One-pot atmospheric pressure synthesis of [H3Ru4(CO)12]−

Abstract

Reductive carbonylation of RuCl₃·3H₂O at CO-atmospheric pressure results in the [H₃Ru₄(CO)₁₂]⁻ (1) polyhydride carbonyl cluster. The one-pot synthesis involves the following steps: heating RuCl₃·3H₂O at 80 °C in 2-ethoxyethanol for 2 h, addition of three equivalents of KOH, heating at 135 °C for 2 h, addition of a fourth equivalent of KOH and heating at 135 °C for 1 h. The resulting K[1] salt is transformed into [NEt₄][1] upon metathesis with [NEt₄]Br in H₂O. The IR, ¹H and ¹³C{¹H} NMR spectroscopic data are in agreement with those reported in the literature. [Ru₈(CO)₁₆(X)₄(CO₃)₄]⁴⁻ (X = Cl, Br, I; 2-X) is formed as a by-product during the synthesis of 1, and the two compounds are separated on the basis of their different solubilities in organic solvents. The nature of the halide of 2-X depends on the [NEt₄]X salt used for metathesis. 2-Br is transformed into [Ru₁₀(CO)₂₀(Br)₄(CO₃)₄]²⁻ (3) upon reaction with an excess of HBF₄·Et₂O. 1 is readily deprotonated by strong bases affording the previously known [H₂Ru₄(CO)₁₂]²⁻ (4). The reaction of 1 with [Cu(MeCN)₄][BF₄] affords [H₃Ru₄(CO)₁₂(CuMeCN)] (7), whereas [H₂Ru₄(CO)₁₂(CuBr)₂]²⁻ (8) is obtained from the reaction of 4 with [Cu(MeCN)₄][BF₄]/[NEt₄]Br. All the compounds have been spectroscopically characterized, their molecular structures determined by single crystal X-ray diffraction (SC-XRD) and investigated using DFT methods in selected cases in order to confirm the hydride positions and to study the relative stability of possible isomers.