Exploring the Chemistry of Ruthenium-Phosphine Complexes

The interaction of RuCl3 with tributylphosphine, especially under specific conditions, leads to intriguing outcomes in organometallic chemistry. Brief reflux in ethanol combined with concentrated hydrochloric acid yields monomeric mer-RuCl3(PBu3)3. However, when the reaction conditions vary, such as with room temperature ethanol, the formation of dimeric species occurs, producing two distinct diruthenium(III, III) dimers: edge-shared Ru2Cl6(PBu3)4 and face-shared Ru2Cl6(PBu3)3. These complexes demonstrate significant differences in ruthenium-to-ruthenium distances, with the edge-sharing variant exhibiting a longer distance of 3.733 Å, in contrast to the closer distance of 3.176 Å found in the face-sharing variant.

The reduction of these complexes introduces further complexity, resulting in the formation of various isomers, including Ru2Cl5(PBu3)4 and Ru3Cl8(PBu3)4. Notably, these compounds contain both ruthenium(II) and ruthenium(III) oxidation states, reflecting the mixed-valence nature of the complexes. Among these, the diruthenium(II, III) cation [Ru2Cl3(PBu3)6]+ stands out, characterized by its three chlorine bridges and representing a classic example of diruthenium chemistry.

The behavior of these complexes is not exclusive to tributylphosphine, as similar trends are observed with other alkyl phosphines. The mixed-valence compounds generally possess one unpaired electron per dimer unit. Variations in Ru-Ru distances among different complexes highlight the electronic and geometric diversity present in these organometallic systems, ranging from 2.854 Å in Ru3Cl8(PBu3)4 to 3.279 Å in a green form of Ru2Cl5(PBu3)4.

Furthermore, bidentate phosphine complexes have played a significant role in early ruthenium-phosphine chemistry. The synthetic pathways for these complexes often involve the displacement of halide groups, leading to the formation of various chelating ligand complexes. For instance, bis(dimethylphosphino)ethane (dmpe) complexes have been synthesized, showcasing the versatility and adaptability of ruthenium coordination chemistry.

On another front, hydride complexes of ruthenium, denoted as RuH2(PR3)4, exhibit classical hydride characteristics, with both cis and trans structures being observed. These complexes demonstrate varying bond lengths between ruthenium and phosphorus, while the presence of dihydride species further illustrates the rich chemical landscape within ruthenium-phosphine coordination chemistry. The ability to manipulate these complexes has allowed chemists to explore new synthetic routes and applications in catalytic processes.