427
Organometallics 1986, 5, 427-431
Synthesis of Diphenacyl Telluride and Related Substances Lars Engman Department of Organic Chemistry, Royal Institute of Technology, S- 100 44 Stockholm, Sweden Received July 2, 1985
Diphenacyl telluride (la) was prepared for the first time by a mild NazSz06reduction of diphenacyltellurium dichloride (2a) in a two-phase system. A series of related diorganyltellurium dichlorides (ArC(=O)CHz)zTeClz(2), prepared from tellurium tetrachloride and various acetylaromatic compounds, ArC(=O)CH3, were similarly reduced to tellurides. It was also possible to synthesize the unsymmetrical compounds 4-methoxyphenyl phenacyl telluride (14a)and 2-naphthyl phenacyl telluride (14b) by a similar procedure. The new materials, although unstable, could be handled and characterized without special precautions. Treatment of diphenacyl telluride with m-chloroperbenzoic acid or sodium sulfide caused decomposition with formation of acetophenone. Photolysis in dry benzene under nitrogen also resulted in formation of acetophenone. and the closely related a-telluro amide 6a" and the atelluro esters 7.1'712
Introduction An early as in 1901 Rohrbaech' reported an unsuccessful attempt to prepare diphenacyl telluride (la) by reduction of diphenacyltellurium dichloride (2a), which had been synthesized some years earlier by Rust.2 Morgan has later reported the separation of elemental tellurium upon attempted reduction of the three dichlorides 2 (R = Ph, Me, ~ - B u ) .These ~ compounds have recently received renewed
Ef"3' -
3
a X=YHPh b X=OEt
2
R=butyl
amyl
Results and Discussion The reaction of sodium telluride, NazTe, with 2 equiv of a phenacyl halide would constitute an obvious way to synthesize diphenacyl telluride (eq 1).
a 4=Me
2 FhCCH2X
+
NaZTe
-
U
IPhCCY2SiTe
* 2NaX
(1)
However, when sodium telluride, generated in aqueous solution, was allowed to interact a t ambient temperature with methanolic phenacyl bromide, only acetophenone (50%)and unreacted phenacyl bromide (39%) were isolated in addition to elemental tellurium. This result was quite expected in view of the known ability of NaHTe13 and lithium 2-thienyltell~rolate~~ to reductively remove a variety of electronegative a-substituents of carbonyl compounds. A similar disappointing results was obtained when sodium telluride and phenacyl bromide were brought together in dry dimethylformamide. Uemura has recently d e m o n ~ t r a t e dthe ' ~ successful introduction of tellurium, via a normal substitution reaction, into the a-position of propiophenone ethylene glycol ketal (eq 2). We similarly prepared bis[ (2-phenyl-1,3-dioxa-
interest as a result of new imaging applications of organotellurium compounds in p h ~ t o g r a p h y . ~In a typical non-silver amplification process, diphenacyltellurium dichloride was incorporated with a reducing agent and a catalytic amount of Pd(0) in a polymeric binder. Upon physical development (heating to 100-185 "C) a highdensity image of elemental tellurium was produced. Although never isolated, diphenacyl telluride was postulated as an unstable intermediate in this p r o ~ e s s . ~ Photodecomposition of diphenacyltellurium dichloride also failed to produce any detectable amount of diphenacyl telluride.6 Petragnani7 has reported similar difficulties in preparing unsymmetrical tellurides where one of the organic moieties is a phenacyl group. Thus, reduction of compounds 3 (R = Me, Et, Ph) with a variety of mild reducing agents afforded only decomposition products instead of the expected aryl phenacyl tellurides. The reported inherent instability of diphenacyl telluride and related tellurides is somewhat surprising in view of the successful isolation of the cyclic tellurides 4* and 59
n
0
0
?h2CLCHCh3 fir
+
NvtTePh
-
rPb%'%HCH3 Te Pb
(2)
lan-2-yl)methyl] telluride (8) in 60% yield from sodium telluride. It was our plan to mildly hydrolyze the ketal in order to obtain the desired diphenacyl telluride (la). However, all attempts to carry out this hydrolysis failed. When compound 8 was heated a t reflux in dry acetone containing a catalytic amount of p-toluenesulfonic acid (transketalization conditions), acetophenone ethylene
(1) Rohrbaech, E. Justus Liebigs Ann. Chem. 1901, 315, 9. (2) Rust, E. Ber. Dtsch. Chem. Ges. 1897, 30, 2828. (3) Morgan, G. T.; Elvins, 0. C. J . Chem. SOC.1925, 2625. (4) Gysling, H. J.; Lelental, M.; Mason, M. G.; Gerenser, L. J. J . Photogr. Sci. 1982, 30, 55 and references cited therein. ( 5 ) Lelental, M.; Gysling, H. J. J . Photogr. Sei. 1980, 28, 209. (6) Marsh, D. G.; Chu, J. Y. C.; Lewicki, J. W.; Weaver, J. L. J . Am. Chem. SOC.1976, 98, 8432. (7) Petragnani, N. Tetrahedron 1961, 12, 219. (8) Talbot, J. M.; Piette, J. L.; Renson, M. Bull. SOC.Chim. Fr. 1976,
(10) Engman, L.; Cava, M. P. J. Org. Chem. 1982, 47, 3946. (11) Balfe, M. P.; Chaplin, C. A.; Phillips, H. J . Chem. SOC.1938, 341. (12) Balfe. M. P.: Nandi. K. N. J . Chem. SOC.1941, 70. (13) Osuka, A,; Suzuki, H. Chem. Lett. 1983, 119. (14) Uemura, S.; Fukuzawa, S.; Yamauchi, T.; Hattori, K.; Mizutaki, S.; Tamaki, K. J. Chem. SOC.,Chem. Commun. 1984, 426.
294.
(9) Morgan, G. T.; Drew, H. D. K. J . Chem. SOC.1920, 1456.
0276-7333/86/2305-0427$01.50/0
0 RTeCH2COEl
We felt that it should also be possible to isolate diphenacyl telluride if only sufficiently mild reaction conditions could be found for its formation. In the following we report several different strategies toward this goal.
2 a R=Ph
?=Ph
5
I
Ll 3
3
(S&TeCH2CX
Q
1986 American Chemical Society
428 Organometallics, Vol. 5, No. 3, 1986
Engman
Table I. Synthesis of (RC(=O)CH2-)2Te ( 1 ) by Na2SzOaReduction of Compounds 2 [(RC(=O)CH,-)2TeC12] anal. calcd found compd R yield, 70 mp, "C C H C H la phenyl 53 78-79 52.52 3.86 52.53 3.89 4-methylphenyl 63 95 54.88 4.61 54.69 lb 4.65 4-bromophenyl 76 131-132 36.70 2.31 36.24 IC 2.29 44.20 4-chlorophenyl 63" 128 2.78 41.98 2.67 Id 4-methoxyphenyl 67-68 50.76 4.26 49.86 le 4.30 75 1-naphthyl 101 3.89 61.25 61.86 If 51 3.88 2-naphthyl 108-110 61.86 3.89 61.52 3.90 74" 1g 2.67 2-thienyl 93-94 38.14 38.01 2.64 lh 69" 67.45 9-anthryl 168 67.89 3.92 4.02 li 45" 52.72 P-benzo[b]furanyl 100-102 53.87 3.16 3.08 63" Ij Yield after chromatographic purification.
glycol ketal (9) was isolated in 76% yield together with elemental tellurium. Wet acetone containing a trace of sulfuric acid readily produced acetophenone and elemental tellurium. (2-Phenyl-1,3-dioxolan-2-yl)methyl 2-thienyl telluride (10) failed to give any phenacyl2-thienyl telluride when submitted to hydrolysis or transketalization conditions.
s
2
1:-
After these initial failures we turned our attention to the old problem of finding a mild reducing agent for the reduction of diphenacyltellurium dichloride to diphenacyl telluride. This type of reduction has been successfully executed in the selenium series using zinc in carbon disulfide'j or thiourea in acetone.16 In fact, the reduced species, e.g., diphenacyl selenide, are much more stable than the corresponding Se(1V) dichlorides. In organic tellurium chemistry diorganyltellurium dichlorides are commonly reduced to diorganyl tellurides employing reagents such as potassium disulfite, sodium hydrogen sulfite, sodium sulfite, or sodium sulfide.17 The reactions proceed in aqueous alkaline solution at ambientg or elevated18 temperature in the absence of an organic solvent. As already mentioned in the introduction, diphenacyltellurium dichloride is decomposed by using these reaction conditions. However, we felt that the intermediate diphenacyl telluride might survive if it could escape into an added organic solvent. This indeed proved to be the case. When diphenacyltellurium dichloride in dichloromethane was shaken in a separatory funnel with an aqueous solution containing 1.15 equiv of sodium disulfite, Na2S205,the organic phase slowly turned yellow with almost no separation of elemental tellurium. After 15 min of vigorous shaking the organic phase was separated, washed with water, and dried for 5-10 min over CaC1, (upon longer drying, the solution darkened considerably as elemental tellurium started to precipitate). Evaporation gave an oil which crystallized in yellow flakes (53% yield) from petroleum ether. The infrared spectrum of diphenacyl telluride showed a remarkably low carbonyl absorption, which appeared as a broad peak at 1640 cm-'. This lowering effect is less pronounced for its chalcogen analogues diphenacyl selenide (1660 and 1670 cm-') and diphenacyl sulfide (1690 cm-l). (15) Kunckell, F.; Zimmermann, R. Justus Liebigs Ann. Chem. 1901, 314,
281.
(16) Appa Rao, G. V. N.; Seshasayee,M.; Aravamudan, G.; Sowrirajan, S. Acta Cr3stallogr., Sect. C: Cryst. Struct. Commun. 1983,C39, 620. (17) Irgolic, K. J. "The Organic Chemistry of Tellurium"; Gordon and Breach New York, 1974; p 107. (18) Vernon, R. H. J . Chem. SOC.1920, 889.
Table I contains yields as well as physical and analytical data of a series of compounds prepared by this reduction procedure. The required diorganyltellurium dichlorides 2 were in all cases prepared from tellurium tetrachloride and an excess (2.2-4.0 equiv) of the appropriate acetylated aromatic compound RC(0)CH3 (eq 3).
As can be seen from Table I, the analytical data were not always satisfactory (*0.4%) for compounds 1. The microcrystalline materials were especially difficult to obtain in pure form even after several recrystallizations. Some derivatives (Table I) were passed through an SiO, column to remove acetylated aromatic compound ArC(0)CH3,which was the main byproduct in the reduction. Small amounts of elemental tellurium were always deposited on top of the column during this process. Bis(4-methoxyphenacyl)telluridewas not stable enough to survive drying (0.1 mmHg) at ambient temperature. Very soon the crystals started to darken with separation of elemental tellurium. All compounds 1 could be stored in a freezer (-15 "C) for several months without any visible decomposition. However, when exposed to daylight in the open air, considerable decomposition occurred within a few days. It would be of interest to investigate the stability of some derivatives where the carbon atom bonded to tellurium is secondary. Such compounds, as well as their corresponding Te,Te-dichlorides, were not known at the outset of this project. Therefore, we attempted to react some cycloalkanones with tellurium tetrachloride in order to obtain the 2:l condensation products 11-all possible candidates for further reduction. These reactions were carried out in refluxing carbon tetrachloride in the presence of some calcium oxide. Considerable amounts of a black insoluble material always were formed, but when the reaction of cyclohexanone was disrupted after 1 h, a 54% yield of 2-(trichlorotelluro)cyclohexanone(12a) could be isolated after filtration, evaporation, and recrystallization of the resulting oily product. When the reaction time was increased to 4 h, no crystalline material could be isolated. Cycloheptanone similarly afforded 2-(trichlorotelluro)cycloheptanone (12b) in 42% yield. C;yclooctanone yielded the desired 2:l-adduct bis(1-oxo-2-cyclooctyl)tellurium dichloride ( l l c ) in 40% yield after 4 h in refluxing CC1,. This compound was submitted to the usual Na2S205reduction in a two-phase system. The oily reduction product was very unstable and did not survive passage through an SiOz column. The quickly recorded NMR spectrum indicated the complete disappearance of the starting material and the formation of a new compound, presumably the desired bis(1-oxo-2-cyclooctyl) telluride ( 1 3). Due to its
Organometallics, VoE. 5, No. 3, 1986 429
Synthesis of Diphenacyl Telluride
11 0 n z $
b n.2 c n=3
'3
12 0
n=l b n=2
lability, this compound could not be further characterized. However, chlorination of a freshly prepared material with sulfuryl chloride in CCl, regenerated compound l l c in 54% yield. The stability of a C-Te bond next to a carbonyl is apparently decreased with increasing substitution on carbon. We also turned our attention to the problem of synthesizing aryl phenacyl tellurides 14. It was known from previous work that certain a-halo carbonyl compounds would undergo nucleophilic substitution reactions with tellurolate ions. The a-telluro amide 6a could be obtained from a-bromoacetanilide (15a) by careful treatment with sodium 2-thienyl tellurolate (eq 4).1° A successful sub-
-
''
'5
>TeW
-
?
+
arCH2CX 12 c X=NHPh b XzOEI
C tTTeCH2CX
+
NaBr
(4)
o X=NHPh 5 X=OEI
stitution reaction does also occur with ethyl bromoacetate (15b), if the product (6b) is isolated a t low conversion of the starting material. Attempts to increase the conversion resulted in formation of the debrominated ester. However, as soon as the hetero substituent X (NHPh, OEt) was replaced by an aryl group, only products of a-reduction were isolated.'O Therefore the nucleophilic substitution approach is not useful for the preparation of compounds 14. Petragnani' has reported the formation of bis(4-methoxyphenyl) ditelluride (16) when (4-methoxypheny1)phenacyltellurium dichloride (3a) was treated with either hydrated sodium sulfide, sodium bisulfite, zink in chloroform, or hydrazine sulfate. By the use of NazS20, and the two-phase system outlined above, we could readily reduce compound 3a to 4-methoxyphenyl phenacyl telluride (14a) in 72% yield. 2-Naphthyl phenacyl telluride (14b) was similarly obtained in 86% yield from compound 17. 0
ArTeCHZCPh 3 0 Ar=l-rnethorypbenyl b A r = 2-naphthyl
M e Oe T e -Te -0Me -
5
m; "I
u
Ch2CPh
r Both compounds 14 survived chromatographic purification, but recrystallization from ethanol always caused formation of the corresponding ditellurides ArTeTeAr. Compounds 3a and 17 were prepmed in excellent yields by the reaction of acetophenone with the corresponding aryltellurium trichloride in refluxing CCl, containing a small amount of acetic acid (eq 5). 0 PbCCH3 * A r T e C l j
% HOAc
0
Cl
PhCCHZTeAr
* HCI
c1
(5)
Finally, we have also carried out a few chemical reactions with diphenacyl telluride (la). By the use of photochemical tellurium extrusion it was our hope to convert telluride la into dibenzoylethane (eq 6). However, all such efforts IPhFCH2kTe
"3
i
i
v
PhZCH2CH2Wh
(6)
met with failure. When the photolysis was carried out in dry benzene for a prolonged time (18 h) a t 300 nm under
Nz, only acetophenone was isolated in addition to some unreacted starting material and precipitated elemental tellurium. Apparently, dimerization of the slowly formed phenacyl radicals cannot compete with hydrogen abstraction. When diphenacyl telluride was oxidized in methylene chloride with m-chloroperbenzoic acid, acetophenone was again formed as the only isolable product (84%). Some experiments with sodium sulfide nicely exemplify our hypothesis that diphenacyl telluride is incompatible with certain mild reducing agents, even in a two-phase system: when diphenacyltellurium dichloride (2a) was reduced in methylene chloride with aqueous Na& only acetophenone (98%)was isolated from the organic phase. Diphenacyl telluride (la), when submitted to the same reaction conditions, was also effectively decomposed to yield acetophenone (96% ). In summary we have shown that diphenacyl telluride and many related compounds can be synthesized by the mild Na2S206reduction of their corresponding Te,Te-dichlorides. These materials, although unstable, can be handled by using ordinary laboratory manipulations. Their significance in organic synthesis has yet to be explored. However, we feel that the weak carbon-tellurium bonds present in these compounds might be of value for carbon-carbon bond-forming reactions.
Experimental Section Melting points were uncorrected. NMR spectra were obtained at 200 MHz by using a Bruker WP 200 instrument. They were recorded in CDCl, solutions containing Me4%as internal standard and are reported in 6 units. IR and UV spectra were obtained by using a Perkin-Elmer 257 and a Perkin-Elmer Hitachi 200 instrument, respectively. The photochemical experiment was performed by using a Rayonet photochemical reactor. Elemental analyses were performed by Novo Microanalytical laboratory, Bagsvaerd, Denmark. All acetylated aromatic compounds used were commercially available. 2-(Bromomethyl)-2-phenyl-1,3dioxolane was prepared by ketalization of phenacyl bromide with ethylene glycol in toluene in the presence of p-toluenesulfonic acid: yield 76%; mp 61 "C (lit." 60-61 "C). Di-2-thienylditelluride,z0 (4-methoxyphenyl)tellurium trichloride,21 2naphthyltellurium trichloride,2zdiphenacyl sulfide,23and diphenacyl selenide15were all synthesized by literature methods. Phenacyl Bromide and Na2Te. Sodium telluride was prepared as previously describedz4from elemental tellurium (1.0 g, 7.8 mmol) and sodium borohydride (0.8 g) in water (15 mL). To this solution was added phenacyl bromide (3.10 g, 15.5 mmol) in MeOH (30 mL) dropwise. A black precipitate of elemental tellurium was immediately formed, and after workup, acetophenone (0.93g, 50%) and unreacted phenacyl bromide (1.20 g, 39%) were isolated. Bis[ (2-phenyl-1,3-dioxolan-2-yl)methyl] Telluride (8).
Finely pulverized elemental tellurium (0.30 g, 2.3 mmol) and sodium (0.22 g, 9.6 mmol) were stirred under Nzin dry DMF (15 mL) at 110 "C until all tellurium metal had disappeared (-15 min). To the resulting yellowish white inhomogeneous solution was added 2-(bromomethyl)-2-phenyl-1,3-dioxolane (1.15g, 4.7 mmol) in dry THF (10 mL). After 2.5 h at ambient temperature, the reaction mixture was poured into water and extracted with CHzClz.Chromatographic separation [SiO,; CHzC12/petroleum ether (bp 40-60 "C), 1/11from some unreacted starting material afforded 0.65 g (60%) of telluride 8: mp 67-68 "C (EtOH); IH NMR 6 3.14 (s, 2 H), 3.73-3.80 (several peaks, 2 H), 4.04-4.11 (several peaks, 2 H), 7.28-7.35 (several peaks, 3 H), 7.44-7.49 (several peaks, 2 H). Anal. Calcd for Cz0Hz2O4Te: C, 52.91; H, (19) Marquet, A.; Dvolaitzky, M.; Kagan, H. B.; Mamlok, L.; Quannes, C.; Jaques, J. Bull. SOC.Chim. Fr. 1961, 1822. (20) Engman, L.; Cava, M. P. Organometallics 1982, 1 , 470. (21) Morgan, G. T.; Kellett, R. E. J. Chem. SOC.1926, 1080. (22) Bergman, J.; Engman, L. Tetrahedron 1980, 36, 1275. (23) Tafel, J.; Mauritz, A. Ber. Dtsch. Chem. Ges. 1890, 3474. (24) Bergman, J.; Engman, L. Org. Prep. Proced. Int. 1978, I O , 289.
430
Organometallics, Vol. 5, No. 3, 1986
4.88. Found: C, 53.02; H, 4.97.
(2-Phenyl-1,3-dioxolan-2-yl)methyl 2-Thienyl Telluride
(IO). A solution of di-2-thienyl ditelluride (0.30 g, 0.71 mmol) in dry DMF (10 mL) under N2was heated at 110 "C with sodium (0.08 g, 3.4 mmol) until the red color faded. At this point 2(bromomethyl)-2-phenyl-l,3-dioxolane (0.35 g, 1.44 mmol) in dry T H F (4 mL) was added and the solution stirred at ambient temperature for 2.5 h. Workup as for telluride 8 and chromatography [petroleum ether (bp 40-60 "C)/CH,Cl,, 2/11 yielded 0.24 g (45%) of telluride 10: mp 37-38 "C (EtOH); 'H NMR 6 3.46 (s 2 H), 3.79-3.86 (several peaks, 2 H), 4.12-4.15 (several peaks, 2 H), 6.88 (dd, 1 H, J = 3.5 Hz and J = 5.2 Hz), 7.30-7.40 (several peaks, 5 H), 7.46-7.50 (several peaks 2 H). Anal. Calcd for C,,H1,02STe: C, 44.97; H, 3.77. Found: C, 44.91; H, 3.79. Attempted Transketalization of Telluride 8. Telluride 8 (0.20 g, 0.44 mmol) was heated at reflux in dry acetone (10 mL) containing p-toluenesulfonic acid (0.015 g). Black elemental tellurium was gradually precipitated, and after 2 h the reaction mixture was poured into an alkaline aqueous solution and ex(9) [0.11 tracted with ethyl ether. 2-Methyl-2-phenyl-l,3-dioxolane g (76%); mp 63 "C sublimation (lit." 60 "C)] was the only isolable product. Preparation of Diorganyltellurium Dichlorides 2. Typical Procedure: Diphenacyltellurium Dichloride (2a). TeC1, (5.0 g, 18.5 mmol) and acetophenone (9.0 g, 75.0 mmol) were heated at reflux for 8 h in dry CCl, (100 mL). Filtration from a small amount of elemental tellurium and evaporation of the solvent afforded a semisolid which crystallized upon trituration with diethyl ether. The weight of the precipitated diphenacyltellurium dichloride was 5.0 g (62%); mp 195-197 "C dec (CHC1,) (lit.6190 "C dec). All other compounds 2 were similarly prepared, the relative molar ratio of TeC1, and the acetylaromatic compound varying between 1:3 and 1:4. This ratio was lowered to L2.2 in the preparation of compounds 2c, 2e, 2g, 2i, and 2j. The yields and melting points (CH2C12/petroleumether) are reported in the following. All compounds seem to gradually decompose with heating, and it is sometimes difficult to determine the melting point [compound no., yield (%), mp ("C)]: 2b, 62, 213-15 dec (lit.2 200); 2c, 57, 204-205 dec; 2d, 93, 195-197 dec; 2e, 92, 197 dec; 2f, 84,205-207 dec (lit,' 203-204); 2g, 75,200-201 dec; 2h, 37, 180-182 dec; 2i, 34,265-267 dec when dropped on a Kofler bench; 2j, 33, 190-195 dec. Preparation of Diorganyl Tellurides 1. Typical Procedure: Diphenacyl Telluride ( l a ) . Diphenacyltellurium dichloride (1.0 g, 2.3 mmol) was dissolved in CH2C12(100 mL) and shaken vigorously in a separatory funnel for 15 min with an aqueous solution (50 mL) of NazS,05 (0.50 g, 2.6 mmol). The yellow organic phase was separated, washed once with water, and dried for 5-10 min over CaC1,. Evaporation and crystallization from petroleum ether (bp 4 H O "C) afforded 0.44 g of diphenacyl telluride (53%) as yellow flakes: mp 78-79 "C; IR 1640 cm-' (C=O); UV XmsrEtoH 204, 248 nm; 'H NMR 6 4.26 (s, 2 H), 7.44-7.58 (several peaks, 3 H), 7.95-8.00 (several peaks, 2 H). The other compounds 1 were similarly prepared. Some sparingly soluble Te,Te-dichlorides were added as solids to the separatory funnel. The insoluble material gradually disappeared as the reduced species was extracted into the organic phase. As indicated in Table I, some reduction products were passed through an SiO, column (CH2C12)to remove some acetylated aromatic compound, RC(=O)CH,. The reported yields were those obtained after this process and the following recrystallization (usually from CCl,/petroleum ether). 'H NMR data (6) of compounds lb-j: l b , 2.42 (5, 3 H), 4.23 (s, 2 H), 7.26 (d, 2 H), 7.87 (d, 2 H); IC, 4.19 (s, 2 H), 7.61 (d, 2 H), 7.83 (d, 2 H); Id, 4.21 (9, 2 H), 7.45 (d, 2 H), 7.91 (d, 2 H); le, 3.88 (s, 3 H), 4.22 (s, 2 H), 6 34 (d, 2 H), 7.96 (d, 2 H); If, 4.27 (s, 2 H), 7.42-7.59 (several peaks, 3 H), 7.81-7.90 (several peaks, 2 H), 7.98 (d, 1 H), 8.46 (d, 1 H); lg, 4.40 (s, 2 H), 7.54-7.61 (several peaks, 2 H), 7.85-8.05 (several peaks, 4 H), 8.53 (s, 1 H); l h , 4.19 (9, 2 H), 7.15 (dd, 1 H), 7.65 (dd, 1 H), 7.80 (dd, 1H); li, 4.23 (s, 2 H), 7.42-7.50 (several peaks, 4 H), 7.83-7.97 (several peaks, 4 H), 8.39 (s, 1 H); lj, 4.23 (s, 2 H), 7.32 (t, 1 H), 7.44-7.60 (several peaks, 2 H), 7.65 (s, 1 H), 7.72 (d, 1 H). Bis( 1-oxo-2-cyclooctyl)telluriumDichloride ( 1 IC). TeC1, (3.0 g, 11.1 mmol), cyclooctanone (4.0 g. 31.7 mmol), and CaO (0.80
Engman g) were heated at reflux in CC14 (50 mL) for 4 h. Filtration from 1.1g of dark insoluble material and evaporation of the solvent afforded an oil which crystallized upon trituration with diethyl ether/petroleum ether (bp 40-60 "C). After recrystallization from CCl,/petroleum ether, 2.0 g (40%) of compound l l c (mp 174 "C) was obtained: 'H NMR 6 1.47-1.65 (several peaks, 5 H), 1.88-1.98 (several peaks, 3 H), 2.46-2.71 (several peaks, 4 H), 4.49 (dd, 1 HI. Anal. Calcd for C16H26C1202Te: C, 42.81; H , 5.84. Found: C, 42.32; H , 5.80. When cyclohexanone was submitted to the same reaction conditions, the resulting oil did not afford a crystalline product. However, when the reaction was disrupted after 1 h, 2-(trichlorotel1uro)cyclohexanone(12a) was obtained in 54% yield; mp 140-143 "C dec (CCI,); 'H NMR 6 1.71-1.82 (several peaks, 2 H), 2.39-2.97 (several peaks, 6 H), 5.34 (dd, 1 H). Anal. Calcd for C6HQC130Te:C, 21.77; H, 2.74. Found: C, 21.70; H, 2.76. Cycloheptanone similarly yielded 2-(trichlorotelluro)cycloheptanone (12b) in 42% yield: mp 123-124 "C dec (CCl,/petroleum ether); 'H NMR 6 1.47-1.84 (several peaks, 3 H), 1.94-2.16 (several peaks, 2 H), 2.29-3.02 (several peaks, 5 H), 5.48 (dd, 1 H). Anal. Calcd for C7HI1Cl30Te:C, 24.36; H, 3.21. Found: C, 24.44; H, 3.27. Bis( 1-oxo-2-cyclooctyl)Telluride (13). Compound 1 IC (0.50 g, 1.1 mmol) was reduced in a two-phase system with Na,S,O, (0.22 g, 1.2 mmol) as described above. The yellow oil obtained did not survive passage through an SiO, column (CH,Cl,). The NMR spectrum of some freshly prepared crude material showed the complete disappearance of the signals a t 4.49 ppm of the starting material. Instead, there appeared a triplet (4.05 ppm) and a doublet of doublets (3.94 ppm), which we have assigned to the two possible diastereomers of compound 13. When the freshly prepared, crude reduction product was treated with S02Cl, (0.20 g) in CCl, (5 mL), compound l l c (0.27 g, 54%) precipitated. Carbethoxymethyl2-Thienyl Telluride (6b). To a solution of ethyl bromoacetate (1.0 g, 6.0 mmol) and di-2-thienyl ditelluride (0.126 g, 0.30 m o l ) in EtOH (40 mL) under N2 was added sodium borohydride (5% aqueous) dropwise until the red color faded. Another portion of ditelluride (0.125 g) was then added and the borohydride treatment repeated. After workup with CH,Cl,/water and chromatographic purification, 0.26 g (73%) carbethoxymethyl 2-thienyl telluride was isolated as a yellowish oil: 'H NMR 6 1.20 (t, 3 H), 3.44 (s, 2 H), 4.09 (q, 2 H), 6.98 (dd, 1H), 7.47-7.51 (several peaks, 2 H). At higher conversion of the bromo ester, di-2-thienyl ditelluride was the only isolable product. Phenacyl (4-Methoxypheny1)telluriumDichloride (3a). (4-Methoxyphenyl)tellurium trichloride (0.50 g, 1.46 mmol) and acetophenone (0.70 g, 5.8 mmol) were heated at reflux overnight in CCl, (10 mL) containing HOAc (0.5 mL). The homogeneous solution was then evaporated and the excess acetophenone pumped off. Trituration with ethyl ether afforded 0.60 g (96%) of phenacyl (4-methoxypheny1)tellurium dichloride, mp 136-137 "C (lit.7 136-137 "C). By an analogous procedure phenacyl 2-naphthyltellurium dichloride (17) was obtained in 91% yield: mp 147-148 "C (benzene/petroleum ether). Phenacyl 4-Methoxyphenyl Telluride (14a). Phenacyl(4methoxypheny1)tellurium dichloride (0.50 g) was submitted to two-phase reduction with Na2SzO5(0.23 g) as described above. After chromatography (CH,Cl,), 0.30 g (72%) of telluride 14a was isolated: mp 56-58 "C (EtOH); 'H NMR 6 3.80 (s, 3 H), 4.20 (s, 2 H), 6.74 (d, 2 H), 7.33-7.42 (several peaks, 2 H), 7.50 (m, 1 H), 7.66 (d, 2 H), 7.75-7.81 (several peaks, 2 H). Anal. Calcd for CI5H1,O2Te: C, 50.91; H , 3.93. Found: C, 50.89; H, 4.02. Phenacyl2-naphthyl telluride (14b) was similarly prepared in 86% yield: mp 53-55 "C (EtOH); 'H NMR 6 4.34 (s, 2 H), 7.32 (t, 2 H), 7.44-7.52 (several peaks, 4 H), 7.65-7.83 (several peaks, 5 H), 8.26 (s, 1 H). Anal. Calcd for C18HlhOTe: C, 57.82; H, 3.77. Found: C, 57.09; H, 3.78. Oxidation of Diphenacyl Telluride. T o a solution of diphenacyl telluride (0.20 g, 0.55 mmol) in CH,C12 at 0 "C was added 80% m-chloroperbenzoic acid (0.118 g, 0.55 mmol) in CH2C1, dropwise. After 2 h at 0 "C the solution was extracted with NaHCO, (5% aqueous). Acetophenone (0.11 g, 85%) was the only isolated product. Reduction of Diphenacyltellurium Dichloride (2a) and Diphenacyl Telluride ( l a ) with Na2S. Compound 2a (0.50
Organometallics 1986, 5, 431-435 g, 1.15 mmol) was dissolved in CH2C12and extracted with water containing Na2S.9H20 (1.0 g, 4.16 mmol). Acetophenone (0.27 g, 98%) was the only product contained in the organic phase. When diphenacyl telluride (la) was similarly treated, acetophenone was isolated in 96% yield.
Acknowledgment. Financial support by the Swedish Natural Science Research Council is gratefully acknowledged. Registry No. l a , 99766-21-9; l b , 99766-22-0; IC, 99766-23-1; Id, 99766-24-2; le, 99766-25-3; If, 99766-26-4; lg, 99766-27-5; l h , 99766-28-6; li, 99766-29-7; l j , 99766-30-0; 2a, 36362-83-1; 2b, 77017-00-6; 212, 99766-31-1; 2d, 99766-32-2; 2e, 66839-13-2; 2f, 99766-33-3; 2g, 77840-07-4; 2h, 73537-53-8; 2i, 99766-34-4; 2j,
43 1
99766-35-5; 3a, 67096-37-1; 6b, 99766-36-6; 8, 99766-37-7; 9, 3674-77-9; 10,99766-38-8; 1IC, 99766-39-9; 12a, 98797-28-5; 12b, 99766-40-2; 13 (isomer l),99766-41-3; 13 (isomer 2), 99766-42-4; 14a, 99766-43-5; 14b, 99766-44-6; 17, 99766-45-7; acetophenone, 98-86-2; 4-methylacetophenone, 122-00-9;4-bromoacetophenone, 99-90-1;4-chloroacetophenone, 99-91-2;4-methoxyacetophenone, 100-06-1; 1-(1-naphthyl)ethanone, 941-98-0; 1-(2-naphthyl)ethanone, 93-08-3; 1-(2-thienyl)ethanone, 88-15-3; 1-(9anthryl)ethanone, 784-04-3; 1-(2-benzo[b]furanyl)ethanone, 1646-26-0; phenacyl bromide, 70-11-1; 2-(bromomethyl)-2phenyl-l3-dioxolane, 341821-1; di-Zthienyl ditelluride, 66697-24-3; cyclooctanone, 502-49-8; cyclohexanone, 108-94-1; cycloheptanone, 502-42-1;ethyl bromoacetate, 105-36-2;(4-methoxypheny1)tellurium trichloride, 36309-68-9; 2-naphthyltellurium trichloride, 71578-23-9.
Kinetics and Mechanism of Pyrolysis of 1,3-Disilacyclobutane, 1,3-Dlmethyl-l,3-disilacyclobutane, and 1,1,3,3-Tetramethyl-I ,3-disilacyclobutane in the Gas Phase Norbert Auner Anorganisch-Chemisches Znstitut, Westfalische Wlihelms-Universltat, 4400 Miinster, Federal Republic of Germany
Iain M. T. Davidson," Sina Ijadi-Maghsoodi, and F. Timothy Lawrence Department of Chemistry, The University, Leicester LE1 7RH, Great Britain Received June 11, 1985
Kinetic d a t a a n d product analyses are reported for t h e pyrolysis of t h e title compounds. Pyrolysis mechanisms are discussed with reference t o recent developments in organosilicon chemistry.
Introduction There has been considerable interest in the kinetics and mechanism of pyrolysis of silacyclobutanes. While 1,ldimethylsilacyclobutane is well-known to undergo pyrolysis cleanly to give ethene and dimethylsilene, Me2Si=CH2, which dimerizes quantitatively to 1,1,3,3-tetramethyl-1,3disilacyclobutane (1),l the pyrolysis mechanisms of 1methylsilacyclobutane2 and silacy~lobutane~ are considerably more complex, with good evidence for the involvement of silylene intermediates. It has now been established that these complications arise partly because hydridosilenes isomerize reversibly to silylenes4aand partly because hydridosilacyclobutanes can decompose by a silylene-forming 1,2-hydrogen shift as well as by silene formation.6 Kinetic data for these hydridosilacyclobutanes have been reported.6 Less attention has been paid to disilacyclobutanes. Pyrolysis of 1 is known to be complex, yielding methane, C2 hydrocarbons, and some high molecular weight produ c t . ~ . ~Pyrolysis ,~ with added benzaldehyde at 700 "C gave (1) Flowers, M. C.; Gusel'nikov, L. E. J. Chem. SOC.B 1968,428,1396. (2) Conlin,.R. T.; Wood, D. L. J. Am. Chem. SOC.1981, 103, 1843. ( 3 ) Conlin, R. T.; Gill, R. S., J. Am. Chem. Soc. 1983, 105, 618. (4) Davidson, I. M. T.; Ijadi-Maghsoodi, S.; Barton, T. J.; Tillman, N. J . Chem. SOC.,Chem. Commun. 1984, 478. (5) Davidson, I. M. T.; Scampton, R. J. J. Organomet. Chem. 1984, 271, 249. (6) Davidson, I. M. T.; Fenton, A.; Ijadi-Maghsoodi, S.; Scampton, R. J.; Auner, N.; Grobe, J.; Tillman, N.; Barton, T. J. Organometallics 1984, 3, 1593. (7) Barton, T. J.; Marquardt, G.; Kilgour, J. A. J. Organomet. Chem. 1975, 85, 317.
evidence for the intermediacy of dimethylsilene,' as did pyrolysis above 600 "C with added methanol, although the product methoxytrimethylsilane might have resulted from direct reaction of 1 with methanol.8 The onset of pyrolysis of 1 was observed a t 600 "C, as opposed to 450 "C for 1,l-dimethylsilacyclobutane;dimethylsilene was not trapped below 600 "C, indicating that the observed thermal stability of 1 was not attributable to an equilibrium between l and dimethylsilene.8 Extensive pyrolysis of l and of 1,l-dimethylsilacyclobutanegave similar product^.^ Analogous results were obtained for the pyrolysis of 1,3dimethyl-1,3-disilacyclobutane(2), 1,3-disilacyclobutane (3), and their monosilacyclobutane c o u n t e r p a r t ~ . ~ J ~ We now report kinetic results and further product analysis for the pyrolysis of these three disilacyclobutanes, enabling some mechanistic conclusions to be drawn in the light of recent developments in organosilicon chemistry.
Experimental Section Product composition after extensive pyrolysis of 2 and 3 was determined a t Miinster from pyrolyses in a flow system a t ca. mmHg and 850 O C . Products were trapped at low temperature and analyzed by GC, NMR, IR,and GC/MS. Kinetic experiments and product analysis in the early stages of pyrolysis of 1,2, and 3 were carried out at Leicester by low-pressure pyrolysis (LPP)," (8) Nametkin, N. S.; Gusel'nikov, L. E.; Volpina, E. A.; Vdovin, V. M. Dokl. Akad. Nauk SSSR 1975, 220, 386 (English translation, p 81). (9) Auner, N.; Grobe, J. J. Organomet. Chem. 1980, 197, 13. (10) Auner, N.; Grobe, J. 2.Anorg. Allg. Chem. 1979, 459, 15. (11) Davidson, 1. M. T.; Ring, M. A. J. Chem. SOC.,Faraday Trans. 1 1980, 76, 1520.
0276-7333/86/2305-0431$01.50/0 @ 1986 American Chemical Society
