Understanding the exceptional hydrogen-atom donor characteristics of water in TiIII-mediated free-radical chemistry

Journal of the American Chemical Society

Volumn 132, Issue 36, 2010, Pages 12748-12756

  Paradas, Miguel ^a   Campaña, Araceli G ^b   Jiménez, Tania ^a   Robles, Rafael ^a   Oltra, J Enrique ^a   Buñuel, Elena ^b   Justicia, José ^a   Cárdenas, Diego J ^b   Cuerva, Juan M ^a  

^a UNIVERSITY OF GRANADA   (Spain)

^b UNIVERSIDAD AUTÓNOMA DE MADRID   (Spain)

Author keywords

[No Author keywords available]

Indexed keywords

AQUA COMPLEXES; BINDING CAPABILITY; HYDROGEN ATOMS; KEY FEATURE; LOW-ACTIVATION ENERGY; PREDICTIVE CAPABILITIES; RADICAL CHEMISTRY; RADICAL REACTIONS; TITANOCENES;

ACTIVATION ENERGY; HYDROGEN; REACTION KINETICS;

COMPRESSED AIR MOTORS;

FREE RADICAL; HYDROGEN; REAGENT; TITANIUM; TITANOCENE; WATER;

ARTICLE; ATOM; CHEMISTRY; COMPLEX FORMATION; ENERGY; METAL BINDING; PREDICTION; PROTON TRANSPORT; REACTION ANALYSIS;

FREE RADICALS; HYDROGEN; MOLECULAR DYNAMICS SIMULATION; MOLECULAR STRUCTURE; ORGANOMETALLIC COMPOUNDS; STEREOISOMERISM; THERMODYNAMICS; WATER;

EID: 77956422154     PISSN: 00027863     EISSN: 15205126     Source Type: Journal    
DOI: 10.1021/ja105670h     Document Type: Article

References (65)

1. Curran, D. P., Porter, N. A., and Giese, B. Stereochemistry of Radical Reactions; VCH: Weinheim, Germany, 1996; p 4.
2. Curran, D. P. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., and Semmelhack, M. E., Eds.; Pergamon: Oxford, 1991; Vol. 4, pp 715 - 777
3. HAT mechanism is a subfamily of the more general proton-coupled electron transfer (PCET) mechanism
4. Mayer, J. M. Annu. Rev. Phys. Chem. 2004, 55, 363-390
5. Huynh, M. H. V. and Meyer, T. J. Chem. Rev. 2007, 107, 5004-5064
6. Organometallic compounds, derived from a radical heterocoupling between a carbon radical and metallic species, can be involved in the initial reduction step, leading the global ET/PT after a subsequent protonolysis.
7. Ruscic, B., Wagner, A. F., Harding, L. B., Asher, R. L., Feller, D., Dixon, D. A., Peterson, K. A., Song, Y., Qian, X., Ng, C.-Y., Liu, J., Chen, W., and Schwenke, D. W. J. Phys. Chem. A 2002, 106, 2727-2747
8. 2 species; see
9. RajanBabu, T. V. and Nugent, W. A. J. Am. Chem. Soc. 1994, 116, 986-997
10. Enemærke, R. J., Larsen, J., Skrydstrup, T., and Daasbjerg, K. J. Am. Chem. Soc. 2004, 126, 7853-7864
11. 2TiCl(L) related species
12. Gansäuer, A., Barchuk, A., Keller, F., Schmitt, M., Grimme, S., Gerenkamp, M., Mück-Lichtenfeld, C., Daasbjerg, K., and Svith, H. J. Am. Chem. Soc. 2007, 129, 1359-1371
13. Cuerva, J. M., Campaña, A. G., Justicia, J., Rosales, A., Oller-López, J. L., Robles, R., Cárdenas, D. J., Buñuel, E., and Oltra, J. E. Angew. Chem., Int. Ed. 2006, 45, 5522-5526
14. Jiménez, T., Campaña, A. G., Bazdi, B., Paradas, M., Arráez-Román, D., Segura-Carretero, A., Fernández- Gutiérrez, A., Oltra, J. E., Robles, R., Justicia, J., and Cuerva, J. M. Eur. J. Org. Chem. 2010, 4288-4295
15. This observation was also extended to the reduction of ketyl radicals
16. Paradas, M., Campaña, A. G., Marcos, M. L., Justicia, J., Haidour, A., Robles, R., Cárdenas, D. J., Oltra, J. E., and Cuerva, J. M. Dalton Trans. 2010, DOI: 10.1039/c001689f.
17. For other precedent of water acting as HAT reagent
18. Spiegel, D. A., Wiberg, K. B., Schacherer, L. N., Medeiros, M. R., and Wood, J. L. J. Am. Chem. Soc. 2005, 127, 12513-12515
19. 2, has been described
20. Gansäuer, A., Fan, C.-A., and Keller, F. J. Am. Chem. Soc. 2008, 130, 6916-6917
21. Jin, J. and Newcomb, M. J. Org. Chem. 2008, 73, 7901-7905
22. Newcomb, M. Tetrahedron 1993, 49, 1151-1176
23. Barrero, A. F., Oltra, J. E., Cuerva, J. M., and Rosales, A. J. Org. Chem. 2002, 67, 2566-2571
24. Barrero, A. F., Rosales, A., Cuerva, J. M., and Oltra, J. E. Org. Lett. 2003, 5, 1935-1938
25. Justicia, J., Rosales, A., Buñuel, E., Oller-López, J. L., Valdivia, M., Haidour, A., Oltra, J. E., Barrero, A. F., Cárdenas, D. J., and Cuerva, J. M. Chem.-Eur. J. 2004, 10, 1778-1788
26. Justicia, J., Oller-López, J. L., Campaña, A. G., Oltra, J. E., Cuerva, J. M., Buñuel, E., and Cárdenas, D. J. J. Am. Chem. Soc. 2005, 127, 14911-14921
27. Justicia, J., Oltra, J. E., and Cuerva, J. M. J. Org. Chem. 2005, 70, 8265-8270
28. Campaña, A. G., Estévez, R. E., Fuentes, N., Robles, R., Cuerva, J. M., Buñuel, E., Cárdenas, D. J., and Oltra, J. E. Org. Lett. 2007, 9, 2195-2198
29. Pozzi, D., Scanlan, E. M., and Renaud, P. J. Am. Chem. Soc. 2005, 127, 14204-14205
30. 17O NMR) of titanocene(III) aqua complexes see reference (8).
31. 2O of 1:2.
32. The corresponding UV-vis study of a 0.01 M solution of complex 2 in benzene in the presence of increasing amounts of THF was also carried out. We did not observe significant changes in the UV-vis spectrum even in the presence of high amounts of THF. See Supporting Information for details.
33. We could not obtain a titration curve for N, N -dibutyl amine.
34. For a recent reference see
35. Paniagua, C., Mosquera, M. E. G., Jacobsen, H., Jimenez, G., and Cuenca, T. Organometallics 2009, 28, 6975-6980
36. 2TiCl. Nevertheless, it has been described that changes in the Cp substitution in titanocene(III)- complexes have significant variations in their chemical reactivity and consequently coordination capabilities can be also affected
37. Duthaler, R. O. and Hafner, A. Chem. Rev. 1992, 92, 807-832
38. -1, respectively.
39. In our preliminary communication (ref 6a), we selected 6,7-epoxyneryl acetate as model substrate for tertiary radical generation and study. It presented some unique characteristics which helped us to distinguish between different mechanisms. Nevertheless, we obtained mixtures of cyclized and uncyclized products complicating the comparison between experiments.
40. The benzoate group was introduced to avoid losses by evaporation, guaranteeing the homogeneity of the results and as a UV marker for an easy detection by analytical techniques.
41. 2TiCl is the active species in the mixed disproportionation process
42. Justicia, J., Jiménez, T., Morcillo, S. P., Cuerva, J. M., and Oltra, J. E. Tetrahedron 2009, 65, 10837-10841
43. 2TiCl is high enough to promote secondary reactions such as deoxygenation processes. Pre-association processes between aqua complex and the tertiary radical cannot be ruled out either
44. Hammerum, S. J. Am. Chem. Soc. 2009, 131, 8627-8635
45. See also: Miyazaki, S., Kojima, T., Mayer, J. M., and Fukuzumi, S. J. Am. Chem. Soc. 2009, 131, 11615-11624
46. 2 obtaining similar results.
47. a values, a higher amount of reduced product should be expected in the reaction with phenol compared with water. Nevertheless, the actual yields follow the opposite trend (17% and 84%, respectively).
48. -1) are operative: see ref 9.
49. Franchi, P., Lucarini, M., Pedulli, G. F., Valgimigli, L., and Lunelli, B. J. Am. Chem. Soc. 1999, 121, 507-514
50. For a similar analysis of the transition state, see
51. DiLabio, G. A. and Johnson, E. R. J. Am. Chem. Soc. 2007, 129, 6199-6203
52. In the literature, there are some cases where the activation energy in HAT processes can be correlated with Hammett σ parameters. In that case the activation energies, the spin densities and the HOMO levels of the TS correlated well with the σ parameters
53. Wang, Y., Kumar, D., Yang, C., Han, K., and Shaik, S. J. Phys. Chem. B 2007, 111, 7700-7710
54. -1.
55. Gansäuer, A., Pierobon, M., and Bluhm, H. Angew. Chem., Int. Ed. 2002, 41, 3206-3208
56. 2O, which suggests that the HAT from THF is the main reaction.
57. Barrero, A. F., Herrador, M. M., Quílez del Moral, J. F., Arteaga, P., Arteaga, J. F., Diéguez, H. R., and Sánchez, E. M. J. Org. Chem. 2007, 72, 2988-2995
58. Throssel, J. J. Int. J. Chem. Kinetics 1972, 4, 273-276
59. -1
60. Claridge, R. F. C. and Fischer, H. J. Phys. Chem. 1983, 87, 1960-1967
61. The functionalization was selected to obtain reduction products which would not be volatile.
62. Barrero, A. F., Herrador, M. M., Quílez del Moral, J. F., Arteaga, P., Akssira, M., El Hanbali, F., Arteaga, J. F., Diéguez, H. R., and Sánchez, E. M. J. Org. Chem. 2007, 72, 2251-2254
63. Gansäuer, A., Ndene, N., Lauterbach, T., Justicia, J., Winkler, I., Mück-Lichtenfeld, C., and Grimme, S. Tetrahedron 2008, 64, 11839-11845
64. Fernández-Mateos, A., Encinas Madrazo, S., Herrero Teijón, P., and Rubio González, R. J. Org. Chem. 2009, 74, 3913-3918
65. Compound 17 was isolated as a 1:2 mixture of meso:dl stereoisomers.