Indian Journal of ChemistryVol. 25A, August 1986.pp. 729-732

Some Organoperoxo Complexes of Zr(IV), Th(lV), Mo(VU, W(VU & U(Vn

M T H TARAFDER· & ALA UDDIN AHMEDDepartment of Chemistry. University of Rajshahi, Rajshahi, Bangladesh

Received 6 November 1985; revised and accepted 28 February 1986

New organoperoxo complexes containing Ssbenzyldithiocarbazate, NH 2NHCSSCH 2C6H5 (L) have been synthesized andcharacterized. The complexes have the general formulae. M(L -MOJ. [M = ZJ(IV) and Th(lv)J. M'(L·-h(02h. [M' = Mo(VI).W(VO and U(VI)J and M'(L -h(02h.L'. [M' = W(VO and U(VO. L' =OPPh3 or OAsPh) and L - =deprotonated form of S-benzyldithiocarbazate]. The complexes could only be prepared in alkaline medium where L behaves as a uni-negativebidentate ligand. The IR spectra of the complexes reveal that VI mode of the M(OJ grouping. which is essentially V(0 - 0).shifts to lower wavenumbers with increase in atomic number of metals in a particular group. The IR spectra also indicate thatthe VI mode vanes somewhat with the choice of L'L; arsine oxides give rise to generally lower frequencies. The complexesoxidize PPh3 and AsPh3 to OPPh3 and OAsPh). respectively.

In recent years, a great deal of interest has been shownin the dioxygen complexes of transition metals as suchcompounds serve as reagents and catalysts in organicsynthesis I -8. No attempt seems to have been made sofar to isolate peroxo complexes of transition metalscontaining nitrogen-sulphur donor ligands, e.g. S-benzyldithiocarbazate. It was, therefore, of interest tosynthesize and characterize some new peroxocomplexes of different elements of Group 4A and 6Acontaining such ligands.

We report here the synthesis and properties (inparticular, with respect to oxygen transfer to varioussubstrates) of the new Zr(IV), Th(IV), Mo(VI), W(VI)and U(VI) peroxocomplexes (1-9). An attempt has alsobeen made to study the effect of the size of the metalions and the electronic nature of auxiliary Iigands(OPPh3 and OAsPh3) on 1(0 -0) modes of thecomplexes in their IR spectra.

Materials and MethodsThe ligand, S-benzyldithiocarbazate was prepared

by the literature method? and its purity checked byelemental analyses. m.p. 125°e.

Physical Measurements and Elemental AnalysesIritrared spectra (nujol mull or as KBr pellets) were

recorded on a Pye-Unicam SP3-300 infraredspectrophotometer; spectra between 600 and 200 em -I

were recorded as nujol mulls sandwiched betweencaesium iodide plates. Conductivities of solutions indimethyl sulphoxide (DMSO) were measured at 298Kusing a conductivity bridge type M.e. 3 (ElectronicSwitchgear Ltd, London).

MetaI6,7,10,11 and sulphur!" contents of thecomplexes were determined gravimetrically. Metha-nolic solutions of the peroxo complexes were titrated

with Ce(IV) to determine the number of active oxygenatoms present", Carbon and hydrogen analyses wereobtained from Mikroanalytisches Labor Pascher.Bonn-I, Germany.

Preparation of complexes: General method for thepreparation of (a) M(L -M02) [M=Zr(IV) andTh(IV)] (complexes 1 and 2)

S-Benzyldithiocarbazate(L) (8 mmol) was added to asolution of KOH (8 mmol) in 30% H202 (20 ml). Thesolution was stirred for 5 min. filtered and to thefiltrate was added, with stirring, a solution ofM(N03)4.4H20 (4 mmol) in water (20 ml), Theresulting colourless precipitate which separated outwas filtered, washed several times with water and driedin vacuo over P4010'

(b)M'(L -M02h [M'=MO(Vl)and W(VI)] (complexes3 and 4)

M'03 (5 mmol) was stirred and heated in 30~;; H202(20 ml) at 50° for 48 hr. The solution was filtered andthe filtrate added to a solution of S-benzyldithiocarbazate (10 mmol, 30 ml). The orange-yellow precipitate then obtained was filtered offwashed successively with water and ether and dried i~vacuo over P40IO.

(c) U(L -h(Ozh (complex 5)

A solution of uranyl nitrate hexahydrate (3 mmol) inwater (15 ml) was added to a solution of S-benzyldithiocarbazate (6 mmol, 20 ml), The solutionwas boiled and the yellow precipitate obtained wasfiltered, washed successively with water and ether andstored.

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

(d) M'(L -M02h.L' [M= W'(VI) and U(VI); L'=OPPh3 and OAsPh3J (complexes 6-9)

M'(L -h(OJ2 complexes (0.01 mol) synthesized asabove were dissolved in boiling acetone (100 ml) andthis solution was added to a solution of L' (0.01 mol) inacetone (15 mI). The resulting mixture was stirred,heated for 24 hr, and kept standing overnight. Theyellow precipitate obtained was filtered and stored asabove.

Reaction of3t with allyl alcohol (reaction-A)Compound (3, 3.3 g, 0.006 mol) was dissolved in

tetrahydrofuran (30 ml) and a stoichiometric amountof allyl alcohol added to it. Refluxing the mixture at60°C for 36 hr failed to give any reaction product.

Reaction of 1t with triphenylphosphine (reaction-B)Triphenylphosphine (0.52 g, 0.002 mol) was added

to a solution of 1(1.03 g, 0.002 mol) in tetrahydrofuran(25 mI). The mixture was heated at 55-60°C for 96 hrafter which the solution was filtered and the solventevaporated. The residue was placed on a column ofsilica gel (JO g, 35-230 mesh, Merck) and eluted firstwi th benzene (300 ml) and then wi th methanol (250 ml).Unreacted triphenylphosphine (0.08 g) was recoveredfrom the benzene fraction. Evaporation of methanol

solution yielded triphenylphosphine oxide (0.42 g),m.p. 155-56° (lit. m.p. 15r).Reaction of 2, with triphenylarsine (reaction-C)

Triphenylarsine (0.61 g, 0.002 mol) was added to asuspension of 2 (1.5 g, O.O~ mol) in tetrahydrofuran(20 mI). The mixture was stirred under reflux for 48 hrafter which the solution was filtered and the solventevaporated. The residue was extracted with ether, andthe extract placed on a column of silica gel (25 g) andeluted first with benzene (250 ml) and then withmethanol (250 mI). Unreacted triphenylarsine (0.3 g)was recovered from the benzene fraction. Evaporationof the methanol fraction yielded triphenylarsine oxide(0.31 g), m.p. 188-89° (lit. m.p. 189°).

Results and DiscussionElemental analyses and conductivity data of the

complexes (1-9) are presented in Table 1. Titration ofmethanolic solution of the peroxo complexes withCe(IV) indicated that complexes 1,2 and 3-9 are mono-and diperoxo complexes, respectively. The con-ductivity data (Table 1) for solutions in DMSOindicate that 1-9 are nonelectrolytes.

We have previously? demonstrated that S-benzyldithiocarbazate forms NS chelated structure

Table I-Analytical Data and Other Physical Properties of the Complexes".

Compd.· Found (Calc.), % NM'(n -1 cmZ mol -1)

M C H S Peroxide"

[Zr(L -h(OZ}J (1) 17.2 37.3 3.4 24.0 6.2 3(17.6) (37.1) (3.5) (24.7) (6.2)

(Th(L -)z{Oz)] (2) 35.0 28.9 2.6 19.0 4.8 0(35.2) (29.2) (2.7) (19.4) (4.8)

[Mo(L -h(Oz}zJ (3) 17.8 34.5 3.0 22.9 11.5 5(17.3) (34.6) (3.2) (23.1) (11.5)

[W(L -h(Oz}z] (4) 28.2 29.5 2.7 19.9 9.9 7(28.6) (29.9) (2.8) (19.9) (9.9)

[U(L -h(Oz}z] (5) 34.0 27.3 2.5 17.9 9.2 8(34.2) (27.6) (2.6) (18.4) (9.2)

[W(L -h(Ozh·OPPh3] (6) 19.6 44.1 3.4 13.8 6.9 8(19.9) (44.3) (3.6) (13.9) (6.9) ,.

[W(L -MOzh·OAsPh3] (7) 19.0 42.2 3.3 12.9 6.6 ""6'(19.0) (42.3) (3.4) (13.3) (6.6)

[U(L -h(Oz}z·OPPh3J (8) 24.0 41.6 3.2 13.0 6.5 0(24.4) (41.9) (3.4) (13.1) (6.5)

[U(L -h(Oz}z.OAsPh3] (9) 23.1 39.9 3.1 12.1 6.3 3(23.3) (40.1) (3.2) (12.5) (6.3)

. ...SCHZC6H5(a) Ligand L-=NHz-N=C, S-

(b) Titration of methanolic solutions of the peroxo complexes by aqueous acidified standard eerie sulfatesolution.(c) Values are for::::: 10-3 M solutions of the complexes in DMSO.

tSee Table l.

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TARAFDER & AHMED: ORGANOPEROXO COMPLEXES OF z-uvi Th(lV), Mo(VI), W(VI) & U(VI)

(Ia) in neutral medium. In alkaline medium, however,the ligand undergoes deprotonation and behaves as abidentate uni-negative ligand (Ib)9. The IR spectrum

SCH2C6Hs /SC~C6~J --=eNH< II NH~ I

M-S _s(re) (I b)

of S-benzyldithiocarbazate displays strong bands at3238 and 3180 em - I, assignable to vasN - Hand v.N- H of the NH2 group. Both the bands are shifted tolower wavenumbers in the metal peroxo complexes(~1'±35 cm :" for vosN-H and ±70 cm :' for vsN- H). This shift of I{NH2) bands to lowerwavenumbers may be taken as an indication ofcoordination of metal ion via the amino nitrogen. Aband of medium intensity at 3300 em -I is assigned tothe v(N- H) of the secondary NH group of the freeligand. As expected, this band disappears in all thecomplexes (1-9), suggesting deprotonation . andpossible coordination via structurej lb) of the ligand.The NS chelation in 1-9, is also evident {rem jheappearance of v(M- N) and I{M-S) modes 7.12.-14at275-368 and 250-265 em -1, respectively The IRspectra of the complexes display V(C= N) in the regionof 1510-1580 em -1. The metal peroxo grouping (localC2vsymmetry) gives rise to three IR and Raman activevibrational modes. These are predominantly vO-O(VI), the vsM-0(1'2) and vosM-0 (1'3)' Thecharacteristic 1'1(0 -0) band of the present thoriumperoxo complex (2)(at 840 ern -1) occurs at a frequency30cm -1 lower than that (at 870cm -1) of the zirconiumanalogue (1). Very recently, Mimoun et al.8 havereported that in the complex Ti(OzXCsH4NCOOhHMPTt, the 1'1(0 -0) appears at 895 em -I. Again, inthe cases of peroxo complexes of the elements ofGroup 6A, there is a decrease of VI upon passing frommolybdenum complex (3) (at 880 em -1) to thecorresponding tungsten complex (4) (at 845 em -1)which is further decreased in the uranium peroxocomplex.is) (802 em -1). The present data, thus clearlyreveal that for M(02) grouping, the 1'1(0 -0) modesdecrease with the increase in the atomic number ofmetals in a particular group. In the present examples,1'3and 1'2modes appear at 662-685 and 600-612 cm -1,

respectively. Complexes (6) and (8) show a decrease inv(P- 0) by 142 and 117 em -1, respectively comparedto the free ligand value (1192 em -1)IS: suggestingcoordination by the oxygen of OPPh3. Complexes (7)

tHMPT = Hexamethylphosphorictriamide.

and (9)show a decrease in I(As - 0) of 35and 32ern -1,

respectively from the free ligand value (880 em -1)1&,indicating coordination through the oxygen ofOAsPh3. Further, in the far infrared region, thecompounds (6-9) exhibit single bands in the region 400-410cm -I assignable to I'M-0'(0' = oxygen in OPPh3

or OAsPh3). For 6-9, the frequency of the VI modesappear at lower wavenumber in the arseniccompounds (7, 840; 9, 810 em -1) as compared to thatin the phosphorus analogue (6,858; 8, 832 cm -1). It isargued that vO -0 in peroxo complexes is decreasedby replacing a given ligand by one which is a strongerdonor+". The derived charge separations in the E-O(E=P or As) bonds show that the oxygen in the arsineoxide is more negative, and values of2.45 x 10-10 and1.78x 10-10 e.s.u. were obtained for arsine oxide andphosphine oxides, respectively, using 0.74, 1.10 and1.21A as the covalent radii for oxygen, phosphorusand arsenic, respectively I 7. This points to a greaterpolarity in the case of arsine oxides and hence == As-0 is a stronger donor than =P-O. This argumentseems to account for the lower 1'1values for 7 and 9compared to those for 6 and 8 respectively.

ReactivityThe present peroxo complexes were not found to be

explosive. Treatment with aqueous iodide gave adiscernible liberation of iodine within 1-2 min. Basedon this observation the possible reactivity of thepresent peroxo complexes toward olefinic compoundscould be explored, compound (3) was allowed to reactstoichiometrically with allyl alcohol (reaction-A)which failed to produce any reaction. Negative resultswere also obtained by Mimoun et al. IS fororganoperoxo complexes of Ti(IV). However,reaction-B produced triphenylphosphine oxide asrevealed by its m.p. and IR data!". Reaction-Cproduced triphenylarsine oxide, characterized by itsm.p. and the IR spectrum which exhibited I{As-0) at880 cm -1 (ref. 17).

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