1748
Organometallics 1995,14, 1748-1755
Catalytic Cyclooligomerization of Thietane by Dirhenium Carbonyl Complexes Richard D. Adams* and Stephen B. Falloon Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208
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Received January 23, 1995@ The reactions of RedCO)dNCMe), 1,with thietane and 1,5,9-trithiacyclododecane,12S3, have yielded the compounds Re2(CO)g(SCH2CH,CH2), 2, Re2(CO)g(SCH2CH2CH2SCH,CH2CH2SCH2CH2CH2),3, and [Re2(C0)912($CH,CH2CH2SCH2CH2CH,SCH,CH2~Hd, 4, respectively. The molecular structures of 3 and 4 were established by single-crystal X-ray diffraction analyses. The structure of 3 is analogous to that of Rez(C0)lo but has a 12S3 ligand coordinated to one of the rhenium atoms in an equatorial coordination site. Compound 4 is similar to 3,but has two Re2(CO)gunits attached to two adjacent thioether sulfur atoms on a single molecule of 12S3. The reaction of 2 with thietane was found to yield 3 together with large amounts of the free molecule 12S3 by a cyclotrimerization process that is catalytic 2486, are formed in this in 2. Small amounts of 1,5,9,13,17,21-hexathiacyclotetracosane, catalytic reaction in the early stages, but its yield increases substantially in the later stages of the reaction. A kinetic study showed that the catalytic formation of 12S3 is first order in the concentration of 2, which is consistent with the catalysis being produced by 2 and not by mononuclear metal fragments. The PMe2Ph derivative of 2, Rez(C0)dPMezPh)(SCH2CH2CH2),5, was also prepared. It also catalyzes the cyclooligomerization of thietane to 12S3 and 2486,but the rate is lower and the selectivity for 12S3 is substantially lower than that of 2. Crystal data for 3: space group = P21/c,a = 14.545(4)A,b = 13.425(4)A, c = 14.682(3)A,p = 118.24(1)",2 = 4,3148 reflections, R = 0.035. For 4. '/2C~H14: space group = P21/n, a = 16.215(3)A,b = 9.836(4)A,c = 27.171(8)A,,8 = 99.71(2)",Z = 4,3742 reflections, R = 0.036.
Introduction The cleavage of carbon-sulfur bonds in sulfurcontaining heterocycles is an integral step in the important process of hydrodesulfurization of these ~ recent molecules for the purification of fossil f u e l ~ . l -In studies we have demonstrated the controlled opening of the saturated four-membered sulfur-containingheterocycles known as thietanes by nucleophiles when the thietane is coordinated as a bridging ligand in metal cluster c ~ m p l e x e s . ~We , ~ have found that thietanes, themselves, are also capable of producing ring-opening Abstract published in Advance ACS Abstracts, March 15, 1995. (1)(a)Angelici, R. J. Acc. Chem. Res. 1988,21,387.(b) Friend, C. M.; Roberts, J. T. Acc. Chem. Res. 1988,21,394.( c ) Markel, E. J.; Schrader, G. L.; Sauer, N. N.; Angelici, R. J. J . Catal. 1989,116,11. (d) Prins, R.; De Beer, V. H. H.; Somorjai, G. A. Catal. Rev. Sci. Eng. 1989,31,1. (e) Sauer, N. N.; Markel, E. J.; Schrader, G. L.; Angelici, R. J. J . Catal. 1989,117,295.(DKwart, H.; Schuit, G. C. A,; Gates, B. C. J. Catal. 1980, 61, 128. ( g ) Curtis, M. D.; Penner-Hahn, J. E.; Schwank, J.; Beralt, 0.; McCabe, D. J.; Thompson, L.; Waldo, G. Polyhedron 1988,7,2411. (h) Ogilvy, A. E.; Draganjac, M.; Rauchfuss, T. B.; Wilson, S. R. Organometallics 1988,7,1171. (i) Kaesz, H. D.; King, R. B.; Manuel, T. A,; Nichols, L. D.; Stone, F. G. A. J . Am. Chem. SOC. 1960, 82, 4749. (j) Luo, L.; Ogilvy, A. E.; Rauchfuss, T. B.; Rheingold, A. L.; Wilson, S. R. Organometallics 1991,10, 1002 and references therein. (2)( a ) Roberts, J. T.; Friend, C. M. J . A m . Chem. SOC.1987,109, 7899.(b) Roberts, J. T.; Friend, C. M . J. Am. Chem. SOC.1987,109, 3872. (3)Calhorda, M. J.; Hoffmann R.; Friend, C. M. J . Am. Chem. SOC. 1988,110,749. (4) ( a ) Adams R. D. J.Cluster. Scz. 1992,3,263.(b) Adams, R. D.; Pompeo, M. P. Organometallics 1992, 11, 1460. ( c ) Adams, R. D.; Belinski, J. A.; Pompeo, M. P. Organometallics 1991, 10 2539. (d) Adams, R. D.; Belinski, J. A., Pompeo, M. P. Organometallics 1992, 11, 3129.
additions upon coordinated thietanes, and in these cases ring-opening oligomerization processes Using I
the trirhenium complex Re3(CO)1oCu-SCH2CH,CH2)@-HI3we have recently developed the first example of a process that leads to the production of polythioether macrocycles catalytically, eq 1; 12S3 = 1,5,9-trithiacyclododecane, 16S4 = 1,5,9,13-tetrathiacyclohexadecane, and 2496 = 1,5,9,13,17,2 1-hexathiacyclotetracosane.7a Polythiaether macrocycles have recently attracted considerable interest for their potential to serve as ligands for the transition metals.8 H,C-CH,
@
0276-733319512314-1748$09.00/0
1 ) n
I
S-CH,
I
-
R e 3 cluster
catalyst
thietane
12S3, n=3
1654, n=4
2486, n=6
In this report our studies of the coordination of thietane and 12S3 to the dirhenium grouping Ren(5) Adams, R. D.; Cortopassi, J. E.; Falloon, S. B. Organometallics 1992,11, 3794.
1995 American Chemical Society
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Organometallics, Vol. 14, No. 4,1995 1749
Catalytic Cyclooligomerization of Thietane (C0)g are described. We have found that the complex Re2(CO)&3CH2CH2CH2)is also capable of producing 12S3 and 2486 catalytically. Interestingly, the selectivity for 12S3 formation is much higher than that found with the trirhenium complex Res(CO)&m SCH2CH2CH&-H)3. Unlike the trirhenium complex in which the thietane molecule is a bridging ligand, the thietane and polythioether macrocycles in these Re2( C 0 ) g complexes are coordinated to one metal atom only.
condenser, and a nitrogen inlet. A 26.0-mg amount of 12S3 (0.12 mmol) was added, and the resulting solution was stirred at reflux for 3 h. The volatiles were removed in uucuo, and the products were separated by TLC using a hexane/methylene chloride 3/1 solvent mixture to yield 69.5 mg of Rez(C0)gI
I
(SCH2CH2CH2SCH2CH,CH,SCH,CH,CH~), 3, 70%, yield, and 14.4 mg of [Re2(CO)g12(SCH2CH,CH2SCH2CH2CH2I
SCH2CH2CH2),4, 9% yield. IR vco for 3 (cm-I in hexane): 2102 (m),2039 (s), 2014 (m), 1988 (vs), 1977 (w), 1966 (SI, 1951 (w), 1933 (s). 'H NMR spectra for 3 (6 in CDC13): 3.01 (t, 4H, JH-H = 7.2 Hz), 2.73 (t, 4H, JH-H= 6.3 Hz), 2.59 (t, 4H, JH-H Experimental Section = 6.2 Hz), 2.00 (quintet, 4H, JH-H= 7.0 Hz), 1.80 (quintet, 2H, JH-H = 6.3 Hz). Anal. Calcd for 3: C, 25.54; H, 2.14. General Data. Unless otherwise indicated, all reactions Found: C, 25.36; H, 1.69. IR YCO for 4 (cm-' in CH2C12): 2102 were performed under a nitrogen atmosphere. Reagent grade (m), 2040 (s), 1989 (vs), 1962 (s), 1926 (4.'H NMR spectra solvents were stored over 4-A molecular sieves. Rez(C0)gfor 4 ( 6 in CDC13): 3.13 (t,br, 4H), 2.89 (t,br, 4H), 2.65 (t, br, (NCMe),g1, Re2(CO)a(NCMe)2,9and Re2(CO)g(PMe2Ph)9were 4H), 2.12 (quintet, br, 2H), 1.94 (quintet, br, 4H). Anal. Calcd prepared according to the published procedures. Rez(CO)lowas for 4: C, 22.04; H, 1.23. Found: C, 22.28; H, 1.27. purchased from Strem Chemicals Inc. and was used without Preparation of 13CO-Enriched Rez(C0)lo. A 152-mg further purification. Trimethylamine N-oxide dihydrate (Alamount of Re2(CO)s(MeCN)z(0.22 mmol) and 7 mL of octane drich) was dehydrated by using a Dean-Stark apparatus with were placed in a Parr high-pressure reaction unit. The reactor benzene as the solvent prior to use. 1,5,9-Trithiacyclododewas cooled in liquid nitrogen, and three freeze-pump-thaw cane, 12S3, was prepared as described in our previous report.7a cycles were performed. The reaction unit was then placed Thietane was purchased from Aldrich and was purified by under vacuum, and I3CO was introduced to the reaction unit vacuum distillation before use. All other reagents were to a pressure of 1atm at 25 "C. The unit was then sealed and purchased from Aldrich and were used as received. Infrared placed in an oil bath a t 150 "C for 24 h. After cooling, the spectra were recorded on a Nicolet 5DXB FTIR spectrophovolatiles were removed in uucuo, and the product was sepatometer. 'H NMR spectra were obtained on Bruker AM-300 rated by TLC using hexane solvent t o yield 134 mg of 13Cor AM-500 spectrometers operating at 300 or 500 MHz, enriched Rez(C0)lo (5). A mass spectrum of the product respectively. I3C NMR spectra were obtained on a Bruker AMshowed that the Rez(C0)lo was enriched with 13C0 to ap500 spectrometer operating at 125.76 MHz. Separations were proximately 40%. As expected, the I3C NMR spectrum in performed by TLC in air on Analtech 0.25" silica gel 60-A CDCl:, showed two broad CO resonances at 191.00 (8CO) and F254 plates. Elemental analyses were performed by Oneida 181.78 (2CO) ppm. This sample was used in the preparation Research Services, Whitesboro, NY. of the substituted derivatives listed below. Preparation of WO-Enriched 2. A 55.6-mg amount of Preparation of R~~(CO)O(SCH,CH,CH,), 2. A 52.0-mg 1 (40% enriched with I3CO)was converted to 2 (40% enriched amount of Re2(CO)g(NCMe),1, (0.078 mmol) was dissolved in with I3CO)in 63% yield by the procedure described above. The 30 mL of acetone in a 50-mL three-neck round bottom flask I3C NMR spectrum of this sample showed the following equipped with a stir bar, a reflux condenser, and a nitrogen resonances in CDC13 (ppm): at 25 "C, 199.87, 194.4 (br), inlet. A 25;uL amount of thietane (0.34 mmol) was added, and 191.97, 187.77, 185.3 (br); at -80 "C (in CDC13), 201.02 (2CO), the resulting solution was stirred at reflux for 2 h. The 195.52 (4CO), 193.57 (lCO), 188.9 (lCO), 185.66 (1CO). volatiles were removed in uucuo, and the products were Preparation of WO-Enriched 3. A 102-mg amount of separated by TLC using a hexanelmethylene chloride 211 1 (40% enriched with I3CO)was converted t o 3 (40% enriched solvent mixture t o yield 21.0 mg of Rez(CO)g(SCH,CH2CHd, with I3CO)in 70% yield by the procedure described above. A 2, 67% yield, and 22.2 mg of unreacted 1. IR YCO for 2 (cm-' 20.5-mg amount of 4 (40% enriched with I3CO) in 9% yield in hexane): 2104 (m), 2043 (s), 2017 (m), 1997 (vs), 1991 (vs), was also obtained. l3C NMR for 3 (in CDCl3, 6 in ppm): 1978 (w), 1970 (s), 1957 (w), 1935 (s). 'H NMR spectra for 2 201.35, 195.17 (br), 191.47, 188.08, 184.42 (br); at -80 "C, (6 in CDC13): 3.66 (t, 4H, JH-H = 7.7 Hz), 2.88 (quintet, 2H, 202.22 (2CO), 196.35 (4CO), 193.07 (lCO), 189.12 (lCO), JH-H= 7.7 Hz). The mass spectrum of 2 showed the parent 185.99 (1CO). I3C NMR for 4 (at 25 "C in CDC13, 6 in ppm): ion at mle = 698. Ions at 670, 586, 558, 530, and 502 are 201.24, 195.1 (br), 191.20, 187.79, 184.6 (br). attributed to the loss of 1, 4, 5, 6, and 7 CO ligands from the Catalytic Cyclooligomerizations. All catalytic reactions parent ion, respectively. Additional ions at 628, 600, and 572 were performed under nitrogen in 25-mL three-neck round are attributed to M+ - 3 CH2 groups and 1-3 CO ligands. bottom flasks equipped with a stir bar, a reflux condenser, and The loss of three CH2 groups is indicative of fragmentation of a nitrogen inlet, using preweighed amounts of recrystallized the thietane ligand. catalyst and thietane without solvent at the reflux temperaPreparation of R~~(CO)B(SCH,CH,CH,SCH~CH,CH,- ture of the thietane by heating in an oil bath. Unless indicated otherwise, the reaction apparatus was routinely wrapped I SCH,CH,CH2), 3, and [R~~(CO)B]~(SCH~CH,CH,SCH,-completely in aluminum foil to minimize possible effects of light on the reaction. Results of the experiments are listed in CH,CH,SCH,CH,bH,), 4. A 78.0-mg amount of 1 (0.12 Table 1. mmol) was dissolved in 30 mL of acetone in a 50-mL threeA typical treatment is as follows: a 6.0-mL amount of neck round bottom flask equipped with a stir bar, a reflux thietane (81 mmol) and a 15.0-mg amount of 2 was added to the 25-mL three-neck round bottom flask. The reaction (6)Adams R. D.; Pompeo, M. P. J.A m . Chem. SOC.1991,113,1619. mixture was heated to reflux and was a stirred under nitrogen (7j(a) Adams, R.D.; Falloon, S. B. J. A m . Chem. SOC.1994, 116, at this temperature for 24 h. After cooling, the excess thietane 10540. (b)Adams, R. D.; Cortopassi, J. E.; Falloon, S. B. J.Organomet. Chem. 1993,463, C5. was removed in uucuo. The resulting residue weighed 829 mg. (8)(a) Cooper, S. R. In Crown Compounds: Toward Future ApplicaA 'H NMR spectrum was taken of a portion of the residue. tions; Cooper, S. R., Ed.; VCH Publishers: New York, 1992;Chapter The spectrum showed two products only: 1,5,9-trithiacy15. (b)Cooper, S. R.; Rawle, S. C. Struct. Bonding 1990,72,l.(c) Blake,
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A. J.; Schrtider, M. Adu. Inorg. Chem. 1990, 35,1. (d) Cooper, S. R. Acc. Chem. Res. 1988,21, 141. (9)Koelle, U.J. Organomet. Chem. 1978,155,53
I
clododecane,'O SCH2CHzCH2SCH2CH2CH2SCH2CH2CH2, 12S3 ['H NMR (6 in CDC13): 2.67 (t, 12H, JH-H = 6.7 Hz),
1750 Organometallics, Vol. 14,No. 4, 1995
Adams and Falloon
Table 1. Results of the Catalytic Cyclooligomerization of Thietane by Dirhenium Complexes catalyst"
catalyst amt (mg)
reagent amt (mL)
products
ratio"
reactn time (h)
RedC0)in
20.0 17.0 15.0 15.0 16.8 12.0 8.0
4.0 4.0 6.0 6.0 6.0 6.0 4.0
12S3124S6 12S3124S6 12S3/24S6 12S3124S6 12S3124S6 12S3124S6 12S3/24S6
3.511 3.611 5.711 1.311 1.6/1 5.611 1.8/1
24 24 24 12 24 24 24
1
2 2 2" 3 5'
product amt (mg)
55 527 829 2070 849 530 153
TOF for 12S3' 0.3 3.0 6. I 3.8 4.0 6.0 1.9
'
'' All reactions were performed at the boiling point of thietane, 94 "C. Product ratios were determined by NMR. I TOF = moles of 12S3/moles of catalyst.hour. ['Performed in the presence of light, see Experimental Section. '' Mixture of isomers, see Experimental Section.
1.87 (4, 6H, JH-H = 6.7 Hz)] and 1,5,9,13,17,21-hexathiacyclotetracosane, 24S611 ['H NMR (6 in CDC13): 2.60 (t, 24H, JH-H = 7.2 Hz),1.84 (9, 12H, JH-H = 7.2 Hz)], which were present in a 5.7/1 ratio based on the NMR integration. The products were separated by TLC using a hexane/chloroform/ ethyl acetate 2/1/1 solvent mixture as the eluent to give two bands. The first band contained the macrocycle 12S3,lo and the second band contained the macrocycle 24S6.11 In general, the nonvolatile residues are completely soluble in methylene chloride, which indicates the near absence of polymer formation. The results of these tests are listed in Table l. Catalytic Cyclooligomerizationof Thietane by 2 LongTerm Test. Under a nitrogen atmosphere was added 6.0 mL (54.0 mmol) of thietane to a 25-mL three-neck round bottom flask equipped with a stir bar, a reflux condenser, a nitrogen inlet, and 15.0 mg (0.022 mmol) of 2. The thietane itself served as the solvent in this reaction. The solution was heated to reflux and was stirred under nitrogen at this temperature for 72 h. After cooling, the unreacted thietane was removed in uucuo. The resulting residue weighed 2.07 g. A 'H NMR spectrum was taken of a portion of the residue. The spectrum showed the presence of only two products, 12S3 and 2486, in a 1.3/1 ratio based on the NMR integration. Catalytic Cyclooligomerization by 2 in the Presence of Light. A 6.0-mL amount of thietane (81 mmol) was added to a 25-mL three-neck round bottom flask equipped with a stir bar, a reflux condenser, a nitrogen inlet, and 16.8 mg (0.024 mmol) of 2. The reaction mixture was heated t o reflux and was stirred under nitrogen at this temperature for 24 h with a 100-W lamp placed 6 in. from the reaction flask. After cooling, the excess thietane was removed in. uacuo. The resulting residue weighed 849 mg. A lH NMR spectrum was taken of a portion of the residue and showed that it consisted entirely of 12S3 and 2486 in a 1.55/1 ratio. Catalytic Cyclooligomerization of Thietane by 1. A 4.0-mL amount of thietane (54.0 mmol) was added to a 25mL three-neck round bottom flask equipped with a stir bar, a reflux condenser, a nitrogen inlet and 17.0 mg (0.026 mmol) of 1. The solution was heated to reflux and was stirred under nitrogen at this temperature for 24 h. After cooling, the excess thietane was removed in vucuo. The resulting residue weighed 527 mg. An NMR spectrum taken of a portion of the residue showed only two products, 12S3 and 2486, which were in a 3.611 ratio based on integration. Analysis of the Metal-Containing Species after Catalysis by Using 13CO-Enriched2 as the Catalyst. A 2.5mL amount of thietane (34.0 mmol) was added t o a 25-mL 3-neck round bottom flask equipped with a stir bar, a reflux condenser, a nitrogen inlet, and 20.0 mg (0.029 mmol) of 13CO-enriched 2. The reaction was heated to reflux and was stirred under nitrogen at this temperature for 1 h. After cooling, the excess thietane was removed in vacuo. The entire residue was dissolved in CDC13, and a 13CNMR spectrum was recorded. It showed the presence of only two metal-containing products, compounds 2 and 3 in a 2/1 ratio. There were no (10) Rawle, S. C.; Admans, G. A.; Cooper, S. R. J . Chem. Soc., Dalton Trans. 1988, 93. (11)Ochrymowycz, L. A.; Mak, C.-P.; Michna, J. D. J . Org. Chem. 1974, 14, 2079.
detectable amounts of any other metal carbonyl complexes present in these solutions as measured by 13C NMR spectroscopy in the CO region. A 47-mg amount of 12S3 was formed in this reaction.
Analysis of the Metal-Containing Species after Catalysis by Using 13C0 Enriched 3 as the Catalyst. A 5.0mL amount of thietane (68.0 mmol) was added to a 25-mL three-neck round bottom flask equipped with a stir bar, a reflux condenser, a nitrogen inlet, and 31.0 mg (0.037 mmol) of 3. The reaction mixture was heated to reflux and was stirred under nitrogen at this temperature for 1 h. After cooling, the excess thietane was removed in uucuo. The residue was dissolved in CDC13, and a 13CNMR spectrum was recorded. It showed the presence of only two metal-containing products, compounds 2 and 3 in a 1/1 ratio. In reactions that were allowed to proceed for 6 h, the ratio of 2/3was 2/1, the same as found when 2 was used as the catalyst. No detectable amounts of any other metal-carbonyl complexes were found in these solutions as determined by 13C NMR spectroscopy in the CO region. After 1 h of catalysis, 27 mg of 12S3 was isolated from this residue.
Analysis of the Metal-Containing Species after Catalysis by Using 13CO-Enriched1 as the Catalyst. A 4.0mL amount of thietane (54.0 mmol) was added to a 25-mL three-neck round bottom flask equipped with a stir bar, a reflux condenser, a nitrogen inlet, and 20.0 mg (0.037 mmol) of Re2(13CO)9(NCMe).The reaction mixture was heated to reflux and was stirred under nitrogen at this temperature for 1 h. After cooling, the excess thietane was removed in uucuo. The residue was dissolved in CDC13, and a 13CNMR spectrum was recorded. It showed the presence of only two metalcontaining products, compounds 2 and 3 in a 2/1 ratio. A 52mg amount of 1253 was subsequently isolated from this residue. There were no detectable amounts of any other metal-carbonyl complexes present in these solutions as determined by 13C NMR spectroscopy in the CO region. Study of the Dependence of the Rate of Catalysis on the Concentration of 2. In a typical procedure a 4.0-mL amount of thietane (54 mmol) was added to a 25-mL threeneck round bottom flask equipped with a stir bar, a reflux condenser, and a nitrogen inlet. An appropriate amount of the catalyst 2 was added under nitrogen. All measurements were made at 93.0 f 0.1 "C for a period of 1 h and were repeated in duplicate. At the end of 1 h, the excess thietane was removed in vacuo, and the amount of product was then determined by weighing the resulting residue and subtracting the preweighed weight of the catalyst. NMR spectra of the residues showed the presence of only one product, 12S3, and the remaining catalyst.
Preparation of Re~(CO)dSCH,CH,CH,)(PMe2Ph), 5. A 55.0-mg amount of Rez(CO)g(PMezPh)(0.072 mmol) was dissolved in 30 mL of acetone in a 50-mL three-neck round bottom flask equipped with a stir bar, a reflux condenser, and a nitrogen inlet. A 20-pL amount of thietane (0.27 mmol) and a 3.0-mg amount (0.041 mmol) of Me3NO was added, and the resulting solution was stirred at reflux for 12 h. The volatiles were removed in vacuo, and the products were separated by TLC using a hexane/acetone 3/1 solvent mixture to yield 20.1 5, 35% yield. IR vco mg of Rez(C0)9(SCH2CHzCHz)(PMezPh),
Catalytic Cyclooligomerization of Thietane
Organometallics, Vol. 14, No. 4, 1995 1751
Table 2. Crystallographic Data for Conmounds 3 and 4 ~
formula formula wt cryst syst lattice garam a (A) h (A) c
(A)
a (deg) P (deg) space group Z D,,~,(g/cm)~ p(Mo K a ) (cm-') temp ("C) 2t",, (deg) no. of obs used ( I > 3u(f)) no. of variables residuals: R , R," goodness of fit indicator max shift in final cycle largest peak in final diff map (e A-3) abs cor
RezS109C1KH18 846.93 monoclinic 14.545(4) 13.425(4) 14.682(3) 90.0 1 18.24(I ) 90.0 2526( 1) P21/C, NO. 14 4 2.23 98.7 20 48.0 3 148 290 0.035, 0.033 2.28 0.02 1.68 empirical
For each analysis the positions of all hydrogen atoms on the ligands were calculated by assuming idealized geometries and C-H = 0.95 A. Their contributions were added to the Re&Ol K C ? ~ H I X * I / ~ C & ~ structure factor calculations, but their positions were not I47 I .44 refined. monoclinic Compound 3 crystallized in the monoclinic crystal system. The space group P21lc was established on the basis of the 16.215(3) patterns of systematic absences observed during the collection 9.836(4) 27.171(8) of data. The structure was solved by a combination of direct 90.0 methods (MITHRIL) and difference Fourier syntheses. All 99.71(2) non-hydrogen atoms were refined with anisotropic thermal 90.0 parameters. 4271(2) Compound 4 crystallized in the monoclinic crystal system. P21l1-1,No. 14 The space group P21ln was established on the basis of the 4 patterns of systematic absences observed during the collection 2.36 of data. The structure was solved by a combination of direct 115.2 methods (MITHRIL) and difference Fourier syntheses. All 20 45.0 non-hydrogen atoms were refined with anisotropic thermal 3742 parameters. In the final stages of the analysis a molecule of 470 hexane was located in the lattice positioned about a center of 0.036, 0.037 symmetry. The carbon atoms were refined partially on their 1.81 positional parameters using an isotropic thermal parameter 0.01 and were subsequently fixed for the final cycles of refinement 1.11 when they failed to converge. 4
3
-
empirical
Results
for 5 (cm-' in CHzClZ): 2068 (w), 2011 (m), 1965 (vs), 1940 (m), 1906 (m). 'H NMR spectra for 5 (6 in CDC13) indicate that this compound exists in solution as a mixture of two isomers which could not be separated by TLC: major isomer, 7.46 (m, 5H), 3.59 (t, 4H, JH-H= 7.7 Hz), 2.77 (quintet, 2H, JH-H = 7.7 Hz), 2.14 (d, 6H, JP-H = 8.6 Hz); minor isomer, 7.46 (m, 5H), 3.57 (t, 4H, JH-H = 7.7 Hz), 2.77 (quintet, 2H, JH-H= 7.7 Hz), 1.99 (d, 6H, JP-H = 8.4 Hz). The mass spectrum of 5 showed the parent ion at mle = 808 and ions corresponding to the loss of the thietane ligand and each of 7 CO ligands. Catalytic Cyclooligomerization of Thietane by 5. A 4.0-mL amount of thietane (54.0 mmol) was added to a 25mL three-neck round bottom flask equipped with a stir bar, reflux condenser, a nitrogen inlet, and an 8.0-mg amount (0,010mmol) of 5. The solution was heated to reflux and was stirred under nitrogen at this temperature for 24 h. After cooling, the excess thietane was removed in uucuo. The resulting residue weighed 153 mg. A lH NMR spectrum taken of a portion of the residue showed the presence of only two products, 12S3 and 2456 in a 1.78/1 ratio. Crystallographic Analyses. Colorless crystals of 3 and 4 suitable for X-ray diffraction analysis were grown from solution in a 211 CHzClfiexane solvent mixture by slow evaporation of solvent at 25 "C. The crystals used in intensity measurements were mounted in thin-walled glass capillaries. Diffraction measurements were made on a Rigaku AFC6S fully automated four-circle diffractometer using graphite-monochromated Mo Ka radiation. The unit cells were determined and refined from 15 randomly selected reflections obtained by using the AFC6S automatic search, center, index, and least-squares routines. Crystal data, data collection parameters, and results of these analyses are listed in Table 2. All data processing was performed on a Digital Equipment Corp. VAXstation 3520 computer by using the TEXSAN structure-solving program library obtained from the Molecular Structure Corp., The Woodlands, TX. Neutral atom scattering factors were calculated by the standard procedures. lZa Anomalous dispersion corrections were applied to all non-hydrogen atoms.lZb Lorentzpolarization (Lp) and absorption corrections were applied in each analysis. Full matrix least-squares refinements minimized the function &iw(lFOj - lFc1)2,where w = llu(F)2, utF) = u(F,2)12Fo,and u(Fo2)= [u(Z,,,)2 + (0.02Z,,t)211'z/Lp.
The compound Re2(CO)g(SCH2CH2CH2), 2, has been obtained in 67% yield from the reaction of 1 with thietane. Compound 2 is spectroscopically similar to the related compound Re2(C0)9(SCH2CMe2CH2),6, which we have prepared and structurally characterized previ0us1y.l~Compound 6 contains a 3,3-dimethylthietane ligand terminally coordinated in an equatorial site on one of the two metal atoms. Compound 2 is believed to be structurally similar to 6.
o(
S
t/
/
-i-Y2
6
The 13CNMR spectrum of 2 in the CO region was also obtained. The spectrum at 25 "C in CDC13 exhibits five resonances: 199.87,194.4 (br), 191.97,187.77,and 185.3 (br). Two of these are very broad. This broadening appears to be due to partial coupling to the neighboring rhenium nuclei due to incomplete quadrupolar relaxation effects.l* At -80 "C the quadrupole relaxation has removed nearly all of the coupling, and five relatively sharp resonances with relative intensities based on the proposed structure are observed: 201.02 (2C), 195.52 (4C), 193.57 (lC), 188.9 (10, and 185.66 (10. This spectrum is consistent with the proposed structure 2 assuming that conformational rotations about the ReRe bond are rapid on the NMR time scale and thus (12) (a) International Tables for X-ray Crystallography; Kynoch Press: Birmingham, England, 1975;Vol. IV, Table 2 2 B , pp 99-101; (b)Table 2.3.1,pp 149-150. (13)Adams, R. D.;Belinski, J. A,; Schierlmann, J. J. Am. Chem. SOC.1991, 113, 9004. (14)Todd, L. J.; Wilkinson, J. R. J . Organomet. Chem. 1974, 80, C31.
1752 Organometallics, Vol. 14,No. 4,1995
Adams and Falloon
to one of the rhenium atoms in an equatorial site. The equatorially positioned ligands on the two metal atoms adopted a staggered rotation conformation similar to that found in Re2(CO)1ol5and 6.13 The Re-Re distance in 3,3.0554(8)A, is similar to that found in Rez(CO)lo, 3.041(1) A,15 and in 6, 3.0422(8) A.g The 12S3 ligand exhibits the same conformation as that found for the free molecule in the solid state and in a number of its coordination complexes.16 The coordinated sulfur atom is pyramidal, so all of the hydrogen atoms on the ligand are inequivalent according t o the solid state structure, but the lH NMR spectrum of the complex in solution at I Figure 1. An ORTEP diagram of Re2(CO)@CH225 "C is very simple L3.01 (t,4H, JH-H = 7.2 Hz), 2.73 (t, 4H, JH-H= 6.3 Hz), 2.59 (t,4H, JH-H = 6.2 Hz), 2.00 CHzCH2SCH2CH2CH,SCH2CH2bH2)(3) showing 50% (quintet, 4H, JH-H = 7.0 Hz), 1.80 (quintet, 2H, JH-H = probability thermal ellipsoids. Selected interatomic dis6.3 Hz)l and consistent with a CzUsymmetry. This can tances (A) and angles ("1 are as follows: Re(lkRe(2) = be explained by a combination of rapid conformational 3.0554(8), Re(l)-S(l) = 2.498(3), S(l)-C(l) = 1.81(1), S(l)-C(9) = 1.82(1),S(2)-C(3) = 1.77(1),S(2)-C(4) = 1.80rearrangements in the ring and inversions in configu(11, S(3)-C(6) = 1.81(1),S(3)-C(7) = 1.80(1),Re(21-Reration at the coordinated sulfur atom.17 The 13C NMR (l)-S(l) = 87.96(6),C(l)-S(l)-C(9) = 100.9(5). spectrum of 3 in the CO region at 25 "C is similar to that of 2: L201.35, 195.17 (br), 191.47, 188.08, and Table 3. Positional Parameters and B(eq) for 3 184.42 (br)] in which two of the resonances are broadatom X v B(es) ened due to incomplete quadrupole relaxation of the 3.07(2) 0.35418(4) 0.015 13(3) 0.67006(3) At -80 "C sharp coupling to the rhenium nu~1ei.l~ 3.90(2) 0.16344(3) 0.68637(3) 0.20329(4) of the resonances: resonances were observed for all 3.6(1) 0.1364(2) 0.7684( 2) 0.4976(2) 202.22 (2CO), 196.35 (4CO), 193.07 (lCO), 189.12(lCO), 5.2( I ) 0.0196(2) 0.9155(3) 0.8523(3) 185.99 (1CO). 4.9( I ) 0.2256(2) 0.7735(3) 0.6850(2) 6.0(4) -0.0632(5) 0.3855(7) 0.8841(6) An ORTEP diagram of the molecular structure of 4 6.3(4) 0.1 156(6) 0.2972(7) 0.4590(6) is shown in Figure 2. Final atomic positional param6.1(4) -0.1256(6) 0.55 19(6) 0.1699(7) eters are listed in Table 4. This molecule is very similar 5.1(3) -0.1274(5) 0.51 lO(6) 0.6559(6) to that of 3 except that it has two Rez(C0)g groups 6.4(4) -0.0207(6) 0.1135(7) 0.7483(7) 8.9(5) 0.1 134(8) 0.4553(7) 0.0563(8) coordinated to one 12S3 ring. The Rez(C0)ggroups are 8.7(6) 0.3 169(7) 0.0581(9) 0.7077(8) coordinated to different sulfur atoms. The Re-Re 6.3(4) 0.3179(6) 0.3128(7) 0.6118(6) distances, Re(l)-Re(2) = 3.049(1) and Re(3)-Re(4) = 6.4(4) 0.1825(6) 0.9159(6) 0.3758(8) 3.052(1), are quite similar to those found in 3, 6, and 4.0(4) 0.0665(7) 0.8615(7) 0.6083(9) Rez(C0)lo. The conformation of the 12S3 ligand is again 5.3(5) 0.1275(9) 0.699( 1) 0.9316(8) 0.066( 1) 5.5(5) 0.799( I ) 0.9931(8) the same as that found in the free molecule 3 and other 0.1290(8) 4.6(5) 0.92 I ( 1) 0.909 1(8) related 12S3 complexes. The ability of 12S3 t o coordi5.9(6) 0.122(1) 0.947( I ) 0.823( 1) nate more than one sulfur atom to separate metal units 5.9(6) 0.854( 1) 0.1 15( I ) 0.7 159(9) has been observed previously. Indeed, in the complex 4.4(5) 0.5907(7) 0.6510(9) 0.1741(8) 4.1(4) 0.1 187(7) 0.6347(8) 0.5899(9) [Ag(12S3)I(CF3S03).NCMe,each sulfir atom of the 12533 4.1(4) 0.1883(7) 0.6884(8) 0.5505(9) ligand is coordinated to a silver atom in the solid 3.9(4) 0.8059(8) -0.0352(7) 0.3741(9) state.lGcIn the solid state structure the two metal4.1(5) 0.0806(7) 0.317( 1) 0.5365(9) coordinated sulfur atoms are conformationally different 4.0(4) -0.0741(8) 0.5970(8) 0.237 l(9) and thus inequivalent; however, the lH NMR spectrum -0.0744(7) 3.4(4) 0.6607(7) 0.45 16(8) 0.049( 1) 5.0(6) 0.7252(9) 0.145( I ) of 4 at 25 "C indicates that the structure has an overall 0.107( 1) 0.132( I ) 5.8(6) 0.539( 1) CzUsymmetry, [d = 3.13 (t,br, 4H), 2.89 (t,br, 4H), 2.65 0.1 12(1) 0.259( I ) 5.7(6) 0.701( 1) (t,br, 4H), 2.12 (quintet, br, 2H), 1.94 (quintet, br, 4H) 0.271( 1) 0.2606(8) 435) 0.6399(8) ppml, indicating that conformational averaging and 0.1782(8) 4.35) 0.8314(9) 0.3 I2( 1) inversions of configuration a t the pyramidally coordinated sulfur atoms are rapid on the NMR time scale. average the four equatorially positioned CO groups on The I3C NMR for 4 in the CO region can be interpreted the Re(C0)5 grouping. I in terms of two equivalent Rez(CO)g groups although Two products, Rez(CO)9(SCH2CH2CH2SCH2CH2- the CO ligands within a given Re2(C0)9 group are not v averaged: 201.24 (2CO),195.1(br) (4C0),191.20(lCO), CHzSCH2CH2CHz)3, 70% yield, and [Re2(C0)932187.79 (lCO), 184.6 (br) (1CO) ppm. Broadening in I I (SCH2CHzCH,SCH2CH2CH,SCH,CH,CH2), 4, 9% some of the resonances is believed to be due to incomyield, were obtained when equimolar amounts of 1 and (15) Churchill, M. R.; Amoh, K. N.; Wasserman, H. J. Inorg. Chem. 12S3 were allowed to react in an acetone solution at 1981,20,1609. reflux. Both of these products were characterized by (16) ( a ) Rawle, S. C.; Admans, G. A.; Cooper, S. R. J . Chem. Soc., Dalton Trans. 1988,93. (b) Edwards, A. J.; Johnson, B. F. G.; Khan, combination of IR, lH NMR, 13C NMR, and singleF. K.; Lewis, J.; Raithby, P. R. J . Organomet. Chem. 1992,426,C44. crystal X-ray diffraction analyses. A n ORTEP diagram (c) Blower, P. 3.; Clarkson, J. A,; Rawle, S. C.; Hartman, J . R.; Wolf, of the molecular stucture of 3 is shown in Figure 1.Final R. E.; Yagbasan, R.; Bott. S. G.; Cooper. S. R. J . Chem. Soc., Dalton Trans. 1989,28,4040. atomic positional parameters are listed in Table 3. The ( 1 7 ) ( a )Abel, E. W.; Bharagara, S. K. Orrell, K. G. Prog. Inorg. molecule is structurally similar to compound 6, with a Chem. 1984,32, 1. (b) Wu,H.; Lucas, C. R. Inorg. Chem. 1992,31, 12S3 ligand coordinated through one of its sulfur atoms 2354.
Catalytic Cyclooligomerization of Thietane
Organometallics, Vol. 14, No. 4, 1995 1753 Table 4. Positional Parameters and B(ed for 4
024
012
7
Figure 2. An ORTEP diagram of [Re2(C0)&(SCHZ-
CHZCH,SCHzCH2CH2SCH,CHZhH~), (4) showing 50% probability thermal ellipsoids. Selected interatomic distances (A) and angles (") are as follows: Re(l)-Re(2) = 3.049(1), Re(3)-Re(4) = 3.052(1), Re(l)-S(l) = 2.499(4), Re(3)-S(3) = 2.501(4), S(l)-C(l) = 1.80(1), S(l)-C(9) = 1.82(1), S(2)-C(6) = 1.81(2),S(2)-C(7) = 1.77(2), S(3)C(3) = 1.83(2), S(3)-C(4) = 1.86(2), Re(Z)-Re(l) - S(1) = 88.1(1), Re(4)-Re(3)-S(3) = 90.1(1), C(l)-S(l)-C(9) = 102.0(8),C(3)-S(3)-C(4) = 99.7(9). plete quadrupole relaxation of the coupling t o the rhenium nuclei.14 Catalytic Cyclooligomerizationof Thietane. We have shown previously that thietane can be cyclooligomerized catalytically by the trirhenium complex m
Re3(CO)&-SCH2CH2CHz)@-H)3, 7.7a In those reactions the cyclooligomers 12S3 and 2486 were the two principal products and the amount of 2496 was substantially greater than that of the 12S3. Accordingly, we have also investigated the ability of Rez(C0)lo and and 6 to produce cyclooligomerization compounds 1,2,3, of thietane. As in the previous studies, these reactions were performed in pure thietane solutions at the reflux temperature of thietane (94 "C). All of these compounds produce cyclooligomerization of thietane catalytically to yield 12S3 and 2486, see Table 1. No other cyclooligomers were formed. The catalytic activity of Rez(C0)lo is much less than that of 1, 2, 3,or 6. Compounds 2 and 3 are the most active and have virtually the same activity and selectivity for 1283 formation. In fact, 2 is only slightly less active than 7.7a A major difference between 2 and 7 is in the relative amounts of the 12S3 and 2486 that are formed. With 2,12S3 was by far the major product after a 24-h period, whereas with 7,2486 was by far the major product. The 12S3/24S6 ratios were 5.711 and 1/35 for 2 and 7,7arespectively. With 2 it was observed that the relative amount of 2486 increases as the reaction progresses, but even after 72 h, the amount of 12S3 was still greater than that of 2486, see Table 1. The activity of 1 was similar to that of 2, but the amount of 2486 was significantly higher than that obtained from 2 in the first 24 h. The activity of Rez(C0)lo is only about l/zo that of 2. We have also
0.13252(4) 0.2662 l(4) -0.35 134(4) -0.30629(4) 0.0766(2) -0.0050(3) -0.1997(3) -0.0007(9) 0.0259(9) 0.21 16(8) 0.2634(8) 0.233(1) 0.3969(8) 0.396( 1) 0.2727(8) 0.1146(8) -0.330( 1) -0.405( 1) -0.5355(7) -0.3703(8) -0.1978(9) -0.457( 1) -0.4309( 8) -0.264( I ) -0.1579(8) -0.036(1) -0.078( I ) -0.173( 1j -0.181( I ) -0.176( 1) -0.104( 1) 0.064(1) 0.058(1) 0.093( I ) 0.050(1) 0.065( I ) 0.183( 1) 0.217( 1) 0.243 I ) 0.350(1) 0.349( 1) 0.271( 1) 0.170( I ) -0.336( I ) -0.385( 1) -0.467( 1) -0.363( 1) -0.240( 1) -0.402( I ) -0.385(1) -0.280( 1) -0.210( I ) 0.029 I 0.0764 0.04 I8
-
0.15792(6) 0.17362(8) -0.14972(7) 0.11810(7) -0.0489(4) -0.4588(4) -0.1949(4) 0.152( I ) 0.343( I ) 0.4 IO( 1) -0.030( I ) 0.486(2) 0.191( I ) 0.183(2) -0.144( 1) 0.145(2) -0.268( 1) -0.4 I6( I ) -0.086( I ) 0.029(2) 0.192(I ) 0.252(I ) 0.01 l(2) 0.369( 1) -0.052( I ) -0.035(1) -0.150(2) -0.148(2) -0.38 l(2) -0.45 l(2) -0.406( 2) -0.332(2) -0.192( 1) -0.198(1) 0.152(2) 0.275(2) 0.316(2) 0.040(2j 0.372(2) 0.189(2) 0.180(2) -0.027(2) 0.156(2) -0.229(2 j -0.318(2) -0.1 I l(2) -0.040(2) 0.165(2) 0.203(2) 0.05 l(2) 0.274(2) 0.01 l(2) 0.0448 0.0849 0.0194
0.38266(2) 0.3 1626(3) 0.35174(3) 0.40645(3) 0.3350(2) 0.4 198(2) 0.351 l(2) 0.4492(5) 0.3019(5) 0.4370(5) 0.4476(4) 0.3 186(7) 0.4144(5) 0.2480(5) 0.3259(6) 0.2298(5) 0.4608(5) 0.2956(6) 0.3556(6) 0.2566(5) 0.3275(5) 0.3362(6) 0.4744(6) 0.4731(6) 0.4657(4) 0.3239(6) 0.293 l(5j 0.2907(5) 0.3498( 8) 0.400( 1j 0.4366(7) 0.4494(6) 0.4241(6) 0.3749(6) 0.4236(7) 0.3307(7) 0.4163(7) 0.4243(6) 0.3 177(8j 0.3791(7) 0.2749(8) 0.3230(6) 0.2609(7) 0.42 12(8) 0.3 169(7) 0.3545(7) 0.2920(7) 0.3567(7) 0.3621(8) 0.4500(7) 0.4475(7) 0.4445(6) 0.0171 0.0626 0.1058
4.05(3) 4.94(4) 4.45(3) 4.64(3)
prepared a phosphine derivative of 2, Rez(CO)s(PMezPh)(SCH2CH2CH2),6, and tested it for its ability to produce cyclooligomerizations of thietane. The activity of 6 is lower than that of 2 or 3,and its selectivity for 12S3 is also lower, but it is significantly more active than Rez(C0)lo. To obtain more information about the mechanism a kinetic study of the rate of formation of 12S3 as a function of the concentration of 2 was performed. A plot of these results is shown in Figure 3. As can be seen, the plot is linear in the concentration of 2. This indicates that the catalysis is being produced by 2 and not by mononuclear fragments derived from 2.18 (18)Laine, R. M.J . Mol. Cutul. 1982,14, 137.(b)Hilal, H. S.;Jondi, W.; Khalaf, S.; Abu-Halawa, R. J . Orgunomet. Chem. 1993, 452, 161. ( c ) Hilal, H.S.; Khalaf, S.; Jondi, W. J . Orgunomet. Chem. 1993,452, 167.
Adams and Falloon
1754 Organometallics, Vol. 14, No. 4, 1995
zE
Scheme 1
L-.
31
f
/0
10
20
Concentration of 2 mollL ( x l O - 4 ) Figure 3. A plot of the rate of formation of 12S3 as a function of the concentration of 2. Rates were determined after the first 1 h of reaction time.
I
I
Catalytically active solutions obtained from 2 were examined by I3C NMR spectroscopy. For this purpose compound 2 was prepared in a form enriched to 40% with l3C in the CO ligands. Catalysis was performed for a period of 1 h, and after removal of all volatile components a 13C NMR spectrum was recorded of the entire residue, It showed the presence of only two metal-containing products, compounds 2 and 3 in a 211 ratio. A 47-mg amount of 12S3 was also obtained in this reaction. In a similar manner the catalysis produced by 3 was also examined by I3C NMR spectroscopy using a sample of 3 enriched by 40% with 13C0. After 1 h an NMR spectrum of the residue showed the presence of only the two complexes 2 and 3 in a 111ratio. After 6 h this ratio had changed to 211. Similarly, a test of the catalysis of 1 was performed using 13COenriched 1. At the end of the catalysis, a 13C NMR spectrum of the residue showed the presence of only two metal-containing products, compounds 2 and 3,in a 211 ratio. A proposed mechanism for the catalytic cyclotrimerization of thietane by 2 and 3 is shown in Scheme 1. It is proposed that the coordination of the thietane molecule to one of the rhenium atoms in 2 activates it toward nucleophilic addition of an uncoordinated thietane molecule at one of the methylene groups bonded to the coordinated sulfur atom. The activation occurs by the removal of some of the electron density from the sulfur atom by the metal atom. This should lead t o the formation of a partial positive charge at the sulfur atom and to a lesser extent at the neighboring carbon atoms. This is apparently sufficient to promote a nucleophilic addition at the neighboring a-carbon atoms of the coordinated thietane, by the sulfur atom of an uncoordinated thietane molecule, resulting in the cleavage of the carbon-sulfur bond and opening the four-membered ring, step A.4b This will lead to a zwitterionic intermediate, such as 8, containing a negatively charged terminally coordinated thiolate grouping and a positively charged thietanium group linked to the thiolate sulfur atom via a trimethylene tether. Similar ringopening reactions have been observed for thietane ligands in bridging coordination mode^.^-^ The dangling thietanium group should be sufficiently reactive to react with uncoordinated thietane molecules spontaneously by ring-opening additions, step B. The cationic ring-opening polymerization of thietanes via thietanium intermediates is well-kn~wn.'~ Polymerization
3
\/
9 could ensue, but instead a ring-opening cyclization occurs afier the addition of a second molecule of thietane by an attack of the coordinated thiolato sulfur atom at one of the a-carbon atoms of the thietanium ring, step C, which leads to the 12S3 complex 3. The tendency toward cyclization in these complexes may be enhanced by the zwitterionic nature of the intermediate 9, which should tend to keep the head and tail of the growing chain proximate to one another. Catalyst 2 can be regenerated from 3 simply by the substitution of the 12S3 ligand by thietane, step D in the scheme. This step should be enhanced in the solvent-free thietane solutions used in these studies. A mechanism similar to this has been proposed for the Lewis acid catalyzed cyclooligmerization of oxetane by BF3.20 The observed catalysis by 3 is also explained by the proposed catalytic cycle since 3 is a species in the cycle. Indeed, the catalytic activity of 3 is not significantly different from that of 2. This can be seen in the turnover frequencies (TOF) for the formation of 12S3 by 2 and 3 as shown in Table 1. The catalysis by 1 can be explained by a similar mechanism by adding as a first step the substitution of its NCMe ligand by thietane. The presence of 2 and 3 in the catalyst solutions of 1 was confirmed by 13C NMR spectroscopy. Interestingly, all the resonances detected by 13C NMR spectroscopy in the CO region of these catalytic reactions can be explained, indicating that the catalysis is very clean, at least in the early stages. The catalysis by Rez(C0)lo can also be explained by this cycle, but this would require the displacement of a less labile CO ligand from the Rez(C0)loby the thietane. This should be much slower than the NCMe displacement in 1; thus Rez(CO)loshould be a poorer catalyst, as observed. (19)(a) Goethals, E J. Makromol. Chem., Mucromol. Symp. 1991, 42/43,51. (b) Goethals, E. J.; Drijvers, W.; van Ooteghem, D.; Buyle, A. M. J. Mucromol. Sci., Chem. 1973,A7, 1375. (c) Goethals, E. J.; Florquin, S. M. Makromol. Chem. 1981,182,3371. (20) Dale, J.; Fredriksen, S. B. Acta Chem. Scund. 1991,45,82.
Organometallics, Vol. 14, No. 4, 1995 1755
Catalytic Cyclooligomerization of Thietane The catalysis by 5 can be explained by a mechanism similar to that for 2. However, since phosphines are better donors than CO, the replacement of a CO ligand by the PMezPh ligand in 5 will result in more electron density at the metal atoms. Accordingly, there should be less removal of electron density from the sulfur atom of the coordinated thietane ligand in 5 than in 2. Thus, ring-opening addition in the catalytic cycle for 5 may be slower than for 2, and the overall catalytic activity is lower, as observed. The formation of 2486 could be explained by a mechanism similar to that shown in Scheme 1 for 12S3 by allowing the addition of 4 equiv of thietane to the intermediate 8 prior to the cyclization step C. It is not yet clear to us why the formation of 2436 is increased relative to that of 12S3 with longer reaction periods. We have shown that 12S3 is not converted t o 2486 in the presence of 2 in heptane solvent at 93 "C, which seems to rule out the possibility that the 12S3 is being converted to the 2486 under the reaction conditions. We have observed previously that visible light can promote the opening of thietane ligands in dirhenium ~omp1exes.l~ Accordingly, we investigated the effects of visible light on this catalysis. We have found that the formation of 2486 is substantially increased at the expense of 12S3 formation in the presence of visible light. This indicates that there are factors that can promote the formation of 2496. Other mechanisms may also be involved. It is possible that thietane could react with the 12S3 ligand in 3 in a ring-opening process that could lead to the transformation of some of the 12S3 into 2436. Alternatively, it is possible that 12S3 could
react with 2 by opening the coordinated thietane ligand leading to the formation of a thiolato ligand containing a 12S3 grouping linked to the R e 2 group by a SCH2CHzCHz chain at a sulfonium center. An opening of the 12S3 grouping at this sulfonium center by thietane could lead to enlargement of the 12S3 ring. These processes would be less important in the early stages of the catalysis when there is little 12533 present in the solutions. Further studies of the formation of 2456 are in progress. The fundamental difference between the catalytic activity of the dirhenium complexes reported here and that of V7" is that, with 7, the thietane ligand is coordinated in a bridging mode, whereas for the dirhenium complexes it appears that only terminal coordination is involved. It thus appears that the ability of heavy metals to activate thietanes toward ring-opening reactions through coordination has a wider scope than we originally suspected. We suspect that a wider range of metal-promoted organic reactions of thietanes can be anticipated as well.
Acknowledgment. These studies were supported by the Office of Basic Energy Sciences of the US.Department of Energy. Supplementary Material Available: Tables of interatomic distances and angles and anisotropic thermal parameters (14 pages). Ordering information is given on any current masthead page. OM950048Z
