Indian Journal of ChemistryVol. 25A, February 1986, pp. 162-165

Pyrrole- & Indole-thiocarbamates of Tin(IV)

V D GUPTA·, V K GUPTAt & D K SRIVASTAVADepartment of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005

Received 30 May 1985; revised and accepted 29 July 1985

A few rnono-, bis-, tris- and tetrakis-pyrrole- and indole-thiocarbamates of tin(IV) have been synthesized andcharacterized. Bonding modes and probable structures of the newly synthesized complexes have been discussed in the light ofIR, NMR and Mossbauer spectral data.

Chemistry of unsymmetrical sulphur Iigands likethiocarbamates I is in infancy; these Iigands areexpected to exhibit features not observed withsymmetrical oxygen? or sulphur ligands ':". Within thethiocarbamate class, further peripheral changes due tosubstituents may be expected to affect reactivity andbonding properties of the COS moiety. Presence ofaromatic ring containing nitrogen seems toinfluence=" substantially electronic structure ofthiocarbamates. Positive charge on the amine nitrogenwould destabilize the aromatic system and thereby

contribution of the form) N = C::~ ~ (I) in

comparison to other two)N -C~~_(IIA)<--.':>N

- C.;~ - (lIB) may get considerably diminished. This

has prompted us to examine the behaviour of pyrrole-and indole-thiocarbarnates and compare it with ourearlier findings on dialkylthiocarbamates of tin{lV) 7.~.

Materials and MethodsAl1 manipulations were carried out. under oxygen-

free anhydrous nitrogen atmosphere. Purification ofsolvents and preparation of the ligands were carriedout by the standard methods ':". Stannic and organotinchlorides were distilled prior to use 7. Nitrogen analysiswas carried out by the microanalytical method. Detailsof analytical methods and molecular weight,conductance and IR spectral measurements have beendescribed earlier 7. PM R spectral studies were carriedout on an EM-360, 60 MHz NMR spectrometer and13C NMR spectra were recorded on a JEOL FT,90 MHz NMR spectrometer using TMS as an internalreference. Mossbauer spectral data in solid state wereobtained with a Texas Instrument Cryoflask , ModelCLF3. 119Sn02 in a lucite matrix at room temp. was

tPresent Address: Department of Chemistry, University of Alabamain Birmingham, Birmingham. 35294. USA.

162

used as the source whereas absorbers were examined at80 K (Liquid nitrogen temperature).

General method for the preparation of Tin(/V)thiocarbamates

The compounds (Table I) were synthesized byadding stoichiometric amount of the appropriate tintetrachloride or organotin(lV) chloride into asuspension of potassium salt of the thiocarbamate indichloromethane. The reaction mixture was eitherrefluxed or stirred at room temperature (~30cC). Itwas filtered to remove the separated potassiumchloride. The solvents were removed from filtrateunder reduced pressure and the products obtainedwere dried at 0.1 mm and ~ 30DC for nearly 6-8 hr. Thesolid products were crystallized fromdichloromethane/a-hexane or benzene/a-hexane.

Results and DiscussionTin(lV) pyrrole- and indole-thiocarbamates have

been synthesized in exce\1ent yields by reacting theappropriate organotin(IV) chloride or tin tetrachloridewith stoichiometric amount of potassium salt of theligand in dichloromethane (Scheme I).These are crystalline solids or viscous liquids.extremely sensitive to air and moisture and are solublein common organic solvents. Molecular weights oftin(lV) derivatives, determined cryoscopically inbenzene or nitrobenzene, indicate their unimolecularnature. All the complexes are non-conducting insolvents of high dielectric constants.

n = ,

E=2

n-3R4-n SnCln + nL -

n=4

RSnCI3-n(SOCNR')n + nKCI

Sn (SOCNR')n .•. nKCI

SCHEME 1

GUPTA et al.: PYRROLE- & INDOLE-THIOCARBAMATES OF TIN(IV)

Compounds',

Table l=-Analytical Data of Tin(IV) Complexes or Pyrrole- and Indole-thiocarbarnates

Sn(SOCN C .•H .•).•

BU2Sn(SOCNC .•H .•h

Me2Sn(SOCNC .•H .•),

C1Bu2Sn(SOCNC .•H .•)

C1Bu,Sn(SOCNCsHo)

CI2BuSn(SOCNC .•H .•)

BuSn(SOCNCH .•h

Reaction Natureperiod

12(S) Yellow solid

7h(S) Reddish brownsolid

5h(R) Y e I low ishbrownviscous liquid

6h(S) Brown viscousliquid

4h(R) Yellow solid

16h(S) Reddish brownsolid

3h(R) Yellow solid

12h(S) Brown solid

6h(S) YellowishbrownliquidReddish brownliquidYellow liquid

m.p.b.p. eC)

Found (Calc.) (%)

146

98

Sn

19.8(19.05)14.48

(14.30)

S

20.27(20.50)15.21

(15.58)

12.90(13.20)10.20

(10.90)16.8

(15.7)12.5

(12.7)11.5

(12.2)9.83

(10.2)

8.42(8.12)7.48

(7.20)6.94

(7.70)6.12

(6.87)10.59(11.0)

9.55(9.42)6.83

(6.72)5.48

(6.08)8.46

(8.58)13.9

(13.8)14.7

(15.5)13.11

(13.64)

--.-- ..---"Decomposed; t Yield 73-80%; !AlIempted distillation failed; R = refluxing period; S =stirring period.

8h(S)

3h(S)

12h(S) Brown liquid

108-110*

23.80(24.40)21.10

(20.20)29.0

(29.6)22.5

(23.6)21.7

(22.6)19.4

(19.9)

--_._---------_._------------

2h(R) Yellow liquid

4h(S) Orange liquid

4h(R) Yellow solid

12h(S) Orange solid

2h(R) Brown viscousliquidBrown viscousliquidYellow viscousproductBrown viscousproduct

6h(S)

15h(S)

15h(S)

Infrared spectral absorption, specially the vC-=--=Omode provides a reasonably good method to ascertainthe nature of bonding pattern of thiocarbarnates?'!".The potassium salts of pyrrole- and indole-thiocarbamates exhibit a sharp band at slightly higherfrequencies than that of sodium salts of dialkylthiocar-bamates due to purely v(C--=--=O) vibration+". This isascribed to relatively less significant contribution of

dipolar resonating forms> N= C::: ~ = (I) in the

present compounds since the positive charge on thenitrogen destabilise itll.l2.

145-148*

93

134-136

++

28.9(30.1)26.5

(26.7)28.9

(28.5)24.9

(25.4)39.2

(40.9)33.2

(34.9)23.6

(24.9)23.5

(22.6)32.1

(31.8)26.0

(25.6)21.53

(21.78)16.19

(16.85)

N

9.12(8.99)7.15

(6.92)

5.10(5.77)4.55

(4.80)7.2

(6.99)5.48

(5.58)6.1

(5.33)

3.55(2.74)2.93

(3.15)3.95

(3.36)

4.15(4.81)3.75

(4.12)3.1

(2.43)2.74

(2.66)3.89

(3.74)5.81

(6.4)

5.52(5.96)

Mol. Wt.Found(Calc.)

598(622)802

(823)

464(485)

366(401)513

(501)

434(394)416

(444)

434(466)256

(290)

513(476)

340(373)432

(463)538

(554)701

(704)

A comparison of vC=O modes (Table 2) of tin(IV)pyrrole- and indile-thiocarbamates substantiates theabove point and reveals new features with respect tothe stereochemistry of non-transition metal com-plexes.

Absorption at higher frequencies in triorganotincomplexes is not surprising since with sulphur ligandsthese tend to remain tetrahedral in structure 13. J(119Sn_1 HMe) (Table 3) 10 the trimethyltin (IV)complexes have been found to be -60Hz suggestingalmost tetra-coordination for tin in solution.Mossbauer spectral data of Ph3Sn(SOCNC4-H4-)also

++

73'/0.7 mm

++

140

103-105

163

INDIAN J. CHEM., VOL. 25A, FEBRUARY 1986

substantiate four-coordinated structure for tri-organotin (IV) complexes in the solid state. TheMossbauer spectrum of Ph3Sn(SOCNC4H4) is shownin Fig. I and the Mossbauer parameters keepingabsorber at 80K are: isomer shift (IS) = 1.46± 0.06 mmS -I, quadrupole splitting (QS) = 1.95±0.12mmS -I and p value (QS/IS)= 1.34. The ISvalue indicates that tin is present as tin(IV). The p valuesuggests a four-coordinated structure!".

In other complexes the frequencies of the carbonylabsorptions (Table 2) appear to follow an increasingtrend: RzSnLz < RSnL3 <SnL4. In diorganotin bis-complexes it is concluded that carbonyl oxygen isweakly bonded. This inference is borne out by theabsorption position of v(C"":":O) (at 1568 em -I) in

Table 2~v(C-:-:O) Absorption (in em -1) in Pyrrole- andIndole-thiocarbamates of Tin(IV)

Ligand R3SnL R2SnL2 RSnL3 SnL4(L)

C4H4COS- 1642-32 1600-1587 1610 1643

C8H6NCOS - 1635-32 1593-83 1610 1635

Ni(ptchPy15 and detailed structural data ondimethyltin (IV) bisdithiocarbarnate,MezSn(Mezdtc)16. PMR spectrum of the pyrrole-derivative, MezSn(SOCNC4H4h shows J (,19Sn_1HMe) value (Table 3) of around 76 Hz, a value lowerthan that reported 17 for bisdithiocarbarnates (-84Hz).

Position of carbonyl stretching (Table 2) in tetrakiscomplexes is surprisingly high. This is not far form thefree carbonyl absorption value of

~ 95.0woz<l:: 90.0~IIIZ<l~ 85.0

10.0 ~,..•...,t--'-t-", 't,~,~,~""""""~ .•..•..•..LJ

cnQ'l~WN-O-NWI'UlQ)000000 006000vELOCITY (MM/SEC)

Fig. I-Mossbauer spectrum of triphenyltin (IV) pyrrolethiocar-bamate.

Table 3-NMR SpectraData of Tin(lV) Pyrrole- and Indole-thiocarbamatesSI. Compounds 1 H NMR signals l3C NMR signals (c;, ppm)No. (.5, ppm)

COS Pyrrole- or Alkyl or arylindole carbons

carbonsI Me3Sn(SOCNC.H.)* - NC.H. (7.30t, 6.15t);2 Ph3Sn(SOCNC.H.) Sn - Me (0.55) 168.3 120.1, 112.3 136.9, 126.3,

129.4, 128.43 Sn(SOCNC.H.). 172.4 120.9, 114.54 BuSn(SOCNC.H.h 171.5 120.3, 113.9 36.1, 23.4,

21.7, 9.75 BuzSn(SOCNC.H.h 173.6 119.9, 113.1 28.7,27.1,

16.4,14.66 MezSn(SOCNC.H.)! - NC.H. (7.26t, 6.16t);

Sn ~ Me (1.17)7 Me3Sn(SOCNC8H6)* - NC8H6d (6.36-8.36);

Sn-Me (0.52)8 Ph3Sn(SOCNC8H6) 168.7 127.6, 124.4 137.5, 136.5,

123.6, 120.7 130.1, 128.7116.1, 110.9108.7, 102.3

9 BU3Sn(SOCNC8H6) 169.2 127.5, 124.3 28.3, 26.5,122.9, 120.4 15.1, 13.4116.1,110.7107.8, 102.1

10 Me2Sn(SOCNC8HJ! - NC8H/ (6.31-8.2); 173.5 127.9, 125.3 5.23Sn - Me (1.14) 123.9, 121.2

116.1,111.1109.5, 102.6

* J( 119Sn[ I HM,) for No.1 and 7 - 60 Hz, for No.6 -76 Hz and for No. 10.73Hz; t centre of triplet due to (X-H;t centre of triplet due to {1-H:d:enlre of multiplets.

164

GUPTA et al.: PYRROLE- & INDOLE-THIOCARBAMATES OF TIN(lV)

bis(indolylcarbamoyl)disulphide reported at1680cm -I (ref. 6). The results call not be interpretedunless it is assumed that all the four thiocarbamatemoieties are bonded through sulphur only in aunidentate fashion. If so, this may be the first exampleof a neutral four-coordinate complex wherepotentially all bidentate chelating ligands exhibitunidentate bonding pattern. Significantly, one of thestereochemical consequence of sulphur ligands isknown to be depolymerization 'f''!".

Regarding the carbonyl stretching absorptionposition, monoorganotin (IV) complexes lie betweendiorganotin (IV) bis and tetrakis complexes.Determination of molecular structure alone can settlethis unusual trend in bonding mode ofthiocarbamatesof tin complexes. Attempts to prepare suitable crystalsfor X-ray analysis of some of these complexes have notbeen successful so far.

In addition to carbonyl absorption, infrared spectraof tin complexes show a few other characteristic bands.An intense band appearing in the range 1272-1304 ern -I is observed in all the complexes owing tov(C - N) vibration, unlike in the spectra ofcorresponding N,N-dialkyIthiocarbamates where noabsorption occurs in this region21.22. In the farinfrared region, a few medium to strong bands areobserved due to metal-ligand vibrations. These bandsare in addition to or overlap with the pyrroleabsorption around 580cm -I and indole absorptionsat 607, 493 and 425 cm -I. It can be inferred thattriorganotin (IV) thiocarbamates show only oneabsorption due to v(Sn - C) vibration whereasdiorganotin bis-products display two such modes at593 ± )4 and 559 ± 16, assignable to asymmetric andsymmetric. tin-carbon stretchings+' suggesting non-linearity of C - Sn - C moiety.

All the complexes invariably display an intensemedium band at 366±30cm-1 due to v(Sn-S)mode24.25. Assignment of tin-oxygen absorptionremains uncertain since it is observed in a relativelywider range, 600-400cm -I. Moreover, in thesecomplexes, particularly the indole ones, it is even moredifficult due to the ligand vibrations. However, indiorganotin bis-pyrrolethiocarbarnates a band in theregion 508-487 em -I can be considered to be due tov(Sn _0)26. In the corresponding triorganotin andtetrakis complexes no such absorption can be seen. Inchloro derivatives the lowest frequency absorption at332±27cm -I is attributed to v(Sn -Cl) mode?".

13C NM R spectra of all the complexes givecharacteristic 3 and 9 resonances (Table 3) respectivelyfor pyrrole- and indole-thiocarbamates. The values of

chemical shift of COS carbon are very close and assuch it has not been possible to substantiate theconclusion drawn from the infrared spectral datadescribed earlier.

AcknowledgementThe authors are grateful to the CSIR, New Delhi for

a Junior Research Fellowship (to OKS) and a SeniorResearch Fellowship (to V K G) and to MIS NittoKasei for the gift of organotin (IV) chloride samples.Their grateful thanks are also due to Prof J.J.Zuckerman, University of Oklahoma for providingMossbauer spectrum of Ph3Sn(SOCNC4H4).

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