Indian Journal of ChemistryVol. 23A, March 1984, pp. 204-208

Reactions of 2-Thiopyrrole-l ,2-dicarboximide & N-Carbamoylpyrrole-2-thiocarboxamide with Some Second & Third Series Transition Metal Ions

& Their Complexes

R SAHEB, S K DIKSHIT* & U C AGARWALADepartment of Chemistry, Indian Institute of Technology, Kanpur 208016

Received 19 August 1983; revised and accepted 10 October 1983

Reactions of 2-thiopyrrole-1 ,2-dicarboximide (TPH) and N-carbamoylpyrrole-2-thiocarboxamide (CPTH) with Ru(I1I),Rh(l), Rh(III), Pd(O), Pd(II) and Pt(IV) lead to the formation of [Ru(TPhJ. [Ru(CPTH)2Ci2]' [RhCI(PPh3) (TPH)]2,[Rh(TPXTPH)], [Rh(CPTXCPTH)], [Pd(TPh], [Pt(TPh], [Pd(CPT),] and [Pt(CPT)2] complexes. These complexes have beencharacterised on the basis of analytical, IR and electronic spectral and magnetic measurement studies. Tentative structures forthe complexes have been proposed.

The complexes of 2-thiopyrrole-I,2-dicarboximide(TPH) and N-carbamoylpyrrole-2-thiocarboxamide(CPTH) with Cu(I), Cu(II), Ni(II) , Co(II), Co(lI I),Ag(I), Cd(II), Hg(II) and Pb(II) have been previouslyreported and the formation of complexes involves N, Sor 0 atom(s) of the -C(S)NHC(O)-moiety of theligands as the donor atom(s) 1 ~-3. The eventualoutcome of a particular interaction, as expected,depends on the character of the acceptor cation, thereaction conditions as well as other factors which areknown to affect the behaviour of ambidentateligands". The results so far gathered are fascinating,especially with cobalt? and this prompted us to studythe complexing behaviour of these ligands withRu(1II), Rh(I), Rh(III), Pd(O), Pd(II) and Pt(IV) ionsand reactions with Pd(PPh3)4 and PhCI(PPh3h

[QL.sOJ-IHTPH

Hfill /N /NH2~N.!J.....C 'c

I II "H 5 0CPTH

Materials and MethodsThe chemicals used were either chemically pure or

AR grade.

(I) Bi~2-thiopyrrole-1 ,2-dicarboximidato)-ruthenium(lI)[Rr( TPhJ

An aqueous solution (25 ml) of hydrated rutheniumtrichloride (0.26 g, I mmol) was added to an ethanolicsolution (25ml) of the ligand (0.35 g, 2.3 mmol) and theresulting solution refluxed on a water bath for 10min.The black brown complex which precipitated out wasseparated by centrifugation, washed successivelyseveral times with water, ethanol and ether, and driedin vacuo; .m,p. > 280°.

204

(il) (2- Thiopyrrole-l ,2-dicarboximidato)-(2-thiopyrrole-I,2-dicarboximide)rhodium(J)+ rhodium sulphide, [Rh(TPXTPH)J + Rh2S3J

A clear ethanolic solution (25 ml) of hydratedrhodium trichloride (0.26 g, 1mmol) was added to anethanolic solution (25 ml) of the ligand (0.35 g,2.3 mmol) and the resulting coloured solution slowlyevaporated to almost dryness on a water-bath. Thepasty mass was treated with excess of water, digestedon a water-bath, the residue separated bycentrifugation, washed several times with water, smallamounts of ethanol and finally with ether, and dried invacuo. The analytical data indicated that the finalproduct consisted of a mixture of 90% Rh(TPXTPH)and 10% Rh2S3.

(iil) Di-J1.-chloro-bi~triphenylphosphine)-bis(2-thiopyrrole-I,2·dicarboximide)-dirhodium(J) [RhCl(PPh3XTPH)J2

A solution of [RhCI(PPh3hJ (0.46 g, 0.5 mmol) indichloromethane (25 ml) was added to a solution of theligand (0.1 g, 0.66 mmol) in the same solvent (25ml).The reddish brown solution so obtained was refluxedon a water-bath for 15 min and then evaporated toalmost dryness. The pasty mass, thus obtained, wasdissolved in methanol and filtered. Pet. ether (40-60°)was added to the filtrate to initiate precipitation. Thesolution was cooled in a refrigerator. The complex,thus precipitated, was separated by centrifugation,washed with pet. ether and dried in vacuo. Thecompound was reprecipitated by dissolving it in eitherCH2Cl2 or MeOH and adding pet. ether; m.p. 207°.

(iv) (a) Bis(2-thiopyrrole-l,2-dicarboxi-midato)paliadium(II), [Pd(TPhJ

A solution (25 ml) of palladium chloride (0.18g,1mmol) in dil. hydrochloric acid was added with

SAHEB et al.: COMPLEXES OF 2-THIOPYRROLE-l,2-DICARBOXIMIDE

stirring to an ethanolic solution (25 ml) of the ligand(0.31 g, 2 mmol) and the mixture stirred for 5 min. Abrown complex which precipitated out was suction-filtered, washed several times successively with dil.hydrochloric acid (10- 3 M), distilled water, ethanol,ether and dried in vacuo.(b) Reaction of [Pd(DMSOhC/2r with TPH

Palladium chloride (0.1 g) was dissolved in dimethylsulphoxide (1 ml) and the resulting solution treatedwith ether. The yellow crystals of [Pd(DMSO)zCI2Jwhich appeared were filtered and redissolved inminimum quantity of DMSO. The resulting solutionwas treated with an ethanolic solution (25 ml) of theligand (0.2 g, 1.3 mmol). The solid complex thusobtained was filtered, washed as in (a) above and dried.It was found to be identical with Pd(TP)2 obtainedabove.

(c) Reaction uf[Pd(DMFhC/2J with TPHThis was prepared as described in (iv)(b) using DMF

in place of DMSO.

(d) Reaction of [Pd(P Ph3)4J with TP H: Preparationof [Pd(PPh3h(TPH)ZJ

Freshly prepared [Pd(PPh3)4J (0.1 g), dissolved indichloromethane (30 ml), was added with stirring to anethanolic solution (25 ml) of the ligand (0.3 g, 2 mmo\).A yellow complex was precipitated on keeping thereaction mixture for 2-3 hr. This was filtered off,successively washed several times with dichloro-methane, ethanol and ether and dried in vacuo.(v) Bis(2-thiop yrrole-I,2-dicarboximidato)-platinumil I) monohydrate [Pt( TPhJ .H20

An aqueous solution (25 ml) ofH2PtC16. x H20 wastreated with an ethanolic solution (25 ml) of the ligandin stoichiometric ratio and heated for 30 min on aboiling water-bath. The brown coloured precipitate ofPt(TPh.H20 was allowed to stand at roomtemperature for 30 min and separated by centri-fugation. It was successively washed several times withwater, small quantity of ethanol, ether and dried invacuo. It was reprecipitated by dissolving it in ethanoland adding water.

(vi) Dichlorobis(N -carbamoylpyrrole-l-thio-carboxamide)ruthenium(II) [Ru(CPTHhCI2J

This compound was prepared by the method similarto that described in (i) except that 1ml of dil. HCI wasadded to the metal chloride solution (25 ml) and CPTHwas used in place of TPH.

(vii) (N -carbamo yip yrrole-l-thiocarbox-amidato)(N-carbamoylpyrrole-2-thiocarbox-amide) rhodium(l) [Rh(CPTXCPTH)]

This complex was prepared by the same method asdescribed in (ii) except that CPTH was used in place ofTPH.

(viii) Bis(N-carbamo yip yrrole-Z-thio-carboxamidato )palladium(l I), [Pd( CP ThJ

This was prepared by the procedure described in (iv),using CPTH in place of TPH.

(ix) Bis(N-carbamoylpyrrole-2-chiocarb-oxamidaio)platinum(ll), [Pt(CP7)2J

This complex was prepared by the method describedin (v) using CPTH in place of TPH.

AnalysisRhodium was analysed by taking a known weight of

the complex and decomposing it with a mixture (1:1) ofcone. H2S04 and cone. HN03. The solution wasevaporated to almost dryness and the residue extractedwith water. The process of decomposition with theconcentrated acid was repeated three to four times toensure complete decomposition. Rhodium wasestimated as [Co(NH3)6Rh(N02)6J in the solution",For the estimations of palladium and platinum,samples were decomposed in aqua regia. In phos-phorus containing complexes, the decomposition wascarried out as described in the foregoing paragraph forthe estimation of rhodium. The excess nitric acid wasremoved by repeated evaporation with HCl acid. Theresidue was taken in dil. HCl (10-3 M) and palladiumwas estimated as Pd(DMGh and platinum, as(NH4}z[PtCI6J in the solution.

Results and DiscussionThe complexes are, in general, diamagnetic, stable in

air, slightly soluble in most of the organic solvents,except [RhCl(PPh3){TPH)]2 which is found to be quitesoluble. The analytical data (Table 1) and the preferredgeometries which the metal ions generally adoptsuggested that the ligands in some complexes acted asbidentate while in others, as monodentate. Theirinfrared spectra were recorded in the region 4000-200em -1 (on a Perkin-Elmer 580 spectrophotometer). Asreported in the previous papers 1 - 3 also, the IR spectraof the complexes were quite complicated because of theextensive mixing of various modes of vibrations in theligand. The systematic shifts of the positions of thebands due to various modes in the complexes aregrouped under the following headings for the sake ofconvenience in discussion.

TPH complexes of Ru(II), Rh(I), Pd(lI) and Pt(ll)The shifts in the band positions in the IR spectra of

the complexes of these metal ions have been found tobe similar. The following are the general observationsin their spectra.

(i) The v(NH) of the ligand at 3200 cm - 1 disappearedin the spectra of all the complexes suggesting thedeprotonation of the ligand.

205

INDIAN J. CHEM., VOL 23A, MARCH 1984

Table I-Analytical Data of the Complexes

Complex Found (Calc.) e/;,)

C H N S M X P

[Ru(TPhJ 35.2 1.7 13.7 16.0(35.5) (1.5) (13.8) (15.8)

90% [Rh(TP)(TPH)] 32.5 1.8 15.1 17.4 27.9+ 10% [Rh2S3] (32.8) (1.5) (15.3) (17.1) (28.6)[RhCI(PPh3)(TPH)]2 52.5 3.0 5.2 6.0 18.1 6.1 6.8

(51.1) (3.3) (5.1) (5.8) (18.6) (6.4) (5.6)[Pd(TP)J 35.0 1.5 14.2 15.5 26.2

(35.3) (1.3) (13.7) (15.7) (26.0)[Pt(TPh]' H 20 27.7 1.9 10.9 12.6 37.5

(28.0) (\.6) (10.7) (12.4) (38.1)[Ru(CPTHhCI2] 28.0 2.9 16.3 12.4 13.7

(28.2) (2.7) (16.5) (12.6) (13.9)[Rh(CPT)(CPTH)] 32.5 2.7 19.3 14.3 22.9

(32.7) (3.0) (19.1) (14.5) (23.4)[Pd(CPTh] 32.2 2.4 18.8 14.2 23.8

(32.4) (2.7) (19.0) (14.5) (24.0)[Pt(CPTh] 27.4 2.1 15.5 12.1 36.2

(27.1) (2.3) (15.8) (12.0) (36.7)

(ii) The amide band I (vC=0) in some of thecomplexes was shifted to the lower wavenumbers (ilv= 30 em - 1) indicating the involvement of carbonyloxygen in bond formation 7.

(iii) The position of the thioamide bands havingcontribution from V(C= N), b(NH) and those of amidebands in the region 8 1500 to 1000 em - 1 either did notshift or the shifts were too small to draw any definiteconclusions from the direction of shifts.

(iv) The thioamide bandtlv)? (840 em -1) present inthe ligand was shifted slightly towards higherwavenumbers suggesting the non-involvement ofthiocarbonyl sulphur in the bond formation. In someof the complexes like Ru(II), the V(C=S) shifted toslightly lower wavenumbers suggesting thiocarbonylsulphur also as the donor site. It appears that in thesecomplexes, the thiocarbonyl sulphur is alsoparticipating in bond formation, making the ligandbehave as tridentate and giving an octahedralgeometry around the metal.

(v) New bands of weak to medium intensity in theregion 300-500 em - 1 in the spectra of the complexes

A'I \1 'I-RiI-{L) S-R~S (L}-/RlI-I' /\ '

NJL

~U(TP>i]

206

may be assigned 10 to the coupled vibrations due to v(M-S), v(M -0) or v(M -N).

The above observations clearly indicate that thebonding of the ligand occurs via Nand 0 of -C(S)- NH - C(O )-moiety. The diamagnetism of thecomplexes is due to the reduction of ruthenium andrhodium metal ions by the ligand giving Ru(II) andRh(I) complexes, respectively.

Since the complexes of ruthenium are highlyinsoluble, the polymeric structure could be suggestedfor them. The slight solubility of the other complexessuggest that these are also polymeric but the degree ofpolymerisation might be relatively less. The structure(I) may, therefore, be suggested for the complexes ofTPH with Ru(II), Rh(I), Pd(II) and Pt(II).

The complex, [RhCI(TPH)(PPh3)]2' similarly, maybe assigned to possess a square planar geometry withchloride bridges. Thus, ligand is supposed to behave asunidentate with oxygen of the carbonyl group involvedin the bond formation. The bonding in this complex isas shown in structure (II). The spectra of the DMSOand DMF complexes of palladium showed the

M • Pd ond PtL • Inc:IIcGtd the llgond

SAHAB et al.: COMPLEXES OF 2-THIOPYRROLE-l,2-DlCARBOXIMIDE

formation of a mixture of products since most of thecharacteristic frequencies of the ligand were absent.

CPTH complexes of RU(ll), Rh(/), Pd(II) and Pt(II)The major shifts in the band positions in the IR

spectra of the complexes with CPTH are as follows:(i)The v(NH) ofthe ligand at 3200em - I disappeared

in the Pt and Pd complexes suggesting deprotonationof the NH group. In the spectra of Rh(l) and Ru(II)complexes, this band remained intact, suggesting non-involvement of NH in bond formation.

(ii) The position of the amide band (I), (vC=O),shifted to lower wavenumbers (/1v= 25 em - I)confirming the carbonyl oxygen as the donor site.

(iii) The position of the thioamide band (IV) havingmajor contribution from v(C=S), remained practicallystationary (/1v= ± 5 em - I) suggesting that thethiocarbonyl sulphur may be involved in the bondformation.

(iv) The shifts in the thioamide and amide bandpositions between 1500 and 1200 em - I were erraticand, therefore, no inference could be drawn.

On the basis of the above shifts in the IR bandpositions and assuming the preferential geometrieswhich these metal ions assumed in their complexes, thebonding in these complexes could be shown as instructure (III).

Electronic spectraThe electronic spectra of the complexes were

recorded on a Cary-17 UV-visible spectrophotometerin nujol, owing to the lack of solubility. in suitable non-coordinating solvents. Though the complexes weresoluble in pyridine, it has not been used because of thepossibility ofthe change of geometries ofthe complexesin solution 11. Near IR region did not show any bandwhile in visible region the broad bands appeared. Insome cases the maximum was quite defined while inothers it was difficult to decide the maxima. In the UVregion also the spectra of the complexes did not showany well-defined maxima in nujol possibly because oflarge concentration of the compound.

In most of Ru(II) complexes, ruthenium pre-ferentially has an octahedral geometry I 2. If one

or other Isomers

~u(CPTH)2 Clij

assumes an octahedral environment around the metalion in a strong ligand field, one should expect fourbands, two spin-allowed corresponding to thetransitions A Ig-+ 1 T1g and I T2gand two spin-forbiddenbands corresponding 1A Ig -+ 3 Tig and 3 T2g transitions.If the symmetry is lowered from Olr>Tig and T2g levelsshould further split up giving more levels and thus thenumber of bands arising out of the transitions betweenthese levels should increase. The TPH complex ofruthenium, viz. Ru(TPh, showed only one well-definedbroad band at 395nm (25319 cm-I) which may beassigned to IAIg-+ I T2g spin-allowed transition. Otherlow energy transitions were probably masked by thetail of the band.

The spectrum of the ruthenium complex withCPTH, however, exhibited a very broad band, whosemaximum could be approximated around 480 nm(20833 cm-I). This was assignable to IAlg-+IT2g

transition.The spectrum of [RhCl(PPh3>\TPH)h recorded in

chloroform, displayed three bands at 365 (27400cm-I), 310 (32258 em-I) and 280nm (35714 cm-I).The first two bands were present in the spectrum of theligand but the positions of these bands were shiftedtowards lower wavelength in the spectrum of thecomplex indicating the metal interaction with theligand. These bands were, therefore, assigned tointra ligand transitions. The higher energy band at35714 em -I was possibly a characteristic band oftriphenylphosphine. No d-d bands were observed inthe spectrum probably because they were masked bythe strong CT bands. The spectrum of the rhodiumcomplex of CPTH showed a broad absorption bandwith a maximum around 440 nm (22727 ern - I). Insquare planar rhodium complexes (d8-system), threespin-allowed d-d transitions are anticipated. Besidesthese, the spectrum should show three spin-forbiddensinglet-triplet transitions from lA2g-+3A2&' 3Blr and

207

INDIAN J. CHEM., VOL 23A, MARCH 1984

3Ell' respectively. The 22727 em -I band of Rh(I)complex is present relatively at high energy side.Generally, Rh(I) square planar complexes I 3 absorb inthe 400 nm region because of the transition IA 2g --+ IE,.The band at 440 nm is, therefore, assigned to thistransition.

The visible spectrum of Pd(TPh exhibitedmaximum at 470nm (21270 cm-I). The literaturevalue'4.'s of the absorption maxima in the visibleregion for the square planar complexes of palladiumand platinum falling in this region are assigned to x2_ y2

--+xy eAIg--+IBIg) transition. The bands at 21277 and19231 em -I in the spectra of the palladium andplatinum complexes, respectively are, therefore,assigned to x2_y2 --+xy transition.

Thus, on the basis of the analytical, magnetic andspectroscopic data, the following tentative geometrieshave been assigned to the complexes:

[Ru(TPh], [Ru(CPTHhCI2], octahedral;[RhCl(PPh3)(TPH)]2' [Rh(TP)(TPH)],[Rh(CPT)(CPTH)], square planar; and [Pd(TPh],[Pt(TPh], [Pd(CPTh], [Pt(CPTh], square planar.

208

References1 Saheb R, Agarwala U C & Dikshit S K, IndianJ Chern,lOA (1981)

1196. .i:»>:

2 Saheb R, Dikshit S K & Agarwala U C, IndianJ.9Jem, 22A (1983)24.

3 Saheb R, Dikshit S K & Agarwala U C, Indian~rn, 22A (1983)1050. 2--.J

4 Balahura R J & Lewis N A, Coord Chern Rev, 20 (1976) 109.5 Price J H, Williamson AN, Schramn'R F & Wayland B B, Inorg

Chern, 11 (1972) 1280.6 Beamish F E, The analytical chemistry of noble ~Is, Vo1.24,

(Pergamon Press, Oxford) 1966,269. '\7 Nakamoto K, Infrared and Raman spectra of~rganic and

coordination compounds (John Wiley, New York) 1978,231.8 Rao C N R & Venkatraghavan R, Spectrochim Acta, 17 (1962)

541.9 Suzuki I, Bull chern Soc Japan, 3S (1962) 1286, 1456.

10 Adam 0 M, Metal ligands and related vibrations~t)MartinsPress, New York) 1968, 316, 249, 284.

11 Figgis B N, Introduction to ligand fields'(Wiley E~ Limited,New Delhi) 1976, 319. '\ '

12 Cotton F A & Wilkinson G, Advanced inorganic cttefniJtry, acomprehensive text (John Wiley, New York) 197~ (001.

13 Lever A B P, Inorg Chern, 4 (1965) 763.14 Siiman 0 & Fresco J, J Am chern Soc, 92 (1970) 2652.15 Hendrickson A R & Martin R L, Inorg Chern, 12 (1973) 2582.