Two Isomeric Structures of Hydridoruthenium Complexes Supported by Hydrotrispyrazolylborates, TpRRu(H)(1,5-cyclooctadiene):  An Octahedral Structure with Additional 3-Center-2-Electron Ru−H−B Interaction Is More Stable than a Square-Pyramidal Structure with a κ2-TpR Ligand

Hydrido-cod-ruthenium complexes containing hydrotris(3,5-diisopropylpyrazolyl)borate (TpiPr) and its 4-brominated derivative (TpiPrBr), TpRRu(H)(cod), are reported. Spectroscopic and crystallographic analyses reveal the presence of two isomeric structures, a square-pyramidal structure with a κ2-TpR ligand and an octahedral structure with an additional 3-center-2-electron Ru−H−B interaction, and isomerization from the former structure to the latter structure is observed for the first time by means of 1H NMR analyses.