Development of Catalytic Reductions with Hydride Complexes in Water

水溶性氢化物配合物是由水配合物与供氢体在水中的反应合成的，在酸性条件下对羰基化合物在水中的酸催化还原具有强大的活性催化剂作用。氢化物配合物的分离使我们能够研究氢化物配合物在酸性介质中的强大能力，以及氢化物配合物在化学计量和催化条件下与羰基化合物反应的还原能力。酸催化还原的速率很大程度上取决于溶液的pH值、反应温度和给氢体的浓度。pH值对还原速率的影响是由氢络合物的pH依赖形成和质子对羰基化合物的活化过程来解释的。酸催化还原的高转换频率不仅归因于氢化物配合物对质子激活的羰基的亲核性，而且归因于氢化物配合物的氢化物配体的质子性，这种质子性抑制了氢化物配体的质子化。

Water-soluble hydride complexes, that were synthesized from the reactions of aqua complexes with hydrogen donors in water, serve as robust and active catalysts for acid-catalyzed reductions of carbonyl compounds in water under acidic conditions. The isolation of the hydride complexes allowed us to investigate robust ability of the hydride complexes in acidic media and reducing ability of the hydride complexes in the reactions with carbonyl compounds under both stoichiometric and catalytic conditions. The rate of the acid-catalyzed reductions are drastically dependent on pH of the solution, reaction temperature, and concentration of the hydrogen donors. The effect of pH on the rate of the reductions is rationalized by the pH-dependent formation of the hydride complexes and activation process of the carbonyl compounds by protons. High turnover frequencies of the acid-catalyzed reductions are ascribed not only to nucleophilicity of the hydride complexes toward the, carbonyl groups activated by protons but also to a protonic character of the hydrido ligands of the hydride complexes that inhibits the protonation of the hydrido ligands.