Preparation, Spectroscopic Characterization, X-ray Structure, and Theoretical Investigation of Hydride−, Dihydrogen−, and Acetone−OsTp Complexes:  A Hydridotris(pyrazolyl)borate−Cyclopentadienyl Comparison

Complex OsH₃Cl(PⁱPr₃)₂ (1) reacts with KTp (Tp = hydridotris(pyrazolyl)borate) in tetrahydrofuran at room temperature to give OsH₃(κ²-Tp)(PⁱPr₃)₂ (2). In toluene at 80 °C, the κ²-Tp complex 2 is transformed to the κ³-Tp derivative OsH₃Tp(PⁱPr₃) (3) in quantitative yield after 7 h. Protonation of 3 with HBF₄ affords the bis(dihydrogen) compound [OsTp(η²-H₂)₂(PⁱPr₃)]BF₄ (4). In acetone complex 4 releases the coordinated hydrogen molecules in a sequential manner. At room temperature, the dihydrogen-solvate complex [OsTp(η²-H₂)(κ¹-OCMe₂)(PⁱPr₃)]BF₄ (5) is formed, while at 56 °C the loss of both hydrogen molecules gives rise to the bis-solvento derivative [OsTp(κ¹-OCMe₂)₂(PⁱPr₃)]BF₄ (6). Complexes 2−6 have been characterized by X-ray diffraction analysis, and DFT calculations support their formulation. The structures of 3−5 have been compared with those of their Cp counterparts OsH₃Cp(PⁱPr₃), [OsH₂Cp(η²-H₂)(PⁱPr₃)]BF₄, and [OsH₂Cp(κ¹-OCMe₂)(PⁱPr₃)]BF₄. The results show that the Tp ligand avoids piano stool geometries, while it enforces dispositions allowing N−Os−N angles close to 90° such as octahedron and pentagonal bipyramid.