(para-Diphenylphosphino)benzenesulfonic acid and its ruthenium(II) complexes: an old water soluble phosphine ligand in a new perspective

Chloro- and hydrido-complexes of ruthenium(II) with potassium (4-diphenylph osphino)benzenesulfonate (pTPPMS) were prepared and their properties were c ompared with those of the related complexes of (3-diphenylphosphino)benzene sulfonates. An X-ray crystal structure determination revealed that the para -sulfonated ligand has a Tolman cone angle slightly smaller than that of PP h3. It was established by pH-potentiometric measurements and by H-1 and P-3 1 NMR studies that the distribution of the hydride derivatives [RuClH(pTPPM S)(3)] and [RuH2(pTPPMS)(3,4)] is strongly pH-dependent. Hydrogenation of t rans-cinnamaldehyde in aqueous-organic mixtures is catalyzed by [RuCl2(pTPP MS)(4)] and is also strongly influenced by the pH of the aqueous phase due to the pH-dependent formation of the above hydrides. In acidic solutions (p H < 2) an exclusive C=C reduction takes place, while in alkaline solutions (pH > 6) a selective C=O hydrogenation was observed.