Oxo-Rhenium-Catalyzed Deoxydehydration of Polyols with Hydroaromatic Reductants

Abstract

Several dihydroaromatic compounds are shown to be effective reducing agents in the oxo-metal-catalyzed deoxydehydration of diols and polyols to produce olefins and the corresponding arenes. NH4ReO4 and MeReO3 are active catalysts for the reactions. The most effective of the hydroaromatic reductants is indoline, which is oxidized to indole. Yields for a variety of diols and polyols range from 35% to 99%. Two hydrogen donors, 1,3-cyclohexadiene and dihydroanthracene, engage in tandem DODH/cycloaddition reactions. Competition experiments show that indoline is more reactive than representative alcohols in H-transfer. Indoline is shown to reduce MeReO3 to MeReO2 via an isolable adduct, MeReO3(indoline) (4), which has been structurally characterized and is suggested to be an intermediate in the catalytic DODH process.

Preparation of Highly Active Monometallic Rhenium Catalysts for Selective Synthesis of 1,4‐Butanediol from 1,4‐Anhydroerythritol

“…Homogeneous Re catalysts and non‐H 2 reductants such as alcohols are commonly used in the DODH reaction. The Re species act as active sites that can form the diolate by coordination with cis ‐vicinal OH groups of the substrate . The Re species are reduced by two electrons, and the reduced Re diolate releases product alkene to form oxidized Re species.…”

“…The Re species act as active sites that can form the diolate by coordination with cis-vicinal OH groups of the substrate. [7,[14][15][16] The Re speciesa re reduced by two electrons, and the reduced Re diolate releases product alkene to form oxidized Re species. The first report on heterogeneous DODH catalysts used carbonsupported perrhenate, [17] and the development of heterogeneous DODH catalysts has been recentlyc arried out.…”

Mechanistic Investigation of Molybdate‐Catalysed Transfer Hydrodeoxygenation

“…With respect to the p-benzyl complex formation, two possible pathways werec onsidered (Scheme 4). In pathway A, con-densation of the Mo IV moiety [4]w ith PhCH 2 OH gives [5], which was followed by a [ 2,3]-sigmatropic rearrangement to yield the p-benzyl complex [6]. In pathway B, direct reaction through transitions tate [4][5][6]w ith the expulsion of water yields the same p-benzyl complex [6].…”

“…The two energetic profiles for the generation of the Mo/sbenzylc omplex [7]s how that the energy barrierf or the oxidative rearrangement [5][6]i ss ignificantly lower than the [4][5][6] transition by 26.2 kcal mol À1 (Figure 7). Furtherc alculations showedt hat complex [6]w ould isomerise toward the s-benzyl complex [7], thus leaving the molybdenum centre bondedt o the CH 2 group through a s bond.T his isomerisation is driven by the energeticallyf avourable re-aromatisation of the ben- Figure 6.…”

“…The production of organic platformc hemicals from renewable feedstocks requires the development of reactions capable of reducing the oxygen content of biomass.Ap articularly abundant motif in biomass is the hydroxy group, and an emerging strategyt ot ransform vicinal diols into the correspondinga lkenes in as ingle step is the deoxydehydration (DODH)r eaction, which typically involves the use of ar henium-, [1][2][3][4][5][6] molybdenum-, [7][8][9][10] or vanadium-based [11] catalyst. We have recently shown [10] that the molybdate ion, prepared in situ by the addition of as light excesso fB u 4 NOH to as olution of [(NH 4 ) 6 Mo 7 O 24 ]·4 H 2 O( AHM), catalyses the DODH reaction of aliphatic diols in iPrOH, which serves as both the solvent and reductant(Scheme 1).…”