New d4 dihydrides of Ru(iv) and Os(iv) with π-donor ligands: M(H)2(chelate)(PiPr3)2 with chelate = ortho-XYC6H4 with X, Y = O, NR; R = H or CH3

Abstract

The synthesis and characterization of Ru(H)₂(ortho-OC₆H₄E)L₂ (L = PⁱPr₃, E = NH, O) show these to be dihydrides with a nonoctahedral structure. The former compound reacts with H₂ to give Ru(H)₃(OC₆H₄NH₂)L₂, which has the ability to hydrogenate ^tBuHCCH₂. Osmium analogs are available from Os(H)₃ClL₂, and the mono-N-methyl example Os(H)₂[N(Me)C₆H₄NH]L₂ shows inequivalent hydrides by ¹H NMR at 20 °C. It exchanges with D₂ faster into the NH site than into the OsH sites. Triflic acid protonates Os(H)₂[N(Me)C₆H₄NH]L₂ at the metal to give a trihydride. Catechol protonates Os(H)₂[N(Me)C₆H₄NH]L₂ to displace the ortho-diamine to give Os(H)₂(OC₆H₄O)L₂. The collective evidence is consistent with a dianionic, not a quinoid oxidation state for the chelate ligands and a d⁴, six-coordinate potential energy surface, often with low barriers between alternative non-octahedral structures.