Rearrangement of Metallabenzynes to Chlorocyclopentadienyl Complexes

Treatment of the osmabenzyne complex Os­{C-C­(SiMe₃)C­(CH₃)-C­(SiMe₃)CH−}­Cl₂­(PPh₃)₂ with Mo­(CO)₆ in refluxing benzene produced the η⁵-chlorocyclopentadienyl complex Os­{η⁵-C₅HCl­(CH₃)­(SiMe₃)₂}­Cl­(CO)­(PPh₃) and Mo­(CO)₅­(PPh₃). A computational study suggests that the chlorocyclopentadienyl complex is most likely produced via the carbene intermediate Os­{C­(C­(SiMe₃)C­(CH₃)-C­(SiMe₃)CH−)}­Cl₂(CO)­(PPh₃) formed by a migratory insertion reaction of the osmabenzyne complex Os­{C-C­(SiMe₃)C­(CH₃)-C­(SiMe₃)CH}­Cl₂(CO)­(PPh₃). DFT calculations show that the relative thermal stability of metallabenzynes Os­(C-CHCHCHCH)­Cl₂(L)₂ and the corresponding isomeric carbene complexes Os­{C­(−CHCHCHCH−)}­Cl₂(L)₂ as well as the chlorocyclopentadienyl complexes Os­(η⁵-C₅ClH₄)­Cl­(L)₂ (L = CO, phosphine, pyridine, amine) is strongly dependent on ligand L