Syntheses of ring-fused B-N heteroaromatic compounds

Article abstract of DOI:10.1021/om058048e

3a,7a-Azaborindene (14) has been prepared by two multistep syntheses using the Grubbs ring-closing metathesis from appropriate B-vinyl,N-allyl- aminoboranes. 14 was deprotonated by KN(SiMe₃)₂ to give 3a,7a-azaborindenylpotassium (5). The reaction of 5 with Cp*ZrCl ₃ afforded the corresponding Zr(IV) complex 18, which on activation with excess methylaluminoxane, forms a good catalyst for the polymerization of ethylene. The reaction of 5 with methylene chloride and BuLi gave 4a,8a-azaboranaphthalene (6), which is isoelectronic and isostructural with naphthalene. DFT calculations on 6 gave a structure that is in good agreement with X-ray diffraction data.

Full text of DOI:10.1021/om058048e

Organometallics 2006, 25, 513-518
513
Syntheses of Ring-Fused B-N Heteroaromatic Compounds
Xiangdong Fang, Hong Yang, Jeff W. Kampf, Mark M. Banaszak Holl, and
Arthur J. Ashe, III*
Department of Chemistry, UniVersity of Michigan, Ann Arbor, Michigan 48109-1055
ReceiVed September 15, 2005
3a,7a-Azaborindene (14) has been prepared by two multistep syntheses using the Grubbs ring-closing
metathesis from appropriate B-vinyl,N-allyl-aminoboranes. 14 was deprotonated by KN(SiMe
3 2
) to give
3
a,7a-azaborindenylpotassium (5). The reaction of 5 with Cp*ZrCl afforded the corresponding Zr(IV)
3
complex 18, which on activation with excess methylaluminoxane, forms a good catalyst for the
polymerization of ethylene. The reaction of 5 with methylene chloride and BuLi gave 4a,8a-
azaboranaphthalene (6), which is isoelectronic and isostructural with naphthalene. DFT calculations on
6
gave a structure that is in good agreement with X-ray diffraction data.
azaborindenyl (5)11a and 4a,8a-azaboranaphthalene (6).11b 5 and
are isoelectronic and possibly isostructural with indenyl and
Introduction
6
Cyclopentadienyl and benzene are the most important aro-
matic rings and can be regarded as progenitors of all other five-
and six-membered aromatic rings. The replacement of one of
the C-C π-bonds of cyclopentadienyl and benzene by an
isoelectronic B-N π-bond leads to 1,2-azaborolyl (1) and 1,2-
dihydro-1,2-azaborine (2), respectively. 1,2-Azaborolyl has been
used as a replacement ligand for Cp in a variety of transition
naphthalene. Yet since 5 and 6 are constructed only from B-N
heterocyclic rings, they should be electronically perturbed from
their carbocyclic parents. 6 was first reported in 1968 in a
1
2
masterful paper by Dewar and Jones. Unfortunately the yield
of their synthesis was abysmally low (0.2%), which has limited
subsequent investigations of 6. We have previously reported
3
b
metal complexes.1 Of particular interest is the observation that
,2-azaborolyl zirconium(IV) complexes, e.g. 3, have high
-4
on the synthesis of 5. We report here on details of our work
on 5 and on a new efficient synthesis of 6.
1
activity as Ziegler-Natta catalysts for the polymerization of
5
olefins. The aromatic character of 1,2-dihydro-1,2-azaborines
6
-10
has been of interest to chemists for more than 40 years.
Computational studies suggest that 2 has a considerable delo-
9
calization energy. Derivatives of 2 can form arene-like metal
complexes, such as 4.10
We have been interested in extending the chemistry of 1 and
2
by developing syntheses of the fused-ring compounds 3a,7a-
*
To whom correspondence should be addressed. E-mail: ajashe@
umich.edu.
(
1) (a) Schulze, J.; Schmid, G. Angew. Chem., Int. Ed. Engl. 1980, 19,
5
4. (b) Amirkhalili, S.; Boese, R.; H o¨ hner, U.; Kampmann, D.; Schmid,
G.; Rademacher, P. Chem. Ber. 1982, 115, 732. (c) Schmid, G.; Boltsch,
O.; Bl a¨ ser, D.; Boese, R. Z. Naturforch. 1984, 39b, 1082. (d) Schmid, G.;
Sch u¨ ltz, M. J. Organomet. Chem. 1995, 492, 185, and earlier papers in
this series.
(2) (a) Schmid, G. Comments Inorg. Chem. 1985, 4, 17. (b) Schmid, G.
In ComprehensiVe Heterocyclic Chemistry II; Shinkai, I., Ed.; Pergamon:
Oxford, UK, 1996; Vol. 3, p 739.
(
3) (a) Ashe, A. J., III; Fang, X. Org. Lett. 2000, 2, 2089. (b) Ashe, A.
J., III; Yang, H.; Fang, X.; Kampf, J. W. Organometallics 2002, 21, 4578.
c) Yang, H.; Fang, X.; Kampf, J. W.; Ashe, A. J., III. Polyhedron 2005,
(
2
4, 1280.
(
4) (a) Liu, S.-Y.; Lo, M. M.-C.; Fu, G. C. Angew. Chem., Int. Ed. 2002,
4
1, 174. (b) Liu, S.-Y.; Hills, I. D.; Fu, G. C. Organometallics 2002, 21,
4
323.
(5) (a) Nagy, S.; Krishnamurti, R.; Etherton, B. P. PCT Int. Appl. WO96
3
4, 021, 1996; Chem. Abstr. 1997, 126, 19432j. (b) Ashe, A. J., III; Yang,
H.; Timmers, F. J. PCT Int. Appl. WO2003 087114 A1 20031023, 2003;
Chem. Abstr. 2003, 139, 323949.
(
6) (a) Dewar, M. J. S.; Marr, P. A. J. Am. Chem. Soc. 1962, 84, 3782.
(
b) Davies, K. M.; Dewar, M. J. S.; Rona, P. J. Am. Chem. Soc. 1967, 89,
6
294.
(
(
(
7) White, D. G. J. Am. Chem. Soc. 1963, 85, 3634.
8) Fritsch, A. J. Chem. Heterocycl. Compd. 1977, 30, 381.
9) (a) Massey, S. T.; Zoellner, R. W. Int. J. Quantum Chem. 1991, 39,
7
87. (b) Kranz, M.; Clark, T. J. Org. Chem. 1992, 57, 5492.
10) Ashe, A. J., III; Fang, X.; Fang, X.; Kampf, J. W. Organometallics
001, 20, 5413.
(
2
1
0.1021/om058048e CCC: $33.50 © 2006 American Chemical Society
Publication on Web 11/25/2005

5
14 Organometallics, Vol. 25, No. 2, 2006
Fang et al.
Scheme 1. Syntheses of 1 and 2a
a
2 2
Key: a, Grubbs catalyst; b, LDA; c, CH Cl /base.
Scheme 2. Initial Synthetic Plan
the B-N analogue of indene outlined in Scheme 3 was
successful, the overall yield of 14 from the dibutyldivinylstan-
nane was rather modest (3%). Thus an alternate route has been
developed.
Allyltributylstannane reacted with BCl3 at -78 °C in pentane
to give allylboron dichloride, which was not isolated.15 In situ
addition of 1 equiv of diallylamine followed by 1 equiv of
triethylamine afforded 15 in 95% yield. Reaction of 15 with
vinylmagnesium bromide gave aminoborane 16 in 84% yield.
The treatment of 16 with 5 mol % of Grubbs catalyst in
methylene chloride converted it to 17 in 59% yield. Finally the
oxidation of 17 with DDQ gave 14 in 30% yield. This sequence,
outlined in Scheme 4, allows the preparation of 14 in 14%
overall yield from the starting stannane. Thus it represents a
significant improvement over the prior preparation.
Results and Discussion
Syntheses. 1,2-Dihydro-1,2-azaborines (2) have been pre-
pared by a carbenoid ring expansion from the corresponding
,2-azaborolides (1), which in turn can generally be prepared
Azaborindene 14 is readily deprotonated by potassium bis-
(
trimethylsilyl)amide in toluene to afford 5 as a yellow powder
1
1
in 85% yield. The H NMR spectrum of 5 in either DMSO-d6
or THF-d8 could be only partially assigned since signals for
four of the ring protons occur as a very closely spaced pattern
centered at δ 6.70 (DMSO). Fortunately after the addition of
10
by LDA deprotonation of their conjugate acids (8). The Grubbs
ring-closing metathesis (RCM) on appropriate B-vinyl,N-allyl
aminoboranes 7 usually affords 8.3 See Scheme 1. Hence our
initial plan was to convert aminoborane 9 to 10 by RCM and
then convert 10 to 5 and 6 by sequential ring expansions
a
1
8-crown-6 ether to 5 followed by dissolution in benzene-d6, a
1
beautiful first-order H NMR spectrum was obtained. This
spectrum is completely consistent with structure 5. The reaction
of 5 with Cp*ZrCl3 in ether gave a 60% yield of complex 18,
for which an X-ray crystal structure has been obtained.
Finally the reaction of 5 with methylene chloride and BuLi
gave a 43% yield of 4a,8a-azaboranaphthalene (6) as pale yellow
crystals, which have a strong naphthalene-like odor. The mp
(Scheme 2).
The reaction of dibutyldivinylstannane with BCl3 in pentane
at -78 °C afforded divinylboron chloride.13 Although this
sensitive boron halide can be isolated and characterized by NMR
spectroscopy, it is more convenient to treat it in situ with 2
equiv of diallylamine to afford 9 directly in 79% yield. Upon
treatment of 9 with 5 mol % of Grubbs catalyst at 25 °C in
methylene chloride, the monocyclized product 11 was obtained
in 62% yield. Even under forcing conditions (higher temperature,
excess catalyst) the [5,5]-fused-ring compound 10 was not
observed. This observation is precedented by the failure of
certain 1-allyl-2-vinyl heterocycles to form [5,5]-fused rings on
1
11
and H and B NMR spectra of 6 show that it is identical to
the material originally reported by Dewar and Jones.
12,16
Furthermore we have obtained an X-ray crystal structure for 6
that establishes its structure. The overall yield of the above
preparation from commercially available allyltributylstannane
is 5.6%. This is nearly a 30-fold improvement over the Dewar-
Jones preparation. Thus 4a,8a-azaboranaphthalene is now more
readily available for study.
1
4
attempted RCM. We speculate that 10 is somewhat ring
strained and its formation may not be thermodynamically
favored.
Polymerization Studies. Indenyl zirconium(IV) derivatives
have been widely used as highly active and stereoselective
Deprotonation of 11 with LDA in THF gave a 67% yield of
the azaborolide 12, which could be isolated as a brown solid.
Treatment of 12 with LDA and methylene chloride at -78 °C
followed by warming lead to the ring-expanded product 13 in
17
catalysts for olefin polymerization. Thus it was of major
interest to prepare and study the polymerization activities of
30% yield. The treatment of 13 with 5 mol % of Grubbs catalyst
(15) (a) Halligan, N. G.; Blaszczak, L. C. Organic Syntheses; Wiley:
in methylene chloride led to RCM formation of the [6,5]-ring-
fused product in 30% yield. Apparently the more favorable
geometry about the six-membered 1,2-dihydro-1,2-azaborine
ring allowed formation of the ring-closed product. Compound
New York, Collect. Vol. VIII; 1993; p 23. (b) Singleton, D. A.; Waller, S.
C.; Zhang, Z.; Frantz, D. E.; Leung, S. W. J. Am. Chem. Soc. 1996, 118,
9
986.
(16) Davis, F. A.; Dewar, M. J. S.; Jones, R.; Worley, S. D. J. Am. Chem.
Soc. 1969, 91, 2094.
(17) For a recent review see: (a) Brintzinger, H. H.; Fischer, D.;
M u¨ lhaupt, R.; Rieger, B.: Waymouth, R. M. Angew. Chem., Int. Ed. Engl.
1
4 is isoelectronic with indene. Interestingly, the odor of 14
closely resembles that of indene. Although this preparation of
1995, 34, 1143. (b) Ziegler Catalysts; Fink, G., M u¨ lhaupt, R., Brintzinger,
H. H., Eds.; Springer-Verlag: Berlin, Germany, 1995. (c) Coates, G. W.;
Waymouth, R. M. In ComprehensiVe Organometallic Chemistry II; Hegedus,
L. S., Ed.; Pergamon: Oxford, U.K., 1995; Vol. 12, p 1193. (d) Aulbach,
M.; K u¨ ber, F. Chem. Unserer Zeit 1994, 28, 197. (e) Janiak, C. Metallocene
Catalysts for Olefin Polymerization. In Metallocenes; Togni, A., Haltermann,
R. L., Eds.; Wiley-VCH: Weinheim, Germany, 1998; Vol. 2, pp 547-
623. (f) Gladysz, J. A., Ed. Chem. ReV. 2000, 100, 1167.
(
11) Chemical Abstracts names: (a) 1H-[1,2]azaborolo[1,2-a][1,2]-
azaborinyl. (b) [1,2]Azaborino[1,2-a][1,2]azaborine.
(
(
12) Dewar, M. J. S.; Jones, R. J. Am. Chem. Soc. 1968, 90, 2137.
13) Brinckman, F. E.; Stone, F. G. A. J. Am. Chem. Soc. 1960, 82,
6
218.
14) Huwe, C. M.; Blechert, S. Tetrahedron Lett. 1995, 36, 1621.
(

Ring-Fused B-N Heteroaromatic Compounds
Organometallics, Vol. 25, No. 2, 2006 515
Scheme 3. Preparation of Azaborindenea
a
Key: a, BCl
3
; b, HN(allyl)
2 2 2
; c, Grubbs catalyst; d, LDA; e, CH Cl /base.
Scheme 4. Alternate Synthesis of 14 and Its Conversion to 5 and 6a
a
3 2 3 2 3 3 2 2 2
Key: a, BCl ; b, HN(allyl) ; c, NEt ; d, C H MgBr; e, Grubbs catalyst; f, DDQ; g, KN(SiMe ) ; h, CH Cl /BuLi.
Table 1. Comparison of the Efficiency of Ethylene/1-Octene
Polymerization of 3, 18, and 19
azaborindenyl zirconium(IV) complexes. As previously reported,
the reaction of 5 with Cp*ZrCl3 afforded a 60% yield of 18.
Similarly the reaction of 17 with LDA followed by Cp*ZrCl3
gave a 55% yield of complex 19. The crystal structures of 18
complex
efficiency (g polymer/mol Zr atom)
ref
4
3
18
19
234 × 10
3c
this work
this work
4
and 19 show that the complexes have very similar structures,
120 × 10
4
which closely resemble that of Cp*(Ind)ZrCl218 (20).
66 × 10
On activation by 1000 molar excess of methylaluminoxane
the incorporation of approximately 1% 1-octene. It has been
(
MAO) in a hydrocarbon solvent, 18 and 19 form active catalysts
19
estimated that complex 3 is approximately 10 times more active
for the polymerization of ethylene and 1-octene. The polym-
erization results are summarized in Table 1, which also shows
data for complex 3. All three complexes gave polyethylene with
3a
than Cp2ZrCl2 for ethylene polymerization. Thus it seems safe
to conclude that 18 and 19 must form more active catalysts
than does Cp2ZrCl2.
(
18) Schmid, M. A.; Alt, H. G.; Milius, W. J. Organomet. Chem. 1996,
14, 45.
19) For details of polymerization conditions see refs 3c and 5b and Ashe,
A. J., III; Fang, X.; Hokky, A.; Kampf, J. W. Organomettalics 2004, 23,
197.
MAO-activated indenyl zirconium(IV) complexes are usually
found to be more active catalysts than are the corresponding
Cp zirconium(IV) complexes. For example Alt and co-workers
reported that Cp*(Ind)ZrCl2 was 3 times more active than Cp*-
5
(
2

5
16 Organometallics, Vol. 25, No. 2, 2006
Fang et al.
crystallographically distinguished. This partial disorder severely
limits the structural information available for 6. To a first
approximation the B-N bond length and the C(1)-C(4) bond
length are unaffected by this disorder. However the C(2)-N
and the B-C(3) distances must average, as do the C(1)-C(2)
and C(3)-C(4) distances.
The B-N bond distance (1.461(1) Å) of 6 is 0.03 Å longer
than that of 21 (1.430(5) Å). Similarly the C(1)-C(4) distance
(
1.431(1) Å) of 6 is 0.02 Å longer than the corresponding C-C
2
0
distances of 21. The longer bonds in the fused-ring 6 vs the
monocyclic 21 find analogy in the difference between naph-
thalene and benzene. The C-C bond at the ring-fusion of
naphthalene is also 0.03 Å longer than C-C bond of benzene,
and the C(2)-C(3) bond of naphthalene is 0.02 Å longer than
2
1-23
that of benzene.
There are several prior theoretical studies of 6, although there
24
are no reported computational structural data. To obtain more
information about the structure of 6, we have performed density
functional theory (DFT) calculations at the B3LYP/6-31G*
level. The calculated distances are tabulated in Table 2. The
calculated B-N distance is 0.018 Å longer than the crystal-
lographic distance, while the calculated and crystallographic
distances for C(1)-C(4) are identical. The calculated mean
values for the heteroatom-C distances (1.453 Å) and the mean
of C(1)-C(2) and C(3)-C(4) distances (1.366 Å) are within
0.01 Å of the crystallographic distances. Thus the calculated
and experimental structures for 6 are in reasonable agreement.
Summary. In summary the synthesis of the B-N fused
analogue of indenyl 5 allows exploration of its coordination
chemistry. Zr(IV) complex 18 behaves as a perturbed indenyl
complex. On activation by excess MAO, 18 shows significant
activity as a polymerization catalyst. The carbenoid ring
expansion of 5 allows a facile preparation of the B-N fused
naphthalene analogue 6. The way is now open for further
exploration of the chemistry of these fused-ring aromatics.
Figure 1. Solid-state structure of 6 (ORTEP). B(1) and N(1) are
not crystallographically distinguished. Thermal ellipsoids are at the
50% probability level.
Table 2. Comparison of Experimental and Calculated Bond
Distances (Å) for 6
bond
experimental (X-ray)
calculated (DFT)
B(1)-N(1)
C(1)-C(4)
N(1)-C(2)
B(1)-C(3)
C(1)-C(2)
C(3)-C(4)
1.461(1)
1.431(1)
1.445(1)
1.455(1)
1.360(1)
1.479
1.430
1.383
1.522
1.370
1.362
a
a
b
b
1.357(1)
a
Distances N(1)-C(2) and B(1)-C(3) are averaged by disorder.
Distances C(1)-C(2) and C(3)-C(4) are averaged by disorder.
b
(
Cp)ZrCl2.18 Thus it was surprising to find that azaborolyl
complex 3 was 2 times more reactive than azaborindenyl
complex 18. However the difference in substitution between
the complexes makes this comparison tenuous. The structural
similarity of 18 and 19 makes them a better pair for comparison.
The 2-fold greater activity of 18 vs 19 indicates that the BN
complexes show the normal effect. The significant polymeri-
zation activity of 18 and 19 makes the syntheses of their bridged
derivatives attractive targets for future investigations.
Experimental Section
General Methods. All reactions were carried out under an
atmosphere of argon or nitrogen. Solvents were dried using standard
procedures. High-resolution mass spectra were recorded on a VG-
250S spectrometer with an electron inact at 70 eV. The NMR
spectra were obtained using either a Varian INOVA 400 or 500, a
1
Brucker WH 300, or an AM 300 spectrometer. The H NMR and
13
C NMR spectra were calibrated by using signals from solvents
referenced to Me
Si. The 11B NMR spectra were referenced to
external BF ‚OEt . Elemental analyses were obtained by the
4
3
2
Analytical Services of the Department of Chemistry at the
University of Michigan using a Perkin-Elmer 240 CHN analyzer.
(
Diallylamino)divinylborane (9). A solution of dibutyldivinyl-
stannane (56 g, 0.194 mol) in 30 mL of pentane was added dropwise
to a solution of BCl (20.7 g, 0.176 mol) at -78 °C. The mixture
3
was stirred at -78 °C for 1 h and at 25 °C for 30 min. After cooling
to -78 °C the mixture was further stirred until it solidified.
Diallylamine (17.1 g, 0.176 mol) was added via a syringe followed
by triethylamine (17.8 g, 0.176 mol). The mixture was stirred for
10 h. After filtration and removal of the volatiles the product was
X-ray and DFT Structures for 6. It was of interest to obtain
structural data for 4a,8a-azaboranaphthalene. Crystals of 6
suitable for an X-ray diffraction study were obtained by
recrystallization from pentane. The molecular structure of 6 is
illustrated in Figure 1, and bond distances are listed in Table 2.
It was found that 6 is isostructural with naphthalene. There is
an inversion center located at the midpoint of the B-N bond,
which means that the boron and nitrogen atoms are not
(20) Pan, J.; Kampf, J. W.; Ashe, A. J., III. Organometallics 2005, in
press.
(21) Brock, C. P.; Dunitz, D. J. Acta Crystallogr. 1982, B38, 2218.
22) (a) Almenningen, A.; Bastiansen, O.; Dyvik, F. Acta Crystallogr.
(
1961, 14, 1056. (b) Ketkar, S. N.; Fink, M. J. Mol. Struct. 1981, 77, 139.
(23) Millefiori, S.; Alparone, A. J. Mol. Struct. 1998, 422, 179.
(
24) (a) Michl, J. Collect. Czech. Chem. Commun. 1971, 36, 1248. (b)
Maouche, B.; Gayoso, J.; Ouamerali, O. ReV. Roum. Chim. 1984, 29, 613.
c) Kar, T.; Elmore, D. E.; Scheiner, S. J. Mol. Struct. 1997, 392, 65. (d)
Chen, Z.; Jiao, H.; Hirsch, A.; Thiel, W. J. Org. Chem. 2001, 66, 3380.
(

Ring-Fused B-N Heteroaromatic Compounds
Organometallics, Vol. 25, No. 2, 2006 517
obtained by vacuum distillation (21.9 g, 79%), bp 38 °C at 0.05
Table 3. Crystal and Data Collection Parameters for 6
1
Torr (oil bath temperature was kept under 80 °C). H NMR (C
6 6
D ,
empirical formula
fw
C8H8BN
128.96
4
4
4
00 MHz): δ 6.39 (dd, 2H, J ) 19.0, 14.3 Hz, CHB), 5.91 (m,
H, alkene), 5.60 (m, 2H, alkene), 5.00 (m, 4H, alkene), 3.60 (d,
temp K
123(2)
13
wavelength, Å
cryst syst
space group
a, Å
0.71073
monoclinic
P2(1)/c
2 6 6
H, J ) 5.2 Hz, CH ). C NMR (C D , 100.6 MHz): δ 138.6
11
(br), 136.7, 132.8, 115.9, 52.1. B NMR (C
6
1
D
6
, 115.5 MHz): δ
1
+
37.8. HRMS (EI, m/z): calcd for C10
H
15 BN ([M - H] ),
7.961(2)
1
60.1298; found, 160.1305. Anal. Calcd for C10H16BN: C, 74.57;
b, Å
5.989(2)
H, 10.01; N, 8.70. Found: C, 75.21; H, 10.18; N, 8.74.
-Allyl-2,5-dihydro-2-vinyl-1,2-1H-azaborole (11). A solution
of 9 (7.3 g, 45.3 mmol) in 90 mL of CH Cl was added dropwise
to a flask containing bis(tricyclohexylphosphine)benzylidene-
ruthenium(IV) dichloride (5 mol %) at -78 °C. The mixture was
stirred at -78 °C for 1 h and at 25 °C for 9 h. After slow removal
of the solvent at 0 °C, the product was obtained by vacuum
c, Å
â, deg
V, Å , Z
calcd density, Mg/m
abs coeff, mm
F(000)
cryst size, mm
limiting indices
8.112(2)
114.284(7)
352.6(2), 2
1.215
0.070
136
1
3
2
2
3
-1
0.50 × 0.40 × 0.22
-12 e h e 11; -9 e k e 9;
-
13 e l e 13
9633/1533
distillation as a clear colorless liquid (62%), bp 25 °C at 0.05 Torr.
no. of reflns collected/unique
abs corr
refinement method
no. of data/restraints/params
final R indices (I > 2σ(I))
largest diff peak and hole, e/Å3
1
H NMR (C
.52 (d, 1H, J ) 10 Hz, C(4)H, 6.43 (dd, 1H, J ) 16, 14.4 Hz,
vinyl BCH), 6.18 (dd, 1H, J ) 16, 4 Hz, cis-vinylH), 6.05 (d(br),
H, J ) 14.4 Hz, trans-vinylH), 5.59 (m, 1H, allyl), 4.90 (m, 2H,
allyl), 3.65 (d, 2H, J ) 4 Hz, ring-CH ), 3.44 (m, 2H, allyl-CH ).
, 100.6 MHz): δ 148.3, 137.3, 134.5, 134.2 (br),
6 6
D , 400 MHz): δ 6.83 (d, 1H, J ) 10 Hz, C(3)H,
none
6
2
full-matrix least-squares on F
1533/0/62
R1 ) 0.0491, wR2 ) 0.1247
0.381 and -0.168
1
2
2
13
6 6
C NMR (C D
1
1
colorless liquid, bp 25-26 °C at 0.05 Torr. HRMS: m/z calcd for
1
33.6 (br), 114.9, 60.3. B NMR (C
6
D
6
, 115.5 MHz): δ 37.4.
1
1
1
1
1
+
C
7
H
10 BN 117.0750, found 117.0752. H NMR (C
MHz): δ 3.52 (br s, 2H, CH N), 6.11 (t, J ) 6.3 Hz, 1H, C(5)H),
.52 (m, 2H, C(1)HC(2)H), 6.94 (d, J ) 6.3 Hz, 1H, C(4)H), 7.06
d, J ) 11.1 Hz, 1H, BCH), 7.61 (dd, J ) 11.1, 6.3 Hz, 1H, C(6)H).
6 6
D , 400
HRMS (EI, m/z): calcd for C
8
H
13 BN (M ), 134.1141; found,
2
1
34.1147.
Lithium 1-Allyl-2-vinyl-1,2-azaborolide (12). A solution of 11
4.3 g, 32 mmol) in 15 mL of ether was added dropwise to a
6
(
(
1
1
13
B NMR (C
MHz): δ 58.8, 109.5, 124 (br), 133.6 (br), 135.3, 143.2, 144.2.
Anal. Calcd for C 10BN: C, 71.87; H, 6.91; N, 11.98. Found: C,
1.77; H, 7.04; N, 11.85.
a,7a-Azaborindenylpotassium (5). A 0.5 M toluene solution
6 6 6 6
D , 115.5 MHz): δ 34.2. C NMR (C D , 100.5
solution of LDA (1 equiv) in 12 mL of ether at -78 °C. The mixture
was stirred at -78 °C for 2 h and at 25 °C for 10 h. The volatile
components were removed under reduced pressure, and the residue
was washed with 2 × 20 mL of pentane. The residue was dried
7
H
7
3
1
under vacuum to give the product as a brown solid (67%). H NMR
of potassium bis(trimethylsilyl)amide (41.0 mL, 20.5 mmol) was
added dropwise to a solution of 14 (2.4 g, 20.5 mmol) in 15 mL of
toluene at -78 °C. The mixture was stirred at -78 °C for 4 h and
then 2 h at -20 °C. The solution was decanted, and the solid residue
was washed first with toluene and then pentane. A yellow powder
was obtained (2.7 g, 85%). H NMR (500 MHz, C
crown-6): δ 8.29 (dd, J ) 6.4, 0.7 Hz, 1H, C(4)H); 7.70 (d, J )
1 Hz, 1H, C(7)H); 7.49 (dd, J ) 11.1, 6.3 Hz, 1H, C(6)H; 7.38
dd, J ) 5.9, 2.2 Hz, 1H, C(2)H); 7.26 (t, J ) 20 Hz, 1H, C(3)H;
.49 (td, J ) 6.3, 1.2 Hz, 1H, C(5)H; 5.70 (d, J ) 5.9 Hz, 1H,
(
THF-d
8
, 400 MHz): δ 6.39 (dd, 1H, J ) 19.4, 13.5 Hz, vinyl
BCHd), 5.92 (m, 1H, allyl), 5.79 (m, 2H, H(4) and H(5)), 5.29
(
5
4
dd, 1H, J ) 19.4, 5.1 Hz, trans-vinylH), 5.11 (dd, 1H, J ) 13.5,
.1 Hz, cis-vinylH), 4.92 (dq, 1H, J ) 17.2, 2 Hz, trans-allylH),
.84 (dq, 1H, J ) 10.3, 2 Hz, cis-allylH), 4.34 (dd, 1H, J ) 5.1, 2
1
6
D
6
and 18-
13
2 8
Hz, H(3)), 4.23 (dt, 2H, J ) 5.5, 2 Hz, NCH ). C NMR (THF-d ,
1
00.6 MHz): δ 141.1, 140.6 (br), 117.9, 113.0, 112.2, 112.1, 86.2
1
(
6
(
br), 51.4. 11B NMR (THF-d
-Allyl-1,2-dihydro-2-vinyl-1,2-azaborine (13). A suspension
of 12 (2.53 g, 18.1 mmol) in 15 mL of CH Cl was treated dropwise
with a solution of LDA (1.93 g, 18.1 mmol) in 12 mL of ether at
78 °C. The mixture was stirred at -78 °C for 2 h and at 25 °C
8
; 115.5 MHz): δ 27.6.
1
2
2
C(1)H). H NMR (400 MHz, DMSO-d
H, C(4)H); 6.65-6.76 (m, 4H); 5.90 (m, 1H); 4.77 (d, J ) 5.9
6
Hz, 1H, C(1)H). C NMR (100.6 MHz, DMSO-d ): δ 127.1, 123.0,
1
6
): δ 7.84 (d, J ) 6.2 Hz,
1
-
13
for 10 h. The volatile components were removed under reduced
pressure. The residue was extracted with 20 mL of pentane. After
filtration and removal of the solvent at 0 °C, the brown oily residue
11
1
21.6, 104.5, 103.3, 88 br. C(7) not observed. B NMR (115.5
MHz, C ): δ 25.8.
a,8a-Azaboranaphthalene (6). Methylene chloride (25 mL)
6 6
D
4
was vacuum distilled to give the product as a clear colorless liquid
was added to 3a,7a-azaborindenylpotassium (5) (2.7 g, 17.41 mmol)
at -78 °C. Then a solution of n-BuLi (6.70 mL, 17.50 mmol, 2.5
M in hexane) was added. The black mixture was stirred for 4 h at
1
(
0.79 g, 30%), bp 28 °C at 0.05 Torr. H NMR (C
D
6 6
, 300 MHz):
δ 7.51 (dd, 1H, J ) 11, 6.6 Hz, H(4)), 7.11 (d, 1H, J ) 6.6 Hz,
H(6)), 6.57 (d, 1H, J ) 6.6 Hz, H(3)), 6.52 (dd, 1H, J ) 19.5, 13.5
Hz, vinyl-BCH), 6.17 (dd, 1H, J ) 19.5, 4.1 Hz, trans-vinylH),
-
78 °C and another 2 h at 25 °C. After removing the solvent, an
orange liquid was obtained. The pure product was obtained by
chromatography on silica gel using pentane as eluant. On concen-
tration of the solution, pale yellow crystals of 6 were formed (1.22
6
.07 (t, 1H, J ) 6.6 Hz, H(5)), 5.92 (dd(br), 1H, J ) 13.5, 2.8 Hz,
cis-vinylH), 5.49 (m, 1H, allyl), 4.78 (m, 1H, allyl), 4.67 (m, 1H,
13
allyl), 3.83 (d, 2H, J ) 2.8 Hz, allyl-CH
2
). C NMR (C
6 6
D , 90.6
1
g, 43%). H NMR (500 MHz, DMSO-d
6
): δ 8.18 (d, J ) 7.0 Hz,
MHz): δ 142.9, 138.5, 138 (br), 136.0, 130.9, 129 (br), 115.7,
2
1
H, C(4)H); 7.67 (dd, J ) 11.0, 7.0 Hz, 2H, C(2)H; 7.30 (d, J )
1
11.3, 55.7. 11B NMR (C
6
D
6
+
, 115.5 MHz): δ 33.1. HRMS (EI,
13
1.0 Hz, 2H, C(1)H); 6.81 (dt, J ) 7.0, 1.5 Hz, 2H, C(4)H).
C
11
9
m/z): calcd for C H12 BN (M ), 145.1063; found, 145.1064. Anal.
6
NMR (100.6 MHz, DMSO-d ): δ 138.4 (C(2)); 134.1 (C(4)); 132.0
Calcd for C
H, 8.52; N, 9.48.
a,7a-Azabora-1-indene (14). A solution of 13 (3.24 g) in 20
mL of CH Cl was added dropwise to a solution of bis(cyclohexy-
lphosphine)benzylideneruthenium(IV) dichloride (5 mol %) in 20
mL of CH Cl at 25 °C. Bubbles formed intensively. The mixture
9
H12BN: C, 74.55; H, 8.34; N, 9.66. Found: C, 74.40;
11
(
br, C(1); 114.3 (C(3)). B NMR (160.4 MHz, DMSO): δ 28.1.
HRMS: calcd for C
Calcd for C H BN: C, 74.49; H, 6.26; N, 10.86. Found: C, 74.56;
H, 6.42; N, 10.69.
Single-Crystal X-ray Crystallography. Crystals of 6 suitable
for X-ray diffraction were obtained from recrystallization from
pentane. Crystallographic and data collection parameters are
collected in Table 3. An ORTEP drawing of 6 showing the atom-
numbering scheme used in refinement is illustrated in Figure 1.
11
8
H
8
BN 129.0750, found 129.0749. Anal.
11
3
8 8
2
2
2
2
was stirred at 25 °C for 10 h. The reaction was followed by GC-
MS. The volatile components were removed under reduced pressure
at 0 °C. The product was obtained by vacuum distillation as a clear,

518 Organometallics, Vol. 25, No. 2, 2006
Fang et al.
Selected bond distances are collected in Table 2. Additional
crystallographic data are available in the Supporting Information.
DFT Calculations. DFT calculations at the B3LYP/6-31G* level
were performed using Spartan (Wavefunction, Inc.).
polymerization experiments. We are also grateful to the Boulder
Scientific Company for a generous gift of the Grubbs catalyst.
Supporting Information Available: X-ray characterization of
1
6
. Copies of the H NMR spectra of all new compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. This work was supported by the National
Science Foundation and the Dow Chemical Company. We are
grateful to the Dow Chemical Company for running the
OM058048E