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.