Structure and spectroscopic characteristics of 2'-diethylboryl-4''- dimethylaminochalcone bearing an intramolecular boron-oxygen coordinate bond

Article abstract of DOI:10.1039/a902282a

How formation of an intramolecular coordinate bond affects the molecular structure was examined in the structural comparison of 2'-diethylboryl-4''- dimethylaminochalcone (1) and 2'-ethylenedioxyboryl-4''-dimethylaminochalcone (2) with chloro-{2-[(4-dimethylaminostyryl) carbonyl] phenyl} (4-methyl- phenyl)] bismuthane (3) and 4''-dimethylaminochalcone (4).

Full text of DOI:10.1039/a902282a

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Structure and spectroscopic characteristics of
2º-diethylboryl-4/-dimethylaminochalcone bearing an intramolecular
boron–oxygen coordinate bond
Toshihiro Murafuji,*a Yoshikazu Sugihara,*a Tomokazu Moriya,a Yuji Mikatab and Shigenobu
Yanob
L e t t e r
a Department of Chemistry, Faculty of Science, Y amaguchi University, Y amaguchi City,
753-8512, Japan
b Department of Chemistry, Faculty of Science, Nara W omenÏs University, Nara-shi, Nara
630-8506, Japan
Received (in Montpellier, France) 22nd March 1999, Accepted 19th May 1999
How formation of an intramolecular coordinate bond a†ects
the molecular structure was examined in the structural com-
parison of 2º-diethylboryl-4/-dimethylaminochalcone (1) and 2º-
ethylenedioxyboryl-4/-dimethylaminochalcone (2) with chloro-
{2-[(4-dimethylaminostyryl) carbonyl]phenyl}(4-methyl-
phenyl)]bismuthane (3) and 4/-dimethylaminochalcone (4).
benzaldehyde (DMAB) and acetophenone with potassium
hydroxide. Firstly, the aldol reaction of 2@-diethylborylaceto-
phenone and DMAB with lithium diisopropylamide pro-
ceeded to give 1 despite the presence of a trivalent boron atom
having a high affinity for bases. Secondly, when potassium
tert-butoxide in a mixture of benzene and tert-butanol was
used,
2 equiv. of 2@-diethylborylacetophenone added to
It is an important issue for us to examine how coordination
a†ects molecular structure and properties. In preceding
papers1 we reported a marked structural change in the non-
alternant ligand of low resonance energy by formation of
coordinate bonds with a diethylboryl group in comparison
with the alternant ligands.1b Herein we disclose how the intra-
molecular coordinate bond a†ects the synthetic, structural,
and spectral features of 4A-dimethylaminochalcone chromo-
phore.
DMAB, giving the undesired product 5 in moderate yield,
contrasting with the synthesis of 4. Thus, due to the intramol-
ecular coordinate bond, the b-hydroxy intermediate in the
aldol condensation easily su†ered from dehydroxylation, fol-
lowed by nucleophilic attack of the second enolate of 2@-
diethylborylacetophenone.
Thirdly,
upon
attempted
deacetalization of the carbonyl group with p-toluene sulfonic
acid in the synthesis of 2, transacetalization to the boron atom
efficiently took place. Thus, protection of the acidic hydrogens
of the hydroxy groups could be omitted in the subsequent
aldol condensation employing basic conditions.
While 4 is yellow crystals, compounds 1, 2, and 3 are
reddish-violet, reddish-violet and greenish yellow crystals,
respectively. The longest wavelength absorption band of the
UV/VIS spectrum of 1 in acetonitrile shows an 86 nm batho-
chromic shift similar to that of 3, compared to 4.” Since the
large bismuth atom would be placed more closely to the
oxygen atom of the carbonyl group, the high Lewis acidity of
the diethylboryl group is responsible for this similar batho-
chromic shift. On addition of amines, such as triethylamine,
the color of a solution of 1 turns yellow, indicating that the
intramolecular boronÈoxygen coordinate bond is cleaved with
formation of an intermolecular boronÈnitrogen coordinate
bond. The change is irreversible and results in decomposition
when dilute aqueous hydrochloric acid is added to remove the
amine.
The spectrum of 2 shows two bands in the regions of the
longest wavelength absorption bands of 1 and 4, indicating a
weaker Lewis acidity of the ethylenedioxyboryl group than
that of the diethylboryl group. Compound 1 is moderately
Ñuorescent with an emission maximum at 576 nm (excitation
at 494 nm).3
The solvatochromism of the longest wavelength absorption
bands is noteworthy, although the shift dependences on
solvent polarity not large.° Thus, when the solvent is changed
from cyclohexane to methanol a bathochromic shift of 23 nm
is observed for 1. A linear solvation energy relationship
(LSER) [l(1) \ 21.555 [ 1.692n*] is obtained between the
solvent shifts and the KamletÈTaft parameter n*4 where
n \ 11, R \ 0.948 and p \ 0.139 kK, including both protic
The synthetic routes to 2@-diethylboryl-4A-dimethylamino-
chalcone (1), 2@-ethylenedioxyboryl-4A-dimethylaminochalcone
(2) and chloroM2-[(4-dimethylaminostyryl)carbonyl]phenylN(4-
methylphenyl)]bismuthane (3)2 are shown in Scheme 1.¤
Three experimental Ðndings should be stressed in comparison
to the simple synthesis of
4 from 4-dimethylamino-
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Hence, it can be concluded that, when compared with the
respective ground states, the increasing polarity of the excited
state of 4 is greater than that of 1 by the greater value of the
n* coefficient. According to the LippertÈMataga equation,5
the shifts in various solvents and a measure for solvent
polarity deÐned as (e [ 1)/(2e ] 1) [ (n2 [ 1)/(2n2 ] 1) also
give
a good linear relationship for both compounds
(Y \ 1.7168 ] 3.6745X and Y \ 2.8469 ] 8.9390X where
n \ 10, R \ 0.963 and p \ 0.0994 kK or n \ 10, R \ 0.950
and p \ 0.282 kK for 1 or 4, respectively), exhibiting a more
pronounced polarity in the excited state than in the ground
state in both compounds. Since the Onsager e†ective radii6 for
1 and 4 are estimated from the volume taken from the X-ray
structure analysis7 of 4 to be 4.35 A, the di†erences between
the dipole moment vector of the excited state and that of the
ground state o k [ k o are calculated to be 5.48 and 8.55 D,
e
g
respectively.
These spectroscopic characteristics are well interpreted by
the intramolecular boronÈoxygen coordinate bond, which pre-
vents positive hydrogen-bond formation between protic sol-
vents and the oxygen atom placed at the end of the
chromophore.
A single-crystal X-ray crystallographic study at [120 ¡C
reveals the enhanced coplanarity of the skeletal atoms, all the
skeletal atoms of 1 being coplanar with a maximum deviation
of only 3¡ (Figs. 1 and 2).p The intramolecular coordinate
bond between the boron and oxygen atoms, together with the
charge transfer from the dimethylamino group to the carbonyl
Scheme 1 Reagents and conditions: (i) BunLi (3 equiv.), TMEDA (3
equiv.), hexane, RT, 24 h, then Et BOMe (2 equiv.), RT, 30 min; brine,
2
74.7%; (ii) LDA (1.1 equiv.), DMAB (1 equiv.), Et O, RT, 45 min;
2
brine, 39.3%; (iii) DMAB (1 equiv.), ButOK (1.3 equiv.), C H ÈButOH
Fig. 1 Computer-generated thermal ellipsoid of 1. Some important
bond distances (A) and dihedral angles (¡) are as follows: B1ÈO1
1.608(2), B1ÈC1 1.616(3), C1ÈC6 1.408(3), C6ÈC7 1.455(3), C7ÈO1
1.294(2), C7ÈC8 1.424(3), C8ÈC9 1.367(3), C9ÈC10 1.434(3), C10ÈC11
1.411(3), C10ÈC15 1.405(3), C11ÈC12 1.372(3), C12ÈC13 1.420(3), C13È
C14 1.412(3), C14ÈC15 1.372(3), C13ÈN1 1.359(2), O1ÈC7ÈC6ÈC1
[0.1(2), C1ÈB1ÈO1ÈC7 [3.0(2), C6ÈC7ÈC8ÈC9 [177.0(2), C7ÈC8È
C9ÈC10 177.5(2), C8ÈC9ÈC10ÈC11 [2.6(3), C12ÈC13ÈN1ÈC16 6.1(3),
C12ÈC13ÈN1ÈC17 [176.9(2).
6
6
(1 : 1 v/v), RT, 3 h, 30.3%; (iv) BunLi (3 equiv.), TMEDA (3 equiv.),
hexane, RT, 24 h, then Tol BiCl (1 equiv.), RT, 1 h; brine, 39.4%; (v)
2
DMAB (1.3 equiv.), ButOK (1.3 equiv.), C H ÈButOH (10 : 3 v/v), RT,
4 h, 77.6%; (vi) BF É OEt (3 equiv.), C H6 , ice cooling; brine, 87.7%;
6
3
2
6 6
(vii) BunLi (1 equiv.), B(OPri) (1 equiv.), THF, [78 ¡C to RT, 80 min;
3
brine, 83.3%; (viii) TsOH (0.01 equiv.), acetone, 45 min, then removal
of acetone; (ix) DMAB (1 equiv.), ButOK (3 equiv.), THFÈButOH (1 : 1
v/v), 0 ¡C, 15 min; brine, then conc. HClÈMeOH (1 : 1 v/v), 24 h, neu-
tralization with NaHCO , 27.6%.
3
and aprotic solvents. A larger bathochromic shift of 33 nm is
observed from the same solvent change for 4. However, in
contrast to 1, two separate LSERs [l(4) \ 25.994 [ 2.256n*
and l(4) \ 24.730 [ 1.448n*] are obtained where n \ 8,
R \ 0.931 and p \ 0.263 kK or n \ 3, R \ 0.995 and
p \ 0.012 kK for aprotic or protic solvents, respectively, due
to the deviation of the absorption maxima in protic solvent in
the longer wavelength regions. If the hydrogen-bond donor
parameter a is included, the behavior for 4 is described by a
single LSER, that is, l(4) \ 25.924 [ 1.993n* [ 0.989a where
n \ 11, R \ 0.957 and p \ 0.232 kK.
The Ñuorescence spectra of 1 and 4 display solvatochro-
mism as well.Ò For example, when the solvent is changed from
carbon tetrachloride to ethanol, bathochromic shifts of 50 and
96 nm are obtained for 1 and 4, respectively. A KamletÈTaft
approach works for the Ñuorescence study as well. Thus,
l(1) \ 19.684 [ 2.844n* and l(4) \ 22.929 [ 4.432n* [ 2.33a
are obtained where n \ 10, R \ 0.805 and p \ 0.387 kK or
n \ 10, R \ 0.953 and p \ 0.477 kK for 1 or 4, respectively.
Fig. 2 Computer-generated thermal ellipsoid of 4. Some important
bond distances (A) and dihedral angles (¡) are as follows: C1ÈC2
1.385(5), C1ÈC7 1.488(4), C7ÈO1 1.231(4), C7ÈC8 1.464(4), C8ÈC9
1.337(4), C9ÈC10 1.452(4), C10ÈC11 1.400(4), C10ÈC15 1.403(4),
C11ÈC12 1.384(4), C12ÈC13 1.413(4), C13ÈC14 1.401(4), C14ÈC15
1.382(4), C13ÈN1 1.372(4), O1ÈC7ÈC1ÈC2 [19.0(5), C1ÈC7ÈC8ÈC9
177.3(3), C7ÈC8ÈC9ÈC10 [176.6(3), C8ÈC9ÈC10ÈC11 [2.1(6), C12È
C13ÈN1ÈC16 [3.1(5), C12ÈC13ÈN1ÈC17 [176.9(4).
684
New J. Chem., 1999, 23, 683È685

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J \ 7.5, BArH), 7.58 (1H, t, J \ 7.5, BArH), 7.59 (1H, s, COCH), 7.64È
7.66 (4H, m, ArH), 8.03 (1H, d, J \ 7.9, BArH), 8.16 (1H, d, J \ 7.9,
BArH).
” UV/VIS (acetonitrile) j /nm (log e): 1: 292 (4.09), 494 (4.72); 2:
'
264 (4.08), 434 (4.27), 500 sh (4.12); 3: 285 (4.19), 484 (4.68); 4: 262
(4.22), 328 (3.69), 408 (4.45).
° Solvatochromism in the longest wavelength absorption bands of 1
and 4 (nm): cyclohexane (464, 386), Et O (478, 390), CCl (468, 394),
2
4
PriOH (481, 416), EtOH (486, 418), AcOEt (486, 402), THF (490, 405),
MeOH (487, 419), CH CN (494, 408), CHCl (486, 414), CH Cl (492,
3
3
2 2
414).
Ò Solvatochromism of the Ñuorescence of 1 and 4 (nm): CCl (512,
4
449), CHCl (546, 505), Et O (533, 465), AcOEt (552, 493), THF (559,
3
2
485), CH Cl (559, 520), PriOH (559, 542), EtOH (562, 545), CH CN
Fig. 3 Bond distances changed by the intramolecular coordinate
bond and contributing charge transfer electronic structure of 1: elon-
gated bond distances denoted by a plus and shortened bond distances
denoted by a minus, compared with 4.
2
2
3
(576, 530), MeOH (563, 546).
p Data were collected at 153 K on a Rigaku AFC7R di†ractometer
with graphite-monochromated Mo-Ka radiation (j \ 0.71069 A) and
a rotating anode generator. The structure was solved by direct
methods. The non-hydrogen atoms were reÐned anisotropically.
group, seems to be responsible for the coplanarity. Thus, as
shown in Fig. 1, the shortened distance between the boron
and oxygen atoms [1.608(2) A] clearly exhibits the formation
of the intramolecular coordinate bond. The di†erence between
the corresponding bond distances of 1 and 4, shown in Fig. 3,
is indicative of the contribution from the canonical structure
with the charge transfer electronic structure. In particular, the
increased double bond character of the bonds between C7 and
C8, and C9 and C10 is deduced from the respective shortened
bond distances.
Crystal data for 1: C
H
BNO É 1.5 H , M \ 436.42, red, prismatic
21 26
6 6
crystal (0.20 ] 0.40 ] 0.80 mm), triclinic, P1 (°2), a \ 9.622(4),
b \ 15.155(5),
c \ 9.522(3)
A,
a \ 101.21(3),
b \ 95.90(4),
c \ 108.32(3)¡, U \ 1272.9(9) A
Ž
3, Z \ 2, D \ 1.139 g cm~3, k \ 0.67
c
cm~1, F(000) \ 470. The Ðnal cycle of full-matrix least-squares reÐne-
ment was based on 3338 observed reÑections [I [ 3.00 r(I)] and 438
variable parameters and converged with unweighted and weighted
agreement factors of R \ 0.040 and R \ 0.046. Crystal data for 4:
w
C
H
NO, M \ 251.33, yellow, prismatic crystal (0.20 ] 0.40 ] 0.60
17 17
mm), monoclinic, P2 /a (°14), a \ 9.491(4), b \ 11.884(3),
1
c \ 12.912(3) A, b \ 108.35(2)¡, U \ 1382.3(7) A
Ž
3, Z \ 4, D \ 1.208 g
c
cm~3, k \ 0.75 cm~1, F(000) \ 536. The Ðnal cycle of full-matrix
least-squares reÐnement was based on 1347 observed reÑections
[I [ 3.00 r(I)] and 241 variable parameters and converged with
This work was supported by The Research Fund Grant-in-
Aid for Exploratory Research (No. 09874134) and that for
ScientiÐc Research on Priority Area (A) (No. 10146235) from
the Ministry of Education, Science, Sports and Culture, Japan.
unweighted and weighted agreement factors of R \ 0.051 and R \
w
0.065. CCDC reference number 440/119. See http://www.rsc.org/
suppdata/nj/1999/683/ for crystallographic Ðles in .cif format.
Notes and references
¤ All the compounds were identiÐed spectroscopically and by means
1 (a) Y. Sugihara, R. Hashimoto, H. Fujita, N. Abe, H. Yamamoto, T.
Sugimura and I. Murata, J. Chem. Soc., Perkin T rans. 1, 1995, 22,
2813; (b) Y. Sugihara, T. Murafuji, N. Abe, M. Takeda and A.
Kakehi, New J. Chem., 1998, 22, 1031.
2 For the stabilization of chlorobismuthanes by the hypervalent
bond, see: (a) H. Suzuki, T. Murafuji and N. Azuma, J. Chem. Soc.,
Perkin T rans. 1, 1993, 1169; (b) T. Murafuji, T. Mutoh, K. Satoh, K.
Tsunenari, N. Azuma and H. Suzuki, Organometallics, 1995, 14,
3848.
3 For the Ñuorescence of 4, see: (a) Y.-B. Jiang and X.-J. Wang, J.
Photochem. Photobiol. A: Chem., 1994, 81, 205; (b) P. Wang and S.
Wu, ibid., 1995, 86, 109.
4 M. J. Kamlet, J.-L. M. Abboud, M. H. Abraham and R. W. Taft, J.
Org. Chem., 1983, 48, 2877.
5 (a) E. Lippert, Z. Naturforsch. A, 1955, 10, 541; (b) N. Mataga, Y.
Kaifu and M. Koizumi, Bull. Chem. Soc. Jpn., 1955, 28, 690; ibid.,
1956, 29, 465.
6 L. Onsager, J. Am. Chem. Soc., 1936, 58, 1486.
7 C. A. van Walree, H. Kooijman, A. L. Spek, J. W. Zwikker and
L. W. Jenneskens, J. Chem. Soc., Chem. Commun., 1995, 35.
of high resolution mass spectrometry. NMR (CDCl ) 1: 1H d 0.65È
3
0.69 (10H, m, Et B), 3.11 (6H, s, Me N), 6.72 (2H, d, J \ 9.2,
2
2
AB
Me NArH), 7.30 (1H, t, J \ 7.9, BArH), 7.39 (1H, d, J \ 15.3,
2
AB
CH2CHCO), 7.51 (1H, t, J \ 7.9, BArH), 7.66 (2H, d, J \ 9.2,
AB
Me NArH), 7.68 (1H, d, J \ 7.3, BArH), 8.00 (1H, d, J \ 7.9, BArH),
2
8.28 (1H, d, J \ 15.3, CH2CHCO); 13C d 10.0, 14.8, 40.1, 108.6,
AB
119.9, 122.2, 125.1, 125.7, 128.9, 131.9, 132.4, 132.8, 137.9, 150.5, 153.3,
192.5; 11B d 14.8. 2: 1H d 3.10 (6H, s, Me N), 4.34 (4H, s, CH CH ),
2
2
2
6.71 (2H, d,
J
\ 9.2, Me NArH), 7.33 (1H, d,
J
\ 15.3,
AB
2
AB
CH2CHCO), 7.44 (1H, t, J \ 7.3, BArH), 7.58 (1H, t, J \ 7.3, BArH),
7.62 (2H, d, J \ 9.2, Me NArH), 7.70 (1H, d, J \ 7.3, BArH), 7.93
AB
2
(1H, d, J \ 7.9, BArH), 8.18 (1H, d, J \ 15.3, CH2CHCO). 3: 1H d
AB
2.22 (3H, s, Me), 3.10 (6H, s, Me N), 6.70 (2H, d, J \ 8.5,
2
AB
Me NArH), 7.30 (2H, d, J \ 7.9, MeArH), 7.51 (1H, d, J \ 15.3,
2
AB
AB
CH2CHCO), 7.61 (2H, d, J \ 8.5, Me NArH), 7.62 (1H, t, J \ 7.3,
AB
2
BiArH), 7.94 (1H, t, J \ 7.3, BiArH), 8.06 (2H, d, J \ 7.9, MeArH),
AB
8.08 (1H, d, J \ 15.3, CH2CHCO), 8.41 (1H, d, J \ 7.3, BiArH),
AB
9.11 (1H, d, J \ 7.3, BiArH). 5: 1H d 0.49È0.55 (20H, m, Et B), 3.07
2
(6H, s, Me N), 5.31 (2H, s, CH ), 6.70 (2H, d, J \ 8.6, Me NArH),
2
2
AB
2
7.31 (1H, t, J \ 7.5, BArH), 7.35 (1H, t, J \ 7.0, BArH), 7.51 (1H, t,
L etter 9/02282A
New J. Chem., 1999, 23, 683È685
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