Source: http://reag.paperplane.io/00001504.htm
Timestamp: 2019-04-23 20:13:22+00:00

Document:
Alternate Names: CPA; chloroplatinic acid; hexachloroplatinic acid; Speier's catalyst.
Physical Data: mp 60 °C, d 2.431 g cm-3.
Solubility: sol water, alcohol, ether.
Form Supplied in: brownish-yellow crystalline mass; very deliquescent; widely available. Drying: compound decomposes on heating.
Handling, Storage, and Precautions: harmful if inhaled, swallowed, or absorbed through skin. The compound may be carcinogenic. Use in a fume hood.
Hydrosilylation is a process in which one or more silicon-hydrogen bonds add to a substrate.1 The reaction typically involves the addition of silanes to alkenes, carbon-heteroatom double bonds, and alkynes (eq 1).
This reaction can be catalyzed by a variety of metals and metal complexes. One of the most useful catalysts for hydrosilylation is CPA. A dilute solution of CPA in isopropanol is typically used as the catalyst (Speier's catalyst).2 CPA also serves as the starting material for a very active form of homogeneous platinum(0) catalyst known as the Karstedt catalyst.3 The major features of hydrosilylations are: an induction period; moderate to good yields; facility of the reaction on the nature of the silane, substrate, and the catalytic species; isomerization of the alkene substrate; and applications to a wide variety of substrates. A generally accepted mechanism for hydrosilylation has been proposed by Chalk and Harrod.4 It involves the coordination of the metal to the alkene followed by oxidative addition of the silane to the metal to give a PtIV intermediate. Rearrangement gives s-bonded PtIV and subsequent reductive elimination gives the hydrosilylated product and PtII species.
Internal alkenes produce a mixture of hydrosilylated products upon treatment with dichlorosilane and CPA (eq 6).5 In this reaction, products from bond migration followed by hydrosilylation were not observed.
Hydrosilylation of alkenes with chiral silanes and CPA catalysis proceeds with retention of configuration at the silicon center (eq 7).10 Similarly, Si-H to Si-D exchanges can also be carried out with retention of configuration using CPA catalysis.
Molecular oxygen and CPA can effectively catalyze the addition of unreactive monoalkyl silanes to terminal alkenes to furnish tetrasubstituted silicon compounds in high yields (eq 9).12 In the absence of oxygen, these reactions do not go to completion since it is believed that the oxygen reactivates the CPA for hydrosilylation.
Intramolecular hydrosilylations of alkenylsilanes with CPA catalysis gives a mixture of regioisomeric cyclic silanes (eq 10).13 The yields and ratio of products depends on the ring size, while the product distribution has been explained using the Chalk and Harrod mechanism for the hydrosilylation reaction. Vinylsilanes and allylsilanes gave no cyclized product.
Hydrosilylations using silane have not been extensively investigated. One example involves the hydrosilylation of 1,5-hexadiene with silane and CPA (pretreated with oxygen) catalysis and subsequent intramolecular hydrosilylation of the intermediate to provide a silaheptane as shown in eq 11.14 Pt(PPh3)4 was a better catalyst than CPA for this reaction.
Unsaturated sulfides undergo hydrosilylation with triethyl- and triethoxysilanes.16 These reactions are generally nonselective and proceed in only moderate yields (eq 13). The selectivity and yields depend upon the nature of the substrate, hydrosilylating agent, and catalyst. In the case of diallyl sulfide, hydrosilylation using Triethylsilane and CPA produces the monosilylated product and a byproduct arising from cleavage of the sulfur-carbon bond (eq 14).
Acetylene undergoes hydrosilylation with trialkylsilanes in the presence of CPA to provide a mixture of mono- and diadducts (eq 16).19 A convenient laboratory method for hydrosilylation of acetylene with a variety of silanes to provide synthetically useful vinylsilanes has been reported by Watanabe.20 Although CPA gives good selectivity and high yields with trichlorosilane, ruthenium, rhodium, and platinum triphenylphosphine complexes were found to be better suited for these reactions.
Voronkov and Sushchinskaya26 have shown that the hydrosilylation of phenylacetylene with triethylsilane and CPA catalysis can be markedly influenced by the addition of aluminum or germanium chlorides. For example, the reaction in the presence of Aluminum Chloride (CPA:AlCl3 = 1:200) gave 93% of the hydrosilylated products, while in the absence of AlCl3 the yield was only 24% (eq 18).
Doyle and co-workers have reported an alternate mode of selectivity of silane addition to monosubstituted alkynes, wherein allylsilanes are formed as the major products, along with minor amounts of the vinylsilanes (eq 19).27 The reaction involves the slow addition of alkyne to a solution of silane and CPA catalyst. The allylsilanes are formed in good yields. Use of rhodium(II) perfluorobutyrate in place of CPA gave higher yields of the allylsilane. Addition of silane to a solution of alkyne and CPA gave the normal vinylsilane product.
Intramolecular hydrosilylations of silicon-substituted silaalkynes have been achieved using CPA as the catalyst (eq 23).33 Similar to the results obtained for intramolecular hydrosilylations of alkenes, the product distribution depends on the size of the ring formed.
Hydrosilylations of dienes generally provide three 1:1 adducts arising from 1,2- and 1,4-addition. Isoprene, a simple diene, reacts with a variety of silanes in the presence of catalytic CPA to furnish hydrosilylated products. For example, the reaction of isoprene with trichlorosilane and catalytic CPA gave the 1,4-adduct, with addition occurring across the least hindered double bond (eq 24).34 However, trimethylsilane gave both 1,2- and 1,4-adducts with addition occurring at both ends of the diene.
1,4-Bis(trimethylsilyl)-1,3-butadiyne, a stable alternative to the highly reactive 1,3-butadiyne, undergoes hydrosilylation with CPA catalysis and a variety of silanes (eq 25).35 The product distribution depends on the nature of the silane. The more reactive dimethylchlorosilane gave the 1:2 adduct (12) in moderate yields, while reactions with the less reactive and bulkier triisopropylsilane furnished the 1:1 adduct (14) in higher yields. Reaction with triethylsilane was unusual in that the product was an allene (13) arising from 1,4-addition of a second silane molecule to the intermediate 1:1 adduct (14).
Hydrosilylations of enynes occur at the more reactive alkyne end. An example of enyne hydrosilylation with methyldichlorosilane is shown in eq 26.36 The reaction requires a small amount of either Dibenzoyl Peroxide or trichlorosilane as a cocatalyst and is believed to proceed by a radical pathway. An example of a highly chemoselective hydrosilylation has been reported by Voronkov (eq 27).37 The reactions occur at the alkyne terminus in the presence of an alcohol and alkene.
Hydrosilylations of a,b-unsaturated esters, ketones, and nitriles with CPA catalysis have also been examined. The course of these reactions depends on the nature of the silane and the electron-withdrawing substituent. Hydrosilylation of a series of a,b-unsaturated esters using CPA catalysis was evaluated by Yoshii and co-workers (eq 28).38 The reactions were generally nonselective and gave all three possible 1,2- and 1,4-addition products. When Wilkinson's catalyst (Chlorotris(triphenylphosphine)rhodium(I)) was used in place of CPA, the 1,4-addition products, silylketene acetals, were obtained as the major products.
The hydrosilylation-oxidation sequence can be effectively used for the transformations of terminal alkenes to the corresponding anti-Markovnikov alcohols (eq 30).44 The silane used in these experiments, methyldiethoxysilane, is commercially available and air stable. Thus the hydrosilylations can be carried out without solvent under air using CPA catalysis. Hydrogen Peroxide oxidation proceeds smoothly only if there is at least one alkoxy group on the silicon. The reactivity of the carbon attached to silicon can be controlled by the nature of the alkoxy group.
The hydrosilylation-oxidation sequence can also be effectively used for the conversion of an alkyne to a ketone. An application of this methodology in the synthesis of 5-decanone is shown in eq 31.44 The reaction involves the hydrosilylation of an alkyne to a vinylsilane using CPA catalysis followed by hydrogen peroxide oxidation to the decanone. The procedure can be carried out without isolating the intermediate vinylsilane.
The hydrosilylation-oxidation sequence is a convenient route for the preparation of a-hydroxy ketones from alkynes (eq 32).47 The process involves hydrosilylation of an alkyne to a vinylsilane, epoxidation of the vinylsilane using m-Chloroperbenzoic Acid, and final oxidative cleavage using hydrogen peroxide.
Terminal alkenes under relatively mild reaction conditions can be converted to a mixture of linear and branched esters by using CO and methanol with a CPA-SnCl2 couple as the catalyst (eq 37).51 Use of water in place of methanol produced the corresponding carboxylic acids in similar ratios. Internal alkenes gave a mixture of products in very low yields under these carbonylation conditions.
Methyl acetate can be hydrocarbonylated under a carbon monoxide-hydrogen atmosphere using a mixed Rhodium(III) Chloride-CPA catalyst to furnish ethylidene diacetate (eq 38).52 The reaction gave higher yields with rhodium trichloride-Palladium(II) Acetate as the catalyst.
Arenes react with CPA to give the s-aryl complexes of PtIV.55 Regioselectivity of the metallation with monosubstituted benzenes is quite poor, giving both m- and p-substituted complexes. These complexes then undergo further reaction to produce mixtures of chlorinated arenes and substituted biphenyls (eq 41).
Chlorination of alkanes and arenes in the presence of stoichiometric CPA in refluxing trifluoroacetic acid has been reported (eq 42).56 These reactions furnish chlorinated arenes or n-chloroalkanes and require PtII as a cocatalyst.
2-Allyloxypyridines may be rearranged to N-allylpyridones when using CPA (eq 44).59 The reaction is carried out by heating the pyridine at 125 °C for 36 h without solvent. The reaction can also be catalyzed by Pt(PPh3)4.
Alcohols can be converted to carbonyl compounds through a two-electron oxidation process using molecular oxygen, CPA, and visible light.60 The reaction is catalytic in PtIV and requires CuII cocatalysis.
1. (a) Speier, J. L. In Advances in Organometallic Chemistry; Stone, F. G. A.; West, R., Eds.; Academic: New York, 1979; Vol. 17, p 407. (b) Marciniec, B.; Gulinski, J.; Urbaniak, W.; Kornetka, Z. W. In Comprehensive Handbook on Hydrosilylation; Marciniec, B., Ed.; Pergamon: Oxford, 1992. (c) Marciniec, B.; Gulinski, J. JOM 1993, 446, 15. (d) Ojima, I. In The Chemistry of Organic Silicon Compounds; Patai, S.; Rappoport, Z., Eds.; Wiley: New York, p 1479.
2. (a) Benkeser, R. A.; Kang, J. JOM 1980, 185, C9. (b) Lewis, L. N.; Lewis, N. JACS 1986, 108, 7228.
3. Chandra, G.; Lo, P. Y.; Hitchcock, P. B.; Lappert, M. F. OM 1987, 6, 191 and references therein.
4. Chalk, A. J.; Harrod, J. F. JACS 1965, 87, 16.
5. (a) Benkeser, R. A.; Muench, W. C. JOM 1980, 184, C3. (b) Benkeser, R. A.; Dunny, S.; Li, G. S.; Nerlekar, P. G.; Work, S. D. JACS 1968, 90, 1871.
6. Capka, M.; Svoboda, P.; Hetflejs, J. CCC 1973, 38, 3830.
7. Kuncova, G.; Chvalovsky, V. CCC 1980, 45, 2085.
8. Benkeser, R. A.; Mozdzen, E. C.; Muench, W. C.; Roche, R. T.; Siklosi, M. P. JOC 1979, 44, 1370.
9. Watanabe, H.; Aoki, M.; Sakurai, N.; Watanabe, K.-i.; Nagai, Y. JOM 1978, 160, C1.
10. Sommer, L. H.; Lyons, J. E.; Fujimoto, H. JACS 1969, 91, 7051.
11. Braun, F.; Willner, L.; Hess, M.; Kosfeld, R. JOM 1987, 332, 63.
12. Onopchenko, A.; Sabourin, E. T. JOC 1987, 52, 4118.
13. Swisher, J. W.; Chen, H.-H. JOM 1974, 69, 83.
14. Itoh, M.; Iwata, K.; Takeuchi, R.; Kobayashi, M. JOM 1991, 420, C5.
15. Plueddemann, E. P.; Fanger, G. JACS 1959, 81, 2632.
16. (a) Voronkov, M. G.; Vlasova, N. N.; Bolshakova, S. A.; Kirpichenko, S. V. JOM 1980, 190, 335. (b) Voronkov, M. G.; Chvalovsky, V.; Kirpichenko, S. V.; Vlasova, N. N.; Bolshakov, S. T.; Kuncova, G.; Keiko, V. V.; Tsetlina, E. O. CCC 1979, 44, 742.
17. (a) Vybiral, V.; Svoboda, P.; Hetflejs, J. CCC 1979, 44, 866. (b) Belyakova, Z. V.; Knyazeva, L. K.; Chernyshev, E. A. ZOR 1978, 48, 1258. (c) Belyakova, Z. V.; Knyazeva, L. K.; Chernyshev, E. A. ZOR 1984, 53, 1435.
18. (a) Chernyshev, E. A.; Belyakova, Z. V.; Shevchenko, V. M.; Yagodina, L. A.; Kisin, A. V.; Bernadskii, A. A.; Sheludyakov, V. D.; Bochkarev, V. N. ZOR 1984, 54, 1812. (b) Lukevits, E.; Khokhlova, L. N. ZOR 1978, 48, 753. (c) Kireev, V. V.; Kovyazin, V. A.; Kopylov, V. M.; Zaitseva, M. G.; Kostylev, I. M. ZOR 1984, 54, 327.
19. (a) Benkeser, R. A.; Ehler, D. F. JOM 1974, 69, 193. (b) Onopchenko, A.; Sabourin, E. T.; Beach, D. L. JOC 1984, 49, 3389. (c) Onopchenko, A.; Sabourin, E. T.; Beach, D. L. JOC 1983, 48, 5101.
20. Watanabe, H.; Asami, M.; Nagai, Y. JOM 1980, 195, 363.
21. (a) Pukhnarevich, V. B.; Sushinskaya, S. P.; Pestunovich, V. A.; Voronkov, M. G. ZOR 1973, 43, 1283. (b) Matsumoto, H.; Hoshino, Y.; Nagai, Y. CL 1982, 1663. (c) Benkeser, R. A.; Cunico, R. F.; Dunny, S.; Jones, P. R.; Nerlekar, P. G. JOC 1967, 32, 2634. (d) Asatiani, L. P.; Zurabishvili, D. S. ZOR 1984, 54, 1816.
22. Lewis, L. N.; Sy, K. G.; Bryant, Jr., G. L.; Donahue, P. E. OM 1991, 10, 3750.
23. Gevorgyan, V.; Borisova, L.; Popelis, J.; Lukevics, E.; Foltynowicz, Z.; Gulinski, J.; Marciniec, B. JOM 1992, 424, 15.
24. Oda, H.; Morizawa, Y.; Oshima, K.; Nozaki, H. TL 1984, 25, 3221.
25. Corriu, R. J. P.; Moreau, J. J. E. JOM 1972, 40, 73.
26. Voronkov, M. G.; Sushchinskaya, S. P. ZOR 1986, 56, 555.
27. Doyle, M. P.; High, K. G.; Nesloney, C. L.; Clayton, Jr., T. W.; Lin, J. OM 1991, 10, 1225.
28. (a) Voronkov, M. G.; Ushakova, N. I.; Tsykhanskaya, I. I.; Pukhnarevich, V. B. JOM 1984, 264, 39. (b) Voronkov, M. G.; Pukhnarevich, V. B.; Ushakova, N. I.; Tsykhanskaya, I. I.; Albanov, A. I.; Vitkovskii, V. Yu. ZOR 1985, 55, 80.
29. Pannell, K. H.; Rozell, J. M.; Li, J.; Tien-Mayr, S-Y. OM 1988, 7, 2524.
30. Yamamoto, K.; Nokawa, O.; Tsuji, J. S 1977, 721.
31. Lukevics, E.; Gevorgyan, V. N.; Goldberg, Y. S.; Shymanska, M. V. JOM 1984, 263, 283.
32. Sonnek, G.; Drahs, E.; Jancke, H.; Hamann, H. JOM 1990, 386, 29.
33. Steinmetz, M. G.; Udayakumar, B. S. JOM 1989, 378, 1.
34. Benkeser, R. A.; Merritt II, F. M.; Roche, R. T. JOM 1978, 156, 235.
35. (a) Kusumoto, T.; Hiyama, T. CL 1985, 1405. (b) Kusumoto, T.; Ando, K.; Hiyama, T. BCSJ 1992, 65, 1280.
36. Licchelli, M.; Greco, A. TL 1987, 28, 3719.
37. Voronkov, M. G.; Mustafaev, R. M.; Kulieva, L. G.; Sadykhzade, S. I. ZOR 1985, 55, 1856.
38. (a) Yoshii, E.; Kobayashi, Y.; Koizumi, T.; Oribe, T. CPB 1974, 22, 2767. (b) For other other work in this area see: Petrov, A. D.; Sadykh-Zade, S. I.; Filatova, E. I. ZOR 1959, 29, 2896; Rijkens, F.; Janssen, M. J.; Drenth, W.; Van Der Kerk, G. J. M. JOM 1964, 2, 347.
39. Sadykh-Zade, S. I.; Petrov, A. D. ZOR 1959, 29, 3194.
40. (a) Yoshii, E.; Ikeshima, H.; Ozaki, K. CPB 1972, 20, 1827. (b) Nambara, T.; Shimada, K.; Goya, S. CPB 1970, 18, 453.
41. Ojima, I.; Kogure, T. JOM 1982, 1, 1390.
42. Belyakova, Z. V.; Golubtsov, S. A.; Yakusheva, T. M. ZOR 1965, 35, 1183.
43. Ojima, I.; Kumagai, M.; Nagai, Y. JOM 1976, 111, 43.
44. Tamao, K.; Ishida, N.; Tanaka, T.; Kumada, M. OM 1983, 2, 1694.
45. Tamao, K.; Maeda, K.; Tanaka, T.; Ito, Y. TL 1988, 29, 6955.
46. Tamao, K.; Kobayashi, K.; Ito, Y. TL 1989, 30, 6051.
47. Tamao, K.; Maeda, K. TL 1986, 27, 65.
48. (a) Tamao, K.; Nakajima, T.; Sumiya, R.; Arai, H.; Higuchi, N.; Ito, Y. JACS 1986, 108, 6090. (b) Tamao, K.; Tanaka, T.; Nakajima, T.; Sumiya, R.; Arai, H.; Ito, Y. TL 1986, 27, 3377.
49. Cramer, R. D.; Jenner, E. L.; Lindsey, Jr., R. V.; Stolberg, U. G. JACS 1963, 85, 1691.
50. (a) Frankel, E. N.; Emken, E. A.; Itatani, H.; Bailar, Jr., J. C. JOC 1967, 32, 1447. (b) Bailar, Jr., J. C.; Itatani, H. JACS 1967, 89, 1592.
51. Kehoe, L. J.; Schell, R. A. JOC 1970, 35, 2846.
52. Kudo, K.; Mori, S.; Sugita, N. CL 1985, 265.
53. (a) Benkeser, R. A.; Yeh, M-H. JOM 1984, 264, 239. (b) Belyakova, N. R.; Mileshkevich, V. P. ZOR 1989, 59, 640.
54. (a) Pikies, J.; Wojnowski, W. JOM 1989, 378, 317. (b) Pikies, J.; Wojnowski, W. JOMC 1990, 393, 187.
55. Shul'pin, G. B.; Shilov, A. E.; Kitaigorodskii, A. N.; Zeile Krevor, J. V. JOM 1980, 201, 319.
56. Sanders, J. R.; Webster, D. E.; Wells, P. B. JCS(D) 1975, 1191.
57. Cushman, B. M.; Earnest, S. E.; Brown, D. B. JOM 1978, 159, 431.
58. Earnest, S. E.; Brown, D. B. JOM 1976, 120, 135.
59. (a) Balavoine, G.; Guibe, F. TL 1979, 3949. (b) Stewart, H. F.; Seibert, R. P. JOC 1968, 33, 4560.
60. Cameron, R. E.; Bocarsly, A. B. JACS 1985, 107, 6116.

References: V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V. 
 V.