Fluoride-promoted aryl and allyl migration from boron to tin in 1-stannyl-2-borylferrocenes

Article abstract of DOI:10.1021/om700967a

Transmetalation reactions where organotin reagents are used for the transfer of organic groups to boron halides are among the most selective and hence synthetically useful methods for the preparation of organoboranes. We describe here a rare example of the reverse reaction, where migration of the organic group from boron to tin is promoted by addition of fluoride. The bidentate Lewis acids Fc(BMeR)(SnMe₂Cl) (Fc = 1,2-ferrocenediyl; R = phenyl (Ph), thienyl (Th), allyl (All)) react with KF at 45°C to give the rearranged fluoroboranes Fc(BMeF)(SnMe₂R) as oily liquids. With an excess of KF, the fluoroborate complexes K[Fc(BMeF₂)(SnMe ₂R)] are obtained, which are readily isolated as light yellow solids in good to high yields. For the phenyl derivative it was demonstrated that the borate salt can be converted back to the fluoroborane by treatment with Me ₃SiOTf or addition of pyridine, which gives the adduct Fc(BMeF)(SnMe₂Ph) · Py as a crystalline solid. The fluoride and pyridine complexes have been characterized by multinuclear NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction (for R = Ph). Preliminary mechanistic studies suggest an intramolecular process and indicate that Lewis acid induced Sn-F bond activation may play an important role.

Full text of DOI:10.1021/om700967a

1534
Organometallics 2008, 27, 1534–1541
Fluoride-Promoted Aryl and Allyl Migration from Boron to Tin in
1-Stannyl-2-borylferrocenes
Ramez Boshra, Ami Doshi, and Frieder Jäkle*
Department of Chemistry, Rutgers UniVersity-Newark, 73 Warren Street, Newark, New Jersey 07102
ReceiVed September 28, 2007
Transmetalation reactions where organotin reagents are used for the transfer of organic groups to boron
halides are among the most selective and hence synthetically useful methods for the preparation of
organoboranes. We describe here a rare example of the reverse reaction, where migration of the organic
group from boron to tin is promoted by addition of fluoride. The bidentate Lewis acids
Fc(BMeR)(SnMe2Cl) (Fc ) 1,2-ferrocenediyl; R ) phenyl (Ph), thienyl (Th), allyl (All)) react with KF
at 45 °C to give the rearranged fluoroboranes Fc(BMeF)(SnMe2R) as oily liquids. With an excess of KF,
the fluoroborate complexes K[Fc(BMeF2)(SnMe2R)] are obtained, which are readily isolated as light
yellow solids in good to high yields. For the phenyl derivative it was demonstrated that the borate salt
can be converted back to the fluoroborane by treatment with Me3SiOTf or addition of pyridine, which
gives the adduct Fc(BMeF)(SnMe2Ph) · Py as a crystalline solid. The fluoride and pyridine complexes
have been characterized by multinuclear NMR spectroscopy, elemental analysis, and single-crystal X-ray
diffraction (for R ) Ph). Preliminary mechanistic studies suggest an intramolecular process and indicate
that Lewis acid induced Sn-F bond activation may play an important role.
Chart 1
Introduction
Transfer of organic groups from tin to boron is one of the
most useful tools for the preparation of organoboron compounds,
including that of polymeric materials, with the main benefits
being the mild reaction conditions and high selectivity com-
monly achieved.1 In contrast, the reverse reaction, the transfer
of organic groups from boron to tin, is only rarely encountered.2
An interesting example is the reaction of B(C6F5)3 with
AllSnBu3 studied by Piers, which leads to formation of
C6F5SnBu3 along with AllB(C6F5)2, which in turn reacts further
to a mixture of unidentified organoboron products (Chart 1).3,4
Wrackmeyer demonstrated that intramolecular transfer of an
alkynyl group from boron to a tin cation occurs readily in
1-stannyl-2-borylalkene derivatives.5 In fact, these compounds
establish an equilibrium between the neutral form and a
zwitterionic species, in which a formally cationic tin moiety is
stabilized by side-on coordination of the boron-bound alkynyl
group (Chart 1). Intriguingly, the equilibrium can be shifted
with complete transfer of the alkynyl group to tin by addition
of pyridine, which coordinates to boron. Migration of phenyl
groups from boron to carbon has been observed, for example,
in reactions of organoboranes with chiral sulfonium ylides and
in the base-promoted bromide replacement of R-bromo alky-
lborates.6 Related to these migration reactions are also 1,3-
isomerization reactions of allylic stannanes7 and ligand redis-
tribution reactions between organotin species and organotin
halides.8 The latter are especially facile with allyltin reagents.9
* To whom correspondence should be addressed. E-mail: fjaekle@
rutgers.edu.
(1) (a) Ko¨ster, R. Methods of Organic Chemistry (Houben-Weyl); G.
Thieme Verlag: Stuttgart, New York, 1982; Vol. 13/3a. (b) Pelter, A.; Smith,
K.; Brown, H. C. Borane Reagents; Academic Press: New York, 1988. (c)
Matteson, D. S. Stereodirected Synthesis with Organoboranes; Springer:
Berlin, Heidelberg, New York, 1995. (d) Kaufmann, D. E., Matteson, D. S.,
Eds. Organometallics: Boron Compounds; G. Thieme Verlag: Stuttgart, New
York, 2004; Science of Synthesis Vol. 6. (e) Jäkle, F. Boron: Organoboranes
In Encyclopedia of Inorganic Chemistry, 2nd ed.; King, R. B., Ed.; Wiley:
Chichester, U.K., 2005; pp 560–598. (f) Jäkle, F. Coord. Chem. ReV. 2006,
250, 1107–1121.
We are interested in ferrocene-based bidentate Lewis acids,
in which two Lewis acid sites are attached adjacent to one
another at one of the Cp rings.10,11 During the course of our
studies we found that the heteronuclear bidentate Lewis acids
Fc(BMeR)(SnMe2Cl) (R ) Cl, 1-Cl; R ) Ph, 1-Ph), which
contain neighboring stannyl and boryl groups attached to
(2) The use of Na[BEt4] for the qualitative and quantitative determination
of organotin species in aqueous medium through conversion to the ethylated
tetraorganotin derivatives has been described; see: Carlier-Pinasseau, C.;
Lespes, G.; Astruc, M. Appl. Organomet. Chem. 1996, 10, 505–512.
(3) Blackwell, J. M.; Piers, W. E.; McDonald, R. J. Am. Chem. Soc.
2002, 124, 1295–1306.
(6) (a) Aggarwal, V. K.; Fang, G. Y.; Schmidt, A. T. J. Am. Chem.
Soc. 2005, 127, 1642–1643. (b) Robiette, R.; Fang, G. Y.; Harvey, J. N.;
Aggarwal, V. K. Chem. Commun. 2006, 741–743. (c) Matteson, D. S.; Mah,
R. W. J. Am. Chem. Soc. 1963, 85, 2599–2603.
(7) Marshall, J. A.; Gill, K. J. Organomet. Chem. 2001, 624, 294–299.
(8) Davies, A. G. Organotin Chemistry; 2nd ed.; Wiley-VCH: Weinheim,
Germany, 2004.
(4) Morrison, D. J.; Blackwell, J. M.; Piers, W. E. Pure Appl. Chem.
2004, 76, 615–623.
(9) (a) Gambaro, A.; Marton, D.; Tagliavini, G. J. Organomet. Chem.
1981, 210, 57–62. (b) Naruta, Y.; Nishigaichi, Y.; Maruyama, K. Tetra-
hedron 1989, 45, 1067–1078.
(5) Wrackmeyer, B.; Kehr, G.; Willbold, S. J. Organomet. Chem. 1999,
590, 93–103.
10.1021/om700967a CCC: $40.75
2008 American Chemical Society
Publication on Web 03/04/2008

Fluoride-Promoted Aryl/Allyl Migrations
Organometallics, Vol. 27, No. 7, 2008 1535
Scheme 1
ferrocene, are readily obtained through regioselective borylation
of 1,1′-bis(trimethylstannyl)ferrocene in R-position with BCl3
and PhBCl2, respectively.12,13 The initial electrophilic attack of
the boron halide is followed by a proton migration and
elimination of Me3SnCl, leading to the 1,2-disubstituted species
Fc(BCl2)(SnMe3) and Fc(BPhCl)(SnMe3). Subsequent moderate
heating of the reaction mixture results in migration of one of
the methyl groups from tin to boron.14 This process follows
the typical reactivity pattern of tin/boron exchange reactions
and is believed to proceed through intramolecular activation of
one of the Sn-Me groups in the “trans” position to a bridging
boron-bound chlorine atom leading to intermolecular transfer
of the methyl group and intramolecular migration of the chlorine
atom to tin.
Currently we are investigating the binding properties of the
resulting heteronuclear bidentate Lewis acids 1 and studying
their use in asymmetric synthesis.15–17 When they are reacted
with KF in the presence of 18-crown-6, 1-Cl and 1-Ph form
stable fluoride complexes in which the fluoride anion assumes
a bridging position between boron and tin.16,18 Here we
demonstrate that, surprisingly, in the absence of 18-crown-6 a
very different reactivity path is observed in that compounds
Fc(BMeR)(SnMe2Cl) (R ) Ph, Th, All) undergo an unusual
and highly selective fluoride-promoted rearrangement reaction
that involves facile transfer of the R group from boron to tin.
Scheme 2
Results and Discussion
Compounds 1-Cl and 1-Ph were prepared as previously
reported.12,13 Transmetalation of 1-Cl with ThSnMe3 (Th )
2-thienyl) afforded Fc(BMeTh)(SnMe2Cl) (1-Th) as a red
crystalline solid in 65% yield (Scheme 1). Using a similar
procedure, the allyl derivative Fc(BMeAll)(SnMe2Cl) (1-All)
was obtained from 1-Cl and AllSnMe3 as an orange-red oil in
ca. 95% spectroscopic yield. The latter was used directly in
subsequent reactions without further purification.
Each of the bidentate Lewis acids 1-R (R ) Ph, Th, All)
was treated with 1 equiv of KF in THF at 45 °C for 3 h in an
attempt at preparing the fluorostannane derivatives through
replacement of the tin-bound chlorine for a fluorine substituent.19
After filtration from insoluble salts, removal of the solvents,
and extraction into hexanes the products were obtained as orange
Table 1. Comparison of NMR Data for Compounds 1-R, 2-R,
and 3-R
δ(11B) (w1/2
)
δ(19F)
δ(119Sn)
1-Pha
1-Tha
1-Alla
2-Pha
2-Tha
2-Alla
3-Phb
3-Thb
3-Allb
68 (500)
62 (430)
70 (600)
53 (500)
53 (490)
53 (530)
9.2 (230)
13.5 (210)
9.0 (160)
102.3
95.4
130.8
-32.1
-33.5
-9.9
-39.0
-46.5
-12.5
-55.8
-55.8
-55.8
-137.5/-142.6
-130.9/-135.6
-132.0/-137.0
(10) (a) Venkatasubbaiah, K.; Bats, J. W.; Rheingold, A. L.; Jäkle, F.
Organometallics 2005, 24, 6043–6050. (b) Venkatasubbaiah, K.; Zakharov,
L. N.; Kassel, W. S.; Rheingold, A. L.; Jäkle, F. Angew. Chem., Int. Ed.
2005, 44, 5428–5433. (c) Venkatasubbaiah, K.; DiPasquale, A. G.; Bolte,
M.; Rheingold, A. L.; Jäkle, F. Angew. Chem., Int. Ed. 2006, 45, 6838–
6841. (d) Venkatasubbaiah, K.; Nowik, I.; Herber, R. H.; Jäkle, F. Chem.
Commun. 2007, 2154–2156.
a Data acquired in CDCl3 at 25 °C. b Data acquired in CD3CN at 25 °C.
oils. Surprisingly, multinuclear NMR spectroscopy revealed the
formation of the fluoroboranes 2-R due to concomitant migration
of the aryl/allyl group from boron to tin (Scheme 2, Table 1).20
(11) Heteronuclear bidentate Lewis acids with stannyl and boryl groups
attached to vinylene, phenylene, and naphthalene scaffolds have been
reported. See ref 14 and: (a) Ko¨ster, R.; Seidel, G.; Boese, R.; Wrackmeyer,
B. Chem. Ber. 1988, 121, 597–615. (b) Wrackmeyer, B.; Kerschl, S.; Maisel,
H. E.; Milius, W. J. Organomet. Chem. 1995, 490, 197–202. (c) Schulte,
M.; Gabbaï, F. P. Can. J. Chem. 2002, 80, 1308–1312.
Attachment of fluorine to boron in 2-R is evident from a 19
F
NMR signal at –55.8 ppm that is in a region typical of
organofluoroboranes21 and is further supported by a considerable
upfield shift of the 11B NMR resonances from a range of 62 to
(12) Jäkle, F.; Lough, A. J.; Manners, I. Chem. Commun. 1999, 453–
454.
(13) Gamboa, J. A.; Sundararaman, A.; Kakalis, L.; Lough, A. J.; Jäkle,
F. Organometallics 2002, 21, 4169–4181.
(19) For examples of Sn-Cl for Sn-F exchange, see: (a) Krause, E.
Ber. Dtsch. Chem. Ges. 1918, 51, 1447–1456. (b) Altmann, R.; Gausset,
O.; Horn, D.; Jurkschat, K.; Schurmann, M.; Fontani, M.; Zanello, P.
Organometallics 2000, 19, 430–443. (c) Beckmann, J.; Horn, D.; Jurkschat,
K.; Rosche, F.; Schürmann, M.; Zachwieja, U.; Dakernieks, D.; Duthie,
A.; Lim, A. E. K. Eur. J. Inorg. Chem. 2003, 164–174. (d) Chaniotakis,
N.; Jurkschat, K.; Müller, D.; Perdikaki, K.; Reeske, G. Eur. J. Inorg. Chem.
2004, 2283–2288.
(14) For related studies with 1-stannyl-2-borylbenzene derivatives, see:
Eisch, J. J.; Kotowicz, B. W. Eur. J. Inorg. Chem. 1998, 761–769.
(15) Boshra, R.; Sundararaman, A.; Zakharov, L. N.; Incarvito, C. D.;
Rheingold, A. L.; Jäkle, F. Chem. Eur. J. 2005, 11, 2810–2824.
(16) Boshra, R.; Venkatasubbaiah, K.; Doshi, A.; Lalancette, R. A.;
Kakalis, L.; Jäkle, F. Inorg. Chem. 2007, 46, 10174–10186.
(17) Boshra, R.; Doshi, A.; Jäkle, F. Angew. Chem., Int. Ed. 2008,
17, 1134–1137.
(20) Treatment of 1-Cl with KF under similar conditions resulted in
full recovery of the starting material, indicating that transfer of alkyl groups
does not occur under these conditions.
(21) Bardin, V. V.; Frohn, H.-J. Main Group Met. Chem. 2002, 25, 589–
613.
(18) For related work with Hg/B heteronuclear bidentate Lewis acids
see: (a) Solé, S.; Gabbaï, F. P. Chem. Commun. 2004, 1284–1285. (b)
Melaïmi, M.; Gabbaï, F. P. J. Am. Chem. Soc. 2005, 127, 9680–9681.

1536 Organometallics, Vol. 27, No. 7, 2008
Boshra et al.
Figure 1. Ortho phenyl resonance (left) and methyl region (right)
of the 1H NMR spectrum of 2-Ph. The 117/119Sn satellites are
marked with asterisks.
Figure 2. Molecular structure of 3-Ph′ (ORTEP, 30% probability).
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg): Sn(1)-C(1) ) 2.122(2), Sn(1)-C(12) ) 2.140(3),
Sn(1)-C(13) ) 2.142(2), Sn(1)-C(14) ) 2.157(3), B(1)-C(2) )
1.603(3), B(1)-C(11) ) 1.605(4), B(1)-F(1) ) 1.448(3), B(1)-F(2)
) 1.450(3), Sn(1) · · · F(1) ) 3.142(2), K(1) · · · F(1) ) 2.8116(15),
K(1) · · · F(2) ) 2.6295(15); C(1)-Sn(1)-C(12) ) 117.50(10),
C(1)-Sn(1)-C(13))112.67(10),C(12)-Sn(1)-C(13))109.13(10),
C(13)-Sn(1)-C(14) ) 106.99(11), C(1)-Sn(1)-C(14) ) 101.79(9),
C(12)-Sn(1)-C(14) ) 107.93(10), C(2)-B(1)-C(11) ) 113.7(2),
C(2)-B(1)-F(1) ) 109.7(2), C(11)-B(1)-F(1) ) 108.3(2),
C(2)-B(1)-F(2) ) 110.4(2), C(11)-B(1)-F(2) ) 109.1(2),
F(1)-B(1)-F(2) ) 105.2(2), F(1) · · · Sn(1)-C(14) ) 168.01(7).
70 ppm to ca. 53 ppm, which is attributed to enhanced π-overlap
of boron and fluorine. Migration of the aryl group from boron
to tin, on the other hand, results in a strong upfield shift of the
119Sn NMR signals to ca. –10 to –34 ppm (1-R from 95 to 131
ppm). These data are consistent with formation of diarylstan-
nanes, and for example, the value of –32.1 ppm for 2-Ph
compares favorably to that of -34.6 ppm for the nonborylated
analogue Fc(SnMe2Ph). Aryl group transfer to tin is also evident
1
from the H NMR spectra, which display tin satellites for the
ortho phenyl and thiophene protons in 2-Ph (J(117/119Sn, H) )
46 Hz; Figure 1) and 2-Th (J(117/119Sn, H) ) 25 Hz),
respectively, that are absent in the starting materials. Tin
satellites are also found for the R-protons of the allyl group in
2-All but are not well resolved. As a result of fluorine attachment
to boron a doublet with a coupling constant of 3J(19F, H) of ca.
14 Hz is observed for the B-Me groups in compounds 2-R
(Figure 1).
a toluene solution of the product.23 The molecular structure of
3-Ph′ confirms the phenyl group migration from boron to tin
(Figure 2). This migration results in a change from the distorted-
trigonal-bipyramidal tin environment observed for 1-Ph to an
almost perfect tetrahedral structure in 3-Ph′. The latter is, for
example, evident from a sharp decrease in the degree of
pentacoordination (%TBPeq ) [(120° – Avgeq)/(120° – 109.5°)]
× 100%, where Avgeq is the average of the equatorial-to-
equatorial angles)24 from 74.3% for 1-Ph to 34.2% for 3-Ph′.
The geometry change is further reflected in a significant increase
of the tin atom displacement25 from the plane defined by C(1),
C(12), and C(13) from 0.352 Å for 1-Ph to 0.571 Å for 3-Ph′.
The complex 3-Ph′ displays a coordination mode where
electrostatic interactions lead to simultaneous interaction of both
boron-bound fluorine atoms to the potassium ion and no
additional donor ligands are found in the trans position. This
arrangement results in unusually short K · · · F distances of
2.8116(15) and 2.6295(15) Å for K(1) · · · F(1) and K(1) · · · F(2),
respectively.26 Furthermore, the K ion is displaced by 0.629 Å
from the plane defined by O(1)-O(6) toward the fluoride
substituents. An even larger K displacement (0.8296 Å) has been
previously observed for the fluoride complex [K(18-crown-
6)]+[Fc(BMeF2)]–.16 The decrease in the K atom displacement
in 3-Ph′ as compared to the monodentate [K(18-crown-
6)]+[Fc(BMeF2)]– may be a consequence of a weak intermo-
lecular interaction between the phenyl group and the neighboring
K atom through C(17) and C(18) with intermolecular distances
measuring 3.565 and 3.875 Å, respectively. For [K(18-crown-
6)]+[Fc(BMePhF)]– similar intermolecular phenyl/K contacts
have been observed, which give rise to a polymeric structure
in the solid state.16
The oily nature of species 2-R prevented further characteriza-
tion by elemental analysis or X-ray crystallography. Hence, we
converted the products to the respective fluoroborate complexes
3-R by reaction with another 1 equiv of KF in THF. Alterna-
tively, the bidentate Lewis acids 1-R may be directly treated
with 2 equiv of KF in THF for 6 h at 45 °C (Scheme 2). The
rearranged fluoride complexes 3-Ph, 3-Th, and 3-All were
obtained as light yellow microcrystalline solids in 78%, 89%,
and 94% isolated yields, respectively, and fully characterized
by multinuclear NMR, elemental analysis, and X-ray crystal-
lography (for 3-Ph).
The NMR data of compounds 3-R are given in Table 1. An
upfield shift of the 11B NMR signals (9.0 to 13.5 ppm) in
comparison to the signals for compounds 1-R and 2-R is
consistent with tetracoordination at boron.22 As expected for
the formation of difluoroborate complexes, the 19F NMR spectra
reveal two distinct broad signals for the diastereotopic fluorine
atoms. The 1H NMR spectra display pseudotriplets for the boron
methyl group as a result of coupling to the diastereotopic
fluorines and, as in the case of compounds 2-R, tin satellites
are observed for the ortho protons of the organic group that is
transferred to tin. Attachment of the aryl substituents to tin is
also evident from the NOESY spectra for compounds 3-Ph and
3-Th, which display strong cross peaks between the ortho phenyl
and thiophene protons, respectively, and the Cp proton adjacent
to tin.
Various attempts at obtaining single crystals of compounds
3-R resulted in light orange, microcrystalline precipitates that
were not suitable for X-ray analysis. Suitable crystals were,
however, readily obtained for the crown ether complex [K(18-
crown-6)]+[Fc(BMeF2)(SnMe2Ph)]- (3-Ph′) by addition of 1
equiv of 18-crown-6 to 3-Ph and slow diffusion of hexanes into
(23) The 1H NMR of [K(18-crown-6)]+[Fc(BMeF2)(SnMe2Ph)]– (3-Ph′)
displayschemicalshiftsthatareverysimilartothoseofK+[Fc(BMeF2)(SnMe2Ph)]–
(3-Ph).
(24) Tamao, K.; Hayashi, T.; Ito, Y.; Shiro, M. Organometallics 1992,
11, 2099–2114.
(25) Altmann, R.; Jurkschat, K.; Schürmann, M.; Dakternieks, D.;
Duhtie, A. Organometallics 1998, 17, 5858–5866.
(26) Related literature complexes: (a) Groux, L. F.; Weiss, T.; Reddy,
D. N.; Chase, P. A.; Piers, W. E.; Ziegler, T.; Parvez, M.; Benet-Buchholz,
J J. Am. Chem. Soc. 2005, 127, 1854–1869. (b) Fei, Z.; Zhao, D.; Geldbach,
T. J.; Scopelliti, R.; Dyson, P. J. Eur. J. Inorg. Chem. 2005, 860–865.
(22) Yamaguchi, S.; Akiyama, S.; Tamao, K. J. Am. Chem. Soc. 2001,
123, 11372–11375.

Fluoride-Promoted Aryl/Allyl Migrations
Organometallics, Vol. 27, No. 7, 2008 1537
Scheme 3. Proposed Mechanism for the Fluoride-Induced
Rearrangement of 1-Pha
Figure 3. Molecular structure of 2-Ph · Py (ORTEP, 30% prob-
ability). Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (deg): Sn(1)-C(1) ) 2.113(5), Sn(1)-C(13)
) 2.152(6), Sn(1)-C(12) ) 2.148(6), Sn(1)-C(14) ) 2.158(5),
B(1)-C(2) ) 1.600(7), B(1)-C(11) ) 1.598(8), B(1)-F(1) )
1.417(7), B(1)-N(1) ) 1.665(6), Sn(1) · · · F(1) ) 3.059(3),
C(1)-Sn(1)-C(12) ) 117.0(2); C(1)-Sn(1)-C(13) ) 105.5(2),
C(12)-Sn(1)-C(13) ) 107.4(3), C(1)-Sn(1)-C(14) ) 107.81(17),
C(12)-Sn(1)-C(14) ) 109.9(2), C(13)-Sn(1)-C(14) ) 108.9(2),
F(1)-B(1)-C(11) ) 112.3(5), F(1)-B(1)-C(2) ) 110.5(4),
C(11)-B(1)-C(2) ) 116.9(4).
a
LA ) BR3 from another ferrocenylborane molecule.
toluene resulted in full recovery of the starting material even
after prolonged treatment at higher temperatures. This may be
related to the poor solubility of KF in nonpolar solvents. The
need for polar solvents might also suggest the involvement of
charged intermediate(s) that require solvent stabilization.
To assess whether the reaction proceeds through an intra- or
intermolecular process, we conducted parallel experiments with
varying amounts of THF as the solvent. At higher dilution the
rearrangement of 1-Ph proceeded considerably more slowly,
consistent with an intermolecular component to the migration
process. Next we reacted the monofunctional Lewis acid
Fc(BMePh) with Fc(SnMe2Cl) and KF under similar conditions.
Almost no conversion was found after 3 h at 45 °C, and the 1H
NMR spectrum taken after 2 days revealed a mixture of the
following major components: Fc(SnMe2Cl) (∼20%), Fc(B-
MePh) (∼40%), Fc(SnMe2F) (∼25%), and Fc(SnMe2Ph) (∼15%).
This suggests that there is also an intramolecular component to
the migration process and that cooperativity of the neighboring
Lewis acid groups facilitates the rearrangement reaction.
The complexes 3-R can be readily converted back to the free
bidentate Lewis acids as illustrated for 3-Ph. The compound
Fc(BMeF)(SnMe2Ph) (2-Ph) was obtained by treatment of the
fluoride complex 3-Ph with 1 equiv of Me3SiOTf in toluene in
94% yield.27 Alternatively, a strong Lewis base may be applied
to replace the fluoride. Treatment of 3-Ph with excess pyridine
in toluene resulted in elimination of KF and the formation of
the pyridine adduct [Fc(BMeF)(SnMe2Ph)] · Py (2-Ph · Py) in
52% isolated yield. The latter was identified by multinuclear
NMR and further characterized by X-ray diffraction analysis
of orange single crystals obtained from toluene/hexanes at –35
°C. The most striking feature of the structure of 2-Ph · Py is
the apparent π-stacking of the phenyl and pyridine rings, which
adopt an almost coplanar conformation at an interplanar angle
of 7.26° (Figure 3). A slight slippage is observed, and the
shortest C-C distances are in the range of 3.6- 3.7 Å. The
B-N bond distance of 1.665(6) Å is relatively long, suggesting
only weak binding of pyridine to boron.28
Mechanistic Aspects. We have carried out a series of
experiments in an attempt to probe the unusual aryl/allyl
migration from boron to tin and to answer the following
questions. (1) What is the significance of the fluoride anion and
does solvent polarity play a role? (2) Does the reaction proceed
inter- or intramolecularly and what effect does the 1,2-
substitution pattern have on the course of the reaction? (3) What
are the likely intermediates of this process?
On the basis of the unique ability of fluoride to promote the
rearrangement, we propose that the initial step involves replace-
ment of the Sn-bound chlorine for fluorine (Scheme 3).
Exchange reactions of Sn-Cl for Sn-F are well-known and
occur readily with aqueous KF.19 Moreover, fluoride-promoted
phenyl group migrations from silicon to carbon are commonly
observed and known to proceed through either nucleophilic or
electrophilic activation.29 These reactions are commonly referred
to as Meerwein-Wagner type rearrangements and in some cases
have been dubbed as “relay substitution” reactions. To further
probe this step, we reacted the preformed fluoride complex
[K(18-crown-6)]+[Fc(BMePh)(SnMe2F)F]–16 with organoborane
Lewis acids: e.g., FcB(C6F5)230 and B(C6F5)3. These Lewis acids
should be able to effectively compete for the complexed fluoride
Fluoride shows a unique ability to promote the observed
rearrangement, as other salts such as KH, KCl, and KBr do not
give any reaction with 1-Ph under similar conditions. Solvent
polarity was found to be also of great importance. Reactions of
1-Ph in acetonitrile proceeded more quickly, whereas those in
(29) See, for example: (a) Corey, J. Y.; Corey, E. R.; Chang, V. H. T.;
Hauser, M. A.; Leiber, M. A.; Reinsel, T. E.; Riva, M. E. Organometallics
1984, 3, 1051–1060. (b) Eisch, J. J.; Chingchen, S. C. Heteroat. Chem.
1994, 5, 265–274. (c) Damrauer, R.; Yost, V. E.; Danahey, S. E.; O’Connell,
B. K. Organometallics 1985, 4, 1779–1784. (d) Märkl, G.; Horn, M.;
Schlosser, W. Tetrahedron Lett. 1986, 27, 4019–4022. (e) Hudrlik, P. F.;
Abdallah, Y. M.; Kulkarni, A. K.; Hudrlik, A. M. J. Org. Chem. 1992, 57,
6552–6556. (f) Morihata, K.; Horiuchi, Y.; Taniguchi, M.; Oshima, K.;
Utimoto, K. Tetrahedron Lett. 1995, 36, 5555–5558. (g) Aronica, L. A.;
Morini, F.; Caporusso, A. M.; Salvadori, P. Tetrahedron Lett. 2002, 43,
5813–5815. (h) Aronica, L. A.; Raffa, P.; Caporusso, A. M.; Salvadori, P.
J. Org. Chem. 2003, 68, 9292–9298.
(27) Defluoridation of potassium fluoroborates can be accomplished by
treatment with fluoride anion acceptors. (a) With BF3: Frohn, H.-J.; Bailly,
F.; Bardin, V. V. Z. Anorg. Allg. Chem. 2002, 628, 723–724. (b) With AsF5:
Frohn, H.-J.; Bardin, V. V. Z. Anorg. Allg. Chem. 2001, 627, 15–16. (c)
With Me3SiCl: Vedejs, E.; Chapman, R. W.; Fields, S. C.; Lin, S.; Schrimpf,
M. R. J. Org. Chem. 1995, 60, 3020–3027. (d) With Me3SiOTf: Burgos,
C. H.; Canales, E.; Matos, K.; Soderquist, J. A. J. Am. Chem. Soc. 2005,
127, 8044–8049.
(30) Carpenter, B. E.; Piers, W. E.; Parvez, M.; Yap, G. A.; Rettig, S. J.
Can. J. Chem. 2001, 79, 857–867.
(28) Höpfl, H. J. Organomet. Chem. 1999, 581, 129–149.

1538 Organometallics, Vol. 27, No. 7, 2008
Boshra et al.
Chart 2. Possible Intermediate for the Fluoride-Induced
Rearrangement of 1-All
and hence lead to (partial) liberation of the neutral fluorostan-
nane [Fc(BMePh)(SnMe2F)] (A). However, the reaction resulted
in formation of the rearranged product 2-Ph, which suggests
the presence of A as an intermediate in the observed rearrange-
ment. It is important to point out that similar treatment of the
chloro derivative [K(18-crown-6)]+[Fc(BMePh)(SnMe2Cl)F]–
with FcB(C6F5)2 or Me2SnCl2 did not result in phenyl migration
but rather in quantitative decomplexation of fluoride with
formation of the unrearranged species 1-Ph.
Partial tetracoordination of the boryl groups by fluoride is
likely to be important to activate the aryl/allyl group in the actual
rearrangement step. Precedents of Wagner-Meerwein type
rearrangements of organoborates can be found in the literature
(see ref 6). The observation that Na[BPh4] reacts slowly with
R3SnCl (R ) Me, Bu) in THF at elevated temperature (85 °C)
over a period of 2 days to give Ph3B and PhSnR3 is also in
agreement with the proposed involvement of a borate intermedi-
ate.31 Given the demonstrated ability of tetraorganoborates to
transfer an aryl group from boron to tin, attack of a catalytic
amount of F– (or of a Sn-F moiety of another molecule) in B
is likely to promote aryl (allyl) migration to the electron-deficient
organotin moiety through a Wheland-type intermediate32 (C;
Scheme 3).
Partial abstraction of the tin-bound fluorine by another
ferrocenylborane molecule (B, LA ) [Fc(BMePh)(SnMe2F)]
in Scheme 3) should result in an activated organotin moiety
that is stabilized by π-complexation with the adjacent aryl/allyl
substituent on boron. Complexes of triorganotin cations with
aromatic species are well-known and typically form upon
generation of the highly reactive cations in aromatic solvents,
unless prevented by extremely bulky substituents on tin.35 In
this context we should also reemphasize that alkynyl groups
have been shown to coordinate to adjacent cationic Sn atoms
in the zwitterionic alkynylborates reported by Wrackmeyer and
bridging of allyl groups between B(C6F5)3 and -SnBu3 moieties
has been demonstrated by Piers, as outlined in Chart 1.3,4
π-Complexation of tin is further supported by the X-ray structure
of the precursor 1-Ph,12,13 which already shows relatively short
contacts between the meta and para carbon atoms of the boron-
bound phenyl group and tin (Cmeta · · · Sn ) 3.516(4) Å and
Cpara · · · Sn ) 3.216(4) Å). 119Sn NMR measurements for 1-Ph13
also suggest the presence of such interactions in solution, as
evidenced by an upfield shift to 102 ppm as compared to 130
ppm for the monodentate Fc(SnMe2Cl).36
The Wheland-type intermediate C allows for transfer of the
aryl/allyl group and is itself likely stabilized by additional
coordination of solvent (THF). Bridging aryl groups of this type
are believed to be key intermediates in electrophilic substitution
of arylstannanes with boron halides (the reverse aryl transfer
reaction)8 and commonly observed in organoaluminum chem-
istry: for example, in the dimeric structure of Ph3Al, bis(µ-
phenyl)bis(diphenylaluminum).37 The ability of allyl groups to
assume a bridging position as outlined in Chart 2 has been
demonstrated by Piers3 for the adduct of B(C6F5)3 with AllSnBu3
shown in Chart 1.
At this point the following question arises: why are stable
fluoride complexes formed in the presence of 18-crown-6 and
rearrangement only occurs when an organoborane is added as
an external Lewis acid? We propose that in the presence of 18-
crown-6 a stable and soluble fluoroborate complex is formed,16
while in the absence of 18-crown-6 only a fraction of the
organoborane is converted to the borate at any given time.33
Given the pronounced ability of organoboranes to form com-
plexes with fluoride,34 the remaining uncomplexed borane (or
the added external Lewis acid in the experiment with [K(18-
crown-6)]+[Fc(BMePh)(SnMe2F)F]–) may then be able to
activate the organotin moiety.
(31) Not surprisingly, these intermolecular reactions proceed consider-
ably more slowly at the temperature of 45 °C used for the synthesis of
compounds 2-R.
(32) Rathore, R.; Hecht, J.; Kochi, J. K. J. Am. Chem. Soc. 1998, 120,
13278–13279.
(33) Indeed, the mixture with KF in the absence of 18-crown-6 remains
turbid throughout the reaction, indicating the presence of insoluble potassium
salts.
Conclusions
(34) For recent examples of anion binding to organoboranes see: (a)
Yamaguchi, S.; Akiyama, S.; Tamao, K. J. Am. Chem. Soc. 2001, 123,
11372–11375. (b) Suri, J. T.; Cordes, D. B.; Cappuccio, F. E.; Wessling,
R. A.; Singaram, B. Angew. Chem., Int. Ed. 2003, 42, 5857–5859. (c) Kubo,
Y.; Yamamoto, M.; Ikeda, M.; Takeuchi, M.; Shinkai, S.; Yamaguchi, S.;
Tamao, K. Angew. Chem., Int. Ed. 2003, 42, 2036–2040. (d) Herberich,
G. E.; Englert, U.; Fischer, A.; Wiebelhaus, D. Eur. J. Inorg. Chem. 2004,
4011–4020. (e) Zhu, L.; Zhong, Z.; Anslyn, E. V. J. Am. Chem. Soc. 2005,
127, 4260–4269. (f) Koskela, S. J. M.; Fyles, T. M.; James, T. D. Chem.
Commun. 2005, 945–947. (g) Kubo, Y.; Ishida, T.; Kobayashi, A.; James,
T. D. J. Mater. Chem. 2005, 15, 2889–2895. (h) Liu, Z.-Q.; Shi, M.; Li,
F.-Y.; Fang, Q.; Chen, Z. H.; Yi, T.; Huang, C. H. Org. Lett. 2005, 7,
5481–5484. (i) Melaïmi, M.; Gabbaï, F. P. AdV. Organomet. Chem. 2005,
53, 61–99. (j) Bresner, C.; Aldridge, S.; Fallis, I. A.; Jones, C.; Ooi, L.-L.
Angew. Chem., Int. Ed. 2005, 44, 3606–3609. (k) Bresner, C.; Day, J. K.;
Coombs, N. D.; Fallis, I. A.; Aldridge, S.; Coles, S. J.; Hursthouse, M. B.
Dalton Trans. 2006, 3660–3667. (l) Neumann, T.; Dienes, Y.; Baumgartner,
T. Org. Lett. 2006, 8, 495–497. (m) Sakuda, E.; Funahashi, A.; Kitamura,
N. Inorg. Chem. 2006, 45, 10670–10677. (n) Liu, X. Y.; Bai, D. R.; Wang,
S. Angew. Chem., Int. Ed. 2006, 45, 5475–5478. (o) Parab, K.; Venkata-
subbaiah, K.; Jäkle, F. J. Am. Chem. Soc. 2006, 128, 12879–12885. (p)
Chiu, C.-W.; Gabbaï, F. P J. Am. Chem. Soc. 2006, 128, 14248–14249. (q)
Agou, T.; Kobayashi, J.; Kawashima, T. Inorg. Chem. 2006, 45, 9137–
9144. (r) Lee, M. H.; Agou, T.; Kobayashi, J.; Kawashima, T.; Gabbaï,
F. P. Chem. Commun. 2007, 1133–1135. (s) Sun, Y.; Ross, N.; Zhao, S.-
B.; Huszarik, K.; Jia, W.-L.; Wang, R.-Y.; Macartney, D.; Wang, S. J. Am.
Chem. Soc. 2007, 129, 7510–7511.
We have discovered a facile migration of aryl and allyl groups
from boron to tin in 1,2-disubstituted ferrocenes. This process
is promoted by addition of KF to the triorganoborane and leads
to selective formation of fluoroboranes in high yields. The
reaction resembles the so-called Meerwein-Wagner rearrange-
ments that are commonly observed in organosilicon chemistry
and also referred to as “relay substitutions”.29 Migration is
believed to proceed through an intramolecular reaction pathway
that likely involves Lewis acid activation of a fluorostannane
intermediate with formation of a transient triorganotin cation
(35) (a) Lambert, J. B.; Zhao, Y.; Wu, H.; Tse, W. C.; Kuhlmann, B.
J. Am. Chem. Soc. 1999, 121, 5001–5008. (b) Lambert, J. B.; Lin, L.;
Keinan, S.; Müller, T. J. Am. Chem. Soc. 2003, 125, 6022–6023. (c)
Henderson, L. D.; Piers, W. E.; Irvine, G. J.; McDonald, R. Organometallics
2002, 21, 340–345. (d) Müller, T. AdV. Organomet. Chem. 2005, 53, 155–
215.
(36) A similar interaction was observed in the case of 1-Th but not for
1-All, as evidenced by 119Sn NMR chemical shifts of 95.4 ppm for the
former and 130.8 ppm for the latter.
(37) Malone, J. F.; McDonald, W. S. J. Chem. Soc., Dalton Trans. 1972,
2646–2648.

Fluoride-Promoted Aryl/Allyl Migrations
Organometallics, Vol. 27, No. 7, 2008 1539
2-Ph · Py
Table 2. Crystal Data and Structure Refinement Details of 3-Ph′ and 2-Ph · Py
compd
3-Ph′
empirical formula
Mr
C31H46BF2FeKO6Sn
777.13
C24H27BFFeNSn
533.82
T, K
100(2)
100(2)
wavelength, Å
cryst syst
space group
a, Å
1.54178
monoclinic
P21/n
1.54178
orthorhombic
Pbca
12.0378(3)
10.6477(3)
b, Å
13.3122(3)
15.8820(3)
c, Å
24.4814(6)
23.9342(5)
R, deg
90
90
90
90
ꢀ, deg
93.1760(10)
90
3464.77(15)
4
1.490
10.584
γ, deg
V, Å3
4575.84(17)
8
1.550
13.897
Z
F
calcd, g cm–3
µ(Cu KR), mm–1
F(000)
1592
2144
cryst size, mm
limiting indices
0.18 × 0.33 × 0.12
-12 e h e 12
-15 e k e 15
-29 e l e 29
4.44-68.22
23 820
0.29 × 0.13 × 0.06
-14 e h e 11
-18 e k e 16
-27 e l e 28
3.69-67.72
θ range, deg
no. of rflns collected
no. of indep rflns
19 748
6268 (R(int) ) 0.0545)
3962 (R(int) ) 0.0445)
abs cor
numerical
numerical
refinement method
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))a
R indices (all data)a
full-matrix least-squares on F2
6268/0/391
1.027
full-matrix least-squares on F2
3962/0/265
1.091
R1 ) 0.0305, wR2 ) 0.0737
R1 ) 0.0344, wR2 ) 0.0761
0.956/-0.483
R1 ) 0.0435, wR2 ) 0.1076
R1 ) 0.0506, wR2 ) 0.1117
1.795/-0.975
peak/hole (e Å–3
)
2
2 2
a R1 ) ∑||Fo| – |Fc||/∑Fo; wR2 ) [∑[w(Fo – Fc ) ]/∑[w(Fo2)2]]1/2
.
species that is partially stabilized by π-interaction with the aryl/
allyl group. The respective rearranged fluoroborate complexes
are accessible in the presence of excess of KF. These complexes
are readily purified and can be converted back to the fluorobo-
ranes via treatment with Me3SiOTf or an excess of pyridine.
Future work will focus on expanding the applications of this
synthetic strategy to other group 13 and 14 elements.
Varian INOVA NMR spectrometer (Varian Inc., Palo Alto, CA)
equipped with a boron-free 5 mm dual broadband gradient probe
(Nalorac, Varian Inc., Martinez, CA). Solution 1H spectra were
referenced internally to the solvent signals, and 19F, 119Sn, and
11B NMR spectra were referenced externally to R,R′,R′′-
trifluorotoluene (0.05% in C6D6; δ -63.73), SnMe4 (δ 0), and
BF3 · Et2O (δ 0) in C6D6, respectively. Splittings of NMR signals
are abbreviated as pst (pseudotriplet), dpst (doublet of pseudot-
riplets), nr (not resolved). Elemental analyses were performed
by Quantitative Technologies Inc., Whitehouse, NJ.
Experimental Section
Materials and General Methods. 18-crown-6 and KF were
purchased from Sigma Aldrich and dried under high vacuum
for 24 h. Trimethylsilyl triflate (Me3SiOTf) was purchased from
Acros and used without further purification. CD3CN and CDCl3
(>99.7%) were obtained from Cambridge Isotope Laboratories
(CIL). The deuterated solvents were degassed via several
freeze–pump–thaw cycles and stored over 3 Å molecular
sieves. The compounds 1,2-Fc(SnMe2Cl)(BClMe),12,13 1,2-Fc
(SnMe2Cl)(BMePh),12,13 Fc(BMePh),15 Fc(SnMe2Cl),38 [K(18-
crown-6)]+[Fc(BMePh)(SnMe2F)F]–,16 and [K(18-crown-6)]+
[Fc(BMePh)(SnMe2Cl)F]– 16 were prepared according to litera-
ture procedures. All reactions and manipulations were carried
out under an atmosphere of prepurified nitrogen using either
Schlenk techniques or an inert-atmosphere glovebox (MBraun).
Ether solvents were distilled from Na prior to use. Hydrocarbon
and chlorinated solvents were purified using a solvent purifica-
tion system (Innovative Technologies; alumina/copper columns
for hydrocarbon solvents), and the chlorinated solvents were
subsequently degassed via several freeze–pump–thaw cycles.
The 499.9 MHz 1H NMR, 470.36 MHz 19F NMR, 186.4 MHz
119Sn NMR, and 160.3 11B NMR spectra were recorded on a
Crystal Structure Determinations. X-ray data were col-
lected on a Bruker SMART APEX CCD diffractometer using
Cu KR (1.541 78 Å) radiation. Crystallographic data for 3-Ph′
and 2-Ph · Py and details of X-ray diffraction experiments and
crystal structure refinements are given in Table 2. Numerical
absorption correction was applied in both cases. Structures were
solved using direct methods, completed by subsequent difference
Fourier syntheses, and refined by full-matrix least-squares
procedures on F2. All non-hydrogen atoms were refined with
anisotropic displacement coefficients. The H atoms were placed
at calculated positions and were refined as riding atoms. All
software and source scattering factors are contained in the
SHELXTL program package.39 Crystallographic data for the
structures of 2-Ph · Py and 3-Ph′ have been deposited with
the Cambridge Crystallographic Data Center as Supplementary
Publication Nos. CCDC-669585 and CCDC-669586, respec-
tively. Copies of the data can be obtained free of charge on
application to the CCDC, 12 Union Road, Cambridge CB21EZ,
U.K. (fax, (+44)1223-336-033; e-mail, deposit@ccdc.cam.ac.uk).
Synthesis of 2-Ph. A solution of 1-Ph (21 mg, 0.044 mmol)
in 1 mL of THF was mixed with KF (2.8 mg, 0.048 mmol,
1.1 equiv) in 1 mL of THF. The reaction mixture was stirred
at 45 °C for 3 h, followed by removal of insoluble salts by
filtration. The product was obtained as an orange oil. Yield:
(38) Kabouche, Z.; Dinh, N. H. J. Organomet. Chem. 1989, 375, 191–
195.
(39) Sheldrick, G. M. SHELXTL, Version 6.14; Bruker AXS, Inc.,
Madison, WI, 2004.
1
1
18 mg (90%), purity 95% by H NMR. H NMR (500 MHz,

1540 Organometallics, Vol. 27, No. 7, 2008
Boshra et al.
CDCl3, 25 °C): δ 7.58 (dd, J ) 1.5 Hz, 7.5 Hz, J(117/119Sn,H)
) 46 Hz, 2 H, Ph Ho), 7.36 (overlapped, 3 H, Ph Hm,p), 4.74
(m, 1 H, Cp H), 4.60 (m, 1 H, Cp H), 4.46 (dd, J ) 1.5, 2.5
Hz, J(117/119Sn,H) ) 12.5 Hz, 1 H, Cp H), 4.11 (s, 5 H, Cp),
Synthesis of 3-Th. A solution of 1-Th (25 mg, 0.052 mmol)
in 1 mL of THF was mixed with KF (7.6 mg, 0.13 mmol, 2.5
equiv) in 1 mL of THF. Using a procedure similar to that for
the preparation of 3-Ph, the product was obtained as a yellow
1
3
0.73 (d, J(19F,H) ) 14.0 Hz, 3 H, B-Me), 0.53 (d, J(19F,H)
microcrystalline solid. Yield: 24 mg (0.046 mmol; 89%). H
) 1.0 Hz, J(117/119Sn,H) ) 55 Hz, 3 H, Sn-Me), 0.49 (d,
J(19F,H) ) 1.5 Hz, J(117/119Sn,H) ) 56 Hz, 3 H, Sn-Me). 119Sn
NMR (186.4 MHz, CDCl3, 25 °C): δ -32.1. 19F{1H} NMR
(470.36 MHz, CDCl3, 25 °C): δ -55.8. 11B NMR (160.3 MHz,
CDCl3, 25 °C): δ 53 (w1/2 ) 500 Hz).
NMR (500 MHz, CD3CN, 25 °C): δ 7.67 (d, J ) 5.0 Hz, 1 H,
γ-Th), 7.34 (d, J ) 3.5 Hz, J(117/119Sn,H) ) 22 Hz, 1 H, R-Th),
7.25 (dd, J ) 3.5, 4.5 Hz, 1 H, ꢀ-Th), 4.09 (br, 2 H, Cp H),
4.00 (s, 5 H, Cp), 3.82 (br, 1 H, Cp H), 0.55 (s/d, J(117/119Sn,H)
) 61 Hz, 3 H, Sn-Me), 0.38 (s/d, J(117/119Sn,H) ) 60 Hz, 3
H, Sn-Me), -0.25 (pst, 3J(19F,H) ) 12 Hz, 3 H, B-Me). 119Sn
NMR (186.4 MHz, CD3CN, 25 °C): δ -46.6. 19F{1H} NMR
(470.36 MHz, CD3CN, 25 °C): δ -130.9, -135.6. 11B NMR
(160.3 MHz, CD3CN, 25 °C): δ 13.6 (w1/2 ) 210 Hz). Elemental
analysis was performed on crystals grown from a solution of
THF/ether in the presence of 1.0 equiv of 18-crown-6 at -38
°C. Anal. Calcd for C29H44BF2FeKO6SSn (783.18): C, 44.47;
H, 5.66. Found: C, 44.61; H, 5.75.
Synthesis of 3-Ph. A solution of 1-Ph (100 mg, 0.212 mmol)
in 1 mL of THF was mixed with KF (27 mg, 0.47 mmol, 2.2
equiv) in 1 mL of THF. The reaction mixture was stirred at
45 °C for 6 h, followed by removal of insoluble salts by
filtration. The solvents were removed under high vacuum,
and the remaining yellow microcrystalline solid was washed
with hexanes (3 × 2 mL). Yield: 102 mg (0.198 mmol; 94%).
1H NMR (500 MHz, CD3CN, 25 °C): δ 7.67 (dd, J ) 1.5, 8.0
Hz, J(117/119Sn,H) ) 41 Hz, 2 H, Ph Ho), 7.30 (overlapped, 3
H, Ph Hm,p), 4.10 (nr, 2 H, Cp H), 3.97 (s, 5 H, Cp), 3.78 (m,
J(117/119Sn,H) ) 13 Hz, 1 H, Cp H), 0.42 (s/nr, J(117/119Sn,H)
) 55 Hz, 3 H, Sn-Me), 0.38 (s/nr J(117/119Sn,H) ) 56 Hz, 3
H, Sn-Me), -0.25 (pst, 3J(19F,H) ) 12 Hz, 3 H, B-Me). 119Sn
NMR (186.4 MHz, CD3CN, 25 °C): δ -39.0. 19F{1H} NMR
(470.36 MHz, CD3CN, 25 °C): δ -137.6, -142.7. 11B NMR
(160.3 MHz, CD3CN, 25 °C): δ 9.2 (w1/2 ) 230 Hz). Anal.
Calcd for C19H22BF2FeKSn (512.84): C, 44.50; H, 4.32. Found:
C, 44.18; H, 4.14.
Synthesis of 1-All. A solution of AllSnMe3 (58 mg, 0.28
mmol) in 2 mL of dichloromethane was added dropwise to a
solution of 1-Cl (119 mg, 0.28 mmol) in 2 mL of dichlo-
romethane. The reaction mixture was stirred for 24 h at room
temperature followed by removal of all volatile components
under high vacuum. An orange oily material was obtained
after solvent removal. Yield: 114 mg (95%), purity 95% by
1
1H NMR. H NMR (500 MHz, CDCl3, 25 °C): δ 6.09 (m, 1
H, allyl-ꢀ), 4.99 (m, 2 H, allyl-γ), 4.93 (overlapping, 2 H, Cp
H), 4.77 (dd, J ) 1.5, 2.5 Hz, J(117/119Sn,H) ) 14 Hz, 1 H, Cp
H), 4.19 (s, 5 H, Cp), 2.29 (d, J ) 8.0 Hz, 2 H, allyl-R), 0.91
(s/d, J(117/119Sn,H) ) 58/60 Hz, 3 H, Sn-Me), 0.88 (s, 3 H,
B-Me), 0.78 (s/d, J(117/119Sn,H) ) 56/58 Hz, 3 H, Sn-Me).
119Sn NMR (186.4 MHz, CDCl3, 25 °C): δ 130.8. 11B NMR
(160.3 MHz, CDCl3, 25 °C): δ 70 (w1/2 ) 600 Hz).
Synthesis of 1-Th. A solution of 2-(trimethylstannyl)th-
iophene (115 mg, 0.465 mmol) in 2 mL of acetonitrile was
added dropwise to a solution of 1-Cl (200 mg, 0.465 mmol) in
2 mL of acetonitrile. The reaction mixture was stirred for 48 h
at room temperature, followed by removal of all volatile
components under high vacuum. Dark red crystals were obtained
from a 1:3 mixture of CH2Cl2/hexanes at -35 °C. Yield: 144
Synthesis of 2-All. A solution of 1-All (21 mg, 0.048 mmol)
in 1 mL of THF was mixed with KF (3.1 mg, 0.053 mmol, 1.1
equiv) in 1 mL of THF. Using a procedure similar to that for
the preparation of 2-Ph, the product was obtained as an orange
1
mg (0.301 mmol; 65%). H NMR (500 MHz, CDCl3, 25 °C):
δ 7.81 (dd, J ) 1.0, 4.5 Hz, 1 H, γ-Th), 7.52 (dd, J ) 1.0, 3.5
Hz, 1 H, R-Th), 7.28 (dd, J ) 3.5, 4.5 Hz, 1 H, ꢀ-Th), 5.03
(pst, J ) 2.5 Hz, J(117/119Sn,H) ) 7.0 Hz, 1 H, Cp H), 4.98
(dd, J ) 1.0, 2.5 Hz, J(117/119Sn,H) ) 12 Hz, 1 H, Cp H), 4.97
(dd, J ) 1.0, 2.5 Hz, J(117/119Sn,H) ) 14 Hz, 1 H, Cp H), 4.22
(s, 5 H, Cp), 1.22 (s, 3 H, B-Me), 0.73 (s/d, J(117/119Sn,H) )
58/61 Hz, 3 H, Sn-Me), 0.26 (s/d, J(117/119Sn,H) ) 60/63 Hz,
3 H, Sn-Me). 119Sn NMR (186.4 MHz, CDCl3, 25 °C): δ 95.4.
11B NMR (160.3 MHz, CDCl3, 25 °C): δ 62 (w1/2 ) 430 Hz).
Anal. Calcd for C17H20BClFeSSn (477.23): C, 42.79; H, 4.22.
Found: C, 42.76; H, 4.34.
1
oily material. Yield: 19 mg (94%), purity 90% by H NMR.
1H NMR (500 MHz, CDCl3, 25 °C): δ 5.98 (m, 1 H, allyl-ꢀ),
4.85 (m, 1 H, allyl-γ), 4.77 (m, 1 H, Cp H), 4.73 (m, 1 H,
allyl-γ), 4.60 (br, 1 H, Cp H), 4.52 (dd, J ) 1.0 Hz, 2.5 Hz,
J(117/119Sn,H) ) 12 Hz, 1 H, Cp H), 4.18 (s, 5 H, Cp), 1.96 (m,
2 H, allyl-R), 0.72 (d, 3J(19F,H) ) 13.5 Hz, 3 H, B-Me), 0.29
(nr, 6 H, Sn-Me). 119Sn NMR (186.4 MHz, CDCl3, 25 °C): δ
-9.9. 19F{1H} NMR (470.36 MHz, CDCl3, 25 °C): δ -55.8.
11B NMR (160.3 MHz, CDCl3, 25 °C): δ 53 (w1/2 ) 530 Hz).
Synthesis of 3-All. A solution of 1-All (68 mg, 0.16 mmol)
in 1 mL of THF was mixed with KF (23 mg, 0.40 mmol. 2.5
equiv) in 1 mL of THF. Using a procedure similar to that for
the preparation of 3-Ph, the product was obtained as a yellow
Synthesis of 2-Th. A solution of 1-Th (19 mg, 0.039 mmol)
in 1 mL of THF was mixed with KF (2.5 mg, 0.043 mmol,
1.1 equiv) in 1 mL of THF. Using a procedure similar to
that for the preparation of 2-Ph, the product was obtained
as an orange oily material. Yield: 18 mg (98%), purity 90%
1
microcrystalline solid. Yield: 58 mg (78%), purity 90% by H
1
NMR. H NMR (500 MHz, CD3CN, 25 °C): δ 6.05 (m, 1 H,
allyl-ꢀ), 4.76 (m, 1 H, allyl-γ), 4.59 (m, 1 H, allyl-γ), 4.10 (br,
1 H, Cp H), 4.07 (dd, J ) 1.0, 2.5 Hz, J(117/119Sn,H) ) 9 Hz,
1 H, Cp H), 3.98 (s, 5 H, Cp), 3.89 (dd, J ) 1.0, 2.5 Hz,
J(117/119Sn,H) ) 12 Hz, 1 H, Cp H), 1.90 (m, 2 H, allyl-R),
0.18 (s/d, J(117/119Sn,H) ) 54 Hz, 3 H, Sn-Me), 0.16 (s/d,
1
1
by H NMR. H NMR (500 MHz, CDCl3, 25 °C): δ 7.70 (d,
J ) 4.0 Hz, J(117/119Sn,H) ) 13 Hz, 1 H, γ-Th), 7.33 (d, J )
3.0 Hz, J(117/119Sn,H) ) 25 Hz, 1 H, R-Th), 7.29 (pst, J ) 4.0
Hz, 1 H, ꢀ-Th), 4.75 (m, 1 H, Cp H), 4.62 (m, 1 H, Cp H),
4.50 (dd, J ) 1.0, 2.5 Hz, J(117/119Sn,H) ) 13 Hz, 1 H, Cp H),
3
J(117/119Sn,H) ) 55 Hz, 3 H, Sn-Me), -0.27 (pst, J(19F,H)
3
4.14 (s, 5 H, Cp), 0.76 (d, J(19F,H) ) 14.5 Hz, 3 H, B-Me),
) 11 Hz, 3 H, B-Me). 119Sn NMR (186.4 MHz, CD3CN, 25
°C): δ -12.5. 19F{1H} NMR (470.36 MHz, CD3CN, 25 °C): δ
-132.0, -137.0. 11B NMR (160.3 MHz, CD3CN, 25 °C): δ
9.0 (pst, J(11B,19F) ) 72 Hz, w1/2 ) 160 Hz). Elemental analysis
was performed on crystals grown from a solution of toluene in
the presence of 1.0 equiv of 18-crown-6 at -38 °C. Anal. Calcd
3
0.62 (d, J(19F,H) ) 1.5 Hz, J(117/119Sn,H) ) 58 Hz, 3 H, Sn-
Me), 0.53 (nr, J(117/119Sn,H) ) 58 Hz, 3 H, Sn-Me). 119Sn
NMR (186.4 MHz, CDCl3, 25 °C): δ -33.5. 19F{1H} NMR
(470.36 MHz, CDCl3, 25 °C): δ -55.8. 11B NMR (160.3 MHz,
CDCl3, 25 °C): δ 53 (w1/2 ) 490 Hz).

Fluoride-Promoted Aryl/Allyl Migrations
Organometallics, Vol. 27, No. 7, 2008 1541
for C28H46BF2FeKO6Sn (741.12): C, 45.38; H, 6.26. Found: C,
45.04; H, 6.21.
ature for 30 min, followed by removal of all volatile components
under high vacuum. The residue was extracted three times with
3 mL of hexanes. The product obtained upon removal of solvent
from the combined extracts was identified as 2-Ph by 1H NMR
analysis. Similar results were obtained when the reaction was
carried out in C6D6.
Reactionof[K(18-crown-6)THF]+[Fc(BMePh)(SnMe2Cl)
F]- with FcB(C6F5)2. A solution of [K(18-crown-6)THF]+
[Fc(BMePh)(SnMe2Cl)F]- (8.2 mg, 9.4 µmol) in 1 mL of THF
was added to FcB(C6F5)2 (5.0 mg, 9.4 µmol) in 1 mL of THF
with stirring. Using a procedure analogous to that for the
preparation of 2-Ph from [K(18-crown-6)THF]+[Fc(BMePh)
(SnMe2F)F]-, the product 1-Ph was obtained as a red micro-
crystalline solid. Similar results were also obtained when the
reaction was carried out with Me2SnCl2 as the Lewis acid.
Conversion of 3-Ph to 2-Ph. A solution of Me3SiOTf (44
mg, 0.199 mmol) in 1 mL of toluene was added to 3-Ph (102
mg, 0.199 mmol) in 1 mL of toluene with stirring. The reaction
mixture was stirred at room temperature for 1 h, followed by
removal of insoluble salts by filtration. Toluene was removed
under high vacuum, and the remaining oily material was
extracted with hexanes (1 mL). Yield: 85 mg (94%), purity 95%
1
by H NMR.
Synthesis of 2-Ph · Py. A solution of pyridine (16 mg, 0.202
mmol) in 1 mL of toluene was added to 3-Ph (32 mg, 0.062
mmol) in 1 mL of toluene with stirring. The reaction mixture
was stirred for 1 h at room temperature, followed by removal
of insoluble salts by filtration. The reaction mixture was layered
with 1 mL of hexanes and kept at -35 °C for several days.
Light orange crystals were collected and dried under vacuo.
Yield: 17 mg (0.032 mmol; 52%). 1H NMR (500 MHz, CDCl3,
25 °C): δ 8.43 (d, J ) 5.5 Hz, 2 H, Py Ho), 7.75 (t, J ) 8.0 Hz,
1 H, Py Hp), 7.38 (d, J ) 7.0 Hz, J(117/119Sn,H) ) 43 Hz, 2 H,
Ph Ho), 7.27 (overlapped, 1 H, Ph Hm), 7.20 (overlapped, 3 H,
Py Hm, Ph Hp), 4.44 (br, 1 H, Cp H), 4.39 (br, 1 H, Cp H), 4.15
(overlapped, 6 H, Cp H), 0.41 (d, J ) 2.0 Hz, J(117/119Sn,H) )
56 Hz, 3 H, Sn-Me), 0.40 (nr, J(117/119Sn,H) ) 54 Hz, 3 H,
Sn-Me), 0.32 (d, 3J(19F,H) ) 14 Hz, 3 H, B-Me). 119Sn NMR
(186.4 MHz, CDCl3, 25 °C): δ -33.6. 19F{1H} NMR (470.36
MHz, CDCl3, 25 °C): no signal detected. 11B NMR (160.3 MHz,
CDCl3, 25 °C): δ 14.7 (w1/2 ) 520 Hz). Anal. Calcd for
C24H27BFFeNSn (553.84): C, 54.00; H, 5.10; N, 2.62. Found:
C, 53.90; H, 5.02; N, 2.57.
Reaction of Fc(SnMe2Cl) with Fc(BMePh) in the
Presence of KF. A mixture of Fc(SnMe2Cl) (2.5 mg, 6.7 µmol,
3.4 mM), Fc(BMePh) (1.9 mg, 6.7 µmol), and KF (0.4 mg, 6.9
µmol) in 1 mL of THF was stirred at 45 °C for 3 h, followed
by removal of insoluble salts by filtration. Only the starting
materials were observed by 1H NMR. The reaction was repeated
with an excess of KF (1 mg, 17 µmol) and run for 2 days. The
1H NMR spectrum now showed the presence of the following
ferrocene-containing species: Fc(SnMe2Cl) (∼20%), Fc(BMePh)
(∼40%), Fc(SnMe2F) (∼25%), and Fc(SnMe2Ph) (∼15%). In
a similar experiment that was run for 3 days at 45 °C using 6.5
mg of Fc(SnMe2Cl), 5.1 mg of Fc(BMePh), and 2.3 mg of KF
a larger amount of Fc(SnMe2Ph) (∼40%) was produced.
Concentration Dependence of the Rearrangement
Reactions. Two samples, each of which contained the com-
pound 1-Ph (10 mg, 0.021 mmol, 21.2 mM) and KF (1.4 mg,
0.024 mmol, 1.1 equiv), were prepared and 1 and 4 mL of THF
were added as the solvent, respectively. The mixtures were
stirred at 45 °C for 1.5 h, followed by removal of insoluble
Synthesis of Fc(SnMe2Ph). A solution of PhMgBr (57 µL,
1 M in THF, 0.057 mmol) was added via syringe to
Fc(SnMe2Cl) (20 mg, 0.054 mmol) in 1 mL of THF. The
reaction mixture was stirred at room temperature for 2 h,
followed by removal of all volatile components. The product
was extracted by adding 1 mL of hexanes, followed by
removal of insoluble magnesium salts by filtration. An orange
oil was obtained after evaporation of the solvents. Yield: 22
1
salts by filtration. The conversion was estimated by H NMR
to be 95% for the sample prepared with 1 mL of THF and 70%
for the sample with 4 mL of THF.
1
1
mg (99%), purity >95% by H NMR. H NMR (500 MHz,
CDCl3, 25 °C): δ 7.58 (dd, J ) 1.5 Hz, 7.0 Hz, J(117/119Sn,H)
) 45 Hz, 2 H, Ph Ho), 7.36 (overlapped, 3 H, Ph Hm,p), 4.39
(pst, J ) 1.5 Hz, 2 H, Cp H), 4.12 (pst, J ) 1.5 Hz, 2 H, Cp
H), 4.09 (s, 5 H, Cp), 0.51 (s/d, J(117/119Sn,H) ) 54/56 Hz, 6
H, Sn-Me). 13C NMR (125.7 MHz, CDCl3, 25 °C): δ 142.0
(ipso-Ph), 136.2 (s/d, J(117/119Sn,C) ) 37 Hz, meta Ph), 128.7
(s/d, J(117/119Sn,C) ) 9.5 Hz, para Ph), 128.4 (s/d, J(117/119Sn,C)
) 48 Hz, ortho Ph), 74.4 (s/d, J(117/119Sn,C) ) 51 Hz, Cp C2,5),
71.0 (s/d, J(117/119Sn,C) ) 41 Hz, Cp C3,4), 68.3 (C5H5), 67.8
(Cp C2,5), -9.1 (s/d, J(117/119Sn,C) ) 358/375 Hz, Sn-Me).
119Sn NMR (186.4 MHz, CDCl3, 25 °C): δ -34.6. GC-MS (70
eV, EI): m/z (%) 412 (86) [M+], 397 (89) [M+ – CH3], 382
(14) [M+ – 2CH3], 305 (100) [M+ – 2CH3 – Ph].
Acknowledgment is made to the donors of the Petroleum
Research Fund, administered by the American Chemical
Society for support of this research. F.J. thanks the Alfred
P. Sloan foundation for a research fellowship and the
National Science Foundation for a CAREER award (Grant
No. CHE-0346828). Funding of an X-ray diffractometer was
possible through a grant from the National Science Founda-
tion (Grant No. NSF CRIF-0443538). We are indebted to
Prof. Lalancette for helpful discussions and Dr. Krishnan
Venkatasubbaiah for acquisition of X-ray data for 2-Ph · Py.
Supporting Information Available: Figures giving NMR
spectra of the compounds 1-All, 2-Ph, 2-Th, 2-All, and
Fc(SnMe2Ph) and CIF files and tables giving crystallographic data,
including crystal data, atomic coordinates, bond lengths and angles,
and anisotropic thermal parameters. This material is available free
of charge via the Internet at http://pubs.acs.org.
Reaction of [K(18-crown-6)THF]+[Fc(BMePh)(SnMe2F)
F]-with FcB(C6F5)2. A solution of [K(18-crown-6)THF]+
[Fc(BMePh)(SnMe2F)F]- (16 mg, 0.019 mmol) in 1 mL of THF
was added to FcB(C6F5)2 (10 mg, 0.019 mmol) in 1 mL of THF
with stirring. The reaction mixture was stirred at room temper-
OM700967A