Effect of Iodide on the pH-Controlled Hydrogenations of Diphenylacetylene and Cinnamaldehyde Catalyzed by Ru(II)-Sulfonated Triphenylphosphine Complexes in Aqueous–Organic Biphasic Systems

The effect of NaI on hydrogenation diphenylacetylene catalyzed by the water-soluble [{RuCl(mtppms-Na)2}2(µ-Cl)2] (1) (mtppms-Na = meta-monosulfonated triphenylphosphine sodium salt) is reported. Hydrogenations were performed under mild conditions (P(H2) 1 bar, T 50–80 ?) in aqueous–organic biphasic reaction mixtures wherein catalyst was dissolved aqueous phase various pHs. In acidic solutions, addition to + mtppms-Na increased selective conversion stilbenes from 10% 90% but did not high Z-selectivity (up 98%). contrast, basic solutions major product diphenylethane 70%), and yield E-stilbene exceeded that Z-isomer. 1H 31P NMR measurements revealed depending absence or presence NaI, catalytically active Ru(II)-hydride species [RuHCl(mtppms-Na)3], 2, [RuHI(mtppms-Na)3], 5, respectively, while both 2 5 hydrogenated further same hydride species, cis,fac-[RuH2(H2O)(mtppms-Na)3]. [RuHI(mtppms-Na)3] proved superior [RuHCl(mtppms-Na)3] as a for cinnamaldehyde dihydrocinamaldehyde. This finding explained facile formation (putative) dihydrogen complex [Ru(H2)I2(H2O)(mtppms-Na)2] intermediate, resulting fast heterolytic activation H2.