The Pd4(dppm)4(H)22+ Cluster: A Precatalyst for the Homogeneous Hydrogenation of Alkynes
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- 作者：David Evrard ; Katherine Groison ; Yves Mugnier ; and Pierre D. Harvey
- 刊名：Inorganic Chemistry
- 出版年：2004
- 出版时间：January 26, 2004
- 年：2004
- 卷：43
- 期：2
- 页码：790 - 796
- 全文大小：130K
- 年卷期：v.43,no.2(January 26, 2004)
- ISSN：1520-510X
文摘
The catalytic properties of the title cluster toward the homogeneous hydrogenation of phenylacetylene, diphenylethyneand phenyl-1-propyne have been investigated as a function of temperature, pressure, solvents, substrate andcluster concentrations, and counterions. The title cluster is a precatalyst that exhibits a good catalytic activity undermild conditions (1 atm of H2 at 20 
C) for the hydrogenation of alkynes and alkenes. For the alkyne substrates, theturnover frequencies (tof's) range between 200 and 500 h-1, and the product distribution varies as: cis-products,75-90%; trans-products; 0-8% after 3 h of reaction. Based on the graphs -d[substrate]/dt vs [Pd4]1/2, the mechanismindicates a cluster dissociation into two dimers (presumably of the type Pd2(dppm)2(H)(solvent)+). The variations oftof (or -d[substrate]/dt) as a function of [substrate] and pressure of H2 are linear. At 1600 psi of H2, the tof canreach 2500-3000 h-1 (in THF). The tof also increases with temperature reaching a maximum at ~35 C (tof:1000-1300 h-1), but at higher temperatures cluster decomposition begins to occur, leading to a rapid decrease inrates of catalysis. At 50 C, no catalysis is observed. The hydrogenation reaction can be stopped at the correspondingcis-alkenes with ~95% yields, depending on the substrate and experimental conditions used. The tof's also varywith the solvent, where stronger coordinating solvent molecules give higher tof's. In addition, the tof's do notchange with the nature of the counterion, which acts as "spectator" in the catalysis.
C) for the hydrogenation of alkynes and alkenes. For the alkyne substrates, theturnover frequencies (tof's) range between 200 and 500 h-1, and the product distribution varies as: cis-products,75-90%; trans-products; 0-8% after 3 h of reaction. Based on the graphs -d[substrate]/dt vs [Pd4]1/2, the mechanismindicates a cluster dissociation into two dimers (presumably of the type Pd2(dppm)2(H)(solvent)+). The variations oftof (or -d[substrate]/dt) as a function of [substrate] and pressure of H2 are linear. At 1600 psi of H2, the tof canreach 2500-3000 h-1 (in THF). The tof also increases with temperature reaching a maximum at ~35 C (tof:1000-1300 h-1), but at higher temperatures cluster decomposition begins to occur, leading to a rapid decrease inrates of catalysis. At 50 C, no catalysis is observed. The hydrogenation reaction can be stopped at the correspondingcis-alkenes with ~95% yields, depending on the substrate and experimental conditions used. The tof's also varywith the solvent, where stronger coordinating solvent molecules give higher tof's. In addition, the tof's do notchange with the nature of the counterion, which acts as "spectator" in the catalysis.