Preparation and Characterization of Novel Os−Diolefin Dimers: New Entry to Os−Cyclooctadiene Complexes

The complex [H(EtOH)2][{OsCl(η4-COD)}2(μ-H)(μ-Cl)2] (1) has been prepared in high yield by treatment of OsCl3·3H2O (54% Os) with 1,5-cyclooctadiene in ethanol under reflux. Under air, it is unstable and undergoes oxidation
by action of O2 to afford the neutral derivative {OsCl(η4-COD)}2(μ-H)(μ-Cl)2 (2). The terminal chlorine ligands of
the anion of 1 are activated toward nucleophilic substitution. Thus, reaction of the salt [NBu4][{OsCl(η4-COD)}2(μ-H)(μ-Cl)2] (1a) with NaCp in toluene gives [NBu4][{Os(η1-C5H5)(η4-COD)}(μ-H)(μ-Cl)2{OsCl(η4-COD)}] (3) as
a result of the replacement of one of the terminal chlorine atoms by the cyclopentadienyl ligand. The CH2 group
of the latter can be deprotonated by the bridging methoxy ligand of the iridium dimer [Ir(μ-OMe)(η4-COD)]2. The
reaction leads to the trinuclear derivative [NBu4][{(η4-COD)Ir(η5-C5H4-η1)Os(η4-COD)}(μ-H)(μ-Cl)2{OsCl(η4-COD)}]
(4) containing a bridging C5H4 ligand that is η1-coordinated to an osmium atom of the dimeric unit and η5-coordinated
to the Ir(η4-COD) moiety. Salt 1a also reacts with LiC⋮CPh. In this case, the reaction produces the substitution
of both terminal chlorine ligands to afford the bis(alkynyl) derivative [NBu4][{Os(C⋮CPh)(η4-COD)}2(μ-H)(μ-Cl)2]
(5). Complexes 1, 2, 3, and 4 have been characterized by X-ray diffraction analysis. Although the separations
between the osmium atoms are short, between 2.6696(4) and 2.8633(5) Å, theoretical calculations indicate that
only in 2 is there direct metal−metal interaction, as the bond order is 0.5.