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

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.