pH-Dependent Selective Transfer Hydrogenation of α,β-Unsaturated Carbonyls in Aqueous Media Utilizing Half-Sandwich Ruthenium(II) Complexes

Half-sandwich ruthenium(II) PTA complexes bearing the 1,2-dihydropentalenyl (C8H9-, Dp) and indenyl
(C9H7-, Ind) ancillary ligands have been synthesized and characterized using multinuclear NMR
spectroscopy and X-ray crystallography. The complexes DpRu(PTA)(PPh3)Cl, DpRu(PTA)2Cl, IndRu(PTA)(PPh3)Cl, and [IndRu(PTA)2(PPh3)]Cl were obtained in good to excellent yields. The solid-state
structures of these compounds exhibit piano stool geometries with η5-coordination of the indenyl and
dihydropentalenyl moieties. DpRu(PTA)2Cl is water-soluble (S25°C = 43 mg/mL), while the mixed
phosphine compounds are slightly soluble in acidic solutions. The Ru−H complexes, Cp‘Ru(PTA)(PPh3)H
(Cp‘ = Ind, Cp), have been synthesized in good yield and spectroscopically and structurally characterized.
The ruthenium hydrides undergo an H/D exchange reaction with CD3OD with relative rates CpRu(PTA)(PPh3)H ≫ IndRu(PTA)(PPh3)H > CpRu(PTA)2H. The air-stable Cp‘Ru(PTA)(PR3)Cl complexes (Cp‘
= Cp, Dp, Ind; PR3 = PPh3 or PTA) exhibit activity in the regioselective transfer hydrogenation of
α,β-unsaturated carbonyls in aqueous media with HCOONa, HCOOH, or isopropanol/Na2CO3 serving
as the hydrogen source. They were found to be effective in the selective reduction of the carbonyl
functionality of cinnamaldehyde and the CC bond of benzylidene acetone and chalcone. IndRu(PTA)(PPh3)Cl was less active than Cp‘Ru(PTA)(PPh3)Cl (Cp‘ = Cp or Dp). Results of the transfer hydrogenation
of unsaturated substrates using CpRu(PTA)(PPh3)H are also reported.

采用多核核磁共振波谱和X射线晶体学方法，已成功合成并表征了携带1,2-二氢戊烯基（C8H9-, Dp）和吲哚基（C9H7-, Ind）辅助配体的半夹心钌(II)PTA络合物。所得络合物包括DpRu(PTA)(PPh3)Cl、DpRu(PTA)2Cl、IndRu(PTA)(PPh3)Cl以及[IndRu(PTA)2(PPh3)]Cl，均以优良至极好的产率获得。这些化合物的固态结构呈现出钢琴凳型几何构型，并表现出吲哚基和二氢戊烯基部分的η5配位。其中，DpRu(PTA)2Cl具有良好的水溶性（S25°C = 43 mg/mL），而混合膦化合物在酸性溶液中仅微溶。Ru−H络合物Cp‘Ru(PTA)(PPh3)H（Cp‘ = Ind, Cp）以优良产率合成，并经光谱学和结构学表征。钌氢化物与CD3OD发生H/D交换反应，相对速率表现为CpRu(PTA)(PPh3)H ≫ IndRu(PTA)(PPh3)H > CpRu(PTA)2H。空气稳定的Cp‘Ru(PTA)(PR3)Cl络合物（Cp‘ = Cp, Dp, Ind；PR3 = PPh3或PTA）在水相介质中表现出对α,β-不饱和羰基的区域选择性转移加氢活性，以甲酸钠、甲酸或异丙醇/碳酸钠作为氢源。这些络合物在选择性还原肉桂醛的羰基官能团以及苯甲酰甲酮和查耳酮的C=O键方面表现出显著效果。与Cp‘Ru(PTA)(PPh3)Cl（Cp‘ = Cp或Dp）相比，IndRu(PTA)(PPh3)Cl的活性较低。此外，还报道了使用CpRu(PTA)(PPh3)H对不饱和底物进行转移加氢的实验结果。