Is it homogeneous or heterogeneous catalysis? Identification of bulk ruthenium metal as the true catalyst in benzene hydrogenations starting with the monometallic precursor, Ru(II)(η6-C6Me 6)(OAc)2, plus kinetic characterization of the heterogeneous nucleation, then autocatalytic surface-growth mechanism of metal film formation

Journal of the American Chemical Society

Volumn 125, Issue 34, 2003, Pages 10301-10310

  Widegren, Jason A ^a   Bennett, Martin A ^a,b   Finke, Richard G ^a  

^a Department of Environmental and Radiological Health Sciences   (United States)

^b AUSTRALIAN NATIONAL UNIVERSITY   (Australia)

Author keywords

[No Author keywords available]

Indexed keywords

BENZENE; CHEMICAL VAPOR DEPOSITION; HYDROGENATION; KINETIC THEORY; NUCLEATION;

PRECATALYST;

CATALYSIS;

BENZENE; MERCURY; METAL; METAL COMPLEX; POLYCYCLIC AROMATIC HYDROCARBON; RUTHENIUM;

ARTICLE; CATALYSIS; CATALYST; FILM; HYDROGENATION; KINETICS; TRANSMISSION ELECTRON MICROSCOPY;

EID: 0042889440     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja021436c     Document Type: Article

References (116)

1. 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. The uncertainty about the identity of the true catalyst when beginning with several Ru organometallics, Table 10.2, entries F.-I., p 550, is discussed on p 555 therein.
2. Widegren, J. A.; Finke, R. G. J. Mol. Catal. A: Chem. 2003, 198, 317-341. Table S1 of the Appendix lists about 30 catalyst systems for which metal-particle heterogeneous catalysts are suspected, including arene hydrogenation systems with Ru-based precatalysts.
3. Hamlin, J. E.; Hirai, K.; Millan, A.; Maitlis, P. M. J. Mol. Catal. 1980, 7, 543.
4. Whitesides, G. M.; Hackett, M.; Brainard, R. L.; Lavalleye, J. P. P. M.; Sowinski, A. F.; Izumi, A. N.; Moore, S. S.; Brown, D. W.; Staudt, E. M. Organometallics 1985, 4, 1819.
5. Anton, D. R.; Crabtree, R. H. Organometallics 1983, 2, 855.
6. Crabtree, R. H.; Mellea, M. F.; Mihelcic, J. M.; Quirk, J. M. J. Am. Chem. Soc. 1982, 104, 107.
7. Crabtree, R. H.; Mihelcic, J. M.; Quirk, J. M. J. Am. Chem. Soc. 1979, 101, 7738.
8. Collman, J. P.; Kosydar, K. M.; Bressan, M.; Lamanna, W.; Garrett, T. J. Am. Chem. Soc. 1984, 106, 2569.
9. Lewis, L. N.; Lewis, N. J. Am. Chem. Soc. 1986, 108, 7228.
10. Lewis, L. N. J. Am. Chem. Soc. 1990, 112, 5998.
11. Lin, Y.; Finke, R. G. Inorg. Chem. 1994, 33, 4891.
12. Lin, Y. Ph.D. Dissertation, Department of Chemistry, University of Oregon, March 1994.
13. Halpern, J. Inorg. Chim. Acta 1981, 50, 11.
14. Halpern, J.; Okamoto, T.; Zakhariev, A. J. Mol. Catal. 1977, 2, 65.
15. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 4th ed.; Wiley-Interscience: New York, 1992; p 780.
16. Stanislaus, A.; Cooper, B. H. Catal. Rev.-Sci. Eng. 1994, 36, 75.
17. Augustine, R. L. Heterogeneous Catalysis for the Synthetic Chemist; Marcel Dekker: New York, 1996; Chapter 17.
18. Lapporte, S. J.; Schuett, W. R. J. Org. Chem. 1963, 28, 1947.
19. Widegren, J. A.; Finke, R. G. J. Mol. Catal. A: Chem. 2003, 191, 187.
20. Fish, R. H. Aspects Homogeneous Catal. 1990, 7, 65.
21. Blum, J.; Amer, I.; Vollhardt, K. P. C.; Schwarz, H.; Hoehne, G. J. Org. Chem. 1987, 52, 2804.
22. Blum, J.; Amer, I.; Zoran, A.; Sasson, Y. Tetrahedron Lett. 1983, 24, 4139.
23. Weddle, K. S.; Aiken, J. D., III; Finke, R. G. J. Am. Chem. Soc. 1998, 120, 5653.
24. v by hydrogen to Nb(0) or Ta(0) metal particles is thermodynamically not possible under the reaction conditions; and (ii) the observed selectivity of the catalyst for the intramolecular hydrogenation of the aryloxide ligands is consistent with and strongly supportive of a homogeneous mononuclear catalyst, but difficult to explain if the true catalyst is heterogeneous (ortho-phenyl substituents on the aryloxide ligand are hydrogenated, while hydrogenation of phenyl rings meta or para to the aryloxide oxygen is not observed nor is hydrogenation of the phenoxide itself ever observed).
25. 5)Th arene hydrogenation catalysts merit mention for their single-metal nature: Eisen, M. S.; Marks, T. J. J. Am. Chem. Soc. 1992, 114, 10358.
26. Rothwell, I. P. Chem. Commun. 1997, 1331.
27. Ennett, J. P. Ph.D. Dissertation, Research School of Chemistry, Australian National University, 1984,
28. Süss-Fink, G.; Faure, M.; Ward, T. R. Angew. Chem., Int. Ed. 2002, 41, 99.
29. Johnson, J. W.; Muetterties, E. L. J. Am. Chem. Soc. 1977, 99, 7395. These authors specifically state that they were unable to detect free hexamethylbenzene following catalytic reactions (their actual detection limits were, unfortunately and however, not stated). Even if their detection limits for free hexamethylbenzene were, say 3-5%, we commonly find - as also seen in the current study - that only a small amount of the precatalyst typically has to evolve before a highly active heterogeneous catalyst is formed, one often able to consume all of the: substrate before the remaining precatalyst evolves to the heterogeneous catalyst. In addition, one of the main messages of this work, our prior work, and a review of the literature of the "is it homogeneous or heterogeneous catalysis" problem is that kinetic studies are essential to identification of the true catalyst.
30. Bennett, M. A.; Huang, T.-N.; Turney, T. W. J. Chem. Soc., Chem. Commun. 1979, 312.
31. Tocher, D. A.; Gould, R. O.; Stephenson, T. A.; Bennett, M. A.; Ennett, J. P.; Matheson, T. W.; Sawyer, L.; Shah, V. K. J. Chem. Soc., Dalton Trans. 1983, 1571.
32. Garcia Fidalgo, E.; Plasseraud, L.; Süss-Fink, G. J. Mol. Catal. A: Chem. 1998, 132, 5.
33. Plasseraud, L.; Süss-Fink, G. J. Organomet. Chem. 1997, 539, 163.
34. Dyson, P. J.; Ellis, D. J.; Welton, T.; Parker, D. G. Chem. Commun, 1999, 25.
35. Bennett, M. A.; Ennett, J. P.; Gell, K. I. J. Organomet. Chem. 1982, 233, C17.
36. Bennett, M. A.; Ennett, J. P. Organometallics 1984, 3, 1365.
37. Cook, J.; Hamlin, J. E.; Nutton, A.; Maitlis, P. M. J. Chem. Soc., Dalton Trans. 1981, 2342.
38. Black, colloidal material is reported to form from several mononuclear Ru precatalysts used in lignin aromatic ring reduction in: James. B. R.; Wang, Y.; Alexander, C. S.; Hu, T. Q. Chem. Ind. 1998, 75, 233.
39. Platt, J. R. Strong Inference. Science 1964, 146, 347.
40. Bennett, M. A.; Ennett, J. P. Inorg. Chim. Acta 1992, 198-200, 583.
41. 2.
42. Sheldon, R. A.; Wallau, M.; Arends, I. W. C. E.; Schuchardt, U. Acc. Chem. Res. 1998, 31, 485.
43. Schmid, G. Chem. Rev. 1992, 92, 1709.
44. Lewis, L. N. Chem. Rev. 1993, 93, 2693.
45. Bradley, J. S. In Clusters and Colloids. From Theory to Applications; Schmid, G., Ed.; VCH: New York, 1994; pp 459-544.
46. Finke, R. G. In Metal Nanoparticles: Synthesis, Characterization, and Applications; Feldheim, D. L., Foss, C. A., Jr., Eds.; Marcel Dekker: New York, 2001; Chapter 2.
47. Aiken, J. D., III; Finke, R. G. J. Mol. Catal. A: Chem. 1999, 145, 1. See refs 1-35 therein for additional reviews and introductory references to the interest, uses, and current research problems of nanoclusters and colloids in catalysis and other areas of science.
48. Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.; The Applications and Chemistry of Catalysis by Soluble Transition Metal Complexes; Wiley: New York, 1992.
49. In Chem. Engr. (N.Y.) 1990, 97 (Dec 20), 25.
50. Hu. S.-C.; Chen, Y.-W. J. Chin. Inst. Chem. Eng. 1998, 29, 387.
51. Stanislaus, A.; Cooper, B. H. Catal. Rev.-Sci. Eng. 1994, 36, 75.
52. Hu, T. Q.; James, B. R. J. Pulp Pap. Sci. 2000, 26, 173.
53. Tullo, A. New DVDs Provide Opportunities for Polymers. In Chem, Eng. News 1999, 77, 14.
54. Unlike the literature, we formulate 1 as the anhydrous complex. The justification for this is that 1 is synthesized and stored in a drybox and because we have no evidence for waters of hydration. Further comments are provided in the Materials section.
55. Noyes, R. M.; Field, R. J. Acc. Chem. Res. 1977. 10, 273.
56. Field, R. J.; Noyes, R. M. Acc. Chem. Res. 1977, 10, 214.
57. Watzky, M. A.; Finke, R. G. J. Am. Chem. Soc. 1997, 119, 10382.
58. Widegren, J. A.; Aiken, J. D., III; Özkar, S.; Finke, R. G. Chem. Mater. 2001, 13, 312.
59. Watzky, M. A.; Finke, R. G. Chem. Mater. 1997, 9, 3083.
60. Lin, Y.; Finke, R. G. J. Am. Chem. Soc. 1994, 116, 8335.
61. Aiken, J. D., III; Finke, R. G. Chem. Mater. 1999, 11, 1035.
62. Özkar, S.; Finke, R. G. J. Am. Chem. Soc. 2002, 124, 5796.
63. Özkar, S.; Finke, R. G. Langmuir 2003, 19, 6247.
64. Strey, R.; Wagner, P. E.; Viisanen, Y. J. Phys. Chem. 1994, 98, 7748.
65. A very nice example showing how soluble metal particle, seeded growth gives kinetically faster, well-controlled nanocluster formation is: Yu, H.; Gibbons, P. C.; Kelton, K. F.; Buhro, W. E. J. Am. Chem. Soc. 2001, 123, 9198. Note, however, that these authors use the term "heterogeneous" in their title ("Heterogeneous Seeded Growth...") to mean different metal nucleation, an unfortunate usage as it will get confused with the earlier. well-defined term heterogeneous nucleation.
66. 1 as we have seen.
67. 3 variability is the same as the reliability of current nucleation theory, Oxtoby having noted "Nucleation theory is one of the few areas of science where agreement between predicted and measured rates to within several orders of magnitude is considered a major success": Oxtoby, D. W. Acc. Chem. Res. 1998, 31, 91.
68. Epstein, I. R. Nature 1995, 374, 321 (The Consequences of Imperfect Mixing in Autocatalytic Chemical and Biological Systems).
69. 2 (solution) mass transfer results in very poorly formed, broad dispersions of nanoclusters in a system that otherwise produces near-monodisperse nanoclusters: Aiken, J. D., III; Finke, R. G. J. Am. Chem. Soc. 1998, 120, 9545.
70. 2-derived system.
71. The Hg(0)-poisoning experiment is occasionally performed improperly and with a lack of understanding of what this experiment is designed to test. In one literature example, a solution of precatalyst was stirred with Hg(0) for 1 h, the solution was filtered removing the Hg(0), and a catalytic hydrogenation reaction was then started. The hydrogenation proceeded with the same catalytic activity as an experiment in which Hg(0) was never present. This was then used - erroneously! - to rule out the presence of a nanocluster catalyst. The obvious problem with this experiment is that the Hg(0) was removed by filtration before the catalytic reaction was allowed to start, that is, before any metal-particle heterogeneous catalyst was allowed to be formed. As performed, this experiment shows only that the precatalyst does not react with Hg(0). One needs to add Hg(0) to a solution that already has been shown to be active. In the above example, the Hg(0) should have remained in the reaction solution for the duration of the catalytic reaction or have been added after the catalytic reaction had already begun, as done elsewhere.
72. 2, and then check for catalytic activity.
73. Paal, C.; Hartmann, W. Chem. Ber. 1918, 51, 711.
74. van Asselt, R.; Elsevier, C. J. J. Mol. Catal. 1991, 65, L13.
75. Jones, R. A.; Real, F. M.; Wilkinson, G.; Galas. A. M. R.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1981, 126.
76. Stein, J.; Lewis, L. N.; Gao, Y.; Scott, R. A. J. Am. Chem. Soc. 1999, 121, 3693.
77. Hg(0) is probably most effective in poisoning metals that form an amalgam, such as Pt, Pd, and Ni; metals that do not form amalgams with Hg(0), such as Ir, Rh, and Ru, may be more difficult to poison with Hg(0). Hence, if the addition of Hg(0) to the reaction solution suppresses the catalytic activity, one should perform a control experiment showing that the precatalyst complex does not react with Hg(0); if Hg(0) does react with the precatalyst, then this test becomes ambiguous. Similarly, if the addition of Hg(0) to the reaction solution has little effect on the catalytic activity, one should perform a control experiment showing that an authentic heterogeneous catalyst of the same metal is poisoned under the identical conditions.
78. Muetterties, E. L.; Bleeke, J. R. Acc. Chem. Res. 1979, 12, 324.
79. Bennett, M. A.; Huang, T.-N.; Smith, A. K.; Turney, T. W. J. Chem. Soc., Chem. Commun. 1978, 582.
80. Bergbreiter, D. E.; Chandran, R. J. Am. Chem. Soc. 1987, 109, 174.
81. Lead papers citing autocatalysis in metal film growth: (a) Lee, T. R.; Whitesides, G. M. Acc. Chem. Res. 1992, 25, 266. (b) Lee, T. R.; Laibinis, P. E.; Folkers, J. P.; Whitesides, G. M. Pure Appl. Chem. 1991, 63, 821. (c) Chae, Y. K.; Komiyama, H. J. Appl. Phys. 2001, 90, 3610. (d) Kellerman, B. K.; Chason, E.; Adams, D. P.; Mayer, T. M.; White, J. M. Surf. Sci. 1997, 375, 331. (e) Adams, D. P.; Mayer, T. M.; Chason, E.; Kellerman, B. K.; Swartzentruber, B. S. Surf. Sci. 1997, 371, 445. (f) Crane, E. L.; You, Y.; Nuzzo, R. G.; Girolami, G. S. J. Am. Chem. Soc. 2000, 122, 3422.
82. Lead papers citing autocatalysis in metal film growth: (a) Lee, T. R.; Whitesides, G. M. Acc. Chem. Res. 1992, 25, 266. (b) Lee, T. R.; Laibinis, P. E.; Folkers, J. P.; Whitesides, G. M. Pure Appl. Chem. 1991, 63, 821. (c) Chae, Y. K.; Komiyama, H. J. Appl. Phys. 2001, 90, 3610. (d) Kellerman, B. K.; Chason, E.; Adams, D. P.; Mayer, T. M.; White, J. M. Surf. Sci. 1997, 375, 331. (e) Adams, D. P.; Mayer, T. M.; Chason, E.; Kellerman, B. K.; Swartzentruber, B. S. Surf. Sci. 1997, 371, 445. (f) Crane, E. L.; You, Y.; Nuzzo, R. G.; Girolami, G. S. J. Am. Chem. Soc. 2000, 122, 3422.
83. Lead papers citing autocatalysis in metal film growth: (a) Lee, T. R.; Whitesides, G. M. Acc. Chem. Res. 1992, 25, 266. (b) Lee, T. R.; Laibinis, P. E.; Folkers, J. P.; Whitesides, G. M. Pure Appl. Chem. 1991, 63, 821. (c) Chae, Y. K.; Komiyama, H. J. Appl. Phys. 2001, 90, 3610. (d) Kellerman, B. K.; Chason, E.; Adams, D. P.; Mayer, T. M.; White, J. M. Surf. Sci. 1997, 375, 331. (e) Adams, D. P.; Mayer, T. M.; Chason, E.; Kellerman, B. K.; Swartzentruber, B. S. Surf. Sci. 1997, 371, 445. (f) Crane, E. L.; You, Y.; Nuzzo, R. G.; Girolami, G. S. J. Am. Chem. Soc. 2000, 122, 3422.
84. Lead papers citing autocatalysis in metal film growth: (a) Lee, T. R.; Whitesides, G. M. Acc. Chem. Res. 1992, 25, 266. (b) Lee, T. R.; Laibinis, P. E.; Folkers, J. P.; Whitesides, G. M. Pure Appl. Chem. 1991, 63, 821. (c) Chae, Y. K.; Komiyama, H. J. Appl. Phys. 2001, 90, 3610. (d) Kellerman, B. K.; Chason, E.; Adams, D. P.; Mayer, T. M.; White, J. M. Surf. Sci. 1997, 375, 331. (e) Adams, D. P.; Mayer, T. M.; Chason, E.; Kellerman, B. K.; Swartzentruber, B. S. Surf. Sci. 1997, 371, 445. (f) Crane, E. L.; You, Y.; Nuzzo, R. G.; Girolami, G. S. J. Am. Chem. Soc. 2000, 122, 3422.
85. Lead papers citing autocatalysis in metal film growth: (a) Lee, T. R.; Whitesides, G. M. Acc. Chem. Res. 1992, 25, 266. (b) Lee, T. R.; Laibinis, P. E.; Folkers, J. P.; Whitesides, G. M. Pure Appl. Chem. 1991, 63, 821. (c) Chae, Y. K.; Komiyama, H. J. Appl. Phys. 2001, 90, 3610. (d) Kellerman, B. K.; Chason, E.; Adams, D. P.; Mayer, T. M.; White, J. M. Surf. Sci. 1997, 375, 331. (e) Adams, D. P.; Mayer, T. M.; Chason, E.; Kellerman, B. K.; Swartzentruber, B. S. Surf. Sci. 1997, 371, 445. (f) Crane, E. L.; You, Y.; Nuzzo, R. G.; Girolami, G. S. J. Am. Chem. Soc. 2000, 122, 3422.
86. Lead papers citing autocatalysis in metal film growth: (a) Lee, T. R.; Whitesides, G. M. Acc. Chem. Res. 1992, 25, 266. (b) Lee, T. R.; Laibinis, P. E.; Folkers, J. P.; Whitesides, G. M. Pure Appl. Chem. 1991, 63, 821. (c) Chae, Y. K.; Komiyama, H. J. Appl. Phys. 2001, 90, 3610. (d) Kellerman, B. K.; Chason, E.; Adams, D. P.; Mayer, T. M.; White, J. M. Surf. Sci. 1997, 375, 331. (e) Adams, D. P.; Mayer, T. M.; Chason, E.; Kellerman, B. K.; Swartzentruber, B. S. Surf. Sci. 1997, 371, 445. (f) Crane, E. L.; You, Y.; Nuzzo, R. G.; Girolami, G. S. J. Am. Chem. Soc. 2000, 122, 3422.
87. Kinetic studies of autocatalytic metal film growth: (a) Xue, Z.; Thridandam, H.; Kaesz, H. D.; Hicks, R. F. Chem. Mater. 1992, 4, 162. (b) See also their short review: Zinn, A.; Niemer, B.; Kaesz, H. D. Adv. Mater. 1992, 4, 375.
88. Kinetic studies of autocatalytic metal film growth: (a) Xue, Z.; Thridandam, H.; Kaesz, H. D.; Hicks, R. F. Chem. Mater. 1992, 4, 162. (b) See also their short review: Zinn, A.; Niemer, B.; Kaesz, H. D. Adv. Mater. 1992, 4, 375.
89. Kinetics of the related topic of autocatalytic electrochemical metal film growth: (a) Lyamina, L. I.; Tarasova, N. I.; Gorbunova, K. M. Elektrokhimiya 1979, 15, 1615. (b) Schrebler, R.; Basaez, L.; Gardiazabal, I.; Gomez, H.; Cordova, R.; Quierolo, F. Boletin de la Sociedad Chilena de Quimico 1991, 36, 65.
90. Kinetics of the related topic of autocatalytic electrochemical metal film growth: (a) Lyamina, L. I.; Tarasova, N. I.; Gorbunova, K. M. Elektrokhimiya 1979, 15, 1615. (b) Schrebler, R.; Basaez, L.; Gardiazabal, I.; Gomez, H.; Cordova, R.; Quierolo, F. Boletin de la Sociedad Chilena de Quimico 1991, 36, 65.
91. 2, are: (a) Lin, W.; Wiegand, B. C.; Nuzzo, R. G.; Girolami, G. S. J. Am. Chem. Soc. 1996, 118, 5977. (b) Lin, W.; Nuzzo, R. G.; Girolami, G. S. J. Am. Chem. Soc. 1996, 118, 5988.
92. 2, are: (a) Lin, W.; Wiegand, B. C.; Nuzzo, R. G.; Girolami, G. S. J. Am. Chem. Soc. 1996, 118, 5977. (b) Lin, W.; Nuzzo, R. G.; Girolami, G. S. J. Am. Chem. Soc. 1996, 118, 5988.
93. n on Au(111) deposited from Mo(CO)6 has been monitored at selected times by STM: Song, Z.; Cai, T.; Rodriguez, J. A.; Hrbek, J.; Chan, A. S. Y.; Friend, C. M. J. Phys. Chem. B 2003, 107, 1036.
94. Aiken, J. D., III; Finke, R. G. J. Am. Chem. Soc. 1999, 121, 8803.
95. 3COOH + acetone. We thank a referee for pointing out this possibility.
96. Consistent with this argument, the simple addition of a noncoordinating base such as Proton Sponge produces a much better nanocluster stabilizer: Özkar, S.; Finke, R. G. Langmuir 2002, 18, 7653.
97. The curve-fit is easily within experimental error of the data for at least the first half of the benzene hydrogenation reaction. However, at longer times the hydrogenation is slower than predicted by the curve-fit. Deviations between the curve-fit and the data near the end of the reaction can occur for a variety of understood reasons. For example, the pseudoelementary step method used herein assumes that the catalytic reaction is zero order in substrate. Obviously, at some point later in the reaction, when the substrate concentration approaches zero, this assumption is no longer true. Also, any deactivation process that occurs to a significant extent on the time scale of the experiment will cause deviations such as those seen in Figure 2. For example, a loss of catalyst surface area due to (observed) bulk metal formation will cause the reaction to be slower than predicted. For these reasons, only the first half of the data in Figure 2 was used to generate the curve-fit, a precaution we typically employ.
98. Hornstein, B. J.; Finke, R. G. Submitted for publication.
99. Hornstein, B. J.; Aiken, J. D., III; Finke, R. G. Inorg. Chem. 2002, 41, 1625.
100. 2.
101. Gonzalez-Tejuca, L.; Aika, K.; Namba, S.; Turkevich, J. J. Phys. Chem. 1977, 81, 1399.
102. Frety, R.; Da Silva, P. N.; Guenin, M. Catal. Lett. 1989, 3, 9.
103. Butt, J. B. Catal. Sci. Technol. 1987, 6, 1.
104. 6)], a catalyst previously believed to be homogeneous. The bottom line here is that these criteria are not reliable indicators of whether the catalyst is homogeneous or heterogeneous and, hence, are not recommended, especially now that the now proven methodology in Figure 1 is available. Note also that it is unlikely that further studies of these criteria will ever make them easy to use or reliable (i.e., in comparison to the methods in Figure 1). This follows since one would need, for each system at hand, to have authentic homogeneous and heterogeneous (i.e., both nanocluster and bulk metal) catalysts of the same metal, ligands, and nanocluster stabilizers available for the needed control studies; that is, one would have to have presolved the "is it homogeneous or heterogeneous catalysis?" question before such criteria could be reliably used! The conceptual significance of, and the "Catch 22" situation present by, such up-front control experiments with authentic catalysts is presented and discussed as the topmost part of Figure 5 elsewhere.
105. Hagen, C.; Finke, R. G. Experiments in progress.
106. formation bulk metal (low activity to inactive).
107. Wang, Q.; Lui, H.; Han, M.; Li, X.; Jiang, D. J. Mol. Catal. A Chem. 1997, 118, 145.
108. Temple, K.; Jäkle, F.; Sheridan, J. B.; Manners, I. J. Am. Chem. Soc. 2001, 123, 1355.
109. Crabtree, R. H. Chem. Rev. 1985, 85, 245.
110. Reetz, M. T.; Westermann, E. Angew. Chem., Int. Ed. 2000, 39, 165.
111. Sheldon, R. A.; Wallau, M.; Arends, I. W. C. E.; Schuchardt, U. Acc. Chem. Res. 1998, 31, 485.
112. Arends, I. W. C. E.; Sheldon, R. A. Appl. Catal., A 2001, 212, 175.
113. Davies, I. W.; Matty, L.; Hughes, D. L.; Reider, P. J. J. Am. Chem. Soc. 2001, 123, 10139.
114. Bennett, M. A.; Huang, T. N.; Matheson, T. W.; Smith, A. K. Inorg. Synth. 1982, 21, 74.
115. -1.
116. 2 pressure uptake curve shown in Figure 3.