Iridium complexes with new 1,2-dithioether chiral ligands containing a rigid cyclic backbone. Application in homogeneous catalytic asymmetric hydrogenation †

Abstract

New chiral dithioether compounds (–)-1-benzyl-3,4-bis(methylsulfanyl)pyrrolidine (–)-degusme, (–)-1-benzyl-3,4-bis(isopropylsulfanyl)pyrrolidine (–)-degusprⁱ and (+)-1-benzyl-3,4-bis(phenylsulfanyl)pyrrolidine (+)-degusph were prepared from (+)-L-tartaric acid. The addition of the dithioether compounds to a dichloromethane solution of [Ir(cod)₂]BF₄ afforded the chiral cationic complexes [Ir(cod){(–)-degusme}]BF₄ 1 [Ir(cod){(–)-degusprⁱ}]BF₄·CH₂Cl₂ 2 and [Ir(cod){(+)-degusph}]BF₄ 3. The dithioether ligands were replaced by PPh₃ in complexes 1, 2 and 3 providing the [Ir(cod)(PPh₃)₂]BF₄ complex. The addition of H₂ to 1, 2 and 3 at –70 °C gave cis-dihydridoiridium(III) complexes [IrH₂(cod)L]BF₄ [L = (–)-degusme 4, (–)-degusprⁱ 5 or (+)-degusph 6]. The relative stability of possible isomers for complexes 1–6 was studied by molecular mechanics calculations. Complexes 1–3 were active precursors in the asymmetric hydrogenation of different prochiral dehydroamino acid derivatives and itaconic acid, at room temperature under atmospheric pressure of H₂, and the highest enantiomeric excess obtained was 68%.

References

1. Homogeneous Catalysis with Metal Phosphine Complexes, ed. L. H. Pignolet, Plenum, New York, 1983; H. Brunner and W. Zettlmeier, Handbook of Enantioselective Catalysis, VCH, Weinheim, 1993, vol. 2; H. Takaya, T. Onta and R. Noyori, in Catalytic Asymmetric Synthesis, ed. I. Ojima, VCH, New York, 1993; R. Noyori, in Asymmetric Catalysis in Organic Synthesis, Wiley, New York, 1994; Applied Homogeneous Catalysis with Organometallic Compounds, eds. B. Cornils and W. A. Herrmann, VCH, Weinheim, 1996, vols. 1 and 2.
2. (a) A. S. C. Chan and J. Halpern, J. Am. Chem. Soc., 1980, 102, 838; (b) A. S. C. Chan and J. Halpern, J. Am. Chem. Soc., 1980, 102, 5952; (c) J. Halpern, Science, 1982, 217, 401; (d) C. R. Landis and J. Halpern, J. Am. Chem. Soc., 1987, 109, 1746; (e) J. M. Brown, P. S. Chaloner and G. A. Morris, J. Chem. Soc., Perkin Trans. 2, 1987, 2, 1583; (f) P. A. Chaloner, M. A. Esteruelas, F. Joó and L. A. Oro, in Homogeneous Hydrogenation, Kluwer, Dordrecht, 1994; (g) J. M. Brown, J. A. Ramsden and J. M. Clavidge, J. Chem Soc., Chem. Commun., 1995, 2469; (h) B. R. Bender, M. Koller, D. Nanz and W. von Phillipsborn, J. Am. Chem. Soc., 1993, 15, 5889; (i) C. R. Landis and T. W. Brauch, Inorg. Chim. Acta, 1998, 270, 285.
3. M. T. Ashby and J. Halpern, J. Am. Chem. Soc., 1991, 113, 589; A. S. C. Chan, C. C. Chen, T. K. Yang, J. H. Huang and Y. C. Lin, Inorg. Chim. Acta, 1995, 234, 95.
4. F. Fache, P. Gamez, F. Nour and M. Lemaire, J. Mol. Catal., 1993, 85, 131.
5. (a) C. Claver, S. Castillón, N. Ruiz, G. Delogu, D. Fabbri and S. Gladiali, J. Chem. Soc., Chem. Commun., 1993, 1833; (b) S. Gladiali, D. Fabbri, L. Kollàr, C. Claver, N. Ruiz, A. Alvarez-Larena and J. F. Piniella, Eur. J. Inorg. Chem, 1998, 113.
6. N. Ruiz, A. Aaliti, J. Forniés, A. Ruiz, C. Claver, C. J. Cardin, D. Fabbri and S. Gladiali, J. Organomet. Chem., 1997, 79, 545.
7. (a) M. Diéguez, A. Orejón, A. M. Masdeu-Bultó, R. Echarri, S. Castillón, C. Claver and A. Ruiz, J. Chem. Soc., Dalton Trans., 1997, 4611; (b) A. Orejón, A. M. Masdeu-Bultó, R. Echarri, M. Diéguez, J. Forniés-Cámer, C. Claver and C. J. Cardin, J. Organomet. Chem., in the press.
8. A. M. d'A. Rocha Gonsalves, J. C. Bayón, M. M. Pereira, M. E. S. Serra and J. P. R. Pereira, J. Organomet. Chem., 1997, 7577.
9. U. Nagel, E. Kinzel, J. Andrade and G. Prescher, Chem. Ber., 1986, 119, 3326.
10. P. Didier, L. Jacquet and A. Kirsch, Inorg. Chem., 1992, 31, 4803.
11. M. Green, T. A. Kuc and S. H. Taylor, J. Chem. Soc. A, 1971, 2334.
12. E. W. Abel, S. K. Bhargava and K. G. Orrell, Prog. Inorg. Chem., 1984, 32, 1.
13. K. Nakamoto, in Infrared and Raman Spectra of Inorganic and Coordination Compounds, Wiley, New York, 1978.
14. R. H. Crabtree, H. Felkin, T. Fillebeen-Khan and G. E. Morris, J. Organomet. Chem., 1979, 168, 183.
15. (a) D. G. Hamilton and R. H. Crabtree, J. Am. Chem. Soc., 1988, 110, 4126; (b) J. C. Lee, jun., W. Yao and R. H. Crabtree, Inorg. Chem., 1996, 35, 695.
16. J. C. Rodriguez, C. Claver and A. Ruiz, J. Organomet. Chem., 1985, 293, 115.
17. CERIUS 2, version 3.5, Molecular Simulations Inc., 1997.
18. L. A. Castonguay and A. K. Rappe, J. Am. Chem. Soc., 1992, 114, 583; A. K. Rappe, C. J. Casewit, K. S. Colwell, W. A. Goddard-III and W. M. Skiff, J. Am. Chem. Soc., 1992, 114, 10024; A. K. Rappe and K. S. Colwell, Inorg. Chem., 1993, 32, 3438.
19. A. K. Rappe, C. J. Casewit and W. A. Goddard-III, J. Phys. Chem., 1991, 95, 3358.
20. C. Cativiela, J. Fernandez, J. A. Mayoral, E. Melendez, R. Usón, L. A. Oro and M. J. Fernandez, J. Mol. Catal., 1992, 16, 19.
21. H. Frank, C. J. Nickolson and E. Bayer, J. Chromatogr. Sci., 1977, 15, 174.