Sulphur complexes of quadrivalent titanium

JOURNAL OF THE LESS-COMMON

SULPHUR

Ii. BAKER

COMPLEXES

METALS

OF QUADRIVALENT

TITANIUM

AND G. W. A. FOWLES

Chemzstvy Department, The Cziuersity, (Received

47

September

Sodhamptos

(Great Britain)

5th. 1904)

SUMMARY

Titanium(IV)

chloride and bromide have been shown to react

with a variety

of monodentate sulphur ligands (L) to give complexes of the type TiXJ,zL; L = SMe2, SEta, CdH&, and &Hi&. Molecular weight measurements on benzene solutions on a number of these compounds, showed them to be monomeric, although TiBr4, &Et2 dissociated in solution. SPrzn also gave a Z:I adduct with titanium(IV) chloride,

but only a

I :I

adduct with the bromide.

Both halides gave complexes

of the

type TiXd,B, where B was one of the potentially bidentate sulphur ligands C4H&, PhSCH2CH2SPh, MeSCH$ZH&Me, and EtsP(S)P(S)Etg. The structures of these complexes are discussed.

Metal halides have been divided into two categories

of acceptori,

either A or

B; Class A form the most stable complexes with the ligands of the first series (N, 0, and F), while Class B form their most stable complexes with ligands of the second or subsequent series (P etc., S etc., and Cl etc.). Where the metal has no or very few d electrons, it is considered a class A member. Metals such as copper which have almost full d shells usually bond well with the second row donors, since these d electrons

can

now take part in &-d~ bonding. Quadrivalent titanium has no d electrons, so there is no possibility of such back donation, and the bonding must be purely sigma in type. No previous work has been reported on complexes of the titanium(IV) halides with sulphur donors, apart from early reports2 on unstable adducts formed with hydrogen sulphide and an 1873 reference 3 to the reactions of titanium(IV) chloride with ethyl mercaptan and diethylsulphide. There have been several reports recently4 on complexes of these halides with phosphorus and arsenic ligands, however, which indicate that the second and subsequent row elements can form well-defined complexes with quadrivalent titanium. In this paper we report the results of the reactions of titanium(IV) chloride and bromide with a large number of sulphur ligands, ranging from monodentate to potentially tridentate. The reactions were studied under rigorously anhydrous conditions by mixing benzene solutions of the halide and excess of ligand, and filtering off any precipitate formed; where a precipitate did not form within a few hours, all volatiles (i.e. solvent and excess of ligand) were removed at the pump and the residue recrystallised. Five monodentate ligands were used, the simple thioethers SR2 (R = Me, Et and Pm) and the cyclic thioethers CaH& and &Hi&. Apart from J. Less-Common

Metals, 8 (1965) 47-p

48

K. BAKER, G. W. A. FOWLES

di-n-propylsulphide, all the ligands reacted with both halides to give crystalline products (yellow-orange for chlorides and red for bromides) of overall composition TiX4,zL. These complexes could be sublimed igz vacua. Cryoscopic studies on benzene solutions showed that the complexes TiCl&Mea, TiCl&Et2, TiBr&Mea and TiBr4,zGHaS were monomeric, but the complex TiBr&SEtz gave a twofold depression suggesting that dissociation (TiBr&Etz+TiBr&Eta + SEt2) was occurring. Presumably the lower stability of the bromide complex compared to the chloride analogue is a result of the larger steric requirements of the bromine atoms. When the cyclic ether tetrahydrothiophen is used this occupies less volume and the bromide complex is not dissociated. Both di-n-propylsulphide complexes were liquids, and the bromide contained only one molecule of ligand. Four potentially bidentate sulphur ligands (B) were used, dithian, S-dimethylthioethane, S-diphenylthioethane, and tetraethyldiphosphinedisulphide, and in every case both halides gave I:I complexes, TiX4,B. Only the bromo compound TiBr4,MeSCHzCHzSMe, was soluble enough in benzene for a molecular weight determination (ebullioscopic), and this showed the compound to be monomeric. All the complexes were non-crystalline. S-trithian gave a red product, TiBr&aH&, upon reaction with titanium(IV) bromide in ether solution, but the chloro analogue could not be isolated. The molecular weight experiments showed that in solution all the compounds studied contained 6-co-ordinate titanium except TiBr&Etz. There are two possible arrangements for such TiX4,2L complexes, namely cis (Ca,) and tram (DJ~), and far infra-red measurements were made on several compounds in an attempt to differentiate between the possibilities. BEATTIE reports5 that such data on the tin complex SnC14,2SEt2shows the complex to have a trans configuration. Unfortunately the infra-red spectra of complexes formed by transition metal halides do not permit an unambiguous assignment. The complex TiC14,zPhSCH&H&Ph, which cannot have a trans configuration if the ligand is behaving in a bidentate fashion, shows two strong bands at 409 and 378 cm-r. The spectrum of TiC12,2SMe2shows absorption in exactly the same region, although the resolution is not as good and only a single broad band is found centred around 380 cm-l. In view of the similarity of the spectra we tentatively assign a cis configuration to the complex. The analogous bromide complex TiBr&Me2 shows one very broad band in the region of 300 cm-l. The infra-red spectra have been measured for all the complexes reported in this paper; they show the expected ligand bands virtually unchanged. Since C-S-C vibrations are weak and ill-defined, we were unable to study the modifications of these bands upon co-ordination of the thioether. The diphosphine-disulphide ligand shows two fairly strong bands at 776 and 740 cm- 1, the first of which is presumably the P = S vibratione. When the ligand co-ordinates to titanium(IV) chloride and bromide this band shifts to slightly lower wavenumbers (768 and 763 respectively). The second band shows a much smaller shift in the same sense. The proton resonance spectra have been measured for the dimethylsulphide adducts. The ligand itself shows a single peak at 7.94 tand this peak shifts to 7.54 and 7.55 z when the ligand co-ordinates to titanium(IV) chloride and bromide resp. The usual assertion that titanium prefers to bond to oxygen rather than sulphur is evidently incorrect, in view of the relative stability of the adducts formed by the J. Less-Common

Metals,

8 (1965) 47-5~1

SC’LPHUR COMPLEXES OF QUADRIVALENT Ta titanium(IV)

49

halides with such a range of sulphur ligands. The origin of this stability

is not immediately

clear. There can be no n-bonding

between titanium

and sulphur in

the sense of back donation of d electrons from the metal to sulphur, because titanium is in the quadrivalent state, but there is the possibility of some multiple bonding arising from the delocalisation of the z electrons of chlorine or bromine through the titanium atom on to sulphur. Such z-bonding might be expected to show up in the ultra-violet spectra of the complexes. Cyclohexane, and “iso-octane” solution spectra of the chlorocomplexes (for L = SMe&Etz, and CdH&) each show a single peak (at 43,600, 44,600, and 45,000 cm-l respectively). Since the spectrum of the hexachlorotitanate anion, [TiC16]2-, shows a band at 45,050 cm-i (ref. 7) and those of the ligands themselves absorptions calisation

show shoulders around 44,000 cm-r (ref. S), it seems that the observed are one of these transitions. We therefore rule out any significant deloof the halogen

,T electrons

and propose that the stability

sulphur bond results from the strong polarisation in the high oxidation state.

of the titanium-

of the sulphur lone pair by titanium

It is worth noting that in the thioxan complexes, TiX+z&HsOS, both the infra-red and nuclear magnetic resonance spectra shows that it is sulphur rather than oxygen

that co-ordinates

to titanium.

EXPERIMENTAL Keactioszs. The halide and excess of pure ligand, together with any solvent (normally benzene), were sealed in an ampoule and allowed to react for several hours at room temperature.

The ampoule

was opened

and its contents

examined

by the

usual vacuum-line techniques. When the complex had precipitated from solution in the ampoule it was filtered and washed with pure solvent to remove excess of ligand; otherwise all volatiles were removed at the pump and the solid residue similarly treated. The dimethylsulphide and diethylsulphide products could be purified by sublimation experimental TABLE

in vacua. details.

were diamagnetic.

Tables

I and II

give the

I

DATA ON

COMPOUNDS

Halide (Ti
Ligand

TiCId

SMez

OF

THE

TYPE

Ti&,rL “:

(L)

wrp TiBrr

All products

C4HsS C~HIOS SMez slzt2 CaH*S CsHwS &H&s

orange-yellou

crystals orange-yellow crystals orange liquid orange crystals orange crystals red crystals dark-red crystals red crystals red crystals red solid*

* Et20 used as solvent in reaction, since CsH&

Found

“b Calculated

MO1 wt.

Tz

.Y

Ti

x

‘5.4

45.0

15.3

45.2

,103

12.7

38.2

12.9

38.3

3.53

II.3 12.7 11.8 9.8 8.5 8.8 8.3 7.4

32.5 38.3 35.5 (‘5.6 56.4 j9.2 54.0 jo.0

11.2 13.1

33.3

~

38.7

-

36.0

-

05.0

458

58.3 58.8 55.9 49.6

275 573 ~ --

IL.0

9.7 8.7 8.8 8.4 7.4

is insoluble in benzene. J. Less-Conmon

Metals,

8 (1965)

47-50

K. BAKER,

50 TABLE

G. W. A. E’OWLES

II

DATA ON COMPOUNDS OF THE TYPE TiX4,

B

_ Halide

Tic14

TiBr4

Ligand fB)

Appearance of product

C4HsSz CIHIOSZ CI~HI~SZ CsHzoPzSz CaHsSz CJHIOSZ CI~HI& CsHzoPzSz SPr2”

Yellow solid Yellow solid Purple solid Orange solid Orange-red solid Orange solid* Brick-red solid Brown solid Dark-red liquid

o/oCalculated

O/”Found Ti

X

Ti

x

14.8 14.8 10.6 11.1 10.0

44.7 44.4 33.5 33.2 65.2 63.6 50.9 52.3 63.0

15.4 15.4

45.7 45.5

11.0 II.1

32.5 32.8

9.8 9.5 7.8

65.5 65.3 52.0

7.9 9.7

52.4 65.8

9.2 7.6 8.5 10.3

_ * M=431,

Analysis.

Titanium was determined calorimetrically as the peroxide complex; and bromine were determined gravimetrically as the silver salts. Spectra. Infra-red spectra were measured on Nujol mulls by means of Unicam SPzoo and Perkin Elmer Infracord (KBr) spectrophotometers. Spectra below 400 cm-1 were measured by Dr. I. BEATTIE. Ultra-violet spectra were measured on cyclohexane or “iso-octane” solutions by means of a Unicam SP700 spectrophotometer. A Varian A60 instrument was used for the examination of the N.M.R. spectra (on Ccl.4 solutions). Molecular weight mensurements were generally determined cryoscopically on benzene solutions by a specially adapted apparatus using a Beckmann thermometer. One compound, TiBr,l,MeSCH&H&5Me, was not sufficiently soluble in benzene, for a cryoscopic study, so it was studied ebullioscopically by means of a modified Gallenkamp ebulliometer. chlorine

ACKNOWLEDGEMENT

We greatly appreciate the support given to this work by Laporte Titanium Ltd., through a research award (to K.B.). Dr. I. R. BEATTIE kindly measured the far infra-red spectra quoted in this paper. REFERENCES I S. AHRLAND, J. CHATT AND N. R. DAVIES, Quart. Rev., 12 (1958) 265. 2 A. W. ROLSTON, J. Am. Chem. Sac., 50 (1935) 258; W. BILTZ AND E. KENNECKE, Z. Anorg. Aligem. Chem., 147 (1925) 171. 3 E. DEMARFAY, Compt. Rend., 76 (1873) 1414. 4 J. CHATT AND R. G. HAYTER, J. Chem. Sot., (1963) 1343; G. W. A. FOWLES AND R. A. WALTON, J. Chem. Sot., (1964) in the press. R. J. H. CLARK, J. LEWIS AND R. S. NYHOLM, J. Chem. Sot., (1962) 2460. 5 I. R. BEATTIE, Quart. Rev., 17 (1963) 396. 6 L. J. BELLAMY, The Infra-red Spectra of Complex Molecules, and edn., Mcthuen, 1958, p. 321. 7 C. K. JE~RGENSEN, Absorption Spectra and Chemical Bonding in Complexes, Pergatnon, Oxford, 1962, p. 284. 8 R. C. PASSERINI, in N. KHARASCH (ed.), Organic Sulphur Compounds, Pergamon, Oxford, 1961,

P. 59. g G. W. A, FOWLES AND R. A. WALTON, J. Chem. Sot., (1964) in the press. J. Less-Common

Metals, 8 (1965) 47-50