Triruthenium dodecacarbonyl

Structure and synthesis

The cluster has D_3h symmetry, consisting of an equilateral triangle of Ru atoms, each of which bears two axial and two equatorial CO ligands. Os₃(CO)₁₂ has the same structure, whereas Fe₃(CO)₁₂ is different, with two bridging CO ligands, resulting in C_2v symmetry.

Ru₃(CO)₁₂ is prepared by treating solutions of ruthenium trichloride with carbon monoxide, usually under high pressure. The stoichiometry of the reaction is uncertain, one possibility being the following:

6 RuCl₃ + 33 CO + 18 CH₃OH → 2 Ru₃(CO)₁₂ + 9 CO(OCH₃)₂ + 18 HCl

Reactions

The chemical properties of Ru₃(CO)₁₂ have been widely studied, and the cluster has been converted to hundreds of derivatives. High pressures of CO convert the cluster to the monomeric ruthenium pentacarbonyl, which reverts to the parent cluster upon standing.

Ru₃(CO)₁₂ + 3 CO ⇌ 3 Ru(CO)₅ K_eq = 3.3 x 10⁻⁷ mol dm⁻³ at room temperature

The instability of Ru(CO)₅ contrasts with the robustness of the corresponding Fe(CO)₅. The condensation of Ru(CO)₅ into Ru₃(CO)₁₂ proceeds via initial, rate-limiting loss of CO to give the unstable, coordinatively unsaturated species Ru(CO)₄. This tetracarbonyl binds Ru(CO)₅, initiating the condensation.

Upon warming under a pressure of hydrogen, Ru₃(CO)₁₂ converts to the tetrahedral cluster H₄Ru₄(CO)₁₂. Ru₃(CO)₁₂ undergoes substitution reactions with Lewis bases:

Ru₃(CO)₁₂ + n L → Ru₃(CO)_12-nL_n + n CO (n = 1, 2, or 3)

where L is a tertiary phosphine or an isocyanide.

Ru-carbido clusters

At high temperatures, Ru₃(CO)₁₂ converts to a series of clusters that contain interstitial carbido ligands. These include Ru₆C(CO)₁₇ and Ru₅C(CO)₁₅. Anionic carbido clusters are also known, including [Ru₅C(CO)₁₄]²⁻ and the bioctahedral cluster [Ru₁₀C₂(CO)₂₄]²⁻. Ru₃(CO)₁₂ -derived carbido compounds have been used to synthesize nanoparticles for catalysis. These particles consist of 6-7 atoms and thus are all surface, resulting in extraordinary activity.