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

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 Bronsted base (hydroxy group) sites on the same metal sites. Combined action of the Lewis acid and Bronsted base paired sites can activate various types of organic substrates; for example, alcohols -> alkoxides, amines -> amides, nitriles -> eta(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)/SAl2O3 can also catalyze hydration of nitriles to primary amides, ammoxidation of primary alcohols to nitriles, and formal a-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.