Revisiting borylanilines: Unique solid-state structures and insight into photophysical properties

Article abstract of DOI:10.1021/om301197f

The structure and photophysical properties of two known borylanilines, 4-(dimesitylboryl)aniline (1) and 4-(dimesitylboryl)-3,5-dimethylaniline (2), have been investigated. 1 and 2 have similar donor and acceptor centers but differ in their molecular conformations. Compounds 1 and 2 have been structurally characterized, and they exhibit a rare form of intermolecular N-H- - -π electrostatic interactions. The structure and photophysical properties of 1 and 2 are discussed in the context of computational results.

Full text of DOI:10.1021/om301197f

Note
pubs.acs.org/Organometallics
Revisiting Borylanilines: Unique Solid-State Structures and Insight
into Photophysical Properties
Pagidi Sudhakar, Sanjoy Mukherjee, and Pakkirisamy Thilagar*
Department of Inorganic & Physical Chemistry, Indian Institute of Science, Bangalore-560012, India
S
* Supporting Information
ABSTRACT: The structure and photophysical properties of two known borylanilines, 4-(dimesitylboryl)aniline (1) and 4-
(dimesitylboryl)-3,5-dimethylaniline (2), have been investigated. 1 and 2 have similar donor and acceptor centers but differ in
their molecular conformations. Compounds 1 and 2 have been structurally characterized, and they exhibit a rare form of
intermolecular N−H- - -π electrostatic interactions. The structure and photophysical properties of 1 and 2 are discussed in the
context of computational results.
we used a modification of Asher’s9 procedure for the synthesis
of 1 and 2 (see the Supporting Information and Scheme 1).
riarylboranes1 have been continuously gaining much
Tattention owing to their excellent photophysical proper-
ties. Because of its inherent Lewis acidity, the three-coordinate
boron in triarylboranes has been extensively used as a receptor
for fluoride and cyanide and neutral molecules such as
pyridines. With a suitable donor site attached, triarylboranes
exhibit intense intramolecular charge transfer (ICT) character,
and this phenomenon has been well exploited in linear/
nonlinear optics and electroluminescence (EL).1,2 In the 1970s,
Williams studied extensively the photophysical/chemical
properties of several N,N-disubstituted borylanilines.3−5 Since
then, several groups reported numerous D−A systems based on
N,N-(bis-aryl/alkyl)borylanilines.2,6,12 Although the synthetic
utility of (4-aminophenyl)dimesitylborane has been well
documented in the recent and past literature, surprisingly
there have been no data reported on the crystal structures and
photophysical properties of unsubstituted borylanilines (4-
(dimesitylboryl)aniline (1) and 4-(dimesitylboryl)-3,5-dime-
thylaniline (2)).2b,5,8 Recently, we became interested in
investigating the effect of the molecular conformation on the
photophysical properties of D−A systems.7 As part of this
program, we have investigated the effects of molecular
conformation on the solid-state structures and photophysical
properties of borylanilines 1 and 2, and the results are reported
here.
Scheme 1. Synthesis of 1 and 2
First, the reaction of bromoanilines with 2 equiv of nBuLi in
THF at −78 °C selectively generated a dianion at the nitrogen
center, which was trapped with ClSiMe3 to give the
intermediate N,N-bis(trimethylsilyl) bromobenzenes. The
second step of the process is the selective metal−halogen
exchange with nBuLi and addition of Mes2BF to afford the
desired product in good yield after deprotection of the −SiMe3
group by methanolysis. The structure of borylanilines 1 and 2
were confirmed by NMR (1H and 13C), HRMS, and single-
crystal X-ray crystallography. In 1H NMR, the −NH2 resonance
of 1 (4.01 ppm) is shifted slightly downfield with respect to
1
that of 2 (3.61 ppm). It is worth mentioning that the H
As reported elsewhere, compounds 1 and 2 can be
conveniently prepared by the Williams method.3,4,8 To avoid
the use of a heavy metal (Pd) and to reduce the reaction time,
Received: December 13, 2012
Published: May 3, 2013
© 2013 American Chemical Society
3129
dx.doi.org/10.1021/om301197f | Organometallics 2013, 32, 3129−3133

Organometallics
Note
resonance (3.87 ppm) of the −NH2 group in (E)-4-(2-
(dimesitylboryl)vinyl)benzenamine reported in ref 11 falls
between the resonances of 1 and 2. Interestingly, the aryl C−H
protons of the 3,4-Me2-C4H2-NH2 moiety of 2 gives raise to
two distinct resonances at 6.73 and 6.72 ppm in CDCl3. From
variable-temperature NMR experiments in toluene-d8 (see the
Supporting Information, Figure S4), we conclude that the two
aryl protons are nonequivalent. At 223 K, the two protons are
observed at 6.67 and 6.69 ppm; as the temperature is raised,
these two signals begin to merge and become a broad singlet
(Tc = 313 K and ΔG = 20.26 kcl/mol). From the single-crystal
structure, it is found that the dihedral angle between the 3,4-
Me2-C4H2-NH2 unit and the −B(mes)2 unit is 52.6°;
presumably this twisted arrangement is retained in solution
and renders the two C−H protons of the former unit
nonequivalent.
Supporting Information (Table S1). The boron atom in both 1
and 2 has a trigonal-planar configuration with the sum of angles
around boron being 360°. The B−C(aryl) bond in 1 (1.538(2)
Å) is shorter than the bond length observed in 2 (1.578(3) Å)
and 4-(dimesitylboryl)-N,N-dimethylaniline10 (1.545(2) Å). In
contrast, the B−C(mes) bond length follows the opposite trend
(Table S2, Supporting Information). The C−C bond lengths of
the aniline moiety of 1 show more quinoidal distortion than for
2. A similar feature has been observed for 4-(dimesitylboryl)-
N,N-dimethylaniline by Marder et al.10 The dihedral angle
between the phenyl moiety of H2NPh and the BC3 plane in 1
(12.2°) is significantly less than that in 2 (52.6°). The presence
of two additional methyl groups at ortho positions of the
dimesitylboryl group twisted the H2NPh unit significantly in 2.
However, the nitrogen atoms in 1 and 2 are planar, with the
sum of angles around nitrogen being 360°. The C(aryl)−N
bond length in 1 (1.363(2) Å) is comparatively shorter than the
C(aryl)−N length in 2 (1.502(3) Å). On the basis of these
results, one can tentatively conclude that the donor−acceptor
interaction in 1 is stronger than that in 2 and 4-
(dimesitylboryl)-N,N-dimethylaniline.10
The molecular structures of 1 and 2 were determined (Figure
1 and Table 1), and the crystallographic data are given in the
Interestingly, the crystal structures of 1 and 2 reveal a rare
form of intermolecular N−H- - -π interaction11 (Figure 1).
Though N−H- - -π interactions are widely prevalent in a
number of protein crystal structures, such intermolecular N−
H- - -π interactions were not clearly demonstrated by X-ray
crystal structures previously for D−A molecules, to the best of
our knowledge.2,12 A view of the N−H- - -π hydrogen-bonding
interaction is shown in Figure 1. The electron-deficient boryl
unit and the electron-donating −NH2 moieties of neighboring
molecules are close to each other (Figure 1). In the solid state
the adjacent molecules pack together to form a one-
dimensional chain (Figure 1). The N−H- - -π distances (π is
the centroid of the mesityl moiety) are 3.02 and 4.08 Å for 1
and 2, respectively. This difference in N−H- - -π distances can
be attributed to the structural constraint imposed by the
additional methyl groups at the ortho positions of the
dimesitylboryl group in 2. The positive and negative electro-
static potential surfaces at the two ends of the dyads 1 and 2
clearly demonstrate the head-to-tail arrangement of D−A units,
which can be a stabilizing factor for these dyads in the solid
state (Figure 1).
Figure 1. Crystal structures of 1 (top) and 2 (middle), ORTEP
diagrams of 1 and 2 with ellipsoids at the 50% probability level
(bottom left), and ESP surfaces of 1 and 2 (bottom right) as obtained
from DFT computations (isovalue 0.0004).
In solution both 1 (270 and 325 nm) and 2 (325 and 370
nm) exhibit two characteristic absorption bands (Figure 2).
Since 1 and 2 have a D−A architecture,2,12 solvent polarity
dependent absorption studies of both compounds were carried
out with the objective to rationalize the absorption process
involved in these dyads. For both compounds the shorter
wavelength band does not shift irrespective of the solvent
polarity; however, the lower energy band shows a huge red shift
Table 1. Comparison of Mean Bond Lengths (Å) and
Selected Torsion Angles (deg) in 1, 2 and Me2NC6H4−
a
B(mes)2
1
2
Me2NC6H4−B(mes)2
Bond Lengths
B−C(aryl)
B−C(Mes)
N−C(aryl)
C1−C2
1.538(2)
1.589(1)
1.363(2)
1.412(1)
1.381(1)
1.578(3)
1.575(2)
1.505(3)
1.413(2)
1.394(2)
1.545(2)
1.586(2)
1.368(1)
1.409(2)
1.382(2)
C2−C3, C5−C6
Torsion Angles
C1−B−C7−C8
C1−B−C13−C14
C2−C1−B1−C7
−63.8
−63.8
−12.2
−51.1
−51.1
−52.6
66.8
50.5
20.0
a
See page S8 in the Supporting Information.
Figure 2. Absorption spectra of 1 (left) and 2 (right) in different
−5
solvents, obtained at 10 M.
3130
dx.doi.org/10.1021/om301197f | Organometallics 2013, 32, 3129−3133

Organometallics
Note
with increasing solvent polarity. Thus, the high-energy band can
be ascribed to π−π* transitions, whereas the lower energy band
can be attributed to a charge transfer transition (ICT) between
the amine group and the boron center. On the basis of the NH2
chemical shift, the dihedral angle between the D and A units
and the short N−C bond distances, one may expect that the
ICT band in 1 should be more sensitive to the solvent polarity
than 2. In contrast, the latter exhibits a more bathochromic shift
than the former. To understand the apparent anomaly, DFT
calculations were performed using the B3LYP hybrid functional
and 6-31G(d) basis set for all of the atoms as incorporated in
Gaussian 09 software.13 Optimization of molecular structures
with consequent frequency test provided structures with close
similarity to the X-ray crystallographic geometries.
The FMOs (frontier molecular orbitals) of 1 and 2 are
shown in Figure 3. It is understandable that the differences in
Figure 4. Emission spectra of 1 (top left) and 2 (top right) in different
−5
solvents (10 M; for 1 λex 340 nm and for 2 λex 365 nm).
and literature reports one can assign the corresponding
emitting states of these two emission bands as local excited
state (LE) and twisted intramolecular charge transfer (TICT)
state, respectively.14 The TICT emission only appears in polar
solvents due to the preferential stabilization of the TICT state.
To validate the above argument, solvent viscosity dependent PL
studies were carried out, because it is known that the emission
of the TICT fluorophore is sensitive to solvent viscosity
variations.15 The PL studies were carried out in highly viscous
nonpolar (paraffin) and polar (ethylene glycol) solvents. The
dependency of peak emission intensity on the viscosity of the
solvent can be seen in Figure 5. In viscous nonpolar solvent, 1
Figure 3. Schematic diagram of FMOs (isovalue 0.04) of 1 and 2 as
obtained from DFT computations. Hydrogens are omitted for clarity.
the charge-transfer characteristics of 1 and 2 arise mainly
because of the specific localization of the HOMO and LUMO.
For example, because of the twisted conformation of 2, the
antibonding interaction of the boron pπ orbital with the aryl
ring is diminished; as a result, the energy of the LUMO in 2 is
slightly lower than in 1. In addition, the twisted arrangement of
D−A units in 2 limits the bonding interaction between the
aniline and the boryl units; hence, the HOMO is destabilized in
2. On the other hand, the planar arrangement of D−A units in
1 facilitates the bonding interaction in the whole molecule; as a
result the HOMO is stabilized to a greater extent (0.28 eV
lower than HOMO of 2). Thus, the overall HOMO−LUMO
gap is lower in 2 (3.89 eV) than in 1 (4.26 eV). These results
directly support why compound 2 absorbs and emits at longer
wavelength in comparison to 1. In summary, the DFT results
clearly indicate the CT nature of the HOMO−LUMO
transition and also provide useful information about the effect
of steric perturbation on the electronic band gap.
The solution PL spectra of 1 and 2 in different solvents are
shown in Figure 4. The emission bands of 1 and 2 are red-
shifted and weakened in intensity with an increase in the
solvent polarity (Figure 4). The large Stokes shifts and weak
fluorescence characteristics of 1 and 2 in polar solvents suggest
that a polar CT state is emitting in both compounds (Tables S3
and S4, Supporting Information). Compounds 1 and 2 exhibit a
considerable solvatochromism of fluorescence from blue to
orange colors (Figure 4). These spectral characteristics are
comparable with the behavior of tris(phenylethynylduryl)-
borane-based D−A systems reported by Yamaguchi et al.14 In
hexane both 1 and 2 exhibit a single emission band at 375 and
415 nm, respectively. In contrast, the DMSO/EtOAc solutions
of 1 and 2 exhibit two emission bands (1, 400 and 520 nm; 2,
400 and 540 nm). On the basis of the computational results
Figure 5. Emission spectra of 1 (left) and 2 (right) in paraffin and
−5
ethylene glycol (10 M; for 1 λex 340 nm and for 2 λex 365 nm).
and 2 show only LE emission bands (Figure 5). In viscous polar
solvent the TICT peaks increases with viscosity but the increase
is less in 1 in comparison to that in 2. This result is consistent
with the twisted arrangement of D−A units in 2. Both polarity
and viscosity significantly influence the emission process, and
these spectral characteristics of 1 and 2 are consistent with the
behavior of other TICT luminogens.15
The bright solution luminescence and the characteristic
solid-state packing prompted us to study the solid-state
luminescence of compounds 1 and 2. Thin films of both the
compounds were prepared by spin coating on quartz substrates
from their DCM solutions (1 × 10−2 M). The thin-film
photoluminescence spectra of compounds 1 and 2 retain the
spectral feature of the solution state (DCM) with a slight red
shift of the emission wavelength (Figure 6). The bathochromic
shift in the solid state is presumably due to the N−H- - -π
intermolecular interactions observed for these compounds in
the solid state. However, the peak positions and intensities of
emission bands in dyads 1 and 2 are independent of excitation
3131
dx.doi.org/10.1021/om301197f | Organometallics 2013, 32, 3129−3133

Organometallics
Note
was added, and the reaction mixture was warmed to room temperature
over 12 h. The solvent was evaporated, and the crude residue was
dissolved in methanol and refluxed for 6 h. The reaction mixture was
cooled to room temperature and extracted using ethyl acetate. The
combined extracts were stored over anhydrous Na2SO4, and the
solvent was removed under reduced pressure. The crude product was
purified by column chromatography (5% EtOAc in petroleum ether).
Yield: 85%. 1H NMR (400 MHz, CDCl3, 25 °C): δ (ppm) 7.41 (d, J =
8 Hz, 2H), 6.83 (s, 4H), 6.61 (d, J = 8.4, 2H), 4.02 (s, 2H), 2.32 (s,
6H), 2.07 (s, 12H); 13C NMR (100 MHz, CDCl3, 25 °C): δ (ppm)
151, 141.2, 140.4, 138.2, 128.4, 114.3, 23.9, 21.7. ESI-MS (positive ion
mode): Mcalcd(C24H28BN), 341.2315 Da; found, 342.2393 Da [M +
H]+.
Figure 6. Solid state emission and excitation spectra of 1 (left) and 2
(right) (λex 300 nm). The inset shows the thin film photoluminescence
color of 1 and 2.
4-(Dimesitylboryl)-3,5-dimethylaniline (2). Compound 2 was
prepared following a procedure similar to that used for compound 1.
The quantities involved and characterization data are as follows: 4-
bromo-3,5-dimethylaniline (1 g, 5 mmol), n-BuLi (6.25 mL, 10 mmol)
wavelength. This indicates that the emission is originating from
an excited state which is populated irrespective of the excitation
wavelength.
1
ClSi(CH3)3 (1.24 g, 11.5 mmol). Yield: 98%. H NMR (400 MHz,
CDCl3, 25 °C): δ (ppm) 6.68 (s, 2H), 2.34 (s, 6H), 0.06 (s, 18H).
Step-2: N-(4-bromo-3,5-dimethylphenyl)-1,1,1-trimethyl-N-
(trimethylsilyl)silanamine (1g, 2.90 mmol), n-BuLi (2 mL, 3.19
CONCLUSIONS
■
1
We have followed a facile synthetic route for the synthesis of
borylanilines. The exclusion of a palladium-catalyzed hydro-
genation step would be highly useful for synthesizing materials
containing alkylynic, vinylic, and other functional groups which
are extensively utilized in organoboron chemistry. The two
borylanilines reported here display dual emission and strong
solvatochromic effects, which are explained on the basis of
molecular conformation dependent charge transfer. Detailed
studies on the structures, conformation, and photophysical
properties of a series of borylanilines are under investigation.
mmol), Mes2BF (0.95 g, 3.48 mmol), colorless solid, 80% yield. H
NMR (400 MHz, CDCl3, 25 °C): δ (ppm) 6.73 (d, J = 4 Hz, 4H),
6.28 (s, 2H), 3.66 (s, 2H), 2.26 (s, 6H), 2.02 (s, 6H), 1.95−1.91 (m,
12H). 13C NMR (100 MHz, CDCl3, 25 °C): δ (ppm) 148.09, 145.26,
143.65, 140.89, 140.76, 139.08, 128.93, 128.83, 114.92, 23.70, 23.45,
23.19, 21.74. ESI-MS (positive ion mode): Mcalcd(C26H32BN),
369.2628 Da; found, 370.2706 Da [M + H]+.
ASSOCIATED CONTENT
* Supporting Information
■
S
Text, figures, tables, and CIF files giving crystal structures,
experimental procedures, characterization data, and DFT
computational data. This material is available free of charge
via the Internet at http://pubs.acs.org.
EXPERIMENTAL SECTION
■
All reactions were carried under an atmosphere of purified nitrogen
using standard Schlenk techniques. THF was distilled over sodium.
The 400 MHz 1H NMR and 100 MHz 13C NMR spectra were
recorded on a Bruker Advance 400 MHz NMR spectrometer. All
AUTHOR INFORMATION
Corresponding Author
*P.T.: tel, +91-80-2293-3353; fax, (+91) 8023601552, e-mail,
thilagar@ipc.iisc.ernet.in.
■
1
solution H and 13C spectra were referenced internally to the solvent
signal. Electronic absorption spectra were recorded on a Perkin-Elmer
LAMBDA 750 UV/visible spectrophotometer. Solutions were
prepared using a microbalance ( 0.1 mg) and volumetric glassware
and then charged in quartz cuvettes with sealing screw caps.
Fluorescence emission studies were carried out on a Horiba JOBIN
YVON Fluoromax-4 spectrometer. Single-crystal X-ray diffraction
studies were carried out with a Bruker SMART APEX diffractometer
equipped with a three-axis goniometer. The crystals were kept under a
steady flow of cold dinitrogen during the data collection. Details
regarding the data collection and refinement for compounds 1 and 2
are given in Table S1 (Supporting Information). The data were
integrated using SAINT, and an empirical absorption correction was
applied with SADABS. The structures were solved by direct methods
and refined by full-matrix least squares on F2 using SHELXTL
software.16 All of the non-hydrogen atoms were refined with
anisotropic displacement parameters, while the hydrogen atoms were
refined isotropically on the positions calculated using a riding model.
4-(Dimesitylboryl)aniline (1). To a solution of 4-bromoaniline (4
g, 23.25 mmol) in THF (40 mL) at −78 °C was added dropwise n-
BuLi (29 mL of a 1.6 M solution in hexanes, 46.5 mmol), and the
reaction mixture was stirred for 1 h. Trimethylsilyl chloride (5.8 g, 53.5
mmol) was added, and the reaction mixture was warmed to room
temperature over 6 h. Volatiles were removed in vacuo, and the
product (N-(4-bromophenyl)-1,1,1-trimethyl-N-(trimethylsilyl)-
silanamine) was distilled under reduced pressure. Yield: 99%. 1H
NMR (400 MHz, CDCl3, 25 °C): δ (ppm) 7.38 (d, J = 8.8 Hz, 2H),
6.84 (d, J = 8.8 Hz, 2H), 0.12 (s, 18H). To a solution of N-(4-
bromophenyl)-1,1,1-trimethyl-N-(trimethylsilyl)silanamine (1 g, 3.2
mmol) in THF (30 mL) at −78 °C was added dropwise n-BuLi (2.2
mL of a 1.6 M solution in hexanes, 3.5 mmol), and the reaction
mixture was stirred for 1 h. Mes2BF (1 g, 3.8 mmol) in THF (2 mL)
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
P.T. thanks the Department of Science and Technology (DST)
New Delhi, IISc-Bangalore, and CSIR New Delhi for financial
support. P.S. thanks the IISc, and S.M. thanks the CSIR for
SPMF.
REFERENCES
■
(1) (a) Shirota, Y.; Kinoshita, M.; Noda, T.; Okumoto, K.; Ohara, T.
J. Am. Chem. Soc. 2000, 122, 11021−11022. (b) Entwistle, C. D.;
Marder, T. B. Angew. Chem., Int. Ed. 2002, 41, 2927−2931. (c) Doi,
H.; Kinoshita, M.; Okumoto, K.; Shirota, Y. Chem. Mater. 2003, 15,
1080−1089. (d) Entwistle, C. D.; Marder, T. B. Chem. Mater. 2004,
16, 4574−4585. (e) Yamaguchi, S.; Wakamiya, A. Pure Appl. Chem.
2006, 78, 1413−1424. (f) Heilmann, J. B.; Scheibitz, M.; Qin, Y.;
Sundararaman, A.; Jakle, F.; Kretz, T.; Bolte, M.; Lerner, H. W.;
̈
Holthausen, M. C.; Wagner, M. Angew. Chem., Int. Ed. 2006, 45, 920−
925. (g) Hudnall, T. W.; Chiu, C.-W.; Gabbai, F. P. Acc. Chem. Res.
2009, 42, 388−397. (h) Jakle, F. Chem. Rev. 2010, 110, 3985−4022.
̈
(i) Wade, C. R.; Broomsgrove, A. E. J.; Aldridge, S.; Gabbaı, F. P.
Chem. Rev. 2010, 110, 3958−3984. (j) Bresner, C.; Haynes, C. J. E.;
Addy, D. A.; Broomsgrove, A. E. J.; Fitzpatrick, P.; Vidovic, D.;
Thompson, A. L.; Fallis, I. A.; Aldridge, S. New J. Chem. 2010, 34,
1652−1659. (k) Korich, A. L.; Iovine, P. M. Dalton Trans. 2010, 39,
1423−1431. (l) Poon, C. T.; Lam, W. H.; Yam, V. W. W. J. Am. Chem.
3132
dx.doi.org/10.1021/om301197f | Organometallics 2013, 32, 3129−3133

Organometallics
Note
Soc. 2011, 133, 19622−19625. (m) Tanaka, K.; Chujo, Y. Macromol.
Rapid Commun. 2012, 33, 1235−1255. (n) Vadavi, R. S.; Kim, H.; Lee,
K. M.; Kim, T.; Lee, J.; Lee, Y. S.; Lee, M. H. Organometallics 2012, 31,
(16) (a) SAINT-NT, Version 6.04; Bruker AXS, Madison, WI, 2001.
(b) SHELXTL-NT, Version 6.10; Bruker AXS, Madison, WI, 2000.
̈
31−34. (o) Zhao, H.; Reibenspies, J. H.; Gabbaı, F. P. Dalton Trans.
2013, 42, 608−610.
(2) (a) Sundararaman, A.; Varughese, R.; Li, H.; Zakharov, L. N.;
Rheingold, A. L.; Jakle, F. Organometallics 2007, 26, 6126−6131.
̈
(b) Yuan, M. S.; Liu, Z. Q.; Fang, Q. J. Org. Chem. 2007, 72, 7915−
7922. (c) Hudson, Z. M.; Wang, S. Acc. Chem. Res. 2009, 42, 1584−
1596. (d) Pron, A.; Baumgarten, M.; Mullen, K. Org. Lett. 2010, 12,
̈
4236−4239. (e) Schmidt, H. C.; Reuter, L. G.; Hamacek, J.; Wenger,
O. S. J. Org. Chem. 2011, 76, 9081−9085. (f) Weber, L.; Halama, J.;
Bohling, L.; Chrostowska, A.; Dargelos, A.; Stammler, H.-G.;
̈
Neumann, B. Eur. J. Inorg. Chem. 2011, 3091−3101. (g) Makarov,
́
N. S.; Mukhopadhyay, S.; Yesudas, K.; Bredas, J.-L.; Perry, J. W. J. Phys.
Chem. A 2012, 116, 3781−3793.
(3) Babb, B.; Grisdale, P. J. Canadian Patent CA 912019, 1972.
(4) (a) Doty, J. C.; Babb, B.; Grisdale, P. J.; Glogowski, M. E.;
Williams, J. L. R. J. Organomet. Chem. 1972, 38, 229−236.
(b) Glogowski, M. E.; Grisdale, P. J.; Williams, J. L. R.; Regan, T.
H. J. Organomet. Chem. 1973, 54, 51−60. (c) Glogowski, M. E.;
Williams, J. L. R. J. Organomet. Chem. 1981, 216, 1−8. (d) Glogowski,
M. E.; Williams, J. L. R. J. Organomet. Chem. 1981, 218, 137−146.
(5) (a) Yuan, Z.; Taylor, N. J.; Marder, T. B.; Williams, I. D.; Kurtz,
S. K.; Cheng, L.-T. J. Chem. Soc., Chem. Commun. 1990, 1489−1492.
(b) Yuan, Z.; Collings, J. C.; Taylor, N. J.; Marder, T. B.; Jardin, C.;
Halet, J.-F. J. Solid State Chem. 2000, 154, 5−12.
(6) (a) Zhao, C. H.; Wakamiya, A.; Inukai, Y.; Yamaguchi, S. J. Am.
Chem. Soc. 2006, 128, 15934−15935. (b) Zhao, C.-H.; Wakamiya, A.;
Yamaguchi, S. Macromolecules 2007, 40, 3898−3900. (c) 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. (d) Kim, Y.;
Gabbai, F. P. J. Am. Chem. Soc. 2009, 131, 3363−3369. (e) Chiu, C.-
W.; Kim, Y.; Gabbai, F. P. J. Am. Chem. Soc. 2009, 131, 60−61.
(f) Hudson, Z. M.; Liu, X. Y.; Wang, S. N. Org. Lett. 2011, 13, 300−
303.
(7) P, C. A. S.; Mukherjee, S.; Thilagar, P. Chem. Commun. 2013, 49,
993−995.
(8) Hudson, Z. M.; Sun, C.; Helander, M. G.; Chang, Y,-L.; Lu, Z.-
H.; Wang, S. J. Am. Chem. Soc. 2012, 134, 13930−13933.
(9) Das, S.; Alexeev, V. L.; Sharma, A. C.; Geib, S. J.; Asher, S. A.
Tetrahedron Lett. 2003, 44, 7719−7722.
́
(10) Yuan, Z.; Entwistle, C. D.; Collings, J. C.; Albesa-Jove, D.;
Batsanov, A. S.; Howard, J. A. K.; Taylor, N. J.; Kaiser, H. M.;
Kaufmann, D. E.; Poon, S.; Wong, W. Y.; Jardin, C.; Fathallah, S.;
Boucekkine, A.; Halet, J.-F.; Marder, T. B. Chem. Eur. J. 2006, 12,
2758−2771.
(11) (a) Adams, H.; Harris, K. D. M.; Hernbury, G. A.; Hunter, C.
A.; Livingstone, D.; McCabe, J. F. Chem. Commun. 1996, 2531−2532.
(b) Kumita, H.; Kato, T.; Jitsukawa, K.; Einaga, H.; Masuda, H. Inorg.
Chem. 2001, 40, 3936−3942. (c) Gohlke, H.; Klebe, G. Angew. Chem.,
Int. Ed. 2002, 41, 2644−2676. (d) Gavezzotti, A. CrystEngComm 2003,
5, 429−438. (e) Gavezzotti, A. CrystEngComm 2003, 5, 439−446.
(12) (a) Pan, H.; Fu, G.−L.; Zhao, Y.-H.; Zhao, C.-H. Org. Lett.
2011, 13, 4830−4833. (b) Fu, G.-L.; Zhang, H.-Y.; Yan, Y.-Q.; Zhao,
C.-H. J. Org. Chem. 2012, 77, 1983−1990.
(13) Frisch, M. J. et al. Gaussian 09, revision C.01; Gaussian, Inc.,
Wallingford, CT, 2010. See ref 1 in the Supporting Information for the
complete citation.
(14) (a) Yamaguchi, S.; Shirasaka, T.; Tamao, K. Org. Lett. 2000, 26,
4129−4132. (b) Yamaguchi, S.; Shirasaka, T.; Tamao, K. Org. Lett.
2002, 26, 4129−4132.
(15) (a) Rettig, W. Angew. Chem., Int. Ed. Engl. 1986, 25, 971−988.
(b) Hoffend, C.; Schodel, F.; Bolte, M.; Larner, H.-W.; Wagner, M.
Chem. Eur. J. 2012, 18, 15394−15405. (c) Wang, J.; Wang, Y.;
Taniguchi, T.; Yamaguchi, S.; Irle, S. J. Phys. Chem. A 2012, 116,
1151−1158. (d) Taniguchi, T.; Wang, J.; Irle, S.; Yamaguchi, S. Dalton
Trans. 2013, 42, 620−624.
3133
dx.doi.org/10.1021/om301197f | Organometallics 2013, 32, 3129−3133