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Synthesis and some reactions of tris (pentafluorophenyl) antimony compounds
PREM RAJ et al.
252
by standard methods. Freshly prepared metallic salts except NaN3, were dried in vucuo before use. All solvents were purified and dried by standard procedures and reactions were carried out under anhydrous conditions. IR spectra were recorded in the range 4000-200 cm - 1 by using KBr/CsI pellets on a Perkin-Elmer 577 spectra-photometer. The molar conductance of 10T3 M solutions was determined at 25°C with a Phillips Conductivity assembly PR-9500. Molecular weight was determined cryoscopically in benzene using a Beckmann thermometer of accuracy of f 0.0 1OC. Typical experimental details of the reactions are described below. Relevant IR assignments, analytical data and molar conductance values are listed in Tables l-2.
Oxidative addition reactions Reaction of(CsFS)3Sb with ICI and IBr, (I, II). A solution of iodine monochloride (0.325 g - 2 mmol) in acetonitrile (40 cm3) was added dropwise to a stirred solution of tris(pentafluorophenyl)antimony (1.246 - 2 mmol) in the same solvent (50 cm’) at -5OC during 1 hr. The reactants were allowed to attain room temperature and stirred further for 30
min to ensure complete reaction. Concentration of the solution followed by the addition of petroleumether (bp. 60-80%) afforded off white crystalline solid, tris(pentafluoropheny1) antimony (V) chloride iodide, m.p. 165-66%. Similarly, 1: 1 molar reaction of tris(pentafluorophenyl) antimony (1.246 g, 2 mmol) and iodine monohromide (0.414 g, 2 mmol) yielded tris(pentafluoropheny1) antimony(V) bromide iodide, m.p. 126%. Reaction of (C6Fs),Sb with IN3 and INCO, (III, IV). A freshly generated solution of iodine azide (0.338 g, 2 mmol) in acetonitrile (50 cm3) at - 10°C was added to a precooled (- 10°C) vigorously stirred solution of tris(pentafluoropheny1) antimony (1.246 g, 2 mmol) in the same solvent (50 cm’) during 15 min under nitrogen atmosphere. The reactants were stirred for 1 hr at initial temperature and then allowed to come at room temperature. The solution was evaporated under reduced pressure and cooled overnight, after adding petroleum-ether (bp. 40-60°C) (10 cm3). A pale yellow crystalline solid thus obtained was characterised as tris(pentafluorophenyl)antimony azide iodide (III), m.p. 26OOC. (C6F5),SbINC0 (IV) was obtained as a white crystalline solid by the method described above by
Table 1. Analytical data of tris(pentafluorophenyl)antimony(V) S.No.
Compound
Colour
m.p.
YieAd
(Ohm-' cm*
(Oc)
($1
mo1o-'Ifor ,o-3n eo1utian in .ac*-
derivatives
Analysis Pound(Calod) C
(C6F5)3SbIC1
Brown
165-66
62
(C6F5)3SbIBr
Brow
126
70
32.37
26.00 (26.05)
(C6F5)3SbrN3
Pale yellow
260(d)
56
34.80
27.22 (27.30)
(C6F5)3SbINC0
uhits
62
62
26.21
H
N
Sb
27.35 (27.53)
i5.42 (15.50) 14.56 (14.6'7)
1 .72 (1 076)
(C6F5)3Sb(NCS)2
brownish yellow
205(d)
74
(C6F5)3SbS
Off
122
60
white
280(d)
65
13.02
5.63 (6.24)
uhits
250(d)
70
16.00
3.62 (3.96)
white
245
68
18.42
E(C6F5)3Sb}20] ("'312 (C6F5)3Sb(NCO)2
white
16.42
3.60 (3.7
38.06
9)
(36.12)
0.92 (0.9e)
3.36 (3.42)
(14.86)
0.62 (0.64)
2.62 (2.93)
(:: :“,‘9,
3.36 (3.65)
(:E)
white
210
70
20.20
40.01 (40.23)
m-Bits
196
60
‘8.92
white
55
55
‘9.40
37.49 (37.57) 45.62 (45.62)
14.80
13.26 (13.67)
Reactions of tris(pentafluorophenyI)antimony compounds
253
Table 2. Relevant IR absortions of the anions in tris(pentafluorophenyl)antimony(V) compounds (cm-‘) III
IV
21SOl.n
2lSOm
1275m
123Ow
VII
VIII
IX
2OSSmbr
218Om
2160mbr
-
760
129Ou
v
X
XI
XII
9
6OEm
47Sm
625~
C
$
62%
1700s
16SSm 1 6E2mb
-
1235m
1310mb 13lOm
-
5OSW
36Sma
SY
(c-x)
S(N3/~Cx1
-
ts,(co/oco) 63Sma
3 (C=N)
915m
92Sm
3 (N-O)
48Sw
46Ow
9
1 632ma
572sh
(NCX)
asy
84OVW
665u
ASSIGNMENTS
1
415w
(Sb-0)
+(Sb-N)
568ma 2920m
a I
Overlapped
Q=
weak,
ml
by fledium,
C6FS br
absorptions; P Broad,
li s =
=
In
Strong.
CHC13 solution: Sh -
employing an equimolar ratio of the corresponding reactants, m.p. 82°C. Reaction of (C6F,),Sb with (SCN),, (V). A freshly prepared solution of thiocyanogen (0.25 g, 2 mmol) in CCl,,(30cm3) was added to a stirred tris(pentafluoropheny1) antimony (1.246 g, 2 mmol) solution in CC1,(50 cm3) at -5°C during 15 min. The reaction mixture was subsequently stirred for 1 hr and warmed to room temperature. The removal of the volatiles under reduced pressure afforded a pale yellow solid. After recrystallisation from ethanol it was characterised as tris(pentafluorophenyl)antimony diisothiocyanate (V), m.p. 205°C (d). Reaction of (C,F,),Sb with suiphur, (VI). A solution of tris(pentafluorophenyl)antimony (1.246 g, 2 mmol) in acetonitrile (50 cm’) was refluxed with elemental sulphur (0.064 g, 2 mmol) for 1 hr under nitrogen atmosphere. The solution was concentrated and cooled overnight to afford off-white crystalline solid. It was character&d as tris(pentafluorophenyl)antimonysulphide (VI), m.p. 122OC. The same product (VI) was obtained when the reaction was repeated in benzene as solvent. (ii) Metathetical reactions Reaction of (C~F&SbClr with AgSCN and KNCO, (V and VIII). Tris(pentafluorophenyl)antimony dichloride (1.3888 g, 2 mmol), and silver
shoulder,
2 920m
2925m
3 (C-H)
c - Absent vu
= very
weak
thiocyanate (0.464 g, 4 mmol) were stirred together in benzene (100 cm3) at room temperature for 3 hr and then refluxed for 1 hr to ensure completion of the reaction. Silver chloride was filtered off and concentration of the solution under reduced pressure followed by the addition of petroleum*ther (bp. 40-60%) yielded off-white crystalline tris(pentafluoropheny1) antimony diisothiocyanate (V), m.p. 205OC. Similarly, 1 : 2 molar reaction of tris(pentafluorophenyl)antimony(V) dichloride (1.388 g, 2 mmol) and potassium cyanate (0.324 g, 4 mmol) was found to give tris(pentafluorophenyl)antimony(V) diisocyanate, m.p. 250°C (d). Reaction of (C6FS)3SbC12with NaN,, (VII). An aqueous solution of sodium azide (0.264 g, 4 mmol) was added to an ethereal solution of tris(pentafluorophenyl)antimony dichloride (1.3888.2 mmol) and the mixture was stirred for 3 hr at room temperature. The ether layer was separated and dried over sodium sulphate. It was then evaporated and cooled to yield off-white crystalline solid which was characterised as oxybis(tris(pentafluorophenyl)antimony)diazide (VII), m.p. 280%. Reaction of (C6Fs)3SbICl with KNCO, (IV). A suspension of potassium cyanate (1 g, 1.24 mmol) in acetonitrile was added to a solution of tris(pentatluorophenyl)antimony chloride iodide (0.785 g, 1 mmol) in the same solvent (60 cm’) and refluxed for 3-4 hr. The mixture. was then filtered
254
PREM RAJ
to remove potassium chloride and uureacted potassium cyanate. The filtrate was concentrated under vacuum to afford white solid, which was recrystallised from petroleum-ether (bp. 40-60%) and characterised as tris(pentafluorophenyl)antimany(V) iodide isocyanate, m.p. 82°C. The similar procedure as described above was adopted to obtain tris(pentafluorophenyl)antimany(V) iodide azide from tris(pentafluorophenyl)antimony chloride iodide (0.785 g, 1 mmol) and sodium azide (0.08 g, 1.23 mmol). Compounds (III) and (IV) may also be prepared by the reaction of tris(pentafluorophenyl)antimony bromide iodide with the corresponding metallic salt. Preparation of tris(pentaJluorophenl)antimony disubstituted amide, -oximate and carboxylate derivatives (IX, X-XII). In a typical experiment tris(pentalluorophenyl)antimony dichloride (0.694 g, 1 mmol) and sodium succinimide (0.238 g, 2 mmol) in benzene (60 cm’) was stirred at room temperature for 3 hr. Sodium chloride was filtered off and the filtrate was concentrated under vacuum followed by the addition of n-hexane (10 cm3) and on scratching yielded a white solid. It was recrystallised from petroleum-ether (bp. 40-60%) and characterised as tris(pentafluorophenyl)antimony disuccinimide (IX) m.p. 24Y’C. Compounds (X)-(XII) were synthesised from tris(pentafluorophenyl)antimony dichloride and the corresponding sodium salt of oxime or carboxylate in 1 : 2 molar ratio, respectively.under conditions similar to those described for the disuccinimide.
et al.
was added dropwise a chloroform solution of tris(pentafluorophenyl)antimony diisocyanate (0.707 g, 1 mmol). The reactants were refluxed for 5 hr and then cooled at ice temperature. The solid thus separated was filtered off and identified as diphenyllead diisocyanate m.p. 230-235°C (d). (Found: C, 38.98; H, 2.29; N, 6.29; Calc. for C,4H,0N,0,Pb; C, 39.17; H, 2.348; N, 6.52; IR vJNC02180 cm-‘). The filtrate was concentrated to dryness under vacuum and then treated with n-hexanelbenzene mixture (1 : 1, 10 cm3) to afford insoluble tetraphenyl lead, m.p. 227-238OC (lit.,” .m.p. 228OC). The filtrate on concentration and cooling gave tris(pentafluorophenyl)antimony, m.p. 74OC (lit.,4 m.p. 74OC). Similarly, reaction of tris(pentafluorophenyl)antimony dichloride (0.694 g, 1 mmol) and hexaphenyl dilead (0.876 g, 1 mmol) afforded diphenyllead dichloride m.p. 285OC (lit.,” m.p. 284-286OC), tetraphenyllead m.p. 226-227OC (lit.,” m.p. 228OC) and tris(pentafluorophenyl)antimony, m.p. 73OC (lit.4 m.p. 74°C).
(iv) Action of (CsFs),SbC12 on bis(triorganotin)sulphides Reaction of (C,F,),SbCl, with (Bu,Sn),S. To a well stirred ice cold solution of tris(pentafluorophenyl)antimony dichloride (0.614 g, 1 mmol) in chloroform (50 cm’) bis(tributyltin)sulphide (0.616 g; 1 mmol) in the same solvent (40 cm’) was added drop-wise during half an hour. The reactants were further stirred for 3 hr and simultaneously allowed to attain room temperature. The solution was concentrated to dryness and the residue was dissolved (iii) Reductive cleavage reactions in hot petroleum-ether (bp 60-8OOC). The solution Reaction of (C6FS)3SbS with ArsPbz(l : 1). To was cooled and filtered, the solid was identified as an acetonitrile solution (50 cm’) of tris(pentatris(pentafluorophenyl)antimony sulphide m.p. fluorophenyl)antimony sulphide (0.652 g, 1 mmol) 122°C. The filtrate was concentrated at reduced hexaphenyldilead (0.876 g, 1 mmol) in the same pressure to yield tributyltin chloride, characterised solvent (30 cm’) was added and stirred for 3 hr at as tributyltin fluoride m.p. 242OC (lit.,” m.p. room temperature. The solution was concentrated 244OC). and petroleum-ether (bp. 60-80°C) was added to Under similar conditions tris(pentafluoroprecipitate a white crystalline solid characterised as phenyl)antimony dichloride (0.694 g; 1 mmol) bis(triphenyllead) sulphide, m.p. 140-141°C (lit,14 afforded tris(pentafluorophenyl)antimony sulphide m.p. 139-143OC). After filtering the precipitate, m.p. 122OC and triphenyltin chloride m.p. 1OS%, the filtrate was concentrated and cooled to yield (lit.,” m.p. 105-107°C). off-white crystals of tris(pentafluorophenyl)antimony m.p. 74OC (lit.,4 m.p. 74OC). RESULTS AND DISCUSSION Similarly, reaction of tris(pentaiIuoropheny1) antimony sulphide with hexa-p-tolyl dilead pro- (i) Oxidative addition reactions Freshly generated solutions of tbiocyanogen duced bis(tri-p-tolyllead) sulphide m.p. 143-144OC (lit.,14 m.p. 144OC) and tris(pentafluorophenyl)(SCN), and iodine-azide and -isocyanate in aceto&rile were found to react separately with antimony, m.p. 74OC (lit.,4 m.p. 74OC). tris(pentafluorophenyl)antimony at - 10°C to give Reaction of (C,F,),Sb(NCO), with P&Pb, (1: 1). To a refluxing solution of hexaphenyl di- high yields of respective oxidative addition product lead (0.876 g; 1 mmol in chloroform (50 cm3) in which antimony is in the pentavalent state.
Reactions of tris(pentafluorophenyI)antimony compounds
Reaction with (SCIQ was performed in the dark to retard its polymerization. (C,F,),Sb + (SCN),+(C,Fd,Sb(NCS), (C6FS)sSb + IX+(C6F,),SbIX
(1) (2)
(X = N3, NCO). Whereas reactions of (SC%), have earlier been demonstrated to cleave metal-carbon bonds (M = Sn, Pb)9 those of IN3 and INCO are being reported for the first time with an organometallic compound. However, reactions involving regio and stereospecific additions of IN3 and INCO to olefins and other systems in synthetic organic chemistry are well known.‘2*‘3 Parallel reactions of interhalogens, viz. ICI and IBr with (C6F5)3Sb under identical conditions as described above were found to produce mixed halo derivatives (I & II Table 1). (C,F,),Sb + IX+(C6F&SbIX,
(3)
X = Cl, Br. It may be added that ICI, IBr and (SCN), behave as electrophilic reagents towards symmetrical tetraorganometallic derivatives of group IVB(M = Ge, Sn, Pb)9J’ and cleave the metalcarbon bond(s) to different extents depending upon the relative strength of electrophile used. However, no traces of any pentafluorophenyl-thiocyanate or -halide or of corresponding bis(pentafluorophenyl) derivative, (C6F,),SbX(X = NCS, N3, NCO, Cl, Br), the products normally expected from the possibility of metal-carbon bond cleavage were observed in the above described reactions. Elemental sulphur was also found to add oxidatively to (C6F,),Sb in refluxing benzene or acetone solution in a dry nitrogen atmosphere to give tris(pentafluorophenyl)antimony sulphide (VI). Similar observations have been made .for triarylantimony (III) compounds:’
255
(ii) Metathetical reactions (C,F,),SbCl, is an important source for obtaining various. disubstituted tris(pentafluorophenyl)antimony(V) derivatives (V, VIII-XII, Table 1). Thus the treatment with the corresponding sodium or silver salts in benzene under mild conditions leads to the replacement of both the chloride atoms. The metallic chlorides separate immediately in each case after mixing the reactants.
(C,F,),SbC12 + 2MY-+(C6F5),SbY2 + 2MCl (5) M = Ag; Y = NCO, NCS M = Na; Y = ONCMe2; ONCMePh, gCO(CH,),cO, and 00CC6H.,N02 - p.
In sharp contrast, (C,F,),AsCI, has been reported to give monosubstituted products.“j This difference in behaviour can be attributed to the greater tendency of antimony to expand its coordination sphere, and to the lower element-chlorine bond energy. Formation of oxo-bridge compound (VII). Reaction of aqueous NaN, with (C6F5)3SbC12 in ether solution, however, yielded binuclear oxobridge compound (VIII, Table 1) instead of
(C6F,),SbC12 + 2NaN3+ (6) [(C,F,),Sb-o-Sb(C,F,)&%)~
+ 2NaCl.
(4)
Formation of such a binuclear derivative is not surprising since Gael et al. have reported that R,Sb(N,),(R = Me, Ph) could only be prepared and isolated in the presence of hydrazoic acid in benzene. One of the most usually employed methods for the preparation of organometallic azides involving a water/ether system as described above resulted in the formation of oxo-bridge compound
(C6F5)3SbScan also be obtained by passing H2S gas in alcoholic-ammonia solution of (C6F,),SbCl,. The molecular weight of sulphide derivative determined cryoscopically in benzene indicates that it exists as a monomer. It may be mentioned that tris(perfluoroalkyl)antimony has been reported not to react with sulphur.ls
Selective replacement reactions. Equimolar reactions involving mixed halogen compounds ‘(C,F,),SbIX(X = Cl, Br) and metallic salts in benzene produced mixed iodo-pseudohalo derivatives, through selective replacement of chloride or bromide group by a pseudohalo group. The iodide invariably remains bonded to the antimony irrespective of the nature of the metallic salt used.
(ChF,),Sb + S+(C6F&SbS
~Wb--O-=W W3)z.‘7
PREM RAJ et al.
256 (C,F,),SbICl + NaN,+(C,F,),SbI(N,)
Ar,Pb + XSn(C,F,),-(C,F,),Sb
+ NaCl
+ Ar2PbX2 (11)
(7) (C,F,),SbIBr + MNCO-(C,F&SbI(NCO)
+ MBr (8)
(M = K, Ag). This behaviour of tris(pentafluorophenyl)antimony mixed halides is somewhat different from those observed for similar reactions of mixed halides of diaryl-lead(IV) and -tin(IV), where both the different halo groups are replaced by the anionic groups.‘8*‘9It may be added that in case of group IVB metals identically placed iodide is more readily replaced by silver salts and the chloride and bromide are replaced by the anions attached to the alkali metals.” Selective replacement of halo groups (Cl, Br) have earlier been reported in case of mixed tetrahalocyclopentane tellurates(IV).20 The products (III and IV obtained through exclusive replacement of halo group are similar to those obtained by the oxidative addition method (eqn 2) mentioned above and had similar m.p. and superimposable IR spectra.
(III) Reductive cleavage reactions (a) Reaction of(C6F5)$bXz(X = NCO, Cl) with Ar,Pb*. Exploratory work reveals that higher valent metallic halides, viz. Cu(II),, Hg(I1) and Fe(II1) cleave the Pb-Pb bond in hexaorganodilead compounds while themselves getting reduced to the lower oxidation state.*‘” It was therefore, considered worthwhile to study the reactions of tris(pentafluorophenyl)antimony dichloride and diisocyanate against Pb-Pb bond. The former are readily reduced to (C,F,),Sb in the sense of equation shown below Ar,Pb, + (CsF,)$bX2+Ar.,Pb + Ar,PbX, + (C6F5)$b
(9)
Ar = Phenyl,p-tolyl
(b) Reaction of (C6F5)$bS with Ar,Pb,. It has been reported by Okawara et al. that the Sb-S bond in triorganoantimony sulphides is semipolar in nature, which facilitates the resonance hybrid of sulphides in the ground state due to which triorganoantimony(V) sulphides are more reactive.23,24 R,Sb+-S-
= R,Sb = S.
It is therefore not surprising that on reaction of (C,F,)sSbS with hexaaryldileads insertion of sulphur into Pb-Pb bond takes place. (C6F,)3SbS + Ar,Pb-PbAr3-+ Ar,Pb-S-PbAr,
+ (C6F5)3Sb
(12)
The reaction seems to proceed through initial rupture of Pb-Pb bond followed by the insertion of sulphur which may be attributed to the enhanced semipolar nature of Sb-S bond in tris(pentafluorophenyl)antimony sulphides, which facilitates the homolytic fission of Pb-Pb bond coupled with the remarkable reactivity of Pb-Pb bond.25 In the process tris(pentafluorophenyl)antimany(V) is reduced to tris(pentafluorophenyl)antimony (III). Similar results have been observed for the reactions of triorganoantimony sulphides with hexaarylditins. It can be thus concluded that the reactions of hexaaryldileads with tris(pentafluorophenyl)antimany(V) derivatives proceed via two different pathways depending upon the nature of the anion attached to antimony atom. In the case of sulphide derivative (eqn 12) cleavage of the Pb-Pb bond is favoured while in the other cases (X = NCO, Cl dissociation of hexaaryldileads to Ar,Pb and Ar,Pb occurred (eqn 9). Both these reactions thus lend support to an earlier held view that the reactions of hexaorganodileads with different reagents differed mechanistically.25
X = Cl, NCO. The reaction appears to involve the cleavage of Pb-Pb bond and Pb-C bond in hexaaryldilead yielding stable Ar,Pb and unstable Ar, Pb (eqn 10) which further reduces the perfluorophenyl antimony(V) to perfluorophenyl antimony(II1) (eqn 11).
(iv) Action sulphide
of (CsF5)3SbC12 on bis(triorgunotin)-
Bis(triorganotin)sulphides were found to react with tris(pentafluorophenyl)antimony dichloride in 1 : 1 molar ratio resulting in the complete exchange of anionic groups. (R,Sn),S + (C6F5)3SbC12+
Ar,Pb-PbAr,
= Ar,Pb + Ar,Pb
(10)
2R,SnCl+
(CeF,)3SbS.
(13)
Reactions of tris(pentafluorophenyI)antimony
The separation of the products does not pose much difficulty due t? the difference of the solubilities in organic solvents. The reaction seems to proceed via a four- &ntred cyclic tratyition state involving sulhpur atom as represented below R;T;R (R,Sn),S + R’,SbCl,+Cl - Sp $1
compounds
257
and G(NCX). Thd observed frequencies for these modes of vibrations are listed in Table 2, and are fully consistent with a N-bonded NCX group, in consonance with the usual iso-structure of the hydrocarbon counter parts of the antimony(V).29 The vibrations associated with the NJ stretchings and bending modes (III and VII, Table 2) suggest the presence of a covalently
bonded linear N = N =
N group. The asymmetric N = N = N stretching is I + I fairly shifted to higher frequency as compared to R,Sn - $ SnR, PhjSb(N&2’7.28or Ph,SnI(N&30 but other modes of vibrations are not significantly changed. Compound R$;R (14) (VII), however, exhibits an additional strong band at 705 cm-‘, which can be safely assigned to the [Cl - Sb - S - SnR,] + R,SnCl u(Sb4LSb)29*6 vibration, indicating the formation 1 of an oxo-bridge biniclear derivative. R;SbS + R,SnCl Tris(pentafluorophenyl)antimony disuccinimide (IX) displays a strong’ band at 1700 cm-’ assignable to “ester-like” CO group. The symmetric (where R’ - C,F,; R = C4H9, C,H,). stretching mode appears at 1235 cm - ’ . Pattern and position of the bands are comparable with those of An analogous mechanism has been proposed for reported triarylantimony diamides.7 the reaction of Cph,Sn],O and HgC12.M The separation (375 cm-‘) between the asymThe molar conductance values of 10 - 3M solumetric and symmetric (0 = C = 0) stretching ticon in acetor&fi>e o!i tie newjy syn%nti&b frequencies for tris(pentafluorophenyl)antimony tris(pentafluorophenyl)antimony(V) compounds di(p-nitrobenzoate), which occur at 1685 cm-’ and range between 13-35 mol-’ cm*, which indicate 1310 cm-‘, respectively, in the solid state suggest their non-conducting nature.27 The values for comthe presence of a monodentate “ester-like” carboxpounds (I-IV) containing a halide atom are almost ylate group with a penta-coordinate structure about of the same order and higher than the rest of the the antimony atom. In chloroform solution the 1685 ccmpaunds but do naC suggest canducting be&avcm-’ band is shifted to 1682 cm-’ but the symmetiour. The observed molecular weight data of the com- ric (0 = C-O) stretching frequency remains unchanged and thus carboxylate group retains its pom& jn Ereezjng benzene were found compmabJe unidentate character in solution as we1LW3’The with those of theoretical values which suggests that non-conducting and monomeric nature and the these compounds exist as monomers. absence of carboxylate ion in the IR spectra further The newly isolated compounds are stable at rules out the possibility af au ionic structure. rcoDmrempera’rure anb scinjie ‘In ogatilc s&ven@. Tse Ia sp&sa ofetsjs~~~taA~~~~~~~~~~~~~$jviz, chloroform, acefonitrjfe, benzene etc. Commony dioximates (XI and XII) do not exhibit any pounds (II), (IV) and (VIII), however decompose on band in the region 3000-3380 cm-‘, assignable to storage. Isocyanate derivatives were also found the inttamalecularly hydrogen bonded OH in free tcobe m&me S&-i&t. oximes.A*The C = N vibrations cu. 1630 * 5 cm-’ appear as medium bands and are lowered by cu. 40 IR SPECTROSCOPY cm-’ as compared to the free oximes (- 1668 All the isolated compounds (I-XII; Table 1) cm-‘). The lowering of the VC = N vibration may exhibit IR absorptions characteristic of CQF, group be attributed to the stabilization of the C = N bond and are in conformity with those reported earlier by resonance with the non-bonding electron pair on fcr Iris(~nraAuaraqhn~~~andmany and its &idaxygen aCam aft&e amina graaq. Hawever, this type of lowering may also be related to the mass effect as ides.s,28 The IR frequencies due to fundamental has been observed earlier, in case of group IVB modes of vibrations of the anionic groups are listed Clernears? im”l &le^L. The appearance of a medium band in the region Absorptions associated with the various modes 915-925 cm-’ can be attributed to a N-O stretchof vibrations of the pseudohalide groups have been identified and indicate the nature of bonding to the ing vibration” while the Sb-0 stretching is tenatntimony atom. ne chalcogenate grouup, &&&y as&gn& a1 480-t 5 cm- I on ?ne ‘oasis 02 reported S&O frequencies in the corresponding NCX(X = S or 0) gives rise to three fundamental organoantimony oxinate derivatives.3’ modes of vibrations due to the Y(C=N), v(C - X)
258
PREM RAJ et al.
A noticeable feature of the IR spectra of all the isolated disubstituted compounds is the absence of the v,,, @b-C) absorption corresponding to the r-mode which should be located in the region 250-3OOcm-’ as reported by earlier workers.s*6 Thus on the basis of IR evidences coupled with their monomeric and non-conducting nature and in accordance with the structures of other organoantimony(V) compounds,6*7*17*29 the newly synthesised disubstituted derivatives (except for (VII)) can reasonably be assigned a trigonal bipyramidal structure with the anionic groups at the axial positions and C,F, groups occupying the equatorial positions. A trigonal bipyramidal structure containing an oxygen bridge (Sb-0-Sb) can be proposed for compound (VII).
Acknowledgement-The authors are thankful to the Head of the Chemistry Department, Lucknow University for providing the necessary Laboratory Facilities, the Director RSIC, Lucknow for obtaining IR spectra and Council of Scientific and Industrial Research, New Delhi for financial assistance (KS & AR).
IWFEXWNCE!S 1. G. 0. Doak and L. D. Freedman, Organometallic Compounds of Arsenic, Antimony and Bismuth. Wiley-interscience, New York, (1970). 2. A. T. Rake and J. M. Miller, J. Chem. Sot. A 1970, 1881. 3. J. P. Crow and W. R. Cullen, Organic compounds of arsenic antimony and bismuth. In Inorganic Chemistry, Series One, M.T.P. International Review of Science (Edited by H. J. Emeleus and B. J. Aylett) Vol. 4, p. 383. Butterworths, London (1972). M. Fild, 0. Glemser and G. Christoph, Angew. Chem. 1964,76,953. B. A. Nevett and A. Perry, Spectrochim. Acta 1975, A31, 101. A. Otero and P. Royo, J. Organometal. Chem. 1978, 154, 13. Prem Raj, Ashok Ranjan and A. K. Saxena, Znd. J. Chem. 1983, 22A, 120; Press Raj; Ashok Ranjan, Kiran Singhal and Rajiv Rastogi, Synth. React. Inorg. Metal-Org. Chem. 1984,14(2), 269. 8. R. D. Chambers and T. Chivers, Organometal Chem. Rev. 1966, 1, 279. 9. S. N. Bhattacharya, Prem Raj and R. C. Srivastava, J. Organometal. Chem, 1975, %7, 279. 10. R. C. Poller, The Chemistry of Organotin Compounds, p. 13 1. Logos Press, London (1970).
11. S. N. Bhattacharya, F&n Raj and R. C. Srivsstava, J. Organometal. Chem. 1976, 105, 45. 12. L. F. Fieser and M. Fieser, Reagents for Organic Synthesis, p. 500. Wiley, New York, (1968). 13. S. N. Moorthy and D. Devaprabhakara, Chem. Znd.
1975,217. 14 R. W. Leerier, L. Summers and H. Gilman, Chem. Rev. 1954;54, 101.
15 R. E. Banks and R. N. Haszeldine, Polyfluoroalkyl . derivatives of metalloids and non-metals. In Advances in Inorganic Chemistry and Radiochemistry (Edited by H. J. Emeleus and A. G. Sharp@, Vol. 3, p. 367. Academic Press, New York (1961) 16. A. Otero and P. Royo, J. Organometal. Chem. 1978, 149, 315. R. G. Goel and D. R. Ridley, Znorg. Chem. 1974,13, 17* 1253. 18. S. N. Bhattacharya and Prem Raj, J. Inorg. Nucl. Chem. 1978,40,1699; Prem Raj, Zmf. J. Chem. 1979, 178, 616. 19 S. N. Bhattacharya and Prem Raj, Znt. Conf on Coordination Chemistry of Ge, Sn. Pb. Nottingham, England (1977). 2. T. N. Srivastava, R. C. Srivastava and Mala Singh, . J. Organometal Chem. 1978, 157, 405. 21. D. P. Arnold and P. R. Wells, J. Organometal. Chem. 1976,113,311. 22. D. P. Arnold and P. R. Wells. J. Organometal Chem. 1975, 111, 1285. 23. M. Shindo, Y. Matsumura and R. Okawara, J. Organometal. Chem. 1968, 11, 299. 24. J. Otera and R. Okawara; J. Organometal. Chem. 1969, 16, 335. 25. H. Shapiro and F. W. Frey, The Organic compounds of Lead, p. 166. Wiley, N.Y. (1968). 26. D. Datta, B. Majee and A. K. Ghosh, J. Organometal Chem. 1971, 29, 251. 27. W. J. Geary; Coord. Chem. Reu. 1971,7, 81. 28. D. A. Long and D. Steele, S’ctrochim. Acta 1963, 19, 1955; I. J. Hyams, E. P. Lippincott and R. T. Bailey, Spectrochim. Acta 1966, 22, 695. 29. E. Maslowsky, J. Organometal. Chem. 1974,70, 153. 30. Prem Raj, Ashok Ranjan, Kiran Singhal and A. K. Saxena, Acta. Chem. SC&, submitted. 31. H. Schmidbaur and H. Stiiehler, Angew Chem. Znt. Ed. 1972, 11, 145. 32. R. E. Rundle and M. Parsole, J. Chem. Phys. 1952, 20, 1487. 33. P. G. Harrison and J. J. Zuckernunn, Znorg. Chem. 1970, 9, 175. 34. S. Califanio and W. Luttke. 2. Phys. Chem. 1956,6, 83; J. Fabian, M. Legrand and P. Poirlier, Bull. Sot. Chim. Fr. 1956,1499. 35. H. A. Meinema and J. G. Noltes, J. Organometal. Chem. 1969,16,257.
252
by standard methods. Freshly prepared metallic salts except NaN3, were dried in vucuo before use. All solvents were purified and dried by standard procedures and reactions were carried out under anhydrous conditions. IR spectra were recorded in the range 4000-200 cm - 1 by using KBr/CsI pellets on a Perkin-Elmer 577 spectra-photometer. The molar conductance of 10T3 M solutions was determined at 25°C with a Phillips Conductivity assembly PR-9500. Molecular weight was determined cryoscopically in benzene using a Beckmann thermometer of accuracy of f 0.0 1OC. Typical experimental details of the reactions are described below. Relevant IR assignments, analytical data and molar conductance values are listed in Tables l-2.
Oxidative addition reactions Reaction of(CsFS)3Sb with ICI and IBr, (I, II). A solution of iodine monochloride (0.325 g - 2 mmol) in acetonitrile (40 cm3) was added dropwise to a stirred solution of tris(pentafluorophenyl)antimony (1.246 - 2 mmol) in the same solvent (50 cm’) at -5OC during 1 hr. The reactants were allowed to attain room temperature and stirred further for 30
min to ensure complete reaction. Concentration of the solution followed by the addition of petroleumether (bp. 60-80%) afforded off white crystalline solid, tris(pentafluoropheny1) antimony (V) chloride iodide, m.p. 165-66%. Similarly, 1: 1 molar reaction of tris(pentafluorophenyl) antimony (1.246 g, 2 mmol) and iodine monohromide (0.414 g, 2 mmol) yielded tris(pentafluoropheny1) antimony(V) bromide iodide, m.p. 126%. Reaction of (C6Fs),Sb with IN3 and INCO, (III, IV). A freshly generated solution of iodine azide (0.338 g, 2 mmol) in acetonitrile (50 cm3) at - 10°C was added to a precooled (- 10°C) vigorously stirred solution of tris(pentafluoropheny1) antimony (1.246 g, 2 mmol) in the same solvent (50 cm’) during 15 min under nitrogen atmosphere. The reactants were stirred for 1 hr at initial temperature and then allowed to come at room temperature. The solution was evaporated under reduced pressure and cooled overnight, after adding petroleum-ether (bp. 40-60°C) (10 cm3). A pale yellow crystalline solid thus obtained was characterised as tris(pentafluorophenyl)antimony azide iodide (III), m.p. 26OOC. (C6F5),SbINC0 (IV) was obtained as a white crystalline solid by the method described above by
Table 1. Analytical data of tris(pentafluorophenyl)antimony(V) S.No.
Compound
Colour
m.p.
YieAd
(Ohm-' cm*
(Oc)
($1
mo1o-'Ifor ,o-3n eo1utian in .ac*-
derivatives
Analysis Pound(Calod) C
(C6F5)3SbIC1
Brown
165-66
62
(C6F5)3SbIBr
Brow
126
70
32.37
26.00 (26.05)
(C6F5)3SbrN3
Pale yellow
260(d)
56
34.80
27.22 (27.30)
(C6F5)3SbINC0
uhits
62
62
26.21
H
N
Sb
27.35 (27.53)
i5.42 (15.50) 14.56 (14.6'7)
1 .72 (1 076)
(C6F5)3Sb(NCS)2
brownish yellow
205(d)
74
(C6F5)3SbS
Off
122
60
white
280(d)
65
13.02
5.63 (6.24)
uhits
250(d)
70
16.00
3.62 (3.96)
white
245
68
18.42
E(C6F5)3Sb}20] ("'312 (C6F5)3Sb(NCO)2
white
16.42
3.60 (3.7
38.06
9)
(36.12)
0.92 (0.9e)
3.36 (3.42)
(14.86)
0.62 (0.64)
2.62 (2.93)
(:: :“,‘9,
3.36 (3.65)
(:E)
white
210
70
20.20
40.01 (40.23)
m-Bits
196
60
‘8.92
white
55
55
‘9.40
37.49 (37.57) 45.62 (45.62)
14.80
13.26 (13.67)
Reactions of tris(pentafluorophenyI)antimony compounds
253
Table 2. Relevant IR absortions of the anions in tris(pentafluorophenyl)antimony(V) compounds (cm-‘) III
IV
21SOl.n
2lSOm
1275m
123Ow
VII
VIII
IX
2OSSmbr
218Om
2160mbr
-
760
129Ou
v
X
XI
XII
9
6OEm
47Sm
625~
C
$
62%
1700s
16SSm 1 6E2mb
-
1235m
1310mb 13lOm
-
5OSW
36Sma
SY
(c-x)
S(N3/~Cx1
-
ts,(co/oco) 63Sma
3 (C=N)
915m
92Sm
3 (N-O)
48Sw
46Ow
9
1 632ma
572sh
(NCX)
asy
84OVW
665u
ASSIGNMENTS
1
415w
(Sb-0)
+(Sb-N)
568ma 2920m
a I
Overlapped
Q=
weak,
ml
by fledium,
C6FS br
absorptions; P Broad,
li s =
=
In
Strong.
CHC13 solution: Sh -
employing an equimolar ratio of the corresponding reactants, m.p. 82°C. Reaction of (C6F,),Sb with (SCN),, (V). A freshly prepared solution of thiocyanogen (0.25 g, 2 mmol) in CCl,,(30cm3) was added to a stirred tris(pentafluoropheny1) antimony (1.246 g, 2 mmol) solution in CC1,(50 cm3) at -5°C during 15 min. The reaction mixture was subsequently stirred for 1 hr and warmed to room temperature. The removal of the volatiles under reduced pressure afforded a pale yellow solid. After recrystallisation from ethanol it was characterised as tris(pentafluorophenyl)antimony diisothiocyanate (V), m.p. 205°C (d). Reaction of (C,F,),Sb with suiphur, (VI). A solution of tris(pentafluorophenyl)antimony (1.246 g, 2 mmol) in acetonitrile (50 cm’) was refluxed with elemental sulphur (0.064 g, 2 mmol) for 1 hr under nitrogen atmosphere. The solution was concentrated and cooled overnight to afford off-white crystalline solid. It was character&d as tris(pentafluorophenyl)antimonysulphide (VI), m.p. 122OC. The same product (VI) was obtained when the reaction was repeated in benzene as solvent. (ii) Metathetical reactions Reaction of (C~F&SbClr with AgSCN and KNCO, (V and VIII). Tris(pentafluorophenyl)antimony dichloride (1.3888 g, 2 mmol), and silver
shoulder,
2 920m
2925m
3 (C-H)
c - Absent vu
= very
weak
thiocyanate (0.464 g, 4 mmol) were stirred together in benzene (100 cm3) at room temperature for 3 hr and then refluxed for 1 hr to ensure completion of the reaction. Silver chloride was filtered off and concentration of the solution under reduced pressure followed by the addition of petroleum*ther (bp. 40-60%) yielded off-white crystalline tris(pentafluoropheny1) antimony diisothiocyanate (V), m.p. 205OC. Similarly, 1 : 2 molar reaction of tris(pentafluorophenyl)antimony(V) dichloride (1.388 g, 2 mmol) and potassium cyanate (0.324 g, 4 mmol) was found to give tris(pentafluorophenyl)antimony(V) diisocyanate, m.p. 250°C (d). Reaction of (C6FS)3SbC12with NaN,, (VII). An aqueous solution of sodium azide (0.264 g, 4 mmol) was added to an ethereal solution of tris(pentafluorophenyl)antimony dichloride (1.3888.2 mmol) and the mixture was stirred for 3 hr at room temperature. The ether layer was separated and dried over sodium sulphate. It was then evaporated and cooled to yield off-white crystalline solid which was characterised as oxybis(tris(pentafluorophenyl)antimony)diazide (VII), m.p. 280%. Reaction of (C6Fs)3SbICl with KNCO, (IV). A suspension of potassium cyanate (1 g, 1.24 mmol) in acetonitrile was added to a solution of tris(pentatluorophenyl)antimony chloride iodide (0.785 g, 1 mmol) in the same solvent (60 cm’) and refluxed for 3-4 hr. The mixture. was then filtered
254
PREM RAJ
to remove potassium chloride and uureacted potassium cyanate. The filtrate was concentrated under vacuum to afford white solid, which was recrystallised from petroleum-ether (bp. 40-60%) and characterised as tris(pentafluorophenyl)antimany(V) iodide isocyanate, m.p. 82°C. The similar procedure as described above was adopted to obtain tris(pentafluorophenyl)antimany(V) iodide azide from tris(pentafluorophenyl)antimony chloride iodide (0.785 g, 1 mmol) and sodium azide (0.08 g, 1.23 mmol). Compounds (III) and (IV) may also be prepared by the reaction of tris(pentafluorophenyl)antimony bromide iodide with the corresponding metallic salt. Preparation of tris(pentaJluorophenl)antimony disubstituted amide, -oximate and carboxylate derivatives (IX, X-XII). In a typical experiment tris(pentalluorophenyl)antimony dichloride (0.694 g, 1 mmol) and sodium succinimide (0.238 g, 2 mmol) in benzene (60 cm’) was stirred at room temperature for 3 hr. Sodium chloride was filtered off and the filtrate was concentrated under vacuum followed by the addition of n-hexane (10 cm3) and on scratching yielded a white solid. It was recrystallised from petroleum-ether (bp. 40-60%) and characterised as tris(pentafluorophenyl)antimony disuccinimide (IX) m.p. 24Y’C. Compounds (X)-(XII) were synthesised from tris(pentafluorophenyl)antimony dichloride and the corresponding sodium salt of oxime or carboxylate in 1 : 2 molar ratio, respectively.under conditions similar to those described for the disuccinimide.
et al.
was added dropwise a chloroform solution of tris(pentafluorophenyl)antimony diisocyanate (0.707 g, 1 mmol). The reactants were refluxed for 5 hr and then cooled at ice temperature. The solid thus separated was filtered off and identified as diphenyllead diisocyanate m.p. 230-235°C (d). (Found: C, 38.98; H, 2.29; N, 6.29; Calc. for C,4H,0N,0,Pb; C, 39.17; H, 2.348; N, 6.52; IR vJNC02180 cm-‘). The filtrate was concentrated to dryness under vacuum and then treated with n-hexanelbenzene mixture (1 : 1, 10 cm3) to afford insoluble tetraphenyl lead, m.p. 227-238OC (lit.,” .m.p. 228OC). The filtrate on concentration and cooling gave tris(pentafluorophenyl)antimony, m.p. 74OC (lit.,4 m.p. 74OC). Similarly, reaction of tris(pentafluorophenyl)antimony dichloride (0.694 g, 1 mmol) and hexaphenyl dilead (0.876 g, 1 mmol) afforded diphenyllead dichloride m.p. 285OC (lit.,” m.p. 284-286OC), tetraphenyllead m.p. 226-227OC (lit.,” m.p. 228OC) and tris(pentafluorophenyl)antimony, m.p. 73OC (lit.4 m.p. 74°C).
(iv) Action of (CsFs),SbC12 on bis(triorganotin)sulphides Reaction of (C,F,),SbCl, with (Bu,Sn),S. To a well stirred ice cold solution of tris(pentafluorophenyl)antimony dichloride (0.614 g, 1 mmol) in chloroform (50 cm’) bis(tributyltin)sulphide (0.616 g; 1 mmol) in the same solvent (40 cm’) was added drop-wise during half an hour. The reactants were further stirred for 3 hr and simultaneously allowed to attain room temperature. The solution was concentrated to dryness and the residue was dissolved (iii) Reductive cleavage reactions in hot petroleum-ether (bp 60-8OOC). The solution Reaction of (C6FS)3SbS with ArsPbz(l : 1). To was cooled and filtered, the solid was identified as an acetonitrile solution (50 cm’) of tris(pentatris(pentafluorophenyl)antimony sulphide m.p. fluorophenyl)antimony sulphide (0.652 g, 1 mmol) 122°C. The filtrate was concentrated at reduced hexaphenyldilead (0.876 g, 1 mmol) in the same pressure to yield tributyltin chloride, characterised solvent (30 cm’) was added and stirred for 3 hr at as tributyltin fluoride m.p. 242OC (lit.,” m.p. room temperature. The solution was concentrated 244OC). and petroleum-ether (bp. 60-80°C) was added to Under similar conditions tris(pentafluoroprecipitate a white crystalline solid characterised as phenyl)antimony dichloride (0.694 g; 1 mmol) bis(triphenyllead) sulphide, m.p. 140-141°C (lit,14 afforded tris(pentafluorophenyl)antimony sulphide m.p. 139-143OC). After filtering the precipitate, m.p. 122OC and triphenyltin chloride m.p. 1OS%, the filtrate was concentrated and cooled to yield (lit.,” m.p. 105-107°C). off-white crystals of tris(pentafluorophenyl)antimony m.p. 74OC (lit.,4 m.p. 74OC). RESULTS AND DISCUSSION Similarly, reaction of tris(pentaiIuoropheny1) antimony sulphide with hexa-p-tolyl dilead pro- (i) Oxidative addition reactions Freshly generated solutions of tbiocyanogen duced bis(tri-p-tolyllead) sulphide m.p. 143-144OC (lit.,14 m.p. 144OC) and tris(pentafluorophenyl)(SCN), and iodine-azide and -isocyanate in aceto&rile were found to react separately with antimony, m.p. 74OC (lit.,4 m.p. 74OC). tris(pentafluorophenyl)antimony at - 10°C to give Reaction of (C,F,),Sb(NCO), with P&Pb, (1: 1). To a refluxing solution of hexaphenyl di- high yields of respective oxidative addition product lead (0.876 g; 1 mmol in chloroform (50 cm3) in which antimony is in the pentavalent state.
Reactions of tris(pentafluorophenyI)antimony compounds
Reaction with (SCIQ was performed in the dark to retard its polymerization. (C,F,),Sb + (SCN),+(C,Fd,Sb(NCS), (C6FS)sSb + IX+(C6F,),SbIX
(1) (2)
(X = N3, NCO). Whereas reactions of (SC%), have earlier been demonstrated to cleave metal-carbon bonds (M = Sn, Pb)9 those of IN3 and INCO are being reported for the first time with an organometallic compound. However, reactions involving regio and stereospecific additions of IN3 and INCO to olefins and other systems in synthetic organic chemistry are well known.‘2*‘3 Parallel reactions of interhalogens, viz. ICI and IBr with (C6F5)3Sb under identical conditions as described above were found to produce mixed halo derivatives (I & II Table 1). (C,F,),Sb + IX+(C6F&SbIX,
(3)
X = Cl, Br. It may be added that ICI, IBr and (SCN), behave as electrophilic reagents towards symmetrical tetraorganometallic derivatives of group IVB(M = Ge, Sn, Pb)9J’ and cleave the metalcarbon bond(s) to different extents depending upon the relative strength of electrophile used. However, no traces of any pentafluorophenyl-thiocyanate or -halide or of corresponding bis(pentafluorophenyl) derivative, (C6F,),SbX(X = NCS, N3, NCO, Cl, Br), the products normally expected from the possibility of metal-carbon bond cleavage were observed in the above described reactions. Elemental sulphur was also found to add oxidatively to (C6F,),Sb in refluxing benzene or acetone solution in a dry nitrogen atmosphere to give tris(pentafluorophenyl)antimony sulphide (VI). Similar observations have been made .for triarylantimony (III) compounds:’
255
(ii) Metathetical reactions (C,F,),SbCl, is an important source for obtaining various. disubstituted tris(pentafluorophenyl)antimony(V) derivatives (V, VIII-XII, Table 1). Thus the treatment with the corresponding sodium or silver salts in benzene under mild conditions leads to the replacement of both the chloride atoms. The metallic chlorides separate immediately in each case after mixing the reactants.
(C,F,),SbC12 + 2MY-+(C6F5),SbY2 + 2MCl (5) M = Ag; Y = NCO, NCS M = Na; Y = ONCMe2; ONCMePh, gCO(CH,),cO, and 00CC6H.,N02 - p.
In sharp contrast, (C,F,),AsCI, has been reported to give monosubstituted products.“j This difference in behaviour can be attributed to the greater tendency of antimony to expand its coordination sphere, and to the lower element-chlorine bond energy. Formation of oxo-bridge compound (VII). Reaction of aqueous NaN, with (C6F5)3SbC12 in ether solution, however, yielded binuclear oxobridge compound (VIII, Table 1) instead of
(C6F,),SbC12 + 2NaN3+ (6) [(C,F,),Sb-o-Sb(C,F,)&%)~
+ 2NaCl.
(4)
Formation of such a binuclear derivative is not surprising since Gael et al. have reported that R,Sb(N,),(R = Me, Ph) could only be prepared and isolated in the presence of hydrazoic acid in benzene. One of the most usually employed methods for the preparation of organometallic azides involving a water/ether system as described above resulted in the formation of oxo-bridge compound
(C6F5)3SbScan also be obtained by passing H2S gas in alcoholic-ammonia solution of (C6F,),SbCl,. The molecular weight of sulphide derivative determined cryoscopically in benzene indicates that it exists as a monomer. It may be mentioned that tris(perfluoroalkyl)antimony has been reported not to react with sulphur.ls
Selective replacement reactions. Equimolar reactions involving mixed halogen compounds ‘(C,F,),SbIX(X = Cl, Br) and metallic salts in benzene produced mixed iodo-pseudohalo derivatives, through selective replacement of chloride or bromide group by a pseudohalo group. The iodide invariably remains bonded to the antimony irrespective of the nature of the metallic salt used.
(ChF,),Sb + S+(C6F&SbS
~Wb--O-=W W3)z.‘7
PREM RAJ et al.
256 (C,F,),SbICl + NaN,+(C,F,),SbI(N,)
Ar,Pb + XSn(C,F,),-(C,F,),Sb
+ NaCl
+ Ar2PbX2 (11)
(7) (C,F,),SbIBr + MNCO-(C,F&SbI(NCO)
+ MBr (8)
(M = K, Ag). This behaviour of tris(pentafluorophenyl)antimony mixed halides is somewhat different from those observed for similar reactions of mixed halides of diaryl-lead(IV) and -tin(IV), where both the different halo groups are replaced by the anionic groups.‘8*‘9It may be added that in case of group IVB metals identically placed iodide is more readily replaced by silver salts and the chloride and bromide are replaced by the anions attached to the alkali metals.” Selective replacement of halo groups (Cl, Br) have earlier been reported in case of mixed tetrahalocyclopentane tellurates(IV).20 The products (III and IV obtained through exclusive replacement of halo group are similar to those obtained by the oxidative addition method (eqn 2) mentioned above and had similar m.p. and superimposable IR spectra.
(III) Reductive cleavage reactions (a) Reaction of(C6F5)$bXz(X = NCO, Cl) with Ar,Pb*. Exploratory work reveals that higher valent metallic halides, viz. Cu(II),, Hg(I1) and Fe(II1) cleave the Pb-Pb bond in hexaorganodilead compounds while themselves getting reduced to the lower oxidation state.*‘” It was therefore, considered worthwhile to study the reactions of tris(pentafluorophenyl)antimony dichloride and diisocyanate against Pb-Pb bond. The former are readily reduced to (C,F,),Sb in the sense of equation shown below Ar,Pb, + (CsF,)$bX2+Ar.,Pb + Ar,PbX, + (C6F5)$b
(9)
Ar = Phenyl,p-tolyl
(b) Reaction of (C6F5)$bS with Ar,Pb,. It has been reported by Okawara et al. that the Sb-S bond in triorganoantimony sulphides is semipolar in nature, which facilitates the resonance hybrid of sulphides in the ground state due to which triorganoantimony(V) sulphides are more reactive.23,24 R,Sb+-S-
= R,Sb = S.
It is therefore not surprising that on reaction of (C,F,)sSbS with hexaaryldileads insertion of sulphur into Pb-Pb bond takes place. (C6F,)3SbS + Ar,Pb-PbAr3-+ Ar,Pb-S-PbAr,
+ (C6F5)3Sb
(12)
The reaction seems to proceed through initial rupture of Pb-Pb bond followed by the insertion of sulphur which may be attributed to the enhanced semipolar nature of Sb-S bond in tris(pentafluorophenyl)antimony sulphides, which facilitates the homolytic fission of Pb-Pb bond coupled with the remarkable reactivity of Pb-Pb bond.25 In the process tris(pentafluorophenyl)antimany(V) is reduced to tris(pentafluorophenyl)antimony (III). Similar results have been observed for the reactions of triorganoantimony sulphides with hexaarylditins. It can be thus concluded that the reactions of hexaaryldileads with tris(pentafluorophenyl)antimany(V) derivatives proceed via two different pathways depending upon the nature of the anion attached to antimony atom. In the case of sulphide derivative (eqn 12) cleavage of the Pb-Pb bond is favoured while in the other cases (X = NCO, Cl dissociation of hexaaryldileads to Ar,Pb and Ar,Pb occurred (eqn 9). Both these reactions thus lend support to an earlier held view that the reactions of hexaorganodileads with different reagents differed mechanistically.25
X = Cl, NCO. The reaction appears to involve the cleavage of Pb-Pb bond and Pb-C bond in hexaaryldilead yielding stable Ar,Pb and unstable Ar, Pb (eqn 10) which further reduces the perfluorophenyl antimony(V) to perfluorophenyl antimony(II1) (eqn 11).
(iv) Action sulphide
of (CsF5)3SbC12 on bis(triorgunotin)-
Bis(triorganotin)sulphides were found to react with tris(pentafluorophenyl)antimony dichloride in 1 : 1 molar ratio resulting in the complete exchange of anionic groups. (R,Sn),S + (C6F5)3SbC12+
Ar,Pb-PbAr,
= Ar,Pb + Ar,Pb
(10)
2R,SnCl+
(CeF,)3SbS.
(13)
Reactions of tris(pentafluorophenyI)antimony
The separation of the products does not pose much difficulty due t? the difference of the solubilities in organic solvents. The reaction seems to proceed via a four- &ntred cyclic tratyition state involving sulhpur atom as represented below R;T;R (R,Sn),S + R’,SbCl,+Cl - Sp $1
compounds
257
and G(NCX). Thd observed frequencies for these modes of vibrations are listed in Table 2, and are fully consistent with a N-bonded NCX group, in consonance with the usual iso-structure of the hydrocarbon counter parts of the antimony(V).29 The vibrations associated with the NJ stretchings and bending modes (III and VII, Table 2) suggest the presence of a covalently
bonded linear N = N =
N group. The asymmetric N = N = N stretching is I + I fairly shifted to higher frequency as compared to R,Sn - $ SnR, PhjSb(N&2’7.28or Ph,SnI(N&30 but other modes of vibrations are not significantly changed. Compound R$;R (14) (VII), however, exhibits an additional strong band at 705 cm-‘, which can be safely assigned to the [Cl - Sb - S - SnR,] + R,SnCl u(Sb4LSb)29*6 vibration, indicating the formation 1 of an oxo-bridge biniclear derivative. R;SbS + R,SnCl Tris(pentafluorophenyl)antimony disuccinimide (IX) displays a strong’ band at 1700 cm-’ assignable to “ester-like” CO group. The symmetric (where R’ - C,F,; R = C4H9, C,H,). stretching mode appears at 1235 cm - ’ . Pattern and position of the bands are comparable with those of An analogous mechanism has been proposed for reported triarylantimony diamides.7 the reaction of Cph,Sn],O and HgC12.M The separation (375 cm-‘) between the asymThe molar conductance values of 10 - 3M solumetric and symmetric (0 = C = 0) stretching ticon in acetor&fi>e o!i tie newjy syn%nti&b frequencies for tris(pentafluorophenyl)antimony tris(pentafluorophenyl)antimony(V) compounds di(p-nitrobenzoate), which occur at 1685 cm-’ and range between 13-35 mol-’ cm*, which indicate 1310 cm-‘, respectively, in the solid state suggest their non-conducting nature.27 The values for comthe presence of a monodentate “ester-like” carboxpounds (I-IV) containing a halide atom are almost ylate group with a penta-coordinate structure about of the same order and higher than the rest of the the antimony atom. In chloroform solution the 1685 ccmpaunds but do naC suggest canducting be&avcm-’ band is shifted to 1682 cm-’ but the symmetiour. The observed molecular weight data of the com- ric (0 = C-O) stretching frequency remains unchanged and thus carboxylate group retains its pom& jn Ereezjng benzene were found compmabJe unidentate character in solution as we1LW3’The with those of theoretical values which suggests that non-conducting and monomeric nature and the these compounds exist as monomers. absence of carboxylate ion in the IR spectra further The newly isolated compounds are stable at rules out the possibility af au ionic structure. rcoDmrempera’rure anb scinjie ‘In ogatilc s&ven@. Tse Ia sp&sa ofetsjs~~~taA~~~~~~~~~~~~~$jviz, chloroform, acefonitrjfe, benzene etc. Commony dioximates (XI and XII) do not exhibit any pounds (II), (IV) and (VIII), however decompose on band in the region 3000-3380 cm-‘, assignable to storage. Isocyanate derivatives were also found the inttamalecularly hydrogen bonded OH in free tcobe m&me S&-i&t. oximes.A*The C = N vibrations cu. 1630 * 5 cm-’ appear as medium bands and are lowered by cu. 40 IR SPECTROSCOPY cm-’ as compared to the free oximes (- 1668 All the isolated compounds (I-XII; Table 1) cm-‘). The lowering of the VC = N vibration may exhibit IR absorptions characteristic of CQF, group be attributed to the stabilization of the C = N bond and are in conformity with those reported earlier by resonance with the non-bonding electron pair on fcr Iris(~nraAuaraqhn~~~andmany and its &idaxygen aCam aft&e amina graaq. Hawever, this type of lowering may also be related to the mass effect as ides.s,28 The IR frequencies due to fundamental has been observed earlier, in case of group IVB modes of vibrations of the anionic groups are listed Clernears? im”l &le^L. The appearance of a medium band in the region Absorptions associated with the various modes 915-925 cm-’ can be attributed to a N-O stretchof vibrations of the pseudohalide groups have been identified and indicate the nature of bonding to the ing vibration” while the Sb-0 stretching is tenatntimony atom. ne chalcogenate grouup, &&&y as&gn& a1 480-t 5 cm- I on ?ne ‘oasis 02 reported S&O frequencies in the corresponding NCX(X = S or 0) gives rise to three fundamental organoantimony oxinate derivatives.3’ modes of vibrations due to the Y(C=N), v(C - X)
258
PREM RAJ et al.
A noticeable feature of the IR spectra of all the isolated disubstituted compounds is the absence of the v,,, @b-C) absorption corresponding to the r-mode which should be located in the region 250-3OOcm-’ as reported by earlier workers.s*6 Thus on the basis of IR evidences coupled with their monomeric and non-conducting nature and in accordance with the structures of other organoantimony(V) compounds,6*7*17*29 the newly synthesised disubstituted derivatives (except for (VII)) can reasonably be assigned a trigonal bipyramidal structure with the anionic groups at the axial positions and C,F, groups occupying the equatorial positions. A trigonal bipyramidal structure containing an oxygen bridge (Sb-0-Sb) can be proposed for compound (VII).
Acknowledgement-The authors are thankful to the Head of the Chemistry Department, Lucknow University for providing the necessary Laboratory Facilities, the Director RSIC, Lucknow for obtaining IR spectra and Council of Scientific and Industrial Research, New Delhi for financial assistance (KS & AR).
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