Heterolytic H2 activation by rhodium thiolato complexes bearing the hydrotris(pyrazolyl)borato ligand and application to catalytic hydrogenation under mild conditions
作者:Hidetake Seino、Yoshiyuki Misumi、Yoshihiro Hojo、Yasushi Mizobe
DOI:10.1039/b923557d
日期:——
Thiolato complexes of Rh(III) bearing a hydrotris(3,5-dimethylpyrazolyl)borato ligand (TpMe2) have been prepared, and their reactivity toward H2 has been investigated. The bis(thiolato) complex [TpMe2Rh(SPh)2(MeCN)] (1) reacted with 1 atm H2 at 20 °C to produce the hydrido-thiolato complex [TpMe2RhH(SPh)(MeCN)] (2) and PhSH via heterolytic cleavage of H2. This process is reversible and in equilibrium in THF and benzene. The bis(selenolato) complex [TpMe2Rh(SePh)2(MeCN)] (4) was also converted to [TpMe2RhH(SePh)(MeCN)] and PhSeH under 1 atm H2, but the equilibrium largely shifted to 4. Reaction of the dithiolato complex [TpMe2Rh(bdt)(MeCN)] (3; bdt = 1,2-C6H4S2) with H2 occurred in the presence of amine, giving the anionic hydrido complex [TpMe2RhH(bdt)]− and an equimolar amount of ammonium cations. Catalytic activity for hydrogenation has been examined under 1 atm H2 at 20–50 °C. While 1, 2, and 4 slowly hydrogenated styrene at similar rates at 50 °C, activities for the hydrogenation of N-benzylideneaniline increased in the order, 2 < 1 < 4. Complex 3 was found to be the most active and selective catalyst for hydrogenation of imines, and thus a variety of imines were reduced at 20 °C under 1 atm H2, with the CC and CO bonds in the substrate molecules completely preserved. An ionic mechanism was involved to explain such high chemoselectivity.
已经制备了含有氢三(3,5-二甲基吡唑基)硼酸盐配体(TpMe2)的Rh(III)硫醇配合物,并研究了其对H2的反应性。双(硫醇)配合物[TpMe2Rh(SPh)2(MeCN)](1)在20°C下与1 atm H2反应,生成氢化硫醇配合物[TpMe2RhH(SPh)(MeCN)](2)和PhSH,这个过程通过H2的异裂反应发生。该过程在THF和苯中是可逆的并处于平衡状态。双(硒醇)配合物[TpMe2Rh(SePh)2(MeCN)](4)在1 atm H2下也转化为[TpMe2RhH(SePh)(MeCN)]和PhSeH,但平衡大多偏向于4。在胺的存在下,二硫醇配合物[TpMe2Rh(bdt)(MeCN)](3;bdt = 1,2-C6H4S2)与H2反应,生成阴离子氢化配合物[TpMe2RhH(bdt)]−和等摩尔的铵阳离子。在1 atm H2和20-50°C下,氢化的催化活性进行了研究。虽然1、2和4在50°C下以相似的速率缓慢氢化苯乙烯,但对N-苄亚胺的氢化活性呈现出2 < 1 < 4的顺序。配合物3被发现是氢化亚胺的最活跃和选择性的催化剂,因此在20°C和1 atm H2下对多种亚胺进行了还原,底物分子中的C-C和C-O键完全保留。高选择性的化学选择性解释采用了离子机制。