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Syntheses and characterization of a new class of mono- and heterodinuclear derivatives of boron derived from Schiff bases.

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Full Paper
Received: 20 April 2010
Revised: 6 June 2010
Accepted: 8 June 2010
Published online in Wiley Online Library: 27 July 2010
(wileyonlinelibrary.com) DOI 10.1002/aoc.1697
Syntheses and characterization of a new class
of mono- and heterodinuclear derivatives
of boron derived from Schiff bases
Priyanka Sharma, Vaishali Vajpayee, Jyoti Sharma and Yashpal Singh∗
Reactions of 2-isopropoxy-1, 3, 2- benzodioxaborole with equivalent amounts of Schiff base ligands having two hydroxyl groups
(1a–3a) yield mononuclear derivatives with one residual hydroxy group. The reactions of these mononuclear derivatives with
hexamethyldisilazane in a 2 : 1 ratio yield heterodinuclear derivatives. All these newly synthesized derivatives have been
characterized by elemental analyses and molecular weight measurements. Tentative structures have been proposed on the
basis of IR and NMR (1 H, 13 C, 11 B,29 Si)spectral data and Fab-mass studies. Schiff bases and their corresponding mono- and
c 2010 John Wiley & Sons,
heterodinuclear derivatives of boron have also been screened for antifungal activities. Copyright Ltd.
Keywords: heterodinuclear derivatives of boron; bifunctional tridentate Schiff bases; multinuclei (1 H,13 C,11 B,29 Si) NMR spectra; antifungal
activities
Introduction
A variety of binuclear alkoxides of different elements have been
reported[1 – 10] in the literature during the past three decades.
In addition to these, a large number of mononuclear,[11 – 16]
homodinuclear[17] and trinuclear[18] derivatives of boron in which
the ligand bridges the central atom have been reported in the
literature. Only a few reports on heterodinuclear derivatives
of boron are available in the literature.[19 – 22] Surprisingly,
heterodinuclear derivatives of boron-containing chelating ligands
continue to be evasive.[23 – 26] In view of the above, we have
synthesized and characterized for the first time some new Schiff
bases derivatives of boron as well as heterodinuclear derivatives of
boron with silicon. Antifungal activity of ligands (1a–3a) and some
of their corresponding mono (1Aa–3Da) and heterodinuclear
derivatives (1Ab–3 Db) of boron have also been reported against
Aspergillus niger and A. flavus.
Experimental
774
Solvents were purified and dried by standard procedures.[27] Schiff
bases 1a–3a were prepared by equimolar condensation reactions of β-diketones or salicylaldehyde with appropriate
amino alcohols.[28] Boron isopropoxide and 2-isopropoxy-1,3,2benzodioxaborole were prepared by the literature method.[29]
Hexamethyldisilazane (Aldrich) was distilled prior to use. Isopropyl
alcohol in azeotrope was determined oxidimetrically.[30] Boron
was estimated as methyl borate.[31] The 1 H, 13 C (300 MHz), 11 B
(96.3 MHz) and 29 Si (59.6 MHz) NMR spectra in CDCl3 solution
were recorded with a Jeol FT Al 300 spectrometer.1 H and 13 C NMR
spectra were recorded using TMS as internal refrence and 11 B
NMR and 29 Si NMR were recorded using B(OMe)3 and Me3 SiCl as
external references, respectively. IR spectra were recorded on an
8400s Shimadzu FT-IR spectrophotometer as nujul mull on a KBr
cell in the range 4000–400 cm−1 . The Fab-mass spectrum of one
Appl. Organometal. Chem. 2010, 24, 774–780
representative compound (1Bb) was recorded on a Micromass
Quatro II tripole quadrupole mass spectrometer. Elements (C, H
and N) were analyzed on a Perkin Elmer-2400 C, H, N analyzer.
Details of only one compound of each series are given, and the analytical data as well as preparative details of the rest of compounds
are summarized in Tables 1 and 2.
Synthesis of 1Aa
A reaction mixture (∼50 ml) containing 2-isopropoxy-1,3,2benzodioxaborole (0.87 g; 4.88 mmol) and Schiff base ligand
1a1 (0.70 g; 4.89 mmol) was refluxed on a fractionating column
in benzene solutions for approximately 20 h. Isopropyl alcohol formed during the reaction was continuously distilled off
as bezene–isopropanol azeotrope and estimated periodically to
monitor the progress as well as completion of the reaction. When
the azeotrope showed the presence of a negligible amount of
Pri OH, the reaction was stopped and the excess of solvent was
removed under reduced pressure, yielding a pale yellow solid. The
compound was recrystallized from a benzene–n-hexane mixture.
Synthesis of 1Ab
A benzene solution (∼50 ml) containing mononuclear boron
derivative 1Aa (1.10 g; 4.21 mmol) and NH(SiMe3 )2 (0.34g;
2.10 mmol) was refluxed for approximately 10 h, until the evolution
of NH3 ceased. After completion of the reaction, the solvent was
removed under reduced pressure, yielding a pale yellow solid. The
compound was recrystallized from a benzene–n-hexane mixture.
∗
Correspondence to: Yashpal Singh, Department of Chemistry, University of
Rajasthan, Jaipur 302050, India. E-mail: yashpaluniraj@gmail.com
Department of Chemistry, University of Rajasthan, Jaipur 302050, India
c 2010 John Wiley & Sons, Ltd.
Copyright New class of mono-and heterodi-nuclear derivatives of boron
Table 1. Synthetic and analytical details of some mono-nuclear derivatives of boron
Sample
no.
1
2
3
4
5
6
7
8
Reactants in g (mmol)
Ligand
O C6H4-O-B-OPri
0.70(4.89)
1a1
1.05(5.11)
2a1
2.49(15.84)
1a2
4.16(18.97)
2a2
1.20(7.26)
3a1
1.78(9.93)
3a2
0.38(1.96)
3a3
1.51(8.42)
3a4
0.87(4.88)
0.91(5.11)
2.84(15.84)
3.38(18.98)
1.29(7.24)
1.77(9.93)
0.36(1.96)
1.50(8.42)
Pri OH Found
(calcd)
0.28
(0.29)
0.29
(0.30)
0.94
(0.96)
0.13
(0.14)
0.40
(0.43)
0.61
(0.59)
0.12
(0.11)
0.50
(0.50)
Analyses (%) found (calcd)
Empirical formula, color, physical
state, (yield %), melting point (◦ C)
C13 H16 BNO4 , yellow solid, (98)157
C18 H18 BNO4 , yellow solid, (98) 184
C14 H18 BNO4 , brown solid, (97)175
C19 H20 BNO4 , dark yellow solid, (99) 142
C15 H14 BNO4 , yellow solid, (96) 120
C16 H16 BNO4 yellow solid, (98)181
C17 H18 BNO4 , dark yellow solid, (97) 180
C16 H16 BNO4 , yellow solid, (98) 195
B
N
C
H
4.07
(4.14)
3.41
(3.34)
3.89
(3.93)
5.29
(5.36)
4.40
(4.33)
5.16
(5.09)
59.26
(59.80)
66.99
(66.90)
61.05
(61.12)
6.01
(6.17)
5.42
(5.61)
6.70
(6.59)
3.16
(3.20)
3.79
(3.81)
3.18
(3.63)
3.13
(3.47)
3.11
(3.63)
4.21
(4.15)
4.88
(4.94)
4.61
(4.71)
4.32
(4.49)
4.67
(4.71)
67.57
(67.68)
–
5.84
(5.97)
–
–
–
–
–
–
–
Table 2. Synthetic and analytical details of some heterodi-nuclear derivatives of boron
Reactants in g (mmol)
Sample
no.
9
10
11
12
13
14
15
16
Mononuclear
derivatives
Analyses (%) found (calcd)
NH(SiMe3 )2
Empirical formula, color, physical
state, (yield, %), Melting point (◦ C)
0.34(2.10)
C16 H24 BSiNO4 , creamyellow solid, (99)135
0.38(2.35)
C21 H26 BSiNO4 , yellow solid, (98)120
0.27(1.67)
C17 H26 BSiNO4 , brown solid, (98)148
1.22(3.61)
2Ba
1.57(5.54),3Aa
0.29(1.79)
C22 H28 BSiNO4 , brown solid, (99) 158
0.44(2.77)
C18 H22 BSiNO4 , yellow solid, (98)175
1.35(4.54)
3Ba
0.98(3.14)
3Ca
1.20(4.03)
3Da
0.36(2.27)
C19 H24 BSiNO4 , brown solid, (94)137
0.25(1.54)
C20 H26 BSiNO4 , dark yellow solid, (98)205
0.32(2.01)
C19 H24 BSiNO4 , yellow solid, (97)110
1.10(4.21)
1Aa
1.54(4.75)
2Aa
0.92(3.34)
1Ba
Antifungal Activity
Appl. Organometal. Chem. 2010, 24, 774–780
N
C
H
3.28
(3.24)
2.70
(2.73)
3.18
(3.11)
4.23
(4.20)
3.49
(3.54)
3.98
(4.03)
57.83
(57.66)
63.68
(63.80)
58.91
(58.79)
7.11
(7.25)
6.57
(6.62)
7.61
(7.55)
2.16
(2.64)
2.98
(3.04)
2.95
(2.99)
2.78
(2.88)
2.80
(2.99)
3.35
(3.42)
3.90
(3.94)
3.84
(3.88)
3.68
(3.73)
3.76
(3.88)
64.69
(64.55)
–
6.72
(6.89)
–
–
–
–
–
–
–
(a Petri plate with nutrient agar and fungal suspension spread
on it). The Petri plate with the disk was incubated at a suitable
temperature (28 ± 2 ◦ C) for 48–72 h; after that, the inhibition zone
around each disk was measured. Table 6 shows the inhibition
zone in diameter. The readings are the mean values of three
replicates.
Results and Discussion
The reactions of 2-isopropoxy-1,3,2-benzodioxaborole with two
types of bifunctional bidentate Schiff base ligands 1a–3a (Fig. 1)
c 2010 John Wiley & Sons, Ltd.
Copyright wileyonlinelibrary.com/journal/aoc
775
The ligands and their corresponding mono- and heterodinuclear
boron derivatives were evaluated for growth inhibitory activity
in vitro against fungi (i.e. A. niger and A. flavus).To evaluate
the antifungal activity, we used the paper disk method. In this
method sterilized nutrient agar medium and a Whatman no. 1
paper disk (6 mm in diameter) were used. The agar medium
was poured into the Petri plate and, after solidification, the
fungal suspension was spread uniformly on the medium. A
test sample was prepared by adding 0.1 g compounds in 1 ml
methanol. The paper disk was dipped into the sample for half
an hour and, after that, the disks were placed on seeded plates
B
776
wileyonlinelibrary.com/journal/aoc
c 2010 John Wiley & Sons, Ltd.
Copyright 3Da
3Ca
3Ba
3Aa
2Ba
2Aa
1Ba
1Aa
1 H NMR
165.47/ –
164.51/ –
168.07/ –
164.57/ –
– /173.17
– /174.57
– /172.07
– /173.71
Phenolic/enolic
>C–O
value) of some new mononuclear derivatives of boron
3.86-3.88(t)-CH2 OH, 3.72–3.75(t) CH2 N,
5.46(s)CHCO, 2.10(s)CH3 CO, 2.04(s)
CH3 CN. 6.52–6.75(m)
C6 H4 ,3.96(S)CH2 OH
3.78-3.80(t)-CH2 OH, 3.48–3.69(t) CH2 N,
6.18(s) CHCO, 2.41(s)CH3 CO, 2.04(s)
CH3 CN. 6.74–6.83(m) C6 H4 ,
3.82(S)CH2 OH, 7.26–7.91(m) C6 H5
3.51-3.55(t)-CH2 OH, 3.38–3.40(t) CH2 N,
5.42(s)CHCO, 2.24(s)CH3 CO, 2.12(s)
CH3 CN. 6.63–6.79(m)
C6 H4 ,3.3.60(S)CH2 OH,
3.46-3.49OCH2 CH2
3.68-3.79(t)-CH2 OH, 3.39–3.47(t) CH2 N,
6.08(s) CHCO, 2.31(s)CH3 CO, 2.04(s)
CH3 CN. 6.70–6.80(m) C6 H4 ,
4.04(S)CH2 OH, 7.25-7.89m) C6 H5 ,
3.55-3.61OCH2 CH2
−8.29 (s) -CH=N-, 6.75–7.57 (m) C6 H4 -,
3.64–3.65 (t) N-CH2− 3.74-3.77
(t)-CH2 -O4.41 – (s)OH
8.04 (s)-CH=N-,6.44–7.46 (m) C6 H4 -, −3.66
(t)NCH2 ,1.32 (m)NCH2 CH2 , 2.21
(t)CH2 0,3.79 (s)-OH
8.30 (s), -CH=N-,6.95–7.58
(m) C6 H4 -3.65-0CH2 ,-1.66 C(CH3 )2 4.10
(s)-OH
8.35 (s) -CH=N-,6.61–7.63 (m) C6 H4 -,
3.20–3.24 (d)NCH2 , 4.04–4.09(m)CH
(CH3 ), 1.62–1.64 (d)CH(CH3 ,) 3.77 (s)-OH
1 H,13 C,11 B NMR Spectra (δ
Compound
Table 3.
67.24
69.14
58.18
59.17
60.15
60.27
61.81
63.11
Alcoholic
163.39
160.07
159.28
157.23
169.11
170.80
168.63
169.88
>C N
13 C NMR
109.62–138.38
109.41–136.95
109.36–136.99
108.52–137.45
108.56–131.96
109.86–119.61
109.65–132.88
108.15–118.41
Phenyl carbon
65.93 NCH2
20.44CH(CH3 )
60.06(C(CH3 )2 )
26.56(C(CH3 )2 )
47.93 NCH2 ,
32.52NCH2 CH2 ,
54.68(-CH2− )2
58.81(NCH2 ),
99.28(CHCO),
32.80(CH3 CO),
22.24(CH3 CN)
60.01OCH2 CH2
57.15(NCH2 ),
94.01(CHCO),
32.94CH3 CO
61.14(NCH2 ),
95.41(CHCO),
29.11(CH3 CO),
21.27(CH3 CN)
61.44(NCH2 ),
95.35(CHCO),
21.33CH3 CO),
Alkylene carbon
NMR
(−)10.34
(−)13.69
(−)16.27
(−)15.62
(−)10.61
(−)9.81
(−)9.28
(−)10.35
11 B
P. Sharma et al.
Appl. Organometal. Chem. 2010, 24, 774–780
1
c 2010 John Wiley & Sons, Ltd.
Copyright wileyonlinelibrary.com/journal/aoc
3 Db
3Cb
3Bb
3Ab
2Bb
2Ab
777
Appl. Organometal. Chem. 2010, 24, 774–780
1Bb
1Ab
Compound
Table 4.
H NMR
8.39 (S), -CH N-, 6.59–7.53 (m) C6 H4 ,
3.58–0CH2 ,- 1.52C (CH3 )2 , 0.03–0.19 [s,
Si (CH3 )3 ]
8.29 (S), -CH N-, 6.65–7.58 (m) C6 H4 -, 3.77
(d) NCH2 , 4.04–4.09 (m) CH(CH3 ), 1.24
(d) CH (CH3 ), 0.04–0.07 [s, Si(CH3 )3 ]
3.42–3.46 (t)–CH2 OH, 3.28–3.38 (t) CH2 N,
5.36 (s) CHCO, 2.18 (s) CH3 CO, 2.04
(S) CH3 CN, 6.59–6.79 (m) C6 H4 ,
0.08–0.24 [s, Si(CH3 )3 ]
3.81–3.83 (t)–CH2 OH, 3.60–3.69 (t) CH2 N,
6.15 (s) CHCO, 2.43 (s)CH3 CO, 6.74–6.82
(m) C6 H4 , 3.82 (S) CH2 OH, 7.36–7.91
(m) C6 H5 , 0.05–0.07 [S Si(CH3 )3 ]
3.78–3.81 (t)–CH2 OH, 3.40–3.47 (t) CH2 N,
5.61 (s) CHCO, 2.27 (s) CH3 CO, 2.19 (S),
CH3 CN, 6.59–6.81 (m) C6 H4 ,
3.51–3.54OCH2 CH2 , 0.07–0.1 [s,
Si(CH3 )3 ]
3.78–3.82 (t)–CH2 OH, 3.41–3.49 (t) CH2 N,
6.11 (s) CHCO, 2.59 (s) CH3 CO, 6.74–6.81
(m) C6 H4 , 7.36–7.90 (m) C6 H5 ,
3.66–3.68OCH2 CH2 ,0.05–0.08 [s,
Si(CH3 )3 ]
−8.28(S), -CH N-, 6.66–7.56 (m) C6 H4 ,
3.81 (t) N-CH2 , 3.73 (t)–CH2 –O,
0.03–0.19 [s, Si (CH3 )3 ]
8.04 (S), -CH N-, 6.44–7.46 (m) C6 H4 -,
3.6–3.9 (t) NCH2 (J = 5.31) 1.25
(m) NCH2 CH2 , 2.1–2.23 (t) CH2 O
(J = 10.63), 0.02–0.07 [s, Si(CH3 )3 ]
1
164.89/ –
162.05/ –
167.52/ –
165.36/ –
– /174.17
65.33
71.99
61.34
60.44
61.11
62.11
62.00
– /172.05
– /174.57
63.59
Alcoholic
– /174.01
Phenolic/enolic
>C–O
H,13 C,11 B NMR spectra (δ values) of some new heterodinuclear derivatives of boron
164.35
159.25
157.42
156.30
169.47
170.80
168.72
170.03
>C N
13 C NMR
107.01–136.76
108.86–132.22
109.47–137.56
109.58–138.75
106.82–131.07
109.86–120.00
109.40–132.32
108.19–118.71
Phenyl carbon
70.18[C(CH3 )2 ]
23.75 [C(CH3 )2 ]
1.66 SiCH3
63.74 NCH2
20.51CH (CH3 ),
1.22 SiCH3
54.88 NCH2 ,
30.04 NCH2 CH2
55.95(-CH2− )2 ,
0.99 SiCH3
58.81(NCH2 ),
99.28(CHCO),
32.80(CH3 CO),
22.24(CH3 CN)
60.01OCH2 CH2
57.15(NCH2 ),
94.01(CHCO),
32.94CH3 CO
61.14(NCH2 ),
95.41(CHCO),
29.11(CH3 CO),
21.27(CH3 CN)
61.44(NCH2 ),
95.35(CHCO),
21.33CH3 CO),
Alkylene carbon
(−)10.14
(−)13.55
(−)16.12
(−)10.14
(−)10.19
(−)10.91
22.27
23.41
17.88
17.08
23.11
22.98
22.29
Si NMR
(−)10.29
29
22.69
B NMR
(−)9.69
11
New class of mono-and heterodi-nuclear derivatives of boron
P. Sharma et al.
Y
HO
Y
H
N
O
C
C
Ph
C
H
HO
Me
Me
1a
{Y = (CH2)2 (1a1)}
{Y = (CH2)3 (1a2)}
H
N
O
C
C
C
H
H
C
Me
N
Y
OH
Table 5. Mode of fragmentation of Heterodinuclear derivative of
boron (1Bb)
OH
2a
3a
{Y = (CH2)2 (2a1)}
{Y = (CH2)3 (2a2)}
{Y = (CH2)2 (3a1)}
{Y = (CH2)3 (3a2)}
{Y = C(CH3)2CH2 (3a3)}
{Y = CH(CH3)2CH2 (3a4)}
OC6H4OBOC(CH3)CHCNCH2CH2OSi(CH3)3)C6H5
Complex
m/e
396
OC6H4OBOC(CH3)CHC(NCH2CH2OSi(CH3)3)C6H5
319
OC6H4OBOC(CH3)CHC(NCH2CH2OSi(CH3)3)
Figure 1. Bifunctional tridentate Schiff bases.
were carried out in equimolar ratio in refluxing benzene to
yield mononuclear boron derivatives (1Aa–3Da). The reaction
of mononuclear boron derivatives with NH(SiMe3 )2 in 1 : 2 molar
ratio in refluxing benzene produced a new type of heterodinuclear
derivative of boron (1Ab–3 Db). All these colored solid derivatives
were soluble in benzene and chloroform.
OC6H4OBOCHC(NCH2CH2OSi(CH3)3)
OC6H4OBOC(NCH2CH2OSi(CH3)3)
OC6H4OBOC(NCH2CH2OSiCH3)
OC6H4OBOC(NCH2CH2O)
Spectroscopic Studies
IR spectra
A broad band for νOH present at ∼3300–3600 cm−1 in the spectra
of mononuclear derivatives was found to be absent in the spectra
of heterodinuclear derivatives. The appearence of a new band
in the spectra of 1Ab–3 Db in the region 860–880 cm−1 due
to the νSi–O[32] band indicates the formation of an Si–O bond.
A band due to ν(C N) was observed at 1610–1630 cm−1 in
1Aa–3Da. In the spectra of heterodinuclear derivatives, this band
showed a small shift in its position. This shift may be due to
the presence of two central atoms, boron and silicon, in the
heterodinuclear derivatives. The bands in the regions ∼1280 ± 3
and 808–820 cm−1 may be due to νB–O [33] and νB ← N[34]
vibration mode, respectively. Two bands were observed in the
range 1570–1585 cm−1 in the spectra of compounds 1Aa–2Ba
and 1Ab–2Bb due to the (CH3 )C–O and (Y)C–O of the ligand (1a,
2a) showing a significant shift towards the lower wavenumber as
compared with its position in the spectra of 1Aa–2Aa owing to
coordination of this group with two metal atoms, whereas in the
spectra of compounds 3Aa–3Da and 3Ab–3 Db these bands for
ν > C–O were observed at 1050–1065 and 1205–1220 cm−1 .
A band observed at 1250 ± 7 may be assigned for νSi–Me
deformation[35] in the spectra of heterodinuclear derivatives.
1
OC6H4OBOCCHC(NCH2CH2OSi(CH3)3)
H NMR spectra
In1 H NMR spectra of mononuclear derivatives, the aminol -OH
group was observed as a singlet in the region δ3.39–4.35 ppm,
which was absent in the spectra of heterodinuclear derivatives.
This indicates the removal of the–OH group and the formation of
a Si–O bond. Signals for alkylene and azomethine protons in the
spectra of 1Ab–3 Db appeared with a small shift as compared with
their position in the spectra of compounds 1Aa–3Da (Tables 3
and 4) owing to the replacement of the pendant -OH group
with an Me3 Si group. Me3 Si protons appeared as a singlet at
0.03–0.24 ppm in the spectra of derivatives 1Ab–3 Db.
OC6H4OBOC(NCH2CH2)
OC6H4OBO
OC6H4OB
304
292
279
249
206
190
136
104
the spectra of ligands, which indicates the bidentate nature of
ligands. This signal was further shifted in the spectra of compound
1Ab–3 Db due to the presence of two metalloid atoms, i.e.
B and Si. Two signals for the >C–O carbon were observed
at δ172.05–173.71 and 60.15–63.11 ppm (in the compound
1Aa–2Ba and 1Ab–2Bb) due to (CH3 )CO and (Y)CO groups,
whereas in the spectra of compounds 3Aa–3Da and 3Ab–3 Db
the signals for phenolic >C–O and alcoholic >C–O were observed
at δ160.52–168.07 and 58.18–71.99 ppm, respectively. The signal
for Me3 Si carbon appeared at δ0.99–2.60 ppm in the spectra of
compounds 1Ab–3 Db. All alkylene carbons were observed at
their usual positions (Tables 3 and 4).
11 B NMR spectra
The appearance of a sharp singlet in the region δ − 9.28
(−16.21) ppm with reference to methyl borate in the 11 B NMR
spectra of 1Aa–3 Db indicates the presence of tetracoordinated
boron[36 – 38] atom in the spectra of all these derivatives.
29 Si NMR spectra
The 29 Si NMR spectra of heterodinuclear derivatives exhibited
a signal centered in the range δ17.08–23.11 ppm, which is
consistent with presence of tetracoordinated silicon atom.[39,40]
Fab-Mass Spectra
13 C NMR spectra
778
In the spectra of mononuclear derivatives IAa–3Aa, a signal for
azomethine carbon was observed at δ157.23–170.80 ppm with a
shift of ∼5 ppm in its position as compared with the position in
wileyonlinelibrary.com/journal/aoc
Fab-mass spectra of one of the heterodinuclear compounds (1Bb)
was recorded, showing the monomeric nature of the compound.
The mass spectral fragmentation pattern of compound 1Bb is
summarized in Table 5.
c 2010 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2010, 24, 774–780
New class of mono-and heterodi-nuclear derivatives of boron
OM
Y
B
B
O
O C
Y
N C
O
CH
OM
Ph
Y
N C
O
O
OM
Me
Me
N CH
O
CH
B
O C
O
O
Me
1b
{Y = (CH2)2; M = H (1Aa)
M = SiMe3 (1Ab)}
{Y = (CH2)3; M = H, (1Ba)
M = SiMe3 (1Bb)}
2b
{Y = (CH2)2; M = H (2Aa)
M = SiMe3 (2Ab)}
{Y = (CH2)3; M = H, (2Ba)
M = SiMe3 (2Bb)}
3b
{Y = (CH2)2; M = H (3Aa)
M = SiMe3 (3Ab)}
{Y = (CH2)3, M = H, (3Ba)
M = SiMe3 (3Bb)}
{Y = C(CH3)2CH2, M = H (3Ca)
M = SiMe3 (3Cb)}
{Y = CH(CH3)CH2, M = H, (3Da)
M = SiMe3 (3Db)}
Figure 2. Homo- and heterodinuclear derivatives of boron.
Figure 4. Inhibition zone of ligand and their mono- and heterodinuclear
derivatives of boron against Aspergillus niger. (A) 1 = 3a1 , 2 = 3a2 ,
3 = 3a3 , 4 = 3a4 . (B) 1 = 3Aa, 2 = 3Ba. (C) 1 = 3Ca, 2 = 3Da.
(D) 1 = 3Ab, 2 = 3Bb, 3 = 3Cb, 4 = 3 Db. S, Standard = zynthamycin.
Figure 3. Inhibition zone of ligand and their mono- and heterodinuclear
derivatives of boron against Aspergillus flavus. (A) 1 = 3a1 , 2 = 3a2 ,
3 = 3a3 , 4 = 3a4 . (B) 1 = 3Aa, 2 = 3Ba. (C) 1 = 3Ca, 2 = 3Da.
(D) 1 = 3Ab, 2 = 3Bb, 3 = 3Cb, 4 = 3 Db. S, Standard = zynthamycin.
Structure
In view of the bifunctional bidentate nature of the ligands and
the 11 B and 29 Si NMR spectral data, the three structures in Fig. 2
(1b, 2b and 3b) are suggested for mono- and heterodinuclear
derivatives, in which both B and Si atoms are tetracoordinated.
Antifungal Activity
Appl. Organometal. Chem. 2010, 24, 774–780
Acknowledgment
We are thankful to CDRI Lucknow (SAIF Center) for recording
the Fab-mass of one of the compounds and Chemind Dignosis
Biosolutions, Jaipur for antifungal activity.
c 2010 John Wiley & Sons, Ltd.
Copyright wileyonlinelibrary.com/journal/aoc
779
The representative ligands and their corresponding mono-and
heterodinuclear boron derivatives were screened against A. niger
(Fig. 4) and A. flavus (Fig. 3) to examine their growth inhibitory
potential towards the test organisms. The results (Table 6) indicate
that the metal derivatives were found to be more inhibitory
than the corresponding ligands and the order of the activity is
heterodinuclear > mononuclear > ligands. A similar trend was
seen for the activity in the compounds of aluminum and silicon
with these ligands.[41]
The enhanced activity of the boron complexes compared with
the free ligand may be explained by Tweedy’s chelation theory.[42]
It is natural to hypothesize that more lipophilic compounds are
more active simply because they enter the lipid layers of the cell
membrane more rapidly.
Since the boron derivatives inhibit the growth of microorganisms, it is assumed that the production of ATP and enzymes is
affected by microorganisms as they are unable to utilize food for
themselves, or the intake of nutrient decreases and subsequently
the growth diminishes.
Inhibition of fungal growth was also found to increase with
the compounds’ concentration. All the present fungicides are
metabolic inhibitors, that is, they block some vital metabolic
processes. The results are summarized in Table 6.
P. Sharma et al.
Table 6. Antifungal activities of the ligands and their mono- and
heterodi-nuclear derivatives
Zone size (mm)
Compound Concentration (%) Aspergillus niger Aspergillus flavus
1a1
3a1
3a2
3a3
3a3
1Aa
3Aa
3Ba
3Ca
3Da
1Ab
3Ab
3Bb
3Cb
3Db
10
30
10
30
10
30
10
30
10
30
10
30
10
30
10
30
10
30
10
30
10
30
10
30
10
30
10
30
10
30
8
10
7
10
9
12
8
11
6
11
10
13
10
21
13
15
11
19
13
21
12
15
12
20
16
19
14
23
15
22
5
10
8
12
7
10
7
13
8
12
7
12
12
18
10
16
14
17
14
21
8
16
13
9
14
18
14
19
16
23
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