There are intense efforts to develop new or improved strategies for recovering homogeneous molecular catalysts. [1] Many of these approaches are bi-or multiphasic in nature, and one particularly innovative method involves catalysts that are derivatized with (CH 2 ) m (CF 2 ) nÀ1 CF 3 ((CH 2 ) m R fn ) moieties or fluorous "ponytails". [2, 3] The initial applications of this now-familiar technique utilized perfluoroalkane solvents for recovery. However, the relatively high costs of such fluorous solvents, and other factors, pose limitations for industrial applications.Second-generation methods eliminated the fluorous solvent by exploiting the temperature-dependent solubilities of fluorous catalysts in common organic solvents. [4,5] Appropriately designed fluorous molecules are soluble only at elevated temperatures, and essentially insoluble at low temperatures. Such a thermomorphic character allows homogeneous catalysis at the high-temperature limit, and catalyst recovery by a simple liquid/solid-phase separation at the low-temperature limit. The presence of an insoluble fluorous support can be beneficial, for example, when small quantities are involved. Initial efforts have involved Teflon shavings [4] and fluorous silica gel. [6][7][8] We sought to expand the range of catalysts and fluorous supports that could be applied in such methods, and report herein a surprisingly effective procedure involving common commercial Teflon tape. This approach provides not only a convenient means of catalyst recovery, but also of catalyst delivery. From an engineering standpoint, tapes offer a variety of unique attributes, and it is reasonable to extrapolate that meshes and/or reactor parts, such as liners or stirring assemblies, could be fabricated with similar properties.As a test reaction, we selected the ketone hydrosilylation shown in Figure 1, which in earlier work was catalyzed by the fluorous rhodium complexes 1-R f6 and 1-R f8 in a liquid/liquid biphase system comprising an organic and a fluorous solvent.[9] The red-orange compounds 1-R f6 and 1-R f8 have very little or no solubility in organic solvents at room temperature.[10] However, their solubilities increase markedly with[*] Dr.
Reactions of (eta5-C5H(5-x)Brx)M(CO)3(M = Re, Mn; x= 1, 3, 4, 5) and IZn(CH2)2R(f8) in the presence of Cl2PdL2 catalysts give the title complexes (eta5)-C5H(5-x)(CH2)2R(f8)x)M(CO3), accompanied in the case of x= 5 by hydride-transfer byproducts. Extremely high fluorophilicities are realized, and the cyclopentadienyl ligands are readily detached (hnu) from the manganese complexes.
We report that pincer-ligated iridium catalysts for alkane dehydrogenation can operate in tandem with zeolite catalysts for arene−alkene coupling, to effect the overall intramolecular dehydrocoupling of alkyl−H and aryl−H bonds (i.e., the dehydrocyclization of alkyl benzene). Thus, zeolite and soluble iridium cocatalysts in refluxing pentylbenzene (205 °C) gave high yields of 1-methyl-1,2,3,4-tetrahydronaphthalene. Subsequent dehydrogenation and isomerization affords 1-and 2-methylnaphthalene and 2-methyl-1,2,3,4tetrahydronaphthalene. Total yields of cyclized product as high as 5.4 M (94%) have been obtained, corresponding to 6800 turnovers per mol Ir. Turnover numbers for the tandem-catalyzed dehydrocyclization are much greater than those obtained for simple dehydrogenation by Ir catalysts (to give olefins) in the absence of zeolite.
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