The Os-Os dimer [Cp(CO) 2Os] 2 was synthesized in good yield by reaction of Cp(CO) 2OsI with NaK. The related Cp* dimer [Cp*(CO) 2Os] 2 (Cp* = η 5-C 5Me 5) was prepared by reaction of Cp*(CO) 2OsH with 2,2′-azobis(isobutyrylnitrile) (AIBN). In contrast to [Cp(CO) 2Os] 2, which has only terminal CO ligands, spectroscopic and crystallographic data indicate that [Cp*(CO) 2Os] 2 has two bridging CO ligands. Reaction of tetraisopropylcyclopentadiene with [(CO) 3OsI] 2 provides ( iPr 4C 5H)(CO) 2OsH, which can be converted to ( iPr 4C 5H)(CO) 2OsH through reduction with NaK followed by treatment with EtOH. Reaction of ( iPr 4C 5H)(CO) 2OsH with AIBN gives [( iPr 4C 5H)(CO) 2Os] 2, which is much more soluble than [Cp*(CO) 2Os] 2. DFT (B3LYP) calculations on these Os-Os dimers reveal the energetics of different geometrical isomers. The anti and gauche isomers of [Cp(CO) 2Os] 2, with terminal CO ligands, are significantly more stable than the trans and cis isomers with bridging CO ligands, while the stability of the anti isomer of [Cp*(CO) 2Os] 2 is similar to that of its trans isomer. Computations on the energetics of the isomers with a [C 5(CF 3) 5] ligand suggest that the difference observed for Cp and Cp* complexes is mainly due to electronic rather than steric effects of the Cp groups.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry