Perfluoroaryl-substituted boron dipyrrinato complexes

Article abstract of DOI:10.1021/om900402e

A methodology for the incorporation of fluoroaryl groups into boron dipyrrinato complexes (modified BODIPY dyes) is reported. Two hexaalkylated dipyrrinato ligands with either H or CH₃ occupying the meso position were employed; when they were t

Full text of DOI:10.1021/om900402e

Organometallics 2009, 28, 4845–4851 4845
DOI: 10.1021/om900402e
Perfluoroaryl-Substituted Boron Dipyrrinato Complexes
Catherine Bonnier,† Warren E. Piers,*,† Adeeb Al-Sheikh Ali,‡ Alison Thompson,*,‡ and
Masood Parvez†
†Department of Chemistry, University of Calgary, 2500 University Drive N.W., Calgary, Alberta, Canada
T2N 1N4, and ‡Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J3
Received May 15, 2009
A methodology for the incorporation of fluoroaryl groups into boron dipyrrinato complexes
(modified BODIPY dyes) is reported. Two hexaalkylated dipyrrinato ligands with either H or CH3
occupying the meso position were employed; when they were treated with fluoroaryl haloboranes in
the presence of a weak base, the title compounds were prepared in good to excellent yields. The
structures of seven derivatives were determined using X-ray crystallography, and their spectroscopic,
photophysical, and redox properties are compared.
Introduction
development of cassettes in which a strongly absorbing
group is attached to the BODIPY core.1 Recently, research-
ers have also begun to explore the substitution of the fluoride
ligand(s) to produce new BODIPY dyes with aryl,7 alkynyl,8
and alkoxy9 substituents on boron in an effort to modulate
the Stokes shift.10 To this end, we became interested in
substituting the fluoride substituents with highly electron
withdrawing pentafluorophenyl groups11 and investigating
the properties of the resulting derivatives. We expected the
new complexes to be particularly stable due to the chemical
inertness of perfluorinated groups.
In this paper, a synthetic method for preparing mono- and
bis-substituted perfluorinated aryl BODIPY dyes is de-
scribed, using two dipyrrinato ligands that differ by the
presence or absence of a methyl group at the 8-position
(meso) (Chart 1). The scope and limitations of the method,
which may be generalizable to other BODIPY derivatives,
are discussed.
Dipyrrinato complexes incorporating boron (BODIPY,
LBF2, Scheme 1)1 are used in various applications such as
biological labeling,2 dye lasers,3 and ion sensing4 because of
their favorable photophysical characteristics. These dyes
exhibit high absorptivity and generally fluoresce with excel-
lent efficiency; furthermore, they demonstrate a high level of
photostability. Synthetic procedures have been developed to
install a variety of functional groups at different positions on
the dipyrrinato core in order to further improve their stabi-
lity and/or finely tune their photo- and electrochemical
properties.5,6
Despite their useful properties, areas for improvement
remain. Specifically, known BODIPY dyes generally exhi-
bit small Stokes shifts. Various strategies to address this
issue have been employed, the most successful being the
*To whom correspondence should be addressed. E-mail: wpiers@
ucalgary.ca (W.E.P.); alison.thompson@dal.ca (A.T.).
Results and Discussion
(1) Loudet, A.; Burgess, K. Chem. Rev. 2007, 107, 4891.
(2) (a) Wanninger-Weiss, C.; Di Pasquale, F.; Ehrenschwender, T.;
Marx, A.; Wagenknecht, H.-A. Chem. Commun. 2008, 1443. (b) Janjic
J. M.; Srinivas, M.; Kadayakkara, D. K. K.; Ahrens, E. T. J. Am. Chem. Soc.
2008, 130, 2832. (c) Haugland, R. P. In The Handbook A guide to
Fluorescent Probes and Labeling Technologies, 10th ed.; Spence, M. T.
Z., Ed.; Molecular Probes: Eugene, OR, 2007.
Synthesis. Ziessel and co-workers prepared B-aryl func-
tionalized BODIPY dyes by reaction of LMeBF2 with aryl
Grignard or aryllithium reagents to afford the mono- and
bis-aryl derivatives, respectively.7 Accordingly, reaction of
L
MeBF2 with C6F5MgBr12 yielded the mono-C6F5 complex
1-LMe, albeit in a moderate isolated yield of 40% (Scheme 1),
similar to that achieved by Ziessel for the C6H5-substituted
analogue.7 Use of 2 equiv of the (fluoroaryl)lithium reagent
C6F5Li13 produced only small amounts (5-10%) of the
desired bis-pentafluorophenyl complex 2-LMe, in contrast
with the 34% yield obtained for the analogous bis-phenyl
complex.7 The lack of stability of the (fluoroaryl)lithium
(3) Arbeloa, T. L.; Arbeloa, F. L.; Arbeloa, I. L.; Garcı
´
a-Moreno, I.;
Costela, A.; Sastre, R.; Amat-Guerri, F. Chem. Phys. Lett. 1999, 299,
315.
(4) (a) Huh, J. O.; Do, Y.; Lee, M. H. Organometallics 2008, 27, 1022.
(b) Qin, W.; Baruah, M.; Sliwa, M.; Van der Auweraer, M.; De Borggraeve,
W. M.; Beljonne, D.; Van Averbeke, B.; Boens, N. J. Phys. Chem. A 2008,
112, 6104. (c) Wu, Y.; Peng, X.; Guo, B.; Fan, J.; Zhang, Z.; Wang, J.; Cui, A.;
Gao, Y. Org. Biomol. Chem. 2005, 3, 1387. (d) Bricks, J. L.; Kovalchuk, A.;
Trieflinger, C.; Nofz, M.; B€uschel, M.; Tolmachev, A. I.; Daub, J.; Rurack, K.
J. Am. Chem. Soc. 2005, 127, 13522. (e) Zeng, L.; Miller, E. W.; Pralle, A.;
Isacoff, E. Y.; Chang, C. J. J. Am. Chem. Soc. 2006, 128, 10.
(5) (a) Wood, T. E.; Thompson, A. Chem. Rev. 2007, 107, 1831. (b) Ulrich,
G.; Ziessel, R.; Harriman, A. Angew. Chem., Int. Ed. 2008, 47, 1184.
(6) (a) Umezawa, K.; Matsui, A.; Nakamura, Y.; Citterio, D.;
Suzuki, K. Chem. Eur. J. 2009, 15, 1096. (b) Ventura, B.; Marconi, G.;
Broering, M.; Kruger, R.; Flamigni, L. New J. Chem. 2009, 33, 428.
(c) Cakmak, Y.; Akkaya, E. U. Org. Lett. 2009, 11, 85. (d) Rio, Y.;
Sanchez-Garcia, D.; Seitz, W.; Torres, T.; Sessler, J. L.; Guldi, D. M. Chem.
Eur. J. 2009, 15, 3956.
Chart 1
r
2009 American Chemical Society
Published on Web 07/24/2009
pubs.acs.org/Organometallics

4846 Organometallics, Vol. 28, No. 16, 2009
Bonnier et al.
Scheme 1
Scheme 2
complex has previously been suspected of being suscep-
tible to deprotonation.8d Thus, when LHBF2 was treated
with C6F5MgBr, the isolated yield of the mono-C6F5 com-
plex 1-LH was significantly lower (less than 5%) than that
found for the LMe derivative. Moreover, the reaction with
2 equiv of C6F5Li gave the monofluoro-substituted complex
1-LBu in small amounts as the only isolated product
(Scheme 1). The structure of 1-LBu and the presence of
the meso-butyl group was confirmed using X-ray crystal-
lography (see the Supporting Information for details). Here,
the second equivalent of C6F5Li presumably deprotonates
the meso position, and subsequent butylation occurs via
reaction with nBuBr, the byproduct formed in the preceding
step involving generation of C6F5Li from C6F5Br and nBuLi.
Substitution of the meso proton by lithio reagents has
previously been suggested to account for the low yields
obtained in the preparation of boron-substituted alkynyl
derivatives.8d Clearly, this synthetic route is not viable for
the preparation of the desired boron perfluoroaryl dipyrri-
nato compounds, and thus higher yielding approaches
were sought.
Scheme 3
To do this, we turned to the use of perfluoroaryl halobor-
ane reagents such as C6F5BF215 and (C6F5)2BCl13 to prepare
1-L and 2-L, respectively (Scheme 2). A similar strategy
has been used to prepare bis-alkyl-substituted BODIPYs.16
In this methodology, only a mild base is required to neu-
tralize and sequester the HX (X=Br, Cl, F) byproducts
of complex formation. Thus, the addition of a haloborane
to a solution of LH or LMe and triethylamine immediately
gave dark red solutions that fluoresced yellow under irradia-
tion with a UV lamp. The isolated yields of compounds
1-L and 2-L prepared via this route were significantly higher
than those obtained using the previous methodology, con-
firming the convenience of this synthetic strategy, provided
that suitable Ar3-nBXn (n=1, 2) reagents are available.
Moreover, the crude products are cleaner, thereby simplify-
ing the purification procedure to involve either a short
chromatographic column or even filtration through a silica
plug. The lower yields for the reactions producing mono-
C6F5 compounds 1-L by this method have two causes. One
has to do with the difficulty in handling the C6F5BF2 reagent,
reagents14 at temperatures above -40 °C may be behind the
poor yields in these reactions.
This approach was even less successful for LHBF2, where
the meso H substituent of the boron difluorodipyrrinato
(7) Goze, C.; Urich, G.; Mallon, L. J.; Allen, B. D.; Harriman, A.;
Ziessel, R. J. Am. Chem. Soc. 2006, 128, 10231.
(8) (a) Ulrich, G.; Goze, C.; Guardigli, M.; Roda, A.; Ziessel, R.
Angew. Chem., Int. Ed. 2005, 44, 3694. (b) Goeb, S.; Ziessel, R. Org. Lett.
2007, 9, 737. (c) Goze, C.; Ulrich, G.; Ziessel, R. Org. Lett. 2006, 8, 4445.
(d) Goze, C.; Ulrich, G.; Ziessel, R. J. Org. Chem. 2007, 72, 313. (e) Goeb,
S.; Ziessel, R. Org. Lett. 2007, 9, 737. (f) Bonardi, L.; Ulrich, G.; Ziessel, R.
Org. Lett. 2008, 10, 2183.
(9) (a) Kim, H.; Burghart, A.; Welch, M. B.; Reibenspies, J.; Burgess,
K. Chem. Commun. 1999, 1889. (b) Gabe, Y.; Ueno, T.; Urano, Y.; Kojima,
H.; Nagano, T. Anal. Bioanal. Chem. 2006, 386, 621. (c) Tahtaoui, C.;
ꢀ
Thomas, C.; Rohmer, F.; Klotz, P.; Duportail, G.; Mely, Y.; Bonnet, D.;
Hibert, M. J. Org. Chem. 2007, 72, 269.
(10) Ziessel, R.; Ulrich, G.; Harriman, A. New J. Chem. 2007, 31, 496.
(11) Piers, W. E. Adv. Organomet. Chem. 2005, 52, 1–77.
(12) Cowley, A. H.; Cushner, M.; Fild, M.; Gibson, J. A. Inorg.
Chem. 1975, 14, 1851.
(13) Parks, D. J.; Piers, W. E.; Yap, G. P. A. Organometallics 1998,
17, 5492.
(15) Frohn, H.-J.; Franke, H.; Fritzen, P.; Bardin, V. V. J. Organo-
met. Chem. 2000, 598, 127.
(16) Kee, H. L.; Kirmaier, C.; Yu, L.; Thamyongkit, P.; Youngblood,
W. J.; Calder, M. E.; Ramos, L.; Noll, B. C.; Bocian, D. F.; Scheidt, W.
R.; Birge, R. R.; Lindsey, J. S.; Holten, D. J. Phys. Chem. B 2005, 109,
20433.
(14) Coe, P. L.; Stephens, R.; Tatlow, J. C. J. Chem. Soc. 1962, 3227.

Article
Organometallics, Vol. 28, No. 16, 2009 4847
which is a highly volatile, air- and moisture-sensitive liquid.15
The other is that detectable amounts (up to 15%) of LRBF2
complexes (produced via loss of C6F5H) are observed,
indicating that this is a competing process using the
C6F5BF2 reagent.
Scheme 4
This methodology can be employed to prepare perfluor-
oaryl BODIPY derivatives that would be challenging to
prepare via a Grignard or aryllithium-based methodology.7
For example, preparation of the spiro BODIPY complexes
3-L (Scheme 3) would first require dilithiation or two
successive lithiations of a 2,20-dihaloperfluorobiphenyl deri-
vative17 followed by LiF elimination of the LRBF2 BODIPY
precursor. The higher temperatures necessary (i.e., room
temperature)7 for the latter step preclude the use of an
unstable dilithio perfluorobiphenyl reagent. However, using
the perfluorinated 9-bromoborafluorene C12F8BBr17 in the
methodology of Scheme 2 rapidly gave the desired pro-
ducts as depicted in Scheme 3, demonstrating the applic-
ability of this strategy to other haloboranes. The reason
for the low yield observed for 3-LMe is not clear but may
be related to tautomerization of the dipyrrin to the vinyl
dipyrrole.18
chemical shifts found for other BF2 dipyrrinato com-
plexes.21
The 11B{1H} signal for all compounds is found around
0 ppm, as expected for neutral, tetracoordinated boron
compounds.22 In compounds 1, a 1JBF coupling of ∼60 Hz
was resolved, unlike in the unfluorinated mono-aryl com-
plexes previously reported.7 In the 19F NMR spectra, the BF
signal of compounds 1 is broadened due to further coup-
ling with the ortho fluorine atoms (19F-19F COSY) of the
B-ArF groups and the BF coupling constant could not be
extracted from these spectra.
Monitoring these reactions using NMR spectroscopy
shows that, upon mixing an equimolar amount of LH.HBr
with (C6F5)2BCl or C12F8BBr, an adduct between the halo-
borane and the ligand was quantitatively formed. Upfield
shifts of the 11B NMR resonances to 2.3 and -1.9 ppm for
(C6F5)2BCl or C12F8BBr, respectively, as well as changes in
1
the H and 19F NMR chemical shifts, were consistent with
The compounds were also characterized using mass
spectrometric techniques (ESI or EI), and the analyses of
the spectra for compounds 1-LR and 2-LR revealed infor-
mative fragmentation patterns. For example, detection
of BODIPY borenium ions19,23 A (m/z 285.1 and 298.8, for
R=H, Me, respectively) and B (m/z 433.0 and 446.7) in the
positive ion ESI mode suggests that loss of the pentafluoro-
phenyl anion (C6F-5 ) is facile from both families of compounds;
the assignment of these orange, non-fluorescent intermedi-
ates as Lewis acid/base complexes between the haloboranes
and LH.HBr. Upon subsequent addition of 2 equiv of NEt3
to the NMR tube, signals for the final/isolated products were
rapidly observed.
Characterization. NMR Spectroscopy and Mass Spectro-
metry. All compounds were characterized using multinuclear
1
NMR H, 11B, 13C{1H}, and 19F spectroscopy, in CDCl3
solvent; in the LH series, 15N NMR spectroscopy was also
examined. The resonances most affected by structural
variations at boron are those for the methyl substituents,
and the meso-proton resonances in the LH derivatives. In
general, the resonances of the methyl groups move upfield
as the Lewis acidity of the haloborane starting material
increases. An opposite but less significant trend is observed
for the meso proton of the LH derivatives; while the chemi-
cal shifts of the meso proton for 1-LH and 2-LH are essen-
tially identical (7.08 and 7.07 ppm, respectively), the reso-
nance of this proton is shifted downfield for 3-LH (7.23 ppm).
It has been previously observed that the electron density
at boron influences the chemical shift of that particular
proton (i.e., an electron-deficient boron center will move this
signal to lower fields).19 The 15N chemical shifts for com-
pounds 1, 2, and 3-LH of -193.1, -198.3, and -204.8 ppm,
respectively,20 also reflect the trend in increasingly Lewis
acidic boron centers and are generally consistent with
indeed, this anion was observed (m/z 166.8) in negative
ion mode. The absence of B in the spectra of compounds 1
suggests that loss of the pentafluorophenyl anion is more
facile than loss of F-, as expected, due to the greater
stability of C6F-5 versus fluoride. Because of the chela-
tion of the ArF group in compounds 3, borenium ion
formation is not observed when these compounds are
subjected to mass ESI spectrometric analysis; instead,
losses of various alkyl groups (methyl and ethyl) from the
dipyrrinato core constitute the dominant fragmentation
pathways.
The viability of A and B was confirmed with separate
synthetic experiments; ion A has previously been fully
(17) Chase, P. A.; Piers, W. E.; Patrick, B. O. J. Am. Chem. Soc. 2000,
122, 12911.
(18) Al-Sheikh Ali, A.; Cipot-Wechsler, J.; Cameron, T. S.; Thompson,
A. J. Org. Chem. 2009, 74, 2866.
(21) Wood, T. E.; Berno, B.; Beshara, C. S.; Thompson, A. J. Org.
Chem. 2006, 71, 2964.
(22) Kennedy, J. D. In Multinuclear NMR; Mason, J., Ed.; Plenum
Press: New York, 1987; Chapter 8.
(23) Piers, W. E.; Bourke, S. C.; Conroy, K. D. Angew. Chem., Int.
(19) (a) Bonnier, C.; Piers, W. E.; Parvez, M.; Sorensen, T. S. Chem.
Commun. 2008, 4593. See also: (b) Hudnall, T. W.; Gabbaï, F. P. Chem.
Commun. 2008, 4596.
(20) Cipot-Wechsler, J.; Al-Sheikh Ali, A.; Chapman, E. E.; Cameron,
T. S.; Thompson, A. Inorg. Chem. 2007, 46, 10947.
Ed. 2005, 44, 5017.

4848 Organometallics, Vol. 28, No. 16, 2009
Bonnier et al.
Figure 1. Thermal ellipsoid diagrams (50%) of compounds 1-LH-3-LH. Selected metrical parameters can be found in Table 1.
Figure 2. Thermal ellipsoid diagrams (50%) of compounds 1-LMe-3-LMe. Selected metrical parameters can be found in Table 1.
˚
Table 1. Selected Bond Distance (A) and Angle (deg) Data for 1-
LR-3-LR
B-F
B-N
B-C
N-B-N
C-B-C
1-LH
2-LH
1.400(3)
1.555(3)
1.556(3)
1.588(2)
1.575(3)
1.646(3)
106.90(17)
1.664(3)
1.662(3)
106.82(14)
115.99(14)
3-LH
cis
1.558(5)
1.566(5)
1.552(5)
1.560(5)
1.545(3)
1.541(3)
1.557(2)
1.575(2)
1.561(3)
1.561(3)
1.623(5)
1.625(6)
1.620(6)
1.631(5)
1.650(3)
107.2(3)
97.7(3)
97.0(3)
trans
107.7(3)
1-LMe
2-LMe
3-LMe
1.410(3)
106.31(16)
105.47(13)
106.8(2)
1.667(2)
1.645(2)
1.631(3)
1.631(3)
116.19(13)
98.0(2)
Figure 3. Thermal ellipsoid (50%) diagram of the cationic por-
tion of 5-LH. Selected bond distances (A): B(1)-F(1), 1.566(5);
B(2)-F(1), 1.576(5); B(1)-N(1), 1.532(5); B(1)-N(2), 1.524(5);
B(2)-N(3), 1.528(5); B(2)-N(4), 1.537(5); B(1)-C(19), 1.635(6);
B(2)-C(43), 1.636(5). Selected bond angle (deg): B(1)-F(1)-
B(2), 131.7(3).
spectrometric data and the synthetic chemistry suggest the
viability of a larger family of borenium ions beyond those we
recently reported.19a
Structures. Compounds 1-LR-3-LR and 5-LH were ob-
tained as crystalline materials, and X-ray crystallographic
analysis was performed on the seven derivatives (Figures 1-
3 and Table 1). The structures of compounds 1-3 display
similar features, including a distorted-tetrahedral geometry
at the boron center, an essentially planar dipyrrinato
core (including boron), and generally similar, unremarkable
bond distances for bonds to boron. The dipyrrinato core
was found to be more distorted in the LMe derivatives;
DFT and semiempirical calculations on different LBF2
compounds have shown that methylation of the 1- and
characterized as its [B(C6F5)4]- salt,19a while B was gener-
ated as its N(Tf)-2 salt (4-LH), as shown in Scheme 4. The
borenium ion 4-LH was not isolated, but its NMR spectro-
scopic features are consistent with its proposed formulation,
particularly the broad 11B resonance at 19 ppm. When only
1
/
2
equiv of the Me3SiN(Tf)2 reagent was employed, the
Lewis acidic boron center in 4-LH was quenched by the
1
remaining
/
2
equiv of 1-LH to form a fluoride-bridged
dimer, 5-LH, which was characterized by NMR spectroscopy
and X-ray crystallography (see below). Together, the mass

Article
Organometallics, Vol. 28, No. 16, 2009 4849
Table 2. Electronic Spectroscopic Data for Compounds 1-3
max (nm)c max (M-1 cm-1 b flu (nm)b Stokes shift (cm-1 b
max (nm)a
λ
max (nm)b
λ
ε
)
λ
)
Φflu
τ
flu (ns)b
b
λ
1-LH
534
528
529
524
525
519
532
527
527
521
523
518
527
523
522
517
519
514
55 586
66 410
29 641
28 417
25 563
37 660
541
544
533
540
566
537
313
593
213
675
1452
646
0.78
0.65
0.67
0.61
0.34
0.92
7.0
7.3
7.3
6.6
3.9
7.0
2-LH
3-LH
1-LMe
2-LMe
3-LMe
a Recorded in deoxygenated cyclohexane solution. b Recorded in deoxygenated dichloromethane solution. c Recorded in deoxygenated acetonitrile
solution.
Table 3. Electrochemical Data for Compounds 1-3
E1/2 (V)
7-positions of the dipyrrinato core in LBF2 induces distor-
tion of the central C3N2B ring because of the steric interac-
tion with the meso-methyl group.24 The ethyl groups for 1-3
are mainly arranged transoid to each other with respect to
the dipyrrin plane, with the exception of 1-LH (cisoid) and 3-
LH (both conformations are found in two independent
molecules in the unit cell). The spatial orientations of the
ethyl groups are probably governed by packing effects,
wherein dipyrrin-dipyrrin or ArF-ArF interactions are
balanced.
L•þ/L
L/L•-
HOMO-LUMO gap (eV)a
1-LH
þ1.05
þ1.03
þ1.01
þ1.04
þ1.01
þ1.07
-1.32
-1.41
-1.50
-1.42
-1.50
-1.46
2.19
2.25
2.25
2.27
2.32
2.31
2-LH
3-LH
1-LMe
2-LMe
3-LMe
a Measured at onset.
The molecular structure of dimeric 5-LH is shown in
Figure 3, along with selected metrical data; the N(Tf)2
counterion is not shown. The cation shown can be viewed
as a Lewis acid/base adduct between 1-LH and 4-LH,
although the B(1)-F(1)-B(2) bridge is essentially symmetric
in terms of the boron-fluorine distances observed. The
angle subtended at the bridging fluorine is 131.7(3)°, and
the two dipyrrinato moieties are twisted about the B(1)-
F(1)-B(2) plane to minimize steric repulsions. The two C6F5
groups are similarly rotated away from each other in this
conformation.
Photophysical and Electrochemical Properties. Absorp-
tion and emission spectra of all derivatives show the usual
characteristics of BODIPY dyes;5 the data are summa-
rized in Table 2 ,and typical spectra are given in Figures S2
and S3 (Supporting Information) for LH and LMe complexes,
respectively. The most intense absorption is centered at
∼525 nm and is associated with the S0 f S1 (HOMO-
LUMO) transition; in addition, a less intense S0 f S2
absorption at 360 nm is observed; emission occurs at
∼540 nm. The energy of the maximum absorption and
emission is red-shifted by 5 nm in comparison with the
parent aryl compounds;7 the Stokes shift remains constant
and small for all derivatives, except 2-LMe. The quantum
yields, obtained using rhodamine 6G as a standard, vary
somewhat with the nature of the perfluoroaryl substitution
at boron. In the LMe series, mono-fluorides 1 are more
efficient emitters than the bis-perfluoroaryls 2, meaning that
C6F-5 offers more degrees of freedom for dissipating energy
than does F-. However, the chelating nature of the 9-
borafluorene unit rigidifies this biaryl unit and compounds
3 deliver the highest quantum yield of the series. The values
for the LH derivatives are more consistent and do not
obviously show this trend.
fluorinated aryl groups. Cyclic voltammetry experiments
were conducted, and all compounds showed a reversible
one-electron oxidation and reduction process (Table 3).
The E1/2 values for both processes are 0.25 V more positive
than for their aryl counterparts, as expected from the pre-
sence of the perfluoroaryl group. The observed good agree-
ment between the optical and electrochemical band gaps
confirms that these processes are dipyrrinato ligand cen-
tered.7 In addition to the reversible processes described
above, compounds 2-LH and 3-LH exhibit additional elec-
trochemical activity at intermediate potentials that are likely
due to decomposition of the radical cations formed upon
oxidation.25
In conclusion, six BODIPY complexes incorporating
fluoroaryl groups at the boron center were synthesized using
a novel methodology which complements that developed for
synthesizing nonfluorinated analogues. Electronic spectros-
copy indicates that these perfluoroaryl-substituted boron
dipyrrinato complexes exhibit behavior consistent with re-
lated compounds but that they are more electrochemically
stable toward oxidation.
Experimental Section
General Procedures and Equipment. All operations were per-
formed under a purified argon atmosphere using glovebox
or vacuum line techniques. Toluene and hexanes solvents were
dried and purified by passing through activated alumina and
then vacuum-distilled from Na/benzophenone. NEt3 and
CH2Cl2 were dried over and distilled from CaH2. Silica gel
column chromatography was carried out on Geduran Silica
60 silica gel (particle size 40-63 μm). All NMR spectra were
recorded in dry, oxygen-free CDCl3 on Bruker AMX-300 MHz,
DRX-400 MHz, and AVANCE 500 MHz spectrometers
(operating at 300 and 400 MHz (1H), 128 MHz (11B), 75 MHz
(13C), 50.67 MHz (15N), and 282 or 376 MHz (19F)) at 25 °C,
unless indicated. Chemical shifts are reported in ppm relative
The absorption characteristics for compounds 1-3 sug-
gest that the perfluoroaryl-substituted BODIPY complexes
possess an optical band gap similar to that of their non-
fluorinated aryl derivatives. However, electrochemical data
show that the energies of the HOMO and LUMO orbitals
were altered by the presence of the more electronegative
to residual solvent signal (1H and 13C{1H}), BF3 OEt2
3
(11B{1H}), and C6F6 (19F) standards. The labeling scheme
´
(24) Prieto, J. B.; Arbeloa, F. L.; Martınez, V. M.; Arbeloa, I. L.
Chem. Phys. 2004, 296, 13.
(25) Lai, R. Y.; Bard, A. J. J. Phys. Chem. B 2003, 107, 5036.

4850 Organometallics, Vol. 28, No. 16, 2009
Bonnier et al.
shown below is utilized in making the 1H and 19F NMR
spectroscopic assignments:
pentafluorophenyl carbons were not observed. 11B{1H} NMR
(CDCl3, 128 MHz): δ 0.23 (d, 1JBF = 59 Hz). 19F NMR (CDCl3,
282 MHz): δ -135.9 (m, 2 F, o-F), -157.3 (t, 1 F, J = 20 Hz,
p-F), -163.8 (broad, 3 F, m-F and BF). EI (m/z (nature of peak,
relative intensity)): 452.0 ([M]þ, 46), 285.1 ([M - C6F5]þ, 100).
Anal. Calcd for C23H23N2BF6: C, 61.08; H, 5.13; N, 6.19.
Found: C, 61.14; H, 5.20; N, 6.02.
Synthesis of 2-LH. To a solution of LHH HBr (40 mg,
3
0.14 mmol) in CH2Cl2 (15 mL) was added triethylamine
(40 μL, 0.28 mmol), and the solution was stirred for 15 min.
A solution of (C6F5)2BCl (52 mg, 0.14 mmol) in CH2Cl2 (15 mL)
was added, and the mixture was stirred for 15 min. Volatiles
were removed in vacuo, and the red solution was passed
through a plug of silica (CH2Cl2/hexanes 3/2) to yield the
desired compound (73 mg, 0.12 mmol, 89%). 1H NMR
(CDCl3, 300 MHz): δ 7.07 (s, 1 H, H-meso), 2.36 (q, 4 H,
3JHH=7.6 Hz, 2-CH2CH3), 2.21 (s, 6 H, 1-CH3), 1.89 (s, 6 H,
3-CH3), 1.02 (t, 6 H, 2-CH2CH3). 13C{1H} NMR (CDCl3,
100 MHz): 154.6 (C3), 136.6 (C1), 132.4 (q), 132.2 (C2), 119.3
(C-meso), 17.6 (2-CH2CH3), 14.4 (2-CH2CH3), 13.4 (3-CH3),
9.4 (1-CH3), pentafluorophenyl carbons were not observed.
11B{1H} NMR (CDCl3, 128 MHz): -5.53 (s). 19F NMR
(CDCl3, 282 MHz): -133.4 (m, 4 F, o-F), -156.7 (t, 2 F,
3JFF=20 Hz, p-F), 163.4 (m, 4 F, m-F). UV-vis (CH2Cl2; λ,
nm (ε, M-1 cm-1)): 527 (66 410), 368 (5897), 295 (4017). EI (m/z
(nature of peak, relative intensity)): 600.0 ([M]þ, 81), 433.0
([M - C6F5]þ, 100). Anal. Calcd for C29H23N2BF10: C, 58.02;
H, 3.86; N, 4.67. Found: C, 58.00; H, 3.91; N, 4.46.
Low-resolution mass spectra were obtained using a Bruker
Esquire 3000 spectrometer operating in electrospray ionization
(ESI) mode or using a Finnigan MAT SSQ7000 operating at
70 eV in electron impact (EI) mode. Fluorescence spectra were
obtained using Yvon-Jobin and Cary Eclipse spectrophot-
ometers with excitation and emission set to a 1.0 nm bandpass,
and UV-visible spectra were obtained using Cary 100 Bio and
1E spectrophotometers operating in double-beam mode. Fluor-
escence quantum yield values were measured in CH2Cl2 and
reported relative to rhodamine 6G in methanol (Φflu=0.80).26
Fluorescence lifetime experiments were performed using a Jobin
Yvon Fluorolog Tau-3 lifetime system spectrophotometer using
Ludox solution (aqueous suspension of colloidal silica with zero
lifetime) as a light-scattering standard and a 500 nm filter. The
lifetime experiments were performed at an excitation wave-
length of 530 nm, with interleave processing, and modeled using
Δphase and Δmodulation values of 0.5 and 0.05, respectively.
Electrochemical studies were performed using an EG&G Model
283 potentiostat with a three-electrode cell: a platinum-wire
auxiliary electrode, a silver-wire pseudoreference electrode, and
a platinum-disk working electrode. Solutions were comprised of
1 mM test compound and 0.1 M [nBu4N][PF6] as the supporting
electrolyte in 5 mL of dry, deoxygenated CH2Cl2. All E1/2 values
were referenced internally to [Cp2Co][PF6] (E1/2=-0.87 V in
CH2Cl2 (vs SCE)). X-ray crystallographic analyses were per-
formed on suitable crystals coated in Paratone oil and mounted
on a Nonius Kappa CCD diffractometer. Crystals were grown
by dissolving samples in a minimum of CH2Cl2 and layering
with hexanes, unless otherwise noted. Elemental analyses were
performed using a Perkin-Elmer Model 2400 Series II analyzer
by Johnson Li (University of Calgary). The solvent mixtures are
given in volume/volume (v/v) ratio.
Synthesis of 3-LH. To a solution of LHH HBr (36 mg,
3
0.12 mmol) in CH2Cl2 (10 mL) was added triethylamine
(34 μL, 0.24 mmol), and the solution was stirred for 15 min.
A solution of BrB(C12F8) (44 mg, 0.12 mmol) in CH2Cl2 (10 mL)
was added, and the mixture was stirred for 15 min. Volatiles
were removed in vacuo, and the red solution was passed through
a plug of silica (toluene/hexanes 3/2), to yield the desired
compound (42 mg, 0.075 mmol, 62%). 1H NMR (CDCl3,
3
300 MHz): δ 7.23 (s, 1 H, H-meso), 2.30 (q, 4 H, JHH
7.5 Hz, 2-CH2CH3), 2.26 (s, 6 H, 1-CH3), 1.54 (s, 6 H, 3-CH3),
0.99 (t, 6 H, 2-CH2CH3). 13C{1H} NMR (CDCl3, 100 MHz):
153.1 (C3), 135.8 (C1), 132.4 (q), 132.1 (C2), 119.7 (C-meso),
17.4 (2-CH2CH3), 14.6 (2-CH2CH3), 11.9 (3-CH3), 9.5 (1-CH3),
pentafluorophenyl carbons were not observed. 11B{1H} NMR
(CDCl3, 128 MHz): -2.23 (s). 19F NMR (CDCl3, 282 MHz):
-134.3 (m, 2 F, F1), -135.7 (m, 2 F, F4), -155.0 (m, 4 F, F2,3).
UV-vis (CH2Cl2; λ, nm (ε, M-1 cm-1)): 527 (29 641), 380
(156), 281 (6396), 236 (7176). CI (m/z (nature of peak, relative
intensity)): 563 ([M þ H]þ, 100). Anal. Calcd for C29H23-
N2BF8: C, 61.94; H, 4.12; N, 4.98. Found: C, 61.84; H, 3.87;
N, 4.63.
=
Materials. (C6F5)2BCl,13 BrB(C12F8),17 2,8-diethyl-1,3,7,9-
tetramethyldipyrrin hydrobromide (LHH HBr),20 2,8-diethyl-
3
1,3,7,9-tetramethyldipyrrin hydrochloride (LHH HCl),20 and
3
2,8-diethyl-1,3,5,7,9-pentamethyldipyrrin hydrochloride (LMe
-
H HCl)27 were prepared according to literature procedures.
3
C6F5BF215 was synthesized according to a modified preparation
where the product was not isolated from CH2Cl2 solvent and
was instead used as a solution. [Me3Si][N(SO2CF3)2] was pur-
chased from TCI America and used as received. The concentra-
tion of the solution was obtained by 19F NMR by using R,R,R-
trifluorotoluene as internal standard.
Synthesis of 1-LMe. To a solution of LMeH HCl (20 mg,
3
0.065 mmol) in CH2Cl2 (10 mL) was added triethylamine
(18 μL, 0.13 mmol) was added, and the solution was stirred
for 15 min. A solution of C6F5BF2 in CH2Cl2 (0.065 mmol) was
slowly added with a syringe, and the red solution was stirred for
15 min. Volatiles were removed in vacuo, and the solid was
purified by column chromatography on silica (hexanes/toluene,
3/2) to yield the desired compound (19 mg, 0.041 mmol, 62%).
1H NMR (CDCl3, 300 MHz): δ 2.69 (s, 3 H, CH3-meso), 2.38 (s,
6 H, 1-CH3), 2.35 (q, 4 H, 3JHH=7.3 Hz, 2-CH2CH3), 2.21 (s,
6 H, 3-CH3), 1.01 (t, 6 H, 2-CH2CH3). 13C{1H} NMR (CDCl3,
100 MHz): 151.5 (C3), 140.3 (C-meso), 136.1 (C1), 132.4
(C2), 131.7 (q), 17.1 (CH3-meso), 14.9 (2-CH2CH3), 14.5
(2-CH2CH3 or 1-CH3), 12.2 (2-CH2CH3 or 1-CH3), 12.1 (3-
CH3), pentafluorophenyl carbons were not observed. 11B{1H}
NMR (CDCl3, 128 MHz): -0.20 (d, 1JBF=63 Hz). 19F NMR
(CDCl3, 282 MHz): -135.7 (m, 2 F, o-F), -157.5 (t, 1 F,
3JFF=20 Hz, p-F), -162.9 (broad, 1 F, BF), -163.9 (m, 2 F,
m-F). UV-vis (CH2Cl2); λ, nm (ε, M-1 cm-1)): 521 (28 417), 362
(3000), 288 (7667), 265 (1025). ESI- (m/z (nature of peak,
relative intensity)): 464.57 ([M - H]-, 100), 166.78 ([C6F5]-,
Synthesis of 1-LH. LHH HBr (11 mg, 0.038 mmol) was
3
dissolved in CH2Cl2 (10 mL), and NEt3 (10 μL, 0.076 mmol).
After the mixture was stirred for 15 min at room tempera-
ture, a CH2Cl2 solution of C6F5BF2 (0.038 mmol) was added
dropwise with stirring. After 15 min, volatiles were removed
in vacuo and the compound was purified using column chro-
matography on silica (hexanes/toluene 3/2) to afford an orange
solid: Yield: 8 mg (0.018 mmol, 48%). 1H NMR (CDCl3,
300 MHz): δ 7.08 (s, 1 H, H-meso), 2.34 (q, 4 H, J=7.6 Hz,
2-CH2CH3), 2.21 (s, 6 H, 1-CH3), 2.20 (s, 6 H, 3-CH3), 1.03
(t, 6 H, 2-CH2CH3). 13C{1H} NMR (CDCl3, 100 MHz): δ 154.3
(C3), 136.5 (C1), 132.3 (q), 131.7 (C2), 119.1 (C-meso), 17.3
(2-CH2CH3), 14.5 (2-CH2CH3), 12.2 (3-CH3), 9.4 (1-CH3),
(26) Olmsted, J. J.III J. Phys. Chem. 1979, 83, 2581.
(27) Boyer, J. H.; Hagg, A. M.; Sathyamoorthi, G.; Soong, M.-L.;
Thangaraj, K.; Pavlopoulos, T. G. Heteroat. Chem. 1990, 1, 389.

Article
Organometallics, Vol. 28, No. 16, 2009 4851
62). Anal. Calcd for C24H25N2BF6: C, 61.82; H, 5.40; N, 6.01.
Found: C, 61.57; H, 5.47; N, 5.66.
(10 mg, 0.03 mmol in 0.4 mL) was added. The tube was capped
with a rubber septum, and NMR spectra were acquired. 1H
NMR (CD2Cl2, 400 MHz): δ 7.59 (s, 1H, H-meso), 2.41 (q, 4 H,
3JHH=7.6 Hz, 2-CH2CH3), 2.38 (s, 6 H, 3-CH3), 2.06 (s, 6 H,
1-CH3), 1.07 (t, 6H, 2-CH2CH3), 0.22 (d, 9 H, (CH3)3SiF,
2JSiH = 7.4 Hz). 13C{1H} NMR (CD2Cl2, 100 MHz): 158.5
(C3), 138.4 (C2), 135.3 (C1), 122.4 (C-meso), 17.8 (2-CH2CH3),
14.1 (2-CH2CH3), 13.8 (3-CH3), 10.9 (1-CH3), quaternary
and pentafluorophenyl carbons were not observed. 11B{1H}
NMR (CD2Cl2, 128 MHz): 19.1 (broad). 19F NMR (CD2Cl2,
376 MHz): -79.3 (6 F, CF3), -131.5 (broad, 2 F, o-F), -149.2
(broad, 1 F, p-F), -159.2 (broad, 2 F, m-F). EI (m/z (nature of
peak, relative intensity)): 433.25 ([M]þ, 100).
Synthesis of 2-LMe. To a solution of LMeH HCl (40 mg,
3
0.13 mmol) in CH2Cl2 (15 mL) was added triethylamine
(36 μL, 0.26 mmol), and the solution was stirred for 15 min.
A solution of (C6F5)2BCl (49 mg, 0.13 mmol) in CH2Cl2 (15 mL)
was added, and the mixture was stirred for 15 min. Volatiles
were removed in vacuo, and the crude solid was purified by
column chromatography on silica (hexanes/toluene, 3/2) to
yield the desired compound (53 mg, 0.086 mmol, 67%). 1H
NMR (CDCl3, 300 MHz): δ 2.61 (s, 3 H, CH3-meso), 2.36 (q,
4 H, 3JHH=7.6 Hz, 2-CH2CH3), 2.35 (s, 6 H, 1-CH3), 1.82 (s,
6 H, 3-CH3), 1.00 (t, 6 H, 2-CH2CH3). 13C{1H} NMR (CDCl3,
100 MHz): 152.1 (C3), 140.2 (C-meso), 136.2 (C1), 132.8 (C1 or
q), 132.6 (C1 or q), 18.1 (CH3-meso), 17.4 (2-CH2CH3), 14.8
(2-CH2CH3), 14.5 (1-CH3), 13.7 (3-CH3), pentafluorophenyl
carbons were not observed. 11B{1H} NMR (CDCl3, 128 MHz):
-6.00 (s). 19F NMR (CDCl3, 282 MHz): -134.6 (m, 4 F, o-F),
-156.9 (t, 2 F, 3JFF=20 Hz, p-F), -163.6 (m, 4 F, m-F). UV-vis
(CH2Cl2; λ, nm (ε, M-1 cm-1)): 523 (25 563), 368 (1625),
304 (5000). ESI- (m/z (nature of peak, relative intensity)):
612.92 ([M - H]-, 100), 166.91 ([C6F5]-, 33). Anal. Calcd for
C30H25N2BF10: C, 58.65; H, 4.10; N, 4.56. Found: C, 58.65; H,
4.15; N, 4.50.
Synthesis of 5-LH. To a CH2Cl2 solution of 1-LH (62 mg,
0.14 mmol in 10 mL) was added a solution of [Me3-
Si][N(SO2CF3)2] (24 mg, 0.07 mmol) in 5 mL of CH2Cl2 drop-
wise with stirring. The solution immediately turned dark blue
and was stirred for a further 15 min. Volatiles were removed in
vacuo, and the solid was dried. X-ray-quality crystals were
grown from a CH2Cl2/hexanes solution to afford 5-LH as purple
crystals (70 mg, 0.06 mmol, 86%). 1H NMR (CD2Cl2, 400 MHz,
3
278 K): δ 7.67 (s, 1H, H-meso), 2.39 (q, 4 H, JHH =7.6 Hz,
2-CH2CH3), 2.39 (s, 6 H, 3-CH3), 2.01, (s, 6 H, 1-CH3), 1.50 (t,
6H, 2-CH2CH3). 13C{1H} NMR (CD2Cl2, 100 MHz): 155.8
(C3), 134.4 (C1), 134.0 (q), 121.8 (C2), 118.6 (C-meso), 17.8
(2-CH2CH3), 14.4 (2-CH2CH3), 13.6 (3-CH3), 10.2 (1-CH3),
pentafluorophenyl carbons were not observed. 11B{1H} NMR
(CD2Cl2, 128 MHz, 278 K): 24.33 (broad). 19F NMR (CD2Cl2,
282 MHz): -79.2 (6 F, CF3), -130.3 (broad, o-F), -147.2
(broad, p-F), -157.8 (broad, m-F), the bridging F was not
observed.
Synthesis of 3-LMe. To a solution of LMeH HCl (41 mg,
3
0.13 mmol) in CH2Cl2 (15 mL) was added triethylamine
(36 μL, 0.26 mmol), and the solution was stirred for 15 min.
A solution of BrB(C12F8) (51 mg, 0.13 mmol) in CH2Cl2 (15 mL)
was added, and the mixture was stirred for 15 min. Volatiles
were removed in vacuo, and the remaining solid was purified by
column chromatography on silica (toluene/hexanes, 3:2) to yield
1
the desired compound (12 mg, 0.021 mmol, 16%). H NMR
(CDCl3, 300 MHz): δ 2.78 (s, 3 H, CH3-meso), 2.42 (s, 6 H,
1-CH3), 2.30 (q, 4 H, 3JHH=7.5 Hz, 2-CH2CH3), 1.53 (s, 6 H,
3-CH3), 0.96 (t, 6 H, 2-CH2CH3). 13C{1H} NMR (CDCl3,
100 MHz): 150.1 (C3), 140.9 (C-meso), 135.4 (C1), 132.8 (C2),
132.2 (q), 17.8 (CH3-meso), 17.3 (2-CH2CH3), 14.9 (2-CH2CH3
or 1-CH3), 14.8 (2-CH2CH3 or 1-CH3), 12.0 (3-CH3), penta-
fluorophenyl carbons were not observed. 11B{1H} NMR
(CDCl3, 128 MHz): -2.51 (s). 19F NMR (CDCl3, 282 MHz):
-134.4 (m, 2 F, 1-F), -135.8 (m, 2 F, 4-F), -155.1 (m, 4 F, 2-F
and 3-F). UV-vis (CH2Cl2; λ, nm (ε, M-1 cm-1)): 518 (52 885),
368 (4167), 271 (19 551), 233 (32 212). EI (m/z (nature of peak,
relative intensity)): 576.2 ([M]þ, 100), 561.2 ([M - CH3]þ, 49),
547 ([M - C2H5]þ, 36). Anal. Calcd for C30H25N2BF8: C, 62.52;
H, 4.37; N, 4.86. Found: C, 62.35; H, 4.46; N, 4.68.
Acknowledgment. This work was funded by the Nat-
ural Science and Engineering Research Council
(NSERC) of Canada in the form of Discovery Grants
to W.E.P. and A.T. C.B. thanks the NSERC and the
Alberta Ingenuity Fund for fellowship support. We are
grateful to Prof. Ray Turner (University of Calgary) for
access to his fluorimetry equipment.
Supporting Information Available: CIF files giving crystal-
lographic data for compounds 1-LBu, 1-LH, 2-LH, 3-LH, 1-LMe
,
2-LMe, 3-LMe, and 5-LH and figures giving excitation and
emission spectra for compounds 1-LH/Me-3-LH/Me. This ma-
terial is available free of charge via the Internet at http://pubs.
acs.org.
Generation of 4-LH. 1-LH (13 mg, 0.03 mmol) was loaded in
a NMR tube, and a CD2Cl2 solution of [Me3Si][N(SO2CF3)2]