Effect of Lewis Acidity on the Synthesis of RuHCl(CO)(phosphine)2: Subtle Influence of Steric and Electronic Effects among PiPr3, PiPr2(3,5-(CF3)2C6H3), and PiPr2Me

To evaluate the influence of steric, electronic, and synthetic factors, the synthesis of RuHCl(CO)[P(i)Pr(2)(3,5-(CF(3))(2)C(6)H(3))](2) was carried out, and its Lewis acidity toward Cl- was compared to that of RuHCl(CO)(P(i)Pr(3))(2). In this synthesis, Na(2)CO(3) was shown to be a more effective base than NEt(3), because Na+ can better mask the nucleophilicity of the potential ligand Cl-. An X-ray structure determination of the hydride-free species RuCl(2)(CO)(P(i)Pr(2)Me)(2) shows it to be a dimer, and this solid-state structure persists in solution, but as several different isomers. The synthesis of RuHCl(CO)(P(i)Pr(2)Me)(3) shows that three of this smaller phosphine can crowd around Ru, but dynamic NMR spectra show one phosphine to be weakly bound. The rate of reaction of Me(3)SiC(triple bond)CH with this molecule is suppressed by added free P(i)Pr(2)Me, indicating phosphine dissociation to be a mechanistic component.