Synthesis of 1,2-dihydro-1,2-azaborines and their conversion to tricarbonyl chromium and molybdenum complexes

Article abstract of DOI:10.1021/om0106635

1,2-dihydro-1,2-azaborines (1c, 1d, and 1e) have been prepared by the reaction of the corresponding 2,3-dihydro-1H-1,2-azaborol-3-yllithium reagents (1c, 1d, and 1e). The reaction of 1e with Py₃Mo(CO)₃ and BF₃·OEt₂

Full text of DOI:10.1021/om0106635

Organometallics 2001, 20, 5413-5418
5413
Syn th esis of 1,2-Dih yd r o-1,2-a za bor in es a n d Th eir
Con ver sion to Tr ica r bon yl Ch r om iu m a n d Molybd en u m
Com p lexes
Arthur J . Ashe, III,* Xiangdong Fang, Xinggao Fang, and J eff W. Kampf
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055
Received J uly 24, 2001
1,2-Dihydro-1,2-azaborines (1c, 1d , and 1e) have been prepared by the reaction of the
corresponding 2,3-dihydro-1H-1,2-azaborol-3-yllithium reagents (1c, 1d , and 1e). The reaction
of 1e with Py3Mo(CO)3 and BF3‚OEt2 affords Mo(CO)3 complex 5e, while the reaction of 1c
with Cr(CH3CN)3(CO)3 affords Cr(CO)3 complex 6c. X-ray structures of 5e and 6c show that
the metals are η6-bound to the 1,2-dihydro-1,2-azaborine rings.
In tr od u ction
The replacement of an adjacent pair of carbon atoms
of benzene by boron and nitrogen yields the isoelectronic
1,2-dihydro-1,2-azaborine (1). Derivatives of 1 were first
prepared in very low yield by Dewar in 19621 and White
in 1963.2 The original experimental characterization of
1 was modest and relied heavily on the “aromatic” UV
spectrum of 1a .2,4b Although a number of ring-fused
derivatives of 1 have been prepared,3 there have been
few subsequent reports on monocyclic 1,2-dihydro-1,2-
azaborines.4,5 In 1992 Kranz and Clark carried out a
thorough ab initio MO study of 1, which allowed them
to conclude that the electron delocalization of 1 is less
than that of benzene due to electron localization by the
B-N group.6,7 We recently prepared 1,2-dihydro-1,2-
azaborine 1d via a DDQ oxidation of the corresponding
1,2,3,6-tetrahydro-1,2-azaborine.8 The NMR spectra of
1d are consistent with those of a weakly aromatic
compound, as predicted by the computational work.6
We report here that 1,2-dihydro-1,2-azaborines may
be generally prepared in good yield using a carbenoid
ring expansion from lithium 1,2-azaborolides 4.9 The
availability of 1 has allowed us to prepare metal
carbonyl complexes 5 and 6. Structural data show that
the 1,2-dihydro-1,2-azaborine rings in these complexes
are η6-coordinated aromatic rings.
intermediacy of chlorocarbene generated from CH2Cl2
and base.11 The electrophilic chlorocarbene attacks the
aromatic anion to give an exocyclic carbene intermediate
7. 1,2-Addition of the carbene center to the adjacent
double bond of 7 gives the bicyclo[1.1.0] butane product
8, while 1,2-vinyl migration to the carbene center leads
to ring expansion. Analogous reactions of in situ gener-
ated chlorocarbene with substituted cyclopentadienyl or
cyclohexadienyl anions are important methods for pro-
ducing the bicyclo[1.1.0]butane ring system.12,13 Quite
naturally major attention has focused on these interest-
ing polycyclic products,14 but in all cases simple ring
expansion is also important. In certain cases the ring
expansion products are major.15 For example, the reac-
tion of lithium stannacyclohexadienide (9) with CH2Cl2/
CH3Li gives predominately stannepin 10.16,17 We wished
to explore whether this type of ring expansion could be
used to convert 1,2-azaborolides (4) into 1,2-dihydro-1,2-
azaborines (1). Certain 1,2-azaborolides are readily
available. In 1980 Schmid prepared lithium 1-tert-butyl-
2-methyl-1,2-azaborolide 4e, which was converted to
Resu lts a n d Discu ssion
The reaction of lithium cyclopentadienide with CH2-
Cl2 and CH3Li (the Katz reaction) gives benzvalene 8
and benzene in the ratio of 4:1.10 Mechanistic studies
have shown that the reaction proceeds through the
(10) (a) Katz, T. J .; Wang, E. J .; Acton, N. J . Am. Chem. Soc. 1971,
93, 3782. (b) Katz, T. J .; Roth, R. J .; Acton, N.; Carnahan, E. J . J .
Org. Chem. 1999, 64, 7663.
(1) Dewar, M. J . S.; Marr, P. A. J . Am. Chem. Soc. 1962, 84, 3782.
(2) White, D. G. J . Am. Chem. Soc. 1963, 85, 3634.
(3) Fritsch, A. J . Chem. Heterocycl. Compd. 1977, 30, 381.
(4) (a) Culling, G. C.; Dewar, M. J . S.; Marr, P. A. J . Am. Chem.
Soc. 1964, 86, 1125. (b) Davies, K. M.; Dewar, M. J . S.; Rona, P. J .
Am. Chem. Soc. 1967, 89, 6294.
(5) Gronowitz, S.; Ander, I. Chem. Scr. 1980, 15, 23, 145.
(6) Kranz, M.; Clark, T. J . Org. Chem. 1992, 57, 5492.
(7) Also see: (a) Massey, S. T.; Zoellner, R. W. Int. J . Quantum
Chem. 1991, 39, 787. (b) Carbo, R.; DeGiambiagi, M. S.; Giambiagi,
M. Theor. Chim. Acta 1969, 14, 147.
(11) (a) Burger, U.; Mazenod, F. Tetrahedron Lett. 1976, 2881. (b)
Burger, U.; Thorel, P. J .; Mentha, Y. Chimica 1987, 41, 26.
(12) (a) Murata, I.; Nakasuji. Tetrahedron Lett. 1973, 47. (b) Murata,
I.; Tatsuoka, T.; Sugihara, Y. Tetrahedron Lett. 1973, 4261. (c)
Gandillon, G.; Bianco, B.; Burger, U. Tetrahedron Lett. 1981, 22, 51.
(13) (a) Pagni, R. M.; Watson, C. R. Tetrahedron Lett. 1973, 59. (b)
Pagni, R. M.; Burnett, M.; Hazell, A. C. J . Org. Chem. 1978, 43, 2750.
(14) Christl, M. Angew. Chem., Int. Ed. Engl. 1981, 20, 529.
(15) Burger, U.; Dreier, F. Helv. Chim. Acta 1979, 62, 540.
(16) Nakadaira, Y.; Sato, R.; Sakurai, H. J . Organomet. Chem. 1992,
441, 411; Organometallics 1991, 10, 435.
(8) Ashe, A. J ., III; Fang, X. Org. Lett. 2000, 2, 2089.
(9) The systematic name for 4 is 2,3-dihydro-1H-1,2-azaborol-3-
yllithium.
(17) Ashe, A. J ., III; Klein, W.; Rousseau, R. Organometallics 1993,
12, 3225.
10.1021/om0106635 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 11/01/2001

5414 Organometallics, Vol. 20, No. 25, 2001
Ashe et al.
Sch em e 1
Sch em e 2
Ta ble 1. 11B a n d 13C NMR Ch em ica l Sh ift Da ta for 1,2-Dih yd r o-1,2-a za bor in es (C4H4BR′NR) a n d Selected
Oth er Com p ou n d s
R,R′ (compd)
δ(11B)
δ(C3)
δ(C4)
δ(C5)
δ(C6)
R,R′
Me, Ph (1c)a
Et, Ph (1d )b
35.2
35.4
37.7
26.6
22.9
32.2
36
131.4
132.0
n.o.d
n.o.d
86.4
142.9
142.9
141.5
103.9
104.4
133.5
132.8
111.3
111.8
109.9
82.3
82.5
107.7
107.9
139.9
138.0
135.2
107.1
107.3
133.5
132.8
133.4, 127.8, 127.6 (Ph), 42.3 (Me)
133.0, 128.0, 127.6 (Ph), 48.1, 18.2 (Et)
31.8 (t-Bu), n.o. (BMe)d
t-Bu, Me (1e)b
t-Bu, Me (5e)a
Me, Ph (6c)a
H, Ph (13a )c,e
H, Me (13b)c,f
31.7 (t-Bu), n.o. (BMe)d
134, 129.4, 128.2 (Ph), 45.5 (Me)
123.5
127
a
b
d
Solvent, CDCl3. Solvent, C6D6. c Solvent, C4D8O. n.o., not observed. e Reference 21b. f Reference 22.
several Cp-like transition metal complexes.18,19 In an
initial experiment we added excess CH2Cl2 to 4e at -78
°C. On warming to 25 °C followed by workup, 1-tert-
butyl-1,2-dihydro-2-methyl-1,2-azaborine 1e was iso-
1,2-Azaborolides 4c and 4d can be prepared by LDA
deprotonation of their conjugate acids (3c and 3d ),
which in turn can be prepared by ring-closing metath-
esis on the appropriate B-vinyl, N-allyl aminoboranes
2.8 This allows more general exploration of the ring
expansion route to 1,2-dihydro-1,2-azaborines. The op-
timized method for conversion of 4c to 1c involves the
addition of excess CH2Cl2 to solid 4c at -78 °C followed
by treatment with 1 equiv of LDA in ether at -78 °C.
Reaction occurs during the slow warming to 25 °C. On
workup 1c was isolated as a yellow oil in 67% yield. In
the same manner 4d was converted to 1d in 64% yield.
The sample was identical to 1d previously obtained by
DDQ oxidation of 1-ethyl-1,2,3,6-tetrahydro-2-phenyl-
1,2-azaborine.
1
lated as a yellow oil in 25% yield. The H, 11B, and 13C
NMR spectra (Tables 1 and 2) and other spectroscopies
are consistent with the 1,2-dihydroazaborine structure.
It is interesting that the UV spectrum of 1e in hexane
shows bands at 223 and 283 nm. The low-energy band
is only slightly blue shifted from the 289 nm band
originally reported for 1a .2,4b
(18) (a) Schulze, J .; Schmid, G. Angew. Chem., Int. Ed. Engl. 1980,
19, 59. (b) Amirkhalili, S.; Boese, R.; Ho¨hner, U.; Kampmann, D.;
Schmid, G.; Rademacher, P. Chem. Ber. 1982, 115, 732. (c) Schmid,
G.; Boltsch, O.; Bla¨ser, D.; Boese, R. Z. Naturfosrch 1984, 39b, 1082.
(d) Schmid, G.; Schultz, M. J . Organomet. Chem. 1995, 492, 185, and
earlier papers in this series.
Mech a n ism for th e F or m a tion of Aza bor in es. To
probe the mechanism for the conversion of 4 to 1, 4c
was treated with CD2Cl2 under conditions similar to
(19) Schmid, G. In Comprehensive Heterocyclic Chemistry II; Shin-
kai, I., Ed.; Pergamon: Oxford, U.K., 1996; Vol. 3, p 739.

Synthesis of 1,2-Dihydro-1,2-azaborines
Organometallics, Vol. 20, No. 25, 2001 5415
Ta ble 2. 1H NMR P a r a m eter s of 1,2-Dih yd r o-1,2-a za bor in es (C4H4BR′NR) a n d Selected Oth er Com p ou n d s
R,R′ (compd)
δ(H3) δ(H4) δ(H5) δ(H6) 3J 3,4Hz 3J 4,5Hz 3J 5,6Hz
R,R′
Me, Ph (1c)a
Et, Ph (1d )a
6.97
6.90
6.61
4.50
4.79
6.85
6.47
7.75
7.71
7.41
5.85
5.88
7.18
7.28
6.49
6.48
6.15
5.08
5.32
6.10
6.18
7.32
7.35
7.53
6.51
6.11
7.18
7.28
10.5
10.8
10.6
9.2
9.2
10.2
9.8
6.6
6.8
6.6
5.5
6.2
6.9
7.0
6.6
6.8
7.0
5.5
5.1
6.9
7.0
7.68 (oPh), 7.49 (mPh), 7.44 (pPh), 3.70 (Me)
7.60 (oPh), 7.45 (mPh), 7.41 (pPh), 3.92 (Et), 1.38 (Et)
1.61 (t-Bu), 1.00 (Me)
1.19 (t-Bu), 0.88 (Me)
7.68, 7.43 (Ph), 3.14 (Me)
t-Bu, Me (1e)a
t-Bu, Me (5e)a
Me, Ph (6c)a
H, Ph (13a )b,c
H, Me (13b)b,c,e
a
b
d
Solvent, CDCl3. Solvent, C4D8O. c For consistency boron is numbered 2. Reference 22. e Reference 21b.
Sch em e 3
those described above. The 3-deuterioisomer of 1c was
obtained exclusively, and no other isomers were detected
by NMR spectroscopy. In a similar manner 4e was
converted exclusively to the 3-deuterio isomer of 1e. The
exclusive formation of the 3-deuterio isomer of 1 is
consistent with initial attack of chlorocarbene at C(3)
of 4 followed by the loss of chloride to form intermediate
11. Migration of boron to the carbene center of 11 would
form the 3-deuterio isomer of 1 as illustrated in Scheme
3.
In principle the chlorocarbene might attack azaborolide
4 at either C(3) or C(5). However attack at C(5) would
afford intermediate 12, which might be expected to give
the 5- and/or 6-deuterio isomers of 1. It has been
observed that other electrophiles attack azaborolides at
C(3).19 This regioselectivity is a likely consequence of
the larger negative charge density at C(3), which is
suggested by the higher field 13C NMR signal of C(3)
relative to C(5). The preferential migration of boron over
carbon to the carbene center of 11 is analogous to the
large migratory aptitude of boron found in other sig-
matropic migrations.20
(1c, 1d , 1e) are summarized in Table 1, and the 1H
NMR spectra are summarized in Table 2. Data for the
corresponding B-substituted boratabenzenes, lithium
1-phenylboratabenzene 13a 21 and lithium 1-methyl-
boratabenzene22 13b, are included for comparison.
The 13C NMR spectra of 1,2-dihydro-1,2-azaborines
show an alternating pattern in which the signals for
ring carbon atoms that are R or γ to boron are shielded,
while those that are R or γ to nitrogen are deshielded.
An analogous pattern is shown by boratabenzene and
pyridinium salts. Indeed the observed spectrum of 1c
can be approximately reproduced by averaging the
appropriate signals for lithium 1-phenylboratabenzene
13a 21 and 1-methylpyridinium 1423 as illustrated in
Figure 1.
The 13C NMR chemical shifts are particularly useful
since they correlate with π-charge densities of aromatic
and heteroaromatic rings.24,25 Clark and Kranz have
calculated 13C NMR shifts of the parent 1,2-dihydro-
(21) (a) Ashe, A. J ., III; Shu, P. J . Am. Chem. Soc. 1971, 93, 1804.
(b) Shu, P. Ph.D. Dissertation, University of Michigan, 1973. (c) Ashe,
A. J ., III; Kampf, J . W.; Mu¨ller, C.; Schneider, M. Organometallics
1996, 15, 387.
(22) Herberich, G. E.; Schmidt, B.; Englert, U. Organometallics
1995, 14, 471.
NMR Sp ectr a of 1,2-Dih yd r o-1,2-a za bor in es. The
11B and 13C NMR spectra of 1,2-dihydro-1,2-azaborines
(20) J utzi, P. Chem. Rev. 1986, 86, 983.
(23) Anet, F. A. L.; Yavari, I. J . Org. Chem. 1976, 41, 3589.

5416 Organometallics, Vol. 20, No. 25, 2001
Ashe et al.
F igu r e 1. Observed 11B and 13C NMR chemical shifts of
1c compared with averaged 13C chemical shifts of 13 and
14 and the calculated 11B and 13C chemical shifts of 1b.
F igu r e 2. Molecular structure and atom labeling for 5e.
1,2-azaborine 1b6 using the IGLO method.25,26 Com-
parison of their calculated chemical shift values for 1b
(Figure 1) with the empirical values for 1c shows that
there is a reasonable level of agreement. In particular
the alternating pattern of shielding and deshielding of
adjacent atoms is nicely reproduced.
The 11B NMR shift values of 1,2-dihydro-1,2-azabo-
rines (δ 35.2-37.7) are in the normal range for
boramines.27 Clark and Kranz’s calculated value for 1b
(δ 34.4) is in excellent agreement with the empirical
values.
1
The H NMR signals for the four nonequivalent ring
protons of the three 1,2-dihydro-1,2-azaborines show a
first-order pattern in the range δ 6.15-7.75. The chemi-
cal shift values of the protons that are R (H3) and γ (H5)
to boron are approximately 1 ppm upfield from those
â(H4, H6) to boron. The same relative separation of R
and γ vs â proton signals is shown for boratabenzenes
(13). For both types of compounds the upfield signals
are consistent with partial negative charge at the R- and
γ-positions. For the 1,2-dihydro-1,2-azaborines the val-
ues of the vicinal coupling constants 3J 3,4 (10.5-10.8 Hz)
are much larger than J 4,5 and J 5,6. This effect must
be due to boron since it is also shown by borataben-
zenes22 and borepins.17,28b
Tr ica r bon yl Ch r om iu m a n d Molybd en u m Com -
p lexes. It was of interest to explore the coordination
chemistry of 1,2-dihydro-1,2-azaborines. The reaction of
1e with tricarbonyltris(pyridine)molybdenum and BF3‚
OEt2 gave adduct 5e in 51% yield as yellow crystals,
which were recrystallized from hexane. The reaction of
1c with tricarbonyltris(acetonitrile)chromium in THF
F igu r e 3. Molecular structure and atom labeling for 6c.
afforded a 32% yield of adduct 6c as red needles. The
1H, 11B, and 13C NMR signals of 1,2-dihydro-1,2-azabo-
rine rings of 5e and 6c are shifted markedly upfield in
comparison to those of the free ligands, which indicates
π-complexation.28 In the case of 6c the 1H and 13C NMR
signals of the phenyl ring are relatively little affected
by complexation. Since there are no prior structural data
on 1,2-dihydro-1,2-azaborines, it was of interest to
obtain crystal structures.
Recrystallization of 5e from hexane at -10 °C gave
golden needles. Refinement showed that the crystals
were pseudo-orthorhombic twins. Although the struc-
ture was solved, the quality of the structural parameters
is relatively poorer than those subsequently obtained
for 6c. The molecular structure of 5e is illustrated in
Figure 2. A sample of 6c suitable for X-ray diffraction
was obtained by recrystallization from CH2Cl2/pentane.
The molecular structure of 6c, which is similar to that
of 5e, is illustrated in Figure 3, while selected bond
distances are listed in Table 3.
3
3
(24) Spiesecke, H.; Schneider, W. G. Tetrahedron Lett. 1961, 468.
Olah, G. A.; Asenio, G.; Mayr, H.; Schleyer, P. v. R. J . Am. Chem. Soc.
1978, 100, 4347, and numerous other similar works.
(25) (a) Bremer, M.; Schleyer, P. v. R.; Fleischer, U. J . Am. Chem.
Soc. 1989, 111, 1147. (b) Schleyer, P. v. R.; Bu¨hl, M. Angew. Chem.,
Int. Ed. Engl. 1990, 102, 320. (c) Bu¨hl, M.; Hommes, N. J . R. v. E.;
Schleyer, P. v. R.; Fleischer, U.; Kutzelnigg, W. J . Am. Chem. Soc. 1991,
113, 2459. (d) Bu¨hl, M.; Steinke, T.; Schleyer, P. v. R.; Boese, R. Angew.
Chem., Int. Ed. Engl. 1991, 103, 1179.
(26) (a) Kutzelnigg, W. Isr. J . Chem. 1980, 19, 193. (b) Schindler,
M.; Kutzelnigg, W. J . Chem. Phys. 1982, 76, 1919.
(27) See: No¨th, H.; Wrackmeyer, B. Nuclear Magnetic Resonance
Spectroscopy of Boron Compounds; Springer-Verlag: Berlin, 1978; pp
29-61. Wrackmeyer, B. Z. Naturforsch. B: Anorg. Chem., Org. Chem.
1980, 35B, 439.
The structure of 6c consists of a near planar C4BN
ring which is η6-bound to the Cr(CO)3 unit in typical
piano stool fashion. The B-phenyl ring is not coordinated
and is canted relative to the C4BN ring by 39°. The
juxtaposition of the coordinated ring of 6c relative to
the metal carbonyl group resembles those of borataben-
zene-Mn(CO)3 complex 15,29 where one CO group
(28) (a) Herberich, G. E.; Bauer, E.; Hengesbach, J .; Ko¨lle, U.;
Huttner, G.; Lorenz, H. Chem. Ber. 1977, 110, 760. (b) Ashe, A. J ., III;
Kampf, J . W.; Nakadaira, Y.; Pace, J . M. Angew. Chem., Int. Ed. Engl.
1992, 31, 1255.
(29) Huttner, G.; Gartzke, W. Chem. Ber. 1974, 107, 3786.

Synthesis of 1,2-Dihydro-1,2-azaborines
Organometallics, Vol. 20, No. 25, 2001 5417
Ta ble 3. Selected Bon d Dista n ces (Å) for 6c
with the larger size of boron and conforms to the pattern
shown by other heterocyclic boron ligands.34
In summary, the structural data clearly demonstrate
that 1,2-dihydro-1,2-azaborine can serve as an aromatic
ligand. It would be particularly interesting to obtain
structural data for an uncomplexed 1,2-dihydro-1,2-
azaborine so that a structural comparison can be made
with 6c.
B(1)-N(1)
B(1)-C(4)
B(1)-C(9)
B(1)-Cr(1)
N(1)-C(7)
N(1)-C(8)
N(1)-Cr(1)
Cr(1)-C(2)
Cr(1)-C(3)
Cr(1)-C(1)
Cr(1)-C(7)
Cr(1)-C(6)
Cr(1)-C(5)
Cr(1)-C(4)
0(3)-C(3)
1.466(6)
1.510(6)
1.574(6)
2.366(5)
1.400(5)
1.479(5)
2.200(3)
1.840(4)
1.842(5)
1.848(5)
2.156(4)
2.201(4)
2.216(4)
2.254(4)
1.157(5)
1.151(5)
1.149(5)
1.394(6)
1.410(6)
1.375(6)
1.399(5)
1.402(5)
1.389(5)
1.379(6)
1.386(6)
1.377(6)
0(2)-C(2)
0(1)-C(1)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(9)-C(14)
C(9)-C(10)
C(10)-C(11)
C(11)-C(12)
C(12)-C(13)
C(13)-C(14)
eclipses boron, and pyridine-Cr(CO)3 complex 16,30
where one CO group is trans to nitrogen. This confor-
mational feature has been found for metal carbonyl
complexes of other boron and nitrogen heterocycles31
and has been treated by MO studies.32
Exp er im en ta l Section
Gen er a l Rem a r k s. All reactions were carried out under
an atmosphere of nitrogen. Solvents were dried by using
standard procedures. The mass spectra were determined by
using a VG-70S spectometer, while the NMR spectra were
obtained by using either a Bruker WH-400, WH-360, or AM-
300 spectrometer. The 1H NMR and 13C NMR spectra were
calibrated by using signals from the solvents referenced to
SiMe4. The 11B NMR spectra were referenced to external BF3-
OEt2. The combustion analyses were determined by the
Analytical Services Department of the Department of Chem-
istry, University of Michigan.
1,2-Dih yd r o-1-m eth yl-2-p h en yl-1,2-a za bor in e (1c). A
solution of LDA (1.13 g, 10.6 mmol) in 12 mL of ether was
added dropwise to a suspension of 2,3-dihydro-1-methyl-2-
phenyl-1H-1,2-azaborol-3-yllithium (4c)8 (1.73 g, 10.6 mmol)
in 20 mL of CH2Cl2 at -78 °C. The mixture was stirred at
-78 °C for 2 h and was allowed to warm to 25 °C for 4 h. The
volatiles were removed under reduced pressure, and the
residue was extracted with 30 mL of pentane. After filtration
and removal of pentane the crude product was isolated as a
yellow oil (1.20 g, 67%). A pure sample of the product was
obtained by column chromatography on silica gel, hexane
elution. HRMS (EI): m/z calcd for C11H1211BN(M+), 169.1063;
found, 169.1065. Anal. Calcd for C11H12BN: C, 78.16; H, 7.16;
N, 8.29. Found: C, 78.09; H, 7.17; N, 8.23.
It also seems useful to compare the overall structure
of 6c with those of 15 and 16. The intra-ring distances
of the 1,2-dihydro-1,2-azaborine ring are typical of those
of similarly coordinated aromatic ligands. Thus the
range of C-C bond distances of 6c (1.38-1.41 Å) is
identical to that of 16 and only slightly different from
that of 15 (1.40-1.42 Å). The intra-ring C-N bond of
6c (1.40 Å) is somewhat larger than those of 16 (1.36,
1.37 Å), which may be due to the higher coordination of
the nitrogen atom of 6c. The B-N bond of 6c (1.46 Å)
is considerably longer than the usual values found for
unconjugated aminoboranes (1.41 Å),33 which suggests
that its B-N π-bonding is delocalized. Interestingly the
B-N bonds of (hexaethylborazine)Cr(CO)3 (17)31a (1.46-
1.47 Å) are very similar. Finally the intra-ring B-C
bond (1.51 Å) of 6c is very close to those of 15 (1.52 Å).
The exocyclic B-C bonds are significantly longer for
both 6c (1.57 Å) and 15 (1.58 Å), consistent with their
single-bond character.
The 1,2-dihydro-1,2-azaborine ring of 6c shows a
small deviation from planarity. The B atom is displaced
away from Cr out of the plane defined by N(1) C(4) C(5)
C(6) C(7) by 0.049(3) Å. The structure of 15 and those
of most coordinated boron heterocycles shows similar
displacements of the boron atoms away from the transi-
tion metals.29,33 The B-Cr distance of 6c (2.366(5) Å)
is somewhat longer than the C-Cr distances (2.16-2.25
Å) and the Cr-N distance (2.20 Å). This is consistent
3-Deu t er io-1,2-d ih yd r o-1-m et h yl-2-p h en yl-1,2-a za b o-
r in e (11c). In the same manner as above the reaction of 4c
with CD2Cl2 gave 66% of 11c as a yellow oil. 1H NMR (CDCl3,
400 MHz): δ 7.68 (d, J ) 7.0 Hz, 1H, H(4)), 7.60 (d, J ) 8.0
Hz, 2H, ArH), 7.43 (t, J ) 8.0 Hz, 2H, ArH); 7.39 (t, J ) 8.0
Hz, 1H, ArH), 7.28 (dd, J ) 7.0, 1.1 Hz, 1H, H(6)), 6.41 (t, J )
7.0 Hz, 1H, H(5)), 3.65 (s, 3H, NMe). HRMS (EI): m/z calcd
for C11 H112H111BN, 170.1126, found, 170.1127.
(N-Allyl,N-eth yla m in o)p h en ylvin ylbor a n e (2d ). A solu-
tion of N-allyl,N-ethylamine (3.61 g, 42.5 mmol) in 10 mL of
CH2Cl2 was added to a solution of phenylvinylboron chloride
1
(30) Schmidt, R. E.; Massa, W. Z. Naturforsch. 1984, 39B, 213.
(31) (a) Huttner, G.; Krieg, B. Chem. Ber. 1972, 105, 3437. (b) Ashe,
A. J ., III; Kampf, J . W.; Kausch, C. M.; Konishi, H.; Kristen, M. O.;
Kroker, J . Organometallics 1990, 9, 2944. (c) Ashe, A. J ., III; Al-Taweel,
S. M.; Drescher, C.; Kampf, J . W.; Klein, W. Organometallics 1997,
16, 1884.
(32) (a) Albright, T. A. Acc. Chem. Res. 1982, 15, 149. (b) Bo¨hm, M.
C.; Gleiter, R.; Herberich, G. E.; Hessner, B. J . Phys. Chem. 1985, 89,
2129.
(34) (a) Herberich, G. E.; Boveleth, W.; Hessner, B.; Ko¨ffer, D. P.
J .; Negele, M.; Saive, R. J . Organomet. Chem. 1986, 308, 153. (b)
Siebert, W.; Bochmann, M.; Edwin, J .; Kru¨ger, C.; Tsay, Y.-H. H. Z.
Naturforsch. B 1978, 33, 1410. (c) Herberich, G. E.; Hessner, B.;
Beswetherick, S.; Howard, J . A. K.; Woodward, P. J . Organomet. Chem.
1980, 192, 421. (d) Herberich, G. E.; Hessner, B.; Negele, M.; Howard,
J . A. K. J . Organomet. Chem. 1987, 336, 29.
(33) Paetzold, P. Adv. Inorg. Chem. 1987, 31, 123.

5418 Organometallics, Vol. 20, No. 25, 2001
Ashe et al.
(6.4 g, 42.7 mmol) in 20 mL of CH2Cl2 at -78 °C with stirring.
After the mixture had stirred for 1 h trimethylamine (4.3 g,
42.6 mmol) was added, causing a white precipitate to form.
The reaction mixture was allowed to warm to 25 °C for 3 h.
The solid was removed by filtration, and the solvent was
removed in vacuo. The product was obtained by vacuum
distillation as a clear colorless liquid (84%), bp 67-70 °C at
0.05 Torr. The 1H NMR and 13C NMR spectra are consistent
(M+), 183.1219; found, 183.1226. UV (pentane, nm): λ(ꢀ) max
237 (2090), 282 (2610). Anal. Calcd for C12H14BN: C, 78.73;
H, 7.71; N, 7.65. Found: C, 78.59; H, 7.65; N, 7.48.
1-ter t-Bu tyl-1,2-d ih yd r o-2-m eth yl-1,2-a za bor in e (1e). A
solution of 1-tert-butyl-2,3-dihydro-2-methyl-1H-1,2-azaborol-
3-yllithium in THF was prepared from 1-tert-butyl-2,3-dihydro-
2-methyl-1H-2-methyl-1,2-azaborole (0.74 g, 5.40 mmol) and
an excess of lithium 2,2,6,6-tetramethylpiperidide. The sol-
vents were removed under reduced pressure, the residue was
cooled to -78 °C, and CH2Cl2 (3 mL) was slowly added at -78
°C. The resulting mixture was warmed to room temperature
and stirred for 30 min. After solvent was removed, residue was
extracted with pentane (3×). The pentane was then removed,
and the residue was distilled under full vacuum to give a
mixture of product 1e (0.20 g, 25%) and tetramethylpiperidine
as a colorless liquid, which could not be further separated by
distillation. A small amount of pure sample was obtained by
running the mixture through a silica gel column eluted with
hexane. 1H NMR (360 MHz, C6D6): δ 1.13 (s, 3H), 1.24 (s, 9H),
6.14 (dt, J ) 6.6, 1.8 Hz, 1H, H5), 6.92 (d, J ) 10.7 Hz, 1H,
H3), 7.26 (d, J ) 7.4 Hz, 1H, H6), 7.50 (dd, J ) 10.7, 1.3 Hz,
1H, H4). MS (EI) m/z, relative intensity: 149 (M+, 39), 93 (100).
UV (hexane, λ(ꢀ)): 283 (4182, 223 (2440). When CD2Cl2 was
used instead of CH2Cl2, the 3-deuterio isomer was obtained.
1H NMR (360 MHz, C6D6): 6.16 (dd, 10.9, 5.9 Hz, H5), 7.26
(d, J ) 5.9 Hz, H6), 7.57 (d, J ) 10.7 Hz, H4). MS (EI) m/z
(relative intensity): 150 (M+, 22), 94 (100).
1
with it existing as two B-N rotomers with a ratio of 1:1. H
NMR (C6D6, 400 MHz): δ 7.42 (d, J ) 8.0 Hz, 4H, ArH), 7.31-
7.19 (m, 6H, ArH), 6.64 (dd, J ) 19.0, 13.2 Hz, 1H, BCH), 6.57
(dd, J ) 19.0, 13.2 Hz, BCH′), 6.02 (bt, J ) 13.2 Hz, 2H,
alkene), 5.80-5.50 (m, 4H, alkene), 5.12-4.91 (m, 4H, alkene),
3.68 (dt, J ) 5.2, 1.7 Hz, 2H, dCCH2), 3.51 (dt, J ) 5.2, 1.7
Hz, 2H, dCCH2′), 3.12 (q, J ) 7.1 Hz, 2H, Et), 2.93 (q, J ) 7.1
Hz, 2H, Et′), 0.99 (t, J ) 7.1 Hz, 3H, Et), 0.81 (t, J ) 7.1 Hz,
3H, Et′). 13C NMR (C6D6, 100.6 MHz): shows two sets of
signals. 11B NMR (C6D6, 115.5 MHz): δ 39.4. HRMS (EI): m/z
calcd for C13H1811BN (M+), 199.1532; found, 199.1528. Anal.
Calcd for C13H18BN: C, 78.42; H, 9.11; N, 7.03. Found: C,
78.28; H, 8.59; N, 6.50.
1-Eth yl-2,5-d ih yd r o-2-p h en yl-1H-1,2-a za bor ole (3d ). A
solution of 2d (17.2 g, 86.4 mmol) in 120 mL of CH2Cl2 was
added to a solution of bis(tricyclohexylphosphine)benzylidene-
ruthenium(IV) dichloride (Grubbs’ catalyst) (3.55 g, 4.31 mmol)
in 40 mL of CH2Cl2 at 25 °C. The mixture was stirred at 25
°C for 10 h, after which the color had changed from purple-
red to dark brown. The solvent was removed in vacuo, and
the product (12.6 g, 85%) was obtained as a clear colorless
liquid, bp 60 °C at 0.05 Torr. 1H NMR (C6D6, 400 MHz): δ
7.75 (d, J ) 8.0 Hz, 2H, ArH), 7.33 (t, J ) 8.0 Hz, 2H, ArH),
7.25 (t, J ) 8.0 Hz, 1H, ArH), 6.93 (d, J ) 8.1 Hz, 1H, vinyl),
6.60 (d, J ) 8.1 Hz, 1H, vinyl), 3.51 (m, 2H, NCH2CHd), 3.26
(q, J ) 7.0 Hz, 2H, Et), 0.94 (t, J ) 7.0 Hz, 3H, Et). 13C NMR
(C6D6, 100.6 MHz): δ 148.5, 134.1, 132.1, 128.9, 128.1, 127.6,
60.3 (NCH2Cd), 41.4 (Et), 16.7 (Et). 11B NMR (C6D6, 115.5
MHz): δ 39.4. HRMS (EI): m/z calcd for C11H1411BN (M+),
171.1219; found, 171.1224. Anal. Calcd for C11H14BN: C, 77.24;
H, 8.25; N, 8.19. Found: C, 77.83; H, 8.45; N, 7.68.
Tr ica r b on yl(η6-1-ter t-b u t yl-1,2-d ih yd r o-2-m et h yl-1,2-
a za bor in e)m olybd en u m (5e). BF3‚OEt2 (0.76 mL, 6.04
mmol) was added to a mixture of 1e (0.98 g, 0.60 mmol) and
(tricarbonyltrispyridine)molybdenum (0.63 g, 1.51 mmol) in
ether (12 mL). The mixture was stirred 15 h at room temper-
ature to give a black suspension. Solvent was removed, and
the residue was extracted with hexane (3×) and filtered. The
hexane solution was concentrated and cooled to -78 °C to give
1
product (0.10 g, 51%) as a yellow solid: mp, 138 °C (dec). H
NMR (360 MHz, C6D6): δ 0.79 (s, 3H), 0.84 (s, 9H), 4.23 (dd,
J ) 9.0, 1.7 Hz, 1H), 4.28 (dt, J ) 5.7, 1.8 Hz, 1H), 5.31 (dd,
J ) 9.0, 5.7 Hz, 1H), 5.71 (d, J ) 5.4 Hz, 1H). IR (hexane):
1977, 1909, 1893 cm-1. HRMS (EI): m/z calcd for C12H1611B-
MoNO3, 331.0277; found 331.0270.
1-Eth yl-2,3-d ih yd r o-2-p h en yl-1H-1,2-bor ol-3-yllith iu m
(4d ). A solution of LDA (3.13 g, 29.2 mmol) in 15 mL of ether
was added to a solution of 3d (5.0 g, 29.2 mmol) in 15 mL of
ether at -78 °C. The mixture was stirred at -78 °C for 2 h
and at 25 °C for 10 h. After removal of the solvent the residue
was washed with 3 × 20 mL of pentane. The residue was dried
under vacuum to give the product as a light yellow powder
Tr icar bon yl[η6-1,2-dih ydr o-1-m eth yl-2-ph en yl-1,2-azabo-
r in e]ch r om iu m (6c). 1,2-Dihydro-1-methyl-2-phenyl-1,2-
azaborine (1c) (1.53 g, 9.05 mmol) in 20 mL of THF was added
to Cr(CO)3(CH3CN)3 (2.34 g, 9.05 mmol). The resulting dark
red solution was heated at 50 °C for 24 h. The solvent was
removed under reduced pressure. The residue was washed
with 30 mL of pentane at 25 °C, and the brown extract was
discarded. The dark residue was further extracted with 4 ×
60 mL of hot hexane until no orange red color was observed
in the extracts. The solution was concentrated and crystallized
at -30 °C. The product was obtained after repeated recrys-
tallization at 25 °C in CH2Cl2/pentane as needlelike red
crystals (0.88 g, 32%), mp 125 °C. IR (hexane, film): 1979,
1916, 1900 cm-1. HRMS (EI): m/z calcd for C14H1211B52CrNO3-
1
(3.9 g, 77%). H NMR (THF-d8, 400 MHz): δ 7.51 (d, J ) 8.0
Hz, 2H, ArH), 7.05 (t, J ) 8.0 Hz, 2H, ArH), 6.87 (t, J ) 8.0
Hz, 1H, ArH), 5.91 (m, 1H, H4), 5.86 (m, 1H, H5), 4.16 (m, 1H,
H3), 3.78 (1, J ) 7.0 Hz, 2H, Et), 1.27 (t, J ) 7.0 Hz, 3H, Et).
13C NMR (THF-d8, 100.6 MHz): δ 133.9, 123.8, 112.8, 111.9,
86.5 (br), 43.2 (Et), 19.6 (Et). 11B NMR (THF-d8, 115.5 MHz):
δ 29.4.
1-Eth yl-1,2-d ih yd r o-2-p h en yl-1,2-a za bor in e (1d ). Solid
4d (2.6 g, 14.7 mmol) was mixed with 20 mL of CH2Cl2 and
cooled to -78 °C. A solution of LDA (1.57 g, 14.7 mmol) in 10
mL of ether was added to the above solution. The solid
gradually dissolved. The mixture was stirred at -78 °C for 1
h and gradually warmed to 25 °C, during which time a fine
precipitate formed. The mixture was stirred at 25 °C for 10 h.
After removal of the solvent, the residue was extracted with
2 × 20 mL of pentane. After filtration and removal of pentane,
the product was obtained as a yellow oil. A pure sample of the
product (1.71 g, 64%) was collected by column chromatography
on silica gel, hexane elution. 1H NMR (C6D6, 400 MHz): δ 7.52
(dd, J ) 10.0, 7.0 Hz, 1H, H4), 7.50 (d, J ) 8.0 Hz, 2H, ArH),
7.21 (t, J ) 8.0 Hz, 2H, ArH), 7.16 (t, J ) 8.0 Hz, 1H, ArH),
7.00 (d, J ) 10.0 Hz, 1H, H3), 6.66 (d, J ) 7.0 Hz, 1H, H6),
6.18 (t, J ) 7.0 Hz, 1H, H6), 3.35 (q, J ) 7.2 Hz, 2H, Et), 0.78
(t, J ) 7.2 Hz, 3H, Et). HRMS (EI): m/z calcd for C12H1411BN-
(M+), 305.0315; found, 305.0323. Anal. Calcd for C14H12
-
BCrNO3: C, 55.12; H, 3.96; N, 4.59. Found: C, 55.24; H, 3.91;
N, 4.42.
Ack n ow led gm en t. We are grateful to the National
Science Foundation for the partial support of this
research.
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
distances, angles, positional parameters, aniosotropic thermal
1
parameters, and hydrogen atom coordinates of 5e and 6c. H
NMR spectra of 1c, 1d , 1e, 5e, and 6c. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM0106635