Organometallics 1997, 16, 4237-4239
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A Novel 1,2-Aryl Migration in Metallanethione: Unusual Formation of an Aryl(arylthio)plumbylene from a Plumbanethione Naokazu Kano, Norihiro Tokitoh,* and Renji Okazaki* Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan Received July 1, 1997X Summary: The first aryl(arylthio)plumbylene, Tbt(TbtS)Pb: (2; Tbt ) 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl), was obtained by the desulfurization of tetrathiaplumbolane, 1, with triphenylphosphine at 50 °C, and its structure was established by X-ray crystallographic analysis. The formation of 2 is most likely interpreted in terms of a 1,2-aryl migration in an initially formed plumbanethione, 8, followed by its dimerization and a subsequent metathesis reaction. The chemistry of divalent organic compounds of heavier group 14 elements, R1R2M: (M ) Si, Ge, Sn and Pb), has stimulated wide interest.1 Plumbylenes, the heaviest congener of the carbene analogues, are usually unstable and highly reactive. Although some stable plumbylenes have been synthesized in recent decades,2 the synthetic methods are restricted mainly to nucleophilic substitution reactions on divalent lead compounds, such as lead dichloride or lead diamide. We report here the formation of a stable aryl(arylthio)plumbylene 2 via an unusual 1,2-aryl migration in a plumbanethione.3 In a continuation of our work on the synthesis of heavier congeners of ketones by taking advantage of the kinetic stabilization of an efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (denoted as Tbt hereafter),4 we recently reported the generation of the first lead-sulfur doubly bonded compounds, plumbanethiones, by desulfurization of tetrathiaplumbolane at low temperature and their trapping reactions.5 We have now found that a plumbanethione undergoes an interesting 1,2-aryl migration eventually leading to the aryl(arylthio)plumbylene, 2, Abstract published in Advance ACS Abstracts, September 15, 1997. (1) (a) Raabe, G.; Michl, J. Chem. Rev. 1985, 85, 419. (b) Petz, W. Chem. Rev. 1986, 86, 1019. (c) Lappert, M. F.; Rowe, R. S. Coord. Chem. Rev. 1990, 100, 267. (d) Barrau, J.; Escudie´, J.; Satge´, J. Chem. Rev. 1990, 90, 283. (e) Neumann, W. P. Chem. Rev. 1991, 91, 311. (f) Tsumuraya, T.; Batcheller, S. A.; Masamune, S. Angew. Chem., Int. Ed. Engl. 1991, 30, 902. (2) For stable plumbylenes, see: (a) Davidson, P. J.; Lappert, M. F. J. Chem. Soc., Chem. Commun. 1973, 317. (b) Harris, D. H.; Lappert, M. F. J. Chem. Soc., Chem. Commun. 1974, 895. (c) Brooker, S.; Buijink, J.-K.; Edelmann, F. T. Organometallics 1991, 10, 25. (d) Klinkhammer, K. W.; Schwartz, W. Angew. Chem., Int. Ed. Engl. 1995, 34, 1334. (e) Driess, M.; Janoschek, R.; Pritzkow, H.; Rell, S.; Winkler, U. Angew. Chem., Int. Ed. Engl. 1995, 34, 1614. (f) Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P. Organometallics 1997, 9, 1920. (3) For three- or four-coordinate heteroleptic plumbylenes, see: (a) Eaborn, C.; Izod, K.; Hitchcock, P. B.; So¨zerli, S. E.; Smith, J. D. J. Chem. Soc., Chem. Commun. 1995, 1829. (b) Balch, A.; Oram, D. E. Inorg. Chem. 1987, 26, 1906. (4) (a) Tokitoh, N.; Matsumoto, T.; Manmaru, K.; Okazaki, R. J. Am. Chem. Soc. 1993, 115, 8855. (b) Matsumoto, T.; Tokitoh, N.; Okazaki, R. Angew. Chem., Int. Ed. Engl. 1994, 33, 2316. (c) Suzuki, H.; Tokitoh, N.; Nagase, S.; Okazaki, R. J. Am. Chem. Soc. 1994, 116, 11578. (d) Tokitoh, N.; Matsumoto, T.; Okazaki, R. J. Am. Chem. Soc. 1997, 119, 2337. (5) Kano, N.; Tokitoh, N.; Okazaki, R. Chem. Lett. 1997, 277. X
S0276-7333(97)00556-6 CCC: $14.00
at a higher temperature. We have also established the molecular structure of 2 by X-ray crystallographic analysis. Tetrathiaplumbolane, 1,6 was treated with 3 equiv of triphenylphosphine in toluene at 50 °C in a sealed tube. After the mixture was heated for 22 h, the solution turned deep red and plumbylene 2, which was precipitated from the mixture on standing at room temperature, was isolated by filtration in a glovebox filled with argon as pure deep red crystals in 26% yield. When the mother liquor was subjected to silica gel chromatography, dithiadiplumbetane, 36 (32%), TbtSH, 4 (24%), TbtSSTbt, 5 (4%), TbtH (42%), TipH (32%), and triphenylphosphine sulfide (97%) were obtained (Scheme 1).7,8 The structure of plumbylene 2 was determined by 1H NMR spectrometry, elemental analysis, and X-ray crystallographic analysis.9 In Figure 1 is shown an ORTEP diagram of 2 with some selected bond lengths and angles. Plumbylene 2 exists as a monomer, and (6) (a) Tokitoh, N.; Kano, N.; Shibata, K.; Okazaki, R. Phosphorous, Sulfur Silicon Relat. Elem. 1994, 93-94, 189. (b) Tokitoh, N.; Kano, N.; Shibata, K.; Okazaki, R. Organometallics 1995, 14, 3121. (7) A toluene solution (3.6 mL) of tetrathiaplumbolane 1 (109.3 mg, 0.10 mmol) and triphenylphosphine (78.6 mg, 0.30 mmol) was sealed in a glass tube after five freeze-thaw-cycles. After the mixture ws heated at 50 °C for 22 h, the solution turned deep red and crystals of 2 precipitated from the reaction mixture on standing at room temperature. Filtration of the reaction mixture in a glovebox filled with argon afforded 17.0 mg (26%) of plumbylene 2 as deep red crystals. The filtrate was evaporated and separated with GPLC and then with silica gel chromatography to give dithiadiplumbetane 36 (10.8 mg, 32%), TbtSH, 4 (13.2 mg, 24%), TbtSSTbt, 5 (2.1 mg, 4%), TbtH (23.0 mg, 42%), TipH (6.6 mg, 32%), and triphenylphosphine sulfide (85.5 mg, 97%). 2: deep red crystals, mp 187.0-191.0 °C(dec); 1H NMR (500 MHz, C6D6) δ 0.23 (s, 18H), 0.27 (s, 18H), 0.32 (s, 54H), 0.34 (s, 18H), 1.50 (s, 1H), 1.58 (s, 1H), 2.13 (s, 1H), 2.20 (s, 1H), 3.37 (s, 1H), 3.50 (s, 1H), 6.88 (s, 1H), 7.01 (s, 1H), 7.63 (s, 1H), 7.70 (s, 1H); UV (toluene) λmax 540 nm ( 200 000); HRMS (FAB) m/z 791.2648 ([M - Tbt]+), calcd for C27H59PbSSi6 791.2577. Anal. Calcd for C54H118PbSSi12: C, 48.26; H, 8.85; S, 2.39. Found: C, 48.80; H, 8.95; S, 2.35. 4: pale yellow crystals, mp 183.0-188.0 °C; 1H NMR (500 MHz, CDCl3) δ 0.03 (s, 36H), 0.04 (s, 18H), 1.31 (s, 1H), 2.41 (s, 1H), 2.74 (s, 1H), 2.87 (s, 1H), 6.36 (s, 1H), 6.47 (s, 1H); 13C NMR (125 MHz, CDCl3) δ 0.34 (q), 0.67 (q), 28.06 (d), 30.04 (d), 120.83 (s), 121.84 (d), 126.60 (d), 141.58 (s), 146.79 (s), 146.92 (s); HRMS (EI, 70 eV) m/z 584.3010 ([M]+), calcd for C27H60SSi6 584.3031. Anal. Calcd for C27H60SSi6: C, 55.40; H, 10.33; S, 5.48. Found: C, 55.03; H, 10.09; S, 5.64. 5: yellow crystals, mp 238.0-241.0 °C; 1H NMR (500 MHz, CDCl3) δ 0.05 (s, 108H), 1.32 (s, 2H), 2.75 (s, 2H), 2.83 (s, 2H), 6.34 (s, 2H), 6.49 (s, 2H); 13C NMR (125 MHz, CDCl3) δ 0.76 (q), 0.93 (q), 1.21 (q), 28.29 (d), 28.41 (d), 30.53 (d), 122.17 (d), 127.21 (d), 128.38 (s), 143.74 (s), 149.06 (s), 149.35 (s); HRMS (FAB) m/z 1167.5867 ([M]+), calcd for C54H118S2Si12 1166.5906. Anal. Calcd for C54H118S2Si12: C, 55.50; H, 10.18; S, 5.49. Found: C, 55.20; H, 9.95; S, 5.80. (8) The yields of 2, 3, and 5 were calculated assuming that 1 mol of 1 gives 0.5 mol of 2, 0.25 mol of 3, and 0.5 mol of 5, respectively. The yield of the triphenylphosphine sulfide was based on triphenylphosphine used. The formation of TbtH and TipH is suggestive of radical generation and hydrogen abstraction in the course of the reaction. The generation of an aryl radical, Tbt•, was confirmed by an experiment with toluene-d8 as the solvent; the deuterium content of TbtH(D), after quenching with H2O, was 74%. The authors thank the editor for suggesting this experiment.
© 1997 American Chemical Society
4238 Organometallics, Vol. 16, No. 20, 1997
Communications Scheme 2
Figure 1. ORTEP drawing of Tbt(TbtS)Pb: (2) with a thermal ellipsoid plot (30% probability). Selected bond lengths (Å) and angles (deg): Pb(1)-C(1) 2.228(9), Pb(1)S(1) 2.498(10), S(1)-C(1*) 1.88(1), C(1)-Pb(1)-S(1) 100.2(3), Pb(1)-S(1)-C(1*) 107.4(6). Scheme 1
there is no intermolecular interaction between lead and sulfur atoms unlike bis[(2,6-di-tert-butyl-4-methylphenyl)thio]plumbylene, which exists as an arylsulfidobridged cyclic trimer.11 Two Tbt groups are arranged (9) 2: C54H118PbSSi12, FW ) 1343.81, triclinic, space group P1h , a ) 12.971(4) Å, b ) 17.761(5) Å, c ) 9.309(3) Å, R ) 96.60(3)°, β ) 107.21(2)°, γ ) 105.74(2)°, V ) 1926(1) Å3, Z ) 1, Dc ) 1.158 g cm-3, µ(Mo KR) ) 24.35 cm-1, F(000) ) 708. A dark plate crystal of 2 having dimensions of 0.20 × 0.15 × 0.02 mm was mounted in a glass capillary. The data set was collected on a Rigaku AFC7R diffractometer with graphite-monochromated Mo KR radiation (λ ) 0.710 69 Å) at 296 K and a rotating anode generator. The structure was solved by direct methods with SHELXS-86.10 The intensities were corrected for Lorentz and polarization effects. The non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included but not refined. The final cycle of full-matrix least-squares refinement was based on 1826 observed reflections (I > 4.00σ(I)) and 316 variable parameters and converged (largest parameter shift was 0.79 times its esd) at R (Rw) ) 0.047 (0.053) with GOF ) 1.23. The lead and sulfur atoms were located at disordered positions in two sites with 1:1 occupancy factors. Although the molecule of compound 2 has no center of symmetry, the crystal structure of 2 showed the appearance of an inversion center due to the disordered structure. The structural refinement with a space group of P1 (Z ) 1) failed and diverged. All calculations were performed using the TEXSAN crystallographic software package of Molecular Structure Corp. Atomic coodinates, bond lengths and angles, and thermal parameters have been deposited at Cambridge Crystallographic Data Centre.
in a trans fashion with regard to the Pb-S axis for a steric reason. Interestingly, the aromatic planes of two Tbt groups are almost perpendicular to the plane consisting of C(1)-Pb(1)-S(1)-C(1*). The Pb-C bond, 2.228(9) Å, and the Pb-S bond, 2.498(10) Å, are almost equal to the sum of the covalent radii of the two atoms, 2.23 and 2.50 Å, respectively.12 The S(1)-Pb(1)-C(1) angle, 100.2(3)° is in the range of those for other plumbylenes.2 The 1H NMR spectrum of 2 showed two sets of signals derived from two different Tbt groups.7 The FAB mass spectrum of 2 did not give the molecular ion peak, but the ion peak of [TbtSPb]+ indicates a weak bonding involving the lead atom. The electronic spectrum of 2 in toluene showed a characteristic absorption maximum at 540 nm ( 200 000), most likely due to an n-p transition. Plumbylene 2 was found to be stable at room temperature in the solid state for over 1 year under inert atmosphere and for a few days even in the open air. It is also stable in dry and degassed solution. When 2 was reacted with water in THF at room temperature, the bonds between lead and the substituents were cleaved, giving TbtH and TbtSH quantitatively. Reactions of 2 with 1 equiv of [2,4,6-tris(trimethylsilylmethyl)phenyl]lithium (TtmLi) in ether at -72 °C followed by treatment with methyl iodide at -40 °C gave Tbt(Ttm)Pb(CH3)I 6 (22%), TbtSCH3 7 (55%), and TbtH (59%).13 The formation of 6 and 7 can be reasonably interpreted by the intial formation of diarylplumbylene Tbt(Ttm)Pb: and TbtSLi via an attack of TmtLi on the lead atom and subsequent quenching with the iodide. The fact that 2 and 3 bear only Tbt and Tip groups, respectively, indicates the presence of some comproportionation process in their formation from 1. We propose a mechanism shown in Scheme 2 for the formation of 2 and 3. The tetrathiaplumbolane 1 is first desulfurized to give plumbanethione 8, which undergoes a 1,2-aryl migration to give plumbylenes 9 and 10. They subsequently dimerize to give an arylsulfido-bridged organolead heterocycle 11,11 the retro [2 + 2] cycloaddition (10) Sheldrick, G. M. SHELXS-86, Program for Crystal Structure Determination; University of Go¨ttingen: Go¨ttingen, Germany, 1986. (11) An arylthioplumbylene tends to oligomerize. See, for example: Hitchcock, P. B.; Lappert, M. F.; Samways, B. J.; Weinburg, E. L. J. Chem. Soc., Chem. Commun. 1983, 1492. (12) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, England, 1984; p 431. (13) We have previously reported that diarylplumbylene could be trapped by methyl iodide to give the corresponding iodomethylplumbane. See ref 6.
Communications
reaction of which affords 2 and 12. The less crowded plumbylene 12 undergoes dimerization followed by a 1,2-aryl migration gives dithiadiplumbetane 3. The 1,2-aryl migration suggested above for 8 has never been observed in the preparation of other heavier group 14 element analogues of thioketone, Tbt(Tip)MdS (M ) Si, Ge, and Sn), by desulfurization of tetrathiametallolanes with a phosphine reagent.4,14 In this respect, the recent report by Schleyer and co-workers should be noted. Their theoretical calculations have indicated that a ketone congener, R2MdO (R ) H, CH3), is more stable than a carbene analogue, R(RO)M:, when M ) C and Si, whereas R(RO)M: is more stable than R2MdO when M ) Ge, Sn, and Pb.15 We think the possible formation of 9 and 10 from 8 can be interpreted as an experimental demonstration that R(RS)Pb: is (14) (a) Tokitoh, N.; Matsuhashi, Y.; Goto, M.; Okazaki, R. Chem. Lett. 1992, 1595. (b) Matsuhashi, Y.; Tokitoh, N.; Okazaki, R. Organometallics 1993, 12, 2573. (15) Kapp, J.; Remko, M.; Schleyer, P. v. R. J. Am. Chem. Soc. 1996, 118, 5745.
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more stable than R2PbdS. Further work is in progress to elucidate a detailed mechanism for this interesting reaction. Acknowledgment. This work was partially supported by a Grant-in Aid for Scientific Research (Grant No. 05236102) from the Ministry of Education, Science, Sports, and Culture of Japan. We are also grateful to Shin-etsu Chemical Co., Ltd., and Tosoh Akzo Co., Ltd., for the generous gift of the chlorosilanes and alkyllithiums, respectively. Supporting Information Available: Text giving detailed experimental and spectral data for all new compounds, tables of complete bond legths and angles, atomic coordinates, and positional and thermal parameters, and ORTEP and cellpacking diagrams for 2 (32 pages). Ordering information is given on any current masthead page. OM9705564
