Two water-soluble ruthenium(II) complexes (1 and 2) containing the proton-responsive 6,6′-dihydroxy-2,2′-bipyridine (dhbp) ligand were studied as precatalysts for the solvolysis of ammonia-borane (AB) in water and/or alcohols. Both precursors generate in situ the same catalytic system. In spite of the excellent initial activities observed, it suffered a sudden deactivation at extended conversions. Detailed experimental studies combined with theoretical (density functional theory) calculations permitted us to describe the reaction mechanism as two interrelated pH-dependent catalytic cycles operating within a single run. According to this hypothesis, the deactivation observed occurred as a consequence of the increase in NH₃ concentration and pH along the reaction progress. It was attributed to deprotonation of the dhbp ligand and amination or hydroxylation of the resulting compound. Accordingly, reactions performed in buffered solutions at neutral pH retarded this process, and up to 2.5 equiv of H₂ per mole of AB were liberated in less than 1 min (TOF_50% up to 33 113 h^–1 (TOF = turnover frequency)). When the reaction was run in alcohols (MeOH, EtOH, or iPrOH) it proceeded at faster rates than in water, the one discussed here being the first homogeneous catalytic system active for this process. Actually, in MeOH, the initial TOFs surpasses that of any metallic or organometallic catalyst reported for AB alcoholysis.

中文翻译：

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质子响应性钌（II）催化剂，用于氨解硼烷

研究了两种质子反应性6,6'-二羟基-2,2'-联吡啶（dhbp）配体的水溶性钌（II）配合物（1和2）作为氨硼烷（AB）溶剂化的前催化剂在水和/或酒精中。两种前体原位产生相同的催化体系。尽管观察到了出色的初始活性，但在延长的转化率下却突然失活。详细的实验研究与理论（密度泛函理论）计算相结合，使我们可以将反应机理描述为在一次运行中运行的两个相互关联的pH依赖的催化循环。根据该假设，观察到的失活是由于NH ₃的增加而发生的。反应过程中的浓度和pH值。这归因于dhbp配体的去质子化以及所得化合物的胺化或羟基化。因此，在中性pH的缓冲溶液中进行的反应会延迟该过程，并且在不到1分钟的时间内释放出每摩尔AB高达2.5当量的H ₂（TOF _50％达到33113 h ^–1（TOF =周转频率） ）。当反应在醇（MeOH，EtOH或iPrOH）中进行时，它的速度比在水中的速度快，此处讨论的是该方法中第一个有效的均相催化体系。实际上，在MeOH中，初始TOF超过了报道的AB醇解反应的任何金属或有机金属催化剂的TOF。