Chiral (η⁶‑<i>p</i>‑Cymene)ruthenium(II) Complexes Containing Monodentate Acylthiourea Ligands for Efficient Asymmetric Transfer Hydrogenation of Ketones

The new chiral ligands (R)-/(S)-N-((1-phenylethyl)­carbamothioyl)­benzamide (L1/L2), (R)-/(S)-N-((1-phenylethyl)­carbamothioyl)­thiophene-2-carboxamide (L3/L4), and (R)-/(S)-N-((1-phenylethyl)­carbamothioyl)­furan-2-carboxamide (L5/L6) were synthesized, characterized, and used to prepare novel chiral Ru­(II) complexes. The chiral Ru­(II) complexes 1–6 were obtained from reactions between the chiral ligands L1–L6 and [RuCl2(p-cymene)2]2. The complexes were characterized by analytical and spectroscopic (NMR, FT-IR, electronic) techniques. The solid-state structures of the ligands L1 and L3 and complexes 1, 4, and 6 were determined by single-crystal X-ray diffraction methods. In all of the complexes, the ligand is bound to the Ru­(II) center only via the sulfur donor atom. This monodentate coordination of the acylthiourea ligands was observed for the first time with ruthenium. The Ru­(II) complexes 1–6 all act as efficient catalysts for the asymmetric transfer hydrogenation of aromatic ketones in the presence of 2-propanol and KOH to produce chiral alcohols. All of the catalysts showed excellent conversions of up to 99% and enantiomeric excesses of up to 99%.本研究合成并表征了三类新型手性配体：(R)-/(S)-N-((1-苯基乙基)硫代氨基甲酰)苯甲酰胺(L1/L2)、(R)-/(S)-N-((1-苯基乙基)硫代氨基甲酰)噻吩-2-甲酰胺(L3/L4)以及(R)-/(S)-N-((1-苯基乙基)硫代氨基甲酰)呋喃-2-甲酰胺(L5/L6)，并以此类配体制备了新型手性钌(II)（Ru(II)）配合物。手性配体L1~L6与二聚体[RuCl₂(对伞花烃(p-cymene))₂]₂发生反应，得到手性钌(II)配合物1~6。通过分析化学手段与光谱学技术（核磁共振波谱(NMR)、傅里叶变换红外光谱(FT-IR)、电子光谱）对所得配合物进行了表征。采用单晶X射线衍射法测定了配体L1、L3以及配合物1、4和6的固态结构。在所有配合物中，配体仅通过硫供体原子与Ru(II)中心配位。这种酰基硫脲配体的单齿配位模式在钌配合物体系中尚属首次报道。所有手性钌(II)配合物1~6均可作为高效催化剂，在异丙醇与氢氧化钾(KOH)存在的体系中催化芳香酮的不对称转移氢化反应，制备手性醇。所有催化剂均表现出优异的催化性能，转化率最高可达99%，对映体过量值最高可达99%。