State Key Laboratory and Institute of Elemento-organic Chemistry, Nankai University, Weijin Road 94, Tianjin 300071, China.
Chem Asian J. 2011 Mar 1;6(3):899-908. doi: 10.1002/asia.201000716. Epub 2010 Dec 15.
The iridium complexes of chiral spiro aminophophine ligands, especially the ligand with 3,5-di-tert-butylphenyl groups on the P atom (1c) were demonstrated to be highly efficient catalysts for the asymmetric hydrogenation of alkyl aryl ketones. In the presence of KOtBu as a base and under mild reaction conditions, a series of chiral alcohols were synthesized in up to 97% ee with high turnover number (TON up to 10,000) and high turnover frequency (TOF up to 3.7×10(4) h(-1)). Investigation on the structures of the iridium complexes of ligands (R)-1a and 1c by X-ray analyses disclosed that the 3,5-di-tert-butyl groups on the P-phenyl rings of the ligand are the key factor for achieving high activity and enantioselectivity of the catalyst. Study of the catalysts generated from the Ir-(R)-1c complex and H(2) by means of ESI-MS and NMR spectroscopy indicated that the early formed iridium dihydride complex with one (R)-1c ligand was the active species, which was slowly transformed into an inactive iridium dihydride complex with two (R)-1c ligands. A plausible mechanism for the reaction was also suggested to explain the observations of the hydrogenation reactions.
手性螺环氨基膦配体的铱配合物，特别是磷原子上带有 3,5-二叔丁基苯基的配体（1c），被证明是烷基芳基酮不对称氢化的高效催化剂。在 KOtBu 作为碱和温和的反应条件下，一系列手性醇以高达 97%的对映选择性（TON 高达 10,000）和高转化频率（TOF 高达 3.7×10(4) h(-1)）合成。通过 X 射线分析对配体（R）-1a 和 1c 的铱配合物的结构进行研究，发现配体的磷-苯环上的 3,5-二叔丁基是实现催化剂高活性和高对映选择性的关键因素。通过 ESI-MS 和 NMR 光谱研究由 Ir-(R)-1c 配合物和 H(2)生成的催化剂表明，最初形成的具有一个（R）-1c 配体的铱二氢配合物是活性物种，它会缓慢转化为具有两个（R）-1c 配体的非活性铱二氢配合物。还提出了一个可能的反应机制来解释氢化反应的观察结果。
