Anionic Tantalum Dihydride Complexes: Heterobimetallic Coupling Reactions and Reactivity toward Small-Molecule Activation

The anionic dihydride complex [Cp₂TaH₂]⁻ was synthesized as a well-defined molecular species by deprotonation of Cp₂TaH₃ while different solubilizing agents, such as [2.2.2]­cryptand and 18-crown-6, were applied to encapsulate the alkali-metal counterion. The ion pairs were characterized by multiple spectroscopic methods as well as X-ray crystallography, revealing varying degrees of interaction between the hydride ligands of the anion and the respective countercation in solution and in the solid state. The [Cp₂TaH₂]⁻ complex anion shows slow exchange of the hydride ligands when kept under a D₂ atmosphere, but a very fast reaction is observed when [Cp₂TaH₂]⁻ is reacted with CO₂, from which Cp₂TaH­(CO) is obtained as the tantalum-containing reaction product, along with inorganic salts. Furthermore, [Cp₂TaH₂]⁻ can act as a synthon in heterobimetallic coupling reactions with transition-metal halide complexes. Thus, the heterobimetallic complexes Cp₂Ta­(μ-H)₂Rh­(dippp) and Cp₂Ta­(μ-H)₂Ru­(H)­(CO)­(PⁱPr₃)₂ were synthesized and characterized by various spectroscopies and via single-crystal X-ray diffraction. The new hydride bridged tantalum–rhodium heterobimetallic complex is cleaved under a CO atmosphere to yield mononuclear species and slowly exchanges protons and hydride ligands when exposed to D₂ gas