Synthesis of 1,8-diborylnaphthalenes by the ring-opening reaction of a new anionic boron-bridged naphthalene derivative

Article abstract of DOI:10.1021/om010946x

Synthesis of 1,8-diborylnaphthalenes by the ring-opening reaction of a new anionic boron-bridged naphthalene derivative was studied. The reaction of the derivative with dimesitylboron fluoride led to the formation of a precipitate that can be recrystallized. The NMR spectroscopy revealed the existence of a symmetrically substituted naphthalene ring and a unique mesityl environment.

Full text of DOI:10.1021/om010946x

982
Organometallics 2002, 21, 982-985
Notes
Syn th esis of 1,8-Dibor yln a p h th a len es by th e
Rin g-Op en in g Rea ction of a New An ion ic Bor on -Br id ged
Na p h th a len e Der iva tive
J ames D. Hoefelmeyer and Franc¸ois P. Gabba¨ı*
Chemistry TAMU 3255, Texas A&M University, College Station, Texas 77843-3255
Received October 31, 2001
Summary: The reaction of 1,8-dilithionaphthalene with
dimesitylboron fluoride affords a rare boron-bridged
naphthalene derivative which undergoes ring-opening
reactions to afford unsymmetrically substituted 1,8-
diborylnaphthalene species.
of 1,8-dilithionaphthalene with boron halides11 or alkox-
ides,5 which affords symmetrically substituted products.
Earlier investigations by Pritzkow and Siebert have
shown that 1,8-bridged naphthalene13-16 derivatives
such as naphtho[1,8-bc]boretes17 undergo ring-opening
reactions. It occurred to us that such reactions could be
used to generate unsymmetrically substituted 1,8-
diborylnaphthalene compounds. In this contribution, we
report on the synthesis of an anionic 1,8-boron-bridged
naphthalene compound, namely dimesityl(1,8-naphtha-
lenediyl)borate18 (1), which is converted into unsym-
metrically substituted 1,8-diborylnaphthalene deriva-
tives by ring-opening reactions.
In tr od u ction
Rigid polydentate boranes are used in molecular
recognition,1-3 anion recognition,4-8 and catalysis.7-10
The contribution of Katz is especially noteworthy and
demonstrates the ability of these compounds to chelate
small anions such as hydride, fluoride, and chloride.4-6
Extending the chemistry of these derivatives to the area
of boron-centered radicals, we reported that the reduc-
tion of 1,8-bis(diphenylboryl)naphthalene yields a radi-
cal anion that features a one-electron σ-bond between
the boron atoms.11 In the context of these studies, we
are currently exploring ways to introduce alternative
substituents at the boron centers of 1,8-diborylnaph-
thalene derivatives.12 1,8-Diborylnaphthalene deriva-
tives are typically prepared by the metathesis reaction
Resu lts a n d Discu ssion
The reaction of 1,8-dilithionaphthalene with 1 equiv
of dimesitylboron fluoride leads to the formation of a
precipitate that can be recrystallized from THF to form
high yields of crystalline dimesityl(1,8-naphthalenediyl)-
borate (1) as a Li(THF)4 salt (Scheme 1). If pyridine is
used instead, borate 1 is isolated as a Li(py)4 salt. Both
salts have been characterized by 1H and 13C NMR
spectroscopy, which reveals the existence of a sym-
metrically substituted naphthalene ring and a unique
mesityl environment. The 11B NMR resonance observed
at 2.7 ppm in d5-pyridine and 2.3 ppm in d8-THF is
consistent with that typically observed for tetraarylbo-
rates such as Ph4B- (δ -6 ppm in d8-THF). The same
reaction carried out in the presence of 2 equiv of
dimesitylboron fluoride does not result in the formation
of the expected 1,8-bis(borylated) derivative, which
reflects the high steric demand of the dimesitylboryl
moiety. 1-Li(THF)4 forms single crystals that undergo
rapid THF loss at ambient temperature and shatter
when cooled to low temperatures. In contrast, crystals
* To whom correspondence should be addressed. Fax: 979-845-4719.
E-mail: francois@tamu.edu.
(1) Nozaki, K.; Yoshida, M.; Takaya, H. Bull. Chem. Soc. J pn. 1996,
69, 2043-2052. Nozaki, K.; Tsutsumi, T.; Takaya, H. J . Org. Chem.
1995, 60, 6668-6669.
(2) Katz, H. E. J . Org. Chem. 1989, 54, 2179-2183.
(3) Reilly, M.; Oh, T. Tetrahedron Lett. 1995, 36, 217-220.
(4) Katz, H. E. J . Am. Chem. Soc. 1985, 107, 1420-1421.
(5) Katz, H. E. J . Org. Chem. 1985, 50, 5027-5032.
(6) Katz, H. E. Organometallics 1987, 6, 1134-1136.
(7) J ia, L.; Yang, X.; Stern, C.; Marks, T. J . Organometallics 1994,
13, 3755. Metz, M. V.; Schwartz, D. J .; Stern, C. L.; Nickias, P. N.;
Marks, T. J . Angew. Chem., Int. Ed. 2000, 39, 1312-1316. Chen, E.
Y.-X.; Marks, T. J . Chem. Rev. 2000, 100, 1391-1434.
(8) Ko¨hler, K.; Piers, W. E.; J arvis, A. P.; Xin, S.; Feng, Y.; Bravakis,
A. M.; Collins, S.; Clegg, W.; Yap, G. P. A.; Marder, T. B. Organome-
tallics 1998, 17, 3557-3566. Williams, V. C.; Piers, W. E.; Clegg, W.;
Elsegood, M. R. J .; Collins, S.; Marder, T. B. J . Am. Chem. Soc. 1999,
121, 3244-3245. Williams, V. C.; Dai, C.; Li, Z.; Collins, S.; Piers, W.
E.; Clegg, W.; Elsegood, M. R. J .; Marder, T. B. Angew. Chem., Int.
Ed. 1999, 38, 3695-3698. Piers, W. E.; Irvine, G. J .; Williams, V. C.
Eur. J . Inorg. Chem. 2000, 2131-2142. Williams, V. C.; Irvine, G. J .;
Piers, W. E.; Li, Z.; Collins, S.; Clegg, W.; Elsegood, M. R. J .; Marder,
T. B. Organometallics 2000, 19, 1619-1621.
(13) Tinga, M. A. G. M.; Schat, G.; Akkerman, O. S.; Bickelhaupt,
F.; Smeets, W. J . J .; Spek, A. L. Chem. Ber. 1994, 127, 1851-1856.
Yang, L. S.; Shechter, H. Chem. Commun. 1976, 19, 775.
(14) Meinwald, J .; Knapp, S.; Obendorf, S. K.; Hughes, R. E. J . Am.
Chem. Soc. 1976, 98, 6643-6649.
(9) Reilly, M.; Oh, T. Tetrahedron Lett. 1995, 35, 7209-7212. Reilly,
M.; Oh, T. Tetrahedron Lett. 1995, 36, 221-224.
(15) Yang, L. S.; Engler, T. A.; Shechter, H. Chem. Commun. 1983,
16, 866-868.
(10) Schilling, B.; Kaiser, V.; Kaufmann, D. Chem. Ber. 1997, 130,
923-932.
(16) Tinga, M. A. G. M.; Buisman, G. J . H.; Schat, G.; Akkerman,
O. S.; Bickelhaupt, F.; Smeets, W. J . J .; Spek, A. L. J . Organomet.
Chem. 1994, 484, 137-145.
(11) Hoefelmeyer, J . D.; Gabba¨ı, F. P. J . Am. Chem. Soc. 2000, 122,
9054-9055.
(12) For original work on peri-borylated naphthalene derivatives
see: Letsinger, R. L.; Smith, J . M.; Gilpin, J .; MacLean, D. B. J . Org.
Chem. 1965, 30, 807-812.
(17) Hergel, A.; Pritzkow, H.; Siebert, W. Angew. Chem., Int. Ed.
1994, 33, 1247-1248.
(18) 1,1-Dimesityl-1-borata-cyclobuta[de]naphthalene.
10.1021/om010946x CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/01/2002

Notes
Organometallics, Vol. 21, No. 5, 2002 983
Sch em e 1
F igu r e 1. ORTEP view of 1 in the crystal (50% ellipsoids).
Selected bond lengths (Å) and angles (deg): B-C(1) )
1.715(4), B-C(8) ) 1.696(4), B-C(11) ) 1.646(4), B-C(21)
) 1.643(4); C(8)-B-C(1) ) 80.49(17), C(21)-B-C(11) )
114.4(2), C(9)-C(1)-B ) 87.63(19), C(9)-C(8)-B ) 88.60-
(19).
Ta ble 1. Cr ysta llogr a p h ic Da ta for 1-3
1
2
3
formula
Mr
C
48H48BLiN4
C30H34B2
416.19
C40H38B2
540.32
monoclinic
P21/n
698.65
cryst syst
space group
a (Å)
orthorhombic monoclinic
P212121
P21/n
12.7234(6)
13.4560(6)
23.7193(10)
8.2988(13)
19.918(3)
14.876(2)
98.096(3)
2434.5(7)
1.136
9.846(2)
21.250(5)
15.463(3)
104.576
3131.1(11)
1.146
thalene (2) and 1-(dimesitylboryl)-8-(diphenylboryl)-
naphthalene (3), respectively. The 11B NMR spectra of
2 and 3 show a single unresolved resonance at 71 ppm
(w1/2 ) 1843 Hz) and 65 ppm (w1/2 ) 2404 Hz),
respectively. The 1H NMR spectrum of 2 and 3 indicates
the existence of a rigid structure, since four aryl protons
and six distinct methyl groups are observed for the
mesityl substituent. The methyl groups attached to the
boron center of 2 give rise to two broad resonances
which coalesce at 50 °C. Using the Eyring equation, an
enthalpy of activation (62((6) kJ /mol) can be calculated
for this fluxional process, which most probably corre-
sponds to the hindered rotation of the dimethylboryl
about the B-C(peri-naphthalenediyl) bond. Interest-
ingly, no coalescence or broadening of the mesityl
resonances is detected upon heating. This observation
indicates that the molecular motion of the dimethylboryl
moiety occurs independently. In the case of 3, elevation
of the temperature does not induce any changes in the
appearance of the spectrum.
b (Å)
c (Å)
â (deg)
V (Å3)
4060.9(3)
1.143
4
Fcalcd (g cm-3
Z
)
4
4
F(000) (e)
1488
0.066
110
896
0.062
110
1152
0.063
110
µ(Mo KR) (mm-1
T (K)
)
2θ range (deg)
3.44-50
3.44-50
3.32-50
scan mode
ω
ω
ω
no. of rflns measd
no. of unique rflns
27 697
12 623
15 925
7145 (0.0473) 4273 (0.0818) 5506 (0.0878)
(Rint
no. of refined params 487
R1, wR2 (I > 2σ(I)) 0.0519, 0.1193 0.0780, 0.2034 0.0589, 0.1152
)
289 379
of 1-Li(py)4 are stable when cooled and were therefore
subjected to an X-ray structural analysis (Table 1). The
structure of the anionic component of the salt confirms
the existence of a strained four-membered boracycle19
containing a severely distorted tetracoordinated boron
center (Figure 1). The acute C(1)-B-C(8) angle (80.5°)
and obtuse C(11)-B-C(1) (120.2°) and C(21)-B-C(8)
(119.6°) angles are especially noteworthy. Distortions
are also apparent in the naphthalenediyl fragment with
the C(1)-C(9)-C(8) (103.3°) and C(4)-C(10)-C(5) angles
(132.6°) on either side of the ideal value of 120°. While
the B-C(ipso-mesityl) bonds (av. 1.645 Å) are compa-
rable to those found in the tetraphenylborate anion,20
the B-C(peri-naphthalenediyl) bonds (average 1.706 Å)
appear slightly lengthened. These B-C bonds are also
longer than that observed in the neutral amino-
substituted analogue of 1 that contains an sp2-hybrid-
ized boron center.17 Finally, the plane defined by the
boron atom and the two peri-naphthalenediyl carbon
atoms forms a dihedral angle of 80.7° with the plane
containing the boron atom and the two ipso-mesityl
carbon atoms.
The crystal structures of 2 and 3 have been deter-
mined (Table 1). The structure of both compounds
presents a number of features characteristic of sterically
hindered peri-substituted naphthalene derivatives (Fig-
ures 2 and 3).21 A slight pyramidalization is observed
at B(2) (∑angles ) 357.2° in 2 and 357.3° in 3). The B(1)-
C(1)-C(9) (127.5° in 2, 128.3° in 3) and B(2)-C(8)-C(9)
(129.5° in 2, 128.5° in 3) angles substantially deviate
from the ideal value of 120°. The core of the naphthalene
backbone is slightly twisted, as reflected by the dihedral
angle of 3.1° in 2 and 4.7° in 3 formed between the
planes defined by C(1)-C(8)-C(9) and C(4)-C(5)-
C(10). The resulting intramolecular boron-boron dis-
tances are equal to 3.206 Å in 2 and 3.352 Å in 3, thus
slightly exceeding that observed previously in 1,8-bis-
(diphenylboryl)naphthalene (3.002 Å).11
Compound 1 undergoes ring-opening reactions (Scheme
1). Treatment of 1 with 1 equiv of dimethylboron
bromide or diphenylboron bromide in ether leads to the
formation of 1-(dimesitylboryl)-8-(dimethylboryl)naph-
(20) Knop, O.; Cameron, T. S.; Bakshi, P. K.; Linden, A.; Roe, S. P.
Can. J . Chem. 1994, 72, 1870-1881.
(21) Blount, J . F.; Cozzi, F.; Damewood, J . R., J r.; Iroff, L. D.;
Sjostrand, U.; Mislow, K. J . Am. Chem. Soc. 1980, 102, 99-103.
Schro¨ck, R.; Angermaier, K.; Sladek, A.; Schmidbaur, H. Organome-
tallics 1994, 13(9), 3399-3401.
(19) For three-membered boracycles see: Shcherbakova, I. V. In
Comprehensive Heterocyclic Chemistry II; Elsevier: Amsterdam, 1996;
Vol. 1A, pp 333-346, and references therein.

984 Organometallics, Vol. 21, No. 5, 2002
Notes
dried by reflux under N2 over a drying agent and freshly
distilled prior to use. THF was dried over Na/K. Ether,
chloroform, and acetonitrile were dried over CaH2. Air-
sensitive compounds were handled under an N2 atmosphere
using standard Schlenk and glovebox techniques. Elemental
analyses were performed at Atlantic Microlab (Norcross, GA).
All melting points were measured on samples in sealed
capillaries and are uncorrected. 1H and 13C NMR spectra were
recorded on a Varian VXR-300 spectrometer at 300 and 75.4
MHz, respectively. 11B NMR spectra were recorded on a Varian
Inova 400 broad-band spectrometer at 128.3 MHz. Chemical
shifts for 1H and 13C NMR spectra are reported with respect
to Me4Si standard (δ 0 ppm). Chemical shifts for 11B NMR
spectra are reported with respect to BF3‚OEt2 standard (δ 0
ppm).
Cr ystallogr aph y. The crystallographic measurements were
performed using a Siemens SMART-CCD area detector dif-
fractometer, with graphite-monochromated Mo KR radiation
(λ ) 0.710 69 Å). Specimens of suitable size and quality were
selected and mounted onto glass fibers with Apiezon grease.
The structures were solved by direct methods, which success-
fully located most of the non-hydrogen atoms. Subsequent
refinement on F2 using the SHELXTL/PC package (version 5.1)
allowed location of the remaining non-hydrogen atoms. Fur-
ther crystallographic details can be found in Table 1.
F igu r e 2. ORTEP view of 2 in the crystal (50% ellipsoids).
Selected bond lengths (Å) and angles (deg): B(1)-C(1) )
1.577(6), B(1)-C(11) ) 1.595(7), B(1)-C(21) ) 1.562(7),
B(2)-C(8) ) 1.558(7), B(2)-C(31) ) 1.591(7), B(2)-C(32)
) 1.562(7); C(21)-B(1)-C(1) ) 126.0(4), C(21)-B(1)-C(11)
) 116.0(4), C(1)-B(1)-C(11) ) 117.5(4), C(8)-B(2)-C(32)
) 119.5(4), C(8)-B(2)-C(31) ) 119.5(4), C(32)-B(2)-C(31)
) 118.2(4), C(9)-C(1)-B(1) ) 127.5(4), C(9)-C(8)-B(2) )
129.5(4).
Lith iu m dim esityl(1,8-n aph th alen ediyl)bor ate tetr akis-
(tetr a h yd r ofu r a n ) (1-Li(THF )4). A 1.6 M hexane solution
of n-butyllithium (20.0 mL, 32.0 mmol) was added to a solution
of 1,8-diiodonaphthalene (5.0 g, 13.1 mmol) in diethyl ether
(50 mL) at 0 °C. After 1 h at the same temperature, a solution
of dimesitylboron fluoride (3.51 g, 15.7 mmol) in diethyl ether
(10 mL) was added through a cannula. The resulting reaction
mixture was warmed to room temperature and was stirred
overnight. The reaction afforded a tan powdery precipitate that
was isolated by filtration and washed with diethyl ether. The
resulting solid was further purified by multiple recrystalliza-
tions from THF until clear, colorless needles of 1-Li(THF)4
were obtained. Crystals of 1-Li(THF)4 become opaque and
slowly turn orange when stored at room temperature. Storage
at -25 °C is advised. Yield: 3.4 g (39%). Mp: 25 °C dec caused
by THF loss. 1H NMR (pyridine-d5): δ 2.21 (s, 6H, Mes p-CH3),
2.81 (s, 12H, Mes o-CH3), 6.8 (s, 4H, Mes CH), 7.46-7.58 (m,
4H, naph CH), 7.82 (d, 2H, naph CH). 13C NMR (pyridine-d5):
δ 21.5 (Mes p-CH3), 26.1 (Mes o-CH3), 118.3 (naph C3/6), 123.0
(naph C4/5), 126.2 (naph C9/10), 128.7 (naphth C2/7), 129.1
(Mes CH), 129.4 (C9/10), 130.8 (Mes p-C), 142.4 (Mes o-C).
Crystals of 1-Li(THF)4 are very unstable and become brittle
through loss of part of the THF component. The results of the
elemental analysis suggest partial THF depletion. Anal. Calcd
for C44H60O4BLi: C, 78.80; H, 9.02. Found: C, 82.01; H, 7.43.
F igu r e 3. ORTEP view of 3 in the crystal (50% ellipsoids).
Selected bond lengths (Å) and angles (deg): B(1)-C(21) )
1.573(4), B(1)-C(1) ) 1.577(4), B(1)-C(11) ) 1.603(4),
B(2)-C(31) ) 1.563(4), B(2)-C(41) ) 1.575(4), B(2)-C(8)
) 1.577(5); C(21)-B(1)-C(1) ) 122.0(3), C(21)-B(1)-C(11)
) 119.1(3), C(1)-B(1)-C(11) ) 118.1(3), C(31)-B(2)-C(41)
) 121.3(3), C(31)-B(2)-C(8) ) 118.1(3), C(41)-B(2)-C(8)
) 117.9(3), C(9)-C(1)-B(1) ) 128.3(3), C(9)-C(8)-B(2) )
128.5(3).
1-(Dim esitylbor yl)-8-(d im eth ylbor yl)n a p h th a len e (2).
To a suspension of freshly isolated 1-Li(THF)4 (500 mg, 0.75
mmol) in diethyl ether (10 mL) at 25 °C was added neat
dimethylboron bromide (73 µL, 0.75 mmol). The reaction
mixture was stirred at 25 °C for 1 h. The solution was then
filtered and the ether removed by evaporation. The crude
crystalline solid that remained was recrystallized from pen-
tane, producing large pale yellow crystals. Yield: 250 mg
(79%). Mp: 138-143 °C. 1H NMR (chloroform-d): 0.02 (broad
s, 3H, B-CH3), 0.83 (broad s, 3H, B-CH3), 1.07 (s, 3H, Mes
CH3), 1.60 (s, 3H, Mes CH3), 1.98 (s, 3H, Mes CH3), 2.24 (s,
3H, Mes CH3), 2.31 (s, 3H, Mes CH3), 2.41 (s, 3H, Mes CH3),
6.54 (s, 1H, Mes CH), 6.71 (s, 1H, Mes CH), 6.76 (s, 1H, Mes
CH), 6.89 (s, 1H, Mes CH), 7.33 (d, 1H, naph CH), 7.38-7.46
(m, 2H, naph CH), 7.82 (m, 2H, naph CH), 7.99 (d, 1H, naph
CH). 13C NMR (chloroform-d): 21.36, 22.74, 23.05, 24.52, 24.67,
Con clu sion
In summary, we report the synthesis of an anionic
boron-bridged naphthalene derivative that undergoes
facile ring-opening reactions to afford unsymmetrically
substituted 1,8-diborylnaphthalene derivatives. We note
that the ring-opening reactions of 1 should provide
access to a variety of heteronuclear bifunctional Lewis
acids.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. 1,8-Diiodonaphthalene22 and
diphenylboron bromide23 were synthesized by following litera-
ture procedures. Dimesitylboron fluoride, dimethylboron bro-
mide, and n-butyllithium (1.6 M in hexanes) were purchased
from Aldrich and used without purification. Solvents were
(22) House, H. O.; Campbell, W. J .; Koepsell, D. G. J . Org. Chem.
1972, 37, 1003-1011.
(23) No¨th, H.; Vahrenkamp, H. J . Organomet. Chem. 1968, 11, 399-
405.

Notes
Organometallics, Vol. 21, No. 5, 2002 985
26.42 (Mes CH3); 125.19, 125.75, 128.43, 128.73, 129.15,
129.53, 129.97, 130.71, 135.20, 139.82 (CH); 133.85 (C-9 or -10);
138.31, 141.13, 141.31, 141.59, 144.21, 145.51 (C-CH3); B-CH3,
C-ipso, and C9 or 10 not detected. Anal. Calcd for C30H34B2:
C, 86.58; H, 8.23. Found: C, 86.49; H, 8.29.
131.9 135.0 136.5 139.3 (12C, naph/phenyl CH), 126.5, 127.5,
140.0, 140.4 (8C, phenyl o-/m-CH); 134.0, 138.0, 141.6, 141.7,
142.1, 143.9 (C-CH3); 141.5, 144.2, 148.3, 149.5 (br, ipso-/peri-
C); C9/10 and two ipso-C not detected. Anal. Calcd for
C
40H38B2: C, 88.91; H, 7.09. Found: C, 88.89; H, 7.12.
1-(Dim esitylbor yl)-8-(d ip h en ylbor yl)n a p h th a len e (3).
To a suspension of freshly isolated 1-Li(THF)4 (4.01 g, 5.97
mmol) in diethyl ether (15 mL) at 25 °C was added neat
diphenylboron bromide (1.46 g, 5.97 mmol). The solution was
stirred for 12 h at 25 °C, and the solvent was evaporated. The
resulting solid was extracted with hot chloroform (10 mL). This
solution was filtered, and the chloroform was removed under
vacuum to afford 5 as a white powder. Yield: 2.2 g (71%). Mp:
Ack n ow led gm en t. Support from the Welch Foun-
dation (Grant A-1423), the National Science Foundation
(CAREER CHE-0094264), and the Department of Chem-
istry at Texas A&M University is gratefully acknowl-
edged. The purchase of the X-ray diffractometer was
made possible by a grant from the National Science
Foundation (No. CHE-9807975).
1
241-244 °C. H NMR (chloroform-d): 1.10 (s, 3H, Mes CH3),
1.22 (s, 3H, Mes CH3), 1.58 (s, 3H, Mes CH3), 1.75 (s, 3H, Mes
CH3), 2.08 (s, 3H, Mes CH3), 2.26 (s, 3H, Mes CH3), 6.31 (s,
1H, Mes CH), 6.62 (s, 1H, Mes CH), 6.66 (s, 1H, Mes CH),
6.69 (s, 1H, Mes CH), 7.16-7.31 (m, 9H, naph/phenyl CH),
7.34-7.53 (m, 4H, naph/phenyl CH), 7.79 (d, 1H, naph CH),
8.04 (d, 1H, naph CH), 8.13 (d, 1H, naph CH). 13C NMR
(chloroform-d): 21.23, 21.28, 22.38, 22.50, 22.95, 25.62 (Mes
CH3); 124.3, 126.0, 128.1, 128.3, 129.4, 130.2, 130.5, 131.1,
Su p p or tin g In for m a tion Ava ila ble: Tables of structure
refinement, atomic coordinates, bond lengths and angles,
anisotropic displacement parameters, and hydrogen coordi-
nates for for 1-3. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM010946X