Indian Journal of chemistryVol. 31A, April 1992, pp. 281-284

Synthesis and characterization ofN-alkyl-2-mercaptoacetamide complexes

of antimony(III)

Ajay Kaushik, Yash Pal Singh & Audhesh K Raj*Department of Chemistry, University of Rajasthan,

Jaipur 302 004Received 22 March 1991; revised 30 August 1991;

accepted 19 December 1991

Reactions of antimony(III) isopropoxide withN-alkyl-2-mercaptoacetamides in 1:3 molar ratio inbenzene yield complexes of the general formula{RNHC(O)CH2ShSb where R=C2H5, n-C3H7' i-C3H7'n-C4H9, sec-C4H9 and CH = CH - CH2. Thesecomplexeshave been characterized by elemental analysis and spec-tral (IR, IH and DC NMR) studies. The complexes ap-pear to exist in two isomeric forms in solution and theprobable structures for both the isomers have been pro-posed.

N-Alkyl-2-mercaptoacetamides are known tobehave as bidentate ligands and show linkageisomerism in their complexes 1- 3. These ligands alsoexist in two conformational isomeric forms." Thepresent note deals with the synthesis,characterization and structural elucidation of someantimonyilll) complexes of N-alkyl-2-mercaptoacet-amides.

ExperimentalAll the operations were carried out under strictly

anhydrous conditions and chemicals used were ofreagent grade. Antimony trichloride (Fluka) wasdistilled (80 /10 mm) before use.

Antimony isopropoxide was prepared by theIitera ture method 5. N -alky 1-2-merca ptoacetamideswere synthesized by the condensation of thioglycolicacid and alkyl arnines". Sulphur, antimony andnitrogen were determined gravimetrically,iodometrically and by Kjeldahl's method,respectively 7.

The IR spectra were recorded on a Carl Zeiss JenaSpecord MSO instrument in nujol mull and 1Hand13C NMR spectra on a lEOL FX-90Qspectrometer.

All the derivatives were synthesized by thereactions of Sb(OPrih with the ligands in 1:3molarratio in benzene solution and preparation of only onerepresentative complex is given below.

Preparation o/(rrC3H7NHG., O)CH2S)3SbTo a benzene solution of antimony isopropoxide

(1.57g, 5.25 mmol), the ligand n-C3H7NHC(O)CH2SH (2.09g, 15.71 nunol) dissolved in benzenewas added and the reaction mixture was refluxedunder a fractionating column. The liberatedisopropanol was fractionated off azeotropically in 4hr. A white solid complex separated out from thesolvent. After decanting off the supernatant liquid,the product was dried in vacuo at 60-70°C (yield 92%,m.p. 142°C). The azeotrope on analysis was found tohave 0.98 g isopropanol (calculated 1.00 g for 3 mole).Analysis, [Found: Sb23.31, N7.93, S 18.19%; Calcd.for Sb(n-C3H7NHC(O)CH2Sh: Sb 23.51, N 8.12, S18.56%].Results and discussion

The 1H NMR data of the antimony complexes arelisted in Table 1.

The 1H NMR spectra ofligands RNHC(O)CH2SHshow a broad signal for - NH proton at """8 6.8 ppm,a sharp singlet for - SH at """0 3.5 ppm, alongwithother alkyl proton signals, at ambient temperature(20°C). At low temperature (O°C), the - NH protonsignal splits into two which appear at """0 7.6 and - 06.S ppm, indicating the existence of the ligand in twoisomeric forms (Ia and Ib) :

This has been further supported by the 13CNMRspectra of the ligands, where two signals (at - 8169.50and 175.40ppm) for carbonyl carbon (Table 2)have been observed. This difference of - 5-6 ppm inthe position of carbonyl signals may be attributed tothe steric and anisotropic effects of the alkyl group(R).

The appearance of two sets of signals for alkylcarbons further supports the existence of the ligand intwo isomeric forms.

Reactions of antimonytlll) isopropoxide with someN-alkyl-2-mercaptoacetamides have been carriedout in 1:3 molar ratio in refluxing benzene solution.Sb(OPrih + 3RNHC(O)CH2SH Benzene..(RNHC(0) CH2ShSb + 3PriOH i(where R = C1H5, n-C3H7' i-C3H7' n-C4H9, sec-C4H9

and CH~=CH-CH2-)

282 INDIAN J CHEM, SEe. A, APRIL 1992

Table 1-IH NMR data of antimony(III) complexes of N-alkyl-2-mercaptoacetamides (/) ppm)

SI.No. Complex -CH3 =CH2 -CH= -NH -CH2S-I. (CH3CH2NHC(O)CH2ShSb 1.26t(0.82) 3.26q(2.99) 8.01br(7.65) 3.7Is(3.22)

7.95br(6.80)

a b2. (CH3CH2CH2NHC(O)CH2ShSb 0.98t(0.67) a 1.34-1.78m 8.00br(7.78) 3.7Is(3.28)

(1.07-1.43) 7.86br{6.66)b 2.81t(2.28)

a3. (CHrCH-NHC(O)CHzShSb a l.lld(0.89) 3.75-4.29st 8.00br(7.64) 3.44s(3.31)

ICH3 b 1.20d( l.l6) (3.35-3.89) 6.93br(6.92)b

a b c4. (CH3CH2CH2CH2NHC(O) O.98t(0. 77) a,b l.l1-1.87m 8.44br(7.51) 3.75s(3.25)

CH2ShSb (l.l1-\.75) 8.40br(7.06)c 2.97t(2.63)

a5. (CH,CHzCH3HNHC(O)CH2ShSb a 0.93t(0.89) I.5lm(1.48) 3.93m(3.89) 8.lObr(7.67) 3.48s(3.26)

I b 1.20d( l.l6) 6.92br(6.87)CH,b .

a b6. (CH2 = CHCH2NHC(O) a \.79d(1.74) 5.00-6.03m 8.71 br(7 .64) 3.62s(3.17)

CH2ShSbb 3. I7t(2.59) (4.91-6.25) 8.44br(7.00)

Values in parentheses indicate values for the ligands

The resulting derivatives are found to be lightyellow viscous liquids (solid, when R = n-C3H7),

moisture-sensitive and having poor solubility incommon organic solvents. The reactants,N-alkyl-2-mercaptoacetamides and Sb(OPrih werehighly soluble in benzene but the complexes wereinsoluble, hence the complexes were purified byrepeated washings with benzene. Azeotrope(PriOH), Sb, Nand S estimations (Table 3) andspectral (lH, I3C and IR) studies confirm the purityof the complexes.

Infrared spectraIn the infrared spectra of the complexes,

disappearance of a weak intensity band at 2500-2520em" I v(SH), observed in parent ligands andappearance of a new band in the region 360-380 cm-1v(Sb-S)S." indicate the dcprotonation of - SH protonand formation of Sb-S bond.

A shift of '" 25 em -1 in the position ofv-NH band(3076-3275 em -1 in ligand) towards lower wavenumbers indicates the coordination of amidenitrogen with antimony. This has been further

supported by the appearance of a new band in theregion 405-420 em ~1, assigned to vSb - N9•

A comparison of IR spectra of ligand with those ofthe corresponding complexes indicates a shift of '" 40em -1 towards lower wave numbers, of various amidemodes observed at '" 1560, '" 1270, '" 700 and '" 600cm-I in parent ligands'". The lower shift furthersupports the involvement of nitrogen atom in bondformation. No significant shift in v C =0 band ( '"1640 em -I) indicates the non-involvement ofcarbonyl oxygen in bonding.

IH NMR spectraThe 1H NMR spectra of the complexes have been

recorded in DMSO-d6 solution (Table 1). Thedisappearance of the signal for - SH proton,observed in the parent ligand at '" ()3.5 ppm, confirmsthe deprotonation of - SH group and the formationofSb-Sbond.Ashiftof - 0.2-1.2ppmin the positionof both - NH proton signals in the spectra ofcomplexes as compared to their position in ligandsfurther supports the involvement of nitrogen atom inbonding.

,NOTES 283

Table 2-1JC NMR data of antimony(II1) complexes of N-alkyl-2-mercaptoacetamides (-8ppm)

SI.No. Complex -CH3 =CH2 -CH= -C=O -CH~S-

I. (CH3CH2NHC(O)CH2ShSb 13.09,14.87 32.49,33.57 170.40,182.02 35.00(34.40)i (12.40,12.68) (27.80,29.50) (169.50,175.10) 35.15(34.68)

'01I

a b2. (CH3CH2CH2NHC(O) 12.02,13.80 , a 22.27,23.25 171.34,182.02 45.80(40.26)

CH2ShSb (10.40,10.89) (20.80,21.21) (169.50,174.50) 45.90(41.26)b 32.49,34.30(28.15,28.40)

3. (CH3CHNHC(O)CH2ShSb 19.71,21.49 42.64,44.64 170.14,181.71 32.83(30.95)I (18.80,20.38) (43.00,43.45) ( 169.80,174.20) 33.07(31.80)CH3a b c

4. (CH3CH2CH2CH2NHC(O) 13.20,13.98 a 19.45,20.07 170.40,181.13 43.30(39.00)

CH2Sh (13.00,13.28) (19.20,19.40) (169.40,175.40) 43.40(39.30)b 28.16,29.89(27.90,28.10)

c 31.59,33.64(30.90,31.20)

a5. (CH3CH2CHNHC(O) CHShSb a 12.00,13.78 31.30,33.97 42.20,43.98 170.30,181.10 47.50(46.00)

I - (7.50,7.80) (27.00,27.50) (40.00,40.59) (169.80,174.20) 47.60(47.00)CH3

b b 17.35,19.13(13.00,14.00)

a b6. (CH2 = CHCH2NHC(O) a 32.48,33.57 121.50,122.98 174.00,181.10 44.80(40.83)

CH2ShSb (27.72,28.50) (116.73,117.62) (169.81,171.92) 44.90(41.97)b 138.09,138.98(136.31,137.20)

Values in parentheses indicate values for the ligands

Table 3-Analytica1 data of antimony(lIl) complexes of N-alkyl-2-mercaptoacetamides

SI. Reaction of Sb(OPr'h with Product Found (Calc), %No. Mol. form.

(yield %) C H N S Sb

I. C2HSNHC(O)CH2SH (C2HsNHC(O)CH2ShSb 30.1 5.0 8.7 20.0 25.396 (30.2) (5.0) (8.8) (20.1) (25.5)

2. n-C3H7NHC(O)CH2SH (n-C3H7NHC(O)CH2ShSb 27.6 4.5 8.0 18.3 23.393 (27.8) (4.6) (8.1) (18.5) (23.5)

3. i-C3H7NHC(O)CH2SH (i-C3H7NHC(O)CH2ShSb 7.9 18.3 23.497 (8.1) (18.5) (23.5)

4. n-C.H9NHC(O)CH2SH (n-C4H9NHC(O)CH2ShSb 7.3 16.9 21.695 (7.5) (17.1) (2 I. 7)

5. sec-e.H9NHC(O)CH2SH (sec-C4H9NHQO)CH2S)3Sb 25.5 4.1 7.4 16.9 21.598 (25.7) (4.2) (7.5) (17.1) (2 I. 7)

6. CH2=CH -CH2NHqO)CH~H (CH2 =CH -CH2NHqO)CH~hSb 28.0 4.5 8.0 18.5 23.595 (28.1) (4.6) (8.2) (18.7) (23.7)

284

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INDIAN J CHEM, SEe. A, APRIL 1992

The ~earance of two - NH proton signals in

antimon (III) complexes indicates that the isomericforms of gands interact individually and resulted inthe fo tion of two isomeric metal complexes

(Structur lIa and lIb).

lbl

l3C N spectraThe e istence of two isomeric forms for these

complex s has been further confirmed by theappeara ce of two signals for carbonyl and alkylcarbon oms in 13CNMR spectra. A downfield shiftin - CH S carbon signal indicates the involvement ofsulphur tom in complexation. The carbon atoms ofalkyl g oup, attached to nitrogen atom, alsoexperie ce a downfield shift indicating theinvolve ent of nitrogen in the bonding (Table 2).

In vi of the above, the central antimony atom

may be proposed to acquire a capped octahedralgeomet in which the stereochemically active lonepair of electrons ptesent on the antimony atomoccupie the capping position.

Acknowledgement

One of the authors (Aiay Kaushik) is thankful tothe Govt. of Rajasthan and the UGC, New Delhi, forfinancial support under the Special AssistanceProgramme.

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