Transfer-hydrogenation and transfer-hydrogenolysis. III. Hydrogen transfer from dioxane to olefins catalyzed by chlorotris(triphenylphosphine)rhodium(I)

Abstract

Hydrogen transfer from 1,4-dioxane to olefins catalyzed by RhCl(PPh3)3 occurred. Stoichiometric amounts of paraffins and dioxene were formed from olefins and dioxane. After the reaction, the dioxane complex, RhCl(PPhaMC4H802), was isolated. The large value of the kinetic isotope effect, R1JiRD = 3.1, in the use of octadeuteriodioxane and the kinetic result showed that the rate-determining step of the reaction is the dehydrogenation, that is, the formation of the monohydride complex, RhClH(C4H-02)(PPh3)2, by the oxidative addition of dioxane by the cleavage of a C-H bond.In catalytic transfer-hydrogenation,1 the donation of hydrogen to olefins by alcohols2 and six-membered cyclic olefins3 has clearly been shown. However, with the exception of alcohols there seems to have been no report of double hydrogen abstraction from saturated compounds by soluble complexes.4We have reported previously that a saturated cyclic ether, 1,4-dioxane, donated hydrogen to an olefin to give stoichiometric amounts of dioxene and a paraffin in the presence of RhCl(PPh3)3.5 This complex not only has high catalytic activity in the hydrogen transfer reaction but also has been thoroughly studied in the hydrogenation of olefins by molecular hydrogen by Wilkinson and other researchers.4•6 7It was expected that the information on the properties of this complex in the latter reaction would help to clarify the mechanism of the transfer-hydrogenation easier. Experimental SectionMaterials. RhCl(PPh3)3 was prepared by the method of Wilkinson, et al? Olefins were purified prior to use by passage through a silica gel and neutral alumina column, followed by distillation over sodium. Dioxane and toluene were distilled over sodium. Octadeuteriodioxane (Deutration grade; min 99%, E. Merk) was dehydrated by molecular sieves. Pyrocatechol was purified by recrystallization from benzene. Dioxene was synthesized by the method of Summerbell and Umhoefer.8An Example of Transfer-Hydrogenation. Cyclopentene (0.034 g, 0.5 mmol) and RhCl(PPh3)3 (0.0185 g, 0.02 mmol) were put into a Pyrex glass tube which had been sealed at one side. Into the mixture, dioxane was added, and the total volume of the solution was made 1.0 ml. The tube was sealed under vacuum after two freeze-pump-thaw cycles at 10-3 Torr on a vacuum line with liquid (1) T.

Transfer Hydrogenation Including the Meerwein‐Ponndorf‐Verley Reduction

“…The cationic species (48) then rearranges to a complex in which the dioxane is bound to the rhodium via the carbon atom (40) (Scheme 20.17) [60].…”

“…Cyclic ethers such as [1,4]dioxane (39) and 2,3-dihydrofuran are known to donate a pair of hydrogen atoms to this type of compound. 2,3-Dihydro- [1,4]dioxine (41), the product of dioxane (39), is not able to donate another pair of hydrogen atoms [46,60,73,74]. These heterocyclic compounds are in general also very good solvents for both the catalyst and the substrates.…”

Hydrogen transfer from cyclohexanol to aromatic aldehydes catalyzed by heterogenized ruthenium(II) complexes bound to swellable polymer matrices

“…Based on the results described earlier and a comparison with the mechanism of the transfer hydrogenation from organic compounds to olefins, aldehydes and ketones catalyzed by small molecules of RuH 2 (PPh 3 ) 4 and RhCl(PPh 3 ) 3 [11][12][13][14][15]5], Scheme 3 is reasonably proposed for the catalytic cycle of the hydrogen transfer reaction from cyclohexanol to the aromatic aldehydes catalyzed by the supported heterogeneous catalyst. Here, P-RuHP 3 stands for the CCPAARu catalyst.…”

Kinetic study of hydrogen transfer from benzyl alcohol to aliphatic aldehydes catalysed by heterogenised ruthenium(II) catalysts

“…Based on the results described earlier and on a comparison with the mechanism of transfer hydrogenation of olefins (Imai et al, 1974;Nishiguchi and Fukuzumi, 1974;Nishiguchi et al, 1975), Scheme 2 was reasonably proposed for the catalytic cycle of hydrogen transfer reduction of aldehyde.…”