Trispyrazolylborate and Tetramethylcyclopentadienyl Osmium Chemistry: Toward Methane Coordination Complexes

Abstract

Treatment of H2OsBr6 with 4 equiv. of tetramethylcyclopentadiene (C5Me4H2) in tert-butanol affords [(C 5Me4H)2OsBr]2[Os2Br 8]. The brown color of the salt suggests that the anion adopts an eclipsed conformation (D4h symmetry) and this conclusion has been confirmed by a single-crystal X-ray diffraction experiment. Treatment of [(C5Me 4H)2OsBr]2[Os2Br8] with excess 1,5-cyclooctadiene (cod) in refluxing ethanol gives (C5Me 4H)2Os and [(C5Me4H)2OsBr][Os 2HBr4(cod)2]. An X-ray crystallographic study of the latter compound indicates that the anion adopts a confacial bioctahedral structure in which the hydride ligand and two bromides bridge between the two osmium centers. This anion is the first example of an anionic diosmium complex containing a bridging hydride.