Supported Metal Hydroxides as Efficient Heterogeneous Catalysts for Green Functional Group Transformations

Abstract

This review article mainly describes our research on the development of highly active heterogeneous catalysts based on the properties of metal hydroxides and efficient green functional group transformations using these catalysts. Metal hydroxide species have both Lewis acid (metal center) and Brønsted base (hydroxy group) sites on the same metal sites. Combined action of the Lewis acid and Brønsted base paired sites can activate various types of organic substrates; for example, alcohols alkoxides, amines amides, nitriles η 2 -amidates, and terminal alkynes acetylides. In the presence of supported ruthenium hydroxide catalyst (Ru(OH)x/Al2O3), oxidative dehydrogenation of alcohols and amines efficiently proceeds, forming the corresponding carbonyl compounds (aldehydes and ketones) and nitriles, respectively. Ru(OH)x /Al2O3 can also catalyze hydration of nitriles to primary amides, ammoxidation of primary alcohols to nitriles, and formal α-oxygenation of primary amines to primary amides. In addition, oxidative alkyne homocoupling and 1,3-dipolar cycloaddition efficiently proceed in the presence of supported copper hydroxide catalysts (Cu(OH)x /OMS-2 for homocoupling, Cu(OH)x/TiO2 and Cu(OH)x/Al2O3 for cycloaddition; where OMS-2 is manganese oxide-based octahedral molecular sieve, KMn8O16). The catalytic processes for these transformations are heterogeneous, and the catalysts can be reused several times with maintained high catalytic activity.

RuO4-mediated oxidation of secondary amines: Part 1. Are hydroxylamines main intermediates?

“…Comparison of the reaction products derived from 1a (TI-1,10) with those resulting from 4a (TI-3,12) and/or 9a+10a (TI-5,14 + TI- 7,16) shows that 2a, 2c, 6c, 11, 15a, 16a and 20a were derived from 1a only. On the contrary, 9c, 26 and 27 resulted from 4a only.…”

“…Ruthenium-based catalysts, ruthenium tetraoxide (RuO 4 ) included, have been extensively used to oxidize a wide variety of organic compounds, such as aliphatic and aromatic hydrocarbons, alkenes, alkynes, alcohols, ethers, amines, or amides. [1][2][3][4][5][6][7][8][9][10][11] The versatility, specificity, the high yields obtained in many cases, and the environmentally friendly reaction conditions have strongly recommended ruthenium-containing catalysts be successfully utilized in fine and green chemistry. [1][2][3][4][5][6][7][8][9][10] In the case of tertiary amines of the RCH 2 -NR 1 R 2 type, earlier papers [12][13][14][15][16] indicated that RuO 4 attacks the N-CH 2 positions to afford amides (RCO-NR 1 R 2 ) and for about 30 years, this reaction was viewed as a highly regioselective oxidation.…”

RuO4-mediated oxidation of secondary amines 2. imines as main reaction intermediates

“…The origin and spectral characteristics ( 1 H-NMR, 13 C-NMR and MS) of compounds 1, 2 and 4-25 (except those of 8f and 14d) were previously presented. imines (2,3) hydroxylamines (4) aldehydes (5) amides I (6, 7), amides II (8) nitrones (9,10) others I (11)(12)(13)(14) nitriles I (15,16), nitriles II (17) cyanoimines (18)(19)(20) cyanonitrones (21,22) formamidines & related compounds (23)(24)(25) others Derivatives 3b, 28 8f, 29 26 30,31 and 27 32 are all known from the literature and were prepared according to the indicated procedures. Compound 28 was purchased from Aldrich.…”

“…Several mechanisms for the oxidation of alkanes, 1 arenes, 1 olefins, 2 alcohols 3 and amines [3][4][5][6] using various ruthenium-containing catalysts are known, but they refer to totally different substrates and/or oxidants than those used in the present study. Mechanisms for the oxidation of alkanes, 7,8 alkenes, 9 alcohols, 10 ethers 7 and tertiary amines [11][12][13][14][15] with RuO 4 as an oxidant 16 were previously proposed.…”

Dehydration of Chiral α-Amides to Chiral α-Nitriles Under the Appel Reaction Conditions

“…Many attempts to synthesize nitriles are being made as these are intermediates in the production of polyamides, pharmaceuticals, dyes and numerous fine chemicals (Fatiadi et al 1983;Miller and Marson 2001). And also, nitrile group serves as an important intermediate in organic synthesis for various functional group transformations (Caddick et al 2000;Munoz et al 2011;Yamaguchi and Mizuno 2014;Wanga 2015) and has often been utilized as a versatile precursor to synthesize various heterocyclic compounds (Aureggi and Sedelmeier 2007;Bosch and Vilarrasa 2007;Nishiwaki et al 2011;Heller et al 2002) (Fig. 1).…”