Rhodium Tris(hydroxymethyl)phosphine (THP)/Amine Complexes as Stable Effective Homogenous Hydrogenation Catalysts in Aqueous Solution

Green chemistry, achieved by using water as a reaction medium, has several potential applications. In this work, a number of water-soluble Rh(III)–THP complexes, [Rh(III)Cl3(OH)(THP)2]− (1), [Rh(III)Cl2(OH)(THP)3] (2), [Rh(III)Cl(OH)(THP)4]+ (3), [Rh(III)Cl(OH)(en)(THP)2]+ (4a), [Rh(I)(en)(THP)2]+ (4b) and [Rh(III)(en)2Cl2]Cl (5) (where THP = P(CH2OH)3), were generated in aqueous media by controlling the reaction at different molar ratios of RhCl3/THP/en (en: ethylenediamine). These complexes were fully characterized in situ by 31P NMR spectroscopy, base titration and by X-ray crystallography for the solid compound (4). The catalytic hydrogenation reactivities of freshly prepared complexes (1–5) were tested in situ with the selected substrate of 3,4-dimethoxystyrene under the same experimental conditions; the related catalytic reactivities are discussed in detail.