Orbital symmetry as a tool for understanding the bonding in Krossing's cation

Journal of the American Chemical Society

Volumn 124, Issue 41, 2002, Pages 12312-12318

  Deubel, Dirk V ^a,b,c  

^a Centro Svizzero Di Calcolo Scientifico   (Switzerland)

^b INSTITUTE OF BIOMEDICAL SCIENCES   (Taiwan)

^c UNIVERSITY OF CALGARY   (Canada)

Author keywords

[No Author keywords available]

Indexed keywords

DECOMPOSITION; ETHYLENE; POSITIVE IONS; PROBABILITY DENSITY FUNCTION;

ORBITAL SYMMETRIES;

BONDING;

ALKENE; CATION; COORDINATION COMPOUND; ETHYLENE; KROSSING CATION; LIGAND; METAL; PHOSPHORUS; SILVER; UNCLASSIFIED DRUG;

ARTICLE; CHEMICAL BOND; CHEMICAL REACTION; DENSITY FUNCTIONAL THEORY; ELECTRICITY; ELECTRON; ENERGY; GEOMETRY; MOLECULAR INTERACTION; QUANTUM CHEMISTRY; SOLID STATE; SOLVATION; THEORY;

EID: 0037120832     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja0206691     Document Type: Article

References (75)

1. URL: http://staff-www.uni-marburg.de/∼deubel.
2. Krossing, I. J. Am. Chem. Soc. 2001, 123, 4603.
3. Krossing, J. Chem. Eur. J. 2001, 7, 490.
4. + cations with the counterions freely rotating; for details, see refs 2 and 6.
5. 2d symmetry as shown in the Figures. Cotton, F. A. Chemical Applications of Group Theory, 3rd edition; Wiley: New York, 1990.
6. Krossing, I.; van Wüllen, L. Chem. Eur. J. 2002, 8, 700.
7. (a) Krossing, I., Raabe, I. Angew. Chem. Int. Ed. 2001, 40, 4406.
8. (b) Krossing, I. J. Chem. Soc. Dalton Trans. 2002, 500.
9. (c) Adolf, A.; Gonsior, M.; Krossing, I. J. Am. Chem. Soc. 2002, 124, 711.
10. (a) Ginsberg, A. P.; Lindsell, W. F.; McCullough, K. J.; Sprinkle, C. R.; Welsh, A. J. J. Am. Chem. Soc. 1986, 108, 403.
11. (b) Göer, T.; Baum, G.; Scheer, M. Organometallics 1998, 17, 5916.
12. Bader, R. F. W. Atoms in Molecules; Clarendon Press: Oxford, England. 1994.
13. Hertwig, R. H.; Koch, W.; Schröder, D.; Schwarz, H.; Hrusák, J.; Schwerdtfeger, P. J. Phys. Chem. 1996, 100, 12253.
14. (a) Ziegler, T.; Rauk, A. Theor. Chim. Acta 1977, 46, 1.
15. (b) Ziegler, T.; Rauk, A. Inorg. Chem. 1979, 18, 1755.
16. Decomposition schemes have proved to be valuable tools for an understanding of the chemical bond and reactivity; for recent examples, see: (a) Deubel, D. V.; Frenking, G. J. Am. Chem. Soc. 1999, 121, 2021. (b) Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc. 1999, 121, 12113. (c) Fonseca Guerra, C.; Bickelhaupt, F. M.; Snijders, J. G.; Baerends, E. J. J. Am. Chem. Soc. 2000, 122, 4117. (d) Deubel, D. V.; Sundermeyer, J.; Frenking, G. J. Am. Chem. Soc. 2000, 122, 10101. (e) Uddin, J.; Frenking, G. J. Am. Chem. Soc. 2001, 123, 1683. (f) Cedeño, D. L.; Weitz, E. J. Am. Chem. Soc. 2001, 123, 12857. (g) Bickelhaupt, F. M.; DeKock, R. L.; Baerends. E. J. J. Am. Chem. Soc. 2002, 124, 1500. (h) Baik, M.-H.; Friesner, R. A.; Lippard, S. J. J. Am. Chem. Soc. 2002, 124, 4495. (i) Deubel, D. V. J. Am. Chem. Soc. 2002, 124, 5834.
17. Decomposition schemes have proved to be valuable tools for an understanding of the chemical bond and reactivity; for recent examples, see: (a) Deubel, D. V.; Frenking, G. J. Am. Chem. Soc. 1999, 121, 2021. (b) Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc. 1999, 121, 12113. (c) Fonseca Guerra, C.; Bickelhaupt, F. M.; Snijders, J. G.; Baerends, E. J. J. Am. Chem. Soc. 2000, 122, 4117. (d) Deubel, D. V.; Sundermeyer, J.; Frenking, G. J. Am. Chem. Soc. 2000, 122, 10101. (e) Uddin, J.; Frenking, G. J. Am. Chem. Soc. 2001, 123, 1683. (f) Cedeño, D. L.; Weitz, E. J. Am. Chem. Soc. 2001, 123, 12857. (g) Bickelhaupt, F. M.; DeKock, R. L.; Baerends. E. J. J. Am. Chem. Soc. 2002, 124, 1500. (h) Baik, M.-H.; Friesner, R. A.; Lippard, S. J. J. Am. Chem. Soc. 2002, 124, 4495. (i) Deubel, D. V. J. Am. Chem. Soc. 2002, 124, 5834.
18. Decomposition schemes have proved to be valuable tools for an understanding of the chemical bond and reactivity; for recent examples, see: (a) Deubel, D. V.; Frenking, G. J. Am. Chem. Soc. 1999, 121, 2021. (b) Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc. 1999, 121, 12113. (c) Fonseca Guerra, C.; Bickelhaupt, F. M.; Snijders, J. G.; Baerends, E. J. J. Am. Chem. Soc. 2000, 122, 4117. (d) Deubel, D. V.; Sundermeyer, J.; Frenking, G. J. Am. Chem. Soc. 2000, 122, 10101. (e) Uddin, J.; Frenking, G. J. Am. Chem. Soc. 2001, 123, 1683. (f) Cedeño, D. L.; Weitz, E. J. Am. Chem. Soc. 2001, 123, 12857. (g) Bickelhaupt, F. M.; DeKock, R. L.; Baerends. E. J. J. Am. Chem. Soc. 2002, 124, 1500. (h) Baik, M.-H.; Friesner, R. A.; Lippard, S. J. J. Am. Chem. Soc. 2002, 124, 4495. (i) Deubel, D. V. J. Am. Chem. Soc. 2002, 124, 5834.
19. Decomposition schemes have proved to be valuable tools for an understanding of the chemical bond and reactivity; for recent examples, see: (a) Deubel, D. V.; Frenking, G. J. Am. Chem. Soc. 1999, 121, 2021. (b) Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc. 1999, 121, 12113. (c) Fonseca Guerra, C.; Bickelhaupt, F. M.; Snijders, J. G.; Baerends, E. J. J. Am. Chem. Soc. 2000, 122, 4117. (d) Deubel, D. V.; Sundermeyer, J.; Frenking, G. J. Am. Chem. Soc. 2000, 122, 10101. (e) Uddin, J.; Frenking, G. J. Am. Chem. Soc. 2001, 123, 1683. (f) Cedeño, D. L.; Weitz, E. J. Am. Chem. Soc. 2001, 123, 12857. (g) Bickelhaupt, F. M.; DeKock, R. L.; Baerends. E. J. J. Am. Chem. Soc. 2002, 124, 1500. (h) Baik, M.-H.; Friesner, R. A.; Lippard, S. J. J. Am. Chem. Soc. 2002, 124, 4495. (i) Deubel, D. V. J. Am. Chem. Soc. 2002, 124, 5834.
20. Decomposition schemes have proved to be valuable tools for an understanding of the chemical bond and reactivity; for recent examples, see: (a) Deubel, D. V.; Frenking, G. J. Am. Chem. Soc. 1999, 121, 2021. (b) Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc. 1999, 121, 12113. (c) Fonseca Guerra, C.; Bickelhaupt, F. M.; Snijders, J. G.; Baerends, E. J. J. Am. Chem. Soc. 2000, 122, 4117. (d) Deubel, D. V.; Sundermeyer, J.; Frenking, G. J. Am. Chem. Soc. 2000, 122, 10101. (e) Uddin, J.; Frenking, G. J. Am. Chem. Soc. 2001, 123, 1683. (f) Cedeño, D. L.; Weitz, E. J. Am. Chem. Soc. 2001, 123, 12857. (g) Bickelhaupt, F. M.; DeKock, R. L.; Baerends. E. J. J. Am. Chem. Soc. 2002, 124, 1500. (h) Baik, M.-H.; Friesner, R. A.; Lippard, S. J. J. Am. Chem. Soc. 2002, 124, 4495. (i) Deubel, D. V. J. Am. Chem. Soc. 2002, 124, 5834.
21. Decomposition schemes have proved to be valuable tools for an understanding of the chemical bond and reactivity; for recent examples, see: (a) Deubel, D. V.; Frenking, G. J. Am. Chem. Soc. 1999, 121, 2021. (b) Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc. 1999, 121, 12113. (c) Fonseca Guerra, C.; Bickelhaupt, F. M.; Snijders, J. G.; Baerends, E. J. J. Am. Chem. Soc. 2000, 122, 4117. (d) Deubel, D. V.; Sundermeyer, J.; Frenking, G. J. Am. Chem. Soc. 2000, 122, 10101. (e) Uddin, J.; Frenking, G. J. Am. Chem. Soc. 2001, 123, 1683. (f) Cedeño, D. L.; Weitz, E. J. Am. Chem. Soc. 2001, 123, 12857. (g) Bickelhaupt, F. M.; DeKock, R. L.; Baerends. E. J. J. Am. Chem. Soc. 2002, 124, 1500. (h) Baik, M.-H.; Friesner, R. A.; Lippard, S. J. J. Am. Chem. Soc. 2002, 124, 4495. (i) Deubel, D. V. J. Am. Chem. Soc. 2002, 124, 5834.
22. Decomposition schemes have proved to be valuable tools for an understanding of the chemical bond and reactivity; for recent examples, see: (a) Deubel, D. V.; Frenking, G. J. Am. Chem. Soc. 1999, 121, 2021. (b) Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc. 1999, 121, 12113. (c) Fonseca Guerra, C.; Bickelhaupt, F. M.; Snijders, J. G.; Baerends, E. J. J. Am. Chem. Soc. 2000, 122, 4117. (d) Deubel, D. V.; Sundermeyer, J.; Frenking, G. J. Am. Chem. Soc. 2000, 122, 10101. (e) Uddin, J.; Frenking, G. J. Am. Chem. Soc. 2001, 123, 1683. (f) Cedeño, D. L.; Weitz, E. J. Am. Chem. Soc. 2001, 123, 12857. (g) Bickelhaupt, F. M.; DeKock, R. L.; Baerends. E. J. J. Am. Chem. Soc. 2002, 124, 1500. (h) Baik, M.-H.; Friesner, R. A.; Lippard, S. J. J. Am. Chem. Soc. 2002, 124, 4495. (i) Deubel, D. V. J. Am. Chem. Soc. 2002, 124, 5834.
23. Decomposition schemes have proved to be valuable tools for an understanding of the chemical bond and reactivity; for recent examples, see: (a) Deubel, D. V.; Frenking, G. J. Am. Chem. Soc. 1999, 121, 2021. (b) Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc. 1999, 121, 12113. (c) Fonseca Guerra, C.; Bickelhaupt, F. M.; Snijders, J. G.; Baerends, E. J. J. Am. Chem. Soc. 2000, 122, 4117. (d) Deubel, D. V.; Sundermeyer, J.; Frenking, G. J. Am. Chem. Soc. 2000, 122, 10101. (e) Uddin, J.; Frenking, G. J. Am. Chem. Soc. 2001, 123, 1683. (f) Cedeño, D. L.; Weitz, E. J. Am. Chem. Soc. 2001, 123, 12857. (g) Bickelhaupt, F. M.; DeKock, R. L.; Baerends. E. J. J. Am. Chem. Soc. 2002, 124, 1500. (h) Baik, M.-H.; Friesner, R. A.; Lippard, S. J. J. Am. Chem. Soc. 2002, 124, 4495. (i) Deubel, D. V. J. Am. Chem. Soc. 2002, 124, 5834.
24. Decomposition schemes have proved to be valuable tools for an understanding of the chemical bond and reactivity; for recent examples, see: (a) Deubel, D. V.; Frenking, G. J. Am. Chem. Soc. 1999, 121, 2021. (b) Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc. 1999, 121, 12113. (c) Fonseca Guerra, C.; Bickelhaupt, F. M.; Snijders, J. G.; Baerends, E. J. J. Am. Chem. Soc. 2000, 122, 4117. (d) Deubel, D. V.; Sundermeyer, J.; Frenking, G. J. Am. Chem. Soc. 2000, 122, 10101. (e) Uddin, J.; Frenking, G. J. Am. Chem. Soc. 2001, 123, 1683. (f) Cedeño, D. L.; Weitz, E. J. Am. Chem. Soc. 2001, 123, 12857. (g) Bickelhaupt, F. M.; DeKock, R. L.; Baerends. E. J. J. Am. Chem. Soc. 2002, 124, 1500. (h) Baik, M.-H.; Friesner, R. A.; Lippard, S. J. J. Am. Chem. Soc. 2002, 124, 4495. (i) Deubel, D. V. J. Am. Chem. Soc. 2002, 124, 5834.
25. Frenking, G.; Fröhlich, N. Chem. Rev. 2000, 100, 717.
26. (a) Landis, C. R.; Cleveland, T.; Firman, T. K. J. Am. Chem. Soc. 1995, 117, 1859.
27. (b) Landis, C. R.; Firman, T. K.; Root, D. M.; Cleveland, T. J. Am. Chem. Soc. 1998, 120, 1842.
28. (c) Landis, C. R.; Cleveland, T.; Firman, T. K. J. Am. Chem. Soc. 1998, 120, 2641.
29. (d) Firman, T. K., Landis, C. R. J. Am. Chem. Soc. 1998, 120, 12650.
30. (e) Firman, T. K., Landis, C. R. J. Am. Chem. Soc. 2001, 123, 11728.
31. Bayse, C. A.; Hall, M. B. J. Am. Chem. Soc. 1999, 121, 1348.
32. Diefenbach, A.; Bickelhaupt, F. M.; Frenking, G. J. Am. Chem. Soc. 2000, 122, 6449.
33. Becke, A. D. Phys. Rev. A 1988, 38, 3098.
34. Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
35. Van Lenthe, E.; Ehlers, A. E.; Baerends, E. J. J. Chem. Phys. 1999, 110, 8943 and refs cited therein.
36. (a) Fonseca Guerra, C.; Snijders, J. G.; Te Felde, G.; Baerends, E. J. Theor. Chem. Acc. 1998, 99, 391.
37. (b) Bickelhaupt, F. M.; Baerends, E. J. In Reviews in Computational Chemistry; Lipkowitz, K. B., Boyd, D. B., Eds.; VCH: New York, 2000; Vol. 15, p 1.
38. (c) Te Velde, G.; Bickelhaupt, F. M.; Baerends, E. J.; Fonseca Guerra, C.; Van Gisbergen, S. J. A.; Snijders, J. G.; Ziegler, T. J. Comput. Chem. 2001, 22, 931.
39. +) cannot be analyzed separately because the three orbitals are totally symmetric (Table 3).
40. Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988. 88, 899.
41. Maseras, F.; Morokuma, K. Chem. Phys. Lett. 1992. 195, 500.
42. Atomic charges in both 1 and 2 calculated using the Hirshfeld scheme (ref 25): Ag 0.24, PI 0.07, P3 0.12.
43. Hirshfeld, E. L. Theor. Chim. Acta 1977, 44, 129.
44. (a) Dudev, T.; Lim, C. J. Phys. Chem. B 2001, 105, 10709.
45. (b) Dudev, T.; Lim, C. J. Am. Chem. Soc. 2002. 124, ja0126201-3-316, in press.
46. 2h structure to be preferred strongly depends on atomic radii used. Because of the lack of thermochemical data required for a parametrization, the definition of the molecular cavity is arbitrary.
47. (a) Klamt, A.; Schürmann, G. J. Chem. Soc., Perkin Trans. 2 1993, 799.
48. (b) Klamt, A.; Jonas, V. J. Chem. Phys. 1996, 105, 9972.
49. (a) Advanced Inorganic Chemistry, 6th edition; Cotton, F. A., Wilkinson, G., Murillo, C., Eds.; Wiley: New York. 1999.
50. (b) Catalysis from A to Z; Cornils, B., Herrmann, W. A., Schlögl, R., Wong, C. H., Eds.; Wiley-VCH: Weinheim, Germany, 2000.
51. (c) Applied Homogeneous Catalysis with Organometallic Compounds; Cornils, B., Herrmann, W. A., Eds.; Wiley-VCH: Weinheim, Germany, 2002.
52. Guo, B. C.; Castleman, A. W. Chem. Phys. Lett. 1991, 181, 16.
53. Sievers, M. R.; Jarvis, L. M.; Armentrout, P. B. J. Am. Chem. Soc. 1998, 120, 1891.
54. +: refs 10, 30, and (a) Basch, H. J. Chem. Phys. 1972, 56, 441. (b) Ziegler, T.; Rauk, A. Inorg. Chem. 1979, 18, 1558. (c) Ma, N. L. Chem. Phys. Lett. 1998, 297, 230. (d) Schröder, D.; Wesendrup, R.; Hertwig, R. H.; Dargel, T. K.; Grauel, H. Koch, W.; Bender, B. R.; Schwarz, H. Organometallics 2000, 19, 2608. (e) Boutreau, L.; Leon, E.; Luna, A.; Toulhoat, P.; Tortajada, J. Chem. Phys. Lett. 2001, 338, 74.
55. +: refs 10, 30, and (a) Basch, H. J. Chem. Phys. 1972, 56, 441. (b) Ziegler, T.; Rauk, A. Inorg. Chem. 1979, 18, 1558. (c) Ma, N. L. Chem. Phys. Lett. 1998, 297, 230. (d) Schröder, D.; Wesendrup, R.; Hertwig, R. H.; Dargel, T. K.; Grauel, H. Koch, W.; Bender, B. R.; Schwarz, H. Organometallics 2000, 19, 2608. (e) Boutreau, L.; Leon, E.; Luna, A.; Toulhoat, P.; Tortajada, J. Chem. Phys. Lett. 2001, 338, 74.
56. +: refs 10, 30, and (a) Basch, H. J. Chem. Phys. 1972, 56, 441. (b) Ziegler, T.; Rauk, A. Inorg. Chem. 1979, 18, 1558. (c) Ma, N. L. Chem. Phys. Lett. 1998, 297, 230. (d) Schröder, D.; Wesendrup, R.; Hertwig, R. H.; Dargel, T. K.; Grauel, H. Koch, W.; Bender, B. R.; Schwarz, H. Organometallics 2000, 19, 2608. (e) Boutreau, L.; Leon, E.; Luna, A.; Toulhoat, P.; Tortajada, J. Chem. Phys. Lett. 2001, 338, 74.
57. +: refs 10, 30, and (a) Basch, H. J. Chem. Phys. 1972, 56, 441. (b) Ziegler, T.; Rauk, A. Inorg. Chem. 1979, 18, 1558. (c) Ma, N. L. Chem. Phys. Lett. 1998, 297, 230. (d) Schröder, D.; Wesendrup, R.; Hertwig, R. H.; Dargel, T. K.; Grauel, H. Koch, W.; Bender, B. R.; Schwarz, H. Organometallics 2000, 19, 2608. (e) Boutreau, L.; Leon, E.; Luna, A.; Toulhoat, P.; Tortajada, J. Chem. Phys. Lett. 2001, 338, 74.
58. +: refs 10, 30, and (a) Basch, H. J. Chem. Phys. 1972, 56, 441. (b) Ziegler, T.; Rauk, A. Inorg. Chem. 1979, 18, 1558. (c) Ma, N. L. Chem. Phys. Lett. 1998, 297, 230. (d) Schröder, D.; Wesendrup, R.; Hertwig, R. H.; Dargel, T. K.; Grauel, H. Koch, W.; Bender, B. R.; Schwarz, H. Organometallics 2000, 19, 2608. (e) Boutreau, L.; Leon, E.; Luna, A.; Toulhoat, P.; Tortajada, J. Chem. Phys. Lett. 2001, 338, 74.
59. A typical Pd(II)-C(ethylene) distance is 2.15 Å; for instance, see: Deubel, D. V.; Ziegler, T. Organometallics 2002, 21, 1603.
60. A typical Mo(VI)-C(ethylene) distance is 2.60 Å; for instance, see: Deubel, D. V.; Sundermeyer, J.; Frenking, G. Inorg. Chem. 2000, 39, 2314.
61. Atomic charges in both 3 and 4 calculated using the Hirshfeld scheme (ref 25): Ag 0.46, C -0.02, H 0.08. In ethylene: C -0.08, H 0.04.
62. The presence of bond-critical points can depend on method. Compare ref 10 with Böhme, C.; Wagener, T.; Frenking, G. J. Organomet. Chem. 1996, 520, 31.
63. 2u-symmetric (ref 10).
64. Snijders, J. G.; Baerends, E. J.; Vernooijs, P. At. Data Nucl. Data Tables 1982, 26, 483.
65. Baerends, E. J.; Ellis, D. E.; Ros, P. Chem. Phys. 1973, 2, 41.
66. Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
67. Perdew, J. P.; Wang, Y. Phys. Rev. 1992, B45, 13244.
68. The B3PW91 functional was successfully used for the investigation of phosphorous compounds: Cotton, F. A.; Cowley, A. H.; Feng, X. J. Am. Chem. Soc. 1998, 120, 1795.
69. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Milliam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomberts, R.; Martin, R. L.; Fox, D. J.; Keith, T. A.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian98; Gaussian Inc.: Pittsburgh, PA, 1998.
70. Dolg, M.; Stoll, H.; Preuss, H.; R. M. Pitzer, R. M. J. Phys. Chem. 1993, 97, 5852.
71. Ehlers, A. W.; Böhme, M.; Dapprich, S.; Gobbi, A.; Höllwarth, A.; Jonas, V.; Köhler, K. F.; Stegmann, R.; Veldkamp A.; Frenking, G. Chem. Phys. Lett. 1993, 208, 111.
72. Møller, C.; Plesset, M. S. Phys. Rev. 1934, 46, 618.
73. Simmons, H. E., Bunnett, J. F., Eds. Orbital Symmetry Papers; American Chemical Society: Washington, DC, 1974.
74. (a) Hoffmann, R.; Woodward, R. B. Science 1970, 167, 825.
75. (b) Houk, K. N.; Gonzalez, J.; Li, Y. Acc. Chem. Res. 1995, 28, 81.