Organometallics 2006, 25, 2949-2959
2949
Reactions of r,β-Unsaturated Thioesters with Platinum(0): Implication of a Dual Mechanism Leading to the Formation of Acyl Platinum† Yasunori Minami, Tomohiro Kato, Hitoshi Kuniyasu,* Jun Terao, and Nobuaki Kambe* Department of Molecular Chemistry & Frontier Research Center, Graduate School of Engineering, Osaka UniVersity, Suita, Osaka 565-0871, Japan ReceiVed September 28, 2005
The moderate reactivity of the R,β-unsaturated thioester (ArS)C(O)C(A)dC(B)(H) toward Pt(PPh3)2(C2H4) has been used to extract thermodynamic and kinetic information pertaining to the oxidative addition of R,β-unsaturated acid halide derivatives to low-valent transition-metal complexes. The results indicate acyl platinum product complexes can form by direct C-S bond cleavage or by attack of coordinated Pt(PPh3)2 on the β-carbon. Introduction It has been well-known that the reactions of R,β-unsaturated acid halides with low-valent transition-metal complexes produced acyl metals.1 However, much attention to their reaction mechanism has not been attracted presumably due to the lack of a good reaction system to examine the details. In fact, when the reactions of (Cl)C(O)C(H)dCH2 (A ) B ) H; 1a) or (Cl)C(O)C(H)dC(Ph)(H)-(E) (A ) H, B ) Ph; 1b) with Pt(PPh3)2(C2H4) (2) were performed in toluene-d8 using a freeze-pumpthaw technique, acyl platinums 3a and 3b were quantitatively produced even at -50 °C after 10 min in both cases (eq 1).2 Although the predominant formation of the cis isomer at the
beginning of the reactions suggested its stereochemistry of oxidative addition, more information such as the effect of the introduction of a Ph group at the β-carbon (B ) Ph) was not clearly disclosed from these experimental data. Recently, we have reported that the cleavage and formation of C-S bonds by transition-metal complexes were flexible3 and † This work is dedicated to Prof. Hideo Kurosawa on the occasion of his retirement from Osaka University. * To whom correspondence should be addressed. E-mail:
[email protected]. (1) (a) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition-Metal Chemistry; University Science Books: Mill Valley, CA, 1987. (b) Grabtree, R. H. The Organometallic Chemistry of the Transition Metals, 4th ed.; WileyInterscience: New York, 2003. (2) (a) Stille, J. K.; Lau, K. S. Y. Acc. Chem. Res. 1977, 10, 434. (b) Fahey, D. R.; Mahan, J. E. J. Am. Chem. Soc. 1977, 99, 2501. (c) Dent, S. P.; Eaborn, C.; Pidcock, A. J. Organomet. Chem. 1975, 97, 307. (3) (a) Kuniyasu, H.; Sugoh, K.; Moon, S.; Kurowasa, H. J. Am. Chem. Soc. 1997, 119, 4669. (b) Miyauchi, Y.; Watanabe, S.; Kuniyasu, H.; Kurosawa, H. Organometallics 1995, 14, 5450.
that such characteristics could be utilized for elucidating the mechanism of cleavage of the vinyl-X bonds by low-valent transition-metals4 and for achieving a series of Pt-catalyzed carbothiolation of alkynes.5 Herein we wish to report that the effects of substituents on the reactions of R,β-unsaturated acid halide derivatives with low-valent transition-metal complexes are quite clearly revealed by utilizing the controllable reactivity of the R,β-unsaturated thioester (ArS)C(O)C(A)dC(B)(H) (4) toward 2, substantiating that there are two distinct reaction routes for the formation of acyl complexes.
Results and Discussion Reactions of Thioesters Having a p-MeC6H4S Group with a Platinum(0) Complex. Thioesters 4 with a p-MeC6H4S group shown in Table 1 were prepared, and the reactions with 2 were monitored by 1H and 31P NMR spectroscopies at 25 °C using SdP(C6H4OMe-p)3 as an internal standard.6 When 4a (A ) B ) H) was employed, the quantitative formation of π-complex 5a was confirmed after 20 min in both C6D6 and CD2Cl2 solution. Although it was not clear when the systems reached the equilibrium states due to the low yields of acyl platinum 6a and 7a (dimeric form of 6a), the formation after 3 h of 99.5% of 5a and 0.5% of 7a in C6D6 and of 98.9% of 5a, 0.4% of 6a, and 0.7% of 7a was confirmed in CD2Cl2 (runs 1 and 2). On the other hand, the reaction of trans-3a (0.02 mmol) with p-MeC6H4SNa (8, 0.06 mmol) in CD2Cl2 (0.5 mL) at 25 °C produced 5a (79%), trans-6a (0.6%), and 7a (13%, syn/anti ) 77/23) after 17 h (eq 2). These results clearly showed that the (4) (a) Kuniyasu, H.; Ohtaka, A.; Nakazono, T.; Kinomoto, M.; Kurosawa, H. J. Am. Chem. Soc. 2000, 122, 2375. (b) Kuniyasu, H.; Kato, T.; Inoue, M.; Terao, J.; Kambe, N. J. Organomet. Chem. 2006, 691, 1873. (5) (a) Sugoh, K.; Kuniyasu, H.; Sugae, T.; Ohtaka, A.; Takai, Y.; Tanaka, A.; Machino, C.; Kambe, N.; Kurosawa, H. J. Am. Chem. Soc. 2001, 123, 5108. (b) Kuniyasu, H.; Kurosawa, H. Chem. Eur. J. 2002, 12, 2660. (c) Hirai, T.; Kuniyasu, H.; Kato, T.; Kurata, Y.; Kambe, N. Org. Lett. 2003, 5, 3871. (d) Hirai, T.; Kuniyasu, H.; Kambe, N. Chem. Lett. 2004, 33, 1148. (e) Hirai, T.; Kuniyasu, H.; Kambe, N. Tetrahedron. Lett. 2005, 46, 117. (f) Hirai, T.; Kuniyasu, H.; Terao, J.; Kambe, N. Synlett. 2005, 7, 1161. (g) Kuniyasu, H.; Yamashita, F.; Hirai, T.; Ye, J.; Fujiwara, S.; Kambe, N. Organometallics 2006, 25, 566. (6) No interaction between SdP(C6H4OMe-p)3 and other reagents has been confirmed during the course of the present study.
10.1021/om050834w CCC: $33.50 © 2006 American Chemical Society Publication on Web 05/11/2006
2950 Organometallics, Vol. 25, No. 12, 2006
Minami et al. Table 1. Reactions of 4 with 2a
run 1 2 3 4 5 6 7 8 9 10i 11 12 13j 14
4 4a 4a 4b 4b 4c 4c 4d 4e 4f 4f 4f 4g 4g 4g
solventb a b a b a b a a a a b a a b
timec
5/6(cis/trans)d
timee
-f
-g
-f
-f 3-4 h 5-6 h
