Oxidative Cleavage of vic-Diols to Aldehydes with Dioxygen Catalyzed by Ru(PPh₃)₃Cl₂ on Active Carbon

Abstract

[reaction: see text] A variety of vic-diols were first successfully cleaved to the corresponding aldehydes with dioxygen catalyzed by Ru(PPh3)3Cl2 on active carbon in fair to good yields. For example, treatment of 1,2-octandiol and 1,2-cyclooctanediol with dioxygen in the presence of Ru(PPh3)3Cl2/C in PhCF3 at 60 degrees C for 15 h produced heptanal and 1,8-octanedial in 77% and 76% yields, respectively.

Aerobic Oxidation of Vicinal Diols Catalyzed by an Anderson-Type Polyoxometalate, [IMo6O24]5

“…For example, under the conditions given in Table 1, and acetic acid as solvent there was only 14% conversion and formation of mostly PhC(O)CH 2 OH and PhCH(OH)CHO. However, 10% Na 5 [IMo 6 O 24 ] supported on active carbon with toluene as solvent were also an effective catalyst and reaction medium, respectively, yielding results similar to those reported in Table 1 [b] In the presence of 250 mM CH 3 SO 3 H.…”

“…Thus, an especially attractive catalytic and alternative method would be to oxidize vicinal diols with molecular oxygen. For vicinal diol oxidation there have been only a few reports of catalytic aerobic reactions using as catalysts Ru(PPh 3 ) 3 Cl 2 on active carbon [6] or N-hydroxyphthalimide and Co(acac) 3 . [7] We are interested in the application of polyoxometalates as catalysts for oxidation reactions, especially using molecular oxygen as oxidant or oxygen donor.…”

“…First, stoichiometric reactions were carried out under anaerobic conditions (10 mM substrate, 10 mM Q 3 H 2 [IMo 6 O 24 ], 1 mL CH 3 CN, T 80 8C, 4 h), Eqs. 1 ± 3.…”

“…Important also was the observation that the solution turned brown rather than green, indicating formation of heteropoly browns attributable to formation of highly reduced polyoxometalate species with multiple molybdenum(V) and probably also molybdenum(IV) atoms. [14] A second important observation was that a,b-diketones such as benzil and 1,2-cyclohexanedione, did not react in the presence of Q 3 H 2 [IMo 6 O 24 ] nor did simple alcohols such as cyclohexanol and benzyl alcohol. Benzoin, PhCH(OH)C(O)Ph, was more reactive than hydrobenzoin.…”

“…The hydroxyketone (aldehyde) is always observed either under anaerobic conditions or at low conversions. The association or complexation (step a) of the diol to the polyoxometalate seems to be critical since a simple alcohol such as benzyl alcohol with a lower (compared to cyclohexanediol) oxidation potential and C-H bond energy is not oxidized by the Q 3 H 2 [IMo 6 O 24 ] polyoxometalate. After its formation, the hydroxy-ketone (aldehyde) may disassociate from the polyoxometalate and in the presence of oxygen the catalyst is re-oxidized with formation of water (step c).…”