Synthesis, reactions, and spectral [NMR (1H, 13C, 29Si), IR] studies of trimethylsilyl-substituted N-arylsalicylaldiminates

Article abstract of DOI:10.1081/SIM-100107714

Trimethylsilyl-substituted N-arylsalicylaldiminates Me₃Si (OC₆H₄CH=NAr) [Ar=C₆H₅ (1), C₆H₃Me₂-2,6 (2), C₆H₂Me₃-2,4,6 (3), C₆H₃Et₂-2,6 (4), and C₆H₃(Pr-i)₂-2,6 (5)] have been prepared by the equimolar reactions of Me₃SiCl with N-arylsalicylaldimines (LH) in benzene using Et₃N as a base. Reactions in the desired molar ratios (1:1 or 2:1) of Me₃Si(OC₆H₄CH=NAr) with TiCl₄ and ZrCl₄ afford a convenient and clean synthetic procedure for the preparation of chloride-salicylaldiminate derivatives of early transition metals. Characterisations of all these new derivatives have been carried out by elemental analyses, molecular weight determinations and spectroscopic [IR, NMR (¹H, ¹³C and ²⁹Si)] studies.

Full text of DOI:10.1081/SIM-100107714

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SYNTHESIS, REACTIONS, AND SPECTRAL [NMR (1H, 13C,
29Si), IR] STUDIES OF TRIMETHYLSILYL-SUBSTITUTED N-
ARYLSALICYLALDIMINATES
Manju Goyal a , Shashank Mishra a & Anirudh Singh b
a Department of Chemistry , University of Rajasthan , Jaipur, 302 004, India
b Department of Chemistry , University of Rajasthan , Jaipur, 302 004, India
Published online: 15 Aug 2006.
To cite this article: Manju Goyal , Shashank Mishra & Anirudh Singh (2001) SYNTHESIS, REACTIONS, AND SPECTRAL [NMR (1H,
13C, 29Si), IR] STUDIES OF TRIMETHYLSILYL-SUBSTITUTED N-ARYLSALICYLALDIMINATES, Synthesis and Reactivity in Inorganic and
Metal-Organic Chemistry, 31:9, 1705-1715, DOI: 10.1081/SIM-100107714
To link to this article: http://dx.doi.org/10.1081/SIM-100107714
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SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(9), 1705±1715 (2001)
SYNTHESIS, REACTIONS, AND
13
29
SPECTRAL [NMR (1H, C, Si), IR]
STUDIES OF TRIMETHYLSILYL-
SUBSTITUTED
N-ARYLSALICYLALDIMINATES
Manju Goyal, Shashank Mishra, and Anirudh Singh*
Department of Chemistry, University of Rajasthan,
Jaipur, 302 004, India
ABSTRACT
Trimethylsilyl-substituted N-arylsalicylaldiminates Me3Si
(OC6H4CHˆNAr) [ArˆC6H5 (1), C6H3Me2-2,6 (2),
C6H2Me3-2,4,6 (3), C6H3Et2-2,6 (4), and C6H3(Pr-i)2-2,6 (5)]
have been prepared by the equimolar reactions of Me3SiCl
with N-arylsalicylaldimines (LH) in benzene using Et3N as a
base. Reactions in the desired molar ratios (1:1 or 2:1) of
Me3Si(OC6H4CHˆNAr) with TiCl4 and ZrCl4 a€ord a con-
venient and clean synthetic procedure for the preparation of
chloride-salicylaldiminate derivatives of early transition
metals. Characterisations of all these new derivatives have
been carried out by elemental analyses, molecular weight
determinations and spectroscopic [IR, NMR (1H, 13C and
29Si)] studies.
*Corresponding author. E-mail: vijaya29@id.eth.net
1705
Copyright # 2001 by Marcel Dekker, Inc.
www.dekker.com

1706
GOYAL, MISHRA, AND SINGH
INTRODUCTION
The chemistry of metal-organic compounds containing alkoxo and=or
phenoxo functionalities1,2 has grown considerably in the last thirty years.
These compounds are of great interest due to their potential applications as
precursors for advanced materials in di€erent areas of science and tech-
nology such as ceramics and glasses, as well as catalysis. We have previously
described the preparation and spectral properties of some silicon and or-
ganosilicon aryloxides3,4 with the aim to examine the utility of (i) NMR data
in explaining the variation in the electron density around the silicon atom
with the number of methyl and=or aryloxide groups attached to silicon, and
(ii) trimethylsilyl aryloxides in providing neat and high yield synthesis of
mixed chloride-aryloxide derivatives of titanium(IV) and niobium(V). With
similar objectives in mind, we report herein the synthesis, chemistry and
spectroscopy of trimethylsilyl-substituted N-arylsalicylaldiminates (1)7(5).
The present study assumes further importance due to the fact that al-
though there have been a number of reports5,6,7 during the past 13 years of
compounds that are similar to those described herein, a systematic and detailed
study of trimethylsilicon derivatives of monofunctional bidentate salicylaldi-
mines of the type shown in Fig. 1 does not appear to have carried out so far.
RESULTS AND DISCUSSION
Equimolar reactions of Me3SiCl with N-arylsalicylaldimines (LH) in
benzene in the presence of Et3N as a base a€ord trimethylsilyl-substituted N-
aryl-salicylaldiminates, Me3SiL [L ˆ L1 (1), L2 (2), L3 (3), L4 (4), and L5 (5)], by
the replacement of the phenolic proton of ligands shown in Fig. 1 by Me3Si
group.
The derivatives (1)7(5) (Table I) are yellow or orange volatile liquids,
soluble in common organic solvents (benzene, carbon tetrachloride,
Figure 1. Structure of the ligands (LH).

N-ARYLSALICYLALDIMINATES
1707
dichloromethane, toluene, n-hexane), and show monomeric behaviour
(ebullioscopically) in benzene.
The reactions of (3) and (5) with TiCl4 in 2:1 and 1:1 molar ratios in n-
hexane provide a clean and convenient procedure for the synthesis of mono-
and bis-aldiminate derivatives of titanium(IV) Eq. (1).
ꢀ1†
In contrast, similar reactions with ZrCl4 in benzene produced only the
mono-substituted product according to the reaction (eq. 2) illustrated be-
low, wherein unreacted Me3SiOC6H4CHˆNC6H3Et2-2,6 (b.p. 175=0.2 mm)
was removed by distillation.
ꢀ2†
The derivatives (6) and (7) are red, moisture-sensitive solids, soluble in
organic solvents (C6H6, C6H5CH3, CHCl3), and show monomeric behaviour
(ebullioscopically) in benzene. The derivative (8) is a yellow solid which is
insoluble in benzene but moderately soluble in chloroform and
dichloromethane.

1708
GOYAL, MISHRA, AND SINGH

N-ARYLSALICYLALDIMINATES
IR Spectra
1709
The IR spectra (Table II) of (1)7(5) exhibit (i) the absence of -OH
absorption in the range 350073150 cmÀ1, (ii) the presence of n(CˆN) at
161671632 cmÀ1, (iii) n(C-O) at 128071300 cmÀ1, which shows a shift to
higher frequency of about ꢂ 25 Æ 10 cmÀ1 from those observed for the
parent ligands, (iv) the appearance of a new band at 9047929 cmÀ1 due to
n(Si-O), and (v) strong absorptions at 123771260 and 7507851 cmÀ1 due to
Si-CH3 symmetric deformation and Si-C stretching, respectively. These as-
signments are based on the published data in the literature8712
.
1H NMR Spectra
1H NMR spectra (Table III) of (1)7(5) show a singlet due to the
azomethine proton in the range d 8.4078.83, exhibiting a down®eld shift of
0.15 Æ 0.05 ppm with respect to the parent ligands. The aromatic protons
appear as multiplets in the range d 6.7977.80. Signals due to substituents
(Me, Et, Pr-i) present on the aniline moiety appear in the region d 1.2572.94
with characteristic multiplicity. The methyl groups attached to silicon ap-
pear as singlets at d 0.1670.29.
13C NMR Spectra
13C NMR spectra (Table III) of (1)7(4) exhibit signals due to C-O and
CHˆN carbons at d 155.477157.89 and 152.827155.52, respectively. An
up®eld shift of ꢂ 9 and ꢂ 679 ppm for the C-O and CHˆN group carbons,
respectively, has been observed. Aromatic carbons show signals in the range
d 116.907133.90. The 13C signals due to Me, Et or Pr-i groups on the aniline
moiety appear in the region d 14.89724.75. The trimethyl silicon moiety
shows a singlet at d 0.2171.69
The observed 1J(Si-C) coupling constants, 70.30 Hz for (1) and
68.54 Hz for (4), are consistent with tetrahedral organosilicon compounds13.
29Si NMR Spectra
The derivatives (1)7(5) show 29Si NMR signals (Table III) in the range
d ‡16.08 to 23.04, which is consistent with tetrahedral organosilicon com-
pounds14.

1710
GOYAL, MISHRA, AND SINGH

N-ARYLSALICYLALDIMINATES
1711
Table III. NMR Spectral Data (d, ppm) for the New Compounds
Compound
1H
13C
29Si
(1)
8.80 (s, 1H, CHˆN), 155.47 (C-O), 152.82 ‡21.67
6.7977.68 (m, 9H, Ar-H), (CHˆN), 132.81 (ˆN-C),
0.18 (s, 9H, Me3Si)
128.877117.66 (Ar-C), 0.26
(Me3Si)
(2)
(3)
8.83 (s, 1H, CHˆN), 157.89 (C-O), 155.45 ‡23.04
6.9077.42 (m, 7H, Ar-H), (CHˆN), 151.75 (ˆN-C),
2.25 (s, 6H, Me2-2,6), 0.29 132.80-119.57 (Ar-C), 18.33
(s, 9H, Me3Si)
(Me2-2,6), 0.21 (Me3Si)
8.44 (s, 1H, CHˆN), 157.69 (C-O), 155.48 ‡19.20
6.8377.64 (m, 6H, Ar-H), (CHˆN), 151.69 (ˆN-C),
2.21 (s, 6H, Me2-2,6), 2.34 133.90-116.90 (Ar-C), 20.43
(s, 3H, Me-4), 0.20 (s, 3H, (Me2-2,6), 18.05 (Me-4),
Me3Si)
1.69 (Me3Si)
(4)
(5)
8.64 (s, 1H, CHˆN), 157.42 (C-O), 155.52 ‡22.21
7.1177.80 (m, 7H, Ar-H), (CHˆN), 151.03 (ˆN-C),
2.63 (q, J ˆ 6.27 Hz, 4H, 132.61-119.39 (Ar-C), 24.75
C H 2 C H 3 ) , 1 . 1 7 ( t , ( C H C H ) , 1 4 . 8 9
2
3
J ˆ 6.27 Hz, 6H, CH2CH3), (CH2CH3), 0.26 (Me3Si)
0.16 (s, 9H, Me3Si)
8.40 (s, 1H, CHˆN),
6.8077.64 (m, 7H, Ar-H),
2.94 (sept, J ˆ 6.27 Hz, 2H,
C H M e 2 ) , 1 . 2 1 ( d ,
J ˆ 6.27 Hz, 12H, CHMe2),
0.20 (s, 9H, Me3Si)
7
‡16.08
(6)
(7)
8.45 (s, 2H, CHˆN),
6.8477.64 (m, 12H, Ar-H),
2.32 (s, 6H, Me-4), 2.23(s,
12H, Me2-2,6)
7
7
7
7
8.40 (s, 1H, CHˆN),
6.8877.60 (m, 7H, Ar-H)
3.02 (sept, J ˆ 6.27 Hz, 1H,
C H M e 2 ) , 1 . 2 0 ( d ,
J ˆ 6.27 Hz,12H, CHMe2)
(8)
8.64 (s, 1H, CHˆN),
6.9677.83 (m, 7H, Ar-H)
2.62 (q, J ˆ 6.27 Hz, 4H,
C H 2 C H 3 ) , 1 . 1 7 ( t ,
J ˆ 6.27 Hz, 6H, CH2CH3)
7
7

1712
GOYAL, MISHRA, AND SINGH
EXPERIMENTAL
All experimental work was performed under a moisture-free atmo-
sphere using glass apparatus ®tted with interchangeable quick-®t joints.
The (BDH) solvents were dried by re¯uxing over suitable drying agents
given in parentheses: benzene, toluene, and n-hexane (Na=benzophenone),
CCl4 (P2O5) and distilled under anhydrous conditions prior to use. Tri-
ethylamine was dried by keeping over KOH pellets for ꢂ 48 h and then
re¯uxing for a period of ꢂ 7 h, followed by distillation (b.p. 88.8 ꢁC).
Trimethylsilicon chloride (Fluka) was distilled prior to use (b.p. 57 ꢁC).
The new substituted N-arylsalicylaldimines were prepared by equimolar
reactions of salicylaldehyde with substituted anilines in the presence of
isopropyl alcohol in benzene under re¯uxing conditions with continuous
removal of the liberated H2O as a ternary H2O-i-PrOH-C6H6 azeotrope.
After completion of the reaction volatile components were removed from
the solution under reduced pressure. The analytically pure ligands were
obtained by distillation.
Nitrogen and chloride were determined by Kjeldahl's or Volhard's
methods, respectively15. Silicon and titanium were determined as SiO2 and
TiO2, respectively. Zirconium was precipitated as zirconium mandelate and
determined as ZrO2 after ignition15.
1H (89.55 MHz) and 13C (22.49 MHz) NMR spectra were recorded in
CDCl3 and CCl4 solutions, respectively, on a JEOL FX-90Q FT spectro-
meter using TMS as an internal reference. 29Si (17.75 MHz) NMR spectra
were recorded in CCl4 solutions using TMS as an external reference. IR
spectra (4000-200 cmÀ1) were recorded as Nujol mulls on a Nicolet Magna
550 spectrophotometer using CsI optics. Microanalyses (C, H, N) were
performed using a Perkin Elmer 2400 CHNS=O analyzer. Molecular weights
were measured in benzene with a Gallenkamp ebulliometer using a therm-
ister sensing device.
Synthesis of Me3SiOC6H4CHˆNC6H3Me2-2,6 (2)
To a benzene solution (40 mL) of HOC6H4CHˆNC6H3Me2-2,6
(6.87 g, 30.76 mmol) and Et3N (3.11 g, 30.76 mmol) was added Me3SiCl
(3.31 g, 30.53 mmol) dissolved in benzene (50 mL). The reaction mixture was
allowed to stir at room temperature for ꢂ 12 h, followed by re¯uxing for
ꢂ 2 h. The precipitated Et3NÁHCl (4.21 g, 30.58 mmol) was ®ltered and the
volatile components of the ®ltrate were removed under reduced pressure
to yield an orange liquid (8.98 g, 99%). The product was distilled at 160
ꢁC=0.2 mm. Yield, 8.16 g (90%).

N-ARYLSALICYLALDIMINATES
1713
The derivatives (1), (3), (4), and (5) were prepared by a method similar
to that used for (2). Preparative and analytical data for (1)7(5) are listed in
Table I.
Reactions of Me3SiOC6H4CH ˆ NAr with TiCl4 in n-Hexane
To a solution of TiCl4 (0.31 g, 1.6 mmol) in n-hexane (25 mL), Me3-
SiOC6H4CHˆNC6H2Me3-2,4,6 (1.00 g, 3.21 mmol) was added, and the re-
action mixture was stirred at room temperature for ꢂ 12 h, followed by
re¯uxing for 4 h. During the above mentioned period, the colour of the
reaction mixture changed from yellow to orange-red and ®nally a red solid
precipitated, which was removed by ®ltration. Recrystallization from hot n-
hexane a€orded [TiCl2(OC6H4CHˆNC6H2Me3-2,4,6)2] (6). Yield, 0.81 g
(85%). Anal. Found: Ti, 8.21; Cl, 11.76; N, 4.52. Calcd. for C32H32Ti-
Cl2O2N2 (595.38): Ti, 8.04; Cl, 11.91; N, 4.70%. M.wt., 600.
Adopting a similar procedure as in the previous description, equimolar
reaction of TiCl4 (0.45 g, 2.37 mmol) with Me3SiOC6H4CHˆNC6H3(Pr-i)2-
2,6 (0.85 g, 2.40 mmol) a€orded red solid [TiCl3(OC6H4CHˆNC6H3(Pr-i)2-
2,6)] (7). Yield, 0.80 g (78%). Anal. Found: Ti, 11.00; Cl, 24.35; N, 3.26.
Calcd. for C19H22TiCl3ON (434.61): Ti, 11.02; Cl, 24.47; N, 3.22%. M.wt.,
444.
Reactions of Me3SiOC6H4CHˆNC6H3Et2-2,6 with
ZrCl4 in Benzene
Reaction of equimolar amounts of Me3SiOC6H4CHˆNC6H3Et2-2,6
(1.88 g, 5.78 mmol) with ZrCl4 (1.34 g, 5.72 mmol) in benzene (40 mL) yiel-
ded an insoluble (moderately soluble in CHCl3) yellow, powdery solid (8),
which was washed twice with benzene to obtain an analytically pure pro-
duct. Yield, 2.39 g (92%). Anal. Found: Zr, 20.04; Cl, 23.32; N, 3.01. Calcd.
for C17H18Cl3ONZr (449.91): Zr, 20.27; Cl, 23.63; N, 3.11%.
Interestingly, the 1:2 reaction of ZrCl4 (0.73 g, 3.13 mmol) with Me3-
SiOC6H4CHˆNC6H3Et2-2,6 (2.03 g, 6.03 mmol) in benzene, even after re-
¯uxing for a period of 14 h, produced only the insoluble derivative (8). From
the reaction mixture the unreacted Me3SiOC6H4CHˆNC6H3Et2-2,6 was
recovered by distillation (b.p. 175 ꢁ=0.2 mm). Anal. Found: Zr, 20.15; Cl,
23.54; N, 3.06. Calcd. for C17H18Cl3ONZr (449.91): Zr, 20.27; Cl, 23.63; N,
3.11%.

1714
GOYAL, MISHRA, AND SINGH
ACKNOWLEDGMENTS
Two of us (M. G. and S. M.) are grateful to the University Grants
Commission, New Delhi, the Department of Chemistry and the State
Government of Rajasthan, for Research Fellowships under the Special
Assistance Program.
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1715
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Received November 16, 2000
Accepted August 20, 2001
Referee I: J. R. Bowser
Referee II: L. Stahl