Solutions of MCl^ (M = T i , S n ), AuClj in CHCl^ or SbClg in CCl^ reacted with so lutio ns o f s - t r it h ia n e in the same solvent to p re cip ita te simple 1:1 (M = Au ( I I I ) , Sb (V )) o r 1:2 (M = T i , Sn) adducts. (CH2S)3 reacted with a suspension of ZrCl^ in CHC13 to give an addition compound, but samples were found to be contaminated with unreacted metal h alid e. Attempts to ex tra ct the ZrCl^.ZiCh^S)^ with CHC13 (which proved a su itab le solvent fo r the Sn (IV ) adduct) using a Soxhlet apparatus resu lted in small amounts of free (CH2S )3< Sym -trithiane reacted with two mole equivalents o f T iC l4 in CH2C12 to give a pale yellow so lid analysing approximately as 2 (T iC l^ ). (CH2S )3. Sim ilar products were produced by s t ir r in g a suspension o f TiC1^.2(CH2S)3 with an excess of Ti C l4 in non-coordinating solvents such as CH2C12 and CCl^. The second molecule of TiCl^ was found to be only weakly bonded, however, and could be removed q u ite e a s ily by pumping in vacuo, or by continuous washing with n-hexane in vacuo, eventually to g ive bright orange TiC1^.2(CH2S ) 3. ShCl3 when reacted with a two-fold excess o f ligand gave only the known 1:1 adduct SbCl3.(CH2S)3 (350, 351). In contrast AsClg, A1C13 and GeCl^ gave no is o la b le reactio n products. Ligand su b stitu tio n s as an a lte rn a tiv e syn thetic route proved fa r from sa tisfa c to ry . (CH2S)3
fa ile d to replace the coordinated ligands from MC13.3L (M = T i , V, L = MeCN, THF), ZrCl4.2NMe3 or Mo(C0)33MeCN. Reactions with MoClg and V0C13 in
CCl^ gave dark brown s o lid s in each case. The IR spectra of these products bore l i t t l e resemblance to that o f the free ligand (329) in d icatin g ring opening rath er than complexation as the dominant reactio n. MoClg at le a s t
i s well known for reactio ns in which 0 i s abstracted from donor molecules (2) , and a s im ila r situ a tio n would seem to be in force with (CH2S ) 3 .
The simple 1:2 Sn (.IV ), Ti (IV ) and 1:1 Sb (V) complexes proved to be highly air-m o istu re s e n s it iv e , but AuCl3.(tt^SJ-j could be handled on the
bench without any trace of decomposition. Solution in donor solvents was, in g e n e ra l, accompanied by displacement of the lig an d. In p a r t ic u la r , T iC l4.2(CH2S)3 proved to be extremely su scep tib le to s o lv o ly s is , decomposition occurring even in weak donor solvents such as E t20.
In t e r e s t in g ly , reaction o f TiBr^ and (CH2S) 3 in E t20 leads to the iso la tio n of the sta b le 1:2 adduct (328). T h is i s perhaps a r e fle c tio n o f the
greater c la s s B character of TiBr^ c f . T iC l^ . Adducts of s - t r it h ia n e have been prepared, but most have involved so ft metals such as Ag ( I ) (329, 330), Hg ( I I ) (329-331), C r ( 0 ) , Mo(0), W(0) (332, 333) and Sb ( I I I ) (350, 351). The in a b ilit y of (CH2S) 3 to d isp lace coordinated solvent from Ti ( I I I ) , V ( I I I ) and Zr (IV ) and the ease of removal from Ti (IV ) and Sn (IV ) suggests that i t acts only as a weak donor towards the hard metal h a lid e s .
The IR spectra of the complexes are given in Table 5 .3 .1 . D alziel and coworkers (330) have interp reted the 26 bands in the IR spectrum of (CH2S)3 in terms of 17 fundamentals (7a^ + I0 g) expected fo r a ch a ir (C3v) co nfig uratio n. Planer (D3h) and boat (Cs ) configuration should give r is e to 9. and 30 fundamental bands re sp e c tiv e ly . An X-ray study has confirmed the ch a ir assignment fo r (CH2S) 3 in the s o lid phase, F ig . 5.3.1 (352).
S~-2-i827
'9 9?
S
1 5 7 o o i (CH2S)3 Ti C l4 .21 SnCl4.2L SbClg.L AuC13L SbCl3.L Assignment 2959(w) 2995(m) 2983(m) 2985(m) 2990(s) 2985(m) vCH(e) 2964(m) 2972(s) 2950(sh) 2970(m) 2950(sh) 2980(w) 2928(w) 2920(s) 2911(s ) 2924(m) 2907(m) 2920(m) vCH(a-| ) 2155(w) - - - - - 3 v6 1380(s) 1388(s) 1386(s) 1388(m) 1390(s) 1384(sh) 1374(w) 1375(m) 1367(vw) 1378(s ) 1375(s) CH2wag(e) 1320(w) 1375(m) 1355(m) 1317(w) 1 2 2 1(m) 1216(m) 1218(m) 1262(w) 1 2 2 2(w) 1218(m) CH9tw ist(e ) 1231(vw) 1218(w) C x 7 907(s ) 906(s ) 906(s) 917(m) 902(m) 920(vs) 912(s) CH2rock(a^) 785(w) 796(w) « 808(w) 810(w) - 764(m) v2 + v7 725(s) 749(m) 743(w) 738(s) 745(m) 725(s) 730(w) 732(m) 723(m) 735(w) 722(m) 711(m) 716(w) 715(m) 705(m) s 660(w) 659(w) 661(w) 665(w) 671(w) 667(m) v6 650(w) 646(w) 636(s) 628(w) 635(s) - V1 418(w) - 415(w) - - - v2 390(m) 377(w) 375(w) 391(w) - - V-> 352(w) 367(w) 7 326(w) 306(s) 312(w) 296(m) 326(m) v3 277(m) - - 287(w) - - V o 254(w) 8 391(vs) 322(vs) 345(vs) 365(vs) 340(m) 306(vs) M-Cl
Table 5.8.1 IR Spectra of (CH2S) 3 adducts
The IR spectra of the complexes bear a d is t in c t resemblance to the spectrum of the fre e lig an d, suggesting that the ch a ir configuration of the ligand
p e rsists on complexation. A general lowering of the CS stre tc h in g and CH2 group frequencies from those found in the fre e ligand was observed, in accordance with S donation (350). Complexation i s accompanied by a reduction in the symmetry of the (CH2S)3 rin g . Consequently, bands associated with CS stretch in g modes in the fre e ligand are found as m u ltip lets in the spectra o f the adducts, e .g . the strong ring stre tc h a t 725 cm-1 in (CH2S) 3 appears as a t r ip l e t in T iC l4. 2(CH2S) 3 (749, 730 and 722 cm"^) . For complexes which are co o rd in atively unsaturated, interm olecu lar asso cia tio n in the s o lid phase can increase the symmetry o f the ligand.
This e ffe c t i s ty p ifie d in SbCl3.(CH2S)3 (F ig . 5 .3 .2 ) , the c r y s t a l stru ctu re of which, shows each (CH2S)3 molecule to be c e n t r a lly placed between three d iffe re n t SbCl3 centres (351).
F ig . 5 .3 .2 C rystal Structure of SbCl3.(CH2S)3 (p ro jectio n on xy plane)
Bands in the IR spectra of the SbX3.(CH2S) 3 (X = C l, B r, I) (350) adducts, therefore, show no s p lit t in g due to ligand asymmetry.
159
and 322 (M = Sn) cm- ^ are in accordance with an octahedral trans (D ^ ) arrangement of ligands (F ig . 5 .3 .3 ) . Bands a t 365 and 340 cm“^ in the spectrum of AuC13.(CH2S)3 f a ll well w ith in the range of values found fo r square planer (C2v) AuX3 .L adducts with substituted pyridine (3 5 3 ), a s im ila r stru ctu re i s proposed in the present instance (F ig . 5 .3 .3 ) . An octahedral (C ^ ) geometry i s proposed for SbClg.(CH2S)3 on the b a sis of a sin g le strong Sb-Cl band at 345 cm"^ c f . SbClg” (336 cm- ^) (354) (F iq . 5 .3 .3 ) .
and SbClg.L
Samples of brown AuC13.(CH2S)3 sealed in ampoules under an N2 atmosphere were observed to slo w ly decompose over a 3 month period to give a pale yellow s o lid . An IR spectrum showed bands a ttrib u ta b le to uncomplexed
(CH2S )3, and an intense AuCl mode a t 333 cm"'*. Reduction (Au ( I I I ) -*■ Au ( I ) i s proposed, followed by d isso c ia tio n of the Au (I) .(C H2S)3 complex.
The oxidation product was not id e n t if ie d , but low in te n sity bands in the IR spectrum not a ttrib u ta b le to e it h e r AuC13<(CH2S)3 or free (CH2S ) , suggest a p a r t ia lly chlorinated (CH2S) 3 ring as a possible product.
160
(CI^SJj acts as an e s s e n tia lly monodentate donor. A sim ila r s itu a tio n was recen tly found fo r complexes of 1,4-dithiacycloheptane with SbX3
(X = C l, B r, I ) ; the ligand bridging between two SbX3 units rath er than ch elatin g to a sin g le Sb ( I I I ) atom (3 5 5). Conversely for the 1:1 complexes TiX^.fC^HgSg) (X = C l, B r ), bidentate behaviour on the part of the ligand was proposed (328). Factors a ffe c tin g the coordination
behaviour of these polythioethers appear to be complex, but the s t e r i c d icta te s of the SCS moiety must play an important part in deciding the re su ltin g coordination geometry.
Campaigne and coworkers (.356) have demonstrated that in so lu tio n s - t r it h ia n e re ta in s the ch a ir configuration that i t adopts in the s o lid phase (352). The NMR of s- tr ith ia n e a t 60 MHz showed only a sin g le sharp resonance due to the rapid interconversion o f the axial (a) and e q u ito ria l (e ) m ethylinic protons via ring in v ersio n , Fig . 5 .3 .4 .
pig. 5 .3 .4 . s-Tri.thiane Showing Axial and E q u ito rial Protons
At higher f i e l d s (400 MHz), the sin g le resonance representing the f a s t exchange l im it is seen to broaden on lowering the temperature, due to a reduction in the ring inversion rate (F ig . 5 .3 .5 ) . Between 263 and 253 K the sin g le resonance s p lit s into two corresponding to the a x ia l (a) and eq u ito rial (e ) protons re sp e ctiv e ly . The spectrum a t 238 K i s s u f f ic ie n t ly well resolved to show geminal coupling between the axial and eq u ito ria l protons.
O O l
—
S B B H Ü
2^3K
2 5 3 K
Fig. 5 .3 .5 V ariable Temperature NMR Soectra of (CH?S ) , (400 MHz, CDC13)
The v a ria b le temperature NMR spectra of SnCl^^fCH^S)^ are shown in F ig . 5 .3 .6 . As with the free ligand, dynamic behaviour in the ring is indicated by the broadening of the methylene proton resonance at low temperatures, but here broadening is attrib u ted to a reduction in the rate at which the ligand coordination s i t e interchanges between the three S donor centres (333). The sin g le sharp sig n als, seen at room temperature, correspond to the f a s t exchange lim it o f both the donor s i t e interchange ra te and the ring inversion ra te . At 243 K the spectrum rev ea ls two resonances due to the methylene protons adjacent to the
I I
S donor atom (Ha and Ha ) and opposite the S donor atom (Hb and Hb ) . No evidence was found for any d istin c tio n between the a x ia l (a and b)
I I
and eq u ito ria l (a and b ) protons (F ig . 5 .3 .7 ) . The fa ct that the (220 MHz) spectrum of the free ligand at 233 K (F ig . 5 .3 .5 ) i s much broader (linew idth at h a lf height = ^90 Hz) than th at of the coordinated ligand at the same temperature (33 Hz) suggests that the rate of ring in versio n is g re a tly enhanced on complexation
F ig . 5 .3 .7 SnCl4.2(CH2S)3 Showing Magnetically Inequivalent Protons A th ird type of dynamic phenomenon has been observed fo r the S(CH2 ) 5 ring in trans PtX22(S(CH2) 5) (X = C l, B r, I ) by Abel and coworkers (357).
228K (x 8)
248K (x8)
263 K (x8)
296 K
F ig . 5 .3 .6 Variable Temperature ] H NMR Spectra of SnCl4.2(CH2) 3 (220 MHz, CDCI3)
The S donor atom can coordinate to the metal atom v ia e ith e r the a x ia l (ax) or eq u ito ria l (eq) lone p a ir . With two such ligands coordinated, there are four p o ssib le conformers, namely (ax -ax ), (eq-eq) and the degenerate
(ax-eq) and (e q -a x ). The populations of each o f these conformers were established in the tran s PtXgZiSJCh^Jg) systems by integration o f the
NMR signal observed fo r each conformation, which were found to have s lig h t ly d iffe r e n t chemical s h if t s . There was, however, no in d ica tio n of sim ila r iso m erisatio n in the trans SnCl4.2(CH2S) 3 system. For trans PtX22(S(CH2)5)2* although the Cl and Br complexes gave a mixture of conformers, the I sp ecies was found to resid e t o t a lly in the eq-eq configuration, and t h is was attrib u ted to s t e r ic in te ra ctio n between the I atoms and the methylene protons on the lig a n d . I t i s not then unreasonable to suggest th at the four meridinal Cl atoms in trans SnCl/j .2(CH2S) 3 have approximately the same e ffe c t as the two I atoms in trans P tlg .ZiSfC H g Jg ), and th at only the eq-eq isomer, F ig . 5 .3 .7 , e x is ts in so lu tio n .
Solutions o f SbClg.CCHgSJj in CDjCN also exhib ited lin e broadening in th e ir NMR sp e c tra , but the spectra obtained were found to clo se ly follow those obtained fo r the free lig an d. The inference from t h is i s that e ith e r the rate o f donor s it e interchange i s very f a s t , or the complex i s completely d isso cia te d in so lu tio n , displacement o f the ligand by CD3CN i s u n lik e ly , as spectra of SbCl3.(CH2S) 3 in MeCN so lu tio n showed no sign o f coordinated MeCN. Considering the weak Sb-S bond found fo r SbCl3.(CH2S)3 in the s o lid sta te (350), d isso ciatio n and f a s t donor interchange seem equally l i k e l y . Unfortunately, the s h if t s seen on coordination were too small to make any meaningful d istin c tio n between the two.
9 9