Indian Journal of ChemistryVol. 28A, October 1989, pp. 909-911

Synthesis and characterization of someorganolead(IV) complexes with

bidentate ligands

Purnima Dixit, (Mrs) Kiran Singh & J P Tandon*Department of Chemistry, University of Rajasthan

Jaipur 302 004

Received 21 October 1988;revised and accepted 20 February 1989

Organolead(IV) complexes have been synthesized bythe reactions ofdiorganolead dichloride with one and twoequivalents of thiosemicarbazones of some heterocyclicaldehydes in the presence of one and two equivalents oflithium, respectively. The resulting complexes of thetypes R2Pb(L)Cl and R2PbLz (where R = C6H5;HL= R'CH:NNHC:S.NH2, R' = C5H4N- , C4H)S- ,C4H)O-, C6H5CHCH - ) have been characterized byelemental analyses, molecular weight determination, IR,NMR (1Hand 13C) and X-ray diffraction studies.Trigonalbipyramidal and octahedral geometries have been pro-posed for R2Pb(L )CI and R2PbLz types of complexes,respectively. .

Thiosemicarbazones of heterocyclic aldehydes haveattracted much interest amongst the N, S donor li-gands, since their metal complexes show a remark-able diversity in coordination behaviour dependingupon the nature of the central metal atom 1-7 and thereaction conditions. Besides, their metal complexesexhibit significant biological activity.

An exhaustive survey ofliterature reveals that onlylimited studies have been carried out on the substitu-tion and addition reactions of organolead(N) moiety,which is an interesting biologically active speciesv".

In view of our continuing interest in the study of thecoordination chemistry of organolead(N) com-plexes, it was considered worthwhile to synthesize thediorganolead(N) complexes with the ligands of thetype R'CH:NNHC:SNH2 (R' = CSH4N, C4H3S,C4H30 and C6HsCHCH) and study their mode ofbonding.

ExperimentalChemicals and solvents used were dried and purifi-

ed by the standard methods.Moisture was excludedfrom the glass apparatus using CaCl2 guard tubes.Diphenyl lead dichloride (Fluka) was used as such.The ligands were prepared by the literature meth-ods 1,2 and all the reactions were carried out underperfectly dry conditions. The complexes were ana-

lysed by the methods reported in earlier public-ations 1,2.The molecular weights of some representa-tive complexes were determined on the Knauer va-pour pressure osmometer in DMSO solution at 40°C.IR spectra were recorded on a Perkin Elmer 577 grat-ing spectrophotometer using KBr optics. PMR spect-ra were recorded on a Jeol FX 90 spectrometer inDMSO-£4 at 89.55 MHz. 13CNMR spectra were re-corded in DMSO at 22.49 MHz. X-ray powder dif-fractogram of the compound was obtained on a Phi-lips PM 9929/05 automatic diffractometer. CuKatarget was used with Ni filters.

Synthesis of organolead(N) complexesTo a weighed amount of diphenyllead dichloride in

- 30 em" of dry methanol was added the calculatedamount oflithium salt of the ligand (prepared by treat-ing the ligand with lithium metal in dry - 20 em?methanol). The precipitation of the compound tookplace instantaneously alongwith a change in colour;the contents were refluxed for one hour to completethe reaction. Lithium chloride, being soluble, was re-moved by filtration. The resulting compounds werethen repeatedly washed with the same solvent anddried under reduced pressure for 3-4 hr (yield 70-80%).

Results and discussionReactions of diphenyllead(N) with the lithium

salts of these monofunctional bidentate ligands havebeen carried out in 1:1 and 1:2 molar ratios in reflux-ing methanol:

,,-.... 1:1 ,,-....Ph2PbCl2 + NSLi -+ Ph2PbCl(NS) + LiCl

,..... 1:2 ,.....Ph2PbCl2 + 2NSLi -+ Ph2Pb(NS)2 + 2LiCI

The stoichiometry of the resulting complexes hasbeen confirmed by analytical data (Table 1).The com-plexes are thermally stable and do not melt or decom-pose upto 360°C. These are insoluble in all commonorganic solvents except DMSO in which these aremonomeric.

IRspectraIn the IR spectra of the ligand, C4H30.CH:

N.NH.C:S.NH2, a strong band observed at 2940-3140 em - 1may be ascribed to v(NH) mode. In the so-lution spectraoftheligand, an additional band due tov(SH) also appears at - 2550 cm "! indicatingtautomerization'? of the ligand. These bands do notappear in the spectra of the corresponding complexes

909

INDIAN] CHEM, SEe. A, OCTOBER 1989

indicating the deprotonation of v(NH)/v(SH) oncoordination.

Two sharp bands are observed in the ligand spec-trumat 3225 and 3440 em -I which maybe attributedto the symmetric and asymmetric stretching modes of(NH2)group. No significant shift has been observed inthese bands in the spectra of metal complexes show-ing the noninvolvement of the NH2 group in complex-ation. A sharp band at 1620 ± 5 em - 1 in the com-plexes, compared to the one at 1600 cm - 1in the li-gand, may be assigned to v(C = N); its shifting to thehigher side is probably due to an increase in the bondorder showing the coordination of azomethine ni-trogen to the metal atom 11.12.Further, in the spectra ofcomplexes some new bands have been observed inthe far IR region (400- 500 em - I) which may be as-signed to v(Pb +- N) and v(Pb-S) vibrationsr-".

The participation of both N and S atoms of the li-gands in bonding is further supported by IH and I3CNMR spectral studies,

1H NMR spectraThe 1H NMR spectral data of the ligand and its 1:1

and 1:2Iead(N) complexes are given in Table 2.A sharp singlet observed for - NH proton at

b 11.38 ppm in the spectrum of ligand is found to beabsent in the spectra of the corresponding lead com-plexes, indicating the deprotonation of this group oncoordination with the central metal atom. Theazomethine proton appearing at b7.9 ppm in the li-gand shows a downfield shift of bO.5 ppm and is ob-served at b8.4 ppm in the spectra of complexes. Thisfurther supports the formation of Pb +- N bond.

The singlet observed for the NH2 proton at b3.39and 3.40 ppm in 1:1 and 1:2 complexes, respectively,again supports the nonparticipation of this group incomplexation. However, in the spectra of complexes,the aromatic protons show marked downfield shift.

I3CNMR spectraThe involvement of thiolic sulphur and azomethine

Table I-Analyses and physical properties of organolead(IV) complexes

Complex Found (Calc.), % Mol.wt.Found

C H N Cl S Pb (Calc.)

PhzPbCl( C6H6N3S0) 38.01 2.77 7.48 6.13 5.61 36.58 545(38.35) (2.83) (7.44) (6.29) 5.67) (36.70) (564.69)

PhzPb( C6H6N3S0 lz 41.20 3.21 11.99 9.11 29.68 679(41.31) (3.16) (12.05) (9.18) (29.72) (697.19)

PhzPbCl( C6H6N 3SZ) 36.99 2.68 7.11 6.00 10.98 35.48 561(37.20) (2.76) (7.23) (6.11) (11.02) (35.68) (580.69)

PhzPb( C6H6N 3Szlz 39.41 3.00 11.38 17.43 28.31 701(39.50) (3.02) (1l.52) (17.55) (28.41) (729.19)

PhzPbCl( C7H7N.S) 36.41 2.86 9.69 6.01 5.49 35.98 558(36.60) (2.95) (9.73) (6.17) (5.56) (35.98) (575.69)

PhzPb(C7H7N.Slz 43.18 3.36 15.~6 8.81 28.76 693(43.38) (3.34) (15.57) (8.90) (28.81) (719.19)

PhzPbCl( C IOHION3S) 43.79 3.21 6.86 5.85 5.21 34.35 585(43.95) (3.33) (6.99) (5.91) (5.33) (34.49) (600.69)

PhzPb(CIOHION3Slz 49.85 3.86 10.87 8.21 26.88 752(49.92) (3.90) (10.92) (8.32) (26.94) (769.19)

Table 2-IH NMR data (6, ppm) of ligand and its organolead complexes

NH NH2 Aromatic C-H

C.H3S.C(H)NNHCSNH2 11.38s 3.38s 6.26-7.62m 7.94s(C6HslzPbCl[N(C(H)C.H3S)NCS NH21 3.395 6.72-8.00m 8.45

I I

(C6HslzPb[N(C(H)C.H3S)NCS NHzh 3.40s 6.74-8.02m 8.42sI I

s = singlet, m =multiplet

910

nitrogen in complexation is further confirmed by the13CNMR spectral data.

The 13CNMR spectral data of two representativecomplexes (C6HslzPbCI( C4H3S.CH:N.N:C.S.NH2)and (C6Hs)2Pb(C4H3S.CH:N.N:C.S.NH2)2and the li-gand C4H3S.CH:N.NH.C:S.NH2 have been recordedinDMSO.

In the spectrum of the ligand, the signals for theazomethine carbon and thiolic carbon appear atb142.76 and b178.19 respectively, whereas in thecorresponding 1:1 and 1:2 metal complexes the sig-nals for these carbons appear at b 149.18, b 149.62and b 186.18, b 184.94 respectively. Such a large shiftindicates the involvement of azomethine nitrogenand thiolic sulphur in complexation.

Xvray diffraction dataThe X-ray diffractogram of the compound

R

,,~')~,

R

( I I (11 )

R = ~H5 I

NOTES

Ph2Pb(CSH4N.CH:N.N :C.S.NH2lzwas also recordedand the data show an orthorhombic lattice with theunit cell dimensions as: a - b= 5.95 A, c= 8.60 A.

Thus, on the basis ofIR, NMR and X-ray diffrac-tion studies a trigonal bipyramidal and octahedralgeometry has been proposed for R2Pb{L)CI andR2Pb~ types of complexes respectively (structure I,II).

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(1988) in press.5 Kanoongo N, Singh R V & Tandon JP, Transition met Chern,

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(1988).7 Kanoongo N, Singh R V & Tandon JP, Bull chem soc Japan,

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