Organometallics 1996, 14, 4858-4864
4858
Rhodium-AssistedTransformations of Substituted Thiophenes into Butadienyl Methyl Sulfides Claudio Bianchini," M. Victoria Jimbnez, Andrea Meli, and Francesco Vizza Istituto per lo Studio della Stereochimica ed Energetica dei Composti di Coordinazione, ISSECC-CNR, Via J . Nardi 39, 50132 Firenze, Italy Received May 25, 1 9 9 6 The novel butadienethiolate complex (triphos)Rh(y3-SC(Tyl)=CHCH=CH2I (Tyl= thieny1)has been prepared by reaction of (triphos)RhH3 with 2,Y-bithiophene (2-TylT) in refluxing tetrahydrofinan (THF) (triphos = MeC(CH2PPh2)3). Insertion of rhodium occurs exclusively at the C-S bond of a thienyl group of TylT distal to the other thienyl. Complexes of l-(methylthio)buta-l,3-dienewith the formula [(triphos)Rh(y3-MeSCR=CRCH=CH2)lBPb have been prepared by treatment of the corresponding butadienethiolate complexes (triphodRh(y3-SCR=CRCH=CH2) ( R = H, R = Me, COMe, COzEt, Tyl; R = H, R = Me, COMe, OMe) with MeI, followed by a metathetical reaction with NaBPh4. The Rh thioether complexes react with CO ( 5 atm, 70 "C) in THF to give free butadienyl methyl sulfides (2)MeSCR-CRCH-CH2 and, quantitatively, the dicarbonyl complex [(triphos)Rh(C0)2lBPL. The butadienyl methyl sulfides have been purified by LC and characterized by their NMR and MS properties. Inter alia, the chemistry presented herein provides a novel entry into the synthesis of substituted-butadienylmethyl sulfides, for which a general methodology is still lacking.
Introduction
Scheme 1
Thiophene (T)is a molecule of substantial interest for its extraordinarily wide range of chemical applications. Organic chemists largely use T as a precursor t o a variety of products via electrophilic attack (nitration, halogenation, sulfonation, acylation, alkylation, etc.), often followed by desulfuration (e. g., synthesis of longchain alkanes).' More recent and sophisticated applications span the use of T as a model compound to study the mechanism of the hydrodesulfurization (HDS) reaction of fossil fuels: the preparation of new materials with unusual physical properties (ele~trical,~ magnetic: nonlinear optical5), and the synthesis of complex molecules of biological importance.6 We have recently shown that T can efficiently be used for the synthesis of conjugated organosulfur compounds via metal-promoted C-S bond cleavage, followed by electrophilic attack and ~arbonylation.~ Scheme 1 il@Abstractpublished in Advance ACS Abstmcts, September 15,1995. (1)March, J. Advances Organic Chemistry, 4th ed.; Wiley: New York, 1992. (2) (a)Angelici, R. J. In Encyclopedia of Inorganic Chemistry; King, R. B., Ed.; Wiley: New York, 1994;Vol. 3, p 1433. (b)Sbnchez-Delgado, R. A. J. Mol. Catal. 1994, 86, 287. (c) Wiegand, B. C.; Friend, C. M. Chem. Reu. 1992, 92, 491. (d) Girgis, M. J.; Gates, B. C. Ind. Eng. Chem. Res. 1991, 30, 2021. (e) Rauchfuss, T. B. Prog. Inorg. Chem. 1991, 39, 259. (0 Angelici, R. J. Coord. Chem. Rev. 1990, 105, 61. (g) Prins, R.; deBeer, V. H.J.; Somorjai, G. A. Catal. Rev.-Sci. Eng. 1989, 31, 1. (h) Friend, C. M.; Roberts, J. T.Acc. Chem. Res. 1988,21, 394. (i) Angelici, R. J. Acc. Chem. Res. 1988, 21, 387. (3) (a) Graf, D. D.; Day, N. C.; Mann, K. R. Inorg. Chem. 1995,34, 1562. (b) Shaver, A.; Butler, I. S.; Gao, J. P. Organometallics 1989,8, 2079. (c) Tour, J. M.; Wu, R.; Schumm, J. J. Am. Chem. SOC.1991, 113, 7064. (4) Mitsumori, T.; Inoue, K.; Koga, N.; Iwamura, H.J. Am. Chem. SOC.1995, 117, 2067. (5)Long, N. J. Angew. Chem., Int. Ed. Engl. 1996,34, 21. (6) (a)Jaouhari, R.; GuBnot, P.;Dixneuf, P. H. J. Chem. SOC., Chem. Commun. 1986, 1255. (b) Nicolau, K. C.; Renaud, J.; Nantermet, P. G.; Couladouros, E. A.; Guy, R. K.; Wrasidlo, W. J . Am. Chem. SOC. 1995, 117,2409.
lustrates the procedure for the preparation of butadienyl methyl sulfide. The success of this method has inspired us to investigate alternative methods of synthesizing butadienyl methyl sulfides bearing various substituents in the butadienyl moiety. Such a,B,y,d-unsaturated sulfides are, in fact, generally difficult to prepare using standard organic chemistry procedures,8 even though they are excellent starting materials for further structural elaborations (Diels-Alder additions, reductions, oxidation of either the sulfur or the double bond, polymerization89 as well as molecules endowed with a specific activity (nonlinear optical, radicophilic5J0). The first step of our investigation was to determine whether the 16-electron fragment [(triphos)RhHl,gen(7) Bianchini, C.; Frediani, P.; Herrera, V; Jimenez, M. V.; Meli, A.; Rincbn, L.; Sbnchez-Delgado, R. A.; Vizza, F. J. Am. Chem. SOC. 1995, 117, 4333.
0276-733319512314-4858$09.00/00 1995 American Chemical Society
Organometallics, Vol. 14, No. 10, 1995 4859
Rh-Assisted Transformations of Thiophenes
Scheme 2
Chart 1
2-Me1
2-CO*Etl
2-COMeT
3-MeT
3-OMel
2-TylT
3-COMT
erated by thermolysis of the trihydride (triphos)RhHs (1;triphos = MeC(CH2PPh2)3),11was capable of cleaving substituted thiophenes in a regioselective manner. Our attempt was successful, as the fragment [(triphos)RhHl does react with thiophenes substituted in either the 2or the 3-position to give C-S insertion products of the formula (triphos)Rh(v3-SCR=CR'CH=CH2)(I).12Most
s
k
R'
R' = H, R = Me (3),COMe (4), C02Et (5) R = H, R' = Me (e), COMe (7), OMe (8)
I
importantly, the insertions are regioselective, as they occur exclusively a t the C-S bond distal t o the substituent in the thiophene. On the basis of these previous results, we herein describe the transformation of the substituted thiophenes shown in Chart 1 t o their corresponding butadienyl methyl sulfides.
Experimental Section General Information. All reactions and manipulations were routinely performed under a nitrogen atmosphere by using standard Schlenk techniques, unless otherwise stated. Tetrahydrofuran (THF) and diethyl ether were distilled from LiAlH4, CHzC12 was distilled from CaH2, and n-heptane was distilled from sodium. The solvents were stored over molecular sieves and purged with nitrogen prior to use. 2,2'-Bithiophene (2-5lT) was purchased from Aldrich. All other chemicals were commercial products and were used as received without further purification. The trihydride (triphos)RhH311(1) and the butadienethiolate complexes (triphos)Rh(q3-SCR=CR'CH=CHz) ( R = H, R = Me (3),COMe (41,COzEt (5); R = H, R = Me (6),COMe (7), OMe (8))12 were prepared as previously described. All metal complexes were collected on sinteredglass frits and washed with appropriate solvents before being (8)(a)Crumbie, R. L.; Ridley, D. D. Aust. J. Chem. 1981,34,1017. (b) Onishi, T. Jpn. Kokai Tokkyo Koho, 1991. (c) Tsuchihashi, G.; Ogura, K.; Yamamoto, S. Jpn. Kokai Tokkyo Koho, 1978.(d) Metzner, (e) Masson, S.; P.; Pham, T. N.; Vialle, J. Tetrahedron 1986,42,2025. Thuillier, A.Tetrahedron Lett. 1980,21,4085. (0 Michalik, M.; Peseke, K. J. Prakt. Chem. 1987,329,705.(g) Gupta, A. K.; Ila, H.; Jujappa, H. Tetrahedron 1989,45,1509.(h) Datta, A.;Ila, H.; Jujappa, H. J. Org. Chem. 1990, 55,5589.(i) Hanko, R.; Hammond, M. D.; Fruchtmann, R.; Pfitzner, J.; Place, G. A. J. Med. Chem. 1990,33,1163.(j) Jones, G. D.; Doorenbos, H. E. J. Macromol. Sci., Chem. 1984,-421, 155. (9)(a) Gillard, M.; T'Kint, C.; Sonveaux, E.; Ghosez, L. J.Am. Chem. SOC.1979,101, 5837.(b) Huber, S.;Stamouli, P.; Jenny, T.; Neier, R. Helv. C h i n . Acta 1986,69,1898.(c) Trost, B. M.; Vladuchick, W. C.; Bridges, A. J. J.Am. Chem. SOC.1980,102,3548.(d) Evans, D. A.; Bryan, C. A.; Sims, C. L. J.Am. Chem. Soc. 1972,94,2891. (10)Stevenart-De Mesmaeker, N.;MerBnyi, R.; Viehe, H. G. Tetrahedron Lett. 1987,28,2591. (11)Ott, J.;Venanzi, L. M.; Ghilardi, C. A.; Midollini, S.; Orlandini, A. J. Oganomet. Chem. 1986,291,89. (12)Bianchini, C.;Jimenez, M. V.; Meli, A.; Vizza, F. Organometallics 1996,14, 3196.
R' = H, R = Me (IO),COMe ( I l ) , COPEt(12). Tyl (13)
R = H, R'= Me (14), COMe (15), OMe (16)
dried under a stream of nitrogen. Infrared spectra were recorded on a Perkin-Elmer 1600 Series FT-IR spectrophotometer using samples mulled in Nujol between KBr plates. Deuterated solvents for NMR measurements were dried over molecular sieves. The lH NMR spectra were obtained on a Bruker ACP 200 (200.13 MHz) spectrometer, with shifts recorded relative to the residual lH resonance in the deuterated solvent CD2C12,d 5.32; CDC13,6 7.23. The 13C{lH}NMR spectra were recorded on a Bruker ACP 200 instrument operating a t 50.32 MHz, with shifts given relative t o the solvent resonance: CDzClz, 6 54.4; CDC13, 6 77.7. The 31P{lH} NMR spectra were recorded on a Bruker ACP 200 spectrometer operating at 81.01 MHz; chemical shifts here are relative to external 85%H3P04, with downfield values reported as positive. Broad-band and selective 1H{31P}NMR experiments were carried out on the Bruker ACP 200 instrument equipped with a 5-mm inverse probe and a BFX-5 amplifier device. Finally, 13C DEPT, lH-13C 2D HETCOR, and lH-'H 2D COSY NMR experiments were conducted on the Bruker ACP 200 spectrometer. Conductivities were measured with an Orion Model 990101 conductance cell connected to a Model 101 conductivity meter. The conductivity data were obtained M in nitroethane solutions at sample concentrations of ca. at room temperature. GC/MS analyses were performed on a Shimadzu QP-5000 apparatus equipped with a 30 m (0.25 mm i.d., 0.25 pm FT) SPB-1 Supelco fused silica capillary column. Reactions under controlled pressure of carbon monoxide were performed with a Parr 4565 reactor equipped with a Parr 4842 temperature and pressure controller. Preparation of (triphos)Rh(t13-SC(Ty1)=CHCH-CH2) (9). To a stirred suspension of 1 (0.50 g, 0.68 mmol) in THF (40 mL) was added a 10-fold excess of 2-51T (1.13 g), and then the mixture was heated at reflux temperature. Within a few minutes the solid dissolved. After ca. 3 h, the resulting yellowbrown solution was concentrated to ca. 5 mL. Addition of n-heptane (20 mL) led to precipitation of 9 as orange microcrystals, which were collected by filtration and washed with n-pentane; yield 76%. Anal. Calcd (found) for C49H46P3RhSz: C, 65.77 (65.66); H, 5.18 (5.09); Rh, 11.50 (11.32); S, 7.17 (7.00). IR v(C=C) 1570 (m) cm-l. General Procedure for the Preparation of [(triphodRh(qS-MeSCR=CRCH-CH2)1BPh4 ( R = H, R = Me (lo), COMe (ll),CO2Et (12),Tyl (13);R = H,R = Me (14), COMe (15),OMe (16)). A %fold excess of neat Me1 (48 pL) was syringed into a stirred solution of the appropriate butadienethiolate complex (triphos)Rh(q3-SCR=CRCH=CH2) (R = H, R = Me (3),COMe (41, COzEt (5), Tyl (9); R = H, R = Me (6),COMe (7), OMe (8);0.25 mmol) in CHzClz (30 mL) at room temperature. After ca. 30 min, NaBPh4 (0.85 g, 0.25 mmol) in ethanol (30 mL) was added to the resulting solution. Partial evaporation of the solvents under a steady stream of nitrogen led to the precipitation of yellow-orange microcrystals of 10-16,which were collected by filtration and washed with n-pentane; yield 85-90%. Selective methylation of the sulfur atoms of 3-9 can analogously be achieved by using other alkylating agents such as MeOSOzCF3 and Me30BF4. However, Me1 is the reagent of choise because it is the cheapest and the easiest to handle.
4860 Organometallics, Vol. 14, No. 10,1995
Biunchini et al.
Table 1. slP{lH} NMFt Spectral Data for the N e w Complexesa complex 9 10 11 12 13 14 15 16
pattern AMQX AMQX AMQX AMQX AMQX AMQX AMQX AMQX
chem shift, ppmb 6(M) SCQ) -1.2 -4.2 30.9 1.8 -6.1 28.9 28.5 7.9 -8.1 6.9 -7.8 28.8 3.8 -6.2 29.1 30.2 5.0 -6.9 6.2 -7.1 30.9 5.8 -9.1 29.0 6(A)
J(AM) 34.3 36.5 35.1 35.8 36.4 36.4 36.5 37.5
J(AQ) 29.4 36.5 38.7 38.4 36.4 36.4 36.5 37.5
coupling const, Hz J(MQ) J(ARh) 37.5 108.9 36.5 114.8 29.5 112.9 30.5 114.7 36.4 116.8 36.4 115.2 36.5 116.4 37.5 114.6
J(MRh) 117.9 111.3 117.5 116.3 113.6 113.2 115.5 114.1
J(QRh) 106.3 104.4 100.2 100.5 101.9 101.9 101.1 101.1
a All spectra were recorded at 20 "C in CDzCl2 solutions. The chemical shifts (6's) are relative to 85% H3P04; downfield values are assumed as positive.
[(triphos)Rh(q35-MeSC(Me)-CHCH=CH2)lBPL(10). Anal. Calcd (found) for C71HegBP3RhS: C, 73.45 (73.05);H, 5.99 (5.78);Rh, 8.86 (8.92);S, 2.76 (2.69). AM: 50 S2-1 cm2 mol-'. [(triphos)Rh(q3-MeSC(COMe)=CHCH==CHd]BPh4 (11). Anal. Calcd (found) for C72HegBOP3RhS: C, 72.73(72.33);H, 5.85 (5.51);Rh, 8.65 (8.63);S, 2.69 (2.61). AM: 52 S2-l cm2 mol-'. IR: v(C=O) 1678 (s) cm-l. [(triphos)Rh(q3-MeSC(CO&t)==CHCH=CHdlBP4 (12). Anal. Calcd (found) for C ~ ~ H ~ I B O ~ PC,~ 71.92 R ~ S (71.57); : H, 5.87(5.54);Rh, 8.44 (8.44);S, 2.63 (2.50). AM: 52 S2-1 cm2 mol-'. IR: v(C-0) 1709 (s) cm-'. [(triphos)Rh(q3-MeSC(Ty1)=CHCH=CH~)1BP~ (13). Anal. Calcd (found) for C74HegBP3RhSz: C, 72.31 (71.99);H, 5.66 (5.39);Rh, 8.37 (8.32);S, 5.22 (5.23). AM: 55 S2-l cm2 mol-'. IR. v(C=C) 1569 (m) cm-'. [(triphos)Rh(q3-MeSCH=C(Me)CH=CH2)lBPh4 (14). Anal. Calcd (found) for C71H69BP3RhS: C, 73.45 (73.00);H, 5.99 (5.62);Rh, 8.86 (8.89);S, 2.76 (2.67).AM: 54 9 - I cm2 mol-'. [(triphos)Rh(q3-MeSCH=C(COMe)CHICH~)IBPh4 (15). Anal. Calcd (found) for C72H69BOP3RhS: C, 72.73(72.49);H, 5.85 (5.55);Rh, 8.55 (8.69);S, 2.69 (2.68). AM: 52 W 1cm2 mol-'. I R v(C=O) 1681 (8)cm-'. [(triphos)Rh(q3-MeSCH=C(OMe)CH=CH2)1BP~ (16). Anal. Calcd (found) for C71H69BOP3RhS: C, 72.45(72.13);H, 5.91 (5.55);Rh, 8.74 (8.49);S, 2.72 (2.54). AM: 54 S2-I cm2 mol-'. IR: v(C-0) 1156 (s) cm-'. Synthesis of the Butadienyl Methyl Sulfides 17-23. In a typical experiment, a THF (50 mL) solution of the appropriate methylbutadienethiolate complex [(triphos)Rh(v3MeSCR=CRCH=CH2)]BPL (10-16;ca. 0.3 mmol) was reacted with CO (5atm) at 70 "C for 3 h in a Parr reactor. After the bomb was depressurized and vented under a nitrogen stream, the contents were transferred into a Schlenk-type flask. The volatiles were then removed in vacuo at room temperature and a portion of the residue was analyzed by 'H and 31P{1H} NMR spectroscopy. In all of the reactions, [(triphos)Rh(C0)21BPhJ1 (2)was the only rhodium complex detected in solution. The rest of the residue was chromatographed on a silica column (diethyl ether as eluant) to eliminate the rhodium complex. The diethyl ether phase was then evaporated at atmospheric pressure and the residue, dissolved in CDC13, was appropriately characterized by 'H and I3C{'H} NMR and W/MS spectroscopy. In all cases, the yields of the sulfides 17-23 exceeded 90% based on 'H NMR integration with respect to tert-butyl methyl ether (6 3.21, OMe; 6 1.20,CMe3) as internal standard. Due to the limited preparative scale imposed by the cost of the rhodium precursors, no attempt was made to isolate pure samples of the organosulfur compounds.
{lH} NMR). Selected NMR and MS data for the organosulfur products are collected in Table 3 (lH NMR) and Table 4 (13C(lH} NMR, MS). 13C DEPT, 13C-lH 2D HETCOR, lH-lH 2D COSY,and selective-decoupling spectra allowed the total and unequivocal assignment of all hydrogen and carbon resonances for all metal complexes and organosulfur compounds as labeled in Tables 2 and 3, respectively.
Reaction of the Trihydride (triphos)RU&(1) with 2,a'-Bithiophene. The butadienethiolate com(9; Tyl = plex (triphos)Rh(y3-SC(Tyl)=CHCH=CH2) thienyl) was obtained as orange crystals by following the procedure used for the preparation of the congeners shown by I, e.g. stirring a THF solution of 1 with an excess of 2-TylT at reflux temperature. As previously observed for all of the substituted thiophenes shown in Chart 1, insertion is seen exclusively a t the C-S bond distal to the thienyl substituent.12 Mechanistically,the reaction proceeds through the intermediacy of a transient hydridorhodathiacyclecomplex, (triphos)Rh(H)(y2(C,S)-SC(Tyl)=CHCH=CH), which rapidly undergoes hydride migration to the metalated carbon atom of the thio ligand.13
9
The NMR characteristics of 9 are comparable with those of the butadienethiolate congeners 3-8. Thus, 9 is analogously assigned an octahedral structure with the rhodium center coordinated by a fac-triphos ligand and by a 5-thienyl-substituted butadienethiolate ligand which uses the sulfur atom and the distal olefinic end to bind the metal. In line with previous observations, the Rh-C2-C3 ring exhibits a pronounced metallacyclopropane structure (d(C3) 63.1, d(C2) 40.2, 2J(C2,3P)= 32 Hz17J2
Results and Discussion The preparations and the principal reactions described in this article are illustrated in Scheme 2. Selected NMR spectral data for the metal complexes are collected in Table 1(31P(1H}NMR) and Table 2 (lH, 13C-
(13)(a) Bianchini, C.;Meli, A.; Peruzzini, M.; Vizza, F.; Frediani, P.; Herrera, V.; Sbnchez-Delgado, R. A. J.Am. Chem. Soc. 1993,115, 2731.(b) Bianchini, C.;Meli, A,; Peruzzini, M.; Vizza, F.; Moneti, S.; Herrera, V; Sbnchez-Delgado,R. A. J. Am. Chem. Soc. 1994,116,4370. (c) Bianchini, C.;JimBnez, M. V.; Meli, A.; Moneti, S.; Vizza, F. J. Orgunomet. Chem., in press.
Organometallics, Vol. 14,No. 10,1995 4861
Rh-Assisted Transformations of Thiophenes
Table 2. lH and lsC{lH} NMR Spectral Data for the New Complexe@ ---complex
-------
--------
1H NMR
assignt
G(multlplicily, J)bpc 6.64 3.15 2.95 2.01
-
-
13C(1H)
___-
I
S(muitipiicity, ~ ) b
assignt
-
-
(t, 3J(HqRh) = 1.0, 3J(H4H3) I4.9) (m,2J(HziRh) 2.0, 3J(HziH3) = 9.1) (m,2J(H3Rh) = 1.3, sJ(H3H2) = 7.6) (m, zJ(H2Rh) = 1.5, 2J(H2H2*) = 0.5)
--
NMR
I _
-
63.1 (dt,2J(CP) = 31.8, 9.7) 40.2 (br d, 2J(CP) 32.7) e
e
d
e
6.95f 3.20 (m,2J(H3Rh) = 1.3, 3J(H3H4) = 4.8) 2.58 (m,2J(H2'Rh) = 2.0, sJ(HpH3) 9.3) 2.38 (m, 2J(H2Rh) = 1.6, 2J(H2H29) 2.2, 3J(H2H3) = 7.8) 2.11 (s) 1.74 (s)
149.8 (br s) 58.4 (dd,2J(CP) = 22.2, 10.2) 47.8 (dd,2J(CP) 23.4, 11.2) 22.3 (br s) 18.5 (s) e
8.55 (t, 3J(H4H3) 5.8) 3.44 (m,zJ(H3Rh) = 1.2, sJ(H3H2) = 8.7) 2.71 (m,2J(H2Rh) 2.2, zJ(HzH2) = 2.2, 3J(H2*H3) 8.9) 2.50 (s) 2.21 g 1.62 (br s)
192.7 (s) 170.1 (br s) 54.2 (m) 51.5 (dm,2J(CP) 35.6) 28.1 (s) 24.9 (d,3J(CP) = 5.5) e
8.64 4.31 3.40 2.74
(t, 3J(H4H3) = 5.9) (q, sJ(H8Hg) = 7.2) (m, pJ(H3Rh) 1.2, 3J(H3H2) 8.5) (m,2J(HpRh) 2.1, zJ(HzH2) 2.0, 3J(H2'H3) 9.1) 2.239 1.66 (s) 1.39 (t)
169.4 (br S) 163.2 (s) 62.6 (s) 54.2 (m) 51.0 (dm,2J(CP) 34.8) 24.0 (d,3J(CP) = 5.1) 14.8 (s) e
7.521 3.49 (m,2J(H3Rh) = 1.3, 3J(H3H4) = 5.0, sJ(H3H2) = 7.9) 2.63 (m,zJ(H2fRh) = XX, SJ(HzH3) = 9.1) 2.33 (m,zJ(H2Rh) 1.8, zJ(H2H2l) 2.0) 1.69 (s)
149.3 (br s) 57.8 (dd,2J(CP) = 21.8, 9.5) 48.5 (dd,2J(CP) = 23.4, 10.8) 23.6 (br s) e e
-
--
--
--
-
-
-
d 5.44 (br s, 4J(H5H7) = 1.4) 3.37 (m,zJ(H3Rh) 1.2, 3J(H3H2) = 7.8) 2.48 (m,2J(HzRh) 2.1, 3J(HzH3) = 9.2) 2.34 (d) 2.04 (m,zJ(H2Rh) 1.7, zJ(H2H2') = 2.1) 1.41 (br S)
--
6.44 (br s) 4.05 (m, zJ(H3Rh) 1.4, 3J(H3Hz) 2.52 (S) 2.319 2.02 (m, 2./(H2Rh) 1.7, 2J(H2H2') sJ(H2H3) 8.3) 1.43 (br s)
-
8.9)
2.0,
4.73 (m,4J(H5H3) = 1.5) 3.91 (s) 3.32 (m,zJ(H3Rh) 1.8, sJ(H3H2) 8.0) 2.62 (m,2J(H2+Ih) 2.2, 3J(Hz1H3) = 9.0) 1.96 (m,2J(H2Rh) = 1.2, 2J(H2H2') = 2.2) 1.33 (br s)
-
-
--
167.1 (br s) 110.0 (d,3J(CP) 11.0) 62.2 (dd,2J(CP) 22.0, 11.O) 49.8 (dd,2J(CP) 22.6, 11.6) 24.3 (d, 3J(CP) = 6.1) 22.9 (s) 195.1 (s) 165.0 (br s) 124.2 (d,3J(CP) 12.8) 54.6 (dm,2J(CP) = 21.9) 50.4 (dm,2J(CP) 23.2) 28.6 (s) 23.6 (br s)
-
168.2 (br s) 82.1 (d,3J(CP) 7.8) 63.1 (dd,2J(CP) 22.4, 11.1) 59.8 (s) 48.8 (dd,2J(CP) 22.1, 10.9) 24.1 (d,3J(CP) 6.4) E
-
--
All spectra were recorded a t room temperature in CDzClz solutions at 200.13 ('H NMR) and 50.32 MHz (W{'H} NMR). Chemical shifts are 'ven in ppm and are relative to either the residual 1H resonance in the deuterated solvent ('H NMR) or the deuterated solvent resonance (lSC{'H} EMR). Key: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br, broad. Couplin constants (4are in hertz. The J(HH) values were determined on the basis of 1H{3lP} NMR experiments. d Masked by the aromatic protons ofthe triphos ligand. e Masked b the phenyl carbons of the triphos ligand. f Masked by the aromatic protons of the triphos ligand. The chemical shift was determined from a 'H-'dOD-COSY experiment. g Masked by the aliphatic protons of the triphos ligand. The chemical shift was determined from a 'H-lH 2D-COSY experiment.
4862 Organometallics, Vol. 14, No. 10, 1995
Bianchini et al.
Table 3. 'H NMR Spectral Data for the Butadienyl Methyl Sulfides" ______-_---_________-______-----_-____________________--SH, multlplicityb JHHb
-
e??
-
6.12. 6.81, b r d d
5.07, 5.17,
2.33,
d
h
s
7.38, d
7.15, ddd
5.62, dd
5.73, dd
s
7.43,
7.07,
5.58,
5.68,
2.28,
n
2.24,
2.12, m
-
5.93,
7.51,
-("-" -
5 - ~ 1 2
4
5.22. m
6.76, 7.12, 5.32, 5.45, 2.24, k d d d d d d d d d d s
-
-
-
-
6.63, ddd
5.16, dl
5.27, 2.31, 1.98, ddd S d
6.60, dd
5.55, dd
5.60, dd
6.92, ddd
5.23, 5.66, 2.21, 3.68, dl ddd s s
2.34, S
2.48,
-
-
-
-
-
-
10.6
0.8
0.8
10.3 16.9 2.0
-
-
-
-
-
-
10.8
-
-
9.8
-
-
-
-
-
10.9
0.7
0.7
10.1 16.9 1.7
- - -
-
10.5
0.7
0.7
10.1 16.9 1.8
-
-
-
10.8 17.3 1.4
16.6 1.3
S
b r d d d d d d d d d d S
-
-
-
4.28, q
1.32, I
7.27,
7.04, 7.31,
dd
d d d d
-
2.51,
-
-
-
-
-
-
0.7
-
1.5
-
0.6
1.5
-
-
-
-
-
11.717.91.1
0.6
-
-
-
-
11.2 17.2 1.9
S
-
0.6
1.7
a All spectra were recorded a t room temperature in CDC13 solutions at 200.13 MHz ('H NMR). b Chemical shifts are given in ppm and are relative to the residual 'H resonance in the deuterated solvent. Key: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br, broad. Coupling constants (J)are in hertz. 0 < J(H6&4t), J(HeHc), J(H,$&), J(HsH-2) < 0.5 Hz. J(H7Hs) = 7.1 Hz. e J ( H , & , ) = 5.2 Hz, J(H7H9) = 1.2 Hz, J(H8Hg) = 3.7 Hz.
Although much less abundant than thiophenes, oligothiophenes such as 2-TylT are found in fossil fuels.14 On the other hand, oligothiophenes may form in the course of the HDS process from side reactions involving either thiophene C-H bond activation by metal cent e r or~pyrolysis ~ ~ of ~ the ~ thiophenes.16 ~ It was thus surprising to us to find that no homogeneous modeling study of the reactivity of 2-TylT with transition-metal complexes has appeared in the HDS-relevant literature over the past 30 years. To the best of our knowledge, the only report is the one by Manuel and Meyer in 1964, which describes the insertion of iron from Fe3(C0)12into a C-S bond of 2 - T ~ l T . lAs ~ we found for 9, insertion is seen in the C-S bond distal to the thienyl substituent. The same iron complex, which is a thiaferrole of the formula Fe2(2,2'-C4H3SC4H3S)(co)6,was later also ob(14)(a) Geochemistry of Sulfur in Fossil Fuels; Om,W . L., White, C. M., Eds. ACS Symposium Series 429; American Chemical Society: Washington, DC, 1990. (b) Galpem, G. D. In Thiophene and its Derivatives; Gronowitz, S., Ed.; Wiley: New York, 1985; Part I. (15) Wang, D.-L.; Hwang, W.-S. J . Organomet. Chem. 1991, 406, C29. (16)Katritzky, A. R.; Lagowski, J. M. In The Principles of Heterocyclic Chemistry; Methuen: London, 1967. (17) Manuel, T.A,; Meyer, T. J. Inorg. Chem. 1@64,3,1049.
tained by Rauchfuss by thermal decomposition of the thienyl complex CpFe(C0)2(2-C4H3S).18
Our idea to insert rhodium into a C-S bond of 2-TylT has been motivated not only by the interest to gain insight into the metal-assisted opening of oligothiophenes (as part of our modeling studies on HDS) but also by the purpose of linking a thienyl group to an a,@,y ,&unsaturated hydrocarbon moiety, because of the interest in the resulting product for its potential nonlinear optical activity.5 Methylation of the Butadienethiolate Complexes. Selective methylation of the sulfur atom of the butadienethiolate complexes 3-9 was achieved in THF by treatment with Me1 at room t e m p e r a t ~ r e .Meta~ thetical reaction with NaBPb gives tetraphenylborate salts of the formula [( triphos)Rh(v3-MeSCR=CR CH=CH2)1BPb (R' = H, R = Me, (101,COMe (111, C02Et (121, Tyl(13);R = H, R' = Me (141, COMe (15),OMe (16);Scheme 2). (lS)Ogilvy, A.; Draganjac, M.; Rauchfuss, T. B.; Wilson, S. R. Organometallics 1988, 7 , 1171.
Organometallics, Vol. 14,No. 10, 1995 4063
Rh-Assisted Transformations of Thiophenes
Table 4. W{'H}NMR and MS Data for the Butadienyl Methyl Sulfides
144.7
128.8
130.7 116.9 17.6
24.8
-
-
-' 148.6
134.0
144.6 126.4 19.6 165.9
62.1
14.7
M-Me
99 (100) 84 (20) 65 (80) 45 (52)
M
142 1181
-
-
M M-Me M-OEI
172 (62) 157 (78) 127 (27) 113 (17) M-COzEI 99 (41) 85 (100) 84 (63)
::; :1
45 (71)
M 182 (6) M-Me 167 (100) M-HSMe 134 (49) 146.9
5-s
/=(f 1 2 3-4
a
5-s'
=
128.4
128.0 134.9 120.5 18.9 134.3
142.1
129.0 116.2 22.2
16.2
-
-
91 (18) 69(11) 45 (19)
M M-Me
114 (62) 99(100) 84 (20) 65 (79) 45 (65)
142 (36) 127 (59) M-COMe 99 1191
M-Me 147.4
141.1 144.2 122.4 19.6 195.7
27.2
3-4
&
-
128.3
M
0-6
5-s'
126.3 126.4
98.6
143.8 124.7 116.4 23.2
23-4
All compounds are isolated as yellow-orange crystals, which are fairly air-stable in both the solid state and solution. Like the neutral butadienethiolate precursors,12the thioether compounds 10-16 exhibit, in solution, a rigid octahedral structure in which the thio ligand is still q3anchored to rhodium via the c2-c3 double bond and the sulfur atom. This bonding mode has been authenticated by an X-ray diffkaction analysis on the iridium 14methylthio)butadiene complex [(triphos)Ir(q3-MeSCH=CHCH=CH2)]BPh4.13" A close analog to this system is the 14methylthio)butadiene complex [(triphos)-
Rh(q3-MeSCH=CHCH=CH2)lBPh4.7 The addition of a methyl group to the sulfur atom does not appreciably alter the lH NMR parameters of the vinyl moiety of the starting butadienethiolate ligands, unlike the chemical shifts of the H5 hydrogen in the 4-substituted compounds and of the H4 hydrogen in the 5-substituted compounds, which move upfield and downfield, respectively. This phenomenon may be explained by taking into account that alkylation of the sulfur atom actually reduces the electron density on both the metal and the thio ligand, thus causing a polarization of the
55.6
-
-
-
-
-
65'(44) 45 (73) 43 (100)
M M-Me M-2Me
130 (38) 115 (100) 100 17) 87 ( i 2 j 72 (16) 71 116) 55 j27j 45 (76)
electrons in the double bond toward the metal center. The deshielding effect on the atoms in the 4-position is also evident from the l3C(lH} NMR spectra. As an example, we show in Figure 1that C4 in 12 resonates at ca. 170 ppm, while this signal in the corresponding butadienethiolate complex is masked by the phenyl carbons of triphos (120-140 ppm). CarbonylationReactions. The rhodium thioether complexes 10-16 were dissolved in THF and then subjected to a CO atmosphere (5 atm) in autoclaves. At 70 "C, all complexes quantitatively transform into the known dicarbonyl [(tripho~)Rh(CO)zlBPh4~~ within 3 h, while the neutral l-(methylthio)buta-1,3-dienes(1723), substituted in either the 1- or 2-position, are liberated in solution (Scheme 2). These have been purified by LC and then characterized in CDCl3 solution (Chart 2). A single isomer is obtained for each product with retention of the Z structure adopted in the rhodium precursors, as shown by a comparison of the proton NMR spectra of some of the present 1-(methylthiolbuta1,3-dienes with those of similar compounds.8a-dJo
Bianchini et al.
4864 Organometallics, Vol. 14, No. 10,1995
c9
I
c3
I
160
I
120
140
80
IO0
I
60
,
40
20
(PP4
Figure 1. l3CI1H}NMR (upper) and 13C DEPT (lower) spectra of 12 in CDzClz at 20 “C (50.32 MHz): (#) quaternary carbons of BPh4-; (+) phenyl - carbons of triphos and BPk-; (*) carbons of the ethanol of crystallization;(0)aliphatic carbons of triphos.
Chart 2
17
19
18
21
22
20
23
Butadienes with sulfur substituents are difficult to prepare, and a general methodology for their preparation is lacking. The compound (2)-1-(methylthiobl(carbomethoxy)buta-1,3-diene(similar to 19)has been synthesized by a [3,2]-sigmatropicrearrangement of the corresponding sulfonium while 1-(methylthiob2alkylbuta-1,3-dienes (similar to 21)have been prepared by the reaction of a,/3-unsaturated aldehydes with alkanethiols in the presence of acid Some l-(alkylthio)buta-l,3-dienes, without substituents on the butadienyl moiety, have been synthesized by the baseassisted ring-opening reactions of 2,5-dihydrothiophene 1-oxide,2,5-dihydrothiophene1,l-dioxide,or l-alkyl-2,5dihydrothiophene salts.8a In contrast, the synthesis of the substituted l-(methylthio)buta-1,3-dienesdescribed in this paper is a general methodology which offers several advantages over current organic chemistry procedures. These include the use of cheap, largely available thiophenic molecules, the generally excellent
yields, and the capability of easily varying either the sulfur substituent (by varying the initial electrophile) or the butadiene substituent(s) (by varying the starting thiophene). This last feature is perhaps the most exciting, as it provides access not only to tailored products of great utility as organic synthons8a9but also to molecules with unusual specific properties. For example, 1-(methylthiol-1-acetylbuta-1,&diene (18)and l-(methylthio)-l-(carboethoxy)buta-1,3-diene (19)belong to the class of 1,l-captodative butadienes with application as radicophilic reagents,1° while the conjugated l-(methythio)buta-l,3-diene(20) has potential in the field of second- and third-order nonlinear optical activity.5 An obvious disadvantage of the present methodology is the need to use an expensive metal, rhodium, which, however, is able to be totally recovered at the end of the reaction. Current investigations center upon finding a less expensive metal for these reactions and in the development of a catalyst system for the process.
Acknowledgment. We thank the Progetto Strateg i c ~“Tecnologie Chimiche Innovative”, CNR, Rome, Italy, and the European Community (Contract CHRX CT93-0147) for financial support. A postdoctoral grant to M.V.J. from the Ministerio de Educati6n y Ciencia of Spain is gratefully acknowledged. OM9503860
