
1.0 (s, 12H). 19F NMR: δ -94.37 (dd, 8.6 Hz, 5.2 Hz). 13C NMR
(C6D6): δ 175.52, 175.43, 170.32, 168.23, 135.86, 135.79, 134.88,
131.59, 131.04, 128.53, 128.29, 126.55, 126.52, 118.03, 117.83,
86.00, 24.20.
5-Fluoro-1,4-dihydro-1,4-epoxynaphthalene (8). Compound 6
(60.8 mg, 0.093 mmol) was dissolved in freshly distilled furan
(3 mL). Flame-dried CsF (67 mg, 0.441 mmol) was added in
one portion and the reaction mixture stirred for 4 h. Upon
completion a large amount of white precipitate was present. The
reaction mixture was partitioned between ethyl acetate and H2O
and the aqueous layer washed twice with ethyl acetate. The
organic layers were combined, washed once with brine, and dried
over Na2SO4. The drying agent was filtered off and the clear
solution concentrated in vacuo and purified by SiO2 chroma-
tography (100% hexanes to 5% diethyl ether/95% hexanes). The
desired product was isolated as a colorless residue (8.8 mg, 59%
yield). The NMR spectra were identical with that of the
previously reported compound.31
X-ray Crystallography. The structural and refinement data
for compounds 2-6 are given in Table 1. A suitable crystal was
placed onto the tip of a 0.1 mm diameter glass capillary and
mounted on a Bruker SMART Platform CCD diffractometer for
data collection using monochromated Mo KR radiation (λ )
0.710 73 Å) at 173(2) K. The intensity data were corrected for
absorption and decay (SADABS).32 The structures were solved
by direct methods using SHELXS-97 and refined by SHELXL-
97.33 Full-matrix least-squares/difference Fourier cycles were
performed, which located the remaining non-hydrogen atoms.
All hydrogen atoms were placed in ideal positions and refined
as riding atoms with relative isotropic displacement parameters.
Compound 2
Bi(1)-C(1)
2.266(4)
2.5194(9) Bi(1)-Cl(2)#1
2.582(3)
93.86(10)
73.66(12)
Bi(1)-Cl(2)
2.6543(9)
2.8983(10)
2.8983(9)
83.27(6)
Bi(1)-Cl(1)
Bi(1)-O(1)
C(1)-Bi(1)-Cl(1)
C(1)-Bi(1)-O(1)
Cl(2)-Bi(1)#2
O(1)-Bi(1)-Cl(2)
C(1)-Bi(1)-Cl(2)#1 79.52(10)
Cl(1)-Bi(1)-Cl(2)#1 92.72(3)
O(1)-Bi(1)-Cl(2)#1 90.94(6)
Cl(2)-Bi(1)-Cl(2)#1 164.68(2)
Cl(1)-Bi(1)-O(1) 166.13(7)
C(1)-Bi(1)-Cl(2)
Cl(1)-Bi(1)-Cl(2)
85.23(10)
89.79(3)
Compound 3
Bi(1)-C(13)
2.293(3)
2.300(3)
2.310(3)
95.50(11)
Bi(1)-O(3)
2.887(2)
2.918(3)
2.924(2)
104.47(8)
69.54(9)
69.70(10)
70.16(9)
Bi(1)-C(1)
Bi(1)-O(5)
Bi(1)-C(25)
Bi(1)-O(1)
C(13)-Bi(1)-C(1)
O(5)-Bi(1)-O(1)
C(1)-Bi(1)-O(1)
C(25)-Bi(1)-O(5)
C(13)-Bi(1)-O(3)
C(13)-Bi(1)-C(25) 91.80(11)
C(1)-Bi(1)-C(25)
91.13(11)
O(3)-Bi(1)-O(5) 104.31(10)
O(3)-Bi(1)-O(1) 115.79(7)
Compound 4
Bi(1)-C(13)
2.247(8)
2.270(8)
95.5(3)
Bi(1)-C(19)
2.285(7)
2.885(5)
94.4(3)
Bi(1)-C(1)
Bi(1)-O(1)
C(13)-Bi(1)-C(1)
C(13)-Bi(1)-C(19) 96.0(3)
C(1)-Bi(1)-C(19)
C(1)-Bi(1)-O(1)
70.2(2)
Compound 5
Bi(1)-C(25)
Bi(1)-C(13)
Bi(1)-C(1)
Bi(1)-Cl(2)
C(25)-Bi(1)-C(13) 128.5(3)
C(25)-Bi(1)-C(1) 127.4(3)
C(13)-Bi(1)-C(1) 104.1(3)
Cl(2)-Bi(1)-Cl(1) 169.77(7)
2.225(8)
2.236(7)
2.242(8)
Bi(1)-Cl(1)
Bi(1)-O(3)
Bi(1)-O(5)
2.597(2)
3.197
3.257
3.469
63.84
2.5919(19) Bi(1)-O(1)
C(1)-Bi(1)-O(1)
C(25)-Bi(1)-O(5)
C(13)-Bi(1)-O(3)
68.42
67.17
Compound 6
Bi(1)-C(13)
Bi(1)-C(19)
Bi(1)-C(1)
Bi(1)-Cl(1)
Bi(1)-Cl(2)
Bi(1)-O(1)
2.209(4)
2.224(5)
2.229(4)
Bi(2)-C(37)
Bi(2)-C(25)
Bi(2)-C(43)
2.197(5)
2.214(5)
2.223(5)
2.5832(12)
2.6009(14)
2.967(3)
2.5841(13) Bi(2)-Cl(3)
2.5973(12) Bi(2)-Cl(4)
2.966(3)
Bi(2)-O(2)
C(13)-Bi(1)-C(19) 109.58(16)
C(13)-Bi(1)-C(1) 145.67(17)
C(19)-Bi(1)-C(1) 104.75(17)
Cl(1)-Bi(1)-Cl(2) 172.42(4)
C(37)-Bi(2)-C(25) 141.48(18)
C(37)-Bi(2)-C(43) 111.49(18)
C(25)-Bi(2)-C(43) 107.03(17)
Cl(3)-Bi(2)-Cl(4)
C(25)-Bi(2)-O(3)
175.20(5)
69.05
C(1)-Bi(1)-O(1)
68.43
3H, Ar H), 7.19 (dd, 8.9 Hz, 7.3 Hz, 3H, Ar H), 1.21 (br s, 18H),
1.12 (br s, 18H). 19F NMR: δ -101.8 (dd, 8.9 Hz, 3.8 Hz). 13C
NMR (C6D6): δ 182.06, 171.89, 169.34, 136.45, 136.38, 136.32,
136.29, 127.77, 114.39, 114.15, 84.09, 25.02, 24.71.
Synthesis of [3-F-2-BO2C2(CH3)4]BiPh2 (4). A procedure
related to that used to make compound 3 was used, with 2-(2-fluoro-
6-iodophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (500 mg,
1.46 mmol) and isopropylmagnesium chloride · LiCl (0.95 M THF,
1.53 mL, 1.46 mmol) in 3.5 mL of THF. Then diphenylbismuth(III)
chloride (465 mg, 1.17 mmol) in 3 mL of THF was added. The
resulting residue was purified by silica gel chromatography (3%
EtOAc/97% hexanes) followed by recrystallization (dichloromethane/
MeOH) at -20 °C to give X-ray-quality white crystals (444 mg,
0.760 mmol, 65% yield). Anal. Calcd for C24H25BBiFO2: C, 49.20;
Acknowledgment. We warmly thank Dr. Victor G. Young
and Mr. Benjamin E. Kucera of the University of Minnesota
X-ray Crystallographic Laboratory for data collection and
structure solutions of all compounds described herein. We
also thank the NIH (Grant No. I19AI057229), The Lucas
Foundation, and the Phil Allen Trust for generously funding
this research.
1
H 4.52. Found: C, 49.34; H, 4.31. H NMR (CDCl3): δ 7.73 (dd,
7.8 Hz, 1.4 Hz, 4H, Ar H), 7.55 (ddd, 7.3 Hz, 0.95 Hz, 0.6 Hz,
1H, Ar H), 7.27–7.39 (m, 7H, Ar H), 6.96 (ddd, 9.7 Hz, 8.2 Hz,
0.95 Hz, 1H, Ar H), 1.17 (s, 12H). 19F NMR: δ -100.8 (dd, 9.7
Hz, 5.8 Hz). 13C NMR (C6D6): δ 171.95, 169.40, 169.24, 162.09,
138.07, 136.13, 136.06, 135.36, 135.33, 130.79, 127.66, 115.15,
114.90, 84.21, 24.74.
Supporting Information Available: CIF files giving crystal-
lographic data for compounds 2-6. This material is available free
of charge via the Internet at http://pubs.acs.org.
Synthesis of [3-F-2-BO2C2(CH3)4]3BiCl2 (5). Compound 3 (25
mg, 0.027 mmol) was dissolved in 3 mL of benzene. Freshly
distilled SO2Cl2 was added (3.5 µL, 0.041 mmol) and the reaction
mixture immediately concentrated in vacuo. The residue was
further dried for 1 h at 0.5 mmHg to ensure complete removal
of SO2Cl2. The desired product was obtained in quantitative
OM7009792
(32) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33–38.
(33) SHELXTL V6.14; Bruker Analytical X-ray Systems, Madison, WI,
2000.