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.