5b,7b-diaza-3b,9b-diborabenzo[ghi]perylenes

Article abstract of DOI:10.1139/V10-009

Treatment of a precursor to the chelating Lewis acid 2,2′- diborabiphenyl with 2,6-bisalkynyl-substituted pyridazines, leads to elimination of 2 equiv. of ClSiMe₃; subsequent treatment of the mixture with PtCl₂ catalyzes the cyclizat

Full text of DOI:10.1139/V10-009

426
5b,7b-Diaza-3b,9b-diborabenzo[ ghi ]perylenes
Michael J.D. Bosdet, Warren E. Piers, Ted S. Sorensen, and Masood Parvez
Abstract: Treatment of a precursor to the chelating Lewis acid 2,2’-diborabiphenyl with 2,6-bisalkynyl-substituted pyrida-
zines, leads to elimination of 2 equiv. of ClSiMe3; subsequent treatment of the mixture with PtCl2 catalyzes the cyclization
of observable intermediates to the title 5b,7b-diaza-3b,9b-diborabenzo[ghi]perylene compounds in low isolated yields. The
compounds were characterized by NMR and UV–vis spectroscopies, and in one case, by X-ray crystallography. NICS(1)
computations indicate that the inner ring is less aromatic than the outer rings.
Key words: polycyclic aromatic hydrocarbons, boron heterocycles, nitrogen heterocycles, X-ray structure.
´
´
´
´
´
Resume : Le traitement d’un precurseur de l’acide de Lewis chelatant 2,2’-diborabiphenyle avec des pyridazines substi-
´
`
´
´
tuees dans les positions 2,6 par des groupes bisalkynyles conduit a l’elimination de deux equivalents de ClSiMe3; le traite-
´
´
´
`
ment subsequent du melange avec du PtCl2 catalyse la cyclisation des intermediaires observables et a la formation des
´
´
`
´
´
composes 5b,7b-diaza-3b,9b-diborabenzo[ghi]perylenes mentionnes dans le titre qui sont isoles avec de faibles rendements.
´
´ ´
´
´
Les composes ont ete caracterises par spectroscopies RMN et UV–vis et, dans un cas, par diffraction des rayons-X. Des
calculs NICS(1) indiquent que le noyau interne est moins aromatique que les cycles externes.
´
´ ´
´ ´
Mots-cles : hydrocarbures aromatiques polycycliques, heterocycles du bore, heterocycles de l’azote, structure par diffrac-
tion des rayons X.
´
[Traduit par la Redaction]
compounds we have studied extensively.11,12 While they ex-
hibit favorably modified redox and photophysical properties
relative to the all-carbon triphenylenes, they do not have
long-term stability to ambient conditions, limiting the scope
of their utility. We thus sought to implement the buttressing
strategy that was successful in stabilizing the BN-pyrenes
III and protect the bay region of the triphenylenes IV.
Herein, we report the synthesis of two examples of a 5b,7b-
diaza-3b,9b-diborabenzo[ghi]perylene framework, albeit in
low yields. The limitations of the approach will be discussed
along with the characterization of these intriguing com-
pounds.
Introduction
Transposition of C–C units for isoelectronic B–N modules
in polycyclic aromatic hydrocarbons offers a means of alter-
ing opto-electronic, redox, and chemical properties of these
important organic materials without dramatically affecting
their gross structural features.1–3 One of the most elementary
examples is the BN-biphenyl analog I (Chart 1), the pyri-
dine adduct of borabenzene, which has been known for
many years.4 Unlike biphenyl, I is susceptible to protonation
by Brønsted acids at the carbon alpha to boron,5,6 and facile
Diels–Alder addition with moderately active dienophiles,7
demonstrating the more reactive nature of the BN analog;
indeed, I is quite air- and moisture-sensitive and needs to
be handled accordingly.
Results and discussion
We have been interested in this strategy as a means of
producing novel organic electronic materials and have been
developing synthetic methods to novel BxNx hetercyclic ana-
logs of various PAH frameworks. For example, the BN-phe-
nanthrene8 and BN-pyrene9,10 derivatives II and III (Chart
1) can be prepared via formation of borabenzene pyridine
adducts wherein the pyridine unit is functionalized with al-
kynyl groups alpha to nitrogen. This buttressing of the B–N
bond has a stabilizing effect, in that compounds II can be
handled briefly in air, while pyrene analogs III can be
stored under ambient atmosphere indefinitely; indeed, they
are even unperturbed by treatment with aqueous HCl.
The B2N2-triphenylenes IV (Chart 1) are another class of
Engagement of the buttressing strategy for the stabiliza-
tion of the C2B2N2 heterocyclic core in compounds IV
(Chart 1) required first the synthesis of 3,6-di(alkynyl)pyri-
dazines 1a–1d, which in our hands was best-accomplished
by palladium-catalyzed coupling of 3,6-dichloropyridazine
with alkynylzinc compounds,13 as shown in Scheme 1. Ter-
minal alkynes were first deprotonated with nBuLi at –78 8C,
and subsequently transmetalated with ZnCl2 to generate the
required alkynylzinc reagents. The alkynylzinc compounds
were transferred onto a THF solution of the aryl chloride
and Pd catalyst and stirred for 24 h. After workup, the de-
sired substrates were obtained in low but workable yields
of & 20%–25%. Alternatively, Sonogashira coupling pro-
Received 28 November 2009. Accepted 25 January 2010. Published on the NRC Research Press Web site at canjchem.nrc.ca on
26 March 2010.
M.J.D. Bosdet, W.E. Piers,1 T.S. Sorensen, and M. Parvez. Department of Chemistry, University of Calgary, 2500 University Drive
NW, Calgary, AB T2N 1N4, Canada.
1Corresponding author (e-mail: wpiers@ucalgary.ca).
Can. J. Chem. 88: 426–433 (2010)
doi:10.1139/V10-009
Published by NRC Research Press

Bosdet et al.
427
Chart 1.
of product obtained was insufficient for NMR analysis, and
while its presence may be inferred from a qualitative obser-
vation of pink–red fluorescence in solutions of the material
off column, further analysis was precluded due to lack of
material.
Although B2N2-benzo[ghi]perylenes15 4b–4c were avail-
able only in small quantities, we were able to characterize
them reasonably thoroughly. Unlike the 1H NMR spectra
for compounds 3b and 3c, those of 4b and 4c were much
1
simpler, as expected for C2v symmetric structures; the H
NMR spectrum of 4b is illustrated in Fig. 1. Each derivative
gave rise to four aromatic singlets between 8.0 and 9.5 ppm
for the B2N2-benzo[ghi]perylene framework, corresponding
to H-1, H-3, H-5, and H-6, as well as a single methyl reso-
nance at ~3.1 ppm, and the expected resonances for the R
group. The 11B NMR spectrum showed a single resonance
at 21 ppm, in agreement with other enclosed BN aromatic
compounds (~22 ppm).
Slow evaporation of solvent from a diethyl ether solution
of 4b yielded crystals suitable for analysis via X-ray crystal-
lography. The structure of 4b is essentially planar, with a
maximum dihedral angle of 1.58 within the ring system
(C(18)–C(1)–B(1)–C(5)) (Fig. 2 and Table 1). The B–N
tocols could be employed, but dimerization of the terminal
alkynes was a significant side reaction. The unsubstituted
3,6-bis(ethynyl)pyridazine (1a) was formed from the silyl
derivative 1d by desilylation with KOH(aq) in MeOH
(Scheme 1).
˚
bond is short, at 1.452(2) A, consistent with BN-pyrene III
12
˚
˚
(1.456(4) A) and the B2N2-triphenylene IV (1.464(4) A),
and indicative of some p-character in this bond. However,
in contrast to unbuttressed IV,12 bond localization is evident
throughout the carbon perimeter in 4b, with alternating long
and short C–C bonds within individual rings. Thus, in the
borabenzene rings, C(1)–C(2) and C(3)–C(4) are short
With substrates 1 in hand, reactions with the methyl-
substituted chloroboracyclic precursor, 2,7 were attempted
(Scheme 2). In general, these reactions were not as clean as
those previously observed for pyridazine bases without the
acetylenic groups. While elimination of 2 equiv. of Me3SiCl
was observed, the reactions with pyridazines 1 appear to be
prone to more side reactions, particularly for the parent deriv-
ative 1a. Furthermore, the bis-acetylenic B2N2-triphenylene
complexes (i.e., derivatives of IV), depicted in Scheme 2,
were not detected in any of these reactions. Rather, one ace-
tylenic group underwent spontaneous cyclization, and the
major products observed for R = nBu and Ph were the half-
cyclized compounds 3b and 3c, presumably formed via
intermediates IV. These polycyclic intermediates were not
isolated in pure form, but carried forward to the fully
cyclized compounds 4 using PtCl2 catalysis as shown in
Scheme 2.14 While not isolable in pure form, the nature of
˚
(1.390(3) A avg.), whereas C(2)–C(3) and C(4)–C(5) are
longer (1.414(3) A avg.). The p-electron localization in the
˚
pyridazine ring in 4b also differs from that in compounds
IV, such that the short and long C–C bonds in the latter are
reversed in 4b. Specifically, C(8)–C(9) and C(9’)–C(8’) are
˚
˚
1.406 A, while C(9)–C(9’) is shortened to 1.346(3) A; the
˚
corresponding lengths in unbuttressed IV are 1.345(5) A
and 1.433(6) A. Additionally, the C–N bonds are short-
ened by ~0.02 A (to 1.381(2) A), suggesting better overall
p-electron delocalization about this ring, in contrast to the
cyclohexadiene-type bonding arrangement of heterocycles
IV. The longest C–C bond in 4b is C(1)–C(1)’, at
˚
˚
˚
˚
1.456(3) A, elongated by 2% relative to the same bond in
1
compounds 3 was supported by the H NMR spectral fea-
B2N2-triphenylene IV but of similar length to the analo-
tures observed for the butyl-substituted derivative 3b. Two
distinct methyl resonances were observed at 2.81 and
3.07 ppm in C6D6 solution, highlighting the averaged Cs
symmetry in 3b. Further, two pairs of doublets, correspond-
ing to H-6 and H-7 (5.97 and 6.25 ppm) and H-9 and H-10
(6.96 and 7.28 ppm) were observable, in addition to four ar-
omatic singlets, for H-1 (9.16 ppm), H-3 (7.20 ppm), H-5
(6.56 ppm), and H-12 (8.57 ppm) (See Chart 2 for the num-
bering scheme).
Yields for the target heterocycles 4 were very low
(trace–17%), but the compounds were isolated as moderately
air- and moisture-tolerant, red-brown solids after purification
via column chromatography. The majority of material loss
apparently occurred in the catalyzed cycloisomerization
step, since the mass balance in the production of crude 3b
was upwards of 70%. The inefficient synthesis was particu-
larly evident in the attempted formation of 4a; the amount
gous bond in the all-carbon PAH benzo[ghi]perylene, at
1.484 A.
16
˚
Overall then, the solid-state bond-length patterns suggests
that the ring system is best-represented by resonance form A
(Chart 3), in contrast to the dominant resonance form of tri-
phenylene analogues IV, best-described by resonance form
B. This is supported by NICS(1) calculations17 performed
on 4a, which show a low aromaticity for the inner C2B2N2
ring in 4a, but strong aromaticity for the outer rings. This is
the inverse of trends noted for IV, and it thus appears that
the effect of buttressing the system is to lower the aromatic
stabilization of the inner ring relative to the unbuttressed
system. Indeed, the all-carbon PAH benzo[ghi]perylene ex-
hibits this pattern as well, with the inner ring having low ar-
omatic character relative to the outer rings.18
Unlike the all-carbon frameworks, the B2N2 compounds
have molecular dipoles that are significant enough to influence
Published by NRC Research Press

428
Can. J. Chem. Vol. 88, 2010
Scheme 1.
Scheme 2.
˚
close non-bonding BÁÁÁN distance of 3.71 A is observed. Inter-
Chart 2.
˚
molecular p-stacking distances of 3.42 A exist between paral-
lel sheets of 4b molecules, which is very slightly shorter than
˚
the p–p distance in crystalline benzo[ghi]perylene at 3.44 A.
The unbuttressed B2N2-triphenylene compounds IV ex-
hibit reversible one- and two-electron reduction process,
and indeed the radical anion and dianions are stable and
isolable.12 It was therefore somewhat surprising to find that
cyclic voltammetry on compounds 4a and 4b shows irrever-
sible one-electron reductions, suggesting that the radical
anions are unstable. This may be a reflection of the low ar-
omaticity of the central rings in compounds 4 and a change
in the character of the SOMO in the radical anions.
packing in the solid state. The molecular packing of 4b,
shown in Fig. 3, features two molecules stacked with the di-
poles (calculated to be 3.53 D in 4b) aligned such that a
Published by NRC Research Press

Bosdet et al.
429
1
Fig. 1. H NMR (400 MHz) spectrum of 4b in CD2Cl2.
˚
Fig. 2. Top: X-ray structure of 4b. Numbers are bond lengths in A. Bottom: 4b, viewed along the molecular plane (perpendicular to the
N(1)–N(1)’ bond), with butyl groups removed. Hydrogen atoms have been removed for clarity. Thermal ellipsoids are at the 50% probability
level.
The absorption and emission spectra are indicative of
lowered HOMO–LUMO gaps in comparison to triphenylene
analogs IV, as may be expected by the extended conjugation
afforded by the buttressing alkenyl groups. As for other
BxNx analogs, both absorption and emission bands (621 and
630 nm for 4a and 4b, respectively) are red-shifted in these
compounds in comparison to the all-carbon compound, but
the emission quantum yields (0.023 and 0.015, respectively,
relative to 9,10-diphenylanthracene in cyclohexane) are sig-
nificantly lower than that of benzo[ghi]perylene (0.26).
Conclusions
We have prepared and characterized two examples of
5b,7b-diaza-3b,9b-diborabenzo[ghi]perylenes with a doubly
buttressed B2N2C2 core. Although in previous work a doubly
buttressed B2N2C2 core added stability to bora-aza analogs
of PAHs, here the added benefit in this regard is minimal.
This may stem from the fact that the core ring is of low ar-
omaticity and therefore more reactive towards, for example,
protic reagents and oxygen. Furthermore, the synthetic route
Published by NRC Research Press

430
Can. J. Chem. Vol. 88, 2010
Chart 3.
Table 1. Selected metrical parameters for 4b.
ceived. 3,6-Dichloropyridazine was purchased from Aldrich
and sublimed prior to use. Phenylacetylene was purchased
from Aldrich and passed through a column of alumina im-
mediately prior to use. 1-Hexyne was purchased from Acros
and used as received. PtCl2 was purchased from Alfa Aesar
and used as received. Trimethylsilylacetylene was purchased
˚
Bond lengths (A)
B(1)—N(1)
B(1)—C(1)
B(1)—C(5)
C(1)—C(1)’
C(1)—C(2)
C(2)—C(3)
N(1)—C(8)
N(1)—N(1)’
1.452(2)
1.516(2)
1.516(3)
1.456(3)
1.391(2)
1.415(2)
1.381(2)
1.422(2)
1
from Petra Research, Inc. and distilled prior to use. H NMR
assignments were made by comparison to known chemical
shift patterns.5–9,11,12
Synthesis of 3,6-bis(1-hexynyl)pyridazine, 1b
Bond angles (8)
C(1)–B(1)–N(1)
N(1)–B(1)–C(5)
N(1)’–N(1)–B(1)
B(1)–N(1)–C(8)
B(1)–C(1)–C(1)’
N(1)–C(8)–C(9)
122.63(14)
117.23(14)
119.73(9)
120.76(13)
117.63(9)
119.80(14)
In a microwavable reaction tube, solid Pd(PPh3)4 (8 mg,
7.1 mmol) and CuI (3 mg, 14.1 mmol) were added to a sol-
ution of 3,6-dichloropyridazine (50 mg, 0.33 mmol) in NEt3
(2 mL). This was immediately followed by the addition of a
solution of 1-hexyne (58 mg, 0.71 mmol) in NEt3 (1 mL),
and the mixture was heated in a microwave reactor (115 W,
150 8C) for 25 min. Once cooled, the crude product was ex-
tracted into Et2O and gravity filtered. The solvent was re-
moved in vacuo, and the orange material was dissolved in
hexanes and loaded onto a column of neutral Al2O3. Gra-
dient elution with hexanes/Et2O ultimately gave the product as
a yellow solid. Yield: 20 mg (25%). 1H NMR (C6D6) d (ppm):
6.62 (s, 2H, H-1), 2.12 (t, 4H, 3JHH = 7 Hz, H-5), 1.31 (m, 2 +
Torsion angles (8)
C(8)–N(1)–B(1)–C(1)
179.74(14)
to these frameworks is inefficient (despite many attempts at
improvements), and the photophysical properties are not
unique enough to warrant further efforts directed towards
discovery of more direct routes to the compounds. Nonethe-
less, the structural features and aromatic properties are of in-
terest to add to the database of BxNx compounds in
comparison to their all-carbon counterparts.
3
2H, H-6 + H-7), 0.76 (t, 6H, JHH = 7 Hz, H–). HR-MS for
C16H20N2 (M+): 240.1626 (calcd.), 240.1624 (found).
Experimental section
Synthesis of 3,6-bis(phenylethynyl)pyridazine, 1c
General procedures have been described in detail else-
where.12 Celite 5451 was purchased from Fisher Scientific
and heated at 200 8C under high vacuum for 3 days prior to
use. Neutral alumina (63–200 mm, 70–230 Mesh ASTM))
was purchased from EM Science and heated at 200 8C for
3 days under high vacuum prior to use. Silica-gel column
chromatography was carried out on Geduran Silica 60 silica
gel (particle size 40–63 mm).
Compound 2 was prepared as described previously.12 CuI,
BCl3, LiNMe2, pyridazine, 9,10-diphenylanthracene, and
Pd(PPh3)4 were purchased from Aldrich and used as re-
To a –78 8C solution of phenylacetylene (1.33 g,
13.0 mmol) in THF (50 mL) was added a solution of n-butyl
lithium in hexanes (1.6 mol/L, 8.12 mL, 13.0 mmol). After
stirring at this temperature for 1 h, a solution of ZnCl2
(1.77 g, 13.0 mmol) in THF (50 mL) was transferred in via
canula, and this mixture was stirred for another 45 min with
Published by NRC Research Press

Bosdet et al.
431
Fig. 3. Molecular packing of 4b, including intermolecular BÁÁÁN interactions (red dash). Hydrogen atoms have been removed for clarity.
Thermal ellipsoids are at the 50% probability level.
the temperature maintained at –78 8C. The reaction mixture
was then warmed to 25 8C, and a solution of 3,6-dichloro-
pyridazine (486 mg, 3.3 mmol) and Pd(PPh3)4 (751 mg,
0.65 mmol) in THF (50 mL) was added. The mixture was
stirred for 3 days, then quenched with saturated NaHCO3(aq)
(75 mL), and filtered through Celite. After removing the or-
ganic layer, the aqueous layer was washed with CHCl3 (2 Â
20 mL), and the combined organic fractions were dried with
MgSO4. The crude material obtained following gravity fil-
tration and removal of volatiles in vacuo was purified by
column chromatography, giving a white solid. Yield:
13C{1H} NMR (CDCl3) d (ppm): 145.46 (s, C-2), 129.02 (s,
C-1), 102.09 (s, C-3/4), 100.42 (C-3/4), –0.53 (s, SiMe3). HR-MS
for C14H20N2Si2 (M+): 272.1165 (calcd.), 272.1177 (found).
Synthesis of 3,6-bis(ethynyl)pyridazine, 1a
Desilylation of 3,6-bis(trimethyl-silylethynyl)pyridazine
was accomplished by the addition of KOH(aq) (0.99 mol/L,
1.0 mL, 0.98 mmol) to a solution of 1d (134 mg,
0.49 mmol) in MeOH (5 mL). After stirring for 1.5 h, the
mixture was extracted into CHCl3 (20 mL) and washed with
6 mol/L HCl(aq) (2 Â 10 mL). The organic layer was dried
over MgSO4, filtered, and the solvent removed in vacuo to
1
111 mg (12%). H NMR (CDCl3) d (ppm): 7.65 (m, 4H, H-6),
7.61 (s, 2H, H-1), 7.41 (m, 2 + 1H, H-7 + H-8). 13C{1H}
NMR (CDCl3) d (ppm): 146.00 (s, C-2), 132.38 (s, C-6),
129.92 (s, C-1), 129.01 (s, C-8), 128.72 (s, C-7), 121.59 (s,
C-5), 95.67 (s, C-3/4), 86.10 (C-3/4). HR-MS for C20H12N2
(M+): 280.1000 (calcd.), 280.1001 (found).
1
give 1a as white crystals. Yield: 51 mg (81%). H NMR
(CDCl3) d (ppm): 7.56 (s, 2H, H-1), 3.52 (s, 2H, H-4).
13C{1H} NMR (CDCl3) d (ppm): 145.50 (s, C-2), 129.45 (s,
C-1), 83.86 (s, C-3/4), 79.72 (C-3/4). HR-MS for C8H4N2
(M+): 128.0374 (calcd.), 128.0376 (found).
Synthesis of 3,6-bis(trimethyl-silylethynyl)pyridazine, 1d
Synthesis/characterization of 3b
To a –78 8C solution of trimethylsilylacetylene (1.151 g,
11.7 mmol) in THF (50 mL) was added a solution of n-butyl
lithium in hexanes (1.6 mol/L, 7.3 mL, 11.7 mmol). After
stirring at this temperature for 1 h, a solution of ZnCl2
(1.60 g, 11.7 mmol) in THF (50 mL) was transferred in via
canula, and this mixture was stirred for another 45 min with
the temperature maintained at –78 8C. The reaction mixture
was then warmed to 25 8C, and a solution of 3,6-dichloro-
pyridazine (436 mg, 2.9 mmol) and Pd(PPh3)4 (338 mg,
0.29 mmol) in THF (40 mL) was added. The mixture was
stirred for 3 days at 35 8C and was then quenched with satu-
rated NaHCO3(aq) (75 mL) and filtered through Celite. After
removing the organic layer, the aqueous layer was washed
with CHCl3 (2 Â 20 mL), and the combined organic frac-
tions were dried with Na2SO4. The crude material obtained
following gravity filtration and removal of volatiles in vacuo
was purified by column chromatography (5% EtOAc in hex-
1
anes), giving a white solid. Yield: 135 mg (17%). H NMR
(CDCl3) d (ppm): 7.44 (s, 2H, H-1), 0.17 (s, 18H, -SiMe3).
A solution of 2 (55 mg, 0.14 mmol) in toluene (1 mL)
was added to a solution of 1b (32 mg, 0.13 mmol) in tol-
Published by NRC Research Press

432
Can. J. Chem. Vol. 88, 2010
uene (5 mL) and stirred at 25 8C for 48 h. Volatiles were
removed in vacuo, and the crude product was determined to
be a mixture including the intermediate 3b via 1H NMR
UV–vis (e (104 L mol–1 cm–1), cyclohexane) lmax (nm):
261, 324, 413, 458, 511. Fluorescence (cyclohexane) lmax
(nm): 621, 667; ff = 0.023, tf = 23 ns. H NMR (CD2Cl2) d
1
1
spectroscopy. H NMR (C6D6) d (ppm): 9.16 (s, 1H, H-2),
(ppm): 9.46 (s, 2H, H-1/12), 8.58 (s, 2H, H-3/10), 8.53 (s,
3
3
8.57 (s, 1H, H-15), 7.28 (d, 1H, JHH = 8 Hz, H-13), 7.20 (s,
2H, H-5/8), 8.03 (s, 2H, H-6/7), 3.62 (t, 4H, JHH = 8 Hz,
1H, H-4), 6.96 (d, 1H, 3JHH = 8 Hz, H-12), 6.56 (s, 1H, H-7),
C-13), 3.11 (s, 6H, C-2/11-Me), 2.07 (m, 4H, H-14), 1.64
3
3
3
6.25 (d, 1H, JHH = 8 Hz, H-10), 5.97 (d, 1H, JHH = 8 Hz,
(m, 4H, H-15), 1.07 (t, 6H, JHH = 8 Hz, C-16) ppm.
3
11B{1H} NMR (C6D6) d (ppm): 21 (br s). HR-MS for
H-9), 3.25 (t, 2H, JHH = 8 Hz, C-17), 3.07 (s, 3H, C-3-Me),
3.04 (t, 2H, JHH = 8 Hz, C-23), 2.81 (s, 3H, C-14-Me), 2.35
3
C32H24B2N2 (M+): 418.27516 (calcd.), 418.27679 (found).
(m, 2H, H-18), 2.21 (m, 2H, H-24), ~1.41 (m, H-19), ~1.38
(m, H-25), 0.99 (t, 3H, 3JHH = 8 Hz, C-20), 0.90 (t, 3H, 3JHH
8 Hz, C-26).
=
Synthesis of 4c
Attempted synthesis of 4a
A solution of 2 (157 mg, 0.40 mmol) in toluene (3 mL)
was added to a solution of 1a (51 mg, 0.40 mmol) in toluene
(10 mL) and stirred at 25 8C for 48 h. Volatiles were re-
moved in vacuo and the crude material was re-dissolved in
toluene and transferred onto PtCl2 (2 mg, 7 mmol). The mix-
ture was stirred at 95 8C for 24 h, after which volatiles were
removed, and the brown material was purified by flash chro-
matography through neutral Al2O3. The Et2O fraction was
observed to fluoresce pink–red upon irradiation at 365 nm,
but an insufficient quantity for NMR characterization was
obtained. Yield: trace.
A solution of 2 (74 mg, 0.19 mmol) in toluene (1.5 mL)
was added to a solution of 1c (50 mg, 0.18 mmol) in toluene
(5 mL) and stirred at 45 8C for 48 h. Volatiles were re-
moved in vacuo and the crude product was re-dissolved in
toluene and transferred onto PtCl2 (3 mg, 11 mmol). The
mixture was stirred at 100 8C for 24 h, after which volatiles
were removed, and the brown material was purified by flash
chromatography through neutral Al2O3. Yield: 3 mg (3%).
UV–vis (e (104 L mol–1 cm–1), cyclohexane) lmax (nm):
421, 523, 625. Fluorescence (cyclohexane) lmax (nm): 630,
Synthesis of 4b
1
676; ff = 0.015, tf = 23 ns. H NMR (CD2Cl2) d (ppm):
9.54 (s, 2H, H-1/12), 8.64 (s, 2H, H-3/10), 8.48 (s, 2H, H-5/8
3
or 6/7), 8.19 (s, 2H, H-5/8 or 6/7), 7.92 (d, 4H, JHH = 8 Hz,
H-14), (m, 4 + 2H, H-15 + H-16), 3.04 (s, 6H, C-2/11-Me).
Cyclic voltammetry (vs. SCE) E1/2 (THF): –1.57 (rev.) V.
HR-MS for C28H32B2N2 (M+): 458.2126 (calcd.), 458.2109
(found).
X-ray crystallography
A deep-red – brown needle of C28 H32 B2 N2 was coated
with Paratone 8277 oil (Exxon) and mounted on a glass fi-
ber. All measurements were made on a Nonius KappaCCD
diffractometer with graphite monochromated Mo Ka radia-
tion. Details of crystal data and structure refinement have
been provided in Table 2. The data were collected19 using
u and f scans. The data were corrected for Lorentz and po-
larization effects and for absorption using multi-scan
method.20
The crude material 3b was re-dissolved in toluene and
transferred onto PtCl2 (2 mg, 7 mmol). The mixture was
stirred at 100 8C for 24 h, after which volatiles were re-
moved, and the brown material was purified by flash chro-
matography through neutral Al2O3. Yield: 9 mg (17%).
The structure was solved by the direct methods21 and ex-
panded using Fourier techniques.22 The H atoms were in-
cluded at geometrically idealized positions and were not
allowed to refine. The final cycle of full-matrix least-squares
refinement using SHELXL9723 converged with unweighted
Published by NRC Research Press

Bosdet et al.
433
Table 2. Crystal data and structure refinement for C28H32B2N2, 4b.
References
(1) Bosdet, M. J. D.; Piers, W. E. Can. J. Chem. 2009, 87 (1), 8.
doi:10.1139/V08-110.
Empirical formula
Formula weight
C28 H32 B2 N2
418.18
(2) Marwitz, A. J. V.; Matus, M. H.; Zakharov, L. N.; Dixon, D.
A.; Liu, S. Y. Angew. Chem. Int. Ed. 2009, 48 (5), 973.
doi:10.1002/anie.200805554.
(3) Liu, L. J.; Marwitz, A. J. V.; Matthews, B. W.; Liu, S. Y.
Angew. Chem. Int. Ed. 2009, 48 (37), 6817. doi:10.1002/
anie.200903390.
(4) Boese, R.; Finke, N.; Keil, T.; Paetzold, P.; Schmid, G. Z.
Naturforsch. [B] 1985, 40, 1327.
(5) Ghesner, I.; Piers, W. E.; Parvez, M.; McDonald, R. Orga-
nometallics 2004, 23 (13), 3085. doi:10.1021/om049800z.
(6) Ghesner, I.; Piers, W. E.; Parvez, M.; McDonald, R. Chem.
Commun. (Camb.) 2005, (19): 2480. doi:10.1039/b502448j.
PMID:15886777.
(7) Wood, T. K.; Piers, W. E.; Keay, B. A.; Parvez, M. Org.
Lett. 2006, 8 (13), 2875. doi:10.1021/ol061201w. PMID:
16774279.
(8) Bosdet, M. J. D.; Jaska, C. A.; Piers, W. E.; Sorensen, T. S.;
Parvez, M. Org. Lett. 2007, 9 (7), 1395. doi:10.1021/
ol070328y. PMID:17338544.
Temperature
Wavelength
Crystal system
Space group
173(2) K
0.71073 A
Monoclinic
P2/c
a = 12.473(5) A
b = 10.189(7) A
c = 9.339(8) A
b = 108.70(3)8
˚
˚
˚
Unit cell dimensions
˚
3
˚
Volume
Z
Density (calc.d.)
1124.2(13) A
2
1.235 Mg/m3
0.070 mm–1
448
Absorption coefficient
F(000)
Crystal size
q range for data collection
Index ranges
0.32 Â 0.11 Â 0.10 mm3
3.45 to 27.488
–16 £ h £ 16, –11 £ k £ 13, –12
£ l £ 12
7866
Reflections collected
(9) Bosdet, M. J. D.; Piers, W. E.; Sorensen, T. S.; Parvez, M.
Angew. Chem. Int. Ed. 2007, 46 (26), 4940. doi:10.1002/
anie.200700591.
(10) Liu, Z.; Marder, T. B. Angew. Chem. Int. Ed. 2008, 47 (2),
242. doi:10.1002/anie.200703535.
(11) Emslie, D. J. H.; Piers, W. E.; Parvez, M. Angew. Chem. Int.
Ed. 2003, 42 (11), 1252. doi:10.1002/anie.200390320.
(12) Jaska, C. A.; Emslie, D. J. H.; Bosdet, M. J. D.; Piers, W.
E.; Sorensen, T. S.; Parvez, M. J. Am. Chem. Soc. 2006,
128 (33), 10885. doi:10.1021/ja063519p. PMID:16910684.
(13) Chekmarev, D. S.; Stepanov, A. E.; Kasatkin, A. N. Tetrahe-
dron Lett. 2005, 46 (8), 1303. doi:10.1016/j.tetlet.2004.12.
124.
(14) Mamane, V.; Gress, T.; Krause, H.; Fu¨rstner, A. J. Am.
Chem. Soc. 2004, 126 (28), 8654. doi:10.1021/ja048094q.
PMID:15250709.
(15) IUPAC: 5b,7b-diaza-3b,9b-diborabenzo[ghi]perylenes.
(16) Trotter, J. Acta Crystallogr. 1959, 12 (11), 889. doi:10.1107/
S0365110X59002511.
Independent reflections
Completeness to q = 27.488 99.1%
Absorption correction
Max. and min. transmission 0.9930 and 0.9779, respectively
2555 [R(int) = 0.0302]
Multi-scan method
Refinement method
Full-matrix least-squares on F2
2555/0/147
1.040
R1 = 0.0531, wR2 = 0.1288
R1 = 0.0952, wR2 = 0.1545
˚
0.270 and –0.195 e A
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2s(I)]
R indices (all data)
–3
Largest diff. peak and hole
and weighted agreement factors, R = 0.0531 and wR =
0.1545 (all data), respectively, and goodness of fit, S =
1.040. The weighting scheme was based on counting
statistics and the final difference Fourier map was essen-
tially featureless. The figures were plotted with the aid of
ORTEPII.24
(17) Schleyer, P. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; van Ei-
kema Hommes, N. J. R. J. Am. Chem. Soc. 1996, 118 (26),
6317. doi:10.1021/ja960582d.
(18) Schulman, J. M.; Disch, R. L. J. Phys. Chem. A 1997, 101
(48), 9176. doi:10.1021/jp972391i.
(19) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276,
307. doi:10.1016/S0076-6879(97)76066-X.
(20) Hooft, R. COLLECT; Nonius BV: Delft, The Netherlands,
1998.
(21) Altomare, A.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A.
J. Appl. Cryst. 1993, 26 (3), 343. doi:10.1107/
S0021889892010331.
(22) Smits, J. M. M. The DIRDIF-94 program system; Technical
Report of the Crystallography Laboratory: The University of
Nijmegen, Nijmegen, The Netherlands, 1994.
Supplementary data
Supplementary data for this article are available on the
journal Web site (canjchem.nrc.ca) or may be purchased
from the Depository of Unpublished Data, Document Deliv-
ery, CISTI, National Research Council Canada, Ottawa, ON
K1A 0R6, Canada. DUD 5359. For more information on ob-
taining material, refer to cisti-icist.nrc-cnrc.gc.ca/cms/
unpub_e.shtml. CCDC 753114 (4b) contains the X-ray data
in CIF format for this manuscript. These data can be ob-
tained, free of charge, via www.ccdc.cam.ac.uk/conts/
retrieving.html (Or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
¨
¨
(23) Sheldrick, G. M. SHELXL97; University of Gottingen: Got-
tingen, Germany, 1997.
Acknowledgements
(24) Johnson, C. K. ORTEPII; Oak Ridge National Laboratory:
Oak Ridge, TN, 1976.
Funding for this work was provided by the Xerox Founda-
tion and the Natural Sciences and Engineering Research
Council of Canada (NSERC) of Canada through a CRD grant
to W.E.P. M.J.D.B. acknowledges NSERC and the Alberta
Ingenuity Fund for postgraduate fellowship support.
Published by NRC Research Press